Droplet impact dynamics onto a deep liquid pool of wavy free surface

Abstract

The impact of a droplet on a deep pool of water with a flat-free surface results in a deep cavity followed by the emergence of a thick jet with a secondary drop when the Froude number and Weber number of the impacting droplet are 220 and 252, respectively. The disturbances in the free surface of the liquid pool modify the crater and the jet dynamics under identical drop impact conditions. Here, we present the simulations of the water drop impact on a deep liquid pool having various wavy profiles mimicking the free surface ripples. Long slender jets with the formation of multiple secondary droplets are observed when the droplet impacts the trough of an axisymmetric wavy surface. The influence of wave number on the wavy profile becomes more pronounced at large wave amplitudes. While capillary-inertia instability governs the pinch-off of thick Worthington jets, the pinch-off of these slender jets is found to be mainly inertia driven. However, if the drop impacts the crest of an axisymmetric wave, a short thick jet forms with one or two secondary droplets. Axisymmetric waves with radially outward moving interface, as in ripples, showed the occurrence of complete coalescence when droplet impacted on the crest; but the dynamics remain mostly the same as that of a stationary wave for the droplet impact on a trough. Entrainment of air bubbles after cavity collapse and bent jet occurred for an impact on a sinusoidal planar wave when the impact location was in between the two consecutive extremes.