bubble column reactor
 

Dear all
I want to simulate a 2D bubble column reactor (10cm x 30cm). there is an inlet at the bottom (a sparger with a hole which its diameter is 1 cm) and a free surface on the top. I use velocity inlet for air inlet (0.1m/s), pressure outlet for the top, I use VOF and patch water in the 2 phase system (air-water). I think time step size (0.001s) and mesh size (1mm)are OK but the problem is that after some time steps (flow time around 0.04s), velocity distribution looks terrible as it increases around the inlet (it goes up to 1.1m/s). Does any have any suggestions to solve this problem?
Thanks