Rheology of dense granular chute flow: simulations to experiments

¹ Chemical Engineering, Indian Institute of Science, Bangalore, India
² Civil Engineering, Indian Institute of Science, Bangalore, India

^* e-mail: sagarbharathraj@gmail.com
^** e-mail: tejas@civil.iisc.ernet.in
^*** e-mail: kumaran@chemeng.iisc.ernet.in

Published online: 30 June 2017

Abstract

Granular chute flow simulations reveal an interesting transition from a random disordered structure to an ordered one with hexagonally ordered sheets of spherical particles, when the base roughness is modulated. Two types of base roughness are considered. The first is a fixed base, where glued spherical particles form the base, and the base roughness is varied by changing the ratio of diameters of the base and flowing particles. In the second sinusoidal base, a smooth wall with sinusoidal height variation is used; the amplitude and wavelength of the base modulation determine the base roughness. The transition is studied as a function of these roughness parameters. For the fixed base, there is a critical base particle diameter below which ordered states are observed. For the sinusoidal base, the critical amplitude increases linearly with the wavelength at lower wavelengths, reaches a maximum depending on the height of the flowing layer, and then decreases as the wavelength is further increased. There is flow for angles of inclination from 15 ° ≤ θ ≤ 25 ° for the ordered state and 20 ° ≤ θ ≤ 25 ° for the disordered state. Flow confinement by sidewalls also influences the rheology of the system and we see that the ordering is induced by the sidewalls as well. Experiments on chute flow at low angles indicate the presence of two types of rheology depending on the system height. A transition is observed from an erodible base configuration, where a dead zone at the bottom supports a free surface reposing at the top, to a Bagnold rheology with considerable slip at the bottom.