Slug flow in a vertical pipe

Abe

I am urgently supposed to model air-water slug flow through a vertical pipe of diameter 25.4 mm using fluent.The pipe is partially immersed in a stagnant water and air from compressor is being injected at small distance from bottom and water is being sucked at the bottom. I have tried using VOF method but the solution diverges and gives me error. Would you help me how to handle this problem especially how to set phases at each inlet and outlet,b/cs or how to model Taylor bubble rising in a vertical tube filled with water.

Thanks a lot