Rob
Ansys Employee

You don't specify a mass flow on a velocity inlet, you set the velocity. In which case you get that velocity value on all surfaces in that boundary condition. 

For a mass flow inlet you'll split the mass flow over all of the surfaces. 

As an example. If you have four separate surfaces in one bc:

  • For a velocity boundary you could easily have four times as much mass as you expect (total).
  • For a mass flow boundary each surface would receive a quarter of the total. 

 

Best bet is to build an example and see for your self.