Title: 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.