Dear all, If the flow is annular flow in a pipe, how can i deal with it in fluent? I am not sure which multiphase model is more appropriate for the problem. I have tried eulerian model and used drag force model of annular flow, but the annular character still can't be simulated. The pipe is a manifold with several branches, if you have ever researched about such subject, can you give me some suggestion? Thank you.

Try VOF. It should resolve the free surface position etc.