Negative Drag in Sweeping motion

aamer · April 16, 2011, 08:00

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.

aamer · April 16, 2011, 08:01

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....

April 16, 2011, 08:00	Negative Drag in Sweeping motion	#1
aamer Member Aamer Shahzad Join Date: Mar 2010 Posts: 58 Rep Power: 16	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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April 16, 2011, 08:01		#2
aamer Member Aamer Shahzad Join Date: Mar 2010 Posts: 58 Rep Power: 16	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....