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February 4, 2010, 10:35 
Getting faster convergence in simpleFoam

#1 
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Bastian Nebenfuehr
Join Date: Feb 2010
Location: Sverige
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Hello there,
I am currentliy running simpleFoam on my mesh, which contains half an automotive geometry (station wagon) in order to find out the drag coefficient Cd. The mesh has a total of about 12 million cells and with my settings now, I get convergence after about 2000 iterations. This actually is very time consuming and an entire simulation (up to 5000 iterations) takes about 14 hours. The same case can be run in Fluent, which converges already after about 500 iterations. Is it somehow possible, to speed up the simulation? So for further information, I'm using simpleFoam and the realizable kepsilonmodel with the default values. In order to intialize the pressure field, I run potentialFoam first. I use the GAMG solver for the pressure and the DILUPBiCG solver for the rest. Usually I run in double precision. Hope that somebody can help me. 

February 5, 2010, 05:39 

#2 
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Dirk Voglander
Join Date: Mar 2009
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Hi,
if you don't have stability problems, you could maybe try to increase the relaxation factors in system/fvSolution. 

February 5, 2010, 11:26 

#3 
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Try smoothSolver instead of DILUPBiCG to improve performance.


February 5, 2010, 18:33 

#4 
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BastiL
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February 8, 2010, 04:27 

#5  
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Bastian Nebenfuehr
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Quote:
I will definitely try this, thx. Unfortunately, I did not do the Fluent simulations, so I don't know, which solver was used, but actually it should have been the same one. Will try to find it out, thx. 

February 8, 2010, 12:40 

#6 
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I don't know fluent but I know the definition of residuals differ among CFD packages. So don't base convergence on the absolute residual levels.
I have found simpleFoam to convergence in as many steps as StarCD on the same mesh. 

February 8, 2010, 15:13 

#7 
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Bastian Nebenfuehr
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After trying some stuff today, I can state that playing with the URFs really helps a lot in getting faster convergence. Now I am almost at Fluentlevel. For the rest the use of the "applyBoundaryLayer" function seems to help speeding up the simulation as well. Setting the nonOrthogonalCorrectors to 0 gives a significant change.


February 9, 2010, 03:56 

#8  
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Hi basneb,
Quote:
Regards Thomas Last edited by Thomas Baumann; February 9, 2010 at 04:11. 

February 9, 2010, 05:20 

#9  
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Bastian Nebenfuehr
Join Date: Feb 2010
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Quote:
I don't need the nonOrthogonalCorrectors, since the mesh is really really good. The max. nonOrthogonolaty is very low. However, you are right, you cannot run every mesh without the nonOrthogonalCorrectors. In my case, I compared the results (i.e. drag coefficient) for both simulations (with and without nonOrthogonalCorrectors) and they are really similar, so I conclude that there is no problem for me. Best regards 

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