Physical Review Fluids

Wedge water entry serves as a key model to understand phenomena like high-speed craft slamming, seaplane landings, and diving aquatic birds. In this paper, wedge water entry experiments and simulations are used to examine how hydrodynamic loads, structural deflection, water contact lines, and rigid body motions are influenced by changes in the flexural rigidity of the wedge’s bottom panels. Preliminary findings indicate that the nondimensionalized spray root position and velocity versus time collapse despite significant variations in the panel’s flexural rigidity values (see figure for velocity curves). The study provides insights for future research and model improvements in water entry dynamics.

A radially symmetric sinusoidal wave structure is imprinted on an impacting circular disk to modulate the way the disk forces the free water surface. The experiments support the argument that the surface elevation around the disk edge prior to impact is an instability of the Kelvin-Helmholtz type, as the free surface resonates when the forcing wavelength on the disk is close to the most unstable wavelength predicted by theory. Besides, our wave-structured disk is also found to promote gradual inertial wetting of the impacting surface to effectively retain the entrapped air pocket (as shown in the figure), which, in turn, mitigates the peak impact force.

Elastic hoops can jump on water by harnessing the reaction force from water’s form drag, much like fishing spiders. These artificial jumpers allow us to mathematically understand the drag-based water jumps, which can achieve greater velocities than the surface-tension-based jumps seen in water striders and springtails.

Our study demonstrates how a child’s rubber popper, when snapped underwater, creates fascinating cavitation bubble formations. By using high-speed imaging, we explore the fluid mechanics behind the formation and collapse of these cavitation bubbles due to pressure changes. Interestingly, the cavitation bubble forms a toroidal shape rather than a spherical one, with a lifespan shorter than that of a spherical bubble with the same outer radius. This research illuminates the intricate interplay between bubble dynamics within a thin gap and material elasticity.

While droplet impact on liquid pools is well studied for Newtonian fluids, particle suspensions introduce complex non-Newtonian dynamics. This work experimentally identifies five distinct impact regimes for cornstarch suspension droplets, revealing unique phenomena like “wrapped bubbles” and impact-induced jamming that are absent in simple fluids. Through an energy balance analysis, the authors demonstrate that these behaviors are dictated by a direct competition between pool cavity dynamics and suspension rheology. The resulting transition boundaries offer practical guidance for engineering applications like 3D printing.