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Old   October 16, 2013, 13:50
Default Kutta Condition
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Hi all!
From simple aerodynamic analysis performed by Fluent and Xfoil of the non viscous and incompressible flow around Naca 2412, I noticed that the Kutta condition is not satisfied (the cp is not unitary at trealing edge). Why?
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Old   October 17, 2013, 03:51
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There are three important facts you need to know:

1) The Kutta condition is an arbitrary (but very useful and clever) condition used to make inviscid calculations worth the effort for lifting aerodynamic problems. In a true inviscid flow around an airfoil no lift is generated and the rear stagnation point is not generally expected to be on the trailing edge. I only know of applications with the panel methods.

2) For real flows, the Cp=1 condition is not expected to be recovered at the trailing edge; that is, viscous losses will prevent the pressure from fully recovering in the rear stagnation point. However, it is generally the case (for streamlined bodies) that this point is at the trailing edge (that's why Kutta condition is clever).

3) As soon as you move from panel methods to any Finite Volume/Difference method something else happens as:

- Even if you set the computation as inviscid, the numerical method is likely to introduce a certain amount of numerical viscosity (especially in Fluent); hence the computation is actually resemblant of those in real flows, just with an artificial, grid dependent, numerical viscosity.

- the point above tells you that you don't actually need Kutta here (also because it is nearly impossible to fix it, i guess), just don't expect the Cp to recover stagnation point values at the trailing edge.
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