Abstract
The splash formation and cavity dynamics during the entry of an object into a single-phase liquid system have been investigated considerably in the past, but only a few studies focus on such phenomena in a two-layer liquid system. In the current study, we present an experimental investigation of the entry of a falling sphere into a liquid system consisting of a deep pool of water and a thin layer of dimethicone resting on the water surface. To highlight and support the present findings, experiments of the same sphere entering water were performed and direct comparison were made. As anticipated, the upper-layer viscous liquid introduces a significant change in the splash formation and the differences in behavior are characterized by layered films and wave-like instability structures. In the experiments of the two-layer liquid system, observations show that the early sealing of the splash and the generation of a larger-scale splash fingers are strongly associated with large Froude number, Fr = V0(gD)-1/2 (where V0 is the impact velocity at the still free surface, g is the gravitational acceleration and D is the diameter of the sphere). In addition, the dimensionless cavity depth, the pinch-off depth and the pull-away cavity length behind the sphere are found to be in linear relationship with the Froude number for both water-entry cases and water-dimethicone-entry cases. One of the most interesting results is that the pinch-off time is almost independent of the Froude number. The highly viscous liquid in the upper layer is shown to be critical in determining the cavity dynamics.
Highlights
Water entry process is very complicated and accompanied by many classic physical phenomena, such as the cavity splash, crown seal and pinch-off.1–3 Ongoing investigation of water entry problems is due to its wide applications in industry, sport, biology, and military.4,5 One of the interesting problems has long been studying is the splash formation and cavity dynamics during the entry of an object into liquid.Studies of objects entering into the water have been investigated for more than a century
We investigated the splash formation and cavity dynamics of sphere entry through a viscous liquid resting on the water
A sphere enters water covered by a viscous liquid layer at low Froude number
Summary
Water entry process is very complicated and accompanied by many classic physical phenomena, such as the cavity splash, crown seal and pinch-off. Ongoing investigation of water entry problems is due to its wide applications in industry, sport, biology, and military. One of the interesting problems has long been studying is the splash formation and cavity dynamics during the entry of an object into liquid.Studies of objects entering into the water have been investigated for more than a century. Water entry process is very complicated and accompanied by many classic physical phenomena, such as the cavity splash, crown seal and pinch-off.. Ongoing investigation of water entry problems is due to its wide applications in industry, sport, biology, and military.. One of the interesting problems has long been studying is the splash formation and cavity dynamics during the entry of an object into liquid. Studies of objects entering into the water have been investigated for more than a century. The earliest experiments were conducted by Worthington and Cole, who used single-spark photography to study the shape of the cavity as a sphere entered the water vertically. High-speed cameras have facilitated better and further understanding of transient cavity dynamics of water entry, including flow separation, pinch-off and crown-buckling instability.. High-speed cameras have facilitated better and further understanding of transient cavity dynamics of water entry, including flow separation, pinch-off and crown-buckling instability. Several attempts have been made to characterize the influence of object shape on cavity dynamics. Truscott and Techet performed an experimental study on the complex hydrodynamics of water entry by a spinning sphere at low Froude numbers
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