[ata]

Hi FOAMers
can any one tell me fvc::ddtPhiCorr(rUA, U, phi) in icoFoam code is for what?
best regards

[santiagomarquezd]

Hi, take a look of:

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

and

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

Best.

[ata]

Thank you very much

[timaji]

the term Phi in UEqn and PEqn is not exactly the same:
In the UEqn: corrected flux from the previous iteration or timestep,
In the PEqn: mass flux without the pressure contribution.

The term ddtPhiCorr checks for the dimensional units of U and phi to decide what operation has to be performed, and if phi is defined in terms of mass, a division of phi by rho is performed.

This represents a problem in the case of zero density. Such a case cannot happen in single-phase flows, however it might happen in multiphase flows. For example, let's consider a momentum equation in the form

ddt(alpha*rho*U) + div(alpha*rho*U*U) = ...

where alpha is the phase fraction. The equation is then represented in the code as

fvm::ddt(alphaRho, U) + fvm::div(alphaf*phi, U) == ...

being phi = rho_f * (U_f \cdot S). In such a case, if my understanding is correct, one should compute

surfaceScalarField phi =
fvc::interpolate(rho)*(fvc::interpolate(U) & mesh.Sf())
+ fvc::ddtPhiCorr(rUA, rhoAlpha, U, phi)

At this point, since alpha can be zero, ddtPhiCorr will cause a division by zero.

This does not represent a problem in the incompressible case, since the equation can be divided by rho, which leads phi to be a volumetric flux, and ddtPhiCorr would be ddtPhiCorr(rUA, alpha, U, phi). However, if one wants to deal with the compressible case, keeping equations in conservative form, the problem appears.

[alberto]

The problem is known and was reported (I guess you read it since you pasted it :P):

http://www.openfoam.com/mantisbt/view.php?id=169

[timaji]

Originally Posted by alberto

The problem is known and was reported (I guess you read it since you pasted it :P):

http://www.openfoam.com/mantisbt/view.php?id=169

Yes alberto
I referenced to the link you've mentiond in the title of my post!!!

[hawkeye321]

Hi FOAMERS
I have modified SIMPLEFOAM for unsteady flows bu adding ddt(U) to the U matrix. Do I also have to add fvc::ddtPhiCorr in PEqu.H to calculate fluxes? How ignoring this term will affect my results?