Journal of Fluid Mechanics


On spray formation

a1 IRPHE, Université de Provence, Aix–Marseille 1, Technopôle de Château-Gombert, 49, rue Frédéric Joliot-Curie, 13384 Marseille Cedex 13, France

Article author query
marmottant p   [Google Scholar] 
villermaux e   [Google Scholar] 


We depict and analyse the successive steps of atomization of a liquid jet when a fast gas stream blows parallel to its surface. Experiments performed with various liquids in a fast air flow show that the liquid destabilization proceeds from a two-stage mechanism: a shear instability first forms waves on the liquid. The transient acceleration experienced by the liquid suggests that a Rayleigh–Taylor type of instability is triggered at the wave crests, producing liquid ligaments which further stretch in the air stream and break into droplets. The primary wavelength $\lambda\,{\sim}\,\delta (\rho_{1}/\rho_{2})^{1/2}$ is set by the vorticity thickness $\delta$, in the fast air stream and the liquid/gas density ratio $\rho_{1}/\rho_{2}$. The transverse corrugations of the crests have a size $\lperp\,{\sim}\,\delta {\We_{\delta}}^{-1/3} (\rho_{1}/\rho_{2})^{1/3}$, where $\We_{\delta}\,{=}\,\rho_{2}u_{2}^{2}\delta/\sigma$ is the Weber number constructed on the gas velocity $u_{2}$ and liquid surface tension $\sigma$. The ligament dynamics gives rise, after break-up, to a well-defined droplet size distribution whose mean is given by $\lperp$. This distribution bears an exponential tail characteristic of the broad size statistics in airblast sprays.

(Received November 4 2002)
(Revised July 25 2003)

p1 Present address: Department of Applied Physics, WB Building, University of Twente, 7500 AE Enschede, The Netherlands.
p2 Also at: Institut Universitaire de France.