Double-rebound behavior following immiscible droplet impact into a deep liquid pool

Abstract

In the present study, we experimentally studied the double-rebound jet phenomenon, observed when a water droplet impacts an immiscible liquid (silicone oil, viscosity ≤ 20 cSt). Upon impact, a U-shaped cavity forms beneath the liquid surface, initiating the generation of two distinct jets. The cavity retracts to form a clotted Worthington jet, which is thick, slow-moving, and inhibited by the surrounding liquid, causing it to decelerate back into the pool. This process initiates the formation of a secondary V-shaped cavity, which collapses under capillary and inertial forces, creating a singularity at the base and driving the formation of the double-rebound jet. Unlike the singular jet, which forms from a single collapse, the double-rebound jet emerges sequentially after the Worthington jet, achieving speeds an order of magnitude greater than those of the initial droplet detachment and clotted jet evolution. Through a nondimensional analysis, the parameters influencing the double-rebound jet phenomenon and transitions from capillary-driven to inertia-dominated regimes were elucidated. A higher Froude number deepens the cavity and amplifies rebound jet dynamics, while high Capillary numbers emphasize viscous resistance that inhibits double-rebound jet formation. Surface tension stabilizes the gas–liquid interface, while dimensionless parameters govern double-rebound jet dynamics.