Fluid dynamics of diving wedges

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.

Air cavity deformation by single jointed diver model entry bodies

“…First, it will create a splash crown with water jetting up and around the solid body. Frontal geometry causes significant changes to initial splash [5][6][7]. As seen in Kim and Park (2019) [8] and Bodily et al (2014) [6] the splash crown forms against the walls of a slender axisymmetric body.…”

“…The upper cavity connects to the atmosphere and a lower cavity follows the body. Large air cavities are often pinned to the edge of cones and wedges and experience deep seal depending on a variety of factors [5,10]. When deep seal does occur, the sudden change generates ripples that travel along the lower cavity at a velocity closely related to the impact velocity [10,11].…”