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Old   November 16, 2004, 15:39
Default Wing Drag Values
Ed Reed
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I have been running Fluent simulations of 3D wings lately and having some success. I have been comparing my results to airfoil data collected in a wind tunnel (published in a book) and have found that while lift values are very close, the drags coefficient values I obtain from my CFD analysis are 5-10 times greater than those listed in the book. Does anyone know why this would occur?
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Old   November 16, 2004, 17:30
Default Re: Wing Drag Values
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If you're using a turbulence model be careful of your y+ values. You can find pressure distributions over almost any standard airfoil online (also "Theory of Wing Sections" by Abbott and Doenhoff has a ton of airfoils)... find some of those and compare them to what you're getting. Check your pressure gradients as well. I've seen where people aren't refining the grid upstream of the stagnation point properly and it's over-predicting the pressure at this point, which leads to high drags. Try to find some data online that compares the pressure drag and viscous drag of your airfoil as well. This will help give you a better idea of what the problem is. If you're coming up with a rediculous viscous drag, then it's either your mesh or your viscous model. If you're coming up with a rediculous pressure drag then it's probably a mesh problem. That's where the pressure distribution will really come in handy, and should tell you exactly where the problem is.

Hope this helps.

Goodluck, Jason
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