Topology and cavitation number characteristics of the gaseous jet-induced tail cavity under co-flow

The tail cavity as induced by submerged gaseous jets on the bottom of axisymmetric vehicles is studied in a water tunnel over Froude numbers, which denote co-flow velocities, between 4.8 < Fr < 16.0, and the jet stagnation to ambient pressure ratio in a convergent-divergent nozzle between 1.7 < p0/p∞ < 14.5. The shadowgraph topology of the induced tail cavity falls into three consecutive categories on the regime map: intact cavity, partially broken cavity (PBC), and pulsating foamy cavity. Both the Fr and p0/p∞ are essential drivers for the topology and length of the tail cavity within the current scope. The length of PBC holds a logarithmic relationship to p0/p∞. The fluctuation intensity of the cavitation number is under heavy influence from Fr and p0/p∞ and is regarded as a direct and reliable measurement of jet/closure interaction intensity. Under high Fr, the Rayleigh-Taylor instability is dominant at the cavity surface, which leads to a significant amount of bubble shedding and adds to the total cavity gas leakage. From the perspective of the vehicle, the characteristics of its bottom pressure depend on the cavity regime. The characteristics of jet-induced tail cavity established in the presented study should be helpful for the design and control of submarine vehicles propelled by rockets and supersonic jets.