Symmetry breaking of Worthington jets by gradients in liquid pool depth

We investigate the impact of a vertically falling droplet onto a non-uniform liquid depth having a linear slope of the bottom substrate. Here, we report that the resulting jet direction is inclined to the shallow liquid depth after the droplet impact, which is found to be markedly distinct from a vertically falling droplet onto a uniform liquid bath. From experimental and numerical results, we observe that initially the cavity grows almost axisymmetrically, and then, when it retracts, asymmetric capillary waves exhibit. The asymmetric cavity reversal leads to the inclined jet ejection that is related to pressure distribution and velocity of the interface. For the systematic study, we explore the jet dynamics by varying the surface tension, the droplet size, the droplet impact speed, the inclination angle of the bottom substrate, and the depth of the liquid bath. Finally, we provide a simple scaling model to predict the inclination angle of the resulting jet after the drop impact on the inclined liquid pool.