Droplet impact dynamics on shallow pools

• DOI: 10.1017/jfm.2023.622
• Publication Date: 2023-09-04T04:00:59Z
• Authors: Thomas C. Sykes; Radu Cimpeanu; Ben D. Fudge; J. Rafael Castrej...; Alfonso A. Castre...
• Keywords: thin films; 0103 physical sciences; breakup/coalescence

When a fast droplet impacts a pool of the same fluid, a thin ejecta sheet that dominates the early-time dynamics emerges within the first few microseconds. Fluid and impact properties are known to affect its evolution; we experimentally reveal that the pool depth is a critical factor too. Whilst ejecta sheets can remain separate and subsequently fold inwards on deeper pools, they instead develop into outward-propagating lamellae on sufficiently shallow pools, undergoing a transition that we delineate by comprehensively varying impact inertia and pool depth. Aided by matching direct numerical simulation results, we find that this transition stems from a confinement effect of the pool base on the impact-induced pressure, which stretches the ejecta sheet to restrict flow into it from the droplet on sufficiently shallow pools. This insight is also applied to elucidate the well-known transition due to Reynolds number.