Unsteady forces on spheres during free-surface water entry
Author(s)Truscott, Tadd T.; Epps, Brenden P.; Techet, Alexandra H.
MetadataShow full item record
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.
DepartmentMassachusetts Institute of Technology. Department of Mechanical Engineering
Journal of Fluid Mechanics
Cambridge University Press
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
Final published version