**If I give mass flow rate, temperatures, pressure data from experiment for flow entering a pipe, I noticed the mass flow rate inlet boundary condition only applies the temperature/pressure if the flow is supersonic. What would be the best method to apply these types of inlet boundary conditions to a compressible gas type problem?**

For compressible flows, you can apply either a pressure inlet or mass flow inlet BC. Here's what happens in each case:

Pressure Inlet:

The total pressure and total temperature are known, along with the flow direction, turbulence variables and other scalars. For ** subsonic flow ** the static pressure at the inlet boundary is obtained (predicted) from the CFD solution. You can then determine the Mach number, velocity magnitude, static density and temperature, and mass flow rate. So the mass flow rate is a result of the computation since total pressure is fixed.

The total pressure and total temperature are known, along with the flow direction, turbulence variables and other scalars. For ** subsonic flow ** the static pressure at the inlet boundary is obtained (predicted) from the CFD solution. You can then determine the Mach number, velocity magnitude, static density and temperature, and mass flow rate. So the mass flow rate is a result of the computation since total pressure is fixed.

Mass Flow Inlet:

The mass flow and total temperature are known, along with the flow direction, turbulence variables and other scalars. For ** subsonic flow **, again the static pressure is obtained from the CFD solution. Using the static pressure, you can derive an equation for Mach number knowing mass flow rate and total temperature, and thus obtain total pressure. Therefore, in this case the total pressure is derived from the

CFD solution.

The mass flow and total temperature are known, along with the flow direction, turbulence variables and other scalars. For ** subsonic flow **, again the static pressure is obtained from the CFD solution. Using the static pressure, you can derive an equation for Mach number knowing mass flow rate and total temperature, and thus obtain total pressure. Therefore, in this case the total pressure is derived from the

CFD solution.

Refer to this document for more details.