Vented tube cavity deflation

When objects enter water, air cavities form and persist deep underwater. Cavities decrease drag for energy-saving applications but there are instances where it is beneficial to dissipate cavities before they collapse naturally. This research proposes a method of cavity dissipation by means of cavity deflation after water entry. The method utilizes a tube with radial vent holes attached to a spherical projectile in a manner to provide the air in the cavity a means to escape after deep seal. High-speed video and image processing are utilized to quantify cavity deflation. If the vented tube length is larger than the lower cavity length (at deep seal), the cavity will deflate. We propose a theoretical critical tube length required for deflation to occur for varying projectile sizes and impact conditions. Further, we show that the deflation amount is influenced by experimental parameters such as vented tube length, diameter and impact velocity. Finally, we find that cavity deflation reduces both noise and the forces on the sphere after deep seal.