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SimpleFoam with Komega turbulence model?

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Old   December 8, 2014, 00:49
Default SimpleFoam with Komega turbulence model?
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Hi All,

I have been working on the simpleFoam with the example airfoil2D. I implemented the files that are relevant to kOmega turbulence model into the zero file. I did all required steps in order to get it to work. The case file ran correctly and it gave me similar results to Spalart Allmaras. However, I feel that the drag and left values are a little bit different than the theoretical results. For instance, for angle of attack 2 degree, the CFD lift coefficient result was 0.652044. On the other hand, the theoretical result for the same angle of attack was 0.4865, which gives an error for about 25.4%. I feel unsatisfied from these results. Can someone explain why am I getting these results? I would be greatly thankful

Kind regards,
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Old   December 8, 2014, 20:13
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In general:
- Did you make grid independence study?
- What about the boundary conditions?
- Did you reach converged solution?...

If you are aware about the above facts, then you can blame the 2 equation turbulence model for any inaccurate results.

All the best and success.
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Old   December 8, 2014, 20:31
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I will provide a picture shows the monitor convergence. However, I don't know a lot about making a grid independence. Could you please explain what do you mean about it.
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Old   December 8, 2014, 20:40
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As you are aware, from turbulence equations we have the following:

k=(3/2)(Uinf*I)^2

Where Uinf=26 m/s, and I=0.05 for the external flow.

Therefore, k= 2.535.

Similarly, omega= (0.09*k)/(beta*kinematic viscosity)

kinematic viscosity= 10^-6 m2/s, beta =0.1-1 (I chose 0.5)

Omega= 182.52.

Am I right?

Regards,
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Old   December 8, 2014, 21:20
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Quote:
Originally Posted by tareqkh View Post
I will provide a picture shows the monitor convergence. However, I don't know a lot about making a grid independence. Could you please explain what do you mean about it.
Picture shows the monitor convergence
Attached Images
File Type: png download.png (27.4 KB, 22 views)

Last edited by tareqkh; December 9, 2014 at 22:11.
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Old   December 11, 2014, 17:38
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Dear tareq,

Thanks for the supplied information.

- The provided image shows that there is a trend to convergence. However it doesn't mean that your solution is converged yet... Please check the results after some more hundred iterations and compare them with the previous one.
- Did you use the same boundary conditions as in the experimental case.
- You are using k-omega turbulence model. It worths also to check the results with realizable k-epsilon or v2f models.
- Grid independence study means checking the effect of grid refinement on the results. So make a more fine mesh (taking into account a reasonable y+ value) and compare the results. Do this until you see (engineering) minor difference between the results

All the best and success

Ahmad
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