Unsteady forces on spheres during free-surface water entry
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S0022112012002327a.pdf
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8 MB
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Author(s)
Truscott, Tadd T.
Epps, Brenden P.
Techet, Alexandra H.
Date Issued
July 2012
Journal
Journal of Fluid Mechanics
Publisher
Cambridge University Press
Citation
Truscott, Tadd T., Brenden P. Epps, and Alexandra H. Techet. Unsteady Forces on Spheres During Free-surface Water Entry. Journal of Fluid Mechanics 704 (August 2, 2012): 173-210. © Cambridge University Press 2012
Version
Final published version
Abstract
We present a study of the forces during free-surface water entry of spheres of varying masses, diameters, and surface treatments. Previous studies have shown that the formation of a subsurface air cavity by a falling sphere is conditional upon impact speed and surface treatment. This study focuses on the forces experienced by the sphere in both cavity-forming and non-cavity-forming cases. Unsteady force estimates require accurate determination of the deceleration for both high and low mass ratios, especially as inertial and hydrodynamic effects approach equality. Using high-speed imaging, high-speed particle image velocimetry, and numerical simulation, we examine the nature of the forces in each case. The effect of mass ratio is shown, where a lighter sphere undergoes larger decelerations and more dramatic trajectory changes. In the non-cavity-forming cases, the forces are modulated by the growth and shedding of a strong, ring-like vortex structure. In the cavity-forming cases, little vorticity is shed by the sphere, and the forces are modulated by the unsteady pressure required for the opening and closing of the air cavity. A data-driven boundary-element-type method is developed to accurately describe the unsteady forces using cavity shape data from experiments.
MIT Department
Massachusetts Institute of Technology. Department of Mechanical Engineering
Terms of Use
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
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DOI of Published Version
https://doi.org/10.1017/jfm.2012.232
