Journal of Fluid Mechanics

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On the role of the ambient fluid on gravitational granular flow dynamics

C. MERUANEa1a2 c1, A. TAMBURRINOa1 and O. ROCHEa2

a1 Departamento de Ingeniería Civil, Universidad de Chile, Blanco Encalada 2002, Casilla 228-3, Santiago, Chile

a2 Laboratoire Magmas et Volcans, UMR Unversité Blaise Pascal-CNRS-IRD, 5 rue Kessler, 63038 Clermont-Ferrand, France

Abstract

The effects of the ambient fluid on granular flow dynamics are poorly understood and commonly ignored in analyses. In this article, we characterize and quantify these effects by combining theoretical and experimental analyses. Starting with the mixture theory, we derive a set of two-phase continuum equations for studying a compressible granular flow composed of homogenous solid particles and a Newtonian ambient fluid. The role of the ambient fluid is then investigated by studying the collapse and spreading of two-dimensional granular columns in air or water, for different solid particle sizes and column aspect (height to length) ratios, in which the front speed is used to describe the flow. The combined analysis of experimental measurements and numerical solutions shows that the dynamics of the solid phase cannot be explained if the hydrodynamic fluid pressure and the drag interactions are not included in the analysis. For instance, hydrodynamic fluid pressure can hold the reduced weight of the solids, thus inducing a transition from dense-compacted to dense-suspended granular flows, whereas drag forces counteract the solids movement, especially within the near-wall viscous layer. We conclude that in order to obtain a realistic representation of gravitational granular flow dynamics, the ambient fluid cannot be neglected.

(Received June 03 2009)

(Revised October 29 2009)

(Accepted October 29 2009)

Correspondence:

c1 Email address for correspondence: cmeruane@ing.uchile.cl

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