Mechanism of load reduction in a bottom-cavity wedge during free-fall water entry

This study investigates the air–water flow dynamics and impact load characteristics of a wedge during free fall water entry in calm conditions using a combination of experimental and numerical methods. The load reduction mechanism and hydrodynamic regulation effects of a bottom cavity structure are clarified. Results show that the cavity reduces the peak impact load by decreasing the effective wetted area, physically disrupting the continuous bottom high-pressure region, and redirecting a portion of the incoming flow into the cavity to form an axial jet. Dimensional analysis reveals the influence of the Froude number (Fr): as Fr increases, the effect of gravity on the flow gradually diminishes, and the flow becomes increasingly dominated by inertial effects. Consequently, the peak drag coefficient decreases monotonically and eventually stabilizes, and the flow exhibits self-similar behavior. The cavity demonstrates a stable load reduction capability, with the load reduction ratio ranging from 14.63% to 18.18%. By incorporating three-dimensional effects, a quantitative relationship between the load reduction ratio and a correction coefficient is established. Furthermore, a predictive model for the load reduction ratio is developed based on the morphology of the high-pressure region, using a relative eccentricity parameter to quantify its asymmetry. These findings provide a theoretical foundation for predicting hydrodynamic loads and designing passive load reduction strategies for wedges and related engineering structures.