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Incompressible blood flow simulation inside a 3D curved pipe |
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October 30, 2020, 14:53 |
Incompressible blood flow simulation inside a 3D curved pipe
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#1 |
New Member
Join Date: Oct 2020
Posts: 4
Rep Power: 6 |
Hi,
I'm trying to simulate blood flowing inside an irregularly shaped 3D vessel with one inlet and one outlet. The inlet is not normal to x, y or z. For now, I'm running steady state simulations. I'm using SU2 v 7.0.2 and I started by editing the cfg file from a 2D channel example. In my case, I'm prescribing the an inlet velocity profile from a file. I'm reaching convergence in a few iterations, but I'm not convinced by the results. In particular, I don't understand: - why the INC_VELOCITY_INIT value will affect the computed velocity field so much, - how to properly set the CFL number, - why the velocity profile doesn't seem to fully develop to a parabolic-like profile, - if there is a way to strongly impose the inlet boundary condition. Many thanks. Last edited by semions; November 1, 2020 at 05:08. Reason: attachment |
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October 31, 2020, 18:11 |
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#2 |
Senior Member
Pedro Gomes
Join Date: Dec 2017
Posts: 466
Rep Power: 13 |
You have INNER_ITER set to 20, your case cannot possibly be converged.
I guess that is why you see a dependence on initial conditions and no parabolic profile. Increase INNER_ITER to a large number, say 10000, and monitor the residuals and some post processing metric like drag. For a simple problem you want at least 6 orders of magnitude drop in residuals and the value of drag to be the same for a significant number of iterations. CFL for steady state problems acts as a form of under relaxation. For a laminar problem you should be able to use a large value 1000 or more. With very low values your case will never converge. With very large values the solver will become unstable. |
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November 4, 2020, 06:43 |
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#3 |
New Member
Join Date: Oct 2020
Posts: 4
Rep Power: 6 |
Thanks for the advice.
I increased INNER_ITER and I tried different combinations of CFL number and linear solvers. I can't make my simulation converge. The residuals start from -6 and if CFL > 10, the residuals increase and the simulation eventually diverges; if CFD < 10, the residuals won't go below the initial orders of magnitude even after a few thousand iterations. I wonder if there's something that I'm missing, since I've run this kind of simulation many time with openfoam and it converges in a few minutes. Thanks again. |
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November 4, 2020, 11:13 |
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#4 |
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Akshay Koodly
Join Date: Aug 2017
Location: The Netherlands
Posts: 43
Rep Power: 9 |
Hello,
If possible could you share the mesh file? Also, can you try the simulation by setting the INC_NONDIM to INITIAL_VALUES instead of DIMENSIONAL and see if you notice a difference? I know in theory there shouldn't be, but I have noticed some weird convergence behavior when using dimensional simulations with very large values for density or velocity. Cheers |
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November 5, 2020, 10:34 |
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#5 |
New Member
Join Date: Oct 2020
Posts: 4
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Unfortunately, my mesh is too large (approx. 98 MB) and CFD online won't let me upload such a file.
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November 6, 2020, 07:41 |
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#6 |
Member
Akshay Koodly
Join Date: Aug 2017
Location: The Netherlands
Posts: 43
Rep Power: 9 |
Ok, no problem.
Did you have any progress by changing the non-dimensionalisation? |
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November 6, 2020, 08:47 |
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#7 |
New Member
Join Date: Oct 2020
Posts: 4
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No, no noticeable change in the residuals.
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Tags |
blood flow, incompressible flow, irregular domain |
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