plz help-boundary in VOF

garima chaudhary

hi all

I have a very urgent n quick query which is really uphelding my work a lot. I am working wid the VOF model in a rotor zone of a centrifugal contactor and hence simulating it to know the fluid dynamics in it. One of my boundary conditions is pressure_outlet. There I need to specify the backflow volume fraction for the secondary phase. my system consists of water and air where air is primary phase. My query is that what does this backflow volume fraction means ? I am not clear about it. see at any boundary, fluid can leave or enter or while leaving a part of it can come back into the domain, so i want to ask that does the backflow volume fraction means the fraction of one phase in the amount of total fluid which is whether coming back into the domain or leaving at the boundary. or does this term represent the volume fraction of a phase which is coming back into domain while leaving. please clearly define what does this term actually mean ?

plz try to help me out in this asap.

regards garima