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-   -   kOmegaSST gets the results stalled too early (http://www.cfd-online.com/Forums/openfoam-solving/123853-komegasst-gets-results-stalled-too-early.html)

Juansheng September 22, 2013 23:22

kOmegaSST over-predict the CL when stall happens
 
Hi all,

Thanks for the wonderful CFD software first of all. I'd admit I just learned OpenFOAM just for a week. I'm working on simulating an oscillating airfoil using pimpleDyMFoam solver with kOmegaSST turbulence model. The oscillating function is: 2.1 + 8.2*sin(193*t), Reynold number is about 4e6. So it should be a light stall condition. But the results show that CL seems getting stalled very early. I packed the 0/ directories, and the CL plot as well. I set the alpha to steady 2.1 degree, CL(0.15~0.2) seems not bad comparing with experiment result. Also I tried different K or omega, the data changed a bit but still stay far from the correct results. Hope experts give me some suggestions. Thanks again.

PS, I got and built the OpenFOAM from github, which would be the latest svn afaik.

EDIT: Even with deep stall condition, I also got the full circle for CL. I did something totally wrong. The delay of CL does not indicate the dynamic stall phenomenon. Weird.

Juansheng October 6, 2013 05:01

3 Attachment(s)
OK, the main problem is that I set the oscillating frequency too high (193 as posted before). After lowering that value according to reduced frequency, CL under this light stall condition was predicted correctly (see #1), although there still a bit difference between OF and experimental data.

On the deep dynamic stall, OF tends to over-predict the CL when the stall happens (#2). Is it necessary to change the turbulence model? Hope someone can give me a hint. Thanks.


EDIT: After fixing dynamic viscosity and k and omega for external flows, I got a better circle. But still the CL when stall begins was over-predicted too much. see #3 image.

Best,
Jay


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