Spatiotemporal Instability of Cavity Edge for High-Speed Water Entry of Spherical Projectiles

High-speed entry of spherical projectiles into water results in the formation of a cavity as the projectile penetrates the water surface. As the cavity grows, spatial undulations develop along the cavity interface. These disturbances amplify and eventually break down, causing the cavity bubble to become highly deformed as it collapses. The present study introduces a data-driven approach--wavelet-filtered proper orthogonal decomposition--to extract the spatiotemporal features of the instability waves. Applying this technique to experimental data reveals the key instability dynamics which accompany cavity collapse.