Study on cavity evolution of asynchronous parallel high-speed vertical water entry of cylinders

This study conducted extensive experimental investigations on the asynchronous parallel high-speed vertical water entry of cylinders, examining the effects of varying lateral spacing, time intervals, and entry speeds. The research identified four distinct modes of cavity morphology for both the first and second cavities. For the first cavity, these modes include non-existent/destroyed, compressed, and quasi-single cavity, while the second cavity exhibits non-existent/destroyed, compressed, expanded, and quasi-single cavity forms. Multiple parameters were found to affect cavity morphology, with time interval emerging as a particularly crucial factor. The study revealed complex dynamics in cavity formation: the maximum diameter of the first cavity increases with increasing time intervals, while its maximum length exhibits a non-monotonic trend, initially decreasing and then increasing. The second cavity demonstrates even more intricate behavior, with its maximum diameter initially increasing, then decreasing with time intervals, followed by minor fluctuations. Its maximum length shows a pronounced non-monotonic trend, first decreasing, then increasing, followed by significant fluctuations. Notably, the position of the maximum diameter of the second cavity consistently aligns with the collapse plane of the first cavity. This study reveals complex dynamics in cavity interactions during parallel water entry based on the influence function φ defined. As the time interval increases, the impact of the second cavity on the first cavity progressively attenuates. Conversely, the influence of the first cavity on the second exhibits a non-monotonic trend: initially intensifying, then subsequently diminishing. The peak influence occurs when the time interval equals the ratio of the cylinder length to the water entry speed. Notably, when the time interval exceeds a critical threshold, defined as the ratio of the maximum length of a single cavity at the same speed to the water entry speed, the mutual influence between the first and second cavities becomes negligible. This analysis elucidates the intricate temporal dependencies in cavity formation and interaction during parallel high-speed water entries, providing valuable insights into the fluid dynamics of such phenomena.