How to clarify vortex shedding of airfoil
 

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

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

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

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

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