Gravity-driven flux of particles through apertures

Abstract

The gravity-driven discharge of granular material through an aperture is a fundamental problem in granular physics and is classically described by empirical laws with different fitting parameters. In this Letter, we disentangle the mass flux into distinct velocity and packing contributions by combining three-dimensional experiments and simulations. We define a dimensionless flux ratio that captures confinement-driven deviations from a free-fall limit, which is recovered when the aperture is large compared to the grain size. For spherical cohesionless grains, the deviations from the free-fall limit are captured by a single exponential correction factor over a characteristic length scale of $\sim$ 10-15 grain diameters. This is shown to be the scale over which the packing structure is modified due to the boundary. Building on the $\sqrt{gD}$ exit-velocity scaling, we propose a kinematic framework that explains the universality of granular discharge beyond empirical descriptions.

Main (4 pages, 4 figures) and Supplementary (9 pages, 7 figures)

References in corpus (10)

• Yield Stress Materials in Soft Condensed Matter
• Jamming during the discharge of granular matter from a silo
• Jamming During the Discharge of Grains from a Silo Described as a Percolating Transition
• Pressure and Motion of Dry Sand -- Translation of Hagen's Paper from 1852
• Pressure independence of granular flow through an aperture
• Invited review: Clogging of granular materials in bottlenecks
• Droplet and cluster formation in freely falling granular streams
• Dense bubble flow in a silo: an unusual flow of a dispersed medium
• Local description of the two-dimensional flow of foam through a contraction
• A microscopic picture of erosion and sedimentation processes in dense granular flows