airfoil with negative drag
 

Hi,

I have simulated a 2D rear wing with two airfoils. The drag coefficient of the large airfoil is negative, the drag of the smaller one is positive. In my view this is not possible. I use a structural mesh and the k-e-model.


Can someone help me?

Please take a look at the FAQ before inventing a self-propelling airfoil
http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

I have calculated the rear wing with different turbulence models, structured (fine and coarse) and unstructured mesh, 2D and 3D models. The y+ value is between 30 and 300. The pressure portion of the drag is always negative, the viscous portion is positive.
I have also replaced the larger profile with an ellipse body. In this case the drag coefficient is positive…