Cessation of a dense granular flow down an inclined plane

Bharathraj, S and Kumaran, V (2019) Cessation of a dense granular flow down an inclined plane. In: PHYSICAL REVIEW FLUIDS, 4 (2).

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Abstract

The cessation of a dense granular flow down an inclined plane upon decrease in the angle of inclination is studied using particle-based simulations for the linear and Hertzian particle contact models for ordered and disordered flows. The nature of the flow is examined by progressively decreasing the angle of inclination by fractions of a degree, with the objective of examining the range of angles for which the hard-particle model can be used to describe the flow and the nature of the flow dynamics very close to cessation where the hard-particle approximation fails. For a disordered flow, when the angle inclination exceeds the angle for flow cessation by about 0.5 degrees for the linear contact model and about 1 degrees for the Hertzian model, the flow is well described by Bagnold rheology, and the Bagnold coefficients are independent of layer height and the particle stiffness, implying that the flow dynamics is well described by the hard-particle approximation. When the angle of inclination exceeds the angle for flow cessation by less than 0.5 degrees for the linear contact model and 1 degrees for the Hertzian contact model, the flow transitions into a layered state consisting of a faster shearing zone of height about 30 particle diameters atop a bottom slowly shearing zone. There are sinusoidal oscillations in the velocity of the center of mass of the flow, and the period of these oscillations is proportional to the characteristic time for particle interactions, indicating that the particle contact time does affect the dynamics of the layered flow. The flow evolution is qualitatively different for an ordered flow. In this case, there is an abrupt transition from a Bagnold flow to a plug flow with sliding at the base when the angle of inclination is decreased by 0.05 degrees. There is no discernible intermediate flow regime where the particle contact time becomes relevant. We also examine the deceleration of the flow when the angle of inclination is decreased from a flowing state to a final angle below the cessation angle. The initial decrease in the flow velocity is exponential for both contact models and for all final angles of inclination. This is followed by a more rapid decrease to the static state. The time constant for the initial decrease is significantly higher for an ordered flow in comparison to a disordered flow. The time constant is independent of the contact model and particle stiffness, and increases with height proportional to h(3/2), as expected for the hard-particle model.

Item Type:	Journal Article
Publication:	PHYSICAL REVIEW FLUIDS
Publisher:	AMER PHYSICAL SOC
Additional Information:	Copyright of this article belongs to AMER PHYSICAL SOC
Department/Centre:	Division of Mechanical Sciences > Chemical Engineering
Date Deposited:	19 Feb 2019 05:33
Last Modified:	19 Feb 2019 05:33
URI:	http://eprints.iisc.ac.in/id/eprint/61753

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