Initial surface deformations during impact on a liquid pool

TL;DR

This paper presents a perturbation analysis to predict initial surface deformations during a solid sphere impact on a liquid pool, considering viscous and inviscid gas effects, and relates these to bubble entrapment.

Contribution

It introduces a quantitative model for initial liquid surface deformation during impact, accounting for gas viscosity effects, and derives the evolution of the free surface in different flow regimes.

Findings

Bubble volume is mainly influenced by gas viscosity.

The model recovers existing scaling laws for bubble entrapment.

Both viscous and inviscid gas flow cases are analyzed.

Abstract

A tiny air bubble can be entrapped at the bottom of a solid sphere that impacts onto a liquid pool. The bubble forms due to the deformation of the liquid surface by a local pressure buildup inside the surrounding gas, as also observed during the impact of a liquid drop on a solid wall. Here we perform a perturbation analysis to quantitatively predict the initial deformations of the free surface of the liquid pool as it is approached by a solid sphere. We study the natural limits where the gas can be treated as a viscous fluid (Stokes flow) or as an inviscid fluid (potential flow). For both cases we derive the spatio-temporal evolution of the pool surface, and recover some of the recently proposed scaling laws for bubble entrapment. When inserting typical experimental values for the impact parameters, we find that the bubble volume is mainly determined by the effect of gas viscosity.