Water Entry of Projectiles

TLDR: The free-surface impact of solid objects has been investigated for well over a century as discussed by the authors, and advances in high-speed imaging and visualization techniques have led to critical insights into cavity formation, the depth and time of pinch-off, forces and trajectories for myriad different impact parameters.

Abstract: The free-surface impact of solid objects has been investigated for well over a century. This canonical problem is influenced by many physical parameters, including projectile geometry, material properties, fluid properties, and impact parameters. Through advances in high-speed imaging and visualization techniques, discoveries about the underlying physics have improved our understanding of these phenomena. Improvements to analytical and numerical models have led to critical insights into cavity formation, the depth and time of pinch-off, forces, and trajectories for myriad different impact parameters. This topic spans a wide range of regimes, from low-speed entry phenomena dominated by surface tension to high-speed ballistics, for which cavitation is important. This review surveys experimental, theoretical, and numerical studies over this broad range, utilizing canonical images where possible to enhance intuition and insight into the rich phenomena.