Direct measurement of cavity pressure in high-speed water entry

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 impact velocity an object impacting the water pulls air under the surface forming an air cavity in its wake. Below about 10 m/s the air pressure inside the cavity is near atmospheric. As the impact velocity increases toward 100 m/s the cavity pressure decreases and water vapor enters the cavity altering the cavity dynamics. We experimentally investigate water entry in the range of 10-100 m/s, making direct cavity pressure measurements inside the water-entry cavity. Using these data alongside high-speed photography, we characterize the relationship between projectile entry velocity and cavity pressure.