Journal of Fluid Mechanics



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Falling clouds of particles in viscous fluids


BLOEN  METZGER  a1, MAXIME  NICOLAS  a1 and ÉLISABETH  GUAZZELLI  a1
a1 IUSTI – CNRS UMR 6595, Polytech-Marseille, Technopôle de Château-Gombert, 13453 Marseille cedex 13, France

Article author query
metzger b   [Google Scholar] 
nicolas m   [Google Scholar] 
guazzelli e   [Google Scholar] 
 

Abstract

We have investigated both experimentally and numerically the time evolution of clouds of particles settling under the action of gravity in an otherwise pure liquid at low Reynolds numbers. We have found that an initially spherical cloud containing enough particles is unstable. It slowly evolves into a torus which breaks up into secondary droplets which deform into tori themselves in a repeating cascade. Owing to the fluctuations in velocity of the interacting particles, some particles escape from the cloud toroidal circulation and form a vertical tail. This creates a particle deficit near the vertical axis of the cloud and helps in producing the torus which eventually expands. The rate at which particles leak from the cloud is influenced by this change of shape. The evolution toward the torus shape and the subsequent evolution is a robust feature. The nature of the breakup of the torus is found to be intrinsic to the flow created by the particles when the torus aspect ratio reaches a critical value. Movies are available with the online version of the paper.

(Received July 17 2006)
(Revised December 1 2006)


Key Words: Particle-laden flows; Breakup.


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