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-   -   Differences in Formulation for devRhoReff and divDevRhoReff (http://www.cfd-online.com/Forums/openfoam-programming-development/87897-differences-formulation-devrhoreff-divdevrhoreff.html)

mart.hein May 2, 2011 06:40

Differences in Formulation for devRhoReff and divDevRhoReff
 
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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