WEBVTT 00:00.320 --> 00:01.220 Hello everyone. 00:01.220 --> 00:04.940 Welcome back to the CFD using Openfoam beginner to intermediate course. 00:04.940 --> 00:10.100 This is the class two and in this class we will be seeing some geometry and mesh generation using a 00:10.100 --> 00:11.390 tool called block mesh. 00:11.390 --> 00:14.390 Then setting up boundary and initial conditions. 00:14.390 --> 00:19.100 And then we will also see how to use solvers and run the simulation in Openfoam. 00:19.100 --> 00:24.890 After doing that, we will be using Paraview as the post-processing tool and we will be seeing the results 00:25.370 --> 00:26.000 first. 00:26.000 --> 00:26.960 What is block mesh? 00:26.960 --> 00:31.470 Block mesh is a mesh generation tool which comes with the installation of Openfoam. 00:31.800 --> 00:37.560 It uses a dictionary file to call block mesh dict to define simple geometries and create structured 00:37.560 --> 00:38.070 meshes. 00:38.760 --> 00:44.220 The role of block machine openfoam is that it is used to create initial computational meshes. 00:44.220 --> 00:51.060 It can be highly structured, suitable for simple geometries like square, rectangle, channel or cube, 00:51.060 --> 00:54.320 cuboid or a flow over a cylinder or a wedge. 00:54.350 --> 00:57.020 These kind of things can be easily done using block mesh. 00:57.500 --> 00:58.100 Even. 00:58.100 --> 01:02.030 It can handle complicated mesh like structured mesh around an airfoil. 01:02.030 --> 01:08.960 But for that, we have other tools which might be very efficient in terms of time than block mesh. 01:09.050 --> 01:15.770 So the effort versus, uh, accuracy comes better in other software for a complex mesh. 01:15.770 --> 01:19.200 But block mesh is very efficient for a simple mesh. 01:20.010 --> 01:24.270 So the main key sections of block mesh dict is like vertices will be there. 01:24.270 --> 01:29.010 We have to define the vertices on a 3D space which we are going to use. 01:29.010 --> 01:36.630 Then using those vertices we will be defining boxes or a hexahedral box, meaning it will have six faces, 01:36.630 --> 01:38.010 more like a cube or a cuboid. 01:38.220 --> 01:42.580 Then we will be defining edges if we want specialized curves. 01:42.580 --> 01:49.300 So if there is a two point and we can join the two lines two points using a line. 01:49.300 --> 01:55.900 But if we want to join it using an arc, we can introduce a third point and define that point as a path. 01:55.900 --> 01:59.110 So that can be done using the edge feature. 01:59.860 --> 02:01.360 And then comes the boundary. 02:01.360 --> 02:08.940 So this boundary will define the type of patch, whether it is an inlet or outlet, or empty patch or 02:08.940 --> 02:11.010 wall patch, or if it is symmetric. 02:11.010 --> 02:12.990 We can do those things in the boundary. 02:12.990 --> 02:20.970 But let's say we have two blocks and two blocks share one common face, but we don't want it to be like 02:20.970 --> 02:21.360 a wall. 02:21.360 --> 02:27.690 What we do, we just merge the patch so that those two blocks behave like a single block. 02:27.690 --> 02:32.020 So that is where the mesh merge patch pairs come into play. 02:32.110 --> 02:37.390 So we will be seeing all these practically when seeing the blog mesh dict file as an example. 02:38.200 --> 02:43.030 For the first thing, we will be creating simple geometries like a 2D square cavity. 02:43.720 --> 02:49.450 We will be defining eight vertices, and we will use those eight vertices to create a single block. 02:49.450 --> 02:51.520 And we will be defining boundary condition. 02:51.520 --> 02:54.710 And we will see how the meshes in the next example will be. 02:54.710 --> 03:01.640 We will be doing a 3D rectangular channel where we will be setting boundary condition like inlet, outlet 03:01.640 --> 03:05.030 and wall, same eight vertices, and we'll be creating a block. 03:05.240 --> 03:08.570 So we will first see this and then proceed further. 03:08.660 --> 03:12.560 Now I have my terminal open. 03:12.560 --> 03:15.500 I'm already in the folder for class two. 03:16.190 --> 03:20.580 And we have the first case which is square cavity mesh. 03:20.580 --> 03:22.980 So I will go inside that. 03:25.440 --> 03:25.920 Okay. 03:25.920 --> 03:33.120 Inside this we can see that we have constant uh para dot form and system. 03:33.120 --> 03:34.290 We do not have zero. 03:34.290 --> 03:38.160 So zero is supposed to contain the boundary condition or boundary files. 03:38.160 --> 03:45.080 But we are not having that file here, that folder here because we are not interested in in running 03:45.080 --> 03:49.460 the case, we are just interested in doing the mesh using block mesh data. 03:49.520 --> 03:53.630 So block mesh dict exists inside system folders. 03:53.630 --> 03:54.830 Let me show you. 03:55.010 --> 03:57.590 So this is the case which we are going to use. 03:57.590 --> 04:01.370 And under system folder we will be having the block mesh dict. 04:01.370 --> 04:03.590 We will view what is there inside. 04:04.490 --> 04:05.030 Okay. 04:05.030 --> 04:07.830 Now we have eight vertices as you can see. 04:07.830 --> 04:10.380 So each one corresponds to x, y and z. 04:10.470 --> 04:12.840 But before that we have something called scale. 04:12.840 --> 04:14.160 So what is this scale. 04:14.160 --> 04:21.150 Usually everything in openfoam is an Si unit, meaning whatever vertices we define it is in metres. 04:21.150 --> 04:27.000 So if it is like zero comma, zero comma zero, it is a point, and the next point is one comma zero 04:27.000 --> 04:27.600 comma zero. 04:27.600 --> 04:33.560 It means that this is one metre away from zero comma zero comma zero in x axis. 04:33.560 --> 04:36.620 But if we don't want to work with meters, what do we do? 04:36.650 --> 04:39.620 We just define it as 0.001. 04:39.620 --> 04:45.800 If we want to work with millimeters just 0.01 if we want to work with centimeters. 04:45.800 --> 04:51.680 But if you want to work on a kilometer scale, then you can obviously choose 1000. 04:51.680 --> 04:58.980 If you are doing something like an entire aeroplane with a large amount of, uh, mesh, then you can 04:58.980 --> 05:04.500 choose kilometer scale if you want, but usually scale one, which is meters is fine. 05:04.680 --> 05:06.870 Now let's see what are these vertices. 05:06.870 --> 05:13.590 To explain that, I will just open paint, uh, so that I can explain you physically. 05:13.590 --> 05:15.840 So this is 000. 05:15.840 --> 05:18.990 So let's assume we have a coordinate system. 05:20.590 --> 05:22.390 And let's say this is x. 05:22.690 --> 05:25.300 This is y and this is Z. 05:25.570 --> 05:26.140 Okay. 05:26.140 --> 05:29.290 Now we will be doing one by one. 05:29.290 --> 05:32.680 This is like a an array okay. 05:32.680 --> 05:35.080 Uh openfoam is written in C plus plus. 05:35.080 --> 05:38.260 So everything starts from zero. 05:38.260 --> 05:42.100 So this element in the array starts from zero. 05:42.100 --> 05:46.850 So let's keep it like this is the zeroth point okay. 05:46.970 --> 05:52.490 And we have one comma zero comma zero which is like one meter displaced in the direction of x. 05:52.490 --> 05:54.770 So this will be our point one. 05:55.520 --> 06:00.230 And then we have one comma one comma zero which would be around here. 06:00.230 --> 06:01.760 And this is our point two. 06:02.120 --> 06:06.560 And then we have zero comma one comma zero which will be around here. 06:07.370 --> 06:09.830 So this will be our point three. 06:09.890 --> 06:17.000 Now these four points can form a face a simple 2D face. 06:17.000 --> 06:24.050 Well Openfoam can't really work with 2D structures, but with these four points we can only make a 2D 06:24.050 --> 06:24.470 face. 06:24.500 --> 06:33.830 Now we have got a face, but if you see the other four, the values in the x and y are same, like if 06:33.830 --> 06:40.010 it is zero, one, two, three, then four, five, six, seven have the a corresponding like zero and 06:40.010 --> 06:43.400 four have the same x and y, but the z is different. 06:43.490 --> 06:47.750 And if you see two and five, the x and y is same. 06:47.750 --> 06:49.430 But the z is changing. 06:49.430 --> 06:56.800 What it essentially means is that we are just displacing this entire face or copying the entire face 06:56.800 --> 07:00.010 and putting it at some distance in the Z direction. 07:00.010 --> 07:03.130 Let's say this will be our fourth point. 07:03.820 --> 07:06.880 This will be our fifth point corresponding to one. 07:07.300 --> 07:12.340 This will be our sixth point, and this will be our seventh point. 07:12.340 --> 07:17.620 So what this essentially does is that we have got another face. 07:23.020 --> 07:23.530 Yeah. 07:23.560 --> 07:29.470 Now we have two faces, but it is not yet connected in the Z direction, so we don't have a block. 07:29.470 --> 07:29.830 Right. 07:29.830 --> 07:32.320 So that's where this section comes in. 07:32.320 --> 07:38.560 We are defining it in the name hex because it is a hexahedral block. 07:38.560 --> 07:40.270 And then we are giving the numbers. 07:40.270 --> 07:43.960 So these numbers are the index of these vertices. 07:44.070 --> 07:52.590 So if you had noticed something when I was writing this, I was doing it in counterclockwise because 07:52.590 --> 07:55.050 zero one, two three is in counter-clockwise. 07:55.050 --> 07:57.600 Then 4567 is also counterclockwise. 07:57.630 --> 08:01.080 This is a notion that we have to follow in openfoam. 08:01.080 --> 08:07.320 And also when we are finished doing those the first four points, the next point has to correspond with 08:07.320 --> 08:08.130 the zeroth point. 08:08.140 --> 08:09.610 So that is how it works. 08:09.610 --> 08:11.770 Only then it can make the association. 08:12.010 --> 08:12.490 Okay. 08:12.490 --> 08:20.050 Now we have created the two faces and we are defining 01230123. 08:20.050 --> 08:22.990 And we have 456764567. 08:22.990 --> 08:25.750 So we are defining it as a single block. 08:25.750 --> 08:31.900 Now this will connect these points and make it as a block. 08:33.320 --> 08:33.920 Okay. 08:35.120 --> 08:35.570 Okay. 08:35.570 --> 08:40.940 The next command which we are seeing here is three points or three values. 08:40.940 --> 08:44.030 This is x, this is y and this is z. 08:44.090 --> 08:51.200 So what it means is that we are subdividing the x direction face in the value of 20. 08:51.200 --> 08:53.630 And we are subdividing y by 20. 08:53.630 --> 08:57.100 And we are just keeping one cell in z Z direction. 08:57.100 --> 09:06.100 So after subdivision, the X direction will be getting subdivided 20 times and it will be carried over 09:06.100 --> 09:09.550 throughout the mesh, not just one phase, it will be carried over throughout the mesh. 09:10.240 --> 09:15.160 We will also see this visually and y is also done simple grading. 09:15.160 --> 09:17.740 We will not look at that right now. 09:17.740 --> 09:20.960 Let's uh, assume that it is one, one one as of now. 09:20.960 --> 09:23.450 Most commonly, we will be using one, one one only. 09:23.450 --> 09:29.000 So we will just see up to here, run the block mesh and we will see. 09:29.000 --> 09:34.730 So what I am going to do is I will comment this entire boundary. 09:34.730 --> 09:37.730 We will pretend that this doesn't exist. 09:37.730 --> 09:41.690 Like I have commented this meaning it doesn't exist in the code. 09:41.690 --> 09:43.430 So we are just going to run this. 09:43.430 --> 09:50.970 I will go here and whenever you are running anything in Openfoam, make sure you are in the right working 09:50.970 --> 09:51.510 directory. 09:51.510 --> 09:57.570 So what is working directory mean when you are in a location like in this case I am at one square cavity 09:57.570 --> 10:03.210 mesh and if I type ls I have to see the constant system folders. 10:03.210 --> 10:07.110 Only then we are in the right, uh, location. 10:07.110 --> 10:11.930 Let's say I am inside system because this is where block mesh resides. 10:11.930 --> 10:12.140 Right? 10:12.140 --> 10:14.180 But I should not be doing this. 10:14.180 --> 10:17.900 If I go into system and do block mesh, it will throw an error. 10:17.900 --> 10:19.340 It is not going to work. 10:19.340 --> 10:21.440 So I will go back one directory. 10:22.250 --> 10:23.450 Now I will type ls. 10:23.480 --> 10:25.790 Now we can see constant and system. 10:25.790 --> 10:30.890 So this is the location where we have to execute all our open form commands. 10:30.890 --> 10:34.290 We have to remember this throughout the usage of open form. 10:34.530 --> 10:39.930 Now the command to execute block mesh is just block mesh. 10:40.050 --> 10:41.940 Notice that M is capital. 10:42.390 --> 10:43.500 I will hit enter. 10:44.340 --> 10:53.430 Now you can see that we have 400 cells because we have 20 by 20 and we have many faces. 10:53.430 --> 10:57.300 And the bounding box is like 000 which is the minimum value. 10:57.310 --> 11:02.080 and this is the maximum value of the cube, which is one one, minus one 0.1. 11:02.080 --> 11:05.230 And we have only default faces as all patch. 11:05.230 --> 11:08.680 So we will visualize it to visualize. 11:08.680 --> 11:14.860 As I have explained in the previous class, we will do touch space dot form to create a paraview file. 11:14.860 --> 11:16.780 Then we can go in here. 11:16.810 --> 11:18.160 Double click this. 11:22.320 --> 11:23.730 Wait for it to load. 11:23.730 --> 11:24.810 Click apply. 11:24.810 --> 11:26.460 Then we will have a block. 11:26.670 --> 11:27.690 You see it is a block. 11:27.690 --> 11:29.160 But how do we view the mesh? 11:29.670 --> 11:31.080 We will go here. 11:31.380 --> 11:33.210 Click on surface with edges. 11:33.210 --> 11:35.910 Now you can see the blocks okay. 11:36.690 --> 11:41.490 Uh, if you scroll down on the left panel you can see something called Data Access Grid. 11:41.490 --> 11:42.330 I will turn on. 11:42.330 --> 11:45.510 You can see the x axis ranges from 0 to 1. 11:45.520 --> 11:52.120 Y is also ranging from 0 to 1, and z direction is from 0 to 0.1. 11:52.120 --> 11:54.760 Exactly what we wanted to do. 11:54.790 --> 11:59.650 So if I click this button, it will snap to the z axis normal plane. 11:59.830 --> 12:01.180 Okay now we have this. 12:01.180 --> 12:04.870 So we will see what the 20 by 20 actually did. 12:04.900 --> 12:05.320 Okay. 12:05.320 --> 12:09.980 Now let's say I have only one one in x and y direction. 12:10.700 --> 12:14.420 Uh, now after changing, I will hit control S to save the file. 12:14.480 --> 12:19.400 I will run block mesh again so it will get updated. 12:19.490 --> 12:26.930 I will go to paraview and make sure that you are selected para dot form and click on refresh. 12:26.930 --> 12:29.120 Try to move something like in para view. 12:29.150 --> 12:31.670 Your left mouse will be used to rotate it. 12:31.700 --> 12:36.810 Right mouse button can be used to scale up and scale down. 12:36.840 --> 12:39.060 Middle mouse can be used to move things. 12:39.240 --> 12:44.190 Mouse is highly recommended whenever you are working with any geometry, so get a mouse. 12:44.970 --> 12:48.450 Okay, now I am zooming by scrolling the mouse wheel. 12:48.780 --> 12:55.140 Okay, now you can see even though I am in surface with edges, we are seeing only one cell in this 12:55.320 --> 12:59.330 because we have not divided into anything. 12:59.360 --> 13:04.130 Now let's say I am just dividing this by five five. 13:05.810 --> 13:08.900 I will save the file run block mesh command. 13:09.170 --> 13:10.340 Go to paraview. 13:10.340 --> 13:11.120 Refresh it. 13:11.120 --> 13:15.770 Now you can see we have five on the x axis and five on the y axis. 13:15.770 --> 13:22.220 Now I just want to go back to 20 by 20 let's say okay I will save it. 13:22.630 --> 13:27.190 and run the block mesh refresh. 13:27.190 --> 13:29.110 And you can see we have 20 by 20. 13:29.110 --> 13:35.260 But since I gave one as the value in z direction, we have only one cell in the z direction. 13:35.260 --> 13:39.850 It is because we are trying to make a 2D uh square cavity case. 13:39.850 --> 13:42.400 So we are keeping is it as one. 13:42.400 --> 13:47.710 So because in openfoam there is nothing as pure 2D, Everything has to be 2D. 13:47.710 --> 13:53.800 But what we will do is we will set the front plane and back plane as empty patch, so it will behave 13:53.800 --> 13:54.790 like a 2D case. 13:55.390 --> 13:56.980 Okay, now we have the mesh. 13:57.070 --> 14:00.850 How to define the boundary names like everything is a default patch here. 14:00.850 --> 14:01.930 How do I know? 14:02.140 --> 14:08.590 On the left panel if you see if you click here, I will deselect internal mesh and select on the default 14:08.590 --> 14:09.730 faces click apply. 14:10.540 --> 14:12.570 You see everything is default phase. 14:12.570 --> 14:15.930 Now this is where we will be getting the name of the patches. 14:15.930 --> 14:19.800 Now I will go back to internal mesh as of now okay. 14:20.340 --> 14:27.660 In the block mesh dict file I have typed this so let's see what each of them says. 14:27.660 --> 14:31.260 I will just comment out moving wall. 14:31.260 --> 14:31.980 Save it. 14:32.070 --> 14:33.810 I will go back to the paint. 14:33.900 --> 14:36.820 Now you see, I have given a name. 14:36.820 --> 14:38.950 Moving wall and the curly braces. 14:38.950 --> 14:41.830 Within that I have typed type as wall. 14:42.040 --> 14:44.230 So this is going to behave like a wall. 14:44.500 --> 14:46.270 And this name can be anything. 14:46.600 --> 14:49.750 I just chose moving wall um, in this case. 14:49.750 --> 14:52.510 But it can be anything like a top wall or something. 14:53.560 --> 14:57.640 Then the type is wall and I have to define the faces. 14:57.640 --> 15:01.010 You can see we have four numbers here three, seven, six and two. 15:01.040 --> 15:06.950 So what it is it is three, seven, six and two which is the top face here. 15:07.010 --> 15:13.400 So you can notice that this is also an anticlockwise direction 3762. 15:13.430 --> 15:15.020 We always have to follow this. 15:15.020 --> 15:19.130 Otherwise it will say the face is outward. 15:19.130 --> 15:20.300 It is facing outwards. 15:20.300 --> 15:23.680 So what we are trying to follow is right hand thumb rule. 15:25.450 --> 15:34.120 Assume that this is a hand okay, so whenever you are curling your fingers, the outward normal should 15:34.120 --> 15:35.230 be facing outside. 15:35.230 --> 15:37.240 Your thumb has to face outside. 15:37.300 --> 15:39.400 So we are curling it that side. 15:39.400 --> 15:42.010 So it is facing outside. 15:42.010 --> 15:42.730 You can try it. 15:42.730 --> 15:44.800 It is right hand thumb rule okay. 15:44.800 --> 15:46.660 Now I will save this file. 15:47.780 --> 15:48.890 I'll go here. 15:48.890 --> 15:49.880 Run block mesh. 15:49.880 --> 15:52.880 Now you can see that we have one more patch called moving wall. 15:52.970 --> 15:57.080 Apart from default face I'll go to Paraview refresh. 15:57.230 --> 15:59.210 You can see this just popped up. 15:59.210 --> 16:00.830 We have a moving wall now. 16:00.830 --> 16:02.120 I will select that. 16:02.120 --> 16:05.240 Deselect everything and you can see this is the moving wall. 16:05.960 --> 16:06.560 Very nice. 16:06.560 --> 16:10.310 We just created or given a name to a wall or a patch. 16:10.980 --> 16:17.310 Okay, now similarly I will remove comment for fixed walls. 16:17.910 --> 16:19.650 Fixed walls are also walls. 16:19.890 --> 16:23.010 As you can see I have defined three phases here. 16:23.010 --> 16:28.410 One is 0473 which is 0473, which is this phase. 16:28.410 --> 16:32.130 If you see from that side then that is still anticlockwise. 16:33.090 --> 16:37.390 Then we have two six, five one and then 51540. 16:37.390 --> 16:40.540 So we have defined all these faces as fixed walls. 16:40.720 --> 16:43.630 I will save the file run block mesh. 16:43.750 --> 16:46.630 Now you can see we also got fixed walls. 16:46.630 --> 16:49.690 Now I'll go here refresh. 16:49.960 --> 16:51.760 I will select the fixed walls alone. 16:51.760 --> 16:54.130 Deselect everything you can see. 16:54.130 --> 16:55.240 This is the fixed wall. 16:55.270 --> 16:56.620 Okay, this is annoying. 16:56.620 --> 16:58.630 I will remove the date axis grid. 16:58.840 --> 16:59.560 Okay. 16:59.560 --> 17:00.900 we have the fixed servers. 17:00.930 --> 17:04.770 Now I will select both fixed walls and default faces. 17:06.750 --> 17:08.400 We are seeing everything. 17:09.030 --> 17:12.000 I will select fixed walls and moving wall. 17:12.600 --> 17:14.100 Yeah, these are the walls. 17:14.130 --> 17:16.350 Now we are missing front and back. 17:16.350 --> 17:16.830 Right. 17:16.830 --> 17:20.700 So you can see that only those two are left in the default patch. 17:20.700 --> 17:23.010 Only these two are left without name. 17:24.340 --> 17:30.850 So what we are going to do is we will select those two faces and put it into front and back, and we 17:30.850 --> 17:32.110 are defining it as empty. 17:32.140 --> 17:35.740 Whenever you are working with 2D, the front and back has to be empty. 17:35.740 --> 17:38.110 Only then this will behave like a 2D case. 17:38.260 --> 17:42.130 And here also I have put two face values. 17:42.250 --> 17:48.650 I will save the file run block mesh just like you expected And refresh. 17:48.650 --> 17:51.260 Now you can see we don't have anything in default phases. 17:51.260 --> 17:52.400 We are seeing nothing. 17:52.520 --> 17:54.380 I will remove default phases. 17:54.380 --> 17:54.920 Check. 17:54.920 --> 17:55.670 Fixed walls. 17:55.670 --> 18:00.740 We have fixed walls, we have moving walls and we have front and back. 18:01.160 --> 18:03.590 Yes, we have created the entire mesh. 18:03.590 --> 18:06.830 Now if you want to refine it, it's very simple. 18:06.830 --> 18:10.430 Just go here and maybe put 50 by 50. 18:11.510 --> 18:12.640 Save the file. 18:12.640 --> 18:14.170 Run block mesh. 18:15.070 --> 18:16.210 Give refresh. 18:16.570 --> 18:16.960 Yeah. 18:16.960 --> 18:18.220 You have a finer mesh. 18:18.220 --> 18:21.940 So this is all that you have to do to create a 2D mesh. 18:21.940 --> 18:29.890 If it is a simple square like this can be done if you want to do something like a flow, uh, on a flat 18:29.890 --> 18:33.280 plate, then you can do these things, but you need an inlet and outlet. 18:33.280 --> 18:38.270 You just have to change this as inlet and this as outlet, which we will be seeing in the next case. 18:38.330 --> 18:41.180 So I hope you understood what we did here. 18:41.390 --> 18:43.550 Now we will see about simple grading. 18:43.580 --> 18:47.180 So simple grading is like a gradient for the mesh. 18:47.420 --> 18:53.510 Uh, 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 18:53.510 --> 18:54.260 changes. 18:55.460 --> 18:57.290 Sorry I didn't run the block mesh. 19:00.870 --> 19:03.420 You see, everything is biased towards the right. 19:03.420 --> 19:04.860 Still, the count is same. 19:04.860 --> 19:11.640 It is 50 by 50, but it is a gradient towards one surface. 19:11.640 --> 19:18.570 It is because we have given it as 0.1, which means this is 0.1 times finer than whatever is here. 19:18.570 --> 19:21.900 So it will do that simple uniform grading. 19:21.900 --> 19:25.310 So this will be efficient when you are doing some inflation layer. 19:25.310 --> 19:31.520 Or if you want to, uh, create some boundary layer thickness then this could be useful. 19:32.060 --> 19:34.670 And if I do -0.1. 19:36.920 --> 19:40.970 Then I will get it towards this side okay. 19:40.970 --> 19:53.140 And this can be done for y direction also I'll do Do 0.1 run block mesh and refresh. 19:53.230 --> 19:54.640 Yeah, we have got it. 19:54.640 --> 20:02.290 So to reset everything, all you have to do is put the values to default one, one one, save the file, 20:02.290 --> 20:05.980 run block, mesh and refresh. 20:06.130 --> 20:07.090 That's it. 20:07.090 --> 20:09.820 So we have got the entire mesh. 20:09.820 --> 20:10.870 This is nice. 20:11.050 --> 20:13.330 Okay we are done with this. 20:13.360 --> 20:18.520 Now we will see what we have in the second tutorial, which is rectangular channel. 20:21.130 --> 20:22.090 Um, okay. 20:22.090 --> 20:29.080 In the system folder we have block mesh dict and I have defined eight vertices. 20:29.080 --> 20:33.640 You can pause the video and ponder how these vertices make a block. 20:34.270 --> 20:38.570 Again I have made this, but now you can see there is a slight difference. 20:38.570 --> 20:44.420 We are working with 3D so we don't have front and back and walls is defined as wall, but the inlet 20:44.420 --> 20:50.390 and outlet is defined as patch because in patches we can give values like inlet and outlet. 20:50.390 --> 20:52.040 That is what this makes. 20:52.850 --> 20:54.860 For inlet I have chose the left face. 20:54.860 --> 20:58.970 For outlet it is the right face and everything else is a wall. 20:58.970 --> 21:00.830 This is a 3D case in x direction. 21:00.830 --> 21:05.110 I chose 100 y ten and is it also ten? 21:05.110 --> 21:11.890 No grading okay, and I have chose the scale as 0.1 and I'll save this file. 21:12.730 --> 21:18.100 I'll go to this location which is the second folder rectangular channel mesh. 21:19.570 --> 21:19.900 Okay. 21:19.900 --> 21:21.910 Now I am in the right directory. 21:21.910 --> 21:26.090 I know because I am seeing constant and system and I do list which is list. 21:26.240 --> 21:26.570 Okay. 21:26.570 --> 21:29.060 List is list will listing all the folder. 21:29.090 --> 21:32.180 Now I can type block mesh. 21:32.570 --> 21:33.230 Okay. 21:33.440 --> 21:38.780 And, uh, I have already created the preview file, so I'll double click and open it. 21:40.820 --> 21:41.450 Gonna apply. 21:42.200 --> 21:45.680 So this is the geometry I'll go to surface with edges. 21:46.100 --> 21:47.810 You can see the entire geometry. 21:48.170 --> 21:51.150 Now I can click on inlet. 21:51.540 --> 21:52.890 This is the inlet. 21:53.850 --> 21:55.440 This is the outlet. 21:56.490 --> 21:59.430 And these are the walls. 21:59.430 --> 22:00.930 So you get the point. 22:00.930 --> 22:02.760 How block mesh works. 22:02.760 --> 22:06.540 And once we have the inlet and outlet we can set up a case. 22:06.570 --> 22:10.320 But you might be wondering where are these files getting saved. 22:10.470 --> 22:10.980 Right. 22:10.980 --> 22:13.590 So we will see where it is getting saved. 22:13.590 --> 22:14.990 It is under constant folder. 22:14.990 --> 22:21.170 Generally constant folder has other files also like properties of the fluid or material. 22:21.170 --> 22:26.090 But I have deleted these files because we are just interested in mesh. 22:26.210 --> 22:28.490 Under this we have a folder called poly mesh. 22:28.490 --> 22:30.800 This is where all the mesh information is stored. 22:30.950 --> 22:37.820 Regardless of what mesh you are using, be it block mesh or snappy hex mesh, or if you are importing 22:37.820 --> 22:46.050 mesh from Ansys or Fluent or Mesh or whatever it is, once it is in open form understandable format, 22:46.050 --> 22:47.580 it will be under poly mesh. 22:48.390 --> 22:50.400 Here you will be able to see five files. 22:50.460 --> 22:55.890 These are points which make the mesh and these are the owner which is like a patch. 22:55.890 --> 22:57.390 And the relation. 22:57.510 --> 22:58.380 These are neighbors. 22:58.380 --> 22:58.800 Other. 22:58.800 --> 23:01.320 Another relation and faces. 23:01.320 --> 23:05.920 If you are interested in seeing what is there inside, it is just pure numbers. 23:05.920 --> 23:08.110 Okay, same with this. 23:09.370 --> 23:19.090 You see everything is just number and for owner again it is just numbers, points also obviously numbers. 23:19.090 --> 23:20.860 But we are not interested in those. 23:20.860 --> 23:22.480 We are just interested in boundary. 23:22.690 --> 23:25.120 Okay I will go inside the boundary file. 23:25.120 --> 23:27.060 And now you can see it makes sense. 23:27.060 --> 23:27.660 Right. 23:27.690 --> 23:29.670 We have three patches. 23:29.670 --> 23:33.150 One is inlet, the other is outlet and the other is wall. 23:33.180 --> 23:34.890 So suppose you made the mesh. 23:34.890 --> 23:38.010 Now you don't want to generate block mesh from scratch again. 23:38.610 --> 23:45.360 Because sometimes when the mesh count is too high like a million, then it can take a bit of time to 23:45.360 --> 23:46.050 generate the mesh. 23:46.050 --> 23:47.730 It won't happen quickly. 23:47.850 --> 23:52.600 In that case, you don't want to change just the patch names and run the block mesh again. 23:53.590 --> 23:57.610 All you can do is you can go here and change whatever you want. 23:57.640 --> 24:01.000 Let's say, uh, I don't want this as outlet. 24:01.000 --> 24:04.390 I just want this as, uh, outflow. 24:04.390 --> 24:04.780 Okay? 24:04.780 --> 24:05.950 I'm just changing the name. 24:05.950 --> 24:07.240 Then I can do it. 24:07.240 --> 24:12.610 I'll save the file and it will be appearing there also. 24:14.870 --> 24:16.490 You see, we have outflow. 24:18.140 --> 24:19.820 So this is the outflow. 24:20.150 --> 24:24.440 Uh Paraview has some trouble when we are removing names. 24:24.440 --> 24:27.200 As you can see, this outlet actually doesn't have anything. 24:27.200 --> 24:29.720 Once you open and close, it will be fine. 24:29.750 --> 24:33.230 Now we have the outflow and that is the outlet now. 24:33.230 --> 24:35.480 So that is how you can change the name. 24:35.480 --> 24:37.940 Now I will change this back to outlet. 24:38.710 --> 24:41.590 Save the file and refresh. 24:42.010 --> 24:43.900 See now nothing is there in outflow. 24:43.900 --> 24:45.460 We have it in outlet. 24:45.970 --> 24:48.220 That is what this boundary can do. 24:48.220 --> 24:53.260 Also you can change the patch type like if you don't want this outlet as a patch. 24:53.260 --> 24:56.890 If you want it as um, empty. 24:57.130 --> 25:03.380 Let's say it's not usually how physics works, but let's say that you want to change some patch to empty. 25:03.410 --> 25:07.070 Then you can just change this to empty and it will go to empty. 25:07.880 --> 25:08.390 Okay. 25:08.390 --> 25:11.480 And now we also see something called group walls. 25:11.510 --> 25:16.550 So if we have multiple walls, let's say walls one, walls two, walls three and multiple groups of 25:16.550 --> 25:20.570 walls, then we are just selecting group walls and click on apply. 25:20.570 --> 25:22.400 And we will be seeing all the walls. 25:22.400 --> 25:25.610 So this is also one nice feature in Paraview. 25:26.150 --> 25:29.520 Okay we are done with the second tutorial also. 25:30.810 --> 25:34.590 Now the third is we are going to see curves. 25:34.590 --> 25:36.150 Okay, it's a bend pipe. 25:36.420 --> 25:39.060 I'll jump back to the PPT. 25:40.080 --> 25:41.400 Now introduction to arcs. 25:41.400 --> 25:42.630 So what are arcs? 25:42.630 --> 25:49.170 When I was explaining edges, I mentioned that we can not just join two points through a line, we can 25:49.170 --> 25:51.940 join it through a curve by defining a third point. 25:51.940 --> 25:54.340 That is what the ARX function does. 25:54.640 --> 25:59.290 So we will be doing that ARX in this okay. 25:59.290 --> 26:06.580 So in any rectangular channel you can create a circular outflow or opening. 26:06.580 --> 26:07.870 So that could be done. 26:07.870 --> 26:11.800 Or you can create an entirely circular pipe that is also possible. 26:11.800 --> 26:14.470 So this is the syntax the edges. 26:14.470 --> 26:18.270 You can see we have arc v1 v2 p x p y p z. 26:18.330 --> 26:19.890 So what is v1 v2. 26:20.010 --> 26:26.610 When we were defining the block mesh we have these points four seven, three, two, six, one and so 26:26.610 --> 26:26.850 on. 26:26.850 --> 26:31.140 If I want to create a create an arc between 4 and 5. 26:31.320 --> 26:35.010 So I just have to give these two as the v1 and v2. 26:35.910 --> 26:38.310 Here v one and v two will be four and five. 26:38.340 --> 26:40.180 Now what is p x p y p z. 26:40.180 --> 26:41.560 This is the third point. 26:41.560 --> 26:46.060 So how we usually do is the center of this point. 26:46.180 --> 26:48.370 This will act as the p y p z. 26:49.210 --> 26:52.840 So you can basically choose the third point and it will work. 26:52.840 --> 26:56.530 So how do you actually know what is the third point's coordinate. 26:56.860 --> 27:04.580 Uh, it comes by simple calculation on uh like a geometry. 27:04.580 --> 27:04.880 Right? 27:04.880 --> 27:11.090 We have we know the center of something, and, uh, we know the angle at which this is subtended. 27:11.090 --> 27:17.750 If you want to say you want to create a point here, then you know what is the angle from the normal, 27:17.750 --> 27:24.410 then you can just calculate it, calculate the x and y based on the sine theta and cos theta. 27:25.040 --> 27:28.750 This is just, uh, normal geometrical calculation. 27:28.750 --> 27:31.120 You can do that and select the points. 27:31.150 --> 27:31.690 Okay. 27:32.020 --> 27:37.030 This will be the syntax and we can create an arc. 27:37.030 --> 27:43.900 Now we will see how it is done through a tutorial I'll go to the third bend pipe. 27:43.900 --> 27:50.380 As you can see uh we have the block mesh here okay. 27:51.190 --> 27:56.480 So now let's say that we don't have these two arcs. 27:56.690 --> 27:57.020 Okay. 27:57.020 --> 28:02.240 I have commented it out and I'll go to the location. 28:05.060 --> 28:07.670 I will run sorry. 28:08.780 --> 28:09.890 Block mesh. 28:09.920 --> 28:10.580 Okay. 28:10.790 --> 28:12.440 I will load the mesh. 28:16.410 --> 28:16.680 See? 28:16.680 --> 28:18.240 Now we have a pure rectangle. 28:18.510 --> 28:19.740 Nothing fancy. 28:20.970 --> 28:22.770 We can see surface with edges. 28:22.800 --> 28:26.970 Yeah, we have an inlet. 28:27.510 --> 28:33.060 We have an outlet and we have walls. 28:33.090 --> 28:34.710 Okay, we have everything. 28:36.000 --> 28:36.480 Okay. 28:36.480 --> 28:40.170 Now let's say I want to join two points and create an arc. 28:40.190 --> 28:41.450 So how do I do it? 28:41.480 --> 28:44.570 We will just create one arc and see how it works. 28:44.600 --> 28:46.550 Usually it looks messy. 28:46.580 --> 28:50.600 Arcs are not very efficient in openfoam. 28:50.600 --> 28:53.960 Maybe sometimes it is efficient, sometimes it is not. 28:55.250 --> 29:01.100 Okay, I have just given refresh and you can see it has created an arc here. 29:01.130 --> 29:05.370 Okay, so it just created an arc because we defined it. 29:05.370 --> 29:07.170 It is between 1 and 2. 29:07.170 --> 29:12.900 And I have just created uh, defined a third point and it is creating mesh. 29:13.020 --> 29:13.560 Okay. 29:13.800 --> 29:15.330 So this is how it works. 29:15.330 --> 29:24.120 Now if I want to do it for this phase also, then I will uncomment this save the file, run block mesh 29:24.750 --> 29:26.910 and refresh it again. 29:26.910 --> 29:31.060 You can see now if you really want to see the coordinates matching. 29:32.560 --> 29:33.070 Okay. 29:33.070 --> 29:38.080 Now if you see this point it is zero point in x axis. 29:38.080 --> 29:40.600 It is one. 29:40.870 --> 29:42.910 You can see that it is 0 to 1. 29:42.910 --> 29:49.990 So in x axis it is one and y axis it is 0.5 z axis it is around 1.5. 29:50.620 --> 29:52.960 See that is what we have defined it here. 29:52.960 --> 29:55.880 So it is 10.5 and 1.5. 29:55.910 --> 30:01.490 Now let's say I just want to push it to one this year, not 1.5. 30:01.880 --> 30:02.570 It changed it. 30:03.110 --> 30:07.430 Uh and running the block it is throwing an error because it's not matching well. 30:07.430 --> 30:08.990 So there is it. 30:09.110 --> 30:10.790 This is not fully functional. 30:10.790 --> 30:14.210 So we might have to be very cautious while doing this. 30:15.350 --> 30:15.890 Okay. 30:15.890 --> 30:18.850 So I just defined it and it works fine. 30:18.850 --> 30:20.290 So I will just stick on to it. 30:20.290 --> 30:24.010 But if you want to play with the values, you can definitely do. 30:24.010 --> 30:30.760 And I also have a tutorial on YouTube, uh, in the channel code dynamics where I have done flow over 30:30.760 --> 30:33.190 a cylinder mesh just using block mesh. 30:33.190 --> 30:42.170 So there I have clearly explained on how to calculate the third point, the point where it will create 30:42.170 --> 30:42.680 a curve. 30:42.710 --> 30:46.730 Using Python, the basic mathematical formula, we can evaluate that. 30:46.730 --> 30:50.570 So you can check that video if possible I will drop that in the resources. 30:50.840 --> 30:51.170 Okay. 30:52.460 --> 30:57.440 If I start explaining that this will become a very very long video like 1.5 hours video. 30:58.220 --> 30:58.580 Okay. 30:58.580 --> 30:59.960 Now we have the mesh. 30:59.960 --> 31:03.170 So this is how we are creating Arcs. 31:03.500 --> 31:04.100 Okay. 31:04.760 --> 31:06.810 Now we will go to the next topic. 31:07.140 --> 31:10.440 So we saw all of these how to do run a block mesh. 31:10.440 --> 31:14.670 It is through the command block mesh and usually it is stored in the poly mesh folder. 31:15.060 --> 31:15.570 Okay. 31:15.570 --> 31:20.520 In CFD whenever we are working we will be defining the boundary conditions. 31:20.520 --> 31:27.090 Let's say the inlet velocity at zeroth time step is one meters per second or 0.1m/s. 31:27.180 --> 31:29.840 So this is what is called as boundary condition. 31:29.840 --> 31:32.660 And it will be applied for all the phases. 31:32.660 --> 31:36.470 Let's say in wall it is a no slip condition which means velocity is zero. 31:36.710 --> 31:38.840 It is a fixed value at the outlet. 31:38.840 --> 31:42.800 The pressure will be zero and for velocity it will be zero gradient. 31:42.800 --> 31:44.690 So what is zero gradient? 31:44.690 --> 31:47.450 We have to understand the types of boundary condition. 31:47.450 --> 31:55.020 When you take the regular theoretical CFD course we you would have come across something called the 31:55.020 --> 31:59.010 Dirichlet boundary condition and the von Neumann boundary condition. 31:59.010 --> 32:05.790 So what it actually means is that, uh, the Dirichlet condition, the values are fixed, it doesn't 32:05.790 --> 32:10.770 change or it is not a gradient kind of thing, it is just a fixed value. 32:10.770 --> 32:12.120 It is a specific value. 32:12.120 --> 32:18.280 But if you take Neumann condition, it is a zero gradient or some gradient. 32:18.280 --> 32:23.170 It is a flow which is defined in terms of gradients. 32:23.170 --> 32:23.500 Okay. 32:23.500 --> 32:28.660 So if you want to get into the math you can check the lectures which will talk about it. 32:28.660 --> 32:31.870 But we are just focusing on how to implement those in Openfoam. 32:32.470 --> 32:33.850 So we will see that. 32:33.850 --> 32:36.100 And there is also something called symmetric. 32:36.100 --> 32:41.200 Let's say there is flow over a cylinder, but you don't want to simulate the entire cylinder because 32:41.200 --> 32:42.840 it will be computationally expensive. 32:43.080 --> 32:47.190 If it is laminar, it is going to be symmetric about the center axis, right? 32:47.190 --> 32:49.260 We don't have to do it completely. 32:49.260 --> 32:54.360 So in that case you can do symmetric boundary condition and only simulate flow over half cylinder. 32:54.360 --> 32:57.390 And it all directly applies to the other half. 32:57.390 --> 33:00.150 Also you can do the mirroring and post-processing. 33:00.150 --> 33:02.580 So that is where symmetry boundary condition comes. 33:02.580 --> 33:06.400 And cyclic and periodic boundary conditions are something like. 33:06.400 --> 33:13.240 The outflow can be connected back to the inlet, and whatever values is getting out of the outflow will 33:13.240 --> 33:14.680 be connected back to the inlet. 33:14.680 --> 33:16.750 So it is like repeating geometries. 33:16.750 --> 33:19.000 That's why it is called periodic boundary condition. 33:19.000 --> 33:24.130 And obviously wall will have no slip or slip condition depending on the physics you are working with 33:24.550 --> 33:28.630 and setting the boundary conditions will always happen in the zero folder. 33:28.630 --> 33:32.840 So just like how we had constant and system, we have another folder called zero. 33:33.170 --> 33:39.140 We will be seeing from now on because for the previous videos we did not want the boundary condition 33:39.140 --> 33:40.250 to be confusing. 33:40.970 --> 33:42.680 So we I did not add it. 33:42.680 --> 33:44.960 Now we will be seeing the zero file also. 33:45.590 --> 33:52.820 So each file will have or the each time step in the zeroth condition zeroth folder is just zeroth time 33:52.820 --> 33:53.300 step. 33:54.080 --> 33:59.930 It will have velocity, pressure, uh, temperature pressure minus the hydrostatic forces. 34:00.320 --> 34:06.530 Uh, and there are other turbulence models like k epsilon, nu T omega and so on. 34:06.530 --> 34:10.190 So these files contain the boundary condition for the entire case. 34:10.190 --> 34:14.930 But usually it is mandatory to only to have velocity and pressure. 34:14.930 --> 34:17.570 Depending on physics we will have other mandatory files. 34:18.110 --> 34:18.500 Okay. 34:18.500 --> 34:21.920 Now now for the very simpler case, we will have only velocity and pressure. 34:21.950 --> 34:22.790 No turbulence. 34:22.790 --> 34:23.870 It will be a laminar case. 34:24.740 --> 34:30.860 So this condition will be defined under a section called boundary field which looks something like this. 34:30.860 --> 34:33.500 For an example we have the velocity file. 34:33.500 --> 34:36.950 And under velocity file we will have the function called boundary field. 34:36.950 --> 34:40.040 It is having three conditions like inlet, outlet and wall. 34:40.040 --> 34:42.680 This is what we had in the mesh also. 34:42.690 --> 34:47.790 So this inlet is having type fixed value and the value is one meter per second. 34:47.790 --> 34:51.240 Since it is a unit, this is one meter per second. 34:51.600 --> 34:56.940 And in the x direction in the outlet is zero gradient, which means the solver will calculate the values 34:56.940 --> 34:57.510 for you. 34:57.510 --> 35:02.850 Initially it is just zero in gradients it is a Neumann type boundary condition. 35:02.850 --> 35:06.240 Then the solver will calculate what should be the outlet based on the inlet. 35:06.240 --> 35:15.710 The walls is no slip, so Openfoam offers you this guy a nice keyword no slip to, uh, type that the 35:15.710 --> 35:16.760 velocity will be zero. 35:16.760 --> 35:22.460 But if you don't want to use that, you can't do type fixed value and check the value to uniform 000. 35:22.460 --> 35:25.220 So that is also meaning essentially the same. 35:25.220 --> 35:32.280 And if you take the pressure for the same case, the inlet will be zero gradient because velocity and 35:32.280 --> 35:33.510 pressure are coupled. 35:33.510 --> 35:36.330 It's related, so we should not over define it. 35:36.330 --> 35:38.310 So we will set the inlet as zero gradient. 35:38.310 --> 35:44.370 Because we already defined the inlet as value and the outlet, we will set a specific value for pressure 35:44.370 --> 35:48.930 because we ask the solver to calculate the outflow for velocity. 35:49.500 --> 35:52.560 So we have to give some condition which will be given to the pressure. 35:52.560 --> 35:54.480 And walls will also be zero gradient. 35:54.480 --> 35:57.970 So the solver will calculate the pressure on walls. 35:58.930 --> 35:59.530 Okay. 35:59.530 --> 36:02.980 So we will see, uh, how these things work. 36:02.980 --> 36:07.990 Okay I'll go to the next folder which is a lid driven cavity case. 36:08.110 --> 36:14.320 We have zero constant and system under system we have the block mesh file. 36:14.320 --> 36:17.860 We will just run the mesh and we will see how it looks. 36:25.820 --> 36:26.900 It is throwing an error. 36:26.900 --> 36:29.240 Let's see what happened in the block mesh. 36:34.280 --> 36:36.770 Okay, I have some keywords here. 36:36.770 --> 36:38.180 I should remove it. 36:38.180 --> 36:39.680 I will save the file. 36:41.270 --> 36:43.190 Yes, it is running fine now. 36:43.400 --> 36:46.060 So that was a typo mistake. 36:47.260 --> 36:48.700 Now we can see the mesh. 36:50.470 --> 36:52.360 So this is the mesh we have. 36:54.010 --> 36:57.730 This will be fixed walls. 36:58.720 --> 37:01.150 And this is a moving wall. 37:01.150 --> 37:04.810 Front and back will be empty because, uh, it is a 2D case. 37:04.810 --> 37:10.010 If you just want to see all the empty patches, you can select this and you can see all the empty patches. 37:10.010 --> 37:11.720 So front and back is empty. 37:11.720 --> 37:18.020 Now, what we are trying to do is we are trying to simulate a case, a 2D case where the upper wall 37:18.020 --> 37:22.340 is moving towards the right and other walls are fixed. 37:22.430 --> 37:28.340 So it is going to create a recirculation region inside this domain. 37:28.670 --> 37:30.560 And that is what we are trying to observe. 37:30.560 --> 37:32.700 Okay Okay. 37:32.700 --> 37:34.560 Now we will see. 37:35.040 --> 37:37.170 Uh, it it has created the poly mesh. 37:37.170 --> 37:39.930 Now we will get introduced to the zero files. 37:39.930 --> 37:43.260 Now we have u and p which means velocity and pressure. 37:43.530 --> 37:45.570 I will open the velocity file. 37:45.930 --> 37:49.710 You can see the dimensions are zero one minus one 000. 37:49.710 --> 37:51.960 And don't worry about these errors. 37:51.960 --> 37:54.480 If you are uh ID shows it. 37:54.630 --> 37:57.200 It doesn't matter as long as the syntax is fine. 37:59.060 --> 38:03.860 Uh, we have the moving wall, which is moving at one meter per second in X direction. 38:03.950 --> 38:08.630 We have fixed walls, which is obviously no slip print and back is empty. 38:08.810 --> 38:09.080 Okay. 38:09.080 --> 38:14.150 So this is like a syntax this names has to mandatorily match with these. 38:14.150 --> 38:21.120 Only then it will get uh applied if you make even slight mistake like putting small w W instead of capital 38:21.120 --> 38:22.830 W, it's going to be a problem. 38:23.610 --> 38:25.500 Then we will see the pressure file. 38:26.460 --> 38:29.850 So in pressure for walls we have defined zero gradient. 38:29.850 --> 38:32.070 And front and back is always empty. 38:32.100 --> 38:33.900 So we have given empty. 38:33.930 --> 38:35.490 You can calculate the dimension. 38:35.490 --> 38:37.800 This is m l t. 38:37.800 --> 38:40.740 And the other values also go on like temperature and all. 38:40.740 --> 38:42.810 But we are not interested in that as of now. 38:43.260 --> 38:47.920 Just do m l t and you can know what the dimension of this file is. 38:48.580 --> 38:49.030 Okay. 38:50.110 --> 38:50.440 Okay. 38:50.440 --> 39:00.580 Now we have done the initial conditions, but now we also have to set the turbulence model. 39:00.580 --> 39:00.940 Right. 39:00.940 --> 39:05.710 So for this cavity case we are using something called ICO form. 39:05.740 --> 39:14.480 So ICO form is a solver in Openfoam, which is transient in nature and it is incompressible, but it 39:14.480 --> 39:15.920 cannot handle turbulence. 39:15.920 --> 39:17.030 It is purely laminar. 39:17.030 --> 39:19.760 It can work only in laminar regions. 39:19.760 --> 39:20.150 Okay. 39:20.150 --> 39:23.810 So for that we have a file called transport properties. 39:23.810 --> 39:31.790 Always transport properties will define the values of the kinematic viscosity of the fluid which is 39:31.790 --> 39:32.090 used. 39:32.090 --> 39:33.640 So to change the fluid. 39:33.670 --> 39:40.180 We don't have the facility to choose a fluid by name, unlike commercial software like Ansys. 39:40.210 --> 39:45.670 Instead, what we will do is we will define the kinematic viscosity of the fluid and it will calculate 39:45.670 --> 39:46.990 whatever is necessary. 39:47.170 --> 39:53.230 And since Ecco foam doesn't work with turbulence, we don't have a file here called turbulence properties. 39:53.230 --> 40:00.050 Otherwise we will be having turbulence properties also in Ecco form Without said it is always laminar 40:00.050 --> 40:01.970 so we are not going to set any turbulence. 40:02.450 --> 40:05.750 You can find the polymesh which has all the mesh details. 40:06.620 --> 40:11.960 Okay, now we are not interested in learning these three things just yet. 40:11.960 --> 40:18.500 We will be seeing uh, it quickly, but for now we will see what we are going to do with this Iko form 40:18.500 --> 40:18.770 case. 40:18.770 --> 40:21.300 We are trying to do something called lid driven cavity. 40:21.390 --> 40:27.840 We are going to, uh, move a lid on top and we will be seeing what is the recirculation region inside. 40:28.260 --> 40:28.650 Okay. 40:28.650 --> 40:29.850 Now we will run it. 40:29.850 --> 40:33.390 So we will be using eco foam solver as I said. 40:34.200 --> 40:36.210 Now I will go into control duct. 40:36.660 --> 40:41.610 And this is the file which controls all the running parameters simulation parameters. 40:41.610 --> 40:45.450 So the application is eco foam which is the solver is eco foam. 40:45.450 --> 40:45.470 icofom. 40:45.770 --> 40:49.040 And the simulation has to start from start time. 40:49.040 --> 40:51.710 So in this case the start time is zero. 40:51.710 --> 40:52.970 So it will start from zero. 40:52.970 --> 40:59.600 Suppose if we run till some time let's say 0.5 seconds and we want to continue from there, then we 40:59.600 --> 41:02.210 can use this command latest time. 41:02.210 --> 41:05.630 But in this case the latest time happens to be zero. 41:05.630 --> 41:09.020 So this can be latest time need not be start time. 41:09.120 --> 41:11.430 Then we are setting the start time as zero. 41:11.430 --> 41:14.250 So if we are using start time then this will be essential. 41:14.250 --> 41:16.170 Otherwise you can leave it then stop. 41:16.170 --> 41:18.480 It will be end time and we will define the end time. 41:18.480 --> 41:20.910 In this case I have chosen 0.5 seconds. 41:20.910 --> 41:25.560 Let it be the delta T, which is the, uh time step. 41:25.740 --> 41:28.200 We will be using 0.005. 41:28.200 --> 41:32.010 So I have checked the stability criteria and came up with this time step. 41:32.010 --> 41:39.040 In most cases you have to check it and there is also adaptive time stepping in openfoam, which we will 41:39.040 --> 41:46.690 learn later to set up certain cases where we can do adaptive time stepping based on the current number 41:46.990 --> 41:48.070 or kfl number. 41:48.070 --> 41:50.290 If you know by that name, okay. 41:50.290 --> 41:56.350 And right interval is 20, which means for every 20 time steps a file will be written, the time step 41:56.350 --> 41:57.550 file will be written. 41:58.770 --> 42:02.070 and, uh, perjury will remove older files. 42:02.070 --> 42:07.230 Let's say if I give purge right five, then it will keep only latest five times. 42:07.350 --> 42:13.620 This will be useful in case of steady state scenarios, but now it is not useful if all the details 42:13.620 --> 42:16.920 are going through your head, don't worry, you will catch up. 42:16.920 --> 42:18.360 It is just the first tutorial. 42:18.360 --> 42:23.200 Okay, so you don't have to worry about these things as of now Pretty much all the time. 42:23.200 --> 42:25.030 We'll let it be default. 42:25.360 --> 42:26.020 Okay. 42:26.020 --> 42:33.250 And the FPV schemes and FPV solution contain all the details related to what numerical method you will 42:33.250 --> 42:35.830 be using to solve each of the equation. 42:35.830 --> 42:38.770 So we are not going to go into that. 42:38.770 --> 42:42.700 It will be an advanced course, so we are just leaving it as default. 42:42.700 --> 42:44.230 We are using a Piso solver. 42:44.230 --> 42:47.360 So Piso is an algorithm which is what the ICO form uses. 42:48.170 --> 42:49.820 So we will stick with that. 42:49.820 --> 42:51.650 And I'll go here. 42:51.980 --> 42:53.210 So we have the mesh. 42:53.210 --> 42:56.120 We set up the boundary conditions and initial condition. 42:56.150 --> 43:00.980 Now I will initiate echo form by the command I echo form. 43:02.000 --> 43:02.900 I'll hit enter. 43:02.900 --> 43:04.790 Now the simulation is over. 43:04.790 --> 43:09.080 So you you could see that we have 0.10.2. 43:09.170 --> 43:11.040 So on till 0.5. 43:11.910 --> 43:15.390 I will open the paraview from scratch again. 43:15.420 --> 43:18.720 Usually refresh doesn't work in this kind of things. 43:19.380 --> 43:20.580 I'll apply you. 43:20.580 --> 43:22.620 The colors might be different for you. 43:22.620 --> 43:26.100 If you want to change the color, you can scroll down on the left panel. 43:26.730 --> 43:28.260 You can click on the color map. 43:28.260 --> 43:29.100 It will get. 43:29.520 --> 43:37.520 This might be your color map as of now, but I like to keep this pressure in this color map. 43:37.520 --> 43:41.930 If you want to set this as your default, you can set it and click this button. 43:42.800 --> 43:43.280 Okay? 43:43.280 --> 43:47.390 If you want to choose any other color maps, you are free to do so. 43:47.390 --> 43:50.600 I personally prefer this for, uh, pressure. 43:50.600 --> 43:53.180 So this is the pressure at 0.1 seconds. 43:53.180 --> 43:57.650 Now, if I play, this doesn't pretty much change for till 0.5. 43:57.680 --> 44:03.420 It is being constant, so if I want to view velocity I will go here choose velocity. 44:03.870 --> 44:09.270 And uh, as you can see the velocity changes something like this. 44:09.390 --> 44:09.780 Okay. 44:09.780 --> 44:16.980 So we are not seeing pretty much any change in here, even though the time step is from 0.1 to 0.5. 44:17.010 --> 44:21.060 It is because we have a very coarse mesh. 44:21.060 --> 44:21.630 Let's see. 44:21.630 --> 44:23.080 It's a very very coarse. 44:23.080 --> 44:27.490 And also we are not trying to do a lid driven cavity case. 44:27.490 --> 44:30.250 As such we are just learning the boundary condition. 44:30.250 --> 44:36.190 So this is fine because essentially we might need smaller time steps with a finer grid. 44:36.820 --> 44:42.100 But for now you understood the point on how to set up the boundary condition, the u and p file. 44:42.340 --> 44:47.250 So I will close this, uh, and we have one last tutorial. 44:47.250 --> 44:48.000 Pipe flow. 44:48.300 --> 44:54.510 So the pipe flow, we will be setting the initial fixed value for velocity pressure. 44:54.510 --> 44:58.230 And we will also do, uh, no slip for the walls. 44:58.350 --> 45:03.360 And then we will set up the initial velocity and pressure for boundary conditions. 45:03.360 --> 45:04.950 Then let's see okay. 45:04.950 --> 45:15.340 Now for uh pipe flow we already have a block mesh dict which comes along with this, but this is pretty 45:15.340 --> 45:16.060 crazy, right? 45:16.060 --> 45:17.590 This is advanced thing. 45:17.890 --> 45:23.020 We will see how to create a pipe mesh very simply using snappy mesh. 45:23.020 --> 45:27.100 Without all these values, it will be very simple. 45:27.130 --> 45:32.530 Uh, we will be seeing in forthcoming weeks, but for now, we will be just using, uh, existing block 45:32.530 --> 45:32.740 mesh. 45:32.920 --> 45:38.060 I took this from the tutorials folder, so we will just create block mesh using this. 45:38.060 --> 45:40.700 Now I'll clear this. 45:42.530 --> 45:45.320 Now we will go to the last case which is pipe flow. 45:45.920 --> 45:49.550 I'm in the right directory now I will do block mesh. 45:49.550 --> 45:54.140 The mesh is generated I will view it in paraview. 45:57.980 --> 46:01.000 So we have a pipe case. 46:01.450 --> 46:01.780 Okay. 46:01.780 --> 46:05.800 So this is more like a symmetry blend case. 46:05.800 --> 46:07.660 Like this is your symmetry plane. 46:08.290 --> 46:08.650 Okay. 46:08.650 --> 46:13.570 So we are not interested in understanding what this case physically means. 46:13.570 --> 46:16.450 We are just interested in setting up the boundary conditions. 46:17.140 --> 46:18.580 That's what this tutorial is about. 46:18.580 --> 46:25.730 As you can see we have inlet front back walls, lower wall and wall, startup outlet, upper wall and 46:25.730 --> 46:26.990 so many things here. 46:27.290 --> 46:35.540 So if you go to the zero file in the U file you can see the boundary condition for everything. 46:35.540 --> 46:37.640 Now you might be wondering what is this. 46:37.640 --> 46:44.270 So this is just C plus plus way of telling that this condition applies to both lower wall startup and 46:44.270 --> 46:45.230 upper wall startup. 46:45.350 --> 46:51.630 Same for this okay, so we are doing an inlet of 0.01 the x direction. 46:51.630 --> 46:56.430 This internal field is like the internal scalar field which will be set. 46:56.610 --> 46:59.730 And uh this is only minus eight. 46:59.730 --> 47:01.350 We did not want to set it to zero. 47:01.350 --> 47:03.240 So it is in a pretty low value. 47:03.270 --> 47:04.980 This is the velocity file. 47:04.980 --> 47:07.980 You can pause the video and ponder on what is actually set. 47:07.980 --> 47:11.940 Okay the Dirichlet and Neumann condition then. 47:11.940 --> 47:11.960 Then. 47:11.960 --> 47:16.100 Similarly for pressure we have this. 47:16.190 --> 47:22.010 So you can see that this is set to symmetry plane because they want a symmetry over this plane. 47:22.070 --> 47:23.720 So that's why it is set to symmetry. 47:23.720 --> 47:26.660 Again you can pause and ponder. 47:26.660 --> 47:29.270 You can change values and try on your own. 47:29.270 --> 47:32.510 So this is what we are essentially doing in boundary file. 47:32.510 --> 47:38.520 All I wanted to say is we have to set boundary condition for all the files, unless, unlike commercial 47:38.520 --> 47:44.670 software where you will set only for inlet and it will automatically choose what will be there for pressure 47:44.670 --> 47:46.140 and for the inlet. 47:46.140 --> 47:49.260 So it's not like that in Openfoam you have to define everything. 47:49.380 --> 47:55.770 Okay, we have only U and P and we will see what type of solver we are using. 47:55.770 --> 47:59.280 Again, it's uh incompressible solver. 47:59.280 --> 48:00.460 It's called simple form. 48:00.700 --> 48:05.110 So simple means Semi-implicit method for pressure linked equations. 48:05.110 --> 48:08.650 You would have come across this in your, uh, theoretical CFD course. 48:08.770 --> 48:10.900 So that is what we are going to use. 48:11.050 --> 48:12.160 Simple algorithm. 48:12.700 --> 48:16.570 It is a steady state solver and it is incompressible. 48:16.570 --> 48:22.570 So we will be running this case and we will be running till 200th time step. 48:23.320 --> 48:23.560 Okay. 48:23.560 --> 48:26.780 The start time is zero and the end time is 2000. 48:26.810 --> 48:28.130 We will run this. 48:28.130 --> 48:30.770 I will go here and type simple form. 48:30.770 --> 48:32.450 Notice that F is capital. 48:32.630 --> 48:33.770 I'll hit enter. 48:33.770 --> 48:41.060 It will take a bit of time before it is converged and we will wait for it to converge. 48:41.060 --> 48:42.320 Then I'll get back to you. 48:43.820 --> 48:45.710 Okay, now the simulation is over. 48:45.710 --> 48:49.030 But why did not it go to 2000? 48:49.060 --> 48:49.600 Right. 48:49.600 --> 48:54.130 We set the end time as 2000, but it did not because the solution converged. 48:54.130 --> 48:58.360 Before 2000, it converged at one for two two iterations itself. 48:58.360 --> 49:05.140 So the convergence criteria and everything is set in the FP scheme and FP solution, not in F scheme. 49:05.350 --> 49:13.010 In FP solutions you can see the residual control and uh, how many iterations it has to run for each 49:13.010 --> 49:13.460 thing. 49:13.460 --> 49:15.110 And what is the characters? 49:15.110 --> 49:18.770 That is the number of iterations and what type of solver you want to use? 49:18.770 --> 49:19.970 What is the tolerance for that? 49:19.970 --> 49:21.710 Everything can be set here. 49:22.430 --> 49:26.570 Uh, so that is how it is choosing the convergence criteria. 49:27.020 --> 49:28.280 And it has converged. 49:28.280 --> 49:33.140 Now if you go here you can see only five files, right. 49:33.140 --> 49:37.530 If you go to the control date, you can see that the right right interval is 100. 49:37.530 --> 49:42.720 So we should have been getting files for every 100 iteration. 49:42.720 --> 49:48.720 But we did not because the purge rate is five, which means it will keep only the latest five files. 49:48.720 --> 49:54.150 But for steady state all we care is just one for double two, because that is the solution where it 49:54.150 --> 49:55.050 got converged. 49:55.050 --> 49:57.930 So we are not interested in other files. 49:57.930 --> 49:59.940 We can safely delete those if you want. 50:00.750 --> 50:02.630 Now I will just open paraview. 50:04.610 --> 50:05.630 Click on apply. 50:05.660 --> 50:09.500 You see we have the pressure and we have the velocity. 50:09.500 --> 50:12.110 But this is at 1100. 50:12.140 --> 50:13.790 We have to go to the last time step. 50:13.790 --> 50:19.490 Either you can select it manually or click on this button and it will take you to the last time step. 50:19.910 --> 50:22.670 As you can see this simulation converged. 50:22.700 --> 50:24.830 This is the pressure or sorry velocity. 50:25.200 --> 50:26.700 And this is your pressure. 50:26.790 --> 50:31.020 Always make sure to visualize the cell data so that it will be smooth if you do. 50:31.620 --> 50:33.150 Uh, sorry. 50:33.150 --> 50:34.590 Point data always point data. 50:34.590 --> 50:37.590 If you choose the cell data it will be squared like this. 50:38.700 --> 50:40.860 So always choose point data. 50:42.420 --> 50:42.840 Okay. 50:42.840 --> 50:47.430 So we now know how to do simple form and how to set up the boundary condition. 50:47.430 --> 50:54.520 But as I was saying we also have to define turbulence properties because simple form can handle turbulence. 50:54.520 --> 50:58.120 So what I did here is I just set the simulation type to laminar. 50:58.420 --> 51:02.530 If we are working with any turbulence model, then we will be defining it here. 51:02.530 --> 51:07.810 Like if it is rans, we will be defining what is the Rans model. 51:08.320 --> 51:10.930 If it is less, we will be defining that as well. 51:10.930 --> 51:14.820 But we'll be seeing that in the upcoming weeks for now. 51:15.060 --> 51:21.660 Uh, we have just run a laminar case for, uh, two solvers, ACO form and simple form, and we have 51:21.660 --> 51:23.730 set the boundary condition generated mesh. 51:23.880 --> 51:28.140 I think that is pretty good for this week. 51:28.500 --> 51:29.130 Okay. 51:29.250 --> 51:32.040 And now we also know how control dict works. 51:33.120 --> 51:33.660 Okay. 51:34.170 --> 51:40.420 So ACO form as I said it is an incompressible laminar flow for Newtonian fluids. 51:40.570 --> 51:42.490 It can't handle turbulence. 51:42.910 --> 51:49.030 It solves unsteady Navier-Stokes equation, which is also the transient one or also known as uh. 51:51.040 --> 51:51.520 Yeah. 51:51.520 --> 51:52.810 Unsteady or transient. 51:52.810 --> 51:53.440 That's it. 51:53.440 --> 52:00.250 And for the case setup, all we need is velocity pressure and transport properties. 52:00.490 --> 52:06.320 And, uh, we will be giving the kinematic viscosity in the transport properties file. 52:06.320 --> 52:09.440 Then for running Iko form, the list of commands is. 52:09.440 --> 52:12.710 First we have to do block mesh and then I go home. 52:13.520 --> 52:17.360 And simple form is a steady state solver for incompressible fluids. 52:17.360 --> 52:21.350 It can handle turbulence and it is for uh laminar flows. 52:21.350 --> 52:27.420 Also, it can work both for laminar and turbulence and it solves the steady state Navier-Stokes equation 52:27.420 --> 52:32.010 using this simple algorithm, which is Semi-implicit method for pressure linked equations. 52:32.010 --> 52:36.990 If you want to know the math of it, you can check the documentation or any standard textbook like Versteeg 52:36.990 --> 52:37.680 Malalasekera. 52:39.150 --> 52:46.020 And for simple form the k setup, we need the velocity pressure if it is a laminar case. 52:46.020 --> 52:50.390 Otherwise we will also have the turbulence files which we are not carrying as of now. 52:50.390 --> 52:54.650 And we have to define the transport properties where we will be defining the fluid properties. 52:55.400 --> 53:02.120 And also, as I said, we have the turbulence properties where we have given laminar okay. 53:02.120 --> 53:03.500 For mesh generation. 53:03.500 --> 53:08.510 The command which we used is block mesh to generate the computational domain. 53:08.510 --> 53:15.510 And we set the initial and boundary condition using the zero folder and the files under zero folder 53:15.510 --> 53:18.240 for physical properties like kinematic viscosity. 53:18.270 --> 53:23.160 We use the transport properties and for turbulence we use turbulence properties file. 53:23.160 --> 53:29.190 For control parameters we use control dict if we scheme and if we solution under the system folder. 53:29.190 --> 53:35.100 And for running the simulation we will be using the respective solver and we post-processed with Paraview. 53:36.030 --> 53:36.360 Okay. 53:36.360 --> 53:39.670 So these are just some introduction to Paraview. 53:39.700 --> 53:43.090 This is exactly what I said in the tutorials. 53:43.090 --> 53:47.230 If you want to go through the PPT then you can, uh, ponder over it. 53:47.440 --> 53:54.160 Okay, so if you have any doubts, you can, uh, contact me or there is a big community, as I always 53:54.160 --> 53:58.000 say, there is a huge community online for CFD using Openfoam. 53:58.300 --> 54:03.930 Someone has already faced the issue that you are facing right now, so most probably you will get any 54:03.930 --> 54:04.590 solution. 54:04.680 --> 54:10.860 So by searching yourself online, you will be coming across other problems which other people faced. 54:10.860 --> 54:17.550 So by uh, looking at those problems, if you face it later in the future, you will be able to resolve 54:17.550 --> 54:18.480 it without looking up. 54:18.480 --> 54:19.920 So that's the advantage. 54:19.920 --> 54:24.060 Instead of directly asking someone what the solution could be. 54:24.300 --> 54:26.220 So thank you for watching this video. 54:26.220 --> 54:27.540 See you in the next class.