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airfoil with negative drag

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Old   December 23, 2013, 13:09
Default airfoil with negative drag
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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?
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Old   December 23, 2013, 13:15
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Please take a look at the FAQ before inventing a self-propelling airfoil
http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F
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Old   December 28, 2013, 06:54
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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…
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