multiphase model and drag law

Yasmail AKARIOUH

hi.

I wish study a multiphase flow( mixture model ni Fluent) : air is the principale phase, water is the secondary. the droplets diameter is average 1mm. the model is not convergent, indeed there is a matter with the turbulent viscosity. after reading Fluent documentation, I found that the drag law ( Schiller-Naumann law)for drag coefficient calculation is not available for a model where bubble are larger than 0.1mm. I have desactivate this law ( interactions between phases)and the model converge. However, it's physically wrong, because droplets aren't constrained by the flow.

Do you have some ideas which explain the probleme of drag law?