openfoam/applications/solvers/combustion/engineFoam/pEqn.H

rho = thermo.rho();

volScalarField rAU(1.0/UEqn.A());
U = rAU*UEqn.H();

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

    while (pimple.correctNonOrthogonal())
    {
        fvScalarMatrix pEqn
        (
            fvm::ddt(psi, p)
          + fvm::div(phid, p)
          - fvm::laplacian(rho*rAU, p)
        );

        pEqn.solve(mesh.solver(p.select(pimple.finalInnerIter())));

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

    while (pimple.correctNonOrthogonal())
    {
        fvScalarMatrix pEqn
        (
            fvm::ddt(psi, p)
          + fvc::div(phi)
          - fvm::laplacian(rho*rAU, p)
        );

        pEqn.solve(mesh.solver(p.select(pimple.finalInnerIter())));

        if (pimple.finalNonOrthogonalIter())
        {
            phi += pEqn.flux();
        }
    }
}

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

U -= rAU*fvc::grad(p);
U.correctBoundaryConditions();
K = 0.5*magSqr(U);

dpdt = fvc::ddt(p);