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-   -   Lift Coefficient Oscillates (http://www.cfd-online.com/Forums/fluent/96029-lift-coefficient-oscillates.html)

mingersai January 10, 2012 15:31

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

mingersai January 11, 2012 13:36

Can anyone tell me how to deal with this?

Rhyno466 January 11, 2012 14:59

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

mingersai January 11, 2012 15:26

Quote:

Originally Posted by Rhyno466 (Post 338877)
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...

Rhyno466 January 12, 2012 12:01

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

mingersai January 12, 2012 12:45

Quote:

Originally Posted by Rhyno466 (Post 339061)
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.

Tom A January 12, 2012 14:49

Could it be caused by vortex shedding?


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