Influence of pre-induced multiphase flow field on the cavity evolution and hydrodynamic load of a moving body during water entry

Numerous examples demonstrate that a leading body moving in tandem within a single-phase flow field can reduce the drag on a trailing body by disturbing the flow field. Inspired by this, and addressing the challenge of suppressing impact loads during water entry in multiphase flows, this study proposes a strategy in which a leading body is introduced ahead of the main body to modulate the pre-induced flow field, thereby reducing the impact loads on the main body. High-speed photography and inertial measurement units were employed to conduct vertical water entry experiment. The study investigated the effects of the multiphase flow field induced by a leading body with four distinct head shapes on the trailing main body under low Froude number conditions. Based on the interaction characteristics between the main body and the pre-induced multiphase flow field, seven tandem water entry modes were defined. The transition mechanisms of cavity seal modes were extended from a single body to multiple bodies, based on the Bond number and Weber number. Regression models were established for the load reduction rate η and the square root of the ratio between the release heights of the main body and the leading body (H / h)^1/2. When (H / h)^1/2≳1.30, η for flat, conical, and truncated-conical heads approached 95%, demonstrating excellent load reduction performance. This study provides new insights into improving the water entry impact environment of underwater equipment.