Getting a Negative Drag_Coefficient

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 October 12, 2015, 23:38 Getting a Negative Drag_Coefficient #1 New Member   fangwei Join Date: Sep 2015 Posts: 4 Rep Power: 3 Hello Everyone I am running a 2D simulation over a Airfoil via Fluent. I am getting a good Lift Coefficient, but a negative Drag coefficient. Is there anyone experiencing the same issues while running the CFD? Besides, for the initialization method. Is there difference for Hybird and Standard initialization. which one is better?

 October 12, 2015, 23:59 #2 Member     Bharat Join Date: Jul 2011 Location: Delhi, India Posts: 46 Rep Power: 7 please check 1) is your mesh fine enogh. 2) is your solution converged. 3) values for force vectors, are they defined correctly for specified AoA. __________________ chapter 3: -crossing the threshold-

October 13, 2015, 00:54
#3
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fangwei
Join Date: Sep 2015
Posts: 4
Rep Power: 3
Quote:
 Originally Posted by Bharatt please check 1) is your mesh fine enogh. 2) is your solution converged. 3) values for force vectors, are they defined correctly for specified AoA.
I think the Mesh is fine, I got a decent Lift_coefficient already

for the (3), what is values for force vector?, for the angle of attack, in the farfield setting, the direction of incoming air is defined based on x, y unit vector component.
for zero AOA, x:1 y:0 right?

 October 13, 2015, 01:15 #4 Member     Bharat Join Date: Jul 2011 Location: Delhi, India Posts: 46 Rep Power: 7 yes, for(drag monitor) specific AoA X=cos(AoA) Y=sin(AoA) __________________ chapter 3: -crossing the threshold-

 October 13, 2015, 08:00 #5 Member   Devesh Baghel Join Date: Mar 2009 Posts: 70 Rep Power: 9 Hi, Is direction vector correctly defined while calculation of drag ? sometimes happened, while defining opposite direction of vector which reflects negative value.

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