Conical-focusing: Mechanism for singular jetting from collapsing drop-impact craters

TL;DR

This paper uncovers a new inertial focusing mechanism in collapsing drop-impact craters that produces ultra-fast, narrow jets, with implications for aerosol generation and fluid dynamics understanding.

Contribution

It introduces a novel conical focusing mechanism driven by an entrained air-sheet, explaining the extreme jet velocities observed in drop-impact phenomena.

Findings

Maximum jet velocity of 137 m/s observed.

A new focusing mechanism identified through high-resolution simulations.

The mechanism involves an entrained air-sheet enabling slip at the flow boundary.

Abstract

Fast microjets can emerge out of liquid pools from the rebounding of drop-impact craters, or when a bubble bursts at it surface. The fastest jets are the narrowest and are a source of aerosols both from the ocean and a glass of champagne, of importance to climate and the olfactory senses. The most singular jets, which have a maximum velocity of 137$\pm$4 m/s and diameter of 12 $\mu$m under reduced ambient pressure, are produced when a small dimple forms at the crater bottom and rebounds without pinching off a small bubble. The rebounding of this dimple is purely inertial but highly sensitive on initial conditions. High-resolution numerical simulations reveal a new focusing mechanism, which drives the fastest jet within a converging conical channel, where an entrained air-sheet provides effective slip at the outer boundary of the conically converging flow into the jet. This configuration bypasses any viscous cut-off of the jetting speed and explains the extreme sensitivity observed in detailed experiments of the phenomenon.