1 Reply Latest reply on Sep 11, 2014 7:42 PM by Jared Conway

    Unknown outlet BC for internal transient compressible supersonic flow

    Jimmy Welch

      I am having difficulty understanding how to set boundary conditions for a model. The first goal is to find the pressure with respect to time of the outlet, for which boundary conditions are unknown. Transient inlet boundary conditions are known for pressure and temperature. Velocity is also known but this is a bit of a wildcard because there is a projectile that is being forced in front of the expanding gas (air).  The projectile velocity dictates the Z-velocity (Vz) of the expanding gas, however the X & Y velocities (Vx, Vy), which denote the velocity of the expanding gas normal to the projectile flight path, are Vx = Vy = 4Vz, at the inlet.


      Initial conditions are as follows:




      3000 psia14.7 psia
      Temperature2500 F70 F
      Z-Velocity850 ft/s0 ft/s
      X-Velocity3400 ft/s0 ft/s
      Y-Velocity3400 ft/s0 ft/s


      As stated initially, transient boundary conditions (dependency) of each of these parameters at the inlet are known, and unknown at the outlet.


      Does anyone have any suggestions/experience with this sort of situation?

        • Re: Unknown outlet BC for internal transient compressible supersonic flow
          Jared Conway

          there is no such thing as an "unknown" at the outlet, you would need to define some kind of place holder


          generally problems are broken into 2 types


          flow at the inlet > pressure at outlet, determine pressure at inlet

          pressure at inlet and outlet, determine flow through the system


          i would recommend you start with a really simple problem like a pipe flow problem to get the hang of things

          also make sure that it is steady state

          then move to transient

          then move to your more complicated model