Dynamics of the cavity evolution during vertical water entry of deformable spheres

Despite cavity dynamics have been studied for more than a century, cavity formations during water entry of deformable spheres have rarely been studied. Series of interesting cavities arise during vertical water entry of deformable spheres. We study these phenomena experimentally and numerically. Experimental observations show that deformable spheres can produce three typical cavities: dumpy cavity, tight cavity, and nested cavity. Numerical modeling accounts for the effect of elasticity on the cavity dynamics. Our results show that the motion parameters used to characterize the three typical cavity walls present a hierarchical order. During the first cycle of cavity flows, the dependence of the dynamics of the deformed sphere on the dimensionless ratio of material shear modulus to impact hydrodynamic pressure is determined. Before the pinch-off of cavity, a density correction coefficient is proposed to characterize the linearization of wetted areas. Elasticity can alter the shape of the cavity, which requires sufficient impact conditions and material properties. Within this range, the formation time and number of the nested cavity are analyzed. On this basis, the minimum velocity required to form the nested cavity is theoretically predicted and identified by experimental and numerical techniques.