Study on quasi-two-dimensional submerged vertical over-expanded supersonic jets

Quasi-two-dimensional submerged vertical over-expanded supersonic jets were studied experimentally and numerically. The gas-jet flow patterns under over-expanded conditions were recorded at real time by a high-speed camera at the rate of 1000 frames/s. The development process of supersonic gas jets and the process of the instable flow pattern were visualized clearly. The pure gas flow field inside and outside the Laval nozzle used in the experiment was numerically simulated by FLUENT, and results dedicate a complex shock wave region existing out of the nozzle exit. The simulation results are instrumental in understanding the unstable pattern of submerged vertical supersonic jet flow as an aided reference. The experimental and simulation results indicate that, the frequency of back-attack will be reduced at the operating conditions of relatively small mass flow and a high Mach-number, and this is proved by the discovery of quasi-back-attack phenomenon. The finding in the paper provides an available theoretical reference for weakening or eliminating the cavitation erosion in engineering application field.