Fluid dynamics of diving wedges

TL;DR

This study investigates the fluid dynamics of diving wedges, analyzing impact forces, splash evolution, and cavity shapes, revealing how wedge angle influences impact severity and splash behavior, with implications for engineering and biological applications.

Contribution

It provides experimental characterization and a new splash model considering gravity, surface tension, and aerodynamics, advancing understanding of water entry dynamics for various wedge geometries.

Findings

Smaller impact forces with decreasing wedge angle.

Splash shape is independent of entry velocity at short times.

A model shows splash shape is dominated by air suction and surface tension.

Abstract

Diving induces large pressures during water entry, accompanied by the creation of cavity and water splash ejected from the free water surface. To minimize impact forces, divers streamline their shape at impact. Here, we investigate the impact forces and splash evolution of diving wedges as a function of the wedge opening angle. A gradual transition from impactful to smooth entry is observed as the wedge angle decreases. After submersion, diving wedges experience significantly smaller drag forces (two-fold smaller) than immersed wedges. Our experimental findings compare favorably with existing force models upon the introduction of empirically-based corrections. We experimentally characterize the shapes of the cavity and splash created by the wedge and find that they are independent of the entry velocity at short times, but that the splash exhibits distinct variations in shape at later times. We propose a one-dimensional model of the splash that takes into account gravity, surface tension and aerodynamics forces. The model shows, in conjunction with experimental data, that the splash shape is dominated by the interplay between a destabilizing Venturi-suction force due to air rushing between the splash and the water surface and a stabilizing force due to surface tension. Taken together, these findings could direct future research aimed at understanding and combining the mechanisms underlying all stages of water entry in application to engineering and bio-related problems, including naval engineering, disease spreading or platform diving.