# How to clarify vortex shedding of airfoil

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 September 7, 2010, 03:05 How to clarify vortex shedding of airfoil #1 New Member   Wei Yang Join Date: Jan 2010 Location: Shanghai Posts: 4 Rep Power: 9 Sponsored Links 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

 September 7, 2010, 10:37 #2 Member   ganesh Join Date: Mar 2009 Posts: 40 Rep Power: 10 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

September 8, 2010, 06:36
#3
New Member

Wei Yang
Join Date: Jan 2010
Location: Shanghai
Posts: 4
Rep Power: 9
Dear Ganesh,

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

Quote:
 Originally Posted by ganesh 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

 September 8, 2010, 08:38 #4 New Member   Join Date: Sep 2010 Posts: 3 Rep Power: 8 This doesn't directly answer your question but if you are really doing a 2D simulation then you are not really doing LES..

September 10, 2010, 08:22
#5
New Member

Wei Yang
Join Date: Jan 2010
Location: Shanghai
Posts: 4
Rep Power: 9
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

Quote:
 Originally Posted by pja 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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