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Old   February 12, 2008, 17:43
Default one question about the way the
  #1
pbo
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Patrick Bourdin
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one question about the way the viscous force is computed in turbulentForceAndTorqueFunctionObject.C:

// Viscous component
viscousForces[patchI] =
gSum
(
-nuEff.boundaryField()[curPatch]*
U.boundaryField()[curPatch].snGrad()*
mesh.magSf().boundaryField()[curPatch]
);

This is only valid in regions where the velocity field is more or less linear (snGrad being approximated by a one sided finite difference if I am not mistaken). In other words, for models with wall functions (log law), the above formulation will give incorrect viscous force estimates at the wall. Am I correct?
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Old   February 12, 2008, 18:07
Default I've also wondered about this
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Sung-Eun Kim
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I've also wondered about this and haven;t had time to look into the code. If the slip velocity (extrapolated using the wall-law) is somehow patched on the wall faces and the consistent eddy viscosity is used, the aboce expression should give correct wall-shear.

I'm not sure this is the way the OF works.
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Old   February 14, 2008, 06:29
Default I am not familiar with this fu
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Eugene de Villiers
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I am not familiar with this function object (I guess it does the same as my liftDrag function object), but I can confirm that boundary values of nuEff on a wall will include the effects of wall functions if they are present in the turbulence model.
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