[Yuri Almeida]

Dear all,

The momentum equation in icoFoam.C (OF21) is the following:

fvVectorMatrix UEqn
(
fvm::ddt(U)
+ fvm::div(phi, U)
- fvm::laplacian(nu, U)
);

solve(UEqn == -fvc::grad(p));

If I understood right, the equation would be:

d(U)/dt + div(rho*U*U) - laplacian((mu/rho)*U) = -grad(p) (1)

But the equation found in books is:

d(rho*U)/dt + div(rho*U*U) - laplacian(mu*U) = -grad(p) (2)

or, dividing by rho:

d(U)/dt + div(U*U) - laplacian((mu/rho)*U) = -(1/rho)*grad(p) (3)

My question is: Why are equation 2 and 3 different from 1? Probably they are not, but, where is "rho" in -fvc::grad(p) and why is it present in div(phi, U)??

Thx in advance!