[RodriguezFatz]

Dear all,

I simulate some tank with air and water (mixture model) where the air rises and leaves at the top and water leaves the tank at the bottom.

When I test my grid with single phase water (and gravity), I get nice straight convergence. What I also tryed is to "play" with operating density in single phase and Fluent seems to have strong convergence issues, if the operating density is not the fluid density (which means that a buoyancy term appears in momentum equation as far as I understand it). However, using the correct density everything is fine, setting operating density to zero causes chaos: "turbulent viscosity limited to..." and divergence.

Now with mixture model activated, the simulation converges nicely as long as gravity is switched off. With gravity switched on, I get the same chaos as in the "single phase - zero operating density" case. That leads me to the assumption that the operating density is the crux of the matter. That is where I am stuck... everything I tryed does not work.

Can anyone help me?