Transient dynamic analysis for the submerged gas jet in flowing water

Submerged gas jet is commonly encountered in underwater cutting, underwater jet-propulsion, liquid metal mixing and other applications. In this paper the transient dynamics for the high-speed submerged gas jet in a flowing water environment was investigated. The experiments were carried out in an open water tunnel which could achieve high degassing rate. The jetting flow rate was varied from subsonic to sonic state to obtain different flow patterns. A compressible multiphase model using the coupled Level Set with Volume of Fluid (VOF) model was adopted to investigate on the detail flow structure. Three flow patterns including the transparent cavity mode, the cavity-jetting mode and the periodic jetting mode were observed. The predicted gas–liquid interface profiles, as well as the unstable shedding process agreed well with the experimental data. The evolution of the internal vortex structures and the pressure distributions were analyzed in detail, obtaining the transition mechanism between different modes. The main flow characteristics including the cavity length, the penetration length and the shedding frequency were obtained for different cases. It was found out that with the increase of the jetting flow rate, a local smallest penetration length existed at the cavity-jetting mode. The Strouhal number relating to the shedding frequency firstly descends dramatically and then kept in the level of 10−3 at the periodic jetting mode