[myself]

Hi Folks,

one question regarding the changes from OF 1.6 to 1.7 in the buoyantBoussinesq(Piso/Pimple)Foam solver. I think the implementation of splitting the pressure according to p = p_rgh + rho*g.x is not fully correct.

The pressure equation in OF 1.7 seems OK, since in the Rhie-Chow formulation the contributions from the static pressure cancel and we are left with:

phi = (fvc::interpolate(U) & mesh.Sf())
        + fvc::ddtPhiCorr(rUA, U, phi);

surfaceScalarField buoyancyPhi = rUAf*ghf*fvc::snGrad(rhok)*mesh.magSf();
phi -= buoyancyPhi;

instead of

 surfaceScalarField phiU
    (
        (fvc::interpolate(U) & mesh.Sf())
      + fvc::ddtPhiCorr(rUA, U, phi)
    );

    phi = phiU + rUAf*fvc::interpolate(rhok)*(g & mesh.Sf());

in OF 1.6.

In contrast, in the momentum equation the term for the buoyancy ( and gravity) force has changed from (OF 1.6)

fvc::reconstruct( ...
                    fvc::interpolate(rhok)*(g & mesh.Sf())  ...)

to (OF 1.7)

fvc::reconstruct( ...
  - ghf*fvc::snGrad(rhok)*mesh.magSf() ...)

These are two different expressions: F ~ rhok * g vs. F ~ gradT * g.h

Is this really a bug or do I miss some point? Thanks for any comment...

Regards,
Jan


Edit:
In the meantime I am pretty sure this is indeed a bug and I submitted a bugreport.

Edit:
Problem is solved. This bug was fixed a few days ago in the git repository.

[Anne Lincke]

Dear Foamers,
can someone explain me why OF1.7 still uses

- ghf*fvc::snGrad(rhok)*mesh.magSf()

instead of

fvc::interpolate(rhok)*(g & mesh.Sf())

as it was used in the previous version OF1.6.
I do not understand why the gradient of the densitiy is used while in the equations I find in literature it has to be just the densitiy multiplied with the constant g.
Can someone help me? Is this still a bug or do I overlook something?

[Anne Lincke]

For the answer see

http://www.cfd-online.com/Forums/ope...implefoam.html

[makaveli_lcf]

Originally Posted by myself

Hi Folks,

one question regarding the changes from OF 1.6 to 1.7 in the buoyantBoussinesq(Piso/Pimple)Foam solver. I think the implementation of splitting the pressure according to p = p_rgh + rho*g.x is not fully correct.

The pressure equation in OF 1.7 seems OK, since in the Rhie-Chow formulation the contributions from the static pressure cancel and we are left with:

phi = (fvc::interpolate(U) & mesh.Sf())
        + fvc::ddtPhiCorr(rUA, U, phi);

surfaceScalarField buoyancyPhi = rUAf*ghf*fvc::snGrad(rhok)*mesh.magSf();
phi -= buoyancyPhi;

instead of

 surfaceScalarField phiU
    (
        (fvc::interpolate(U) & mesh.Sf())
      + fvc::ddtPhiCorr(rUA, U, phi)
    );

    phi = phiU + rUAf*fvc::interpolate(rhok)*(g & mesh.Sf());

in OF 1.6.

In contrast, in the momentum equation the term for the buoyancy ( and gravity) force has changed from (OF 1.6)

fvc::reconstruct( ...
                    fvc::interpolate(rhok)*(g & mesh.Sf())  ...)

to (OF 1.7)

fvc::reconstruct( ...
  - ghf*fvc::snGrad(rhok)*mesh.magSf() ...)

These are two different expressions: F ~ rhok * g vs. F ~ gradT * g.h

Is this really a bug or do I miss some point? Thanks for any comment...

Regards,
Jan


Edit:
In the meantime I am pretty sure this is indeed a bug and I submitted a bugreport.

Edit:
Problem is solved. This bug was fixed a few days ago in the git repository.

Hallo Jan!

You wrote that the term in OF17 was formulated with an error, am I correct?

But still if i look OF171 (Ubuntu package installed via apt-get):

            UEqn
         ==
            fvc::reconstruct
            (
                (
                  - ghf*fvc::snGrad(rhok)
                  - fvc::snGrad(p_rgh)
                )*mesh.magSf()
            )

Is this term still there? And how it should be?

Regards,
Alexander