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Supersonic/Initial Gauge Pressure Problem

    • Alex Tharpe

      Hey all,

      I'm a graduate student trying to simulate NOx formation jet engine in-flight. I'm only simulating the downstream power turbine, and I've already figured out how to implement the turbine rotation and NOx chemistry. I'm wanting to use the turbine inlet mass flow and stagnation properties that other students on the project have calculated for the jet's power system as the inlet for my power turbine simulation. The pressure outlet inputs correspond to the atmospheric properties at a given altitude.

      There's a formula that I'm using that relates mass flow to stagnation temperature and pressure, area, specific heat ratio, and Mach number. I'm solving for Mach number to get the static properties to use in the inlet Boundary Conditions. The issue that I'm having is that because the Mach number is most likely subsonic, the pressure inlet or mass flow that I'm using won't keep the static properties and/or mass flow that corresponds to the subsonic Mach number that I hand-calculated and other values are instead in their place when the simulation ends.

      A couple of questions:
      - When Fluent ignores the Supersonic/Initial Gauge Pressure when the flow is subsonic, how does it calculate the values at the inlet that it ultimately concludes with?
      - Keeping in mind that I haven't had an advanced fluids class at this point, what is the logic in Fluent ignoring subsonic static pressure when in a class such as Gas Dynamics the static properties at the inlet and outlet are vital to the problem solution?

      Any clarification and workarounds for this situation would be greatly appreciated.

    • Federico Alzamora Previtali
      Ansys Employee

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