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Negative Drag in Sweeping motion

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Old   April 16, 2011, 07:00
Default Negative Drag in Sweeping motion
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Aamer Shahzad
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Hello All....

i am trying to sweep a wing in STILL AIR, from psi = 0 to pi radian in azimuth direction (i.e about global Y- axis). i have written a udf and used DEFINe CG motion macro. the wing is having constant angle of attack of 5 degrees.

In SOLVE>>MOnitor >>Force, i have used X=0, Y=1 for lift and X=1 and Y =0 for drag.... i am getting right Cl curve. the Cd curve starts correctly, but then gives negative values as psi keep increasing.

Wht can be the reasons of negative drag and correct lift values.
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Old   April 16, 2011, 07:01
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Aamer Shahzad
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PLease note that NO turbulance model is used, so Y+ is not an issue. I have tried the cases with smaller time steps, finer grid and bigger domains too..... but no success....
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