Droplet impact on a thin liquid film: anatomy of the splash

TL;DR

This study explores the mechanisms of splashing when a droplet impacts a thin liquid film, revealing how gas cushioning and inertial effects influence jet formation and bubble entrapment through numerical simulations and scaling analysis.

Contribution

It introduces a new dimensionless number $J$ to distinguish two regimes of splash formation based on gas cushioning effects, advancing understanding of impact dynamics.

Findings

Splash formation depends on inertial and gas cushioning effects.

Two regimes identified: weak and strong gas cushioning.

Jet velocity is influenced by impact Reynolds number and gas effects.

Abstract

We investigate the dynamics of drop impact on a thin liquid film at short times in order to identify the mechanisms of splashing formation. Using numerical simulations and scaling analysis, we show that the splashing formation depends both on the inertial dynamics of the liquid and the cushioning of the gas. Two asymptotic regimes are identified, characterized by a new dimensionless number $J$: when the gas cushioning is weak, the jet is formed after a sequence of bubbles are entrapped and the jet speed is mostly selected by the Reynolds number of the impact. On the other hand, when the air cushioning is important, the lubrication of the gas beneath the drop and the liquid film controls the dynamics, leading to a single bubble entrapment and a weaker jet velocity.