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kOmegaSST gets the results stalled too early

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Old   September 22, 2013, 23:22
Default kOmegaSST over-predict the CL when stall happens
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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.

Last edited by Juansheng; October 10, 2013 at 00:25.
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Old   October 6, 2013, 05:01
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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.

Attached Images
File Type: png CL-2.1.png (26.9 KB, 38 views)
File Type: png CL-7.8.png (34.6 KB, 45 views)
File Type: png CL_2nd_try.png (34.7 KB, 39 views)

Last edited by Juansheng; October 10, 2013 at 00:33.
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airfoil, komegasst, oscillating, pimpledymfoam

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