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drag coeff to high - kOmegaSST turbulence model

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Old   January 26, 2011, 11:51
Default drag coeff to high - kOmegaSST turbulence model
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Martin
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Dear Users,

i have a problem with the drag coefficient calculated by the kOmegaSST turbulence model with the simpleFOAM solver :-(

The aim is to get to know about the drag coefficient of a streamlined body and compare this results with the ones got by the same body out of a wind tunnel experiment. So in fact - compare reality an CFD

The coefficient i should get for cd is about 0.07, the one i got from my calculations is somewhat around 0.96...

I have calculated values for k and omega from the formulas out of the CFDWiki, but they seem to be incorrect - or a BC is the problem - i don't know

The eddy viscosity ratio i took was 1, but i don't know if this is correct for wind tunnel experiments...?

I will post my case files - maybe someone do have an idea...!?

Thank you very much in advance

Regards,

Martin
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File Type: zip case4.zip (6.4 KB, 35 views)
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Old   February 19, 2011, 10:35
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Martin
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I got the solution...

After convergence of the first calculation with the uploaded case i got to high drag coefficients...
One need to change to higher order interpolation and gradient schemes...
i will post my updated fvSolution and fvSchemes here...
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File Type: zip fvS.zip (1.2 KB, 63 views)
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Old   February 19, 2011, 14:51
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Greg Givogue
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What was the calculated CD?
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Old   February 19, 2011, 15:23
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Martin
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With the old fvS it was about 0.27 and now it is about 0.071
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Old   February 20, 2011, 10:59
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Greg Givogue
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Nice work. How long did it take to run 5e10 iterations (5000/0.000001)?
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Old   February 22, 2011, 03:35
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Alexandre Rubel
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Hi, I had a equivalent problem and what I find in my case is that : when I changed
- div(phi,U) Gauss Upwind -> Gauss linearUpwindV Gauss linear; I get 40 % of errror instead of 70%
and next I changed the turbulent quantities too :
- div(phi,k) Gauss linearUpwind Gauss linear;
- div(phi,omega) Gauss linearUpwind Gauss linear;

It's still running but after 100 iterations I get 10% less of error

Alex

Last edited by alex_rubel; February 22, 2011 at 19:32.
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