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Differences in Formulation for devRhoReff and divDevRhoReff

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Old   May 2, 2011, 05:40
Default Differences in Formulation for devRhoReff and divDevRhoReff
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Hello everybody,

I'm using the compressible k-Epsilon turbulence model and I've got a question about the formulation of the total stress term devRhoReff and the source term for the momentum equation divDevRhoReff. The former is defined as

Code:
-muEff()*dev(twoSymm(fvc::grad(U_)))
whereas the latter is defined as

Code:
- fvm::laplacian(muEff(), U) - fvc::div(muEff()*dev2(fvc::grad(U)().T()))
Mathematically the second equation should just be the divergence of the first one. However, when I calculate the divergence of the first one and replace the second one with

Code:
fvc::div( -muEff()*dev(twoSymm(fvc::grad(U_))) )
the solver crashes after some iterations with a time step continuity error .

Can someone explain this behaviour to me? Are my assumptions not correct?

Thanks a lot

martin
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