if(divSigmaExpMethod == "standard")
{
//- calculating the full gradient has good convergence and no high freq oscillations
divSigmaExp = fvc::div(C && epsilon) - fvc::div(K & gradU);
}
else if(divSigmaExpMethod == "surface")
//- this form seems to have the best convergence
divSigmaExp =
fvc::div(mesh.magSf()*
(
(n&(Cf && fvc::interpolate(symm(gradU))))
- (n&(Kf & fvc::interpolate(gradU)))
)
);
else if(divSigmaExpMethod == "laplacian")
//- causes high freq oscillations and slow convergence
divSigmaExp = fvc::div(sigma) - fvc::laplacian(K,U);
else
FatalError << "divSigmaExp method " << divSigmaExpMethod << " not found!" << endl;