Analysis of confined cavity evolution and related pressure created by hydrodynamic ram

Abstract

The impact of high-velocity projectiles on fluid-filled containers can induce the hydrodynamic ram (HRAM) effect, leading to the creation of a cavity within the fluid. The evolution of this cavity is subject to the constraints imposed by the container. This study aims to investigate the decay of projectile velocity and the development of confined HRAM cavities using a combined approach involving experimental and analytical methods. In contrast to existing research, this study accounts for the varying projectile velocities during different HRAM phases. Furthermore, enhancements have been introduced to the established cavity model, encompassing refinements in pressure differentials both inside and outside the cavity, alongside adjustments to the radial extent of liquid disturbance. The effectiveness of these refinements has been substantiated through experimental evidence. The findings illuminate two prominent constraint effects exerted by the container on the dynamics of HRAM cavities. Primarily, it accentuates the disparity in HRAM cavity pressures between the interior and exterior environments, and this pressure differential follows an exponential decay with distance. Secondly, it profoundly influences the flow of liquid near the wall, resulting in a considerably slower contraction of the cavity near the wall compared to its expansion phase. The evolution of the HRAM cavity is observed to manifest across three distinct stages: the unconfined cavity expansion stage, the partial cavity confinement stage, and the full cavity confinement stage.