TY - JOUR
T1 - Early azimuthal instability during drop impact
AU - Li, E. Q.
AU - Thoraval, M. J.
AU - Marston, J. O.
AU - Thoroddsen, S. T.
N1 - Publisher Copyright:
© 2018 Cambridge University Press.
PY - 2018/8/10
Y1 - 2018/8/10
N2 - 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.
AB - 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.
KW - capillary flows
KW - drops and bubbles
KW - interfacial flows (free surface)
UR - http://www.scopus.com/inward/record.url?scp=85048811892&partnerID=8YFLogxK
U2 - 10.1017/jfm.2018.383
DO - 10.1017/jfm.2018.383
M3 - Article
AN - SCOPUS:85048811892
SN - 0022-1120
VL - 848
SP - 821
EP - 835
JO - Journal of Fluid Mechanics
JF - Journal of Fluid Mechanics
ER -