[sharonyue]

Hello guys,

Right now Im working on buoyant driven force flow. I have a miner confusion about the equations implemented in buoyantPimpleFoam.

We know that:

rho1 = rho0 + psi*(p1-p0)
= rho0 + psi*(p_rgh1 - p_rgh0 + rho1 g h - rho0 g h) // neglected?

But in the code, it is:

rho1 = rho0 + psi*(p_rgh1 - p_rgh0)

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

Anybody knows the reason of neglecting the last two terms?

Thanks


Update：

Its neglected. more info:
http://www.openfoam.org/mantisbt/view.php?id=1772#c5033

[Jost K]

Hi All,

I realize this thread is a bit old and the issue seems to be resolved by now.
However, I have a much related question and since the title of the thread is kept quite broad I hope its okay to post this here:

I'm having trouble understanding what buoyantPimpleFoam's pEqn does with the reference pressure (pRef) in an incompressible case.
The pressure equation is solved setting a reference pressure for p_rgh:

p_rghEqn.setReference
    (
        pRefCell,
        compressible ? getRefCellValue(p_rgh, pRefCell) : pRefValue
    );

(This is pEqn.H line 48-52 [OF-v1812])

This is in line with standard pimpleFoam for the incompressible case.
(okay so far)
But then, after caculating p from p_rgh...

p = p_rgh + rho*gh;

(This is pEqn.H line 73 [OF-v1812])

...they go ahead and change p again (if the reference pressure is used)

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);
}

(This is pEqn.H line 78-101 [OF-v1812])

Why do they do that?
Is pRef meant to be a reference value for p or for p_rgh now?
How can they accept, that p is inconsistent with p_rgh (in the sense that p != p_rgh + rho*gh)? And if that's fine, why did they choose a different path for bouyantSimpeFoam, where they do "p_rgh = p - rho*gh;" afterwards?

I would really appreciate if somebody could explain this to me.

Cheers,
Jost