[mchurchf]

To whom can help,

I am trying to reconcile some differences between pisoFoam and buoyantBoussinesqPisoFoam.

In the UEqn.H file of buoyantBoussinesqPisoFoam the following equation is set up to predict velocity:

UEqn
==
fvc::reconstruct((fvc::interpolate(rhok)*(g & mesh.Sf()) - fvc::snGrad(p)*mesh.magSf()))

However, in pisoFoam, this is the equation:

UEqn == -fvc::grad(p)

Aside from the inclusion of the gravity term in buoyantBoussinesqPisoFoam, why are the face values used to reconstruct the cell centered values, whereas in pisoFoam the cell center values are used directly?

The same situation occurs in setting up the pressure equation. In buoyantBoussinesqPisoFoam, the equation is:

volScalarField rUA("rUA", 1.0/UEqn.A());
surfaceScalarField rUAf("(1|A(U))", fvc::interpolate(rUA));
fvm::laplacian(rUAf, p) == fvc::div(phi)

whereas in pisoFoam, it is:

volScalarField rUA = 1.0/UEqn.A();
fvm::laplacian(rUA, p) == fvc::div(phi)

buoyantBoussinesqPisoFoam is solving for pressure on the faces, and pisoFoam is solving for cell centered pressure. Does this make a difference? Why are the two codes different in this manner?

Thank you