[user]

Dear foamers,

I'm struggling with the mass (im)balance of twoPhaseEulerFoam with different boundary conditions. My conclusion is, that there is a mass imbalance when zeroGradient is used as the boundary for p_rgh at the inlet - i.e. it comes more mass out than going in. With fixedFluxPressure at the inlet, everything looks good. In the attached file a test case (a small vertical channel) is included, which can be run with twoPhaseEulerFoam. There are already two logfiles included - one with fixedFluxPressure and one with zeroGradient. From these one can see the mass fluxes at inlet and outlet patches for the phases. There are a lot of discussion about the right / correct / best way to specify the boundary conditions when gravity is considered but I never found statements regarding the imbalance.

Could somebody explain this behavior? I first thought of something like a transient effect, but even after 100 s the mass flux of liquid at the outlet is more than 3 times bigger than at the input. Do I miss something or is my mass flux calculation (alphaRhoPhi) wrong?

I'm using OpenFOAM v2012 / 2112 but this effect can also be reproduced it with multiphaseEulerFoam (OF 9).

Thanks in advance
Ulf

twoPhaseEulerFoam_checkMassBalance.zip