Von K\'arm\'an Vortex Street within an Impacting Drop

TL;DR

This study combines high-speed imaging and simulations to reveal how vortex rings form in the impact of a drop on a liquid pool, leading to irregular splashing and droplet formation.

Contribution

It uncovers the role of von Kármán vortex streets in the breakup of ejecta sheets during drop impact, linking vortex dynamics to splashing behavior.

Findings

Vortex rings shed from the free surface at high Reynolds numbers.

Vortex street destabilizes the ejecta sheet, causing irregular splashing.

High-resolution simulations match experimental observations.

Abstract

The splashing of a drop impacting onto a liquid pool produces a range of different sized micro-droplets. At high impact velocities, the most significant source of these droplets is a thin liquid jet emerging at the start of the impact from the neck that connects the drop to the pool. We use ultra-high-speed video imaging in combination with high-resolution numerical simulations to show how the ejecta gives way to irregular splashing. At higher Reynolds number, its base becomes unstable, shedding vortex rings into the liquid from the free surface in an axisymmetric von K\'arm\'an vortex street, thus breaking the ejecta sheet as it forms.