Abstract
Granular slides are omnipresent in both natural and industrial contexts. Scale effects are changes in physical behaviour of a phenomenon at different geometric scales, such as between a laboratory experiment and a corresponding larger event observed in nature. These scale effects can be significant and can render models of small size inaccurate by underpredicting key characteristics such as flow velocity or runout distance. Although scale effects are highly relevant to granular slides due to the multiplicity of length and time scales in the flow, they are currently not well understood. A laboratory setup under Froude similarity has been developed, allowing dry granular slides to be investigated at a variety of scales, with a channel width configurable between 0.25 and 1.00 m. Maximum estimated grain Reynolds numbers, which quantify whether the drag force between a particle and the surrounding air act in a turbulent or viscous manner, are found in the range 102 − 103. A discrete element method (DEM) simulation has also been developed, validated against an axisymmetric column collapse and a granular slide experiment of Hutter et al. (Acta Mech 109:127–165, 1995), before being used to model the present laboratory experiments and to examine a granular slide of significantly larger scale. This article discusses the details of this laboratory-numerical approach, with the main aim of examining scale effects related to the grain Reynolds number. Increasing dust formation with increasing scale may also exert influence on laboratory experiments. Overall, significant scale effects have been identified for characteristics such as flow velocity and runout distance in the physical experiments. While the numerical modelling shows good general agreement at the medium scale, it does not capture differences in behaviour seen at the smaller scale, highlighting the importance of physical models in capturing these scale effects.
Highlights
Granular slides and flows are common phenomena, in natural contexts such as landslides, avalanches, and pyroclastic flows (Pudasaini and Hutter 2010), and in industrial applications such as chutes, hoppers, blenders, rotating drums (Turnbull 2011; Zhu et al 2008), and heap formation (Bryant et al 2014; Markauskas and Kačianauskas 2011; Zhang and Vu-Quoc 2000)
The simulation data shown is at the medium scale due to minimal differences found in comparison to other scales
This may be caused by Reynolds number (Re) scale effects that may be present in the smaller experiments, which would imply that laboratory experiments at λ = 1 will continue this trend with increased slide velocities and runout distances
Summary
Granular slides and flows are common phenomena, in natural contexts such as landslides, avalanches, and pyroclastic flows (Pudasaini and Hutter 2010), and in industrial applications such as chutes, hoppers, blenders, rotating drums (Turnbull 2011; Zhu et al 2008), and heap formation (Bryant et al 2014; Markauskas and Kačianauskas 2011; Zhang and Vu-Quoc 2000). Granular slides can cause catastrophic damage through their bulk motion (Haque et al 2016), but they can have drastic indirect effects, with slides impacting into bodies of water producing significant tsunamis (Heller et al 2008). This can lead to secondary hazards such as unintentional dam formation (Chang et al 2011), dam overtopping (Yavari-Ramshe and Ataie-Ashtiani 2016), or flooding of nearby coastal areas or settlements (Glimsdal et al 2016). It is expected that between these three numbers, Re will be the dominant source of scale effects for granular slides
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