On Air-Cavity Formation during Water Entry of Flexible Wedges

Elastic bodies entering water might experience fluid–structure interaction phenomena introduced by the mutual interaction between structural deformation and fluid motion. Cavity formation, often misleadingly named cavitation, is one of these. This work presents the results of an experimental investigation on the water entry of deformable wedges impacting a quiescent water surface with pure vertical velocity in free fall. The experimental campaign is conducted on flexible wedges parametrically varying the flexural stiffness, deadrise angle, and drop height. It is found that, under given experimental conditions, cavity pockets form beneath the wedge. Their generation mechanism might be ascribed to a differential between structural and fluid velocities, which is introduced by structural vibrations. Results show that the impact force during water entry of stiff wedges are always opposing gravity, while, in case flexible wedges temporarily reverse their direction, with the body that is being sucked into the water within the time frame between the cavity formation and its collapse. Severe impact might also generate a series of cavity generation and collapses.