Viscous term expansion
Hi all, I'm studying the implementation of the viscous term in NS equations in the general framework used for example in pisoFoam, nevertheless I can't understand some of the things that are done. Viscous term is:
div[nuEff*(grad(U)+grad(U)^T)] due incompressibility and applying div to the product, it becomes laplacian(nuEff, U)+ grad(nuEff)*[(grad(U)+grad(U)^T)] (1) in laminar regime nuEff=nu and in turbulent regime nuEff=nu+nut. Reading the code we have from pisoFoam.C: Code:
00065 fvVectorMatrix UEqn Code:
00181 tmp<fvVectorMatrix> kEpsilon::divDevReff(volVectorField& U) const All ideas are welcome. Regards. |
Hello, Santiago.
Perhaps you have it already solved, but here goes my try: The laminar part of viscous stress tensor is: The turbulent part of viscous stress tensor is Now, summing both contributions: The last term in OpenFOAM code is not the same, though: - it is computed the deviatoric of and not the gradient itself. This is discussed in another topic: http://www.cfd-online.com/Forums/ope...ivdevreff.html The trace of last term is zero because of the explicit formulation using the velocity field from previous time step, that should be divergence free. |
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