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convergence problem / bluff body / k omega

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Old   June 14, 2013, 07:43
Default convergence problem / bluff body / k omega
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Luca
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Dear all

I am trying to simulate the steady state flow around a bluff body in a wind tunnel using RANS k-omega turbulence model. I have attached the code and some pictures.

The problem is that the simulation doesn't converge (after roughly 2000 steps the residuals jump). I have tried to lower the relaxation factors without success. Furthermore the stagnation Cp on the nose is 1.8 instead of 1. It is strange as the simulation fits very well the wind tunnel data o the rest of the body.

Can anybody help me please? thanks a lot

best regards
Luca
Attached Images
File Type: jpg mesh2.jpg (91.3 KB, 59 views)
File Type: jpg 2.jpg (59.5 KB, 55 views)
File Type: jpg residuals.jpg (22.8 KB, 77 views)
File Type: jpg 1.jpg (16.9 KB, 57 views)
Attached Files
File Type: gz code.tar.gz (4.1 KB, 32 views)
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Old   June 15, 2013, 15:52
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Luca
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bump..nobody can help me?
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Old   June 15, 2013, 17:55
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My experience with k-omega SST is that the quality of the residuals is very much related to how "good" your mesh is. Regardless of that, the residuals are usually pretty bad. I am guessing that the highest one in your picture is for pressure. If you run the motorbike tutorial from simpleFoam tutorial directory, you will see that it also has pretty poor residuals.

Somebody has to have the ahmed body in SST k-omega. Maybe ask the author of the discretizer; he has an example with the Ahmed body using Discretizer.

Did you use SnappyHexMesh? If so, can you include the blockMesh, STLs, and snappyHexMesh files. The first opportunity to improve the quality is likely in those files.
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Old   June 16, 2013, 06:28
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I have managed to solve the problem using a higher omega at the inlet. Thank you anyway for the reply
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