OpenFOAM for Absolute Beginners

1. Course Content: Hello, everyone. Welcome to the CFD using Open Form beginner to intermediate course. In this video, we will be looking through the course content. I have split the entire course into ten separate sections, and we will see what will be covered in each section. So in the class one, we will be seeing some introduction to open form, how to install it, and how to set up the software. And we will also be seeing some basic file structure on how open form is built and basic commands which will be useful in running open foam simulations. We will just see the basic commands in the first class. We will be learning more commands as the course progresses. But these basic commands will be essential to get started. In the class two, we will be seeing how to prepare a geometry and generate mesh with a tool called Blockmsh. We will be seeing how to set up the boundary and initial condition for a case in open foam. We will also look through some solvers and how to run simulation using open foam. After running the simulation, we will be using a tool called paraview to post process the results. In the class three, we will be doing Snappy hex mesh. So we'll be using Blokmsh as a dependent tool for snappy x mesh. We will get introduced to Snappy hex mesh, and we will be creating complex measures using it. We will also learn how to use the check mesh command to check quality of the meshes. In the class four, we will get introduced to incompressible, compressible and multiphase solvers. So we will go through the basics of everything and look at some examples. After looking at that, we will be running a lead driven cavity case. This will be a hands on tutorial, and we will also introduce the case study of lead driven cavity. In the Section five, we will be seeing the types of boundary condition and how to implement them in open form, how to do a turbulence modeling in open form, and we will get the introduction of it. And after that, we will be setting up and running our own ran simulation, which is Renault's average vistok simulation. We will be looking at how K Epsilin turbulence model is made, how K Omega SST model is made, or how to run a simple laminarchs. So we will be seeing all those then in the class six, we will be running some transient solvers simulation. We would have run transient cases even before that even the lead driven cavity is a transient case, but still we will be running more in depth analyzed cases for transient solvers. We will set up from scratch and we will run it. And we will also look at how to decompose any case and run it in parallel, so this simulation runs faster. So open foam comes with the installation of MPI. So we will be using MPI to do the parallel processing. We will also look at how to make a mesh using Snapeg mesh, but in parallel. In the class seven, we will get introduced to refinement box in Snappy X mesh, which will be a slightly advanced feature where we can define area locally in Snappy XMsh. And we will also get two hands on tutorials, one on external aerodynamics for the classic CopenFm motorbike case, and we will be doing plotting of force coefficients using GNU plot, and the other is exporting the post process data to Excel and how to plot from Excel. In the class A, we will be importing ANC's workbench mesh, as well as *** fluent mesh, both are different. We will be importing both, and we will use the workbench mesh to run one of the simulation for flu over a cylinder, and we will do a handsome tutorial on that. For the class nine, we will be seeing how to set up an automation file called All run and all plane file. AlternFle will enable the user to run the simulation with series of commands without doing it manually. We can set up the AlternFle If you want to change any boundary condition or initial condition, you can change that, and you don't have to run each and every command one by one. You can just initiate the automation AlternFle and it will run it in series, and it can do. Series in the sense, it will do step by step. It can also do parallel processing. Then the all clean file will be used to clean the case just in case if you want to run this case from scratch again, but you don't want to delete every time step, every mesh generated manually, you can use the all clean file and clean the case, get it back to the default setup, and you can run from scratch. In the class ten, we will get introduced to multiphase flow simulation. This will be a basic introduction and some modeling approaches and practical consideration using open foam, setting up any multiphase case using open foam. Then we will be having one hands on tutorial on the demonstration of dam brease. Usually, dam break case is two phase, but we will be doing four phase using multiphase euler foam in open form. So this is all that we will be covering in this course. Looking forward to seeing in the class. Thank you. 2. Introduction to OpenFOAM, Installation and Basic Commands: Hello, everyone. Welcome to the CFD using open Foam beignet to intermediate course. This will be the first class. In this class, we'll be looking at the introduction to open foam, installation and setup of the software, basic file structure and basic commands, which is used in open form. First, what is open form? Open form stands for open field operation and manipulation. It is an open source software used for computational fluid dynamics, commonly known as CFD. It is designed for solving continuum mechanics problem, including fluid flow, heat transfer, and chemical reactions. Initially, it was developed by OpenCf delimited, a company, a division of the ESI group, first released in the year 2004. Since then continuously enhanced and maintained by the Open form Foundation and an active user community. So we generally say.com and.org version, or it is also known as foundation and Community version. So in this course, we'll be using the community version, which is the ESI version. So what happens is the ORG or foundation version, they release in the format of version one, version two, and the latest one is Version 11. So it is mostly like nine, ten, 11. And when this course is published, the latest is 11. But ESI they do it in a slightly different format. So they release two versions every year. One in the month of June and one in the month of December. So you see the latest version which is released as of this course recording is 2312. So Version 2312, what it means is it is released in the year 23, is 2023, and the 12 means the 12th month of the year, which is December. So the previous release was version 2306. So it was in the June, so 2306. And previous to that, it is obviously 221, two, and it goes on. And as of this course, it is recorded in June 2024, so we are expecting 20 406 soon. We will be using 23 12 for this course. Features and capabilities of open foam. Wide range of solva is present for compile compressible flow solvers. You also have solves for multiphase, heat transfer, combustion, chemical reaction, and everything. It is also highly customizable. Since it is an open source software, you can modify, create your own custom solware, edit the source code. You can play around the coding as much as you want, and there is no restriction, and it is absolutely free. Also, there are extensive libraries for physical models and numerical methods. Even if it is not coming in the installation, you can download it from external websites, contributors from Github. It is called Foam extent version. You can write your own solvers if you need, or you can use solvers written by other people in terms of open form. So it is highly customizable. And its pre processing and post processing utilities are highly powerful like the tools for mesh generation and manipulation comes within the installation. And data analysis and visualization tools can be done using a software called paraview which is also open source, and it comes along with the installation of open foam. And we can also do complex geometries and dynamic meshing where the mesh moves with respect to time. So it is also possible in open form. It supports structured as well as unstructured meses, capable of handling moving boundaries and mesh deformation and also rotating measures in many cases. So we will see how to do the installation and setup. For installation, we need WSL, which is called Windows Subsystem Linux. Open foam works only in Linux system and not in Windows system, but that doesn't mean we have to get a computer which is entirely voted with Linux. That is why we have something called WSL or Windows Subsystem Linux, where we get the terminal window of the Linux inside Windows so that we can use a Linux subsystem within the Windows. So to install that, all you have to do is open your command prompt, run as administrator or you can also open your Power Shell and run this command WSL hyphen install space hyphen D, where D means the distribution version. And space you can type Ubuntu with capital U, hyphen 22.04. So what this will do is it will install the Windows Subsystem Linux, along with the Ubuntu version of Linux, which is 22.04. Along with the installation, and you will get Ubuntu inside your system. But if you know how to do a second second OAS inside your system, then you are free to do a Linux bootup. Or if you have a spare laptop and you can afford to remove Windows OAS and put in Linux completely, you can also do that. So once you enter this command and hit Enter, the process will start. Now, wait for the process to finish. Since I have already installed it, uh, I'm not install it again, so you can just run this command. Now, after it is over, it will prompt you to restart your PC. Now, restart your PC and wait. So you just do the next slide also. Watch the next slide and then do this process. That's what I recommend. After restarting, a window named Ubuntu will open. Wait till it asks you to enter your username and password. So this user name and password will be your login details for your Linux system, which is in Windows subsystem. If the Ubento terminal doesn't open automatically, you can also open from the search Bar. You can just open your search Bar and search for Ubuntu and a terminal window can be open. Note, when you're typing user name, you can see the user name, but when you are typing the password, the password won't be visible. So you might be wondering, I'm typing something, but it is not visible on the screen. It won't even show the stars, like how we generally do. When we type a password, it will show stars. But in this case, it won't show. So instead, what it will do is it will keep a blank space. So when you are typing the password, type it very carefully. I need not be very highly secure. It is just for a small security purpose. It's not going to affect your overall security of a system. So keep it as simple as possible. It need not involve anything like numbers, special characters. There is nothing mandatory like that. You can keep it as simple as you want. So make sure you are typing it very carefully and hit Enter. Then the installation will be done for Ubuntu. Now, there is a quick tip. Since we are talking about installation, now I would recommend you to either install Notepad plus place or Visual Studio code. Since open foam is open source, we will be modifying the codes to run the simulation. There is no specific graphical user interface or GI for this. Any notepad word or any text editor for that matter would work just fine. But some specialized IDs can make your work easier and comfortable. I recommend you to install either Notepad plus plus or VS code. I would personally use VSCode because it has amazing user interface, and it will help me with autofill sometimes. So if you want to follow along, same as mine, you can go with VS code. But if you just want to settle down with Notepad Plus Bliz, it's your personal preference. Okay, now we have the WSL. If you faced any issues, please do contact me, or you can search on the web. There is various resources to help you on how to install WSL. It will be very easy. Now we will do the installation and setup of Open Form Version 2312. In my system, I already have the 2212 version. But now I want to install the 2312 version. So I will do that along with you so that you can also follow along. So for that, we have to visit the website, HTTPS, and so on what is there on the screen. You can also simply search Open Form Install 2312. The first link will do just fine. So what we have to do is we have to open our WSL terminal or it is also the Open to terminal. So I will tell you two methods. One is, click on your Windows button or open the search bar and search for bent. This thing will appear. You can hit Enter and it will open a terminal. Just wait for it to load. Now it is loaded. This is also fine, okay? But if it is not opening or if it is throwing any, there is another method. You can press Windows k plus R, and this run window will open. You can type in WL and hit Enter. Now this will open. Even if this doesn't work, you can do the Windows plus R, type in CMD. This will open your command prompt or you can also search Command Prompt from here and open it. No problem. You don't have to run it as administrator. Just normal command Crampt is fine. And then you can type WSL and head Enter. Now, this will load the WSL for you. Okay, now I got the WSL. How do I know? I have the lab, my username at the device name, and we will see something like slash M&T slash the directory of this. So this is what we call the directory. The location from the base where we are working is called directory. I will use this word very often. If you are comfortable with terminal, you would already know this. So the first command which you'll be knowing is clear. So you type clear, hit Enter, it will clear it. Okay? Now what we are going to do is Um, we are going to type in these commands, and we are going to run it. It will install the open form, but you can also go to the website which I just mentioned and you can copy paste this entire code. But I'm going to type this out. Now, what I'm going to do is I will type CD. Now, you don't have to understand what I'm doing or what these commands mean, but CD is change directory, it will take me to the home directory. Now we are in the home. Just after dollar if we don't see anything that is the home. Again, I will clear it. Now I will type this command, whatever is there on the screen. This curl space HTTPS dealt openfon.com slash AD Hyphen debian hyphenpo dot SHPC Sidebar. I don't know what is that space sudo space Bash. I'll hit Enter. Now it is asking me for the password. So I will type the password, and it is running. This is the only place where we will be needing the password we just set. So it is doing App get update, which is updating what is available already, and it will see if there are any updates for the system. So wait for some time. Make sure your Internet is stable, only then it will be done faster. Then we can do the second command. So by the way, whatever is there after the hash, it is not needed. It is just a command. Now we can do the second command, which is pseudo apt get update. Now this is also going to update whatever is done. So this is getting the update, and then we will install whatever update is there. It will be done automatically. You don't have to worry. Now, this is the command which will actually install open foam. T psudotigate, install Open Foam 23 12 hyphen default. So there are many methods to install. Default is going to install everything that is there. Now, this is sensitive, so don't make anything capital. Everything is small here. Hit Enter. Now it is going to ask you whether do you want to continue? Now, you can just type Y. This is not as sensitive. You can type capital Y or small Y, doesn't matter. Type Y and hit Enter and keep your Internet stable. This is going to take a while, and it will install open foam for you. Now let us wait until it is over, and I'll get back to you. Now the installation is over. As you can see it is asking us to do something. It is asking us to set up open Foam through a command called source from BasrCFle dot space, and this thing. This is what is going to tell the Linux to uh, locate open foam. Whenever we are calling open foam, it has to know where open foam is installed. This is the location where it is installed. So we have to source that. It's called sourcing. Before that, we will check whether open foam is installed properly or not. So to do that, you can type in the next command on this slide, which is open Foam 231, two, and hit Enter. Now, if you see this, then your installation is done well. Okay. Now, you have to see your user name dollar and blinking thing. It will also say open Form 2312 here. If it is saying that, then your installation is great. If you're facing any problem, do ask me, you can contact me or there are again, various resources available on the Internet to sort out any issue which you are getting an installation. Most probably someone has got that before you. So you can always check it out. Now we are going to do the sourcing thing. To come out of this terminal, you can click here and probably Control C or control D will work for me, Control D works. So then I'm going to do something called CD, okay, just to ensure that I'm in the home directory. Now we are going to type explorer dot espy dot. Don't miss the space dot and hit Enter, okay? Now this window will pop up where you will be able to see something called dot bash rc, which is the file open form was talking about dot bash RCFle. Open that. It will ask for permission. You can open it using VS code. I'm using VS code to open it. Go all the way down to the last line. Actually, you won't be seeing any of these, so just forget it. This will be your last line. This FI will be your last line, so don't mind any of these. Okay? Pretend that it doesn't exist here. So what you are going to do is you're going to copy paste this entire thing. I'm just going to copy what to be code. And in the last line of your BRC file, you are going to paste it. In your case, it will be after the FI. Go to the new line and paste it. Now, you are going to do something called source. Okay. So this will work for you. So what you have to do is you have to type source, then you have to type this, then save it. And then you can open a new terminal. I will be preferring to use Windows plusR and then Ws. See now you should not get any errors here. If you are getting any error, it means that you are sourcing has gone wrong somewhere. You can safely close the previous terminal. It is fine. Now, only the new terminal will work with the source. Okay? So if you have done it perfectly, it will not show any error. Otherwise, it will show some command that it is not sourced or something. So I will also explain what I have done here. Whenever you want some shortcut, let's say that I want to go to a specific area in my PC, some directory. Now it is in C slash US slash Jah. This is my home directory. This is the directory where I'm at the terminal at. But if I want to go to a specific directory, say, Udi open Foam course. So if I want to go there, then the command is actually CD space than the location of the folder. Then if I just type that, let's say, I'm typing specifically that. I'll go to my home directory. Now I'm typing Series slash T slash, D slash open foam v221, two, uh UM open foam course. If I'm typing, you can see that I'm entering that location. But if I don't want to do that, let's say, I'm going to use this folder very often. Then what I can do is I'll create something called Allias. So if I want to enter that location, all I have to do is enter the home directory by typing in CD. Then I will type UDI hit enter, and it will take me there directly. So it is an alias to do specific commands. Now, if you have multiple versions of open form or if you also want to do something like this, then what you can do is you can put this entire thing within uh, single quotations. Then after the quotation uses type a dot. So it has to be dot space, then the location instead of source space. Then I'm going to type Allis space. Then you can give whatever word you want. I'm going to use OF 2312 for this. Whenever I type OF 231, two, this file or this location will be sourced. Let's say I want to use open Form 2212 sometime. Then I can type OF 2212 in my terminal. Okay. Now, if I type that, then my terminal is taking me to open from 2212 location wherever it is installed. But if I want to work with open From 2312, say, I will type open fom 231, two, now you see it is taking me to open from 2312. So that is what we are trying to do. That is what we are trying to source here. If I type IF 2312, it will take it will source it automatically. So it is not available as of now. So I have to restart and it will work. So this is what Alias does, this is what I have done here as well. Now, this is what is going to work here as well. So I hope you understood till there. Now the next thing. Now we have typed in CD clear, and we have also sourced this. So this is what we did till now. If you want to go through these slides, you can go through. Now we are going to do something called make directory. Okay? For this, I will open a new terminal. Now I will source Open Foam to 31, two, and I have sourced open Foam 23 12, which is the new version which I have just installed. So whenever you have multiple versions, you might have to source it manually. But if you just did the source space UA USR, then you don't have to do this line. You will find me doing this command throughout this course very often. So you can choose to do it or skip it whenever you want. What we are going to do is create a directory MKDIR space hyphen P, dollar foam underscore run, and hit Enter. What this is going to do is just like how we created Alias. Open foam has its own method of creating as that is this. Now, if I type just run, it will take me to a location, um, where it has created a run directory. Usually, this is the place where we will be doing all the simulations. And this is generally is what is considered as run directory. But I will suggest you to do something else, which I will tell in the next class, we will be creating our own run directory. Okay? So this is what we had to do. Then what you can do is instead of running just run, you can also run CD dollar foam underscore run. Okay. Now, after that, open Foam offers us set of tutorials which we can copy and use it whenever we want. Whenever we are working with Open Foam, we don't set up anything from scratch. We will copy paste some of the tutorials and modify it to cater our knees. So to do that, we have to type in this command, and it is CP, hyphen R dollar Foam underscore tutorials, slash IncompressibE. Slash simple form, make sure that F is capital. It is case sensitive. So make sure everything is set properly. It's daily. Space, dot, and hit Enter. Okay? Now, previously when I typed LS, we did not see anything like here. But now when I type LS, you can see that we have something called Pitch daily. This is what we just copied. So CP is copy command. Hyphen ar is copy recursively. So it means that whatever file is there inside Pitch Daily, copy that also. Now, we have copied that also. But now I will ask you to do something like CP, hyphen R dollar foam underscore two Ls space dot. Don't miss that dot. Then hit Enter. This is going to take a while. Now, if you type LS, you can also see something called tutorials. Now, this tutorials is a main folder, which I was telling you. Like we have various solvers here. We will be using these tutorials to set up our cases. We won't set up it, set it up from scratch. We will just use this, okay? So we have created something called the Pits daily here. This is the way to check whether your installation is done properly or not. Now we are going to enter the Pits daily folder. It is the command CD space Pits daily, make sure that this is capital. Hit Enter. Now if you want to see what is there inside, you can type LS. You have zero constant and system. You don't have to worry what these things mean as of now. Now, the command which you have to run next is block mesh. So I'm just following whatever is there in the PPT. Now, lock mesh, it enter, you have to see something called end here. You don't have you should not see any warning word here. It will be ending smoothly with end. Then the next command is simple form, Ht enter. Now, wait till this is over. It will take a bit of time, but it will be over soon. Okay, now again, you are seeing something called. Now this is over. What we have done is we have just simulated a backward facing stepcase, ok and we will be typing something called Parafom. This is the way to do the post processing. This might or might not work for you. Like, I did not work for me, right, because it might or might not work for some people, so you don't have to worry about that. So what we will be doing is we will be installing something called paraview. So what is PARA V? PRA V is the open source data analysis and visualization tool. It is developed by a company called Kitware and various institutions in collaboration. So the key features is it handles a large data sets. It can be used for any sort of scientific computation, not just open form and CFT. It has a interactive three D visualization platform, and it is scriptable via Python. If you want to automate things or if you want to make it customizable, you can do it using Python. And using para view, along with open foam, it is very powerful to post process all our data. We can perform operations like slicing, contour plots, team line, if you want to do a graph over specific line on the geometry, you can do that. If you want to export the data within some cells in the mesh, you can do that. It has a wide variety of capabilities. So we are going to install paraview so the method to do it is we'll be going to this website, paravw.org, and you can download the latest version. You can install the software in your Cedriv in the default location. Now we are going to do something. I will types. As you can see, we have zero hundred, 202 81. These are the time steps. Now we have to run a command called Touch space para dot, foam, hit Enter. Now, what this essentially does is it created a file called paradtFom. This is the paraview file. Now I have installed paraview already. So what I'm going to do is going to type explorer dot x space dot, hit Enter. It will take me to the location where these files are existing. Now we will be seeing this. So just right click open with choose another app. Then you can click on Choose app on your PC. If you scroll down, you'll be able to see this para view, wherever you have installed. So you will be able to see Para view. This is my previous version. This is my new version, so I am double clicking the new version. So whatever you have installed, you will be able to see that double click. Inside Bin, if you just scroll down, you'll be able to see Para view an application file. See, this is an application file, click on this, click on open and make sure to give always. Now, this will load as the case files. It will take a bit of time for the first time. So once I click the green apply here, you might be able to see something like this in terms of geometry, but the colors might be different. So the color map might be different, but as long as it looks similar, it is fine. So if you go here, you'll be able to choose between velocity, pressure, okay, ESL and nut. We will be seeing these and how these got generated later. But for now, you are just going to check whether the installation works fine or not. And this is the interface where we will be changing the times. As you can see, we have 100, 200 and 281, since this is a steady state case, so we are interested only the last timestep where it got converged. Okay? So this is the pressure data. We have the velocity data. So if you click this button, it is going to take all the data within this window and set the minimum and maximum to the color map accordingly. So this is called rescale to visible data range, I have selected that. This is what we have just simulated. This is a backward phasing step case. If I click here, it will run me through the timestep, but this is a steady state simulation, so it doesn't matter. Now I can close this. If I go back to the terminal, it will be just like how we left it. Now we will see what is left. We have done this. You color might look something like this. I have changed the color map for my preference. Now we will see what is a file structure and basic commands in open form. So we have a case, case is the setup which we will be using to run any simulation. So the case has three different parts. One is time directories. Then there is a folder called constant, which will store all the constant values or properties related to the simulation. And then we have a folder called system, which will store all the control related things, which is related to the simulation. Under time directories will be having zero. And after that, it will progress as the timestep. If your timestep is 0.1, then after zero, you will have 0.1, 0.20 0.3. If your time step is 0.001, then it'll be zero, 0.001, 0.002, and so on. So you get the point. So all these zero files will have corresponding velocity, pressure, temperature and pressure minus the hydrostatic forces. So all these files will be there. And in the constant folder, generally, we have the mesh here, which is stored in the format called polymesh. We will be having a folder called polymesh under which we'll be having the points, cell, phases, boundary details. After that, we will have various properties like turbulence properties, transport properties, which will have the fluids kinemtic viscous and turbulence model. Turbulence properties will have the turbulence details like whether it is laminar or Renault's average simulation or whatever it is. Under system, we will be having the control dit, which will be controlling the application which will be using all the solve which we'll be using any external function, use a defined function to plot any data or if you want to change the timestep, start time, end time, anything related to simulation or setup, we'll be doing through the control **** If we scheme and if we solution correspond to the numerical schemes which we'll be using to generate the data. So we have various AFD numerical schemes, and we will be setting up those through those two files. Block mesh dicta is a file which will be useful in generating basic mesh. Snappy hex mesh can be used for generating complex meshes. So these are the general files under these folders, but usually there will be more files, which is not generic, so we are not plotting it in this chart. So some of the useful commands are these, I will demonstrate by typing it, okay? So first is L S, LS will do list. So it will list whatever, um, folder is there in that specific directory. Let's say I want to. Then the second command is CD space the name of the folder. That is what I'm going to do. CD space. Now here, I have open foam as one of my folders. So if you want to autofill, you just type first one or two letters and hit tab, it will autofill for you. Hit Enter. Now you can see that I am inside open foam. Now if I want to go back, what I will do is I will do cdspace dot dot. It will take me back. Now for demonstration, I'll go back inside. Now, as you can see, I have four folders here. Let's say I want to go into the fourth file. Now it's asking me to choose the one. I'm choosing it and hitting Enter. Now under this, I have run. Now, let's say, if I want to go back to the home again, either I can do CD and hit Enter, it will always take me to home or else if I want to do let's say I am very further into this. Okay. Now, I just want to go back two folders. I will do CD space dot dot slash dot dot for coming out of two folders. And if I want to come out of three folders, what I'll do is CD space dot dot slash dot dot slash dot dot. It will take me back by three folders, okay? I'll clear it. Now, touch is a command which will create files. So generally we'll use it to create paraviewFles. Let's say I have these three. I'll go back to my home. We have only open foam now. Okay. Now I will create the paraviewFle here, touchpasParo dot fom. I'll hit Enter and search what is there. You can see I have parotomFle. Okay. Now if you want to create this is for creating a file. Now if you want to create a folder, then you can use MKDIR, which basically means make directory, and I can type in the folder name. Let's say folder. Okay. Now when I type LS, you can see we have two folders, open form and folder, which we just created. Now, if you want to enter folder, yeah, I will enter. Now, let's say I want to remove the folder, the folder which I just created. It is RM, hyphen R, then I'll type the folder name, Enter. Now if I search, the folder is not there. If I want to remove the paravFle I'll just do RM, and it is also gone. So generally for folders, we will be using hyphen R, but, um, will not be using it to delete files. Now, explorer dot x will generally open just your Windows Explorer. Okay. But if we want to open it in the specific location, let's say I'm inside open foam, here I am in version two, two, one, two, and this I'm under tutorials. Okay, I'm under run. Okay? Now, if I see there is nothing inside, but I just want to open this location. What I'm going to do is explore dot Tx space dot. So that space dot means open it in this location. So dot means this location. It's a second parametric input. I'll head enter, and as you can see, it is exactly opening that location. So that is how that command is useful. So these are the basic commands which we will use very often. Apart from this, we are not going to use much, which is related to Linux directly. So these are Linux commands. We'll be using more commands, which is related to open foam, which we will learn as the course progresses. So that's it for this video. If you have any questions, feel free to contact me. Um, there is a big open form community online. If you have any doubts, first try to check it online. So you'll be learning more than what you just need because you'll be seeing problems from other people also. So you will learn more. Thank you. See you in the next class. 3. Install OpenFOAM v2406 & WSL Ubuntu 24: Everyone. In this video, we are going to see how to install open foam version 20 406 using WSL. So WSL is Windows Subsystem Linux, where you can get almost all the access of Linux system within your Windows mission. So that is what we are going to see. We are going to start from the installation of WSL and get till the installation of Open foam 20 406. And also, I have an additional tip on how to set up the open foam so that it does not consume a lot of space in your hard disk or SSD. So usually WSL has this problem where even after you delete certain files inside the WSL architecture, it will not show us free space in your hard disk. So we will see one method which will rectify that problem. So to install Open foam, you can visit this website, openfom.com. There are two versions. I will suggest using this one. So once you go to openfom.com, you go to Downloads here, press on Linux. Then this will open up this window. So here you can press W plus open two and it will open a new window. And these are the commands that we have to run in a terminal, which is the Linux terminal to install open four. So for that we need a WSL, right. So we will see how to install that. First, you can open your command prompt in a regular fashion. Then you can choose any drive that you want. If you want to use your C drive only, you can just type all the commands which I'm typing directly. But now, let us say that I want to use my D drive. Then I will put D colon. Presenter and it will take me there. It's up to you on which drive you want to do it. I have multiple drives and I don't want to put it in C, so I'm putting it in D. If you want to continue with C, you can do it. In the command is, let me zoom it up slightly. WSL space hyphen D, sorry, hyphen hyphen means space hyphen D, space, bent, hyphen 24.04. Version 24.04 is the latest version. So I'm installing that. If it asks for any permission, you can give it, and it will take a bit of time to install the WSL. So let us wait till it is over. Okay, now the installation is happening. I'll give it the axis. Now after it has downloaded, it is installing. Now let's wait till it installs. Okay, now the installation has been done and it is saying the requested operation is successful, but the changes will not be effective until the system is rebooted. Generally, we will have to reboot. But for some system, it might or might not work without a reboot. Let us see whether it is working without a reboot. If it's not working, then we will reboot. So to check whether it's working or not, just hit your search button, then search for Ubuntu, it is showing Ubuntu 24.04, press Enter. Okay. You can see that it is giving me an error. This may take a few minutes and the WSL register distribution failed and all. So for me, it did not work without a reboot, so I'm going to proceed and reboot. So once the reboot is done, then I will show you what is the procedure. So now I will reboot. Okay, now my system has been rebooted. So what I'm going to do is this search for Ubuntu. This might open automatically or might not open automatically, let it take some time. Then once the installation is over, it will ask for user name and password. Then we will do the setup. Because this is a separate mischie inside your Windows mission. We have to give the user name and password. Now it is asking for a user name. So I'm just entering a user name. Press Enter, then it will ask for a password, but you have to be very careful while typing the password. Because when you type, usually when we type password anywhere, either it will show what we are typing or it will show at least a star or some symbol. Right. But here now it will not show anything. You have to type it very carefully, and it will ask for a confirmation also. So now I'm going to type Enter and it will ask to retype the password, so type it again carefully and make sure that you are not giving any space special character while typing your username or password. So it should not have any special character or it should not have any spaces in between. So once you do that, this window will appear, and this is your WSL massin. So how will you know whether you are in WSL or in command prompt? So when you are in WSL, you will see that your user name at your device name will appear here. But if you are on your command prompt, then this will all be white, right? And it will just say C uses HP, the atop name, all that will come here. So here you will be getting this green color and then it will be followed by blue color. So all that will be there, that is how you know that you are in your WSL. Let me close this and open a new bent terminal. Now we can start installing our open foam. So the first method is just copy this, go to your terminal, either right click Right Mouse button or just press Control V. So mostly write button will work, t button, press Enter. Now it is asking for a password, right? We have to type it very carefully. Have to remember the password all the time. You should not forget it. Otherwise, you have to uninstall your WAL and reinstall it again. It's going to be a big problem. So always remember the password. Now it is saying the repository setup. You can now install packages. So first, we have to update, get updates for the packages. So copy this right click presenter. It will search for any updates available. This might take a bit of time. So once that is done, we are ready to install. So you just copy this entirely. Go here, right click. Use your left arrow button. To change this to 20 406 instead of 23 12, then press Enter. Then it will ask for a confirmation. Now it is asking or no, and it will consume one, two, four, six MB of additional space. So I'll type Y, it enter. It doesn't matter whether it is small Y or capital Y, don't have to worry about that. So once you press type Y, press Enter, just wait for open foam to get installed. So once the installation is done, I'll get back. Okay, now, the installation of Open Foam is also done. But if you see that it is giving us some instructions to do. So now let us do that. To do that, just type explorer dot cspace dot, presenter. Okay. Then this window will open here you can see that you have a file called dot BRC. Now, if this file is not there, this location is not there, then in the terminal, you just type CD once, then you type the Explore dot EXE and it will be fine. Okay. So now you can open this BRC file either in VS code or in notepad, or if you have any other text editor, anything is fine. So once you open it, go to the last line, okay? Create one more line after the FI, this should be the last line. Okay. Now here, you have to type this command that is shown here, okay. I'm just going to type it out. You can also copy paste, but I generally like to type it. So don't miss the dot. It starts with dot space slash USR LIB Open Foam, Open Foam 20 406 slash ETC slash RC. So once you type that without any mistakes, I hope I did not make any mistakes. Save the file. Close this also, then open a new Ubuntu. Okay. Now you have to type the set of commands that I'm telling you, MKDIR space hyphen P, dollar Foam underscore run. Notice that Foam underscore run is capital, press Enter. Okay. Now what we are going to do is we are going to create a location where you can use your open foam. So you don't follow any other YouTube tutorial, they will be using the location where WSL is installed that will cause problems. I will tell you this and you follow this all the time. So go to drive any drive, C or D or E, wherever you have space, then create a new folder. Called Open foam. Here you can create another new folder called version 20 406 recenter. I'm just doing this because if you want to create any other versions later, then you can have it nicely there. Okay. Now what we are going to do is going to open the same explorer dot ExCspagt in this location, open the BasharC Go to the last line and just type out this command, AI as equal to opens colon, CD space, then you have to type slash N T slash. Then you just go to this location. If you are in C drive, then you have to type small C. If you are in Drive, it's small D, form it's small D, slash, then this location. Okay? So it's open form, slash V two, four, 06, then close the single coach. Now here, we have to give this a name. So I'm going to call this OF 20 406. Okay? There is no space between this and this and all. So just save this, close this bash C, open the sorry, close the UbenT, open a new one. Okay. So whenever you want to run any open form simulation, just type this. It will take you to this location. Okay? This is inside Windows. That is what this M&T means. So now let's test it. I'm going to create a new file called file. You can see that it is appearing here instead of WSL location. We don't want this file, okay? So what I'm going to do now is I'm going to copy all the tutorials. If you're familiar with open foam, you will know that all the people use the tutorials to do anything we want. So the command here is CP space hyphen ar, dollar foam underscore, tutorials space dot. Don't miss the dot. So once you do that, the tutorial folder will be copied here. If you're completely new to open foam, just follow this. Trust me with the process. Don't worry what this tutorial means. Why are we doing this and all? You will get ahold of it later. But for now, just copy the tutorials folder here. And whenever you are following any open Foam tutorial, open this location first type IF 06 in your Open two terminal, then you will be able to get to this location. Once you get to this location, then you can do the tutorials that they are telling you. In fact, we will create one more folder where you will be able to copy all the tutorials, create separate folder for all the cases that you are running instead of putting everything in the tutorials. We will also create that once this copying is done. Once your tutorials folder is completely copied, just create a new folder called run. Then you can enter the folder called run through this. Now, in fact, you can open this location every time, when you open a new terminal, this will be something like this. So once the terminal is open, just type OIF 20 406, and it will take you there. Then you can enter the run location. So this is where it is. Then you can run any case that you want. So there is also another way. Let's say you are having multiple folder inside run, then you have to navigate right. Instead of that, you can just right click here, open and terminal. Any location, this works for any location, open any location in Windows. There's right click open and terminal. So once it is open in the terminal, just type WSL, Enter, then it will open the Ubuntu terminal here. Then you don't have to worry about opening the location through your terminal. This will work all the time for any location. This is open. So that's it for the installation of Open foam, then you can follow the other tutorials in other videos. Make sure to like the video if you liked it. If you have any doubts, you can come on down in the video. Thank you. 4. blockMesh, icoFoam and Introduction to ParaView: Hello, everyone. Welcome back to the CFD using open foam, beginner to intermediate course. This is the class two. And in this class, we will be seeing some geometry and mesh generation using a tool called block mesh, then setting up boundary and initial conditions. And then we will also see how to use solvers and run the simulation in open form. After doing that, we will be using Para Vew as the post processing tool, and we will be seeing the results. First, what is Blockmsh? Blockmsh is a mesh generation tool which comes with the installation of open foam. It uses a dictionary file called Blockmshdt to define simple geometries and create structured measures. The role of Blockmhe open form is that it is used to create initial computational measures. It can be highly structured, suitable for simple geometries like square rectangle, channel, cube, cuboid, or a flow over a cylinder or a wedge. These kind of things can be easily done using block mesh. Even it can handle complicated mesh like structured mesh around an airfoil. But for that, we have other tools which might be very efficient in terms of time than block mesh. So the effort is accuracy comes better in other software for a complex mesh, but block mesh is very efficient for a simple mesh. So the main key sections of block Match dt is like vertices will be there. We have to define the vertices on a three D space, which we are going to use. Then using those vertices, we will be defining boxes or a hexahedlbx meaning it will have six faces more like a cube or a cue boy. Then we will be defining edges if we want specialized curves. So if there is a two point, and we can join the two points using a line. But if we want to join it using an arc, we can introduce a third point and define that point as a path. So that can be done using the edge feature. And then comes the boundary. So this boundary will define the type of patch, whether it is an inlet or outlet or empty patch or wall patch, or if it is symmetric, we can do those things in the boundary. But let's say we have two blocks and two blocks share one common pace, but we don't want it to be like a wall, what we do. We just merge the patch so that those two blocks behave like a single block. So that is where the merged patch pairs come into play. So we will be seeing all these practically when seeing the block mesh dit file as an example. For the first thing, we'll be creating simple geometries like two d square cavity. We will be defining eight vertices and we will use those eight vertices to create a single block, and we will be defining boundary condition and we will see how the meshes. Then the next example will be we will be doing a three D rectangular channel where we will be setting boundary condition like inlet outlet and wall, same eight vertices and we'll be creating a block. So we will first see this and then proceed further. Now I have my terminal open. I'm already in the folder for class two, and we have the first case, which is square cavity mesh. So I will go inside that. Okay. Inside this, we can see that we have constant pf dot form and system. We do not have zero. Zero is supposed to contain the boundary condition or boundary files, but we are not having that file here, that folder here because we are not interested in running the case. We are just interested in doing the mesh using block mesh dit. So block mesh dict exist inside system folders. Let me show you. So this is the case which we are going to use. And under system folder, we will be having the block mesh dit. We will view what is there inside. Okay. Now we have eight vertices, as you can see, so each one corresponds to X, Y, and Z. But before that, we have something called scale. So what is this scale? Usually, everything in open form is a unit, meaning whatever vertices we define, it is in meters. So if it is zero comma zero, comma zero, it is a point. And the next point is one comma zero, comma zero. It means that this is 1 meter away from zero comma zero, gama zero in X axis. But if we don't want to work with meters, what do we do? We just define it as 0.001, if we want to work with millimeters, just 0.01 if we want to work with centimeters. But if you want to work on a kilometer scale, then you can obviously choose 1,000. If you are doing something like an entire aeroplane with a large amount of mesh, then you can choose kilometer scale if you want. But usually, scale one, which is meters is fine. Now let's see what are these vertices. To explain that, I'll just open paint so that I can explain you physically. So this is 000. So let's assume we have a coordinate system. And let's say this is X, this is Y, and this is Z. Okay? Now, we will be doing one by one. This is like an array. Okay? Open form is written in Z plus plus. So everything starts from zero. So this element in the array starts from zero. So let's keep it like this is the zero point, okay? And we have one comma zero comma zero, which is like 1 meter displaced in the direction of X. So this will be our 0.1. And then we have one comma one comma zero, which will be around here, and this is our 0.2. And then we have zero comma one comma zero, which will be around here. So this will be our 0.3. Now, these four points can form a phase, a simple two D phase. Well, open foam can't really work with two D structures, but with these four points, we can only make a two d phase. Now we have got a phase. But if you see the other four, the values in the X and Y are same. Like if it is zero, one, two, three, then four, five, six, seven, corresponding zero and four have the same X and Y, but the Z is different. And if you see two and five, the X and Y is same, but this is changing. What it essentially means is that we are just displacing this entire pace or copying the entire face and putting it at some distance in the Z direction. Let's say this will be our fourth point. This will be our fifth point corresponding to one. This will be our sixth point, and this will be our sunnth point. So what this essentially does is that we have got another phase. Yeah. Now we have two phases, but it is not yet connected in the Z direction, so we don't have a block, right. So that's where this section comes in. We are defining it in the name hex because it is a hexahedral block, and then we are giving the numbers. So these numbers are the index of these vertices. So if you had noticed something when I was writing this, I was doing it in counterclockwise. Because 0123 isn't counterclockwise, then 4567 is also counterclockwise. This is a notion that we have to follow in open form. And also, when we are finished doing the first four points, the next point has to correspond with the zero point. So that is how it works. Only then it can make the association. Okay, now we have created the two phases, and we are defining zero, one, two, three, which is zero, one, two, three, and we have 4567, which is four, five, 67. So we are defining it as a single block. Now, this will connect these points and make it as a block. Okay. Okay. The next command which we are seeing here is three points or three values. This is X, this is Y, and this is Z. So what it means is that we are subdividing the X direction phase in the value of 20, and we are subdividing Y by 20, and we are just keeping one cell in Z direction. So after subdivision, the X direction will be getting subdivided 20 times. And it will be carried over throughout the mesh, not just one phase, it will be carried over throughout the mesh. We will also see this visually, and Y is also done. Simple grading, we will not look at that right now. Let's assume that it is 111 as of now. Most commonly, we'll be using 111 only. So we will just see up to here, run the block mesh, and we will see. So what I'm going to do is I will comment this entire boundary, we will pretend that this doesn't exist. Like, I have commented this, meaning it doesn't exist in the code. So we are just going to run this. I will go here. And whenever you are running anything in open form, make sure you are in the right working directory. So what does working directory mean? When you are in a location, in this case, I'm at one square cavity mesh, and if I type LS, I have to see the constant system folders. Only then we are in the right location. Let's say I am inside system because this is where blockmsh resides, right? But I should not be doing this. If I go into system and do block mesh, it will throw an error. It is not going to work. So I'll go back one directory. Now I'll type LS, now we can see constant and system. So this is the location where we have to execute all our open foam commands. We have to remember this throughout the usage of open form. Now the command to execute block mesh is just block mesh. Notice that M is capital. I will hit Enter. Now you can see that we have 400 cells because we have 20 by 20, and we have many faces and the bounding box is zero, zero, zero, which is the minimum value, and this is the maximum value of the cube, which is 11 -0.1. And we have only default pass as all patch. So we will visualize it to visualize, as I have explained in the previous class, we will do touchspacpara.com to create a para view file. Then we can go in here, double click this Wait for it to load, click Apply, then we will have a block. You see, it is a block, but how do we view the mesh? I will go here, click on surface with edges. Now you can see the blocks, okay? If you scroll down on the left panel, you can see something called dtaxisGrid a bit turn on. You can see the X axis ranges 0-1, Y is also ranging 0-1, and Z direction is 0-0 0.1, exactly what we wanted to do. So if I click this button, it will snap to the Z axis normal plane. Okay, now we have this. So we will see what the 20 by 20 actually did. Okay. Now, let's say I have only one, one in X and Y direction. Uh, now after changing, I will hit Controls to save the file. I will run BlockMsh again, so it will get updated. I will go to ParaView and make sure that you are selected ParadotFm and click on Refresh. Try to move something. Like in paravie, your left mouse will be used to rotate it. Right mouse button can be used to scale up and scale down. Middle mouse can be used to move things. Mouse is highly recommended whenever you are working with any geometry. So get a mouse. Okay, now I'm zooming by scrolling the mouse wheel. Okay, now you can see, even though I am in surface with edges, we are seeing only one cell in this because we have not divided into anything. Now, let's say I'm just dividing this by five, five. I will save the file, run block mesh command, go to Paav, refresh it. Now you can see we have five on the x axis and five on the y axis. Now, I just want to go back to 20 by 20. Let's see. I will save it and run the block mesh. Refresh, and you can see we have 20 by 20. But since I gave one as the value in Z direction, we have only one cell in the z direction. It is because we are trying to make a two D square cavity case. So we are keeping as one. So because in open form, there is nothing as pure TD. Everything has to be TD. But what we will do is we will set the front plane and back plane as empty patch, so it will behave like a two D case. Okay, now we have the mesh. How to define the boundary names. Like, everything is a default patch here. How do I know? On the left panel, see if you click here, Uh, I will deselect Internal mesh and select on the default phases. Click Apply. You see, everything is default phase now. This is where we will be getting the name of the patches. Now I will go back to Internal mesh as of now. Okay. In the block mesh dig file, I have typed this. So let's see what each of them says. I will just comment out, moving wall, save it. I will go back to the pate. A you see, I have given a name, moving wall a curly braces. Within that, I have typed type as wall, so this is going to behave like a wall. This name can be anything. I just chose moving wall, in this case, but it can be anything like a top wall or something. Then the type is wall, and I have to define the faces. You can see we have four numbers here, three, seven, six and two. So what it is, it is three, seven, six and two, which is the top face here. So you can notice that this is also in anticlockwise direction. Three, seven, six, two. We always have to follow this. Otherwise, it will say the pace is outward, it is facing outwards. So what we are trying to follow is right hand thumb rule. Assume that this is a hand. Okay. So whenever you are curling your fingers, the outward normal should be facing outside. Your thumb has to face outside. So we are curling it that side, so it is facing outside. You can try it. It is right hand thumb root. Okay, now I will save this file. I'll go here, run Block mesh. Now you can see that we have one more patch called moving Wall apart from default fees. I'll go to ParaView refresh. You can see this just popped up. We have a moving wall now. I will select that, deselect everything, and you can see this is the moving wall. Very nice. We just created or given a name to a wall or a patch. Okay. Now, similarly, I will remove comment for fixed walls. Fixed walls are also walls. As you can see, I have defined three phases here. One is 0473, which is 0473. Just this phase. If you see from that side, then that is still anticlockwise. Then we have 2651, and then 1540. We have defined all these phases as fixed walls. I will save the file. Run block mesh. Now you can see we also got fixer walls now. I'll go here, refresh. I will select the fixer waves alone, deselect everything. You can see this is the fixed wall. Okay. This is annoying. I will remove the data access grid. Okay, we have the fixed walls. I will select both fixed walls and default phases. We are seeing everything. I will select fixer walls and moving wall. Yeah, these are the walls. Now we are missing front and back, right. So you can see that only those two are left in the default patch, only these two are left without name. So what we are going to do is we will select those two phases and put it into front and back, and we are defining it as empty. Whenever you are working with two D, the front and back has to be empty. Only then this will behave like a two D case. And here also, I have put two phase values. I will save the file, run Block mesh, just like you expected. And refresh. Now you can see we don't have anything in default phases. We are seeing nothing. I will remove default phases, check fixed walls, we have fixed walls. We have moving walls, and we have front and back. Yes, we have created the entire mesh. Now, if you want to refine it, it's very simple. Just go here and maybe put 50 by 50, save the file, run block mesh, give refresh. Yeah, you have a finer mesh. So this is all that you have to do to create a two D mesh if it is a simple square. Like this can be done if you want to do something like flow uh, on a flat plate, then you can do these things, but you need an inlet and outlet. You just have to change this as inlet and this as outlet, which we'll be seeing in the next case. So I hope you understood whatever we did here. Now we will see about simple grading. So simple grading is like a gradient for the mesh. Let's say this is one now in the X direction. I will change it to 0.1, and you will see how the effect changes. Sorry, I run the block mesh. You see everything is biased towards the right. Still, the count is same. It is 50 50, but it is gradienting towards one surface. It is because we have given it as 0.1, which means this is 0.1 times finer than whatever is here. So it will do that simple uniform grading. So this will be efficient when you are doing some inflation layer or if you want to create some boundary layer thickness, then this could be useful. And if I do -0.1, then I will get it towards this side. And this can be done for Y direction also. I do 0.1, Run block mesh and refresh. Yeah, we have got it. So to reset everything, all you have to do is put the values to default, one, one, one, save the file, run block mesh, and refresh. That's it. So we have got the entire mesh. This is nice. Okay, we are done with this. Now we will see what we have in the second tutorial, which is rectangular channel. Um, okay, in the system folder, we have lock mesh deck and I have defined eight vertices. You can pause the video and ponder how these vertices make a block. Again, I have made this, but now you can see there is a slight difference. We are working with three D, so we don't have front and back, and waltz is defined as wall, but the inlet and outlet is defined as patch because in patches, we can give values like inlet and outlet. That is what this makes. For inlet, I have chose the left face. For outlet, it is the right face, and everything else is a wall. This is a three D case in X direction. I chose 100, Y, ten, and is it also ten? No grading. Okay? And I have chose the scale as 0.1. I'll save this file. I'll go to this location, which is the second folder, rectangular channel mesh. Okay, now I am in the right directory. I know because I'm seeing constant and system and I do LS, which is list, L S is list, we're listing all the folder. Now I can type Block mesh, okay? And I have already created the Para view five, so I'll double click and open it. On upline. So this is the geometry. I'll go to surface with edges. You can see the entire geometry. Now, I can click on Inlet. This is the inlet. This is the outlet, and these are the walls. So you get the point, how block mesh works. And once we have the inlet and outlet, we can set up a key. But you might be wondering, where are these files getting saved? Right. So we will see where it is getting saved. It is under constant folder. Generally, constant folder has other files also, like properties of the fluid or material. But I have deleted these files because we are just interested in mesh. Under this, we have a folder called polymsh. This is where all the mesh information is stored, regardless of what mesh you are using, be it block mesh or Snappy x mesh or if you're inputting mesh from Mansis or fluent or GMSH or whatever it is. Once it is in open form understandable format, it will be under polymsh here you will be able to see five files. These are points which make the mesh, and these are the owner which is like a patch and the relation. These are neighbors, another relation and faces. If you are interested in seeing what is there inside, it is just pure numbers. Okay? Same with this. I see everything is just number. And for owner, again, it is just numbers, points, also, obviously, numbers, but we are not interested in those. We are just interested in boundary. Okay? I'll go inside the boundary file, and now you can see it makes sense, right? We have three patches. One is inlet, the other is outlet, and the other is at. So suppose you made the mesh, now you don't want to generate blood mesh from scratch again, because sometimes when the mesh count is too high, like 1 million then it can take a bit of time to generate the mesh. It won't happen quickly. In that case, you don't want to change just the patch names and run the block mesh again. All you can do is you can go here and change whatever you want. Let's say I don't want this as outlet. I just want this as outflow. I'm just changing the name. Then I can do it. I'll save the file, and it will be appearing there also. You see, we have outflow. So this is the outflow. Paavw has some trouble when we are removing names. As you can see, this outlet actually doesn't have anything. Once you open and close, it will be fine. Now we have the outflow and that is the outlet now. So that is how you can change the name. Now I will change this back to outlet. Save the file and refresh. See? Now, nothing is there in outflow. We have it in outlet. That is what this boundary can do. Also, you can change the patch type. Like if you don't want this outlet as a patch, if you want it as um empty, let's say, it's not usually how physics works, but let's say that you want to change some patch to empty. Then you can just change this to empty and it will go to empty. Okay. And now we also see something called group walls. So if we have multiple walls, let's say walls, one, walls, two, walls, three, and multiple groups of walls, then we are just selecting group walls and click on Apply, and we will be seeing all the walls. So this is also one nice feature in Para view. Okay, we are done with the second tutorial also. Now the third we are going to see curves. It's a bend pipe. I'll jump back to the PPT. Our introduction to arcs. So what are arcs. When I was explaining edges, I mentioned that we can not just join two points through a line, we can join it through a curve by defining a third point. That is what the arcs function does. So we will be doing the arcs in this, okay? So in any rectangular channel, you can create a circular outflow or opening, so that could be done, or you can create an entirely circular pipe that is also possible. This is the syntax. The edges, you can see we have arc V one, V two, PX PY Ps. So what is V one Vt? When we were defining the block mesh, we have these points four, seven, three, two, six, one, and so on. If I want to create an arc 4-5, so I just have to give these two as the V one and V two. Here, V one and V two will be four and five. Oh, what is PXPYPt? This is the third point. So how we usually do is the center of this point, this will act as the PXPYPz. So you can basically choose the third point and it will work. So how do you actually know what is the third point sordinate? It comes by simple calculation on, like a geometry, right? We know the center of something, and we know angle at which this is subtended if you want to say you want to create a point here, then you know what is the angle from the normal, then you can just calculate the X and Y based on the sine Theta and cos Theta. This is just normal geometrical calculation. You can do that and select the points, okay? This will be the syntax, and we can create an arc. Now we will see how it is done through a tutorial. I'll go to the third bendpipe as you can see, we have the block mesh here. Okay. So now let's say that we don't have these two arcs. I have commented it out, and I'll go to the location. I will run, sorry. Block mesh. Okay. I will load the mesh. See now we have a pure rectangle, nothing fancy. We can see surface with edges. Yeah. We have an inlet. We have an outlet, and we have walls. We have everything. Okay. Now, let's say I want to join two points and create an arc. So how do I do it? We will just create one arc and see how it works. Usually, it looks messy. Arcs are not very efficient in open form. Maybe sometimes it is efficient, sometimes it's not. Okay, I have just given refresh, and you can see it has created an arc here. Okay? So I just created an arc because we defined it. It is 1-2, and I have just defined a third point, and it is creating mesh. Okay? So this is how it works. Now if I want to do it for this phase also, then I will uncomment this, save the file, run block mesh, and refresh it again, you can see. Now if you really want to see the coordinates matching, Okay. Now, if you see this point, it is zero point in X axis, it is one, you can see that it is zero to one. So in X axis, it is one and Y axis it is 0.5. Z axis, it is around 1.5. See? That is what we have defined it here. So it is one, 0.5 and 1.5. Now, let's say I just want to push it to one, the Z and not 1.5. I changed it, and running the block measure is throwing an error because it's not matching well. So This is not fully functional, so we might have to be very cautious while doing this. Okay. So I just defined it and it works fine, so I will just stick onto it. But if you want to play with the values, you can definitely do. And I also have a tutorial on YouTube in the channel codynamics where I have done flow over a cylinder mesh, just using block mesh. So there I have clearly explained on how to calculate the third point, the point where it will create a curve using Python, the basic mathematical formula, we can evaluate that. So you can check that video. If possible, I will drop that in the resources. Okay. If I start explaining that, this will become a very, very long video like one end of hours video. Okay, now we have the mesh. So this is how we are creating arcs. Okay, now we will go to the next topic. So we saw all of these how to do run a block mesh. It is through the command block mesh, and usually it is stored in the polymsh folder. Okay. In CFD, when we are working, we'll be defining the boundary conditions. Let's say the inlet velocity at zero times step is one meters per second or 0.1 meters/second. So this is what is called a boundary condition, and it will be applied for all the phases. Let's say in all, it is a no slip condition, which means velocity is zero. It is a fixed value. At the outlet, the pressure will be zero and for velocity, it will be zero gradient. So what is zero gradient? We have to understand the types of boundary condition. When you take the a regular theoretical CF Dcurs you would have come across something called the Dirichle boundary condition and for Neuman boundary condition. So what it actually means is that the Dirichle condition, the values are fixed. It doesn't change or it is not a gradient kind of thing. It is just a fixed value. It is a specific value, but if you take Neumann condition, it is a zero gradient or some gradient. It is low, which is defined in terms of gradients. Okay? So if you want to get into the math, you can the lectures, which we'll talk about it, but we are just focusing on how to implement those in open foam. So we will see that. And there is also something called symmetric. Let's say there is flow over a cylinder, but you don't want to simulate the entire cylinder because it will be computationally expensive. If it is laminar, it is going to be symmetric about the center axis, right? We don't have to do it completely. So in that case, you can do symmetric boundary condition and only simulate flow over half cylinder, and it directly applies to the other half also. You can do the mirroring and post processing. So that is where symmetric boundary condition comes, and cyclic and periodic boundary conditions are something like the outflow can be connected back to the inlet and whatever values is getting out of the outflow will be connected back to the inlet. So it is like repeating geometries. That's why it is called periodic boundary condition. And obviously all will have no slip or slip condition depending on the physics you are working with. And setting the boundary conditions will always happen in the zero folder. So just like how we had constant and system, we have another folder called zero. We will be seeing from now on, because for the previous videos we did not want the boundary condition to be confusing. So I did not add it. Now we will be seeing the zero file also. So each file will have or each time step. In the zero condition, zero folder is just zero time step. It will have velocity, pressure, temperature, pressure minus the hydrostatic forces, and there are other turbulence models like Epsll Nut, Omega, and so on. So these files contain the boundary condition for the entire case, but usually it is mandatory only to have lostian pressure. Depending on physics, we will have other mandatory files. Okay? Now, for the very simpler case, we will have only Velostian pressure, no turbulence, it will be a laminar case. So these conditions will be defined under a section called boundary field, which looks something like this. For an example, we have the velocity file, and under Velocity file, we will have the function called boundary field. It is having three conditions like inlet outlet and all. This is what we had in the mesh also. So this inlet is having type fixed value, and the value is one meters per second. Since it is SI unit, this is one meters per second. In the X direction. The outlet is zero gradient, which means the solver will calculate the values for you. Initially, it is just zero. In gradients, it is a Neumann type boundary condition. Then the solver will calculate what should be the outlet based on the inlet. The waltz is no slip. So open form offers you this nice keyword, no slip to type that the velocity will be zero. But if you don't want to use that, you can do type fixed value and share the value to uniform zero, zero, zero. So that is also meaning essentially the same. And if you take the pressure for the same case, the inlet will be zero gradient because velocity and pressure are coupled. It's related, so we should not overdfine it. So we will say the inlet as zero gradient because we already defined the inlet as a value. And the outlet, we will set a specific value for pressure because we ask the solvent to calculate the outflow for velocity. So we have to give some condition, which will be given through the pressure. And walls will also be zero gradients, so the solver will calculate the pressure on walls. Okay. So we will see how these things work, okay? I'll go to the next folder, which is a lead driven cavity case. We have zero constant and system under system we have the block mesh dig file. We will just run the mesh and we will see how it looks. It is throwing an error. Let's see what happened in the block mesh dict. Okay, I have some keywords here. I should remove it. I will save the file. Yes, it is running fine now. So that was a typo mistake. We can see the mesh. So this is the mesh we have. This will be fixed walls, and this is a moving wall. Front and back will be empty because it is a toy case. If you just want to see all the empty patches, you can select this and you can see all the empty patches. Front and back is empty. What we are trying to do is we are trying to simulate a case, a Toti case where the upper wall is moving towards the right, and other walls are fixed. So it is going to create a recirculation region inside this domain, and that is what we are trying to observe, okay? Okay. Now we will see it has created the polymesh. Now we will get introduced to the zero files. Now we have U and P, which means veloc temperature. We'll open the velocity file. You can see the dimensions are zero, one minus 100, zero, and don't worry about these errors if your ID shows it. It doesn't matter as long as this index is fine. We have the moving wall, which is moving at 1 meter/second in X direction. We have fixer walls, which is obviously no slip, front and back is empty. Okay? So this is like a syntax. This names has to mandatory match with these. Only then it will get applied. If you make even slight mistake like putting small W instead of capital W, it's going to be a problem. Then we will see the pressure file so in pressure for walls, we have defined zero gradient and front and back is always empty. So we have given empty. You can talglt the dimension. This is L, T, and the other values also go on like temperature and all, but we are not interested in that as of now. We'll just do MLT, and you can know what the dimension of this file is. Okay. Okay. Now we have done the initial conditions, but now we also have to set the turbulence model, right? For this cavity case, we are using something called cofoam. Co foam is a solver in open form, which is transient in nature and it is incompressible, but it can't handle turbulence. It is purely laminar. It can work only in laminar regions. For that, we have a file called transport properties. Always transport properties will define the values of the kyamatic viscosity of the fluid which is used. So to change the fluid, we don't have the facility to choose a fluid by name unlike commercial software like answers. Instead, what we will do is we will define the yamatic viscosity of the fluid and it will calculate whatever is necessary. And since Co foam doesn't work with turbulence, we don't have a file here called turbulence properties. Otherwise, we will be having turbulence properties also. In ICO foam without set it is always laminar, so we are not going to set any turbulence. You can find the polymesh which has all the mesh details. Okay. Now we are not interested in learning these three things just yet. We will be seeing it quickly. But for now, we will see what we are going to do with this CO foam case. We are trying to do something called lid driven cavity. We are going to move a lid on top and we will be seeing what is the recirculation reason inside. Okay? Now, we will run it. So we'll be using Co foam sola as I said. Now I'll go into Control dict, and this is the file which controls all the running parameters, simulation parameters. So the application is ICO foam, which is the solva is Co foam. And the simulation has to start from start time. So in this case, the start time is zero. So it'll start from zero. Suppose if we run till some time, let's say, 0.5 seconds, and we want to continue from there, then we can use this command latest time. But in this case, the latest time happens to be zero. So this can be latest need not be start time. Then we are setting the start time as zero. So if we are using start time, then this will be essential. Otherwise, you can leave it. Then stop at will be end time and we will define the end time. In this case, I have chosen 0.5 seconds, let it be. The Delta T, which is the Time step, we will be using 0.005. So I have checked the stability criteria and came up with this timestep. In most cases, you have to check it. And there is also adaptive times stepping in open form, which we will learn later to set up certain cases where we can do adaptive timestepping based on the Corn number or CFL number, if you know by that name. Ok and write interval is 20, which means for every 20 timesteps, a file will be written. The file will be written. And perjurte will remove older files. Let's say if I give perjurte five, then it will keep only latest five times. This will be useful in case of steady state scenarios, but now it is not useful. If all the details are going through your head, don't worry, you will catch up. It's just the first tutorial. Okay. So you don't have to worry about these things as of now. Pretty much all the time, we'll let it be default. Okay. And the FV schemes and FV solution contain all the details related to what numerical method you'll be using to solve each of the equation. So we are not going to go into that. It will be an advanced course. So we are just leaving it as default. We are using a PO solver. So PSO is an algorithm, which is what the ICO form uses. So we will stick with that, and I'll go here. So we have the mesh. We set up the boundary conditions and the initial condition. Now I will initiate ICO foam by the command ICO foam. I'll hit Enter. Now this simulation is over. So you could see that we have 0.1, 0.2, so on until 0.5. I will open the Para view from scratch again. Usually refresh doesn't work in this kind of things. I'll apply. The colors might be different for you. If you want to change the color, you can scroll down on the left panel, can click on the color map. I will get this might be your color map as of now, but I like to keep this pressure in this color map. If you want to set this as your default, can set it and click this button. Okay. If you want to choose any other color maps, you are free to do. So I personally prefer this for pressure. So this is the pressure at 0.1 seconds 5. How to create a tutorial: Hello, everyone. In this tutorial, we will be seeing how to make a case from open form tutorial. So open foam when it is installed, it comes with a set of tutorials. As we are working with something which is open source, we don't have to build everything from scratch. We will have some examples and we can make our own case with those examples as a base case. So in open form, those examples are commonly known as tutorials. So we will see how we can take tutorial folders or case files and modify it for our own purpose and run our own simulation. So to locate your tutorial folder, all you have to do is first source your open form. If you don't have multiple versions, you can skip till now. So from now, it will be very common. So you can be in any directory. Okay, so it doesn't matter. Now you can type CD, dollar, foam underscore, tutorials. If you type this, you will go to the location where those tutorial cases are there. Now you can type explored dot xspacedt dn. Location will open. If you see here, there is a lot of tutorials. The most common ones are heat transfer incompressible and compressible and multiphase in most cases. So if you see we have the incompressible folder, if I go inside that, you will be able to find all the solvers. These case files will be separate for every solver. If these many solvers are there for incompressible cases, the most popular ones are ICO foam, pimple fam, and simple foam. If you go inside simple foam, again, you will find a lot of tutorials. So these are the base tutorials through which you can build your own case, having this as a reference. So we also have pimple form where, again, it comes in terms of laminar, large Dsimulation or RAS model. So if I go inside laminar, we have these many tutorials, and if I go into LAs, we have some tutorials. If I go into RAs, which is Reynolds AvageNvtokes, we have these many tutorials again. Okay. So if I go into ICO foam, again, we have these many tutorials. Under cavity also, I have multiple different cavity tutorials. Okay? So if you see, let's take Co foam case. If I go here, I have zero constant system folder. So under everything, we will have the block mesh, decompose par, if solution, everything. So if you see Co foam, it is always laminar, so we won't have the turbulent properties files. So all you can do is you can copy this and paste it wherever you want and go to a terminal, navigate to that location, then you can run your simulation. Okay? But if you are using something like pimple foam, let's take RASKs because in ICO foam, we saw the laminar. So if you take RASKs and pimple foam, let's take very simple thing like T junction. If you see here, we have got zero constant and system. We have block MissF solution and controlled it. All necessary files are there. It is a very simple case. If you go under constant, you will be able to find turbulence properties. See? We have these turbulence properties here. It is saying it is using K Epsilon. We will be seeing a video on how to model K Omega SST, but I will not touch upon Kepsilon or spallatalma turbulence models. So instead, what you can do is you can refer to tutorials like this. Okay, it uses Kpsilon. And if you go here in zero, you can find there is Epsilon folder. K is there, new T is there. Also, you have new Tilda, which means you can also use palate almas in this case. So these will be covered when we are seeing RAs turbulence models. But as of now, I'm just saying how to make use of those tutorials. Okay? Now, let's say, we have a simple form and as usual, we have pitch daily case. Now when you are trying to build upon a case, let's see what this turbulence model is. Okay, they have K aslent by default, so we are not going to change these tutorials because if you are making any change to the tutorial at all, you can't use it again, right. So what you will do is, you will copy this folder to some location and then use it. So we will see how to do that. I'll go to some location. Okay. Now, let's say mostly we will do all the things in run directory, so you can run and it will take you to the run directory. Now we will copy the Pits daily case. So the commanders CP hyphen R dollar Foam underscore tutorials. So this will point to this folder. Now, under tutorials, we have to go inside incompressible. I will go inside incompressible. Under incompressible, we had to go into simple form, simple form. Then under that, we have its daily, if I'm not wrong. Yes, we have Pitch daily, and we want to copy this entire folder with the name. So just pace and dot, hit Enter. Okay, now we have copied the folder. I will do LS. Now you can see we have Pitch daily and the tutorial folder. Now I will go inside Pitch daily. And if you see, we have the zero constant system, which means we can't run the case. So for example, I can do block mesh. Now I can run. Let me track this. Simple form. And I can do touch part form. And what I can do is I will open this location. And as you can see, we have all the case files here. This is the way which we will use to modify any tutorials. Now, let's say you want everything from the Pitti you want the boundary names all same. So you want the mesh inlet outlet upper wall over wall and front and back one, and you want the same KEL and everything. And even in constant, you want the turbulence property to be the same or maybe different, but if you want the same thing. And if you just want to make the mesh different, then you can copy this case because it already has the method to implement KSL and turbulence model. And pallet almas. So you can take this and modify as you want it. Okay? So if you want to change the mesh, you can do if you want to change the control dig, you can do, if you want to change the boundary files, you can do. Everything comes with the template, right? So if you open the velocity file, you can see it comes with the template of these things with these headers, and you don't want to type all of these from scratch. So always copy from a tutorial, which is as close as your case which are trying to set up and you can modify it. I wouldn't copy a pimple foam case to run a steady secase. So I can copy something from pimple foam if I want to just run a transient case, and using terminal to copy using this command is just one method. Say I have a folder, okay? Let's say I have this folder and I'm just making something called run. Now I want to run the case here. What I will do is I can go to incompressible. Now let's say I want to run the cavity case, I'll go or better I will take the elbow case. I'll copy the elbow, go here, paste it here. You can use the Windows Explorer if you are in Windows, and then you can run it. For example, I'll go to that location. Now I am in the location under which I have run, okay? So we have elbow here. Okay, now I can run whatever is needed. So you don't worry about the all run and all clean file here. We will learn about that in later video. For now, we can see that many things are there here. So you just want to run this case, then you can load it. Then from the terminal, you can run it. Now, I'm not going to run. So it was just for demonstration. This is what you can do, always make a copy and then do it. Don't change the tutorial folders. That would be not a good idea to do. So this tutorial is all about looking at the tutorials folder and copying a case and trying to simulate it. So I hope now you understand how to use the tutorial folder. So if you see here, we have a lot. For example, we have the multiphase. Under multiphase, we have a lot of solvers. All of these are solvers. And if you go into compressible again, we have a lot of solvers. Under each solver, we will have many tutorials. So you can watch over these tutorials and once we understand what these all run and clean files are, then you will also know what are the set of commands which you have to run to run the simulation. All the tutorials won't have block mesh and then run a simple form. It all depends on a lot of things. There are many uh, many manipulation of the case, like setting a field in a multiphase case, just setting one part of the entire mesh to one specific phase of the fluid. So these things are there. For that, we'll be using something called set fields dig and there is a topo set dig. So there are a lot of things. So when you are not sure about how to run a case, that's where all run file will help you. So we will look into that later in the course. But for now, I just hope you understood how to use the tutorials folder and the resources open form oppose through it. Thank you. See you in the next class. 6. snappyHexMesh and checkMesh: Hello, everyone. Welcome back to the CFD using open foam course beginss to intermediate. This is the third class. In this class, we'll be seeing how to use block mesh tool to generate further complicated mesh using another tool called Snappy Hmsh. So Snappy Hmsh is dependent on block Msh, so we have to use Blockmsh in certain way to use it for snappy H mesh that we will be looking and how to set up a snappy H mesh and what actually snappy H meshes and how to create complex measures using Snappy x mesh. Then we will look at a command called check mesh to check the quality of WR mesh. Okay. So the block mesh is used to create the background mesh in case of snappy hex mesh. So what is background mesh? We will look that. So the mesh must consist purely of hexes. Like, we should have a pure cube or pure cuboid, just like how we created the rectangular cavity in the previous tutor. So the cell aspect ratio should be approximately one that is the ideal condition, so it is good to maintain that. And at least near the surfaces at which the subsequent snapping procedure is applied, which if you did not understand now, you will understand later. But if you are good with meshing in general, you'll understand what snapping is. So near the areas where there will be snapping towards the surface, we have to keep the cell aspect ratio as one. And towards the convergence of the snapping, if the procedure is slow, it could lead to the possibility of failure, and we are not wanting to do that. So we have to make sure that the aspect ratio is one. And there must be at least one interaction, sorry, intersection of a cell edge with the STL surface that is a mesh of one cell will not work. So it has to intersect with some cell edges with the STL surface. If everything till now goes through your head, don't worry, you will understand right when we get into the presentation. Yeah. Okay. Now let's assume that we have an teal surface. This car is the STL. We are interested in simulating flow over a car. Okay? Now the gray area is your fluid domain, and we have the tL surface. STL is basically surface geometry. So we have it. You are interested in mesh in the gray area, not the white area, because we are interested in flow over the car. Okay, now the block mesh will act as the background mesh, which will create the outer box, like you see this black box. The block mesh will create these blocks and it will have some subdivisions over there. It also contains the boundary patch, such as inlet outlet and walls. Let's say that this patch has to be inlet and this has to be outlet, then we will define that in the block mesh itself. We are not going to do using snappy hex mesh because snappy H mesh is going to deal only with the surface. Okay. Then the block mesh will enclose the entire tile and can act as the fluid domain if the mesh is required around the model and inside the block mesh. So what this means is that now we have created this black box is generated enclosing the tL surface. So this block mesh has created a fluid domain, which is the gray area, which encloses the tL surface. So this gray area is the fluid domain. And this is essential, only if we want to make a mesh, which is outside the til surface. But if this estel surface is like a pipe, then it does not have to be this big. It can just enclose the pipe and we can generate the mesh inside the pipe. Then the tile will act as the enclosure, not the block mesh. Okay. So only when the uh, mesh is required outside the surface, then we need block mesh bigger than the TL, and it will act as the fluid domain. You will understand it when we actually do it. Okay. Then the purpose of Snappy hex mesh is that it is advanced mesh generation tool for very complex geometry like this aircraft. So this is generated by Fozzy lab, which is at IIT Bombay. I used to work there. So one of the researchers generated this mesh for the Oki 30 M KI Mark I aircraft. So we were interested in simulating flow over the aircraft. So this is just the surface mesh. Actually, the mesh lies in the fluid domain, but we can view the surface mesh. Okay, that's what this image. The point is we can generate mesh for highly complicated surfaces too. That's what I wanted to say. And the capabilities is it can handle complex geometries. It can handle refinement features, like if you want to refine just one region, you can do that, and mesh quality improvement can be done through an I ratio process. Snappy H mesh workflow is like follows. First, we will be importing the STL file into a folder called Tri surface, which will reside under constant directory. Like how we have polymsh adjacent to polymsh we will create a new folder called Tri surface and put the necessary STL file inside that. Then we will be extracting the surface feature using a feature called surface feature extract or surface feature extract is the command to extract the surfaces from the STL and save it into dot E mesh file, which is open form understandable. Then we will create a castilated mesh. If you are good with meshing and the techniques used in it, you will understand what castilated mesh is. And the snappy hex mesh will initially create a castilated mesh. Using snapping and refinement. Then it will adjust the mesh to confirm the surface geometry through further snapping. And then if you want layer addition, like boundary layers, five layers or six layers through layer thickness for ileus, then you can add layers also. So that can also be done in Snappy X mesh. So now we will see how actually snappy X mesh works. Now the blocks which you are seeing is generated by the block mesh. That is the background mesh. Then we have the car, which is overlapping with the mesh, but we are interested in mesh outside the car, not inside it, right. So this is the first scenario where we have the setup. We have a block mesh, and we have an STL file. Then the snappy hex mesh process will start to split the cells near the surface. The feature edge is what we say for the surface. So wherever there is a feature edge, the snappy hex mesh solve algorithm will split the cells to refine it so that we can capture it accurately. It will do for all the feature edges. So it will look something like this. Okay? It has divided the blocks into smaller blocks to capture the features. Then it will remove whatever is residing inside the tile surface. We are not interested in that. We are interested only in the mesh outside it. So it will remove or dilate all the cells inside the tile surface. Then it will start snapping to surfaces. As you can see, this is not very good. The car wheel is circular, but we are getting mesh inside also, and it's not very nice. So the process of snapping will start and it will confirm the mesh, and it will snap to the surface, and it will not have anything outside or inside the surface. So it will be on the surface exactly. So this is what snapping, uh, snapping does, and we will start adding mesh layers wherever it is necessary. So we can control the mesh layer where it is necessary. We can do. So this is the entire process of how Snappy Hix mesh works. Now, for example, we will mesh a simple cylindrical pipe using pipe geometry pipe dot STL. You will have the STL file already in the resources so you can download and use it. So first, we will set up the file called surface feature extract date because that is what is going to extract the feature from STL and put it into dot EmsEmsh. That's what open Form can understand. Okay, this is how the surface feature extract looks. So I will open the file itself so you can understand it better. Now, I am in the terminal. I will go to the class three. We have the pipe external folder as the first tutorial, so I will enter that. Okay, we have constant para foam and system. We are not going to set up the case, run it, so we don't have the zero file now. Okay. Now, I will first run the block mesh. Okay, we have the block mesh. Now to open this exact location, we can do this command explore dot TXCspace dot and head enter. It will open the exact location. You can see C three, one by Pixon. I'll open the paraew file to view the mesh generated by block mesh. Okay. Yeah. This is the mesh we have, okay? This will act as the background mesh. Now what we are going to do is we are going to mesh up pipe. As I said, under constant folder, we have tri surface, and we have pipe dot test here, lclicono and apply. Now, you can see this is the pipe we are going to work with. I put it in wire frames so you can see it better. This is the background mesh, and this is the pipe. Now we are interested in meshing around the pipe. Please don't ask me why we are doing it. We are just doing it for learning purpose. So we're not going to run any simulation. We are going to mesh around the pipe. So by the block mesh, we have inlet, outlet, upper and lower, and we also have front and back. This is what we have. And I will close this. I will go system. Under this, we will be able to find the surface which are extracdt. I will open that So you can see that we have sourced pipe dot STL. So what is the location? By the way, you will not have this file when you get it. So you will just have polymsh and try surface. The polymesh will contain the mesh from BlokMsh and the tr surface will have only dot STL. Okay? So we have this STL, which we created using any CAD software. I created using free CAT I have put it here, so you'll get it through the resources. So it is inside r surface. And notice that S is capital. Okay. Now we are sourcing that name pipe dot STL. Extraction method is always extract from surface. This include angle, we are setting it to 150. If it is zero, it will select no edge, and if it is 180, it will select all edge. So STL is basically triangulated surface. So it also has edges. And we are giving 150 to be okay I will select everything in a cylinder. For highly complex surveys, we might need 180 degrees. And subset features, we will set non edges as no and open edges as, yes. It is always safe to keep it in this setting. If you want to know more about this, you can read the documentation and you can explore nothing wrong, but I always like to keep non manifold edges as no and open edges as yes. And you have to set write OBJ as, yes. Okay. I will save this file. And the next command which we have to do is Extract. Sorry. Surface feature extract. Notice that every other word has the first letter as capital. A hit Enter. You should be seeing end without any error or warning. Now, what this will do is it will create this folder called Extended feature Edemsh and it has written all these files. So this is what write OBJ does, and this is fine. Now we also have the pp dot Extended feature EdmshFle, but you're not interested in that. If you go to Tri surface, we pasted only dot STL file here, but it also has dot E mesh file. That is what is needed, actually. Okay. Now we are ready to do snappy hex mesh. Okay? So snappy hex mesh. It has these three parameters as the main thing. So cast mesh, it has to be true. Otherwise, you're not going to get the mesh. Snap has to be true. Otherwise, you are not going to get a smooth mesh. Add layers, it can be true or false. It depends on what your necessity is, okay? And by default, we will be giving pipe dottyl in this case. If you are having any other dot till, it has to match with the name under tri surface folder. So you are giving it and the type will be tri surface mesh. The name is pipe. This pipe under name, it is user defined. You can keep anything that you want. Okay? It is not a syntax. You can keep whatever you want. And feature will be given through F pipe dot E mesh. This is what the surface feature extract has generated, and we are setting it to level six for very good refinement. It can be three, four, five, six, anything, but generally three is okay ish, six will be very good. You can also go above that. There is no limit, but generally six is very fine and three is course or a decent mesh. And the next thing is refinement surfaces where we are selecting this pipe, right? So this pipe is same as what you defined in here, the name. So it has to match the pipe, and the level I have set it to five to six minimum and maximum refinement level. So it will see how the surfaces and it will choose whether to do minimum or maximum. So it can be same also. Five, five will also be given, 66 can also be given. And the patch info will be type pipe, and in groups, it is pipe. So as we were seeing in Para view, we have empty patch as well as waltz patch. We can also do pipe. We can give our own group. If there are many pipes in the same case, we can do pipes. Okay. This will be in the patch in form. Then we have to give location and mesh. So this is what is most important. I will try to explain it through visualization. So we have our block mesh here, and I will also load the tri surface here. Our STL file. Yeah, we have it. Okay? So if I want the mesh outside the surface, I have to choose a point outside the surface, but it has to be inside the block mesh. You can turn on data access grade. And see what are the points on X Y and Z. So the point if it lies outside the pipe, but inside the block mesh, it will generate the block mesh as the fluid domain. But if your point lies inside the surface of the pipe, uh, then the mesh will be inside the pipe. The second tutorial will be on inside the pipe. So for now, we are doing outside the pipe. So if you see the PPT, we are choosing 00.5 comma zero, which is around in X, it is zero. Y is 0.5 and is it is zero. So zero, 0.5 and zero. It is slightly above the pipe. It is almost same on the surface of the pipe, but it is outside the pipe. So it is going to generate the mesh outside the pipe and nothing inside. So inside will be hollow. Okay. And the next feature is add layer controls. If you set the initial conditions to falls for add layers in this region, then you don't have to set up anything under Ad layers control function. But if you're setting it to true, then you can add the N phase layers. You have to choose the name of the region, which in this case is pipe. So now we will run Snappy x mesh so that commands to do it is first we will do block mesh. Then the surface feature extract, which two we have already done. Then we have to run the command Snappy x mesh, hyphen override. But before that, we will look at the actual file instead of just screenshots. So it is under snappy x mesh dict. If you go here, we have the same file here. And we also have these things called maximum local cells set to 100,000. Maximum global cells is set to 2 million. So these are limits. You can play over it, but pretty much you can leave it default in most cases. And we have seen this. I have set level three because level six is going to take a lot of time. Uh, that's why I said 23. But if you want to increase six, then it's fine. Then for refinement levels, I said to three and four because it will do it faster and resolve angles. This is very important. Unlike surface which are extracted, the more the angle, the better the capturing. But in this case, lesser the angle, better the capturing. So it is to resolve sharp angles. So usually 30 is fine. It's not good to go like ten or five in general. So 30 is decent and we have refinement regions. We will cover this in a later tutogl. So this is not getting used in our case, okay? So you can pretend that this doesn't exist here. The location and measure is also set. In the Snap controls, it has a lot of parameters, but pretty much you can lay it default in um beginner level or intermediate level. If you want to do very fine level of meshing, then you can maybe play with this. And add layer controls also has this expansion ratio, final layer thickness, minimum thickness, and at what parameters it has to grow. So you can check these commands on what these parameters are actually. So that is why these commands exist. You can read and understand what each of these parameters do, and you can play with the values accordingly. Now we have something called mesh quality controls. So it is including a file called mesh quality dit, which is also in the systems folder. You can always copy paste this mesh quality dit. Mostly this is perfectly fine. You don't have to change anything in this, so we are going to leave it. After this, it can be always default. You don't have to change it pretty much most of the time. Now we will run snappy eggs mesh. Okay. So the command is snappy, hex mesh, and always do overwrite. It is not mandatory to do this space hyphen overt, but what this will do is, since we are running multiple iterations, right? So you can see here. We have refinement levels. So for each refinement level, it will try to write it in a new timestep file. We're not interested in doing that. So we are writing the command overt, so it will override the polymsh itself. So we will have consistent mesh under polymsh folder itself. So I'll hit Enter and it will start to do the meshing. Now the mesh is over. So now you can see that in the poly mesh, we have more files, not just boundary faces, points and owner and neighbor. We have more. We also got a new file called sets. So if I go to boundary now, we have five. Like we also have pipe. Previously, we had only four. Now we also have pipe. This is what Snappy Higgs mesh has added. Now we will actually view the mesh. I'll go here, hide the pipe. For ParadotFm, I'm going to give refresh. You can see it has pipe in it. We have generated the mesh of the pipe. So this is the background mesh. It stays consistent, it doesn't change. Now, I can go here and select inlet outlet and Pipe alone. Okay. We have the inlet, we have the outlet, and we also have the pipe. Yeah, it is a decent enough mesh. It's not good to run simulation, but to learn meshing, it is fine. So as you can see, this is almost all quad, all hexahedral. This is what snappy hex meshes. The x means hexahedral. Mostly, it is hexahydrate. Sometimes it fails and makes tetra, but 99%, it is hexahedral. We have this pipe. If you want to see a slice of it, you can also do that I create a slice. To create a slice, you can click on this button and hide the show plain upl you can see we have the only as a line because we have removed internal mesh. I'll select Internal mesh. I select the slice as surface with edges. As you can see, this is what we have got. We have the layers also, good amount of layers. We have the mesh. This is a very coarse mesh. If you want to work on the refinement levels, it's up to you. But I'm saying that once you start refining the mesh, it is going to take a lot of time. So for tutorial purpose, I have kept it very low. You can go up to 67 refinements also. Okay. Now we have done the pipe meshing outside the pipe. But what if we want to do inside the pipe? The procedure remains literally the same, okay? So I'm going to go to the internal pipe case. We have the block mesh, we have surface met extract date, snap x mesh, and we will pretend that this doesn't exist already. So initially, you will have only this. We have the tri surface and inside that we have the pipe dot STL, and we have these files also. Now, the method to do, as you know already, is go to the right location. Check if it is the right location, then run block mesh, get a good end, and do surface feature extract, get a good end, ensure that it has created the extended feature edge mesh folder and the dotty mesh. And we already set up the snappy hex mesh, but there is a slight change. As you said, the location in mesh is going to change. Previously it was zero, 0.50, but now it is one comma 0.25 comma 0.25 because that is going to reside inside the pipe and not on the block mesh. So I'll show You can see the block mesh is exactly the same. There is no change at all. But the point which I have chosen, it lies inside the pipe, somewhere in the middle. It need not be exactly middle. It just has to reside inside the pipe. Then the enter mesh is going to be inside the pipe and not on the block mesh. Okay. But the problem is, it is not going to do the inlet outlet and all. It's going to be getting completely remote. We will look how to do that also in a later tutorial. But for now, this is fine. Now the next thing is run Snappy x mesh, override. If you want to play and learn what the command without override does, then you can just run Snappy x mesh and see what it does to the timestep. Apart from the zero timestep, it will also have other timesteps. If you want to play around that, you are free to do. The meshing is over very fast. Go here and give refresh. As you can see, this is our only mesh. This is all that we have. I'll close this and open it again so you can see the boundary conditions also properly. You see, we have one pipe here, nothing else. This is what the inside the location will do. Okay. We have this mesh. So this is the internal mesh. So now you understood how to make Snappyx mesh outside as well as inside the geometry. This works pretty much with every geometry, even if it is an aircraft or a ship, it works. Okay. So you can try to download some STL files from Grab card or any online sources or if you're good at designing, you can design your own STL files and try to do this. So we will now do check mesh quality command. So it will ensure the accuracy, it will check the accuracy of the mesh that is generated by the SNAPX mesh or any mesh even if you do just the block mesh, you can do this. And it can be helpful in identifying potential problems in the mesh. So the command is just check mesh. So now, since we have all the mesh, we will do check mesh. You see, it has given all the necessary details right from at what time it has checked the number of points, phases, number of cells, and how many hexahedral is there, how many prism is there, how many wedge or pyramid is there, how many polyhedral is there? And breakdown of the polyhedral number of phases like four phase thing is 16 and six phase thing is 118. So all these data you get, this is very highly informative. And the topology, like what are the patch names and what is the phase uh, how many pass it has, how many points it has, and how is the surface? Like? Is it okay on the topology? Is it closed, singly connected? So these are the things which are uh, known from this check mesh command. And it also gives us simply mesh, okay or mesh problems. If there is some problem, it will say what problem it face, like one error or two error, then you can check what problem it has. It says, Okay for bound ray openness, says okay for a couple point location, for maximum skews it is saying, Okay, non orthoganity check it is saying, Okay, so you can see the cell volume is okay, phase a magnitude is okay. If something is not okay, it will say one error and you can go back and check, which is not fine. Okay, so this is the purpose of doing check mesh command. And it will basically say skewness aspect ratio, non orthogonty and mesh consistency checks. So it will give you an understanding on the common issue and their implication on the mesh and how it will affect your final simulation reset. So tips for resolving common mesh is also found online. You can check the documentation on how to resolve certain things. Let's say if you are facing non orthogonality errors, then you can check the documentation and see how to resolve. It is case by case thing. So we can't generally say how it is. So you have to learn by practicing Snappy X mesh. And refining snappy X mesh will generally resolve most of the errors, but sometimes it also needs some personalized curation on the mesh and how it is generated on certain surfaces and how much refined it is. So it all comes with practice and experience on how to make a better snappy hex mesh. So this is how our final mesh looked, and you have a task now. So create a new mesh where the mesh is inside the pipe using the same TL, but now you have to create a how to say, um, boundary layers inside the pipe. So we did not have the boundary layers when we did this. So you have to create boundary layers inside the pipe, and that is your task. You can practice it on your own. Okay? So if you have any questions, feel free to contact me. See you in the next video. Thank you. 7. Solvers and Case Study: Hello, everyone. Welcome back to the CFD using open form beginner to intermediate course. This is our class four, and we will see overview on incompressible solvers, compressible solvers, and some of the multiphase solvers which are available in open form. Then we will do a hands on tutorial on as study on lid driven cavity, same as what we did in the previous class, but it will be much refined and we will actually see how the simulation goes. Instead of a bad mesh, we will have a very good mesh. So incompressible solvers. Incompressible solvars in open form are used to simulate fluid flows where the fluid density remains constant. So not just in open form. Whenever you are trying to do any analytical calculations or in most of the commercial solvers, the incompressibility is assumed in most of the cases unless you are working with very high speed sonic or external aerodynamics thing. Otherwise, mostly it is incompressible. These always are ideal for simulating flows at very low MAC number where compressible effects can be neglected. So mostly less than Mac mostly subsonic. The key incompressible solva available in open foam or ICO foam. So as we already saw ICO foam is a transient solva for incompressible laminar flow of Newton and fluids. The application can be used for time dependent simulation that is transient simulation involving very simple fluid flow, laminar case, it is useful in simulating transient flow in a pipe or a channel. So it can be very easily set up and we can get good results. The next most widely used solvare is simple foam. It is known among almost everyone using open foam. So it is the most common one. It is a steady state solve for incompressible. It can also work for turbulent flows. Both laminar and turbulence can be simulated here and it has a variety of turbulence models. The application will be suitable for steady state problems in various engineering applications, mostly in cases of air flow or an airfoil or water flow in a hydraulic structure where the flow will get to steady state after some time. So that is where we can generally use. It is always steady. That's why we are using simple algorithm inside. And we have a pimple form. So this is a combination of PO algorithm and simple algorithm. So that is how the name pimple came. It is not available in any other commercial solvers. So the description is this is a transient solver for incompressible, I can handle both laminar and turbulent. It is very similar to simple foam, but this can also work on time dependent simulation. That is transient simulations. So unlike simple foam, this can work on transient simulation. So it is like flow around resilient air or moving airfoil, where the mesh mose dynamic meshing is also possible and where there is vortex shedding. In those cases, we can use pimple foam. This is also widely used equally as simple foam. So the implementation steps are going to remain the same. Either you use block mesh alone or along with Snap x mesh, are generating the mesh, then we will be setting up the zero directory for boundary conditions. Then we will be setting up the transport properties, turbulence properties. Then we will configure whatever we want to do in the system directory under control deck, and we will initiate the simulation. If it is ICO form, just type ICO form and it will get initiated. If it is simple form, then simple form. So you get the point. We have to use the name of the solver to initiate it. So introduction to compressible solvers in open form, handle fluid flows where density changes are very significant. These solvers are essential for high speed flows, shock waves, and other compressible phenomena. So the most important solver is row central form. So it is a density based compressible flow solvers. So whatever we saw in incompressible or pressure based solvers, no row central form is a density based solver. So it is suitable for high speed aerodynamic and shockwave kind of simulation. One of the examples is, if you want to simulate a supersonic flow over a wedge or through a nozzle, then you can use Row central foam. And there is one very popular compressible solver called sonic foam. So as the name says, it works for sonic flows. Uh, a transient solver, and for transonic, supersonic subsonic, anything you can use. But it assumes that the gas or the fluid is compressible. That is the only thing. So if it is compressible, mostly it is gas, it can be a liquid. And applications is useful for simulating time dependent compressible flows, which is transient and simulating a shock tube or expansion of a gas in a nozzle. These are the kind of things sonic foam is good at doing. Then we have row pimple form as it says, row is for density based, and pimple is for transient. So it is a transient for turbulence flows of compressible fluids. Unlike pure simple form, this can also handle compressible fluids. It is applicable to wide range of compressible fluid problems, including high speed train or an aircraft wing. Okay. And implementation step is going to remain the same. But we also have to define the pressure and velocity differently. Since it is density based, we will be defining thermophysical properties because it has to account for the compressible nature. So we will be defining thermophysical properties. Which will handle the compressibility. Otherwise, it is going to remain the same on most of the levels, like, do the mesh, set up the boundary condition, initial condition, then run the simulation. Okay? So for multiphase, the multiphase always in open form are used to simulate fluid flows involving more than one fluid. So whatever we have run till now is like one phase or one fluid, right. So if we are working with two fluids, let's say, water mixing with oil, and we want to see how fast the oil will rise over the water. So if you want to do such kind of multiphase things, then you can use open for multiphase solvers. These always are crucial for application in mostly chemical engineering, environmental engineering, and also fluid structure interactions, where we will be having like a flap of an airfoil and we want to see what it happens. If you want to work on fluid structure interaction, then you can use multiphase solvers. Then the key multiphase always are interfom. This is the most widely used one. So it uses volume of fluid method, uh you can recall it from your CFD theoretical course. If you took multiphase uh, subjects. So it will use volume of fluid, which is highly complicated, but you can set it up easily using open foam. It is ideal for simulating interface between two fluids, and simulating the break of waves or dam breaks it is popularly known as the flow in a mixing tank, if you have a very big tank with oil and if you are pouring water into it and how it will react if you want to see how the bubbles are formed. So those things can be done in the multiphase solve using interfoam. We have multiphase interfoam. So this is also the same as interfoam. But again, it has some, um tweaks to the solver and how it is getting sold. So there is slight difference. If you want to know more, you can check the documentations, because it is beyond the mathematics of the course, okay. Implementation steps will be mesh generation, and we will be setting up the boundary condition, initial condition phase fraction here. It is an additional setting. We have to set which area has what fluid initially. So we have to set that and we will also be defining the thermophysical properties for each of the fluid, each of the phase. And we will do the control dict setup as usual, and we will run the simulation. So now we are going to do a lid driven cavity case. So lead driven cavity flow is a classic benchmark problem in fluid mechanics. It involves a square cavity filled with fluid like how I explained already. There is a big cavity, all our walls, there is a lead on top. We are trying to move the lead towards right side at a constant bit. Now it is going to create a re circulation region. So this is used as a benchmark problem to see whether all the algorithm works in your solver is because it is having a complex flow phenomena like boundary layer separation, vortex shedding. And there is also recirculation zones. Mostly watesding is not happening here because if you're working with LES, then you might get small small vortex, but in most cases, you are not going to get vortex shedding in this. It is mostly recirculation zones, and we are going to check that. So it is a valuable taste case for validating computational flow dynamics codes. So the objective of this case study is that to understand the fundamentals of incompressible flow simulation using open foam, they're going to implement appropriate boundary condition for the lad driven cavity case. And we are going to analyze the flow characteristics such as velocity profile, pressure distribution and vorticity patterns. We are going to validate the simulation against established benchmarks or experimental data, but this is a homework for you, like validating the case. I will tell you how to do the setup in open form, and it's up to you to validate it and see how accurate it is. So the case setup is going to consider these steps. First, we will prepare a geometry. It will be a square cavity. We have already seen how to generate this block mesh for this case. And in the flow regime, you are going to do an incompressible flow with low to moderate renounce number. How we are going to set the renounce number is based on how fast we are moving the lid, and the boundary condition lid will have constant velocity boundary condition, which is no slip and waltz is also going to contain no slip. When I say lid is having no slip, I mean, At the surface of the lead just next to the lead, it is going to have zero velocity. But as there is a shear, it is going to move with a constant velocity with respect to rest of the fluid particles. With respect to the lead, the fluid particle just next to the lead is at zero velocity. But with respect to rest of the fluids, it is moving at a constant velocity. So that is the basic understanding here on setting up the boundary condition. So the simulation parameters or we are going to use block mesh to develop the structure mesh. Then this is a transient simulation, we are going to use Co foam, and the turbulence model is obviously laminar because it is icofoam. Okay. If you want to look at what is the boundary condition, I have displayed it here. You can look at it. As you can see, the first is velocity, you can recognize it by the dimensions. So the velocity of the moving wall is 1 meter/second towards X axis. For the pressure, it is zero gradient and zero gradient. And for Kyamtic viscosity, it has 0.01 and the SI unit only. And the application is ICO form, the start from is start time. So which is zero, and we are going to end at 0.05 and the Delta T here is 0.005 unlike what we did in the previous thing, like 0.005. Here it is much smaller. So after we set the boundary conditions, then we are just going to analyze the velocity profile, pressure distribution, at city patterns, and validation. So this validation is on you. This is like a homer. We have to do it. We will be seeing how to post process for velocity profile, pressure distribution, and at CD patterns using Para view. But validation is up to you. So we will now run this simulation, actually, okay? This is the case, have cavity case. Okay. And we have zero constant paraforman system. So I will open it. Okay. So under zero, we have velocity and pressure. So these are exactly the same as what you saw in the presentation, like these things. So I'm not going to go over every one of them. I'll show you transport properties. The new is 0.01. And in the system, the block mesh is same, and the control date it is slightly going to be different. Like, it is starting from zero, ending as 0.05. That is same, but the delta t is 0.0 005. Write interval is for every two time steps or yeah, time steps, it is going to write one as well, which means 0.001. For every 0.001, there is going to be one sell. Now we can run it to run it. All we have to do is do block mesh, and co foam. It is going to take only that much time. Now we can run it or visualize it using paraview. We got all the time steps. I'll go to Para view, click on Apply. Now you can see we have the pressure profile. I'll choose velocity profile. Now we are in the 0.001 time step. To play, I can click on this and you can see how it is growing. You get how it has converged. Okay. This is the velocity profile. We got the pressure profile also. But how to plot stream lines to understand what a city we have to plot stream lines, right? So to do that, first, we will do a slice. So to click on the slice and choose Z normal, we will have this plane. I usually remove hoplane and click on Apply. So on this slide, you can choose velocity. We have the velocity profile and you see this, right? So it is a stream tracer. If you click on that, it will plot from the minimum to maximum. Click on Apply and usually it is in pressure. You can choose velocity. You can reduce the number of points. Now it is 1,000, you can keep it around 500 or even less. I keep 100. Now you can see how the velocity is in circulation region. That is one thing, but if you want to do the um, vectors also you can work with the glyphs, but that's not going to be very useful in this case. So I'll keep it with stream lines. If you want to hide this line, just click on this and it will be done. You want to save this as animation, click on file, save animation and give some name, let's say, lead driven cavity. Choose as MP four, click on Okay, and you can choose the frame. Let's say I want to do ten frames, which will be 0.1 second will be the one frame. You click on Okay, don't worry about this error. I always appears. We have the pile. We have the stream lines. Now if you want to do just for the pa view, hide this, hide this, and again, can save animation. Now I'll do it driven cavity, velocity, click on Okay and click Okay. Now we got the velocity. Now this will be much lower because I chose one frame per again. So you can actually play with this, and that is all about this tutorial Okay. And the next week's homework task is, go to this link. It will be available in resources. This is a tutorial I made for a mesh preparation using Block Mesh for backward pacing step. So this will be used in our next class. So make sure you understand everything from this tutorial. Pause the video whenever you need, do it hands on, do it parallel and understand everything. If you have any questions, feel free to contact me. Thank you for watching this video. See you in the next class. 8. Boundary Conditions and Intro to Turbulence Modeling: Hello, everyone. Welcome back to the CFD using open Form beginner to intermediate course. In this class, we will be seeing the types of boundary conditions, practical implementation, examples of those boundary conditions, turbulence modeling introduction, and setting up and running some RN simulation. So what are the types of boundary condition? As we already saw, we have two. One is dish lay boundary condition, and the other is Neiman boundary condition. To do a dish ley condition, we will be defining a fixed value. So it specifies a fixed value for a variable at the boundary. The example is like inlet velocity in a pipe. The application will be used when the exact value of the variable is known at the boundary. The open form keyword to do this is fixed value. Notice that the V is capital because it's the second word. I took a velocity file, for example. In this, we will be specifying the inlet as a velocity. Here I have done inlet as a function. This will be defining the U file. So the type will be fixed value, the value will be uniform 100, which means it is one meters per second in X direction. If you want it in the negative X direction, you can just mention it minus one, and it will be directed in the opposite direction. If you see num and boundary condition, it is a fixed gradient. So it specifies a fixed gradient, a rate of change for a variable at the boundary. The example is heat flux at the surface of the wall or a heated wall. The application is it is used when the derivative of the variable is known at the boundary. So the open form keyword is zero gradient. It is not constrained to using zero gradient, but it is the most commonly used he can also define other types of gradients with specific values if you want. So that is also possible. Here I have taken the same velocity file, but here we will be defining the outlet. So this outlet is set to type zero gradient because we do not know what is the value at the outlet because we define at the inlet, so we won't give at the outlet. The solare will calculate it for us. Instead, we will be defining maybe zero pressure at the outlet. Then we have symmetric boundary condition. It assumes no flux across the boundary. The center line of a symmetric flow problem is one such example. The application is used to reduce computational effort by exploiting the symmetry in the problem. The open form keyword is using just symmetry plane. So it is mostly useful in cases like a nozzle. Instead of doing entire three D, even if you take a two D section, you are still going to see the flow. But even in a two D, you don't have to simulate both the top half and the bottom half. Just simulating the top half is enough because it is going to be symmetric along these entraxs. So you can define the entrax phase as symetrblne and it would still work. Then we have the periodic boundary condition, which is also known as cyclic. It assumes the solution repeats itself in a periodic manner, which means the flow in a periodic array of obstacles can be modeled in such a way that the outlet of the pipe or outlet of the flow domain can be given as the input back. So when we are getting an value at the outlet, we can give it as the inlet as well. So that is what the cyclic says. So the application is used in simulations of repetitive structures or flow. And if you have only a small section of pipe, but if you want to consider it as an infinite length, then you can do the outlet, uh, given to the inlet thing. So it is mostly periodic a cyclic and it can be considered as an infinite pipe. The open form keyword is just cyclic. So we have two things. So one is periodic one and periodic two. So if you see both has the type cyclic, but the neighborhood patch corresponds to the opposite of the one. If you see the periodic one, we have neighbor patch as periodic two, and periodic two has the neighbor patches periodic one. This is how we are defining the coupling of both those patches, and it will be coupled so that one of the output value is given to the input of other values. The practical implementation example is what we are going to see now. We have a backward phasing step of a two day. So if you haven't watched the meshing tutorial already, please check out this YouTube link of my YouTube channel where I have step by step explained how to prepare the mesh for this. We will set up both laminar and Turbulen case for this problem. We will use incompressible state solver, which is simple form. So now we will see how to do the laminar case. This is the geometry which we are using. It has inlet, outlet, fixer w, and front and back. If you see the front and back is said to empty because we are treating it as two decays. Then we have the velocity. The velocity we have used directly boundary condition where we are defining the uniform velocity as one minus three which is ten per minus three in the X direction, of course meters per second, and the outlet is zero gradient. If you see correspondingly for the pressure, we are not defining the inlet because we already defined it in the velocity. So we are defining it as zero gradent in the inlet. And for the outlet, we are setting zero pressure. So it is also in SA unit. So we will be defining fixed value, and the value is uniform zero. And for fixed walls for velo state is no slip, it is just a nice way of saying that the fixed value is zero. Notice that the S is capital. And for pressure, we are saying zero gradient. So zero gradient is the way to tell the solver that you have to calculate it for me and I do not know it already. And front and back is obviously empty because we are doing a two D case. If you see the transport properties, we are using a Newtonian model with a kinematic viscosity of 1.56 into ten per minus five, and the simulation type is laminar for this tutorial. And in the control date, the application is simple form. Start time is zero, and we'll be stopping at 2000. That's the maximum number of iterations. But if the solution converges faster, we will not go till 2000. That's how steady state cases work. So these are the results which we are expecting out of the tutorial. So now I will jump to the terminal. Okay. So this is the case where we'll be working on. So I will open that location by doing the command explore dot Exspacdt. So this is exactly the case which I showed you. All the case wells belong to this. Now we are going to run the block mesh. So I run the block mesh, then the next command is simple form. Now, I will let the simulation run and let it converge, and we will wait for it. Okay, now the simulation has converged at 483 iteration. As you can see, since it conversed, it did not bother to go till, uh, 2000 iterations. Now we can visualize the results. I'll open the paraviewFle. I'll click on Apply. Okay, now we have got the pressure, but since we are interested only in the last timestep where it converged, we will press this and go to the last timestep, which is 483. I'll press on this to set the value to the range which is visible here. And we can visualize the pressure. As you can see, we are getting a good steady state over here. Okay. Now, the most important result which we are seeing in a backward phasing step is the reattachment length and the recirculation region. So we will see how to visualize the recirculation region by plotting stream lines. So I'll press on this, which will plot the stream lines, click on Apply. Initially, it will show only the pressure colors. You can change it to lo city colors. Now, if you want to hide the line, you can press on this. I will hide the line. You can see that there is a recirculation reason and a reattachment point for this. But this tutorial is not about calculating the reattachment point, so I'm not going to touch upon that. If you think like there are too many number of stream lines, then you can probably reduce like this is a good number, we are able to see distinct lines here. So this is how we will be plotting streamlines. And if you just want to see how it looks without these stream lines, then you can go here, hide this, and this is your rest. So that's it about the laminar case. Now we will see the turbulent case. So what is turbulence? The characteristics of a turbulent flow are irregularity, diffusivity, and high renune number. The importance of turbulence in engineering is that it is an important aspect to consider as it plays a crucial role in fields like flouid mechanical system, aeronautical engineering, and environmental engineering also we there and HVAC. The turbulence model overview is mostly this. We are mostly interested in only three types of turbulence modeling. One is direct numerical simulation where we will be solving the entire Navy Stokes equation without any modeling. It is computationally expensive and not feasible for high renals number. Then we have large AD simulations, which will resolve large scale turbulence structures while modeling smaller scales, and it is suitable for unsteady flows with moderate computation cost. Then we have renalds average Navy stokes, popularly known as RNs or in open form terms, it's RS RAs. It solves the time averaged equation of motion with turbulence effic modeled, widely used due to its balance between accuracy and computational cost. So this is the introduction to turbulence modeling. You'll be using RNs throughout this course. In RNs, there are mostly three main models. One is known as K Epsilon, where it is a two equation model, where it is modeled based on turbulence kinetic energy, which is K and the dissipation rate Epsilon. It is suitable for general purpose applications. Then we have the most popular one, which is the K Omega SST model. It is also a two equation model based on turbulence kinetic energy and specific dissiputation trait, which is Omega, commonly used in external aerodynamics and turbomachinery where the walls need to be modeled. So SST is shear stress transport model. So we will be modeling Car stress better than this. Then we have the palatalmors model, which is a one equation model designed specifically for aerospace application to predict boundary layer behavior and aerodynamic performance. It is mostly used in external aerodynamics for airfoil, wings and aircraft. So now we will be seeing backward phasing step two D turbulent case tutorial. So I'll go here. I will enter the second tutorial. Clear this. Okay, now we are going to see the boundary files. Again, the boundary is going to remain the same. The message is the same. And for velocity, we have given 0.05 meters/second. It's quite high from what we used already. Then we have the K, which is tubulin kinetic energy. For inlet, we are giving fixed value and value. We are giving a reference value, which is uniform, 1.09 into temper minus three. It is a 0.061 percentage. If you want to know how to calculate K, Omega, and Epsilon, there is a beautiful documentation from open form. You can check that out. So they have given all the standard formula to calculate it, which you will be using as the initial condition. And for fixed as, we are using KQR all function. And again, the value was referenced to internal field. Frontenb is, again, empty. Then for Nut, we are giving the inlet a zero outlet also as zero. Fixed walls as Nut blended all function, which is a function. And if you want to know more about these functions, you really have to check the documentation because there are a lot of function. We can just explain all the function in the videos. So we have the front and back as empty. So nut is just turbulent kynmtic scarcity. Then the next thing is, we are having the Omega here. So sorry, the PPT has went backside. So it is Omega, and we have given it a pretty big value. So there is a reason. Since we want it to converge to a right value, we are giving it a very big value, and it will correct it to the correct value. So we are trying to give a very big value and asking this sold to correct it for us. And if you notice in NT, we are giving it calculated. So that is also same. We are setting it as zero, a very low value and asking the solvat to calculate it for us. So that's what's happening. And in the control date, it is going to remain the same. And this is what we are uh expecting out of this simulation. Okay, now I will run block mesh. It is done. Now I will run simple form. Let's wait for the simulation to end. Now, the simulation has converged at thousand 378 iterations. Now we can visualize it using Para view. Okay, we have got the pressure, and we have also got the velocity. Now, if you want to plot the streamlines, of course, you can do it here. I'll change it to 250. Click on Apply. Now you see, we have got many recirculation regions. So this is what turbulens does to the flow domain. Okay, now we have done the simulation. If you have any questions, please feel free to contact me. And if you want to check the boundary conditions or types of boundary for each of the turbulens values like K, Epsilon and Omega, you can check the documentation and editor. There are many tutorial cases which you can refer to and try it on your own. 9. Transient Simulations and Parallel Processing: Hello, everyone. Welcome back to the CFD using open form beginner to intermediate course. This is our class six. In this class, we will be seeing introduction to transient solvers, decomposing methods, which will be useful in running cases in parallel if you are interested in running parallel processing. Then we will also see how to run parallel processing for Snappy hex mesh. The entire machine process through Snappy hex mesh can be done in parallel. So we will see how to do that. Okay. Now, introduction to transient solvers. So transient solvers, it uses time dependent simulation. So we will be getting a sort of animation where every time step is converged solution, so we will get a feel of the flow progressing over time. The key features are the model here is unsteady or transient flows, such as vortex shedding behind a cylinder. Example, solvers in open form or pimple form, icofoPsofom interfom. So applications are like in most cases, the examples are aerodynamics, combustion or multiphase phenomena like mixing processes. The advantage of using a transient solver is to capture time dependent phenomena, analyze dynamic behavior. So in solver settings, apart from what we have done until now, we will also define our timestep, which is Delta T, and we will be seeing how to set the convergence criteria which defines solution accuracy. We will also set maximum Quran number, CFL number and so on. So we will be seeing multiple tutorial cases. The first one will be backward phasing step two decase in open form terms, it's called pitch daily. We will be seeing Kepsil and turbulence model, and the solare which we will be using is pimple form. So as you can see, this is the part of control dit file, which will control the entire simulation parameters. So the start frame start from is set to latest time. So basically, when we don't have any time steps before running the simulation, zero is the latest time, so it will start at latest time. But if you want to start at start time every time, then you can start you can set the start from to start time instead of latest time too many times in a sentence. Stop at will be end time and you can set the end time. That is the flow time in seconds where your simulation will end. In this case, your simulation will end at 0.3 seconds. So it's like you're starting a simulation, you're starting a flow. And after if you stop the simulation or stop recording the simulation after 0.3 seconds, whatever video you would have got, that is exactly what we are trying to simulate here. Then we have the Delta T, which is the time step. In this case, it is 11e minus four. So that is very small, and we will see why we said that. Okay? In the control deck, sorry, in the control, we are setting it to adjustable and the right interval is 0.01, which means our Delta is 0.0 001. But for every 0.01 seconds, we will be saving a timestep file, which will cater us to the animation finally. We will get a frame of reference for every 0.01 seconds. So the perjurte is mostly useful only for steady state case. What it means is if I set perjurte to five, then only the latest five time steps will be stored. Everything else will be deleted to save some storage space. The format should be aski. You don't have to touch any of these. If you just come below, you'll find runt modifiable. You can set it to S because if you see that this simulation is running and you feel like 0.3 is not enough. Then you can set the time to 0.5 while the simulation is running. If you want to do that, then you have to set the runtime modifiable to S. And in the adjusted timestep, if you keep S, then what it means is you are doing adaptive time stepping. In case of adaptive time stepping, you also have to define your maximum Cora number only then it will, uh, do it. Generally, maximum Cora number has to be one. That is the realistic case. It is also popularly known as CFL Current Friedrich levy number. But in open form terms, it's maximum Cora number. We can monitor Cora number while this emulsion is running for every timestep. By default, this tutorial comes with a maxo of five. Let's tick on to the tutorial. But when you are actually setting up a case, make sure that mostly it is one or depends on the physics. So the next image is from turbulence properties file. The simulation type is going to be RAs and the arrays model is going to be Epsilon, K epsilon. The turbulence is turned on, and the print coefficient is also turned on. What this does is in the command prompt or the console window, you'll be able to see the coefficients of turbulence parameters like K epsilon and nut while the simulation is running. So after running the simulation, we will be getting multiple files from 0.01, 0.02, 0.03. So on to 0.3 seconds, we will be visualizing those things, those frames of animation in Para view after running this case. So this is what we are trying to visualize. So the left one is 0.01 seconds, and the right one is 0.3 seconds. This is how it starts and it ends here. So this is just a backward pacing step. Now we will jump into our command prompt and try to simulate this case. I'm in class six folder. Here we have the first pitch daily tutorial. Here we have zero constant and system. So as you might already know, uh, pitch daily comes with a block mesh. So I will run block mesh. And we will find out what is this solver, as we already saw, this is a pimple foam case. Sorry. This is a pimple foam case. So I will write it to pimple foam. And let's wait for the simulation to end. Meanwhile, I'll just somewhere if you scroll your mouse over here, it will snap to specific time, and it will keep on running. It won't stop, but you can just scroll and it will just stop there. You can see it is progressing, the Delta T is progressing, and it is not same as what we had defined because we have said the maximum Kura number and we also have the Delta T, so it can alter the Delta T to adapt to the maximum CRA number. That's what adjustable timestep is. It's mostly adaptive timestepping. Also you can monitor at what time this simulation is happening. This is 0.018 and so on. And we can see the parameters, residual parameters for UX UI, and we also have for Epsil and K, pressure, continuity, everything. So this goes on. And finally, when it reaches 0.3, this simulation will end. So when you're doing this, you can actually go to that location and see it. So I will tell you what the latest time is all about. Now, if I want to stop this simulation, I can just do Control C, and it will just end there. Now I will do Explore dot x. So this location is open, and you can see we have all the timesteps coming here from 0.01, and it is slowly progressing. We have up to 0.14. So since we have given latest time, now we see the last time it ran was 0.14 1795. So when I run the pimple form again, it will just start from 0.14. It is starting from 0.14 because that is the latest available timestep. So it is starting to write from 0.15. That is the advantage of having the start time as latest time instead of start time. Okay. Now this simulation is over, as you can see it took so much time to finish this though I have got all the running time in the video. So it took a lot of time and you can see how many actual seconds it took here. You can also monitor that and you can see it ended at 0.3. Maximum Delta T was around 0.0 002. So that was much greater than what we defined, like 0.0 001 was what we defined. But you can see, maximum Gura number is just five here. So that's why it got adapted. Okay, now we have all the files here. I'll open the paraviw. Now it has loaded. I'll click on Apply and I'll change it to velocity. Okay. Now, as you can see, we are at 0.01 flow time, it is always advisable to first go to the last frame and click on this thing, which is rescale to visible data range and then go back to your first timestep. Mostly, that would be better if you are running a transient cases. But if you think the physics is like, initially, it will be high in velocity. And finally, it will be lower in velocity. Then you have to do the rescaled visible data range in the first timestep. So in this case, the final timestep has some less velocity than the first timestep. So first time step has to be rescaled so that it can adapt till the last timestep. You will understand when you're actually working on multiple cases and you will get it. So I will click on play. So this is how the flow is progressing. You can see the time is changing here. I'll click Play again and it will start from 0.000 0.01 seconds. Now, as you can see, the minimum is 0.01. But if you want to include the zero time step as well, you can check on this button and click Apply. Now, you would also have the zero timestep, but mostly it wouldn't make sense at all because it is just initial condition. Click on run and it would be done. So it is not generally advised to take the zero time step because it is just initial values. It won't give you any proper insight. Okay, now we got the velocity. Similarly, you can also monitor pressure and go to the first time step, rescale it, click on pressure, and you can see it is getting an animation. Now I can do this same thing for KUTEpsilon. So you get the point. Now if I want to do uh velocity streamlines as an animation, then I can still do. I just plot streamline just like the way I would do normally, I'll hide the line. Maybe reduce the number of lines here. Now I can do the same thing like start, play, and it is running. Now it is a bit slow and loading because it is loading all the time steps and plotting the streamlines. So it is doing multiple things at the same time, so it is a bit glitchy. So what you can do is go to File, click on Save Animation, and probably I will save it as streamlines. Hit Okay, and probably I would take for this case, I would take just one frame per second. But if you want a realistic skill, then you have to choose ten frame per second for for you to get a slowed down animation of ten times. But if you do 100 frames per second, then you would get the exact realistic thing because our lowest timestep is 0.01 and our Delta T, I mean, Delta T in terms of saving animation. Every frame here, as we saved it is 0.01 seconds. When you want everything for 1 second, you just have to multiply it by 100. But that would be too fast because the animation will end in 0.3 seconds. I'll change it to one tlicono. So you don't have to worry about this error. It is because of the resolution. Okay, it doesn't matter. Now we got the file saved, the animation file, and I can open the streamlines, and it would be decent enough and fine. As you can see, it is saving one frame per 1 second. You can get some good insight from this. But if you really want a fast forward kind of thing, like a realistic animation kind of thing, maybe a ten times slow, but animation kind of thing, then you can choose ten frames per second in this case. I'll just save it. Now I will run this. Now you can see it is much better and looking like an animation. Since it is a streamline, we can't infer much as well. I will go here and save this as velocity file. But instead of ten, I'm even going to use 20. It is just half scaled down. Here, run the velocity file. This run very fast, as you can see. This is what a real animation would look like at the end. If we had much higher time steps flow time, then we would have a longer animation. But this was just for demonstration, so this is okay. Now we understood how to set up a transient case and run this. This is the first part of the video. From the second part, we would continue, okay? Okay. Now we are going to see decomposing methods. Decomposing is a method where you will split the mesh into separate sections or regions and give your processors each part of the mesh and ask it to solve for you. This is done through a process called message passing interface, also popularly known as MPI. Open form comes with the MPI installation. Generally, people have to write MPI codes. To parallel process their simulations. But since open foam comes with the installation of MPI, we can use it. So it also depends on the number of cores system has. So cores are the number of physical processors your CPU comes with. You CPU will have certain number of physical cores and logical cores. Open foam can access only physical course. Commercial software like AncesFluent can access even logical processors, but open foam can access only the physical course. We will see how to find out the physical course in UR PC because this is the number or value which you have to remember by decomposing. So I have given a set of methods to find out the course in your PC. So you just have to open your task manager and you will go to the performance section, and inside that, you will go to CPU section. Under there, you will go to course and you can find the number of course. So you just have to remember it. Sometimes your laptop comes with the stickers saying a number of course if it is a gaming laptop. But if you are on a very regular laptop, then mostly it won't be there, so you have to find it. So to do that, either you can open task manager from this or any shortcut methods which you know. There are a lot of shortcuts for this. So I'll go here, click on performance, and on CPU, as you can see, we have the number of cores here. In my system, it is eight. So whenever I'm using eight for decomposing an MPI, please remember that you have to use the value which your PC is supposed to have. This because I'm typing eight somewhere, please don't follow the same and face errors. So just replace it in the appropriate places. I'll close the task manager now. Okay. Now we are going to see the decomposing methods. So decomposing in open form is done through a file called decompose pardto. We will see the file as well. So this is how the file actually looks like. It will have number of subdomains, and it will ask you for a method. If you choose hierarchyal, then you have to define the coefficients. So the coefficients are like, if you have an entire mesh and in each direction, how many subdivisions do you need? So in this example, we are subdividing the X in four subdivisions, the Y into two subdivisions, and the set is going to be just one, which means it might be a two decas we are interested in decomposing one. X and Y. So what is important about the four, two, and one? And why did I choose that? It is like when you multiply X by Y by Z, you have to get the number of processors. So in this case, it is four times two times one, which is eight, which is the same as number of subdomains. It is not mandatory that you always have to use all the cores which you have. If you have eight cores, you can still use just six or just two or just four, okay. But it is very recommended that you use even numbers and not odd numbers. So use two, four, six or eight, things like that, but don't use odd numbers. Mostly, it can't work well. That is why laptops or computers come with even numbers of cores. Okay? So you always use even numbers. If you want to find out why it has to be even numbers, you have to study about message passing interface. Okay, now, in other method, which is called Scotch, you don't have to define the coefficients. The program will do it for you. So you just have to specify the number of subdomains and the method. So to execute the decompose padict file and decompose your case, the command is just decompose par. The purpose of decomposing is to divide the computational domain into smaller parts. The benefit is it enables parallel processing and reduces computational time by splitting the work to all the processors. When you are running in series, the computation will be done in a series manner by one processor. But you are doing parallel processing. The work will be split to multiple processor and it runs in parallel so you get it faster. So the method is like first you split the domain into subdomains and assign different tasks to each processor, and you will be able to run the simulation or mesh. So the open form command is decompose part. Okay. So before we jump into what parallel processing and how to do it, we will see how to do the decomposing. I'll go to the terminal. I'll clear this and go to the second tutorial of today. Okay, we have zero constant and system as usual. But if you see under system, we have one more file called decompose Pardi. So that is what we are going to view now, okay? I will go to the second folder. We have decompose Pardit. Here initially, I have chosen scotch, but if you want to trial with hierarchical, you can do it. So we have the number of subdomains where I have specified eight, you have to specify the number of cores and the method, in this case is scotch. Otherwise, it is just normal Pitch daily case, which we run here for transient phenomena. We will see the control dict. So we are again using pimple foam only, and the timestep is Delta T is equal to 0.0 001 and let the maximum O B five, sorry. This shouldn't be there. That was my mistake. Okay. So we have the delta T as 0.001, and maximum Kura number as five. Okay? So we are going to decompose it now. As you can see, initially, we have only zero constant on system. So this zero file has U, P, Nut, K, and Epsil. Because we are using K epsilon turbulence model, all you need as turbulence parameters is just these three Turbulen viscosity, K and Epsilon. If you want to explore what I said for the boundary condition, you can go in and check it, but that's not the scope of this video. So we have zero. We don't have any other timestep because we didn't run it. Now I will go here and I will execute decomposing. So the command is decompose par with P capital, hit Enter. As you can see, it is saying that it is subdivided. It is subdividing the time zero into 027, which is eight fill transfer, and you can see the number of cells, number of points has been assigned to each processor. So it might be a little bit more or less, but each processor has a set of mesh which it has to work on and do the simulation. Okay? So after we do this, we got these files, processor 02 process seven. So when you go into processor zero, you have made a copy of zero files. And the constant file. Under Polymsh, you will have only the mesh this processor is assigned to. It will not have all the mesh which you generated using block mesh. It will have only the mesh content which is necessary for this processor. And same applies to every processor. So it has the zero file because we are going to run things in parallel and it needs reference for zero. So it has the zero timestep. Now, I will explain what parallel processing is and how to do it. So parallel processing using MPI. So MPI is message passing interface. The definition is it is standard for parallel computing, and the functionality is it allows processes to communicate with each other. In implementation for open form, you will enable parallel processing for faster simulation, which is the same for any CFD software. And you will run a piece of form simulation for this, uh as an example for self, you will try a piece of foam tutorial if you want, and you can try it using MPI. For now, we will be sticking with the pimple foam tutorial and we will see a demonstration. But if you want to do it with ICO foam or simple foam, the methodology remains the same. All you have to do is you have to copy this decompose padick and put it into any system directory of any case, and you can decompose it. You just have to set everything properly, like the number of subdomains. Okay? So that is the only thing which you have to do. Okay. The benefit is it utilizes multiple processes simultaneously, and it scales well with increasing computational resources. So let's see what is the step to do parallel processing using MPI. The first thing is decomposed par. But before that, you must have a mesh and initial boundary condition in 05. So that's what I mentioned as polymsh must be available because not just block mesh, you could have generated that with Snappy hex mesh or imported from ANS is fluent mesh, which we will see later. Anyways, all the mesh will be in polyms, so it has to be there. Then you are running decomposed par which will divide every mesh for each processes. Then the command to initiate the solution or simulation is Pi run space hyphen NP, space the number of processor, which in my case is eight and process, which is in this case, pimple form. If it is a simple form, then you have to do simple form. If it is an ICO form, you have to type ICO foam in place of process and space hyphen parallel. So this is what will initiate the solver to run in parallel. I have put some examples. If it is an eight core processor, it will be pin, space hyphen NP, space eight, and the command if it is simple form space hyphen parallel. If it is six cores, then NP six pimple form parallel. We will see about reconstruct after we run the simulation actually. Now that we have all the decomposed files, we can initiate it through pi ran NP eight, eight in my case, pimple form. Parallel. When I hit Enter, it would start to do the same process which we did previously, but in parallel, so it is going to end super fast. As you can see, it is running super fast than what it was running previously, because it is just eight times faster right now. So let's wait for the simulation to end and I will get back to you. So the simulation is about to end. Okay, it is done. Now I will do LS. Again, all you can see is processes 027. We are not able to see the timestep. But what happened? Because everything is inside processor. So we have 0.1 to 0.3, everything here for every processor. Okay. We have to reconstruct everything and then we can see the visualization. What reconstructing will do is it will take the mesh information from every processor, collectively put it and just save everything as a separate time step. And then it would look something like this. But if you don't want to reconstruct because it takes a bit of time, you can open Para Vew and instead of directly clicking on Apply, you can change it here. Instead of reconstructed case, you can go to decomposed case and then click on Apply. Okay. Now, what if I just click on reconstructed case? You're not going to see anything because it doesn't know if there are any files at all because it is expecting the time 0.01, but it is not there. So you have to give decomposed case, so it will go inside every processor and try to recollect it for you for visualization. Now I can see the velocity. Now, if I play, it is going to be playing because it is trying to recollect. But since the mesh is less, mesh count is less, you are not getting stuck. But when the mesh count is very high, let's say, in a three D case where there are millions of cells, then every loading timestep is going to be very high. That's why we are going to reconstruct and then visualize it very easily. Okay? Be it takes time for Pare to reconstruct every single timestep without storing it and displaying it to you. It's too much on the memory. So we will see how to reconstruct it. To reconstrate, the very simple thing is just run reconstruct par. That's all you have to do. So just like how you did decompose par, now you have to do reconstruct PR. Now I will go to my terminal and I will reconstruct par and you will see what happens. It is starting to reconstruct every single timestep by putting the timestep name. See, it is saying time 0.01, and it is reconstructing all the fields, olim scalar field, vector field and surface scalar fields. So as you can see, it is taking a bit of time. It is running slow. We will also see a method to run this parallel as well. But for now, this is the most popular method, so let it run. You're not going to wait for it to end completely because this is just for demonstration. We will stop it at 0.05. Till then let's wait. Okay. Now it is done before it starts with 0.06. If you want to end any process, just hit Control C, and it will be interrupted by the keyboard. If I go here, now you can see, we have 0.01 to 0.05. Okay. Let's assume that you have reconstructed everything, you don't need these files anymore because these are Going to consume a lot of space. Since this is a very small scale, it is less, otherwise, it's going to be gigabytes. We don't want these anymore because the data has been reconstructed. What you can do is RM space minus R Brock star. It just says that delete everything and everything inside those folder which starts with the four letters PROC and we don't care what comes later. So any folder that starts with PROC will be deleted. When you're doing through terminal, it's going to be faster than what you will be manually clicking and deleting through Windows. Since this is through WSL, it's going to be faster than what Windows can even do. So as you can see, it is slowly getting deleted one by one. And now it is all done. Okay. Now you can go to Para view and click on reconstructed case, click on Apply and it would still work, but we have only 0.05 seconds of data. Okay. Now, let's say you don't want these timestep also. You want to start from scratch by changing, let's say, Delta T or maximum core number. If you want to choose it as two and if you want to run it, you have to delete all the timesteps right. Now it is just like around 100 times step. But what if it is so much? You can't delete everything one by one or even if you select everything and delete, Windows is going to take a lot of time. So open foam gives you this nice command, Foam list times. Notice that L and TR capital space hyphen RM, hit Enter, and all the timesteps will be gone in an instant. So you have deleted all the timesteps through this command. This is just some additional information apart from today's topic. So this is just nice to know because when we are working with terminal, it will be much faster than what you can do directly with Windows. Now we know how to decompose a case and run it in parallel using MPI and also reconstruct par. Now we are going to see how to run snappy hex mesh. Snappy hex mesh is a meshing process and we are going to do meshing itself as, uh parallel processing. As I was saying, we must have a poly mesh to generate any sort of decomposing, because we need a poly mesh to even put it in constant and split the mesh to the processor. But snappy Higgs mesh itself is a mesh. What we are going to do is we will generate the block mesh and split the block mesh to different processor, and we will do Snappy hig mesh as a process to every processor. I think you get the point and we will do the tutorial so you understand it better. I'll clear this go to the third case for this class. Now we just have constant and system no zero file because we are not interested in running simulation. So just this. Now what I'm going to do is I'm going to do block mesh because first we are going to run the block mesh. This is the pipe external case which we made, if you remember, meshing around the pipe. Now I have generated the block mesh. Then the next command is to decompose this. I will decompose using decompose bar. Okay. Now we have decomposed the block mesh. Now the next thing is we have to initiate SnappyHmsh. So the command is same Pn, Np eight in the process name, which is snappy x mesh, as usual parallel. If you remember, we always do snappy H mesh with space overwrite. So we can also include that. It doesn't matter if you put parallel first or overwrite first, it's going to be the same. So what I have done is I'll let my short on this so that you can see it better. Wait. Okay. It is MPI run I'm not able to put it in a single line or can I? Yeah. So it is just like MPI run, MPI snappy hex mesh parallel over right. Now I can hit Enter and this will start this snappy hex mesh process. Now you see this running much faster. If you remember at what speed it was running when you initiated the mesh, you would know that it is much, much faster. So now let's wait for it to end and we will reconstruct the mesh through a special command called reconstruct par mesh. So as you remember, we just did reconstruct par when we are doing the timestep reconstruction. But in this case, we have to do reconstruct par mesh space hyphen constant because we are trying to write this mesh inside the constant folder. So I will do reconstruct parmesh hyphen constant. I'll hit Enter. Now you can see it is taking data from all eight processors and putting it in the volumes. Now, we don't need these processor 027 anymore. So what we can do is minus r rock. It will delete all the processor files so we can save up on some space. If you just want to view the mesh, you can go to Para Para view, click on Apply. You can go to Wireframe. Now you can see we have the mesh. The output is going to be the same, but the process will be faster. That is the advantage of using MPI. I hope you understood how to do the um decomposing, as well as reconstruction. Now, let's say you have a zero file also, and now you want to run things in parallel. So what you can do is after deleting all the processor files, now then reconstruct just like how you would do for any simulation case like this process. So again, you have to decompose, then you can run things in parallel and reconstruct P. So that is the best method. So now we have an additional tip. What if you want to reconstruct in parallel? Because reconstruct if it has too many timesteps, like the previous case, it had a lot of time steps. If the case is like that, then it's going to take a lot of time to reconstruct. You saw how much time it took to reconstruct that. What I will do is I will again run that case and show you how much time it takes when we are reconstructing it in parallel, it's going to take a lot less time. So I'll just run this case and get back to you once this is over. I'm just going to run a few timesteps, not completely. So we have five timesteps or maybe four because I stopped it early. Yeah, we have five timesteps. Now you remember how much time it took when we tried to reconstruct it. It was very, very slow. But now we are going to try to use this command and see how fast it is going to reconstruct because it's running in parallel. It is MPI run, Np eight, again, the same thing. Then we are going to run redistribute par. Par reconstruct Parl new times. So you just type this. I hope I didn't make any mistake in spelling and hit tender now you see just how fast it is reconstructing. Now, it is just done. This was the time it took to just reconstruct two time steps. So this is not very popularly known among a lot of users. So if you use this, it's an advantage to you. Okay, if you have any questions about anything related to this video, please feel free to contact me. See you in the next class. Thank you. 10. Advanced snappyHexMesh, External Aerodynamics and Plotting force Coefficients: Hello, everyone. Welcome back to the CW using open foam beginner to intermediate course. This is our class seven. In this class, we are going to see refinement box feature in Snappygmeshdg, tutorial case on external aerodynamics, which is the classic motorbike case. We are also going to plot force coefficients which are drag coefficient, lift coefficent like CDCL and so on, using GNU plot, and we will also be exporting the post processory data to Excel to plot this. So we are going to see how to include a refinement reason inside the entire Snappy X mesh. So as you can see, this is Snappy HmshFle screenshot. We are defining the motorbike dot OBJ. That is a geometry here, and we are assigning it to the group motorbike. And we are defining something called refinement box under the geometry function, which means apart from motorbike dot OBJ, we are also having a new set of refinement box. So this refinement box is treated as a new geometry under which there will be refinement. Okay? So the refinement box is defined in such a way that you just need two points to define entire box. So you just need the minimum point and the maximum point to define a box. So the minimum point would be minus one -0.70. So if you take a cuboid, and draw the major diagonal, it will have two points. One would be minimum, one would be maximum. So that is what this refinement box defines. If you just want to imagine it better, try to plot it in a three D, and you would know using Python or any programming software you are comfortable with. Sorry, programming language you are comfortable with, then you have the geometry of refinement box now. So what you are going to do is you are going to use a function called refinement region under which you are assigning the refinement box as the location where you want a refinement, and you are going to say move inside, which means you are trying to refine it inside this box. You can also do the negative, but mostly it is used only for refinement inside the box. So we will stick with more inside. And we can also set the levels, which is one E 15 or four refinements. So the one E 15 is a standard value which you might have to use, and four is the number of refinement levels. So we will also see the file and see how this is getting implemented. So I will go to the case file. We have zero constant system and Para view. Under system, we have Snappy hig meshedi as usual. So I'm going inside this and you can see that we have refinement box. And this refinement box is referenced when you go below, and you have refinement surfaces. This is one such area. And similarly, we also have refinement regions. So this is the one which you saw in the PPT. Generally, if you don't want a refinement region, all you can do is just select this, put it in a command, and this would be fine. So this should work even without a refinement box, but you can't remove this function entirely. So you just have to remove the values and make the function stay. In this case, we want a refinement box, so I will have it. So we are just going to generate the Snappyx mesh now. So if you remember the process, the first process is to generate the block mesh. It is throwing an error. I'm not inside the motorbike region, so I have to enter the folder. So this is the mistake you should not make. Always type Ps and make sure that you have the zero constant and system. Okay. Now I'm going to run the block mesh. Now the second thing is surface, which are extract. Now that is also done. Now we just have to run this snappy hex mesh date. But before that, we are going to see decompospatic file. I have eight core, so I put eight and the method is scotch. What I'm going to do is I'm going to decompospa I'm going to run Snappy hex mesh in parallel. I'll get back to you once this is over. Now the snappy hex mesh is done, so I can reconstruct it now. I'll do reconstruct Parmesh if in constant. Okay. Now I can safely remove all the processor files because it's not needed anymore. I will open the PRR view file and show you the mesh which we just generated. Because I did not give initiative on what the geometry actual is. As you can see, we have a big mesh, which is our fluid domain, and we have a bike inside a nice bike. Okay. So we are just going to see the bike now. I'll clic on motorbike group of incompressive, sorry, internal mesh. And I'll choose surface with edges. So this meshing took a lot of time. Okay? You can see it took like 28.4 seconds, okay? So it took really a lot of time. So that's why we have a bad mesh, but still we have a bad mesh. So if you're going to refine it further, it's going to take still more time. So for demonstration purpose, I just kept it low. Okay? So this is the bike, and we are going to do the external aerodynamic analysis on this. This is not the best mesh someone could use, but for demonstration, this would be just fine because we are just learning and we want to learn faster. Okay. Now, we will see what is, uh, external aerodynamics in terms of open form. So first, we ran the block mesh, and we ran surface feature extract. Then we did decompose Par and also we did the Snappy x mesh parallel, right. Now then we reconstructed Par also. So we have reconstructed everything related to mesh. But now we have to start decomposing and running the case, right? But you can see when I try to decompose, it won't be getting all the files properly because we have something called zero dot original. When you copy a case from Tutorials, it is going to come like this in most cases. It's going to be like zero dot original. When it is like this, open foam can't realize that this is the zero file and it won't put it inside the constant folder of each processor. So open foam can't realize that this is the actual zero file and decompose it properly. So we have to copy this original and put it in a normal 05. This is there because if you are wanting to make any changes to the boundary conditions, boundary files, you should not mess up with the original file. So that's why we have this. What we can do is either you just copy, paste it here and rename it to zero. Works fine. No problem. But if you want to do it the cool way, you can do CP hyphen R, zero original and zero. That would still do the same thing, but through the terminal. Okay, now we will see the boundary files. So you can see that there is something called Include Include folder, which we have not encountered till now, so I'll explain what it means. So if I go to Include, we have three files, initial conditions, print back upper patches, and then fix your inlet. Just remember these names. Now I will go inside the U file since open form works with C plus plus, we can call in another file and use the functions inside that. So we are including the file called initial conditions. And from initial conditions, we are taking in the value of inlet. Okay? So we have initial conditions file here. I'll just open it so you understand it better. The initial conditions is saying the flow velocity is this, pressure is this, turbulence is this and turbulent Omega is this. Now when I go to U file, you can see we don't have any inlet patch because for that we have fixed inlet patch here. See, we have the inlet patch here. We are just referencing it here, this location so it can get the function from there. And we also include the set constant types function, which is from Include et cetera. So this is mandatory to include this so that open foam can understand that these references are getting referenced properly. Then we are referencing front and back upper patches also. So I need not be like this. You can just copy and paste this here. But the purpose of having this is when you're just mentioning include initial condition, instead of mentioning all of the values in different files, you just put it here and whatever is necessary, it would be referenced. So I will open let's say I will open Kfile because we have Kfile there. We are referencing initial condition. We are including the fixer inlet, so we don't have to type it one by one in all the files. Now if you are wanting to change just the fixer inlet value, instead of changing the value in every file, all you have to do is change it in the one file and it will get reference to all the files. That is the only motive of doing this. I will open different back upper patches now. It says upper wall is slip, front and back is also slip. When we are seeing any file, all you have to do is reference the upper back friend patch, and it would take it a slip. So it happens with all the files. You see? That is the use of having this kind of include folder. Otherwise, these files are just normal thing and you can play with the values if you want. In this case, we have set the initial condition as 20 meters/second in X direction. Okay. Now we will see what is there in the constant folder, we have the tri surface where you put the motorbike to OBJ. Instead of STL, we use OBJ file. We already saw this. So we have the transport properties. We are using a Newtonian model with kymtic viscosity of 1.5 into 104 minus five, and we have turbulence properties where we are using K Omega IST because it works well with waltz. We are trying to do an external aerodynamics, Komega IST is one of the best. So we already saw how to do KF salon in the previous class, but we did not see K Omega. That's why we are seeing this kind of thing. You also understand K Omega better. So to do K Omega, the essential files are K, Omega, obviously, and Nut. Okay, now we go to the system. As usual, we have Block mesh, decomposPadet, and we have scheme, IV solution, mesh, quality d, snappy, and surface feature extract. Everything is fine. But we also have a new file called force coefficients. If I go inside force coefficient, you will see that there is a function which says the type as force coefficient. It is referencing a library called forces. Right control is saying time step and the time interval is one. This is all intuitively understandable. And the log is saying is to plot it in logarithmic scale. If you have not got what this file means is, it is just going to take the CDCL values from here. So that's why we are plotting it in log. And we are trying to get the data from the patch motorbike group. If you see the mesh, I have plotted only the motorbike group here. So on all these mesh points, the calculation will be done for CD CL, and so on. So we have to define the reference values like density. This case, the density is taken as one for simplification. You can work with original, uh, exact values of density if you want. Then we want to define the lift direction. So if you see this geometry, the lift direction would be positive Z axis. That's what we have mentioned, and the drag direction would be positive X. So that's what we have mentioned again. And the coefficient of, sorry, C of R, which is like the center of rotation. No it's coefficient. I'm so sorry. It is center of rotation. That would be 0.720, comma zero. Where did this value come from? I will turn on data axis grid. You can see that this point is kind of the center of this entire geometry. So 0.72 makes sense, right. So that is why we took 0.72, and we want to pitch axis. So, in which axis it is going to pitch for drag and left. So that is Y because if you take the normal or perpendicular, it's going to be Y. So this will pitch along the Y direction. So we are mentioning Y. And magnitude of U infinite, which is the freestream velocity in this case, is 20, and we also have to do the length reference and the area reference values so that the CDCL values are getting calculated properly because we need reference values. Open foam can't take these values from the geometry, so we have to define it. But just calling this putting this folder in system directory is not going to make it work. If you understood open form by now, it's not going to make it work. You have to reference it somewhere. The way to reference it is in control. You open control dt at the end, you just open a new function called functions inside that you just put this function called the force coefficient, and it will reference to the function of functions in force coefficient one function. So we are having this Icloude force coefficient, so it is going to take a reference from there and it will plot all of these. But if you don't want to do this, then you can just copy entire thing. Then just replace it under functions in open form. Sorry, control date. I would just still work fine. But it's not going to be a nice way to keep your control date. It's going to be messy when you are going to work with a lot of functions later. So it's always fine and better to have things in different files and referencing it. That's how C plus plus works. So we got how to set up the force coefficients also. So I would advise you to download some geometry from Grab card, like a car model. You know how to set up Snappy x mesh now. So set up a car case. Try to do this case in car instead of just this bike. Okay? So I have given this bike geometry already, but it doesn't come with the tutorials directly. We have to find it inside the under tutorials, we have resources folder. Under resources we have geometries. Under geometry, you will have this motorbike geometry which you have to download, copy and paste it in the constant folder. So you will understand it better when you see and understand all run files. So for now, you just don't worry, you can download and do machine using Snapxmsh for any geometry and work with it. Okay, now we will see what we have to do next. We have set up everything, so we can decompose par and run this case, right? Yes. So I'll do decompose par. It's going to decompose the case. I hope it doesn't throw in error. Yeah, I didn't throw error. Okay. All I have to do is initiate this case. So this case, I'll go to Controict It's a simple foam case. It's a steady state case, so I'm just going to do MPI irn NP eight, simple foam Rall, and it enter. So it is going to take a bit of time. I'll get back to you after it is over, but you can notice something different here. It is also giving you the values of CD and the vectors of CD and we have CL and vectors of CL also. We also have coefficient of moment for pitch, roll, ya, and all. Mostly, we just use CD and CL. I'll get back to you once this simulation is over. The simulation is over, but still the solution is not converged as you can see, but I stopped it at the time 500 because it's taking so much time, it's already 4 seconds. But if you want to run it completely, you can run it. But for demonstration purpose, this would just be fine. We can take the latest timestep and work with it. So I have run the decomposed case, as you can see. Now I have to reconstruct it. So if you remember the command to reconstruct it faster, Yeah, I have. Okay. Now the reconstruction is done. I can safely delete all the processor files, though it is going to take a lot of time. Can just go here and click on refresh. So it is going to load all the files which is needed for us. I'll go to internal mesh, click on apply. I will take a sliced plane. So I want it Y normal. Okay. Don't worry about this. We'll go to Y normal. This is the pressure fields. We go to velocity field at the last time step. So as you can see, we have the motorbike case and you can see the velocity profile here. If you want to plot the streamlines, of course, you can. But this tutorial is not about this. It is about plotting force coefficients. Let's look at how to do that. So we have done all of these Now we also saw how to set up the function and what everything in the function means. Since we now know how to set up the case and set up the function to get the force coefficients, we can now see how to post process this data. So to do that, you can go to your working directory, and you will see a folder called post processing just got created. If you go here, you'll see the function name, which is force coefficients one in case. Under that you'll have the zero folder under that you have the force or coefficient dot Data. If you open it, it is just long list of files which generated and stored the values of CDCL and their vectors or components of CDCL and coercion of moment and so on. So you can basically import this into Python also and cross process it for plotting. But open foam gives you easy way, which is called foam monitor. So we are going to do that now. So what we are going to do is we are going to create a plot of the coefficient things. So the command is form monitor space hyphen. This hyphen L is for log. So if you don't want a log plot, you don't have to include that hyphenl, we will also do that. So the location of that file is post processing, pose coefficients one, under that we have zero, under that we have coefficient dot dot. So what it means is you're calling the application form monitor, which is based on GNU plot actually. Then we want a log plot, then the location or the path to the coefficient file. Then you just hit Enter and you'll be able to see the graph. So you can see we have the legends here. So the CD is less than one, and you see we have CL so that is also less than one. We have all this. This is a log plot, as you can see from the Y axis. But if you don't want a log plot, let's just assume that you don't want log plot. When you close the application of GNU plot, just hit Control C, otherwise, it's going to respawn and come again. Now I will remove that hyphen L. You can see we just got an normal plot where everything is less than one and close to zero. So you are not going to see much from this graph. And if you want to zoom and all, you can actually do Zoom and things like that. Yeah. It all happens here. So it just works same as Nu plot. I'll close this and hit Control C. Otherwise, it's going to respond again and again. Okay. Now, we are going to export this post process data to Excel, and we will try to plot the force coefficients values using Excel. Okay. Now I will open Excel I'll open a blank sheet. If you are just working with the library office, it is still fine. What I'm going to do is I'm going to copy this entire thing. Instead of doing that, I'll go here and probably hold shift and click on this. And then just copy here. So this would copy everything. Control C, can control. You can also import if you want, I just find it easier when I do this. So since this is a steady state case, first view iteration would be totally senseless, like these things. Also, we don't want the components of CCL. So I will remove all of these. We don't want the coefficient of mom and all. So I will delete all of these. We just need coefficient of drag and lift against time. We just want to see how good converged against time. I will also delete first nine or ten data. Now if you just know how to plot in Excel, is the same, go here and select data. Now we have got the CDC plots. You can work on beautifying this graph using Excel. You can add Shar title and swan. I just told you how to plot it using Excel, how to input it and all. If you have any questions regarding the content in this video, you can feel free to contact me. See you in the next class. Thank you. 11. Import mesh from ANSYS WB and Fluent, Flow over a cylinder vortex shedding case: Hello, everyone. Welcome back to the CFD using open foam beginner to intermediate course. So this is our class eight. In this class, we'll be seeing importing answers workbench machine to open form, importing answers fluent machine to open form, flow over a cylinder, using workbench machine done mesh. You will use the workbench mesh, imported into open form and do a flow over a cylinder case. Okay. Importing ACS workbench mesh into open foam is a very simple process. But the purpose is it use high quality ASIS workbench mesh and open form simulations. If you are someone who uses open foam and you get a project where they have a workbench mesh from ANCS which is the most popular commercial software, you should not be in a position to not use those mesh and do the simulation because open foam is basically a solver for CFD. So you can use high quality answers you have D mesh inside open form and do simulation. So it leverages ACs robust meshing tools and for complex geometries, which cannot be highly capturable in block mesh or Snappy x mesh in some cases. Snappy X mesh is definitely one of the best tools for meshing in hex. But if you want to tetra mesh, then CIs might be the commercial software which will help you. There is also other software called CF mesh, which you can use as open source in open form. But you are just interested in inputting ASIS mesh as of now. The process is you have to export the mesh from Manss workbench, save it in the format of dot H, which is called workbench mesh format. Then you have to ensure the compatibility with open form requirements, which we will see the commands to check that. Then you will convert the mesh, use the command fluent mesh to form or fluent three D mesh to form, if it is a three D case, using those command, you can import it. So the usage of that command is like fluent mesh to form, space, the file name dot message, or fluent three D mesh to form, space, file dot message. And you can always use the checkmsh command because anyways, even if you are importing ACS workbench mesh, it is going to get stored in the format of polymsh inside open form. So you can always do the checkmsh command, verify the mesh integrity using check mesh, then address any inconsistencies or errors using answers mesh. So importing ANS is fluent mesh is a different process. So you have to export the mesh from ANS is fluent, but in a different way because ANS is fluent meshing will generate a file called dotmsh.h5, which is not supported in open form. You can only use dot sh. So to do that, you have to use the standalone fluent application and not the one which comes with the workbench. So you have to use the standalone fluent machine to generate the mesh. Then you have to save the mesh. Mesh has dotsh dot Hive, which is fluent mesh, and export the generated mesh in ASQ format and not in binary. So by default, it will be in binary, and you have to export it in ASQ format, we will see how to change that and after exporting, you can rename the file to dotmsh.h5 while saving itself. So when you do that, it will get saved as dot Mg instead of dotmsg.h5. But always remember that it doesn't work with workbench, kind of meshing. I mean, when open form is trying to accept dotmsh dot Hive, it won't be able to read. So you have to use standalone fluent machine instead of the fluent mesh, which comes with open with the answers workbench. Okay, the command, as you already know, is fluent mesh to form space, uh, file name dot sh. In this example, it is called mesh mesh dot sh. So for this tutorial, we have done a meshing using solid works. We have created the geometry in solid works, I mean, you can see the dimensions here, and it is saved as dot IGES file, and it is imported inside says workbench, which is design modeler. In Design modeler, you have to choose the object and you have to change it to fluid instead of solid. You can find this panel on the left bottom. Only then open form can understand that this is a fluid region. Also, if you are going to try to make it as a two D case, then you might have to use the convert utilities in design modeler and take a phase from the solid works thing. If you want to know how to import solid works, three D geometry into As a design modeler and convert into two D, you can check the video in our YouTube channel, C dynamics. I have made a video on that. After we convert it into two D and says workbench, then we can do the mesh. In this case, I have done a generic x mesh. You can do with any mesh, I have also added some inflation layers near the cylinder. In the naming selections, I have also given the left as inlet, right as outlet and named the cylinder as cylinder and upper and lower. Okay. Now to change while saving the file and workbench meshing, you can click on Export. Then after Export, you can choose options. From there, if you go inside your export options of meshing. You can change the format of input file as key instead of binary and click on. Then you have to export the mesh in fluent input file method. This is what you have to do. You can see the process, I click on Export, then mesh, then fluent input mesh, then I export. But before that, you have to go to the options and change this. After we do that, we would get the file in dot message, which we can see now. I'm in class eight first case. As you can see, I have the flow over cylinder workbenchmsh, dot H here. Now we are going to use this and import it into open form. I'm in the working directory. Now you know the command. Since it is two D mesh, it's fluent mesh to foam. Space a file name which is flow over cylinder or benchmsh dot mish. I'll click Enter and you can see it is writing the mesh to constant polymsh and it is done. Now we can see the mesh by clicking on Para view. I'll click on Apply, as you can see. Though we said it is a two D mesh, it came with a three D surface because it's going to set the Z to one cell automatically. You don't have to do that, unlike making a block mesh, setting the front and back to empty, you don't have to do those things. It is already set to empty, the front end back by default while importing. So this is the nice thing about open foam. I already does it. Now we are seeing the internal mesh. As you can see, we have inlet outlet, upper and lower. All the naming selection, whatever we gave in answers, it is still there in open form also. Now we have the mesh. Now you can decompose, run the simulation, do whatever you want, because you have the polymsh folder. You can just copy and paste it in any tutorial and you can do it. So this is one nice way to import workbench mesh. Okay, now we are going to see how this, we saw on how it is adding front and back planes. Now we will see how to input fluent mesh. So the geometry is made in design modeler, and you have to give the boundary names, which is naming selection in the design modeler itself. Otherwise, you can't name it in a fluent machining and how you did it in workbench machine because we are going to use standalone fluent machining. It doesn't have those things. It can only mesh. So you have to create the naming selection in design modeler itself, and you also have to assign the body to fluid instead of solid. After that, you have to save the design modeler file and then open the standalone fluid meshing application and you have to import the mesh file and you have to generate the mesh using Ancis fluid. So that is not the tutorial which we are going to see. It is about open form and not Ansis flint. But if you want to see how to use AnsisFlinmsh, you can check out Audio tip channel and check the tutorial. Okay. Now, the methodology to export the fluent mesh is through this. You just click on File and write and then mesh. But in the mesh, you have to deselect the right binary files. And you also have to change the file name to dot sh. Instead of saving it as CFF Mesh files, you just choose all files and save it as whatever name you want to give dot MSH. Always, you have to make sure that it is not written in binary. While saving you just save it as dot MSH and it is just fine. Again, your new thing about fluent mesh is regardless of whether it is two D or three D, the command to import it is fluent mesh to form only. So if you are running fluent three D mesh to form for some mesh, even if it is from bench mesh, and if it is not working, just do fluent mesh to form, give a try and mostly it would work. Either of the command would definitely work. So now in the second tutorial, we are going to see how to import fluent generated mesh. So this is dot MSH, which is generated by fluent, and we have to see whether it is compatible in open form or not. To do that, you can just open the dot MH file using VS core. And if it makes some sense, then it is a good file. It is open foam readable and it can be converted. But if you open it and it is just gibberish and if it doesn't make any sense at all, if there are no characters, only boxes or Xmax, then it isn't binary. Then open foam can't understand it. So you shouldn't export in binary. Just make sure if you are getting the mesh file from someone else. If it is a consultancy work and someone is giving the mesh, then you have to ensure before even trying. Otherwise it's just waste of time for you to check whether it is working or not. Just open, it should make sense. Now we will import this. Now I will do uent mesh to form and the file name. Now it has converted. We can view it using parav. I now, as you can see, we have inlet outlet and walls design which we gave in the design modeler and not in flint machining. Flint machining was used just for meshing, but we still have it here from the design modeler assigned names. So this is a nice thing. This is the mesh. This is a poor mesh, but for demonstration, this is fine. Okay. Now we will see the vortex shedding case, how to set up a vortex shedding case from the mesh which got imported from the workbench mesh, same as the one which we use for the first tutor. Okay. Now we are going to use this palate almors model. We already saw KClan and KOM ICT. So this tutor will be about salt almers, which is the third most popular turbulence model and most probably the most common used one for external aerodynamics. So we will be using one equation model instead of two equation model in palate almers That is the advantage. We are going to use a two D flow or cylinder mesh to make a transient case in pimple form with palate almers turbulence model. This is what we are trying to expect out of this simulation vortex shedding animation since it is transient. I will go to the water shed in case. Now, I'll just close this. Enter the folder. We have zero constant mesh file and system, so I can import the fluent mesh to foam for flow Clint M message. It got converted. Okay. Now I'll go to system. As you can see, I have the decompose pedict right now and I have set it to my processor capabilities. I will decompose par and it will decompose the mesh we just imported because it is in polymsh. It doesn't know it is from *** fluent or Salome or GMsgblock mes gent. It just knows that the mesh is in PolymshFolder. Now we have to copy and paste the zero dot original file. I generally like to do it from the terminal itself. Okay, now we also have the zero folder. I'll go here and show you what this palette almors model is all about. In constant, we have GF, which is gravity. We have said the gravity to negative direction of Y axis in the value of 9.81 meters/second squared, this is an SA unit. So I'll go to transport properties and we are using R as the fluid, one into ten per minus five, and in the turbulence properties, we are using spalalmras model. That is the change here. It is also RAS type, so we are using ppealmas. We will look at the 05. In the velocity file, we have inlet outlet cylinder, upper and lower walls, and front and back patches. Inlet velocity is 10 meters/second. The outlet is set to gradient, zero gradient. The cylinder will have no slip because it is a wall, and we don't want the upper and lower wall to have any effect on the flow, so we are setting it to slip. Which means it is a wall, but it will act as slip. Then front and back planes will be empty because this is a two D case. Now we can see the pressure file. Since we define the inlet for velocity, we don't have to define pressure. So we have zero gradient in inlet and outlet is said to fixed value of zero neutron perimeter square. It is an SA unit. So the cylinder will be zero gradient, upper and lower wall will be zero gradient, which means the solver will calculated for us. Front and back planes are obviously empty. Then we have our turbulent kinematic viscosity. Which is set to calculated and set to zero as initial values. So this is what we generally follow. New TK all function for all the walls, and all the patches will be set to calculate it with a value of zero front and back will be empty. And finally, the main file of this turbulence model, which is new Tilda, if you want to understand what new Tilda is and how this one equation model for spit armas works, there is a beautiful documentation from Open form. Also, there is a beautiful video from YouTube, the channel fluid mechanics one oh one. You can check. It is beautifully explained. So the inlet is set the value of zero. Outlet, cylinder, upper and lower wall, everything is zero gradient and front and back planes are empty. Okay. Now we are going to run the simulation. I actually made a mistake. I changed the name of zero dot original to zero after decomposing. So it was throwing an error, so I deleted all the processor files, and then I decomposed it again so that it would copy zero perfectly. Now we can run this simulation using PRN, Np eight, pimple foam parallel Kit enter, and it will start doing the calculation. Let's just wait for it to end. Okay, now the simulation is over, as you can see the maximum core number was set to one, so it is around one, and Delta T also varied a bit to adjust for the time, it took definitely a long time, full 5 minutes to run this. Okay, now we can reconstruct this. I'll search for the command which I use, you don't want to type it fully. Okay, I'll hit Enter to reconstruct all the time steps. So this definitely is going to take a lot of time. I'll get back to you once it is over. I thought while it is still running, I'll tell you how to view the results while it is still, uh, reconstructing. I mean, it is still in the processor 027. So we can view it as decomposed decase. I'm just going to open instead of reconstructing it completely because it's going to take a lot of time. I'm going to choose decompose case, click on Apply, and we can choose velocity and plate. As you can see, we are getting the flow slowly developed and it is starting to separate. Now we are getting the vortex shedding. If you are very well versed with CFD and you set up a lot of floor ceiling of case for atexhding, you will know this is not how the pattern actually works. I mean, this area, if you look at the zero gradient of the outlet, this is not how usually you would expect it. Also, the domain would be so long than this, not just this length, it would be much longer. I didn't want to make the number of cells high because it would cause the simulation to take a lot of time to end. So I kept the number of cells low, but now you understood how to set up a spartt almas case and perform a vortex shedding using the mesh generated by Anss workbench. So this is the animation which we have got. If you want, you can go on and save it as an animation. And if you want, you can also see the new Delta, it is going to be completely zero throughout the case and same for annuity. And obviously, pressure is going to change. So you get the point of doing the pallet almeras, but if you are really into flow or cylinders, have seen a lot of tutorials, you would also notice that the vortex wouldn't look much like this. It is a bit weird. That is what spaltalmers does. So it makes both the equations K Epsilon and K Omega. And makes it into one equation by dividing those two parameters. So it is a bit of approximation. That's why we are getting values here and there, but it is usually good. So if you just want to do a simple case on wedding or external aerodynamics, then spalt almors is fine. But if you're working with a deep, a aerodynamic case, then kaomeg ACST might be the best choice, especially if you are working with inflation layers, boundary layers, want to calculate Y pleasant or. Like in this case, I have added some inflation layers. So in those cases, kaomeg IST might be the best choice, in my opinion. As you can see, it is still reconstructing is going to take a lot of time. So you can try to reconstruct it, give it some time, and maybe practice by running a reconstructed case. But I'm ending this tutorial here. So if you have any questions, please feel free to contact me. See you in the next class. 12. Allrun and Allclean Files: Hello, Evan. Welcome back to the CFD using Open Foam beginner to intermediate course. So this is our class nine. In this class, we'll be seeing automation with Arn file and all Clean file. So automation with run file works like this. If you have the set of commands like running block mesh, decomposing and then running it in parallel, those commands has to be entered manually in terminal as of now. But if you want to make it automated, then you can use the Aldrn file to do this. The purpose is streamline the execution of open boom simulations. Benefit is, it automates the entire simulation workflow by reducing the manual steps. After initiating the dn file, you don't have to do anything. It just finishes entire simulation, and then you can interact with the computer just to post process. So to create an tern file, generally, the components are like mesh generation, initial condition setup, sola execution, and call for post processing, like force plotting above, not the paraviw thing. So the structure would be it is a shell script that sequentially runs necessary commands. So that is all that an ran file is. So we have an example here. So you can open Arn file in any text editor and you can see it. And the command to initiate AlternFle through WSL is Bash, space dot slash Aran. But if you're on bent, it is just dot slash Aldrin. So you can see that it has a header. It says, dollar WM project directory, bin slash tool slash Run function. So that is essential, that is like header. If you want to clean old case files, then the command would look something like run application. Run application is the shell script command to call the application kind. So it is RM minus RF. It deletes the polymsh under constant. So it points to the program that it has to delete any file that starts with zero to nine any number. So that is one method. And to generate mesh, we will be running the application block mesh. If you want to set up the initial condition by decomposing, then it is decompose par, and the hyphen force is generally not used, but it is a it is just an example from an Alder and file, so you don't have to worry about the force. You can stick to whatever we have learned in this course. Then when you want to run solve in parallel, you use the command run parallel and simple form space hyphen parallel, so you don't have to write MPI, run NPA parallel. All these things are not needed. So have to mention the number of processes somewhere. And for run application, we can do reconstruct per also and post process function like forces. We can do all of these and benefits of Arn file, it ensures that all steps are executed correctly in the right format. When we are working with terminal, we are bound to make mistakes sometimes in the working directory or while typing the commands and we might be wondering what caused the issue. So these things might happen. To prevent those things, we can use Arn file. The efficiency saves time by automating repetitive task. Like you are running block mesh you are waiting for some time, or initiating this all, let's say pimple form and you are waiting for some minutes or hours. And then again, when it is just done, you have to come to computer and do the reconstruction under. Instead of that, what if you just initiate and get back and you can find all the case files that you just need all reconstructed, it removes all the processor file. And if you just need the output, it can be done with an altern file. You can run your own altern file also, just the commands which you want. Documentation is it acts as a record of the simulation procedure. If you are sending open foam case to someone, and if they have no idea on what are the essential steps to run the case, then they have to contact you. But instead of that, if you provide the order and file, they can open the order and file and either know what are the commands that are needed, or they can just initiate the order and file and they can get all the data that is needed, and all they have to do is just post process. They don't even have to know how the case was set up or how to run it. So automation with all clean file is like it cleans up files from previous simulation to prepare for a new run. So it just sits back the entire case to its original version so you can run from scratch. And it also toes a fresh start for simulation by removing old data. So that is the benefit of using all clean files. So to create an urn file, we are just going to remove mesh files and we are going to delete the time directories and clearing log files. Sorry, it has to see automation with all clean file. This slide is about all clean, and it is also a shell script that removes specified files and directories. This is an example of all clean file, sorry it's not Arun, it's all clean. So it removes the constant polymes folder. Again, it removes all the time sets 0-9, and it also removes the post processing folder where we have the force coefficient, and it also removes any log files. When you are running all run files, since you will not be getting anything on the terminal, it would be stored as a log file. So that's what documenting also means. So to initiate this, you can use Bspas dot slash ALCAN when you are on, uh Windows machine WSL. But when you are bintomchine, just dot slash ACN is fine. So we will be seeing some examples from the tutorials folder now. When I was talking about Tutorials folder, I was saying that it can be copied and run even without knowing what that simulation actually means. So I will open the tutorial folder here. So just going to go to the Run directory and open the explorer here. So we have a copy of tutorials here. So let's take incompressible. In incompressible, let's take simple form, and let's see a foil to, and let's see what it has in the all run file. It has a different set of commands. It says, Restore zero directory. If you try to run this command in your command prompt, it won't run, but through shell scripts, it will. You see this is the header and setting, we are setting parallel to true because we have a fails condition here. Okay. It is restoring the zero directory. It means it is copying the zero dot original file and putting it in zero. So that is what restore zero directory means. Then we are doing zero hyphen D constant polymesh and slash slash copy RF, constant slash polys dot original two constants polymsh. So what this does, we have polymh dot original because we don't want to mess with the original polymesh file. So this command essentially copies the polymes dot original and pastes it in the new name polymsh. So that is what this command means. Okay? And we are entering the IL condition, we have set the parallel to true. So when parallel is true, then we will be running decomposed par. Then run parallel would get application. It would be in $1 for a reference. So it would get the application from Control dict and it will run that command here. So it would be running in parallel. And we have run application reconsectP to reconsict whatever is decomposed. If it is parallel, but when the parallel is set to false, then it would just get the application and run it. So it is just basic ILS condition. Now we will see all clean file. So it just says clean case zero. It is going to clean all the time steps. It is same as foam less times RM, but in a shell script way. And we have RM minus RF constant polymerase, so it is going to delete the polymes which we just duplicate it from polymers dot original. Okay, for tutorial purpose, I'm going to copy this and put it in this week's folder. When you get it, it would be empty. Okay. Now we have this airfoil. Now what I'm going to do is I'm not going to do any sort of block mesh or run anything because it already has polymsh. I'm just going to initiate the run file and you can see that it is running everything one by one. First, it restored zero dot original to zero. Yes, it happened. Then it did decompose par. Yes, it happened and it is running simple foam case on eight processes. But you're not getting anything here at all. Because when you are running simple foam, it would keep on saying updating the timesteps because it is getting stored in log dot simple Fam. So you can open it and always see what was happening with the case and you can even post process this if you are very good at dictionary in Python. So this simulation is done. It is also reconstructing now. And if you want to monitor reconstruct par, yes, you can open it in VS code or in text editor, and you can get live updates. All you have to do is maybe change application or refresh the file. When you change application and come back here, it would just change the tab or something. So mostly that works. Okay. So it is reconstructing. That is all that is important. Okay, now let's just wait for this to end. It's probably going to end at 500. Now it is at 300. Or maybe you can also learn to interrupt. Just hit Control C, and it would be interrupted right there. Because anyways, we are going to clean this case. We are not interested in running it completely or post processing it. So we will also run the all clean. Now you have these many files, right. So you can do Bash dot slash, all clean you can see that it is deleting all the time steps first. And then the decomposed processes, it deleted all the log file, I deleted the zero copy. It also deleted polymsh. Now it is just as new as what we copied. Okay? Now, you knew all these steps in this case. You knew what will happen in the Airfoil case. But let's say something like PO form in as, we are not going to see about s but you really don't have an idea about as, right? But if you want to run this case, then you can open this run file and see what are the commands necessary. Obviously, when someone gives you this case file, you wouldn't know, these are the steps, right? But we don't really care whether it is there or not. Like, we have a command called R number mesh potential form. We don't know any of these. But if we still want to get the result out of this, all you have to do is copy, put it wherever you want this to be run. Then go to your terminal, enter that folder, then initiate all run file. That is all that is needed to do this. See it is now running Snappy Hicks mesh also. Anyways, I'm just going to interrupt. I'll interrupt here. Okay. But it is running other commands, so you have to interrupt everything when you are interrupting. It is just running all the commands. I'll clear it. Okay. Now we have all of these files. I'll open all clean. It is going to be very simple. You see, it cleans K zero. It deletes the tri surface, and it also deletes all the decompose padict. I mean, we have made some changes to decompose padi and it is changing it. We really don't want to understand it as of now. All we want to know is how to run. All run and all clean files. I see it is deleting everything. Now the case is just as new. I hope you understood about run and all clean files. So if any case you find in tutorial and you want to run it, you can always do it just using clean files. And you can also see the commands and try to execute them one by one in terminal and find out what each command does or check out the documentation that works too. Okay. Now your project one would start from here. So it is flow around a prism with coefficient of drag and CL plus. So you have to do a flow analysis around a square prism using open foam. The objective is to analyze the flow characteristics around a square prism and compute the drag coefficient and lift coefficient using open foam. This project will involve mesh generation, setting a boundary condition, running simulation, and post processing results to obtain and analyze CDCL plots. So the duration you can take for this is you can take three days for case setup and simulation, two days for plotting and report preparation, and one day for discussing the report if you really want to discuss with me, you can mail to me so you can mail us and we would get back to you if we have any comments on that. Okay. The project description is like this. The project involves simulating the flow around a square prism, placed in a uniform flow. So the students will have to use open foam. I mean, you have to use open foam to generate the computational mesh using block mesh only, or you can do it in snappy hig mesh. You can't import mesh from answers or anything like that. You have to use only open form. Then you have to set up the boundary condition seeing the appropriate problem. If you're using transient turbulent, then you can have higher anos number. But if you're trying to make a steady state laminar case, then you have to keep it very low. Set up the boundary contritions appropriately and run the simulation using a suitable solverare for that problem. So you can decide whatever you want to do. Then you have to extract and analyze the force coefficient CD CL, either using Excel or foam monitor, then you can take screenshots from there. Then you can plot the CD and CL values over time or against other relevant parameters if you are doing with Excel. Then you have to interpret the results and discuss the flow characteristics observed around the prism. So this comes with the knowledge of COD and it is not constrained to knowledge of open form. So you have to interpret and discuss what that result or value from the simulation actually means. So the description would be like this, prepare a geometry, two d or three D it's up to you of a square prism. Then measure it using block mesh or snappy H mesh. Then ensure the mesh is refined around the prism to capture the boundary layer. If it is snappy H mesh, you can also use add layers. Then you have to specify the proper boundary condition setup then choose the solver properly, and it is highly recommended to use K Omega SST, turbulence model and set the maximum COS one. Include the necessary function objects to calculate force coefficient. Post process using Para view, study these streamlines, plot the CDCL graph. You can use either Foam monitor or Excel. Then you have to make a detailed report. Either you can keep it for your own reference or you can mailers and we will get back to you with the commands. So you can work on this question. You can check the PBT for the question or details, and you can do this. If you have any questions, please feel free to contact me. See you in the next class. Thank you. 13. Multiphaseflows and Case Study: Hello, everyone. Welcome back to CFD using open form beginner to intermediate course. This is our last class, which is class ten. In this video, we will be seeing introduction to multiphase flow simulations, modeling approaches, and practical considerations and the demonstration, which we'll be using multiphase Euler foam which is one of the most popular multiphase sola in open form. We'll be doing something called a dam break case. Usually, it is done in two phase, but we are going to consider four phases and we are going to do it in four phase. Introduction to multiphase flow simulation. Multiphase flow simulations involve the simultaneous flow of multiple phases, which can include combinations of gases, liquid, as well as solid sometimes. These simulations are essential in various industries such as chemical processing, oil and gas, power generation, and environmental engineering. The complexity of multiphase flow arises from the interaction between different phases, which can involve mass, momentum, and energy transfers. So modeling approaches and practical considerations. Eulerian Eulerian models are one of the most followed one. Description of the Euler Euler model is both phases are treated as interpenetration continuum, which each phase represent by its own set of conservation equations. Application is suitable for flows where the phases are intermingled, such as bubbly flows or fluid bits. Example, solver is multiphase Euler foam, which is what we are going to see in this video. Then we have Eulerian lagrangian models. The continuous phase is treated as a continuum using the Eulerian approach, while the dispersed phase, which can be particles, droplets, bubbles is tracked using the Lagrangian approach. This is computationally very expensive. Idal for dilute dispersed flows, such as preys and particulate flows, we also need a very fine mesh to do this kind of simulation. Example, solvas DPM foam, which is discrete phase model. Then we have the volume of fluid models. The interface between phases is tracked using a volume fraction function, which is advected with the fluid, effective for free surface flows, such as waves or dam breaks. Example, solver is interfom then we have interface tracking methods also, which is explicit tracking of the interface between phases using methods like level set or front tracking, suitable for detailed phase interface dynamic studies such as droplet coalescence or breakup. Reacting multiphase Euler foam for reactive multiphase flows is one of the example solves, but this is very highly advanced and it's not very popular in industries either. So practical considerations while modeling a multi phase flow, mesh quality, ensure a fine and high quality mesh, especially near phase interface to capture detailed interactions. Then about the time step, choose an appropriate time step to balance the accuracy and computational cost, considering the Kura number. Generally, we will keep the ora number as one, but it would be better to keep even less than one around 0.8 or 0.75. But it also depends on physics and what kind of accuracy are expecting. Then for the boundary condition, we have to carefully set the boundary condition to accurately represent physical phenomena at the boundary domains. For initial condition, proper initialization of the phase distribution can significantly impact the convergence and accuracy of the solution because we have to set the type of phases in every area of the mesh for the initial condition, which would be solved by the solver for further changes in the flow domain. For phase interaction model, we have to implement appropriate models for interface momentum, heat, and mass transfer. Multiphase flows can also do heat equation solving, which will account for the temperature. But for this tutorial, we'll be using multiphase euler foam, which doesn't need to solve the temperature equations. So we will not be seeing any temperature plot. But if you want to see temperatures, you can use solves like two phase euler foam, which would consider temperature changes also. So now we will see the demonstration on using multiphase Euler foam for dam break case for four phase. Now, the picture you are seeing is the all run file. So we have restore zero directory, which will copy the zero dot original and paste it into zero folder. Then we are going to run the application. Block mesh, then we are going to do something called set Phils. This is new, which I will explain. Then as usual, we will decompose, then run the application, which in this case is multiphase Euler foam and reconstruct the case. Now this is the mesh that we are going to use. Now we are seeing the internal mesh. As you can see, we have the left wall, lower wall, right wall, default phases, atmosphere wall and empty. As you can see, there is a big fluid domain, and there is a small obstacle in between, in the lower place. So we will be having fluid all over here and we will release the fluid. So it will tend to move around here, and this obstacle will prevent that prevent the flow or cause the flow disturbance, and we will see how the flow is propagating. So after setting the fields, this is how it will look. So we have four phases here. One is air, one is water, then we have oil, and then mercury. So these are the four phases we are going to work with. So this can be obtained at the initial condition, which will be inside zero folder, and we will see how to do it using the set fields ****. So if you want to see the final simulation video, you can jump in here. This is my YouTube channel. You can check it out. Okay, now we will run the simulations. I am in the working directory. Okay, now, either we can initiate the all run or do it one by one. So I will do it manually. If you want to run the case, you can do it yourself. Okay, now we have the zero, zero dot original constant system. Okay, now, as you know, the first command is Block mesh, so I'll run Block Msh. Then it is set fields. So before we do set fields, I will explain what set fields dit actually does and what that is about. Now we will just see the mesh which we have. As you could recognize from the PPD, this is the mesh we have and this is the obstacle. We had the other three fluids here and rest of the area where yeah, right. So I will keep everything at the zero them step. Now, we don't have any phases at all. Okay? So it will not have any phases. So now we are going to do something called the set fields. What set fields **** does? Under set fields dict, which is under system directory, we have many functions. So first thing is, we are going to set the default field values. So in any atmosphere, all we have is R. That is the default field value. So we are setting Alpha at R as one. Alpha is the phase fraction. And we are setting Alpha dot, water as zero, Alpha dot, oil as zero and Alpha dot mercury as zero, and initial vector field value, which is velocity will be zero, zero, zero in the direction. This is the default field values. Now we are going to set the regions. Under region, we need three phases now because everything is already a, we are going to set three more fields. So the first field would be a box to sell. So that is the function. Then we have to define the box. So that box, as you can see, again, it has a minimum point and the maximum point, just like what we did for Snappyxmsh. So we are going to do this, which is 00 minus one, 0.14 61 to 0.291 to one. So if you want to see what that actually means, you can turn on data axis grade, and you can see we have zero, 020.14 it is somewhere around here, the X direction and Y direction, it is 0.292. This is this region. Here we are setting one field. Then we are setting another field from this 0.0 0.14 610 minus one to some point, you can ponder over what these points actually mean from the data axis grade. I'm not going to exactly show those points. We are just having these points, which you can download this case and check over it. For the first box, we are setting it to Alpha dot value of water as one and everything else as zero, which is oil, mercury and R will be zero. So two phases cannot exist at the same place, so everything else must be zero. Then we have oil phase. This will be one, everything else will be zero. Then we have mercury as one and everything else as zero. So we have set the entire domain into four different phases. If you miss any point while doing this, that would be set to. So that is the entire thing about setting default field values. Otherwise, it would have pure mesh without any values at all. So how is it going to get saved? It is because we have these files, apart from U, which we generally have, we also have something called P underscore RgH Actually, it means P minus RgH as you can realize RgH is the hydrostatic forces. This is pressure minus the hydrostatic effects. That is what P minus RgH means. But since we can't use hyphen in a file name, we are using underscore. Okay. So this is basically pressure minus the hydrostatic forces, and we are defining it as flux pressure, and it is all set to zero. Now we have Alpha dot, Alpha dot mercury, alpha dot oil and Alpha dot water. Similarly, we also have the velocity for H phases. As I explained in the PPT for Euler Euler model, we are solving the transport equation for every different phase separately because everything has its density different. So I'll open the Alpha at her, and you can see that the uniform field is initially set to zero and everything else is also set. So this can be set based on any templates which is already available. So we are doing this called Theta properties. So this Theta properties is the volume fraction. Or also known as the contact angle of the volume fraction. So when two phases are meeting, it will have some angle. So that angle has to be defined so that it is resolved properly. And that Alpha contact angle is called Theta. So we are setting it to orthogonal, which is 90 degrees, so it will meet at the intersection of 90 degrees. We have to set it for every phase. So when you see left wall that has water R as 90, oil R is 90, Mercury errors 90, water, oil has 90, water, Mercury has 90, oil, mercury is 90. So we have to put in all the combination, all different possibilities. So after doing that, you will be setting the atmosphere as inlet outlet, inlet value as one, one, and we have this. So atmosphere here is just basic outlet condition on the top wall. Okay. Similarly, we have for all the four files, you can open and say it just in case I would open the phase alone. See, we have everything else as normally. So we only set the Alpha dot air because it is in the default. So we are setting it. Then this would correspond to other files. I'll open Alpha dot oil. See even this is a normal file. So only the default phase, we have to set all these contact angle on it. Okay. Now, similarly, we will be having just U, which is the overall velocity thing. We are setting the walls as no slip and atmosphere flux corrected velocity is zero, zero, zero, which is an oian condition. Then we have the velocity of air, which is again a normal file. Then we have velocity of mercury. That is also a normal velocity file. So only the alpha at air will be different and P minus Ages is a new thing. So here, apart from transport and turbulence properties and gravity, we also have something called motion properties. Where we are setting it as static Fwmesh. But when you are going to advance level of open foam, you can do adaptive refinement in the mesh. So that can be defined here. Instead of static, we will be using dynamic Fwmesh which we are not going to cover in this course. So it is just going to be static FIMs in this case. Now we can see what other files we have. We have the control deck. So in contradict, you can see the application is multiphase euler form, and apart from maximum CWO, we are also setting maximum Alpha CO. So this is taking care of individual phase current number. So that is 0.5. As I said, one is fine for most cases, but for multiphase, going less than one is preferable. Then we have Delta T as 0.001 and we are ending at time six. So this simulation is going to take a lot of time to get run. So that is why I have pasted the YouTube link for the final simulation video. It is going to take hours of your time. So that is what multiphase does. Now we will do the set fields. Now as you see, at the time zero, we don't have any phases at all. Okay? Yeah, I'll go to time zero. So you can see we can see Alpha dot water is completely zero. Alpha dotir is also completely zero. And if we see VOC, it is also completely zero because we have set everything to zero, so it's no surprise. Now what I will do is I will do set fails. Now the set fields has been done. Now I will refresh this case. You can see we have something called Alpha dotar. You can see the Alpha dotiR. Here, one is the maximum value and blue is zero, everything else is ir. This is the place where we have other three phases. The mercury is just this place oil has this area and water has this area. So apart from whatever these three, everything else is here. Okay. So to see all the four phases in the same map, we will be able to do it only when we run the simulation. Otherwise, we can't. So you can see that every phase has mostly zero velocity only initially. Okay. Now we can run the case by decomposing. Decompose par is a regular decompose case, which we said in previous simulations also. I'm going to run MPI Run NP eight, multiphase oiler, boom. Okay. So it has started and it is running. Now we have around ten timesteps, including the zero. While running the command, I missed the hyphen parallel at the end. So if you followed the video, just make sure that you are typing the hyphen parallel also. I stopped the simulation, run it and reconstructed and dilted all the processor files. Okay. Now I'll go here to the Paire. I'll refresh the case. Now I'll go to the last timestep. I'll choose Alphas. Now you can see that we have the animation, sort of animation, it is moving. So when you run the entire simulation, it would look something like this. So this is the render video. You can check out that link. Now I will play it for you. As you can see, it predicts all the bubbles. It releases air, it accounts for density, it accounts for the waviness. So when you are seeing it, it feels realistic. So that is what we can achieve by having a good mesh and good timestep by maintaining the a number. So I hope you learn a lot in this course. If you have any specific abouts regarding the contents in this course, you can always contact me. Thank you for taking up this course. Look up for advanced level of courses regarding open foam by C dynamics. Also check out our YouTube channel regularly for more information on using open form and specific features inside open form. Thank you. See you in another course.