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??negative drag coefficient when flowstream velocity is at zero

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Old   March 11, 2010, 05:22
Default ??negative drag coefficient when flowstream velocity is at zero
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Hi everyone,

I came across negative coefficient when simulating airfoil flapping motion using dynamic mesh.
My case is:
1.airfoil with flap at the trailing edge,no gap between the main airfoil and the flap,with the flap deflection angles ranging from 0~15.the whole airfoil does the flapping motion. freestream velocity
My settings:
k-e viscous model(RNG,enhanced Wall);velocity=0 when setting the velocity in boundary conditions.

when it converged,I do find the airfoil flaps as I expect but it also destroy the grids around it.Besides,the amount of Cl and Cd(negative) I got is 10 times less than experiment datas.

Can anyone give some advice?
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