Hello,
Now I am trying 3D flow simulation by URANS for simple geometric room.
The room dimensions are about 3m*10m*3m (width, width, hight).
More than 2miliom mesh of tetra is used for this room, and 1cm mesh is piut around outlet condition.
However, I always faced a divergence problem.
The divergence always starts from outlet boundary.
For inlet bounday condition, I put 0.1m/s velocity, and simple outlet condion is used for outlet boundary.
When I check "listing" file, I always had messages like "Incoming flow detained for 51 outlet faces on 8350".
I am wondering what kind of setting casues this problem even though I suppose that simple settings applied to this simulaiton.
Would someone give me tips?
I think this simulation should be done easily because it is simple case.
Best regards.
Tsubasa
Divergence for simple geometry room
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Divergence for simple geometry room
Last edited by Tsubasa on Fri Jun 04, 2021 2:31 am, edited 1 time in total.
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- Posts: 4100
- Joined: Mon Feb 20, 2012 3:25 pm
Re: Divergence for simple geometry room
Hello,
Did you extrude the mesh on at least 1 layer at the outlet so as to have prisms (orthogonal to the outlet) and not tetrahedra there ? This can really help. Also, using an imposed pressure outlet is more robust than a default "free outlet".
There are a few additional recommendations : https://github.com/code-saturne/code_sa ... robustness
Regards,
Yvan
Did you extrude the mesh on at least 1 layer at the outlet so as to have prisms (orthogonal to the outlet) and not tetrahedra there ? This can really help. Also, using an imposed pressure outlet is more robust than a default "free outlet".
There are a few additional recommendations : https://github.com/code-saturne/code_sa ... robustness
Regards,
Yvan
Re: Divergence for simple geometry room
Hello,
Actually, I have to generate only tetra mesh in all region
because I will carry out a postprocessing specialized to tetra mehs result.
That's why I am using tetra mesh only, even at 1 layer at the outlet.
In future, I want impose pressure values at inlet and outlet (pressure driven flow),
but as far as I understand, computations are often unstable when we use tetra.
I tried the recommendation you gave me, but it cannot solve the problem....
so I have to find some solution for this.
Best regards,
Hamada
Actually, I have to generate only tetra mesh in all region
because I will carry out a postprocessing specialized to tetra mehs result.
That's why I am using tetra mesh only, even at 1 layer at the outlet.
In future, I want impose pressure values at inlet and outlet (pressure driven flow),
but as far as I understand, computations are often unstable when we use tetra.
I tried the recommendation you gave me, but it cannot solve the problem....
so I have to find some solution for this.
Best regards,
Hamada
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- Posts: 4100
- Joined: Mon Feb 20, 2012 3:25 pm
Re: Divergence for simple geometry room
Hello,
You can still use a hybrid mesh and output only the tetrahedral part (using a selection filter) for postprocessing.
Did you try the other recommended robustness parameters in the wiki ?
Regards,
Yvan
You can still use a hybrid mesh and output only the tetrahedral part (using a selection filter) for postprocessing.
Did you try the other recommended robustness parameters in the wiki ?
Regards,
Yvan
Re: Divergence for simple geometry room
Hello Yvan,
OK, that's is one of the options.
I tried other recommendated setting, but it did not solve the problem.
Best regards.
Hamada
OK, that's is one of the options.
I tried other recommendated setting, but it did not solve the problem.
Best regards.
Hamada
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- Posts: 4100
- Joined: Mon Feb 20, 2012 3:25 pm
Re: Divergence for simple geometry room
Hello,
How big is your mesh ? If you have a small enough mesh and the computation crashes on it, I am interested if you can provide it so we can use it to test/improve robustness.
Best regards,
Yvan
How big is your mesh ? If you have a small enough mesh and the computation crashes on it, I am interested if you can provide it so we can use it to test/improve robustness.
Best regards,
Yvan
Re: Divergence for simple geometry room
Hello,
Mesh size is very small. Near the outlet boundary, 2cm tetra mesh is used, and other area has 5cm mesh.
Can you download a mesh file and setup file in here?
https://filesender.renater.fr/?s=downlo ... b0910cc9d4
Although this geometry is not same the picture in first post, this geometry and mesh has a same divergence problem.
DIvergence always comes from outlte boundary condition.
The simulation works very well if I use hexa mesh, but I prefer tetra mesh.
Best regards,
Tsubasa
Mesh size is very small. Near the outlet boundary, 2cm tetra mesh is used, and other area has 5cm mesh.
Can you download a mesh file and setup file in here?
https://filesender.renater.fr/?s=downlo ... b0910cc9d4
Although this geometry is not same the picture in first post, this geometry and mesh has a same divergence problem.
DIvergence always comes from outlte boundary condition.
The simulation works very well if I use hexa mesh, but I prefer tetra mesh.
Best regards,
Tsubasa
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- setup.xml
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- Posts: 4100
- Joined: Mon Feb 20, 2012 3:25 pm
Re: Divergence for simple geometry room
Hello,
Yes, I was able to download the mesh. I'll try to run tests with it soon. Thanks.
Best regards,
Yvan
Yes, I was able to download the mesh. I'll try to run tests with it soon. Thanks.
Best regards,
Yvan
Re: Divergence for simple geometry room
Hello Yvan,
Thank you for your help.
I am appreciate if you could let me know your result of testing.
Best regards,
Tsubasa
Thank you for your help.
I am appreciate if you could let me know your result of testing.
Best regards,
Tsubasa
Re: Divergence for simple geometry room
Hello,
How was your test?
I would appreciate if you let me know.
Best regards,
Tsubasa
How was your test?
I would appreciate if you let me know.
Best regards,
Tsubasa