Rheology of surface granular flows

Abstract

The rheology of surface granular flows is investigated by means of measurements of velocity and number density profiles in a quasi-two-dimensional rotating cylinder, half-filled with mono-disperse steel balls. The measurements are made at the center of the cylinder, where the flow is fully-developed, using streakline photography and image analysis . The stress profile is computed from the number density profile using a force balance taking into account wall friction. The profiles for the mean velocity superimpose when distance is scaled by the particle diameter and the velocity by a characteristic shear rate and the particle diameter. The mean velocity is found to decay exponentially with depth in the bed with a decay length of $\lambda =1.1d$. The r.m.s. velocity is nearly constant near the free surface and below a transition point it decays linearly with depth. The shear rate, obtained by numerical differentiation of the velocity profile, shows a maximum which occurs at the same depth as the transition in the r.m.s. velocity profile. The velocity distribution is Maxwellian above the transition point and a Poisson velocity distribution is obtained deep in the layer. The variation of the apparent viscosity ($\eta$) with r.m.s. velocity ($u$) shows a relatively sharp transition at the shear rate maximum, and in the region below this point the apparent viscosity varies as $\eta \sim u^{-1.5}$. The experimental data is compared to predictions of three models for granular flow.

32 pages, 39 figures, submitted to J. Fluid Mech

References in corpus (8)

• On dense granular flows
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Cited by in corpus (6)

• A sidewall friction driven ordering transition in granular channel flows: Implications for granular rheology
• A microscopic picture of erosion and sedimentation processes in dense granular flows
• Granular surface flows confined between flat, frictional walls. Part 1. Kinematics
• Microrollers Flow Uphill as Granular Media
• Scaling laws for velocity profile of granular flow in rotating drums
• Mechanisms for recirculation cells in granular flows in rotating cylindrical rough tumblers