Effect of explosion time on water entry of vehicle in underwater explosion environment

Underwater explosions create complex flow fields that significantly affect the water-entry behavior of trans-media vehicles, leading to strong fluid–structure interactions. Research on such coupled multi-physics processes remains challenging and relatively scarce. In this study, a numerical methodology based on the coupled Eulerian–Lagrangian (CEL) method is developed to simulate the water entry of a vehicle subjected to an underwater explosion. An improved equation of state is adopted to capture multiphase flow under extreme conditions. By superimposing the explosion pressure field, the impact of explosion time on the water-entry dynamics is systematically investigated. The cavity evolution during vertical water entry is examined, revealing the mechanisms by which shock waves govern cavity dynamics. Results indicate that shockwaves reshape the water-entry cavity into a nested structure with noticeable contraction and attenuation. Early shockwaves trigger earlier cavity pinch-off and shorten cavity length, while delayed shockwaves postpone pinch-off and extend the cavity. Shockwave disturbances also weaken the drag reduction capability of the cavity. Earlier explosions exacerbate these effects, causing rapid velocity decay, lateral displacement, and counterclockwise rotation. The study provides a reliable CEL-based framework for simulating such multi-physics interactions, offering insight into interaction mechanisms between underwater explosions and trans-media vehicle dynamics during water entry.