# Lift Coefficient Oscillates

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 January 10, 2012, 15:31 Lift Coefficient Oscillates #1 Member   Ming Cai Join Date: Mar 2011 Posts: 50 Rep Power: 6 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 Thanks for your help. Last edited by mingersai; January 11, 2012 at 13:35.

 January 11, 2012, 13:36 #2 Member   Ming Cai Join Date: Mar 2011 Posts: 50 Rep Power: 6 Can anyone tell me how to deal with this?

 January 11, 2012, 14:59 #3 Member   Ryne Join Date: Jan 2010 Posts: 32 Rep Power: 7 I would guess that the airfoil is stalling and this oscillation comes from the separation and reattachment of the airflow over the airfoil.

January 11, 2012, 15:26
#4
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Ming Cai
Join Date: Mar 2011
Posts: 50
Rep Power: 6
Quote:
 Originally Posted by Rhyno466 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...

 January 12, 2012, 12:01 #5 Member   Ryne Join Date: Jan 2010 Posts: 32 Rep Power: 7 May I ask why you are running a transient case instead of just a steady case?

January 12, 2012, 12:45
#6
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Ming Cai
Join Date: Mar 2011
Posts: 50
Rep Power: 6
Quote:
 Originally Posted by Rhyno466 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.

 January 12, 2012, 14:49 #7 New Member   Tom Join Date: Jan 2012 Posts: 11 Rep Power: 5 Could it be caused by vortex shedding?

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