Truncated cone-shaped cylinder water entry: Dynamics and multiphase flow

Computational Fluid Dynamics (CFD) simulations were performed to study the water entry of a cylinder with an asymmetric head, i.e., a truncated cone-shaped cylinder, in which the head cavity formation, cylinder rotation, and tail cavity generation can be observed. The results demonstrate that this unique head design effectively mitigates stress concentration commonly observed in flat-head configurations. Unlike symmetric bodies, the asymmetric head generates a counterclockwise pitching moment upon water entry, leading to asymmetric cavity evolution and the subsequent formation of a more complex dual-cavity system following tail impact on the cavity wall. Reverse water entry studies indicate that increasing the entry angle significantly enhances cavity stability. The evolution of high-pressure and high-velocity regions in the flow field is influenced by the initial collisions, tail impacts, and cavity closure processes. Notably, this study reveals a critical phenomenon: when the water entry angle complements the head's truncated angle, the head surface aligns nearly parallel to the free surface at impact, shifting the impact mode from "piercing" to "slamming." This transition results in a substantial increase in initial impact pressure—approximately three times greater than that observed at other angles. Furthermore, both the cavity closure patterns and pressure characteristics of the cylinder vary with water entry angles, particularly during the initial stage of entry.