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Engineering
Aerospace Engineering
Airfoil drag prediction in incompressible and inviscid flow
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[QUOTE="lordvon, post: 6088654, member: 516001"] Thanks for your reply! I am actually not sure D'Alembert's paradox should really be a "paradox" for a non-lifting body. As idealized as inviscid and incompressible flow is, why should we be surprised that there is no drag on a non-lifting body? We know plainly that including unsteadiness and viscosity can result in drag. As an analogy, is it paradoxical that gravity alone cannot predict a terminal velocity? It is plain to see that fluid resistance causes terminal velocity. However, I do believe that for a lifting body, drag should be produced, and there is indeed additional physics missing from Thin Airfoil Theory and Vortex Panel Methods. What you say is extremely interesting, because a lot of people believe it -- that there can be no drag without viscosity. However, conservation of momentum must hold for fluid flow -- viscous or not. I believe there is much confusion about what drag is at a fundamental level. My intuition was that we shouldn't need Navier-Stokes CFD (or empirical wake momentum thickness methods) to see any drag at all. Sure, drag (and lift) can be sensitive to turbulence and such, but drag is more fundamental than that level of physics, just like lift. It should be calculable in our inviscid and incompressible flow models. This absence of an elegant explanation for drag (especially since lift is relatively easily calculated) has actually bothered me for a long time, and I finally came up with an elegant model that almost exactly matches NACA airfoil data up until stall. I just wanted to confirm that no such explanation already exists. [/QUOTE]
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Airfoil drag prediction in incompressible and inviscid flow
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