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How to clarify vortex shedding of airfoil

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Old   September 7, 2010, 03:05
Default How to clarify vortex shedding of airfoil
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Wei Yang
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Dear all,

I have carried out a LES simulation for 2D airfoil in big angle of attack. Power Spedtra of CL CD and velocities of some points in wake showed that there are many peaks from tens to hundreds for frequency.
As we know that the typical St=0.2, But how can I clarify the vortex shedding? how to define the frequency for the flow as there are so many peaks.

Thanks all.

Yang
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Old   September 7, 2010, 10:37
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ganesh
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Dear Yang,

I am not too sure if the St=0.2 is also valid for turbulent flow, I have seen this more only with laminar simulations. I have seen simulations for a NACA airfoil at 20 deg AoA at Re~O(10^4) or so and it is run as a laminar simulation; they do show that St is close to 0.2.

Hope this helps

Regards,

Ganesh
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Old   September 8, 2010, 06:36
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Wei Yang
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Dear Ganesh,

Thank you for your reply.

The Reynolds number in my case si 2e5, AOA=18, the wing is stall. It was expected to get a clear vortex sheding characteristics, such as St=0.2. But, I got many frequency peaks, the St vary from 0.03 to 0.5. There is a peak near St=0.2, but it is not the biggest peak. I began to doubt my simulation. But the grids and the LES method is good enough to capture the flow. Or is the vortex shedding of wing uncertain?

Regards,

Yang

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Originally Posted by ganesh View Post
Dear Yang,

I am not too sure if the St=0.2 is also valid for turbulent flow, I have seen this more only with laminar simulations. I have seen simulations for a NACA airfoil at 20 deg AoA at Re~O(10^4) or so and it is run as a laminar simulation; they do show that St is close to 0.2.

Hope this helps

Regards,

Ganesh
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Old   September 8, 2010, 08:38
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pja
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This doesn't directly answer your question but if you are really doing a 2D simulation then you are not really doing LES..
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Old   September 10, 2010, 08:22
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Wei Yang
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Dear all,

Thanks a lot.
I have found some papers. It was reported that the St will decrease from 0.21 to 0.12 with increase of angle of attack for an airfoil. So, St=0.21 is not important.

Yang

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This doesn't directly answer your question but if you are really doing a 2D simulation then you are not really doing LES..
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