taichi_LBM3D
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yjhp1016
2phase outlet boundary condition
Hello Dr. Yang, I have questions about the color-gradient multiphase model. For the phase boundary, you showed in the example that the left side is the fixed phase1 boundary (value=-1) and the right side is the periodic boundary. When calculating, I found that, The value of phase1 will also run to the right. So I want to know what is the reason for this?
This is due to the use of periodic on the right hand side. Because the right BC's neighbour becomes the left BC which is a fixed color... So you can use fixed color for both left and right, this should help to solve the problem.
On Thu, 25 Jan 2024 at 12:03, emwn123 @.***> wrote:
Hello Dr. Yang, I have questions about the color-gradient multiphase model. For the phase boundary, you showed in the example that the left side is the fixed phase1 boundary (value=-1) and the right side is the periodic boundary. When calculating, I found that, The value of phase1 will also run to the right. So I want to know what is the reason for this?
756b968a4ca5366172a89fe3fa2856e.png (view on web) https://github.com/yjhp1016/taichi_LBM3D/assets/63047567/6b1cff7f-3dad-4687-8c79-edf7de7635f9 image.png (view on web) https://github.com/yjhp1016/taichi_LBM3D/assets/63047567/985edbba-2aed-4d2b-9e08-390edc2017b1
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Thanks for the fast reply!
I used the fixed BC as you said, but the problem remains.
Did I misunderstand what you said?
The second line of phase boundary you need to use 1 1.0 not 1 -1.0, 1.0 represent red phase, -1.0 represents blue phase
On Thu, 25 Jan 2024 at 12:18, emwn123 @.***> wrote:
Thanks for the fast reply!
I used the fixed BC as you said, but the problem remains.
Did I misunderstand what you said?
image.png (view on web) https://github.com/yjhp1016/taichi_LBM3D/assets/63047567/34d17754-1a0b-4c7e-aaa9-939fde3fc5ca image.png (view on web) https://github.com/yjhp1016/taichi_LBM3D/assets/63047567/3366b3e0-1167-4ae0-af8a-5fe02c8642b8
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Thanks for the reply.
Now it worked!
But there is a new problem, that is, the blue phase will not continue to displace the red phase after a certain time step, and will always remain in the state shown in the figure below. What could be the reason for this?
Maybe you need bigger driving force, I would suggest using periodic and body force to drive the fluid instead of using fix velocity/pressure BC
On Thu, 25 Jan 2024 at 13:45, emwn123 @.***> wrote:
Thanks for the reply.
Now it worked!
But there is a new problem, that is, the blue phase will not continue to displace the red phase after a certain time step, and will always remain in the state shown in the figure below. What could be the reason for this?
image.png (view on web) https://github.com/yjhp1016/taichi_LBM3D/assets/63047567/3df5baa2-02cb-42ab-8e65-b7b480bc84ce
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Hello Dr. Yang
If I want to simulate as shown below, how should I set the body force or velocity in the y-axis direction? It seems that the body force at the upper inlet and lower inlet of the y-axis are not in the same direction. I tried velocity BC and that doesn't seem quite right either. Can you give me some advice?
You want to inject fluid from three inlets?
It's not an easy case for bodyforce, I think you can only use velocity BC for three inlets and constant pressure BC for outlet.
emwn123 @.***> 于 2024年1月25日周四 下午4:13写道：
Hello Dr. Yang
If I want to simulate as shown below, how should I set the body force or velocity in the y-axis direction? It seems that the body force at the upper inlet and lower inlet of the y-axis are not in the same direction. I tried velocity BC and that doesn't seem quite right either. Can you give me some advice?
image.png (view on web) https://github.com/yjhp1016/taichi_LBM3D/assets/63047567/4f3f8e5f-c120-4e57-a5d5-26ffd9e8404c
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Yes.
So in the y-axis direction I should set the opposite, right? For example, one side is Vy and the other side is -Vy
correct!
On Thu, 25 Jan 2024 at 17:11, emwn123 @.***> wrote:
Yes.
So in the y-axis direction I should set the opposite, right? For example, one side is Vy and the other side is -Vy
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Hi Dr. Yang,
Sorry to bother you again.
Based on your suggestion, I set the velocity BCs on the three inlets, but it doesn’t seem to be very effective.
No matter how I change the velocity, the phase at the left inlet always gets stuck after a certain time step. (If a body force in the x direction is applied on this basis, the phase will continue to drive smoothly. But this is wrong, because the two inlets in the z-axis direction will also be affected.)
The following are the specific settings and post-processing results:
It would be very grateful if you give me some guidance. Thanks a lot!
Maybe you need to change bc_x_right into 1, 0.99, 0.0, 0.0 ,0.0 ?
On Thu, 25 Jan 2024 at 23:34, emwn123 @.***> wrote:
Hi Dr. Yang,
Sorry to bother you again.
Based on your suggestion, I set the velocity BCs on the three inlets, but it doesn’t seem to be very effective.
No matter how I change the velocity, the phase at the left inlet always gets stuck after a certain time step. (If a body force in the x direction is applied on this basis, the phase will continue to drive smoothly. But this is wrong, because the two inlets in the z-axis direction will also be affected.)
image.png (view on web) https://github.com/yjhp1016/taichi_LBM3D/assets/63047567/fdfda826-ce66-4571-93b3-6bd0e2b1d92d The following are the specific settings and post-processing results: image.png (view on web) https://github.com/yjhp1016/taichi_LBM3D/assets/63047567/438acdb7-41b9-49a9-9e7b-56078fab24c1 image.png (view on web) https://github.com/yjhp1016/taichi_LBM3D/assets/63047567/854172ae-c1bc-4846-a246-32c0ac3d2de4 image.png (view on web) https://github.com/yjhp1016/taichi_LBM3D/assets/63047567/1fbd0b59-0b51-4dfc-a4b5-ae92b4ca9ed4 image.png (view on web) https://github.com/yjhp1016/taichi_LBM3D/assets/63047567/ebbb7fe5-f9fb-4711-bf8e-ecca097ac68e image.png (view on web) https://github.com/yjhp1016/taichi_LBM3D/assets/63047567/792c10b9-069f-42b7-a678-1eadc1a0ae1d
It would be very grateful if you give me some guidance. Thanks a lot!
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