Tail cavity kinematic characteristics and in-tube pressure behavior induced by pressure difference and pressure ratio

The development of the tail cavity is recognized as a critical factor affecting motion stability during vehicle water-exit. Investigations on tail cavity evolution and in-tube pressure characteristics under varying conditions are essential for water-exit studies. Based on experimental studies of high-pressure gas-ejected vehicles during water-exit, research was conducted on free water-exit tail cavity evolution and in-tube pressure characteristics under varying front pressure, pressure difference, and pressure ratio conditions. The pull-off formation mechanism of the tail cavity was revealed to be jointly influenced by the entrainment effects of starting vortices and necking effects during vehicle axial motion. Results indicate that tail cavity development was found to be influenced by two competing mechanisms: reentrant jet suppression effects and environmental pressure enhancement effects. Specifically, increased front pressure was observed to elevate vehicle velocity while intensifying in-tube pressure oscillations. Vehicle velocity showed a negative correlation with pressure ratio but a positive correlation with pressure difference. A positive correlation was also identified with gas average flow velocity in the gas chamber. When either pressure difference or pressure ratio was maintained constant, equivalent changes in pressure difference demonstrated a greater impact on vehicle motion velocity compared to pressure ratio adjustments.