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arXiv · 2511.03682

Fast droplet impact onto slowly moving deep pools

Thomas C. Sykes·Luke F. L. Alventosa·J. Rafael Castrejon-Pita·Radu Cimpeanu·Daniel M. Harris·Alfonso A. Castrejon-Pita
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Abstract

When a fast droplet impacts a pool, the resulting ejecta sheet dynamics determine the final impact outcome. At low Capillary numbers, the ejecta sheet remains separate from a deep static pool, whilst at higher viscosities it develops into a lamella. Here, we show that the common natural scenario of a slowly moving deep pool can change the upstream impact outcome, creating highly three-dimensional dynamics no longer characterised by a single descriptor. By considering how pool movement constrains the evolution of the ejecta sheet angle, we reach a length-scale invariant parameterisation for the upstream transition that holds for a wide range of fluids and impact conditions. Direct numerical simulations show similar dynamics for an equivalent oblique impact, indicating that the pool boundary layer does not play a decisive role for low pool-droplet speed ratios. Our results also provide insight into the physical mechanism that underpins pool impact outcomes more generally.

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Thomas C. Sykes, Luke F. L. Alventosa, J. Rafael Castrejon-Pita, Radu Cimpeanu, Daniel M. Harris, Alfonso A. Castrejon-Pita. 2025-11-05. Fast droplet impact onto slowly moving deep pools. https://doi.org/10.1017/jfm.2026.11586

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