The physical structure of high-pressure supersonic gas jets flowing from circular vents

A puncture in the wall of a high pressure gas reservoir leads to a supersonic jet that is associated with many astrophysical, planetary and aerodynamical phenomena, from radio galaxies to volcanic plumes and rockets. We undertake a systematic numerical analysis of a range of different physical parameters focusing on jet pressures exceeding that of its surroundings. We take a particular interest in the first shock generated by the jet, known as the stand off shock, as these are the brightest and easiest to detect in observation. We have shown there is a relationship where the location of the stand off shock not only depends on the overpressure but also on density through a feedback process and we have defined laws for this. We conclude that even steady uniform outflows will rapidly evolve into one of three distinct flow patterns, taking the form of turbulent plumes at high over-pressures and regular oscillations at low over-pressures. We also explore how energy is transferred into the environment as over-pressured jets are thought to contribute to the regulation of star and galaxy formation through the generation of noise and screeching.