pEqn.H

dimensionedScalar compressibility = fvc::domainIntegrate(psi);
bool compressible = (compressibility.value() > SMALL);

rho = thermo.rho();

// Thermodynamic density needs to be updated by psi*d(p) after the
// pressure solution
const volScalarField psip0(psi*p);

volScalarField rAU(1.0/UEqn.A());
mesh.interpolate(rAU);

surfaceScalarField rhorAUf("rhorAUf", fvc::interpolate(rho*rAU));
volVectorField HbyA(constrainHbyA(rAU*UEqn.H(), U, p_rgh));

surfaceScalarField phig(-rhorAUf*ghf*fvc::snGrad(rho)*mesh.magSf());

surfaceScalarField phiHbyA
(
    "phiHbyA",
    fvc::flux(rho*HbyA) + phig
);

if (ddtCorr)
{
    surfaceScalarField faceMaskOld
    (
        localMin<scalar>(mesh).interpolate(cellMask.oldTime())
    );

    phiHbyA +=
        faceMaskOld*MRF.zeroFilter(rhorAUf*fvc::ddtCorr(rho, U, phi));
}

MRF.makeRelative(fvc::interpolate(rho), phiHbyA);

// Update the pressure BCs to ensure flux consistency
constrainPressure(p_rgh, rho, U, phiHbyA, rhorAUf, MRF);

fvScalarMatrix p_rghDDtEqn
(
    fvc::ddt(rho) + psi*correction(fvm::ddt(p_rgh))
  + fvc::div(phiHbyA)
  ==
    fvOptions(psi, p_rgh, rho.name())
);

while (pimple.correctNonOrthogonal())
{
    fvScalarMatrix p_rghEqn
    (
        p_rghDDtEqn
      - fvm::laplacian(rhorAUf, p_rgh)
    );

    p_rghEqn.solve(mesh.solver(p_rgh.select(pimple.finalInnerIter())));

    if (pimple.finalNonOrthogonalIter())
    {
        // Calculate the conservative fluxes
        phi = phiHbyA + p_rghEqn.flux();

        // Explicitly relax pressure for momentum corrector
        p_rgh.relax();

        // Correct the momentum source with the pressure gradient flux
        // calculated from the relaxed pressure
        U =
            cellMask*
            (
                HbyA + rAU*fvc::reconstruct((phig + p_rghEqn.flux())/rhorAUf)
            );
        U.correctBoundaryConditions();
        fvOptions.correct(U);
        K = 0.5*magSqr(U);
    }
}

p = p_rgh + rho*gh;

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

if (p_rgh.needReference())
{
    if (!compressible)
    {
        p += dimensionedScalar
        (
            "p",
            p.dimensions(),
            pRefValue - getRefCellValue(p, pRefCell)
        );
    }
    else
    {
        p += (initialMass - fvc::domainIntegrate(psi*p))
            /compressibility;
        thermo.correctRho(psi*p - psip0);
        rho = thermo.rho();
        p_rgh = p - rho*gh;
    }
}
else
{
    thermo.correctRho(psi*p - psip0);
}

rho = thermo.rho();

{
     fvc::correctRhoUf(rhoUf, rho, U, phi);
}

if (thermo.dpdt())
{
    dpdt = fvc::ddt(p);

    if (mesh.moving())
    {
        dpdt -= fvc::div(fvc::meshPhi(rho, U), p);
    }
}

surfaceScalarField faceMask
(
    localMin<scalar>(mesh).interpolate(cellMask)
);
phi *= faceMask;