I wonder why we use velocity inlet boundaries to incompressible flows, but mass flow at inlet for compressible flows? Could anybody guide me???

I guess that: for incompressible flow the information of pressure in each cell is known, because it can't vary with time due to the incompressible flow itself. So we specify only the velocity at the inflet of the model, because density is know from (p,T) and so is known the mass flux. That's not true in the case of compressible flow...there we need to specify the mass flux through the inlet boundary, to define the velocity of the fluid and the density entering the model

Hi andrea, one other query. For comp flow, if we specify velocity also then also it can calculate mass flux. right? then why mass flux?