Researches on the characteristics of structure and thrust of jets underwater with under-expansion

In order to figure out the mechanism about the structure of jets underwater in differ working conditions, a geometrically symmetric model adopted the Volume of Fluid (VOF) multiphase model was utilized to simulate the practical working process. It was drawn that there is a 'quasi-back-attack' in the jets with high Mach number and in under-expansion. Compared with over-expanded jets involving four typical stages, it can be found that the backflow fails to arrive at the wall for the reason that the shock waves, especially in highly expanding flow, stop the fracture of the flow. In addition, the oscillation amplitude of the thrust shows a sharply descend when the 'quasi-back-attack' phenomenon happens, which is attributed to the limited strength of the flow under the influence of shock wave and expanded gas. According to the flow structure simulated in long term, the boundaries of the jets shape are as an inclining straight line.