Consecutive water entries of two side-by-side spheres: cavity interference and surface closure characteristics

This paper presents an experimental investigation into cavity interference and surface closure characteristics of two side-by-side spheres undergoing consecutive water entries. A high-speed imaging system was employed to capture the dynamic processes of the two cavities, including the cavity elongation and their interaction with the free surface during the closure stage. Four distinct interference modes—rebound, expansion, tail, and bubble-dominated—are found primarily depending on the time interval between the two water entries, Δ[jls-end-space/]t, while showing little sensitivity to the lateral distance. Unlike the single-cavity closure, the following cavity, subject to interference, undergoes two separate detachment events from the free surface, characterized by a closure angle (defined as the acute angle between the cavity tail-end face and the free surface) whose magnitude and orientation scale with Δ[jls-end-space/]t. Statistical analysis indicates that the initial detachment time is independent of the adjacent cavity’s evolution, whereas the emergence of a closure angle significantly prolongs the complete detachment time and increases cavity length, especially at smaller lateral distances.