A Deep Dive into High-Speed Water-Entry Pressure Phenomena

The study of objects entering the water from air has been studied for over a century and has important applications in defense and animal diving. Above a minimum velocity an object impacting the water pulls air under the surface forming an air cavity in its wake. The pressure in the cavity has been shown to be sub-atmospheric due to the flowing air. Previous studies showed that the minimum cavity pressure does not follow the simple Bernoulli pressure drop relation and provide curve fits for impact velocities up to 140 m/s. We measure the cavity pressure overtime alongside high-speed imaging and report on how the pressure changes with impact velocities ranging from 10 to 450 m/s. We focus our pressure reporting on three key times, when the splash domes over on top of the cavity, when the cavity pulls away from the free surface, and the time when the cavity reaches its minimum pressure. We explain these results with a model that accounts for the change in cavity volume and air flow rate into the cavity.