Micro-splashing by drop impacts

• Published in: Journal of fluid mechanics Vol. 706; pp. 560 - 570
• Main Authors: Thoroddsen, S. T., Takehara, K., Etoh, T. G.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 10.09.2012
• Subjects: Applied fluid mechanics; Breakup; Drop size distribution; Drops and bubbles; Ejecta; Ejection; Exact sciences and technology; Fluid dynamics; Fluid mechanics; Free surfaces; Fundamental areas of phenomenology (including applications); Hydrodynamics, hydraulics, hydrostatics; Instability; Instrumentation for fluid dynamics; Liquid sheets; Nonhomogeneous flows; Physics; Rain; Solid surfaces; Splashing; breakup/coalescence; drops; aerosols/atomization; Smooth wall; Ruptures; High speed photography; Drops; Impact phenomena; Hydrodynamics; Splashing; Coalescence; Experimental study
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/jfm.2012.281

We use ultra-high-speed video imaging to observe directly the earliest onset of prompt splashing when a drop impacts onto a smooth solid surface. We capture the start of the ejecta sheet travelling along the solid substrate and show how it breaks up immediately upon emergence from the underneath the drop. The resulting micro-droplets are much smaller and faster than previously reported and may have gone unobserved owing to their very small size and rapid ejection velocities, which approach 100 m s−1, for typical impact conditions of large rain drops. We propose a phenomenological mechanism which predicts the velocity and size distribution of the resulting microdroplets. We also observe azimuthal undulations which may help promote the earliest breakup of the ejecta. This instability occurs in the cusp in the free surface where the drop surface meets the radially ejected liquid sheet.