Mixing with free surface
 

Hi
I have a problem of a mixing tank with free surface which diverges after 15 iterations.
My problem is a simple cylindrical tank of 6m in diameter and 18m high. the tank has two inlets and two outlets at elevation of 1m that mixing two water streams and extract water from two different outlets. the water height in the tank is 5m and rest of the tank is air above the water. I used VOF model in cfx. above the tank, there is a hole that keeps the air pressure above the water atmospheric. I set the inlet and outlet mass flow rates in a way that the total mass balance is zero. I solved the problem as steady state and initially used an expression of WaterHt=if(y<6 [m],1,0) as initial value. My simulation runs for 15 iterations and then it diverges. i do not understand what I did wrong. I am new in the two phase simulation and spent a long time studying VOF modeling in CFX.
I would be grateful if someone can help me on solving this problem.
Regards

How are you defining you inlets and outlets? Does the surface really affect the flow, meaning can you just do single phase?