Early azimuthal instability during drop impact

Erqiang Li, Marie-Jean Thoraval, Jeremy Marston, Sigurdur T Thoroddsen

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


When a drop impacts on a liquid surface its bottom is deformed by lubrication pressure and it entraps a thin disc of air, thereby making contact along a ring at a finite distance from the centreline. The outer edge of this contact moves radially at high speed, governed by the impact velocity and bottom radius of the drop. Then at a certain radial location an ejecta sheet emerges from the neck connecting the two liquid masses. Herein, we show the formation of an azimuthal instability at the base of this ejecta, in the sharp corners at the two sides of the ejecta. They promote regular radial vorticity, thereby breaking the axisymmetry of the motions on the finest scales. The azimuthal wavenumber grows with the impact Weber number, based on the bottom curvature of the drop, reaching over 400 streamwise streaks around the periphery. This instability occurs first at Reynolds numbers of ∼7000, but for larger is overtaken by the subsequent axisymmetric vortex shedding and their interactions can form intricate tangles, loops or chains.
Original languageEnglish (US)
Pages (from-to)821-835
Number of pages15
JournalJournal of Fluid Mechanics
StatePublished - Jun 13 2018


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