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:

Variable | Inlet | Outlet |
---|---|---|

Pressure | 3000 psia | 14.7 psia |

Temperature | 2500 F | 70 F |

Z-Velocity | 850 ft/s | 0 ft/s |

X-Velocity | 3400 ft/s | 0 ft/s |

Y-Velocity | 3400 ft/s | 0 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?

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