Experimental and numerical investigation on dynamic flow separation during water-entry of an open cavity

Abstract

In this paper, the water-entry behavior of an open cylindrical cavity is investigated by laboratory experiments and numerical simulations. Laboratory experiments are conducted in a water flume, with high-speed imaging used to capture cavity bubble evolution across a range of entry velocities, corresponding to Froude numbers Fr from 0 to 2.433. Three distinct flow patterns have been identified: a turbulent pattern (Fr<0.75), a transitional pattern (0.75≤Fr≤1.75), and a wave-forming pattern (Fr>1.75). The process is characterized by periodic liquid inflow and outflow, leading to repeated compression and expansion of the trapped gas, which in turn induces significant wall oscillations and morphological instability. A computational fluid dynamics model is utilized to further study the effect of the open-end bottom on the velocity and acceleration of the cavity. The results show that the open configuration experiences slower penetration, sustained fluctuations in velocity and acceleration, and enhanced unsteady dynamics due to internal fluid exchange.