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Dynamics of water entry

Published online by Cambridge University Press:  10 May 2018

Lionel Vincent ,
Tingben Xiao ,
Daniel Yohann ,
Sunghwan Jung Open the ORCID record for Sunghwan Jung [Opens in a new window]  and
Eva Kanso Open the ORCID record for Eva Kanso [Opens in a new window]
Lionel Vincent
Affiliation:
Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089, USA
Tingben Xiao
Affiliation:
Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089, USA
Daniel Yohann
Affiliation:
Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089, USA
Sunghwan Jung
Affiliation:
Department of Biomedical Engineering and Mechanics, Virginia Tech, Blacksburg, VA 24060, USA
Eva Kanso*
Affiliation:
Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089, USA
*
†Email address for correspondence: [email protected]
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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.

JFM classification

Wakes/Jets: Jets Interfacial Flows (free surface): Thin films
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 846 , 10 July 2018 , pp. 508 - 535
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Copyright
© 2018 Cambridge University Press 

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Vincent et al. supplementay movie 1

Impact force on a diving wedge during water entry.

Download Vincent et al. supplementay movie 1(Video)
Video 9.1 MB

Vincent et al. supplementay movie 2

Splash dynamics following the water entry of a wedge, demonstrating the effect of air flow and air-induced suction force on the splash evolution.

Download Vincent et al. supplementay movie 2(Video)
Video 49 MB