Urgent!!! Co-current flow in bubble column

anji

Dear all, I am working on a problem for which I have to simulate a bubble column opearating in a co-cuurent mode. I am using axisymmetric, unsteady, k-e,euler solver for this problem. At the inlet edge I have defined velocity inlet BC (ul=3cm/s ,k=0.1,e=0.25 and ug= 7 cm/s) and at outlet pressure outlet BC. Initialisation from inlet. With these conditions I am getting reversed flow at presure outlet.I don't have much knowledge on boundary conidtions of this problem( volume fraction of gas at inlet and backflow onditions at oulet) and also on intial conditions. please help me to solve this problem. I will greatly appreciate your help... Thank you, Sincerely, anji