entrainment boundary
 

I have been using CFX for the past year and now I am back to Fluent 6.2. CFX has a B.C. called "entrainment boundary", where fluid (in my case air) can be sucked in and out depening on the local conditions. Is there something equivalent in Fluent. I have been using pressure inlet and outlet boundaries but it keeps whinging about reversed flow.

I am working on an turbomachines type problem where a rotor produces a radial flow field. While air is capable of being sucked into and pushed out of the domain by the rotor, the mass flow rate/velocity of the inlets and outlets is not known.

Any help appreciated.