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Wall Shear stress in 3D

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Old   March 25, 2010, 00:46
Default Wall Shear stress in 3D
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Nikolaos Beratlis
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I am trying to calculate the shear stress on the surface of a golfball but I am having trouble figuring out how the wall shear stress is defined on 3D complex surfaces.
When I am on the main part of the golfball that it is similar to that of the sphere the calculation of the wall shear stress is straightforward. From the surface I move a distance "h" along the normal and compute the tangential velocity. In this case I choose the tangential velocity to be aligned with the azimuthal plane.
However when I am in the dimples, it is hard to choose a single tangential velocity as there are infinite number of tangents and not anyone of them is necessarily aligned with an azimuthal plane. How do I choose the tangential velocity in such a case?

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Old   April 15, 2010, 03:52
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Claus Meister
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tau=mu*(grad U,n) if n is surface normal. By Boussinesq approx is
tau=(mu+mu_T)*(grad U,n)

(*,*) scalar product
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