Can someone help me: VOF + MRF

multiphase-flow

I am modeling air-water flow pattern in a stirring tank. Since there are pitch blades and rushton blades in the tank, I select Multiple Rotating Reference Frames (MRF). I simulated single water phase flow first, it works fine. The inner fluid is moving frame and outer fluid is stationary (interior face between two fluids). I got good results. Now I am adding gas phase into picture. So I turn on the VOF model with MRF, but all residuals increase to 1E+5 with using 0.0001 second time step size. Is it problem with initial patch or other problem? When I patch the region for gas phase, I saw both inner fluid (refernce frame) and outer fluid. Should I patch gas phase in both regions or separtely? Thank you in advance?