foam-extend4.1-coherent-io/applications/solvers/combustion/dieselEngineFoam/pEqn.H

rho = thermo->rho();

volScalarField A = UEqn.A();
U = UEqn.H()/A;

if (transonic)
{
    surfaceScalarField phid
    (
        "phid",
        fvc::interpolate(thermo->psi())
       *((fvc::interpolate(U) & mesh.Sf()) - fvc::meshPhi(rho, U))
    );

    for (int nonOrth=0; nonOrth<=nNonOrthCorr; nonOrth++)
    {
        fvScalarMatrix pEqn
        (
            fvm::ddt(psi, p)
          + fvm::div(phid, p)
          - fvm::laplacian(rho/A, p)
         ==
            Sevap
        );

        pEqn.solve();

        if (nonOrth == nNonOrthCorr)
        {
            phi == pEqn.flux();
        }
    }
}
else
{
    phi = fvc::interpolate(rho)
         *((fvc::interpolate(U) & mesh.Sf()) - fvc::meshPhi(rho, U));

    for (int nonOrth=0; nonOrth<=nNonOrthCorr; nonOrth++)
    {
        fvScalarMatrix pEqn
        (
            fvm::ddt(psi, p)
          + fvc::div(phi)
          - fvm::laplacian(rho/A, p)
         ==
            Sevap
        );

        pEqn.solve();

        if (nonOrth == nNonOrthCorr)
        {
            phi += pEqn.flux();
        }
    }
}

#include "rhoEqn.H"
#include "compressibleContinuityErrs.H"

U -= fvc::grad(p)/A;
U.correctBoundaryConditions();

DpDt = fvc::DDt(surfaceScalarField("phiU", phi/fvc::interpolate(rho)), p);