On the Effect of Cavity Formation during the Water Entry of Flexible Bodies

Elastic bodies entering the water might experience Fluid-Structure Interaction phenomena introduced by the mutual interaction between the structural deformation and the 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 forms beneath the wedge. Their generation mechanism is found to be ruled by a differential between structural and fluid velocities, which is introduced by the structural vibrations. Results show that the impact force during water entry of stiff bodies is always opposing gravity, while in case of flexible bodies might temporarily reverse its direction, with the body that is being sucked into the water within the time frame between the cavity formation and its collapse. Severe impacts might also generate a series of cavity generation and collapses.