When does an impacting drop stop bouncing?

TL;DR

This study uses numerical simulations to understand when impacting drops stop bouncing on non-wetting surfaces, identifying key parameters and energy mechanisms that inhibit rebound.

Contribution

It introduces a new criterion based on Ohnesorge and Bond numbers for predicting bounce cessation, supported by detailed energy analysis.

Findings

The initial spreading phase can be decoupled from retraction near the transition.

The bounce-to-non-bounce transition criterion is Oh_c + Bo_c ≈ 1.

Energy budgets reveal mechanisms inhibiting bouncing in different regimes.

Abstract

Non-wetting substrates allow impacting liquid drops to spread, recoil, and takeoff, provided they are not too heavy (Biance et al. 2006) or too viscous (Jha et al. 2020). In this article, using direct numerical simulations with the volume of fluid method, we investigate how viscous stresses and gravity conspire against capillarity to inhibit drop rebound. Close to the bouncing to non-bouncing transition, we evidence that the initial spreading stage can be decoupled from the later retraction and takeoff, allowing to understand the rebound as a process converting the surface energy of the spread liquid into kinetic energy. Drawing an analogy with coalescence induced jumping, we propose a criterion for the transition from the bouncing to the non-bouncing regime, namely by the condition $Oh_c + Bo_c \sim 1$, where $Oh_c$ and $Bo_c$ are the Ohnesorge number and Bond number at the transition, respectively. This criterion is in excellent agreement with the numerical results. We also elucidate the mechanisms of bouncing inhibition in the heavy and viscous drops limiting regimes by calculating the energy budgets and relating them to the drop's shape and internal flow.