Granular flow in a wedge‐shaped heap: Velocity field, kinematic scalings, and segregation

Abstract

Free surface granular flows in bounded axisymmetric geometries are poorly understood. Here, we consider the kinematics and segregation of size‐bidisperse flow in a rising conical heap by characterizing the flow of particles in a wedge‐shaped silo with frictional sidewalls using experiments and discrete‐element‐method simulations. We find that the streamwise velocity is largest at the wedge centerline and decreases near the sidewalls, and that velocity profiles in the depthwise and spanwise directions are self‐similar. For segregating size bidisperse mixtures, the boundary between small and large particles deposited on the heap is significantly further upstream at the sidewalls than at the centerline, indicating that measurements taken at transparent sidewalls of quasi‐2D or wedge‐shaped heaps are unrepresentative of an axisymmetric heap. The streamwise velocity and flowing layer depth locally satisfy the scaling relation of Jop et al (J Fluid Mech. 2005;541:167‐192) when modified to account for the wedge geometry, highlighting the influence of wall friction on the flow.

Modelling segregation of bidisperse granular mixtures varying simultaneously in size and density for free surface flows

“…2019) and three-dimensional (Isner et al. 2020 a , b ) geometries with known flow kinematics. Moreover, continuous size distributions could be considered in this same framework for polydisperse segregation (Schlick et al.…”

“…2016; Isner et al. 2020 b ). The bounded heap example shown in figure 1 is confined by two parallel plates in the spanwise (normal to the -plane) direction with a gap thickness of mm.…”

“…Our in-house DEM code (Isner et al. 2020 a , b ) runs on CUDA-enabled GPUs and has been previously validated by heap flow experiments with millimetre-sized particles (Xiao et al. 2016; Isner et al.…”

“…plane shear flows and chute flows) is that the local shear rate and the particle species concentration vary throughout the length and depth of a steady flowing layer but remain constant at a particular location in the flow (when analysed from a reference frame that rises with the heap surface), such that time-averaged segregation data for a wide range of flow conditions can be obtained from just one simulation. Segregation model parameters obtained from the steady single-sided quasi-2-D bounded heap geometry are universal in that they can be applied to unsteady flows and other flow geometries (Schlick et al 2015b;Deng et al 2019;Xiao et al 2019;Deng et al 2020;Isner et al 2020a). In this study, we conduct more than 350 simulations with different combinations of particle size and density ratios in developing the SD-disperse segregation model.…”

“…Our in-house DEM code (Isner et al 2020a,b) runs on CUDA-enabled GPUs and has been previously validated by heap flow experiments with millimetre-sized particles (Xiao et al 2016;Isner et al 2020b). The bounded heap example shown in figure 1 is confined by two parallel plates in the spanwise (normal to the xz-plane) direction with a gap thickness of T = 15 mm.…”