Jet dynamics post drop impact on a deep pool

Abstract

We investigate experimentally the jet formed by the collapse of a cavity created by the impact of a drop on a pool of the same aqueous liquid. We show that jets can emerge with very different shapes and velocities, depending on the impact parameters, thus generating droplets with various initial sizes and velocities. After presenting the jet velocity and top drop radius variation as a function of the impact parameters, we discuss the influence of the liquid parameters on the jet velocity. This allows us to define two different regimes: the singular jet and the cavity jet regimes, where the mechanisms leading to the cavity retraction and subsequent jet dynamics are drastically different. In particular, we demonstrate that in the first regime, a singular capillary wave collapse sparks the whole jet dynamics, making the jet's fast, thin, liquid parameters dependent and barely reproducible. On the contrary, in the cavity jet regime, defined for higher impact Froude numbers, the jets are fat and slow. We show that jet velocity is simply proportional to the capillary velocity √ γ /ρ l D d , where γ is the liquid surface tension, ρ l the liquid density, and D d the impacting drop diameter, and it is in particular independent of viscosity, impact velocity, and gravity, even though the cavity is larger than the capillary length. Finally, we demonstrate that capillary wave collapse and cavity retraction are correlated in the singular regime and decorrelated in the cavity jet regime.

Deep pool water-impacts of viscous oil droplets

“…4,27 Drops impacting with large Froude numbers create large craters, which in turn have large associated potential energy. To conclude, crater potential energy is one of the main energy sinks during the early stages of crater expansion process, 28 and the main factor behind its subsequent retraction.…”

Singular jets during the collapse of drop-impact craters

“…The most comprehensive experimental study of these jets to date, is that of Michon et al (2017), who used 8000 fps. They characterize the fast singular jets as "barely reproducible", but observe jet velocities up to 14 times the drop impact velocity.…”

Air evolution during drop impact on liquid pool

“…The change in air viscosity significantly affects the whole dynamics of drop impact 53 and thus it would be crucial to investigate the effect of air viscosity on air entrapment during drop impact on a liquid pool. Further studies should be expanded to understand the oblique impact of droplets on deep liquid pools [54][55][56] , the impact of viscoelastic or viscous droplets [57][58][59] , and the impact-induced fabrication 60,61 , with more facilitating of numerical 62 , theoretical 63 , and experimental approaches 64,65 .…”