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Old   July 7, 2011, 02:58
Default wallShearStress
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Claus Meister
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Hello Foamers,

I have a simple question about computing wall shear stresses: what is the difference between:

(1) tau_w=mu*grad(U) | y=0

and

(1) tau_W=mu [ grad(U)-grad(U)^T ] . n

where mu is the viscosity, U the velocity and n the surface normal.

Cheers
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Old   July 11, 2011, 05:37
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David GISEN
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Hi Claus,
the second one makes no sense to me, why would you substract a transposed tensor from it's original? Where did you find this formula?
Regards,
David
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Old   July 11, 2011, 09:37
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Claus Meister
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It can be found in several books about mechanics; there it is treated as the generalization of newtons law. The term even appears in the incompressible navier stokes equation.
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