In this research, an experimental system that couples the supercavity and the tail jet was established, aiming at exploring on the cavity instability mechanism. Both high pressure gas tank and solid rocket motor were used to generate the tail jet. The model shape and the jet rate were all varied to investigate different flow patterns. Experiments for the cold gas jet were first carried out, obtaining the variation of the flow pattern with the jet strength and the relative location. With strong jet intensity, the supercavity could lose instability by the re-entrained liquid jet, which was mainly generated by the back attack of the tail jet. Furthermore, the effect of the rearward facing step structure on the cavity instability was investigated, validating that the re-entrained jet could be successfully suppressed by this structure. However, when the cavity contacts with the wall surface, another kind of instability induced by cavity/body interaction could be induced. Subsequently, experiments were carried out for the hot jet generated by the solid rocket motor. A new kind of cavity instability at the moment of ignition was observed. The cavity shrinking and collapse processes were compared between different cases. When the ignition process finished, the hot jet transited into a continuous free expansion mode with weak entrainment of liquid. Finally, the cavity instability mechanisms were summarized and compared. Spectral analysis was carried out for different cases. An obvious larger Strouhal number exists for the pressure pulse induced instability.

The objective of this paper is to numerically investigate the three-dimensional side loads and associated flow physics of a conical nozzle during the fire-in-the-hole staging event of the multistage rocket. The transient flow in nozzle is examined by a three-dimensional time-accurate numerical method with the start-up process of the upper-stage motor and the prescribed nominal separating motion of the lower stage. The impacts of asymmetric lateral motion due to non-nominal staging movement on the nozzle side loads are also numerically analyzed. These motion deviations include the relative angle between axes of two stages, relative lateral displacement between two stages, superposition of relative angle with relative lateral displacement, and angle of thrust vector control. As presented in the simulation results, the flow separation in nozzle is significantly prolonged and intensified by the obstruction of the lower stage. With the location of shockwave reflection approaching the dome of lower stag...