Lift Coefficient Oscillates
 

Dear Friends

I'm running simulation on a NACA 64 210 airfoil with k-omega sst model with Re = 2.6 E6 . The chord length is 1m.

Angle of Attack ranges from 0 to 20.

everything is fine before angle of attack getting to 12, both lift coefficient and drag coefficients oscillates periodicly after 12 aoa.

I don't know if this is the correct solution. However, before this angle the results are reasonable :confused:
Thanks for your help.

https://lh3.googleusercontent.com/-7...qI/s912/12.PNG

https://lh4.googleusercontent.com/-k...Ew/s912/16.PNG

https://lh5.googleusercontent.com/-0...HQ/s912/20.PNG

Can anyone tell me how to deal with this?

I would guess that the airfoil is stalling and this oscillation comes from the separation and reattachment of the airflow over the airfoil.

Hi, Rhyno466

Thanks for your reply. I'm comparing my results with experimental ones. The experimental people pick only one value for this angle of attack. I'm not sure how they did that if the airfoil is stalling.

I have no experience in wind tunnel tests...

May I ask why you are running a transient case instead of just a steady case?

Yep, I'm running transient solution with time step size 0.0001.

Could it be caused by vortex shedding?