[natrask]

Can anyone shed some light on what exactly the couplingFactor parameter is doing in the divDevRhoReff function of the LRR turbulence model?

tmp<fvVectorMatrix> highDensityRSTM::divDevRhoReff(volVectorField& U) const
{
if (couplingFactor_.value() > 0.0)
{
return
(
fvc::div(rho_*R_ + couplingFactor_*mut_*fvc::grad(U))
+ fvc::laplacian((1.0 - couplingFactor_)*mut_, U)
- fvm::laplacian(muEff(), U)
- fvc::div(mu()*dev2(fvc::grad(U)().T()))
);
}
else
{
return
(
fvc::div(rho_*R_)
+ fvc::laplacian(mut_, U)
- fvm::laplacian(muEff(), U)
- fvc::div(mu()*dev2(fvc::grad(U)().T()))
);
}
}

It is unclear to me what the advantage is in splitting

fvc::laplacian(mut_, U)

up into

fvc::div(couplingFactor_*mut_*fvc::grad(U))
+ fvc::laplacian((1.0 - couplingFactor_)*mut_, U)

-Nat