Thanks for the reply. Let me further explain my problem. Actually I'm currently using this mesh. I want to make structured mesh to reduce computations.

These are the inlet face sections (1mm diameter each) from which air is injected into the water column. From different papers I have read that "they do not model these sections but create mass point source instead". I shall be very thankful if you guide from ab initio as these things are new to me or please suggest me any guide source from where I can follow complete steps. Thank you again.