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-   -   Problem in cd of oscillating airfoil at high freq. (https://www.cfd-online.com/Forums/fluent/42945-problem-cd-oscillating-airfoil-high-freq.html)

CH November 27, 2006 03:31

Problem in cd of oscillating airfoil at high freq.
 
hi,

I managed to obtain results of cl/cd of an oscillating airfoil using fluent udf define_cg_motion. at frequency f=1, i managed to get a sinusodial graph for both cl and cd. They are quite close to the published results. dt=0.001

however, when i change f to 2 and rerun, i can get a sinusodial graph for cl (similar to published one) but the graph for cd is oscillating irregularly. i tried to reduce the time down to as small as dt=0.00025 but the result is still irregular.

i can't figure out what's wrong since i only changed the f from 1 to 2.

can someone help?

thanks alot!

lfla August 22, 2017 08:29

1 Attachment(s)
Hi
Ive done the same type of problem my results however differ greatly, i got a results file of flow time and lift coefficient and used alpha(t)=alpha(mean)+alpha(amp)sin(2*pi*f*t) in order to get results. Here's a copy of my results its quite clear that cl is decreasing with increasing alpha which shouldnt happen.
Thank you


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