Tail cavity pressure pulsation characteristics under varying ventilation pressure and duration

The development of the tail cavity is a key factor influencing motion stability and structural reliability during water exit, making the study of dynamic pressure evolution crucial. In a high-pressure gas launch experiment, the dynamic pressure evolution of the tail cavity was investigated under varying ventilation pressures and durations, revealing three typical pulsating flow patterns: first order, second order, and third order. Additionally, the impact of pulsation frequency, relative cavitation number, and relative Froude number on the tail cavity's evolution was examined, with underlying mechanisms explained. The results show that the internal and external pressure differences, coiling suction effect, and differences in medium inertial suppression forces are the primary contributors to wake surges. Notably, changes in pulsation order result in abrupt shifts in the principal frequency of pressure pulsation. The pulsation frequency is positively correlated with ventilation pressure and negatively correlated with ventilation duration. Based on the relative Froude number, the tail cavity's dynamic evolution was classified into three states under constant ventilation pressure: the average state, the gas leakage and shedding state, and the post-shedding growth state. Tail cavity shedding was further classified as stable or unstable, depending on the aeration parameters. The relative cavitation number of the tail cavity in the third-order pulsation ranged from 0.2 to 1.4. As the pulsation order decreases, the relative cavitation number at the initial and water-exit moments increases.