WEBVTT 00:00.290 --> 00:01.280 Hello everyone. 00:01.280 --> 00:05.030 Welcome back to the CFD using Openfoam beginner to Intermediate course. 00:05.030 --> 00:11.330 This is our class four and we will see overview on incompressible solvers, compressible solvers and 00:11.330 --> 00:14.570 some of the multiphase solvers which are available in Openfoam. 00:14.570 --> 00:21.200 Then we will do a hands on tutorial on case study on lid driven cavity, same as what we did in the 00:21.200 --> 00:28.760 class previous class, but it will be much refined and we will actually see how the simulation goes. 00:28.760 --> 00:31.040 Instead of a bad mesh, we will have a very good mesh. 00:31.940 --> 00:33.560 So incompressible solvers. 00:33.620 --> 00:39.020 Incompressible solvers in Openfoam are used to simulate fluid flows where the fluid density remains 00:39.020 --> 00:39.710 constant. 00:39.710 --> 00:45.920 So not just in Openfoam whenever you are trying to do any analytical calculations, or in most of the 00:45.920 --> 00:49.370 commercial solvers, the incompressibility is assumed. 00:49.370 --> 00:55.060 In most of the cases, unless you are working with very high speed sonic, uh, or external aerodynamics 00:55.060 --> 00:55.450 thing. 00:56.200 --> 00:58.060 Otherwise, mostly it is incompressible. 00:58.060 --> 01:03.910 The solvers are ideal for simulating flows at very low Mach number, where compressible effects can 01:03.910 --> 01:04.930 be neglected. 01:04.990 --> 01:08.980 So mostly less than, uh, Mach one, mostly subsonic. 01:10.360 --> 01:15.280 The incompressible solver is available in Openfoam or Ecco form. 01:15.280 --> 01:20.550 So as we already saw, Ecco form is a transient solver for incompressible laminar flow of Newtonian 01:20.550 --> 01:20.970 fluids. 01:21.000 --> 01:26.430 The application can be used for time dependent simulation, that is, transient simulation involving 01:26.430 --> 01:27.870 very simple fluid flow. 01:28.200 --> 01:33.120 Laminar case and it is useful in simulating transient flow in a pipe or a channel. 01:33.120 --> 01:36.750 So it can be very easily set up and we can get good results. 01:36.930 --> 01:40.950 The next most widely used solver is simple form. 01:41.130 --> 01:46.080 It is known among almost everyone using Openfoam, so it is the most common one. 01:46.620 --> 01:49.020 It is a steady state solver for incompressible. 01:49.020 --> 01:50.970 It can also work for turbulent flows. 01:50.970 --> 01:56.400 Both laminar and turbulence can be simulated here and it has a variety of turbulence models. 01:56.400 --> 02:02.670 The application will be suitable for steady state problems in various engineering applications, mostly 02:02.670 --> 02:05.940 in cases of airflow over an airfoil or water flow. 02:06.210 --> 02:12.480 Flow in a hydraulic structure where the same flow will get to steady state after some time. 02:12.480 --> 02:15.150 So that is where we can generally use, uh. 02:15.150 --> 02:16.560 It is always steady. 02:16.560 --> 02:18.810 That's why we are using simple algorithm inside. 02:19.320 --> 02:21.120 And we have a simple form. 02:21.120 --> 02:25.980 So this is combination of piezo algorithm and uh simple algorithm. 02:26.520 --> 02:28.440 So that is how the name pimple came. 02:28.440 --> 02:31.300 It is not available in any other commercial solvers. 02:31.300 --> 02:35.620 So the description is this is a transient solver for incompressible. 02:35.620 --> 02:37.690 It can handle both laminar and turbulent. 02:37.690 --> 02:39.700 It is very similar to simple form. 02:39.700 --> 02:45.220 But this can also uh work on time dependent simulation that is transient simulations. 02:45.220 --> 02:48.220 So unlike simple form this can work on transient simulation. 02:48.220 --> 02:53.290 So it is like flow around a cylinder or moving airfoil where the mesh moves. 02:53.530 --> 02:57.340 Uh, dynamic Dynamic meshing is also possible, and where there is vortex shedding. 02:57.340 --> 02:58.990 In those cases we can use simple form. 02:58.990 --> 03:02.200 This is also widely used as equally as simple form. 03:03.160 --> 03:07.270 So the implement implementation steps are going to remain the same. 03:07.270 --> 03:10.840 Either you use block mesh alone or along with snappy mesh. 03:10.840 --> 03:12.130 We are generating the mesh. 03:12.130 --> 03:16.150 Then we will be setting up the zero directory for boundary conditions. 03:16.150 --> 03:20.340 Then we will be setting up the transport properties turbulence properties. 03:20.340 --> 03:24.960 Then we will configure whatever we want to do in the system directory under control dict. 03:25.410 --> 03:29.610 And we will initiate the uh simulation. 03:29.610 --> 03:32.670 If it is ICO form, just type ICO form and it will get initiated. 03:32.670 --> 03:34.440 If it is simple form then simple form. 03:34.440 --> 03:35.790 So you get the point. 03:36.090 --> 03:38.820 We have to use the name of the solver to initiate it. 03:39.930 --> 03:43.500 So introduction to compressible solvers in Openfoam. 03:43.860 --> 03:47.760 Uh handle fluid flows where density changes are very significant. 03:47.760 --> 03:52.890 These solvers are essential for high speed flows, shock waves, and other compressible phenomena. 03:53.130 --> 03:56.580 So the most important solver is rho central foam. 03:56.640 --> 03:59.310 So it is a density based compressible flow solver. 03:59.460 --> 04:05.790 So whatever we saw in incompressible or pressure based solvers now uh rho central foam is a density 04:05.790 --> 04:06.720 based solver. 04:07.370 --> 04:11.300 so it is suitable for high speed aerodynamic and shock wave kind of simulation. 04:11.720 --> 04:16.820 And one of the examples is if you want to simulate a supersonic flow over a ridge or through a nozzle, 04:16.820 --> 04:18.770 then you can use row central foam. 04:19.550 --> 04:23.900 And there is one very popular, uh, compressible solver called sonic foam. 04:23.990 --> 04:32.560 So as the name says, it works for sonic flows, uh, a transient solver and uh, for transonic, supersonic, 04:32.560 --> 04:34.480 subsonic, anything you can use. 04:34.480 --> 04:38.380 But it assumes that the gas or the fluid is compressible. 04:38.380 --> 04:39.610 That is the only thing. 04:39.610 --> 04:41.980 So if it is compressible, mostly it is gas. 04:41.980 --> 04:43.750 It can't be a liquid. 04:43.840 --> 04:50.290 And applications is useful for simulating time dependent compressible flows, which is transient and 04:50.290 --> 04:54.400 simulating a shock tube or expansion of a gas in a nozzle. 04:54.400 --> 04:57.520 These are the kind of things sonic foam is good at doing. 04:57.550 --> 04:59.080 Then we have rho pimple foam. 04:59.080 --> 05:03.580 As it says, Rho is for density based and the pimple is for transient. 05:04.300 --> 05:08.650 So it is a transient solver for turbulent flows of compressible fluids. 05:08.650 --> 05:12.880 Unlike, uh, pure simple foam, this can also handle compressible fluids. 05:13.000 --> 05:18.400 It is applicable to a wide range of, uh, compressible fluid problems, including high speed train 05:18.400 --> 05:19.770 or an aircraft wing. 05:20.220 --> 05:20.640 Okay. 05:20.640 --> 05:23.940 And implementation step is going to remained the same. 05:23.940 --> 05:27.810 But we also have to define the pressure and velocity differently. 05:27.810 --> 05:30.060 Since it is density based. 05:30.060 --> 05:36.840 We will be defining thermophysical properties because it has to account for the compressible nature. 05:36.840 --> 05:43.650 So we will be defining thermophysical properties uh, which will handle the compressibility. 05:43.680 --> 05:47.010 Otherwise, it is going to remain the same on most of the levels. 05:47.010 --> 05:53.460 Like, uh, do the mesh set up the boundary condition, initial condition, then run the simulation. 05:53.850 --> 05:59.820 Okay, so for multiphase, the multiphase solvers in Openfoam are used to simulate, uh, fluid flows 05:59.820 --> 06:01.800 involving more than one fluid. 06:01.800 --> 06:07.670 So whatever we have done till now is like one phase or, uh, one fluid. 06:07.670 --> 06:08.030 Right. 06:08.030 --> 06:14.330 So if we are working with two fluids, let's say water mixing with oil, and we want to see how fast 06:14.330 --> 06:17.510 the oil will, uh, rise over the water. 06:17.510 --> 06:25.520 So if you want to do such kind of multiphase things, then, uh, you can use openfoam multiphase solvers. 06:25.520 --> 06:30.500 These always are crucial for application in mostly chemical engineering, environmental engineering, 06:30.500 --> 06:36.760 and also fluid structure interactions, where we will be having like a flap of an airfoil and we want 06:36.760 --> 06:38.710 to see what it happens. 06:38.710 --> 06:43.180 If you want to work on fluid structure interaction, then you can use multiphase solvers. 06:44.380 --> 06:49.960 Uh, then the key multiphase solvers or inter form, this is the most widely used one. 06:49.960 --> 06:52.120 So it uses volume of fluid method. 06:52.330 --> 06:59.090 Uh you can recall it from your CFD theoretical course if you took multiphase, uh, subjects. 06:59.090 --> 07:04.850 So it will use volume of fluid, which is highly complicated, but you can set it up easily using Openfoam. 07:04.850 --> 07:11.780 It is ideal for simulating interface between two fluids and simulating the break of waves or dam breaks. 07:11.780 --> 07:14.780 It is popularly known as the flow in a mixing tank. 07:14.780 --> 07:20.910 If you have a very big tank with oil, and if you are pouring water into it and how it will react, 07:20.910 --> 07:22.830 if you want to see how the bubbles are formed. 07:22.830 --> 07:25.980 So those things can be done in the multiphase solver using interphone. 07:26.310 --> 07:28.080 We have multiphase interphone. 07:28.800 --> 07:31.950 So this is also the same as interphone. 07:32.070 --> 07:40.440 But again it has some uh, tweaks to the solver and how it is getting solved. 07:40.440 --> 07:42.540 So there is slight difference. 07:42.540 --> 07:44.970 If you want to know more you can check the documentations. 07:44.970 --> 07:48.600 Okay, because it is beyond the mathematics of the course. 07:48.600 --> 07:49.050 Okay. 07:49.830 --> 07:55.560 Uh, implementation steps will be mesh generation and we will be setting up the boundary condition initial 07:55.560 --> 07:56.910 condition phase fraction. 07:56.910 --> 08:02.550 Here it is an additional setting we have to set uh which area has what fluid initially. 08:02.550 --> 08:03.810 So we have to set that. 08:03.810 --> 08:08.900 And we will also be defining the thermophysical properties for each of the fluid, each of the phase. 08:09.860 --> 08:14.570 And we will do the control dict setup as usual and we will run the simulation. 08:14.810 --> 08:18.830 So now we are going to do a lid driven cavity case. 08:18.830 --> 08:23.210 So lid driven cavity flow is a classic benchmark problem in fluid mechanics. 08:23.210 --> 08:25.430 It involves a square cavity filled with fluid. 08:25.430 --> 08:28.700 Like how I explained already there is a big cavity. 08:28.700 --> 08:29.570 All our walls. 08:29.570 --> 08:31.040 There is a lid on top. 08:31.190 --> 08:34.960 We are trying to move the lid towards the right side at a constant speed. 08:34.990 --> 08:39.010 Now it is going to create a recirculation region. 08:39.010 --> 08:46.450 So this is used as a benchmark problem to see whether all the algorithm works in your, uh, solver 08:46.780 --> 08:52.780 is because it is having, uh, complex flow phenomena like boundary layer separation, vortex shedding. 08:53.020 --> 08:58.420 And there is also recirculation zones, mostly vortex shedding is not happening here because if you 08:58.420 --> 09:04.720 are working with alias then you might get small small vortex, but in most cases you are not going to 09:04.720 --> 09:05.440 get vortex shedding. 09:05.440 --> 09:10.000 In this it is mostly recirculation zones and we are going to check that. 09:10.690 --> 09:14.920 So it is a valuable test case for validating computational fluid dynamics codes. 09:15.280 --> 09:21.510 So the objective of this case study is that to understand the fundamentals of incompressible flow simulation 09:21.510 --> 09:27.030 using Openfoam, they are going to implement appropriate boundary condition for the lid driven cavity 09:27.030 --> 09:27.510 case. 09:27.510 --> 09:32.040 And we are going to analyze the flow characteristics such as velocity profile, pressure distribution 09:32.040 --> 09:33.480 and vorticity patterns. 09:34.350 --> 09:39.090 We are going to validate the simulation against established benchmarks or experimental data. 09:39.090 --> 09:40.890 But this is a homework for you. 09:40.890 --> 09:42.300 Like validating the case. 09:42.300 --> 09:48.480 I will tell you how to do the setup in Openfoam, and it's up to you to validate it and see how accurate 09:48.480 --> 09:49.020 it is. 09:50.190 --> 09:53.010 So the case setup is going to consider these steps. 09:53.010 --> 09:54.780 First we will prepare a geometry. 09:54.780 --> 09:56.220 It will be a square cavity. 09:56.220 --> 10:00.510 We have already seen how to generate this block mesh for this case. 10:00.990 --> 10:06.180 And in the flow regime we are going to do an incompressible flow with low to moderate Reynolds number. 10:06.450 --> 10:11.870 How we are going to set the Reynolds number is based on how fast we are moving the lid. 10:11.870 --> 10:12.320 Okay. 10:13.250 --> 10:18.020 And the boundary condition lid will have constant velocity boundary condition, which is no slip. 10:18.260 --> 10:20.900 And waltz is also going to contain no slip. 10:20.900 --> 10:28.910 So when I say lid is having no slip, I mean at the surface of the lid just next to the lid, it is 10:28.910 --> 10:34.760 going to have zero velocity, but as there is a shear, it is going to move with a constant velocity 10:34.760 --> 10:39.050 with respect to the rest of the fluid particles in with respect to the lead. 10:39.080 --> 10:46.520 The fluid particle just next to the lead is at zero position zero velocity, but with respect to rest 10:46.520 --> 10:49.160 of the fluids it is moving at a constant velocity. 10:49.220 --> 10:53.990 So that is the basic understanding here on setting up the boundary condition. 10:54.830 --> 10:59.770 So the simulation parameters are we are going to use block mesh to develop the structured mesh. 10:59.770 --> 11:02.290 Then this is a transient simulation. 11:02.290 --> 11:03.790 We are going to use Icofom. 11:03.790 --> 11:08.740 And the turbulence model is obviously laminar because it is icofom okay. 11:08.740 --> 11:13.030 If you want to look at what is the boundary condition, I have displayed it here. 11:13.030 --> 11:14.350 You can look at it. 11:14.350 --> 11:17.440 As you can see, the first is uh, velocity. 11:17.440 --> 11:19.960 You can recognize it by the dimensions. 11:19.960 --> 11:24.660 So the velocity of the moving wall is one meters per second towards x axis. 11:24.660 --> 11:28.890 For the pressure it is uh zero gradient and zero gradient. 11:29.490 --> 11:38.370 And for uh kinematic viscosity it is 0.01 and the S.I. unit only. 11:38.370 --> 11:41.940 And the application is I go from the start from a start time. 11:42.150 --> 11:43.530 So which is zero. 11:43.530 --> 11:45.840 And we are going to end at 0.05. 11:45.840 --> 11:48.360 And the delta t here is 0.005. 11:48.360 --> 11:54.720 Unless unlike what we did in the previous thing like 0.005 here it is much smaller. 11:54.720 --> 12:01.110 So after we set the boundary conditions then we are just going to analyze the velocity profile, pressure 12:01.110 --> 12:04.800 distribution, vorticity patterns and validation. 12:04.800 --> 12:06.480 So this validation is on you. 12:06.480 --> 12:07.740 This is like a homework. 12:07.740 --> 12:09.000 You have to do it. 12:09.420 --> 12:14.610 Uh we will be seeing how to post-process for velocity profile, pressure distribution and vorticity 12:14.610 --> 12:16.050 patterns using Paraview. 12:16.590 --> 12:17.970 Validation is up to you. 12:19.110 --> 12:22.620 So we will now run the simulation actually. 12:22.710 --> 12:23.160 Okay. 12:23.790 --> 12:27.420 This is the case of cavity case. 12:28.440 --> 12:28.980 Okay. 12:31.800 --> 12:35.630 And we have zero constant para performance system. 12:36.440 --> 12:38.000 So I will open it. 12:41.090 --> 12:41.720 Okay. 12:43.670 --> 12:47.360 So under zero we have velocity and pressure. 12:47.360 --> 12:52.850 So these are exactly same as what you saw in the presentation like these things. 12:52.850 --> 12:55.760 So I am not going to go over every one of them. 12:56.270 --> 12:58.840 Uh I'll show you transport properties. 12:58.840 --> 13:01.450 The new is 0.01. 13:02.020 --> 13:04.900 And in the system the block mesh is same. 13:05.020 --> 13:10.840 And the control dict, it is slightly going to be different, like it is starting from zero ending a 13:10.840 --> 13:11.680 0.05. 13:11.680 --> 13:12.160 That is same. 13:12.160 --> 13:15.100 But the delta t is 0.0005. 13:15.340 --> 13:18.610 And right interval is two for every two time steps. 13:18.640 --> 13:20.560 Or uh yeah, time steps. 13:20.560 --> 13:26.400 It is going to write one case file, which means 0.001. 13:26.400 --> 13:30.720 For every 0.001, there is going to be one case one. 13:30.930 --> 13:32.910 So now we can run it. 13:32.910 --> 13:39.330 To run it, all we have to do is do block, mesh and icofom. 13:40.200 --> 13:43.200 It is going to take only that much time. 13:43.200 --> 13:47.400 Now we can run it or no visualize it using Paraview. 13:47.430 --> 13:49.140 We got all the time steps. 13:49.410 --> 13:51.330 I'll go to paraview. 13:53.130 --> 13:54.150 Click on apply. 13:54.180 --> 13:57.420 Now you can see we have the pressure profile. 13:57.420 --> 13:59.280 I'll choose Velocity Profile. 13:59.340 --> 14:02.550 Now we are in the 0.001 time step to play. 14:02.550 --> 14:05.370 I can click on this and you can see how it is growing. 14:05.910 --> 14:10.980 So you get how it has converged right. 14:11.660 --> 14:12.320 Okay. 14:12.320 --> 14:13.010 To. 14:13.040 --> 14:14.690 This is the velocity profile. 14:14.960 --> 14:17.390 We got the pressure profile also. 14:17.390 --> 14:22.430 But how to plot streamlines to understand what is it we have to plot streamlines. 14:22.430 --> 14:22.760 Right. 14:22.760 --> 14:25.850 So to do that first we will do a slice. 14:25.910 --> 14:34.190 So to click on the slice and choose Z normal we will have this plane I usually remove show plane and 14:34.190 --> 14:35.060 click on apply. 14:35.390 --> 14:38.840 So on this slice you can choose velocity. 14:38.960 --> 14:40.580 We have the velocity profile. 14:40.580 --> 14:42.740 And you see this right. 14:42.740 --> 14:44.270 So it is a stream tracer. 14:44.510 --> 14:47.690 If you click on that it will plot from the minimum to maximum. 14:47.690 --> 14:48.890 Click on apply. 14:49.100 --> 14:50.840 And usually it is in pressure. 14:50.840 --> 14:52.400 So you can choose velocity. 14:53.360 --> 14:56.030 You can uh reduce the number of points. 14:56.060 --> 14:56.870 Now it is thousand. 14:56.870 --> 15:00.970 You can keep it around 500 or even less. 15:00.970 --> 15:02.800 I'll keep like 100. 15:03.280 --> 15:06.940 Now you can see how the velocity is in circulation region. 15:07.390 --> 15:15.730 That is one thing, but if you want to do the uh vectors also you can work with the glyphs. 15:15.730 --> 15:18.790 But that's not going to be very useful in this case. 15:18.790 --> 15:21.400 So I will keep it with streamlines. 15:21.520 --> 15:22.450 You want to hide this line. 15:22.450 --> 15:24.480 Just click on this and it will be done. 15:24.510 --> 15:26.430 You want to save this as animation? 15:26.430 --> 15:31.170 Click on File Save Animation and give some name. 15:31.170 --> 15:37.950 Let's say lid driven cavity such as mp4. 15:38.250 --> 15:41.040 Click on okay and you can choose the frame rate. 15:41.040 --> 15:45.390 Let's say I want to do ten frames which will be 0.1 second will be the one frame. 15:45.930 --> 15:46.590 Click on okay. 15:46.590 --> 15:48.180 Don't worry about this error. 15:48.180 --> 15:51.420 It always appears we have the file. 15:53.820 --> 15:56.010 So we have for the stream lines. 15:56.010 --> 16:02.340 Now if you do want to do just for the paraview, hide this, hide this. 16:02.340 --> 16:06.480 And again can't save animation. 16:06.480 --> 16:11.640 Now I'll do lid driven cavity velocity okay. 16:11.750 --> 16:14.780 Let's click on okay and click okay. 16:16.520 --> 16:18.410 Now we got the velocity. 16:18.440 --> 16:23.210 Now this will be much slower because I chose one frame per second. 16:24.590 --> 16:24.890 Yeah. 16:24.890 --> 16:27.320 So so you can actually play with this. 16:27.320 --> 16:29.660 And that is all about this tutorial. 16:31.010 --> 16:31.400 Okay. 16:33.560 --> 16:36.950 And the next week's homework task is go to this link. 16:36.950 --> 16:38.570 It will be available in resources. 16:38.570 --> 16:44.360 This is a tutorial I made for a mesh preparation using block mesh for backward facing step. 16:44.360 --> 16:46.610 So this will be used in our next class. 16:46.610 --> 16:50.360 So make sure you understand everything from this tutorial. 16:50.660 --> 16:52.040 Pause the video whenever you need. 16:52.040 --> 16:55.370 Do it hands on, do it parallelly and understand everything. 16:56.000 --> 16:58.520 If you have any questions, feel free to contact me. 16:58.520 --> 17:00.110 Thank you for watching this video. 17:00.110 --> 17:01.190 See you in the next class.