interFoam Ueqn
 

the LHS of UEqn is as follows,
fvVectorMatrix UEqn
(
fvm::ddt(rho, U)
+ fvm::div(rhoPhi, U)
- fvm::laplacian(muEff, U)
- (fvc::grad(U) & fvc::grad(muEff))
);

I want to know the physical meaning of the last term,
(fvc::grad(U) & fvc::grad(muEff)) and wher it come form,

Hi Alvin, this term is due spatial variation of muEff. From the Cauchy equation you have for the viscous term div & [muEff*grad(U)], since muEff is not a constant, using the chain rule: muEff*laplacian(U)+grad(muEff)&U.

Regards.

Thanks,very helpful