WEBVTT 00:00.140 --> 00:01.070 Hello everyone. 00:01.070 --> 00:04.790 Welcome back to CFD using Openfoam beginner to intermediate course. 00:04.790 --> 00:07.850 So this is our last class which is class ten. 00:07.850 --> 00:13.520 In this video we will be seeing introduction to multiphase Flow simulations modeling approaches and 00:13.520 --> 00:15.080 practical considerations. 00:15.080 --> 00:21.230 The under demonstration which will be doing uh using multiphase Euler foam which is one of the most 00:21.230 --> 00:28.130 popular uh multiphase solver in Openfoam we will be doing something called a dam break case. 00:28.370 --> 00:33.380 Uh, usually it is done in two phase, but we are going to consider four phases and we are going to 00:33.380 --> 00:34.280 do in four phases. 00:35.120 --> 00:37.310 Introduction to multiphase flow simulation. 00:37.880 --> 00:43.760 Multiphase flow simulations involve the simultaneous flow of multiple phases, which can include combinations 00:43.760 --> 00:45.800 of gases, liquid, as well as solids. 00:45.830 --> 00:51.470 Sometimes these simulations are essential in various industries such as chemical processing, oil and 00:51.470 --> 00:54.260 gas, power generation, and environmental engineering. 00:54.290 --> 00:59.990 The complexity of multiphase flow arises from the interaction between different phases, which can involve 00:59.990 --> 01:02.030 mass, momentum, and energy transfer. 01:03.020 --> 01:05.870 So modeling approaches and practical considerations. 01:05.900 --> 01:09.560 Eulerian Euler models are one of the most followed one. 01:10.130 --> 01:13.400 Description of the Euler Euler model is. 01:13.400 --> 01:20.260 Both phases are treated as interpenetration continuum, which each face represents by its own set of 01:20.260 --> 01:21.700 conservation equations. 01:22.000 --> 01:28.120 Application is suitable for flows where the phases are intermingled, such as bubbly flows or fluidized 01:28.120 --> 01:28.630 beds. 01:28.840 --> 01:33.790 Example solver is multiphase Euler form, which is what we are going to see in this uh video. 01:35.170 --> 01:37.660 Then we have Euler and Lagrangian models. 01:37.660 --> 01:42.670 The continuous phase is treated as a continuum using the Euler approach while the dispersed phase, 01:42.670 --> 01:47.500 which can be like particles, droplets, bubbles, is tracked using the Lagrangian approach. 01:47.620 --> 01:54.340 This is computationally very expensive, ideal for dilute dispersed flows such as sprays and particulate 01:54.340 --> 01:54.940 flows. 01:54.940 --> 01:59.380 We also need a very fine mesh to do these kind of simulations. 01:59.410 --> 02:03.070 Example solver is DPM foam which is discrete phase model. 02:04.870 --> 02:07.030 Then we have the volume of fluid models. 02:07.030 --> 02:12.310 The interface between phases is tracked using a volume fraction function, which is advected with the 02:12.310 --> 02:16.690 flow effective for free surface flows such as waves or dam breaks. 02:16.720 --> 02:18.400 Example solver is interval. 02:19.630 --> 02:25.600 Then we have integer interface tracking methods also, which is explicit tracking of the interface between 02:25.600 --> 02:32.260 phases using methods like level set or print tracking suitable for detailed multi phase interface dynamic 02:32.260 --> 02:36.040 studies such as droplet coalescence or breakup reacting. 02:36.040 --> 02:42.880 Multiphase Euler foam for reactive multiphase flows is one of the example solvers, but this is very 02:42.880 --> 02:46.450 highly advanced and it's not very popular in industries either. 02:47.590 --> 02:54.490 So practical considerations while modeling a multiphase flow mesh quality ensure a fine and high quality 02:54.490 --> 02:58.510 mesh, especially near phase interface to capture detailed interactions. 02:58.510 --> 03:03.400 Then, about the time step, choose an appropriate time step to balance the accuracy and computational 03:03.400 --> 03:03.850 cost. 03:03.850 --> 03:09.790 Considering the Cuda number generally, we will keep the core number as one, but it would be better 03:09.790 --> 03:13.600 to keep even less than one around 0.8 or 0.75. 03:14.110 --> 03:20.560 But it also depends on physics and what kind of accuracy you are expecting Then, for the boundary condition, 03:20.560 --> 03:25.750 we have to carefully set the boundary condition to accurately represent physical phenomena at the boundary 03:25.750 --> 03:26.380 domains. 03:26.500 --> 03:31.750 For initial condition, proper initialization of the phase distribution can significantly impact the 03:31.750 --> 03:33.790 convergence and accuracy of the solution. 03:33.790 --> 03:41.290 Because we have to set the type of phases in every area of the mesh for the initial condition, which 03:41.290 --> 03:43.320 would be solved by the solver. 03:43.320 --> 03:46.260 For further changes in the flow domain. 03:47.280 --> 03:52.140 For face interaction model, we have to implement appropriate models for interface momentum, heat and 03:52.140 --> 03:52.830 mass transfer. 03:52.860 --> 03:58.980 Multiphase flows can also do uh, heat equation solving which will account for the temperature. 03:58.980 --> 04:05.970 But for this tutorial we will be using multiphase Euler form which doesn't need to, uh, solve the 04:05.970 --> 04:07.660 temperature equations. 04:07.660 --> 04:09.880 So we will not be seeing any temperature plot. 04:09.880 --> 04:15.940 But if you want to see temperatures, you can use, uh, solvers like two phase Euler form, which would, 04:16.390 --> 04:18.460 uh, consider temperature changes also. 04:18.910 --> 04:25.570 So now we will see the demonstration on using multiphase Euler form for a dam break case for four phase. 04:26.110 --> 04:26.470 Okay. 04:26.470 --> 04:31.230 Now the picture you are seeing is the old run file. 04:31.680 --> 04:37.080 So we have restored zero directory, which will copy the zero dot original and paste it into zero folder. 04:37.140 --> 04:39.780 Then we are going to run the application block mesh. 04:39.810 --> 04:42.240 Then we are going to do something called set fields. 04:42.240 --> 04:44.490 So this is new which I will explain. 04:45.150 --> 04:47.100 Then as usual we will decompose. 04:47.130 --> 04:52.230 Then run the application which in this case is multiphase Euler form and reconstruct the case. 04:53.100 --> 04:55.950 Now this is the mesh that we are going to use. 04:56.070 --> 04:58.230 Now we are seeing the internal mesh. 04:58.980 --> 05:06.150 So as you can see we have the left wall, lower wall, right wall, default faces, atmosphere wall 05:06.150 --> 05:07.080 and empty. 05:07.440 --> 05:13.950 As you can see, there is a big fluid domain and there is a small obstacle in between uh, in the lower 05:13.950 --> 05:14.520 place. 05:14.640 --> 05:20.070 So we will be having fluid all over here and we will release the fluid. 05:20.070 --> 05:23.760 So it will tend to move around here. 05:23.760 --> 05:29.460 And this obstacle will prevent that, prevent the flow or cause the flow disturbance. 05:29.460 --> 05:32.340 And we will see how the flow is propagating. 05:33.570 --> 05:37.230 So after setting the fields this is how it will look. 05:37.230 --> 05:39.630 So we have four phases here. 05:39.630 --> 05:42.090 One is air, one is water. 05:42.090 --> 05:44.970 Then we have oil and then mercury. 05:45.000 --> 05:48.120 So these are the four phases we are going to work with. 05:48.120 --> 05:53.160 So this can be obtained at the initial condition which will be inside zero folder. 05:53.160 --> 05:56.580 And we will see how to do it using the set fields dict. 05:57.750 --> 06:03.510 So if you want to see the final simulation video you can jump in here. 06:03.510 --> 06:05.520 Uh this is my YouTube channel. 06:05.520 --> 06:06.840 You can check it out. 06:07.370 --> 06:09.650 Okay, now we will run the simulations. 06:10.130 --> 06:12.950 I am in the working directory. 06:12.950 --> 06:13.340 Okay. 06:13.340 --> 06:17.870 Now, either we can initiate the all run or do it one by one. 06:17.870 --> 06:20.150 So I will do it manually. 06:20.150 --> 06:24.710 If you want to run the case, you can do it yourself. 06:26.330 --> 06:26.840 Okay. 06:26.840 --> 06:31.610 Now we have the 00. original uh, constant and system. 06:32.000 --> 06:35.510 Okay, now, as you know, the first command is block mesh. 06:35.810 --> 06:37.280 So I'll run block mesh. 06:37.280 --> 06:39.140 Then it is set fields. 06:39.140 --> 06:45.380 So before we do set fields, I will explain what set fields actually does and what that is about. 06:46.700 --> 06:49.640 Now we will just see the mesh which we have now. 06:57.950 --> 07:02.840 As you could recognize from the PPT, this is the mesh we have and this is the obstacle. 07:03.230 --> 07:08.390 We had the, uh, other three fluids here and the rest of the area where. 07:08.390 --> 07:09.380 Yeah, right. 07:09.380 --> 07:15.200 So I will keep everything at the zeroth time step. 07:15.740 --> 07:18.140 Now, we don't have any phases at all. 07:18.530 --> 07:18.950 Okay. 07:18.950 --> 07:21.740 So it will not have any faces. 07:24.050 --> 07:26.990 Okay, so now we are going to do something called the set fields. 07:27.170 --> 07:29.270 So what set fields does. 07:32.870 --> 07:37.610 Under set fields dict which is under system directory we have many functions. 07:37.610 --> 07:41.090 So first thing is we are going to set the default field values. 07:41.090 --> 07:44.660 So in any atmosphere all we have is here. 07:44.690 --> 07:46.610 That is the default field value. 07:46.610 --> 07:49.490 So we are setting alpha dot air as one. 07:50.030 --> 07:52.430 As alpha is the face fraction. 07:53.180 --> 07:58.970 And we are setting out for water as zero, alpha dot oil as zero and alpha dot mercury as zero, and 07:58.970 --> 08:04.190 initial vector field value, which is velocity will be 000 in all three directions. 08:04.520 --> 08:06.620 This is the default field values. 08:06.620 --> 08:09.370 Now we are going to set the regions and the region. 08:09.400 --> 08:13.270 We need three phases now because everything is already here. 08:13.480 --> 08:16.270 We are going to set three more fields. 08:17.170 --> 08:19.960 So the first field would be a box two cell. 08:19.960 --> 08:21.280 So that is the function. 08:21.280 --> 08:23.020 Then we have to define the box. 08:23.020 --> 08:27.430 So that box as you can see again it has a minimum point. 08:27.430 --> 08:31.930 And the maximum point just like what we did for snapping hex mesh. 08:32.080 --> 08:41.440 So we are going to do this which is zero zero, minus one two, 0.1461 to 0.29 1 to 1. 08:41.440 --> 08:46.390 So if you want to see what that actually means, you can turn on data access grid. 08:46.390 --> 08:51.850 And you can see we have zero zero uh 20.14. 08:53.110 --> 08:56.530 It is somewhere around here, the x direction, y direction. 08:56.530 --> 08:58.300 It is 0.292. 08:58.360 --> 09:00.400 So this is this region. 09:00.400 --> 09:02.500 So here we are setting one field. 09:02.800 --> 09:10.480 Then we are setting another field from this .0.14610 minus one to some point. 09:10.480 --> 09:14.710 You can ponder over what these points actually mean from the data access grid. 09:14.830 --> 09:16.990 I'm not going to exactly show those points. 09:16.990 --> 09:21.880 We are just having these points which you can download this case and take over it. 09:21.910 --> 09:30.100 So for the first box, we are setting it to alpha dot value of water as one and everything else as zero, 09:30.100 --> 09:36.070 which is oil, mercury and air will be zero for two phases cannot exist at the same place, so everything 09:36.070 --> 09:36.850 else must be zero. 09:37.240 --> 09:39.610 Then we have oil phase. 09:40.360 --> 09:41.110 This will be one. 09:41.110 --> 09:42.430 Everything else will be zero. 09:42.430 --> 09:45.640 Then we have mercury as one and everything else as zero. 09:45.730 --> 09:51.550 So we have set the entire domain into a four different phases. 09:51.550 --> 09:57.190 If you miss any point while doing this, that would be set to here. 09:57.190 --> 10:00.100 So that is the entire thing about setting default field values. 10:00.100 --> 10:02.710 Otherwise it would have pure mesh without any values at all. 10:03.190 --> 10:05.650 So how is it going to get saved? 10:05.890 --> 10:09.940 It is because we have these files apart from you. 10:10.480 --> 10:12.040 Uh, which we generally have. 10:12.040 --> 10:14.080 We also have something called p. 10:14.500 --> 10:17.740 Uh, underscore RG actually it means p minus RJ. 10:18.190 --> 10:22.150 As you can realize RG h is the hydrostatic forces. 10:22.150 --> 10:24.940 This is pressure minus the hydrostatic effects. 10:25.180 --> 10:27.520 That is what p minus rg h means. 10:27.520 --> 10:33.840 But since we can't use hyphen in a file name, we are using underscore. 10:34.830 --> 10:35.250 Okay. 10:35.250 --> 10:38.520 So this is basically pressure minus the hydrostatic forces. 10:38.640 --> 10:41.130 And we are defining it as flux pressure. 10:41.130 --> 10:43.050 And it is all set to zero. 10:43.500 --> 10:48.720 Now we have alpha alpha dot mercury alpha dot oil and alpha dot water. 10:48.750 --> 10:52.170 Similarly we also have the velocity for each phases. 10:52.170 --> 10:59.550 As I explained in the ppt for Euler Euler model we are solving the transport equation for every different 10:59.550 --> 11:03.360 phase separately, because everything has its density different. 11:04.290 --> 11:11.550 So I'll open the alphabet here, and you can see that the uniform field is initially set to zero and 11:11.550 --> 11:13.020 everything else is also set. 11:13.020 --> 11:18.600 So this can be set based on any templates which is already available. 11:18.600 --> 11:22.380 So we are doing this called theta properties. 11:22.380 --> 11:29.970 So this theta properties is the uh volume fraction or also known as the contact angle of the volume 11:29.970 --> 11:30.420 fraction. 11:30.420 --> 11:34.740 So when two phases are meeting it will have some angle. 11:34.740 --> 11:39.030 So that angle has to be defined so that it is resolved properly. 11:39.030 --> 11:42.600 And that alpha contact angle is called theta. 11:42.600 --> 11:45.810 So we are setting it to orthogonal which is 90 degree. 11:45.810 --> 11:48.300 So it will meet at the intersection of 90 degrees. 11:48.360 --> 11:50.670 We have to set it for every face. 11:51.510 --> 11:58.620 So when you see left wall that has water air as 90 oil, air as 90, mercury air as 90 and water oil 11:58.620 --> 12:01.470 as 90, water, Mercury as 90, oil, Mercury as 90. 12:01.470 --> 12:04.920 So we have to put in all the combination, all different possibilities. 12:05.280 --> 12:11.220 So after doing that, we will be setting the atmosphere as inlet outlet inlet value as one one. 12:11.220 --> 12:12.750 And we have this. 12:12.750 --> 12:18.180 So atmosphere here is just basic outlet condition on the top wall okay. 12:18.180 --> 12:25.560 Similarly we have for all the four files you can open and see it just in case I would open the port 12:25.560 --> 12:26.040 face alone. 12:27.780 --> 12:30.900 See we have everything else has normally. 12:30.900 --> 12:36.350 So we only set the alpha dot air because it is in the default, so we are setting it. 12:36.350 --> 12:43.940 Then this would correspond to other files while open alpha will see when this is a normal file. 12:43.940 --> 12:45.830 So only the default phase. 12:45.830 --> 12:49.760 We have to set all these uh contact angle at all okay. 12:49.760 --> 12:56.690 Now similarly we will be having just you which is the overall velocity thing okay. 12:56.690 --> 13:00.650 We are setting the walls as no slip and atmosphere is corrected. 13:00.650 --> 13:05.360 A flux corrected velocity is 000, which is a Neumann condition. 13:05.480 --> 13:10.280 Then we have the velocity of air, which is again a normal file. 13:10.430 --> 13:13.190 Then we have velocity of mercury. 13:13.190 --> 13:15.290 That is also a normal velocity file. 13:15.290 --> 13:17.600 So only the alpha dot air will be different. 13:18.080 --> 13:20.690 And p minus r is a new thing. 13:20.810 --> 13:27.140 So here apart from transport and turbulence properties and gravity, we also have something called motion 13:27.140 --> 13:31.250 properties where we are setting it as static of a mesh. 13:31.250 --> 13:37.160 But when you are going to advance level of openfoam, you can do, uh, adaptive refinement in the mesh. 13:37.160 --> 13:43.070 So that can be defined here instead of static, we will be using dynamic f v mesh which we are not going 13:43.070 --> 13:44.000 to cover in this course. 13:44.000 --> 13:47.060 So it is just going to be static f mesh in this case. 13:47.510 --> 13:50.060 Now we can see what other files we have. 13:50.090 --> 13:51.770 We have the control dict. 13:52.790 --> 13:56.240 So in control dict you can see the application is multiphase Euler form. 13:56.390 --> 14:01.190 And apart from maximum SEO we are also setting maximum alpha zero. 14:01.220 --> 14:05.900 So this is taking care of individual phase current number. 14:05.900 --> 14:07.640 So that is 0.5. 14:07.640 --> 14:14.630 As I said one is fine for most cases but for multi phase going less than one is preferable. 14:15.380 --> 14:20.750 Then we have delta t as 0.001 and we are ending at time six. 14:20.750 --> 14:25.730 So this simulation is going to take a lot of time to get run. 14:25.730 --> 14:30.830 So that is why I have pasted the YouTube link for the final simulation video. 14:31.280 --> 14:33.320 Uh, it is going to take hovers of your time. 14:33.440 --> 14:35.660 That is what multiphase does. 14:35.870 --> 14:38.270 Okay, now we will do the set fields. 14:38.270 --> 14:40.640 Now, as you see at the time zero. 14:40.640 --> 14:42.890 We don't have any phases at all. 14:43.100 --> 14:43.580 Okay. 14:44.360 --> 14:52.460 Uh, yeah I'll go to time zero so you can see we can see Alpha dot water is also completely zero. 14:52.460 --> 14:55.130 Alpha dot air is also completely zero. 14:57.530 --> 15:02.260 And if we see velocity it is also completely zero because we have set everything to zero. 15:02.260 --> 15:04.030 So it's no surprise. 15:04.330 --> 15:07.180 Now what I will do is I will do. 15:07.180 --> 15:08.710 Set fails. 15:09.610 --> 15:11.890 Now the set fails has been done. 15:11.920 --> 15:14.140 Now I will refresh this case. 15:15.130 --> 15:19.330 Now you can see we have something called uh, I forgot. 15:19.330 --> 15:21.730 Here you can see the alpha dot here. 15:22.030 --> 15:26.350 Here one is the maximum value and blue is zero. 15:26.350 --> 15:28.660 So everything else is here. 15:28.840 --> 15:29.470 These are. 15:29.470 --> 15:33.430 This is the place where we have other three, three, three phases. 15:33.430 --> 15:35.980 So the mercury is just this place. 15:36.880 --> 15:41.020 Oil has this area and water has this area. 15:41.020 --> 15:45.310 So apart from whatever these three it everything else is here okay. 15:45.310 --> 15:53.620 So to see all the four phases in the same map, we will, uh, be able to do it only when we run the 15:53.620 --> 15:54.100 simulation. 15:54.100 --> 15:55.000 Otherwise we can't. 15:55.000 --> 16:00.910 So you can see that every phase has mostly zero velocity. 16:00.910 --> 16:02.080 Only initially. 16:02.080 --> 16:05.830 Okay, now we can run the case by decomposing. 16:05.830 --> 16:13.210 So decompose power is, uh, a regular decompose case which we set in previous simulations Also, I'm 16:13.210 --> 16:22.300 going to run Mpirun NP eight multiphase Euler form okay. 16:25.870 --> 16:33.100 So it has started and it is running now we have around uh, ten time steps, including the zero. 16:33.100 --> 16:34.570 While running the command. 16:34.570 --> 16:40.630 I missed the hyphen parallel at the end, so if you followed the video, just make sure that you are 16:40.630 --> 16:42.820 typing the hyphen parallel also. 16:43.720 --> 16:47.980 I stopped the simulation, run it, and reconstructed and deleted all the processor files. 16:48.790 --> 16:51.730 Okay, now I'll go here to the Paraview. 16:51.730 --> 16:53.200 I'll refresh the case. 16:53.770 --> 16:56.710 Now I'll go to the last time step. 16:56.980 --> 16:58.510 I'll choose alphas. 16:58.540 --> 16:58.990 Okay. 16:59.470 --> 16:59.650 Okay. 16:59.650 --> 17:07.060 Now you can see that we have, uh, the animation, like, sort of animation. 17:07.060 --> 17:07.840 It is moving. 17:07.840 --> 17:12.460 So when you run the entire simulation, it would look something like this. 17:12.640 --> 17:14.530 So this is the render video. 17:14.560 --> 17:17.680 You can check out that link now I will play it for you. 17:21.460 --> 17:25.770 As you can see it predicts all the bubbles. 17:25.770 --> 17:27.120 It releases air. 17:27.150 --> 17:28.590 It accounts for density. 17:28.620 --> 17:30.630 It accounts for the waviness. 17:30.630 --> 17:34.110 So when you are seeing it, it feels realistic. 17:34.110 --> 17:41.490 So that is what we can achieve by having a good mesh and good time step by maintaining the current number. 17:41.760 --> 17:44.910 So I hope you learned a lot in this course. 17:45.600 --> 17:52.170 If you have any specific doubts regarding the contents in this course, you can always contact me. 17:54.810 --> 17:56.400 Thank you for taking up this course. 17:56.400 --> 18:02.760 Look up for advanced level of courses regarding Openfoam by Code dynamics. 18:03.330 --> 18:09.480 Also, check out our YouTube channel regularly for more information on using Openfoam and specific features 18:09.480 --> 18:10.440 inside Openfoam. 18:10.950 --> 18:11.730 Thank you. 18:11.730 --> 18:12.840 See you in another course!