Gravity-driven, dry granular flows over a loose bed in stationary and homogeneous conditions

Abstract

Flows involving solid particulates have been widely studied in recent years, but their dynamics are still a complex issue to model because they strongly depend on the interaction with the boundary conditions. We report on laboratory investigations regarding homogeneous and steady flows of identical particles over a loose bed in a rectangular channel. Accurate measurements were carried out through imaging techniques to estimate profiles of the mean velocity, solid concentration, and granular temperature for a large set of flow rates and widths. Vertical and transversal structures observed in the flow change as interparticle interactions become more collisional, and they depend on the bottom over which the flow develops. The lateral confinement has a remarkable effect on the flow, especially for narrow channels compared with the grain size, and a hydraulic analogy is able to show how the walls influence the mechanisms of friction and energy dissipation.

Internal structure of intense collisional bedload transport

“…The stereoscopic imaging methods permit measurement of velocity profiles of the three components of the velocity vector (Spinewine et al ., ) and represent a development of the monocular imaging method (Capart et al ., ). They both rely on the Voronoï tessellation and on Delaunay triangulation, but, whereas the former is more complicated and needs two high speed cameras (a set up photograph in Figure ), the latter is simpler and exploits only one camera (Meninno, ; Meninno et al ., ). The main steps of these procedures are implemented in an in‐house Matlab routine and are similar.…”

Barchan Slipface Grainflows: Characteristics and Kinematics

“…Grainflow dynamics in natural aeolian environments differ substantially from those observed in simulated environments. For example, in the latter, there are experimental constraints that limit the magnitude and perhaps speed of simulated grainflows, sediment sizes are often carefully constrained (Börzsönyi et al., 2008; Meninno et al., 2018), and sand surfaces groomed (Russell et al., 2019). After each grainflow, the surface is repaired before an experiment is repeated (Tischer et al., 2001), and grainflows develop in ideal conditions.…”

“…Gravity‐driven grainflows or granular flows (Russell et al., 2019) or avalanches (Sutton et al., 2013a, 2013b) are ubiquitous on the lee slopes of migrating sand dunes on Earth and elsewhere. Grainflows have been the focus of substantial laboratory research and related modeling efforts to address the fundamental physics of particle flow (Dai et al., 2020; Drake, 1990; Li et al., 2016; Meninno et al., 2018; Silbert et al., 2001); applications in manufacturing or food and pharmaceutical processing (Gray, 2001; Rao et al., 2008); the behavior of sand piles in the context of self‐organized criticality (Abate et al., 2007; Dendy & Helander, 1998; Kadanoff et al., 1989; Mosco & Vivaldi, 2020); the controls on grainflow characteristics on inclined planes (Börzsönyi et al., 2008; Meninno et al., 2018; Rendina et al., 2019; Tischer et al., 2001); or grainflows on simulated dune slopes (Allen, 1970; McDonald & Anderson, 1992, 1995). Important studies have focused on key grainflow characteristics such as critical slope angles for the initiation of movement (Börzsönyi et al., 2008; Edwards et al., 2019; McDonald & Anderson, 1992; Sutton et al., 2013b); the dynamics of flow processes (Drake, 1990); relationships between the magnitude and frequency of grainflows and sand transport rates (Sutton et al., 2013a); grainflow shapes (Cornwall, Bourke, et al., 2018; Cornwall, Jackson, et al., 2018; Ewing et al., 2017; McDonald & Anderson, 1995, 1996; Nickling et al., 2002; Nield et al., 2017; Sutton et al., 2013a; Tischer et al., 2001; P. Zhang et al., 2022); and controls on the length and speed of grainflows (Börzsönyi et al., 2008; McDonald & Anderson, 1995, 1996; Meninno et al., 2018; Tischer et al., 2001).…”

Effects of Bed Hydrophobicity on Post‐Fire Debris Flow Entrainment and Momentum Growth

“…This was compared to the PIV analysis, showing a good match (2% difference). Furthermore, for channels that are wide enough compared with the grain size (W/d = 250), lateral walls have a negligible influence (Meninno et al, 2018) on average flow velocity. Considering that the ratio of channel width and particle size here (W/d ∼ 2,000) is much larger than the threshold value (W/d = 250) given by Meninno et al (2018), the observed erosion kinematics from side view are advisable.…”

“…Furthermore, for channels that are wide enough compared with the grain size (W/d = 250), lateral walls have a negligible influence (Meninno et al, 2018) on average flow velocity. Considering that the ratio of channel width and particle size here (W/d ∼ 2,000) is much larger than the threshold value (W/d = 250) given by Meninno et al (2018), the observed erosion kinematics from side view are advisable. Figure 6 shows the observed erosion process in the case of water repellent bed with 20% volumetric water content (test ID: R_20).…”