Varying flowrate for pressure
 

Hello all,

I am Simulating an internal flow using ANSYS Fluent:

Inlet conditions:
The max pressure at the inlet is 30bar
Max flow rate is 0.0004 m3/sec

How should I set this kind of boundary condition?

Thanking you

You can use a pressure inlet to fix the inlet pressure and then pressure outlet with the targeted massflow rate option to also get the flowrate if that is what you are trying to do.

Thank you Lucky Tran for your reply,

when I use with target mass flow of 0.0004 m3/sec and with pressure inlet and pressure outlet boundary conditions.

I got the exit velocity more than the calculated one

Exit mass flow 0.0004 m3/sec
Area of 5.67e-5 m2
velocity should be around 7 m/s but in the simulation result it was 14 m/s

I didn't notice that you had written flowrate with units m^3/s and not massflow. With that being said, I don't know how you specified a massflow rate of 0.0004 m^3/s because that simply is the wrong units. If you put in 0.0004 kg/s then it would make sense that you got the wrong velocity because the density at 30 bar (of whatever your medium is) is unlikely to be 1 kg/m^3.

The BC for a volumetric flowrate is a velocity inlet. Unfortunately, you can't hard fix both velocity and pressure unless the inlet is supersonic for a compressible medium. You'll have to find a workaround. If you are doing a constant density case, then you know the density at the outlet and you can still use the pressure inlet and massflow outlet approach, but you actually do need to put in the right mass flow rate.