Numerical simulations of simultaneous pair-drop impacts and their energetics

TL;DR

This paper uses 3D numerical simulations to analyze the impact dynamics of two droplets on a hydrophobic surface, focusing on the central sheet formation and energetics across different capillary and viscous regimes.

Contribution

It introduces a validated energetic model for the maximum elevation of the central sheet during simultaneous drop impacts, linking it to single-drop spreading behavior.

Findings

The central sheet's rise resembles single-drop impact spreading.

Scaling laws can collapse impact trajectories across regimes.

The model predicts maximum central sheet elevation based on impact parameters.

Abstract

We present three-dimensional direct numerical simulations of the simultaneous impact of two identical drops on an hydrophobic substrate, varying the relative strength of capillary and viscous effects respectively through Weber and Reynolds numbers of impact. The interaction between the two drops is characterized by the appearance of a lamella arising from the collision of the two droplets' spreading rims. We examine the width, the height, and the general morphological evolution of the central sheet; the numerical data is validated against prior experiments and used to guide the development of an energetic model for the maximum elevation of the central sheet. In particular, the rise of the central sheet resembles the spreading behaviour single-drop impacts, especially at high Weber and Reynolds numbers. This fact can be used to estimate scalings in the capillary- and viscous-dominated regimes, which can be used to collapse the trajectories. These insights provide a route for a more complete understanding of the dynamics for the central rising sheet, and anticipate the detailed study of its fragmentation characteristics