Experimental study of the effects of a viscous liquid layer on the cavity dynamics of vertical entry by a sphere into water at low Froude number

Abstract

The water entry process is relevant to a wide range of engineering applications and has been extensively investigated. Most liquids used in such studies are single-layered, and little attention has been paid to how the structure of a two-layer liquid system affects the splash and cavity formation. In this study, we use high-speed photography to experimentally investigate the water entry of a sphere after it has passed vertically through a layer of highly viscous liquid (dimethicone) at a low Froude number. We investigate the effects of different thicknesses of this dimethicone layer and find that the formation of the splash crown is closely related to both the thickness and the Froude number. In a certain range of dimethicone thickness, the height of the splash interface decreases with the increasing thickness and increases with the decreasing Froude number. The dimensionless interface height at the pinch-off time is found to have a linear relationship with the dimensionless initial velocity of the sphere. Furthermore, the formation of the cavity, including its length and pinch-off depth, depends on the Froude number. However, the pinch-off time is almost independent of the dimethicone thickness and the Froude number, and the cavity length is nearly independent of the dimethicone thickness for all Froude numbers examined.