Dynamics of water entry

Abstract

Diving induces large pressure 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 wedges entering water 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, the wedge experiences significantly smaller drag forces (two-fold smaller) than immersed wedges. Our experimental findings compare favourably 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 aerodynamic 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.

Repeated evolution of drag reduction at the air–water interface in diving kingfishers

“…Both length and depth also differ between foraging groups, but these patterns were not significant once phylogeny was taken into consideration. Our study aligns with hydrodynamic expectations based on water piercing studies using geometrically perfect cones [12,14]. Diving species have beaks of lower base width and tend toward longer beaks with lower base depth ( figure 6).…”

“…Additional morphological details not measured in this study likely contribute to dive performance, including the morphology of the head, body and wings of the bird. In Vincent et al's [14] recent work, the larger the radius of the cone base (r, corresponding to depth and width on our kingfishers), the higher the initial impact forces, due to increased frontal and surface area [12], which increase both pressure and friction drag, respectively. This suggests that not only the shape of the beak, but the shape of the frontal area of the bird (which is generally wider than the beak) likely plays a role in plunge diving.…”

Numerical approach for generic three‐phase flow based on cut‐cell and ghost fluid methods

“…The jet velocity versus the entry velocity for the case of α =90 o and α =120 o is plotted in Figure . Generally, our method overpredicts the jet velocity and underpredict the jet angle in comparison with reference data from the work of Vincent et al for α =90. When α =120, our computed jet quantities fit quite well with the experimental and theoretical results.…”

“…The computational domain is illustrated in Figure A. The size of the rectangular domain is 0.51 m of width and 0.32 m of height, as reported in the work of Vincent et al The wedge width d =0.036 m is held constant for the whole simulation. The nonuniform grid of 260×180 is shown in Figure B.…”

Slamming Liquid Impact and the Mediating Role of Air

“…Chuang [83,187,188] performed several insightful experimental studies with different geometries and deadrise angles of the impactor. Works by Tveitnes et al [189] and Vincent et al [190] focussed on the total impact force on the wedge. Takemoto's experimental results validated the Wagner profile (pressure distribution along the wetted surface of the wedge) [191].…”