Asymmetric cavity evolution mechanisms in high-speed vertical water entry under wall confinement

The evolution of the cavity during water entry is critical to the motion stability of the impacting body. Although numerous studies have investigated this process, most have focused on open water conditions. Consequently, the effects of wall confinement—such as those found in ice holes, near reefs, or within liquid-filled tanks—on cavity dynamics remain limited. This study employed numerical simulations to examine vertical water entry at various wall distances. The numerical method was validated against experimental data and theoretical predictions of transient cavity dynamics, yielding satisfactory accuracy and convergence. The results indicated that wall effects introduced notable temporal asymmetry between cavity expansion and contraction phases. In deep water regions, expansion time was shorter than contraction time under far-wall conditions, whereas the opposite trend was observed under near-wall conditions. Quantitative analysis revealed that near-wall effects could increase the dimensionless expansion time by up to 4.5 times, thereby intensifying temporal asymmetry. Flow field analysis further demonstrated that the near-wall effect reduced the adverse pressure gradient during cavity expansion in deep water regions, which decreased the negative work required to overcome the adverse pressure gradient. Consequently, the maximum cavity diameter increased, and the expansion phase was prolonged.