The mechanisms of free surface segregation

Drahun, J.A.; Bridgwater, J.

doi:10.1016/0032-5910(83)80007-2

Cited by 196 publications

(140 citation statements)

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“…As the heap rises, small particles drop out of the flowing layer sooner and remain in the upstream region of the heap, while large particles are advected to the downstream region of the heap. This results in a separation of large and small particles in the streamwise direction (Williams 1963(Williams , 1968Shinohara et al 1972;Drahun & Bridgwater 1983;Goyal & Tomassone 2006;Fan et al 2012), which is also similar to segregation patterns in avalanche flows (Pouliquen et al 1997;Gray & Ancey 2009). …”

Section: Introductionmentioning

confidence: 70%

“…However, quantitative agreement has, until this work, been harder to achieve. Possible reasons for the lack of quantitative agreement in earlier work are the omission of one or more of advection, diffusion, or the dependence of percolation velocity on spatially varying shear rate (Drahun & Bridgwater 1983). In this work we include all three mechanisms and examine their effects on segregation in a granular flow with non-trivial spatial variation: the quasi-two-dimensional (quasi-2D) bounded heap (figure 1(a)).…”

Section: Introductionmentioning

confidence: 99%

“…Many studies have been devoted to understanding the underlying mechanisms and developing predictive frameworks for size segregation and pattern formation in polydisperse, sheared granular flow (Drahun & Bridgwater 1983;Ottino & Khakhar 2000;Yoon & Jenkins 2006;Meier et al 2007;Fan & Hill 2010, 2011aChristov et al 2011). These studies have identified several driving mechanisms for segregation, pattern formation, and mixing of bidisperse particles.…”

Section: Introductionmentioning

confidence: 99%

“…In contrast, in the dense granular flow regime, particle geometry appears to be the primary driving mechanism. A percolation mechanism (Williams 1968;Drahun & Bridgwater 1983;Savage & Lun 1988;Ottino & Khakhar 2000) in which smaller particles are more likely than larger particles to fall through shear generated voids results in smaller particles moving downward while larger particles move upward, an effect that is characterized by a "percolation" velocity. Segregation due to percolation, along with other effects including advection (Hill et al 1999), convection by secondary flow (Khosropour et al 1997;Fan & Hill 2010), and collisional diffusion (Hill et al 1999;Khakhar et al 1999;Gray & Chugunov 2006), determine particle distributions in bidisperse dense flow, sometimes leading to complex patterns (Meier et al 2007;Christov et al 2011).…”

Section: Introductionmentioning

confidence: 99%

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Modelling size segregation of granular materials: the roles of segregation, advection and diffusion

et al. 2014

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Predicting segregation of granular materials composed of different-sized particles is a challenging problem. In this paper, we develop and implement a theoretical model that captures the interplay between advection, segregation, and diffusion in size bidisperse granular materials. The fluxes associated with these three driving factors depend on the underlying kinematics, whose characteristics play key roles in determining particle segregation configurations. Unlike previous models for segregation, our model uses parameters based on kinematic measures from discrete element method simulations instead of arbitrarily adjustable fitting parameters, and it achieves excellent quantitative agreement with both experimental and simulation results when applied to quasi-two-dimensional bounded heaps. The model yields two dimensionless control parameters, both of which are only functions of physically control parameters (feed rate, particle sizes, and system size) and kinematic parameters (diffusion coefficient, flowing layer depth, and percolation velocity). The Péclet number, P e, captures the interplay of advection and diffusion, and the second dimensionless parameter, Λ, describes the interplay between segregation and advection. A parametric study of Λ and P e demonstrates how the particle segregation configuration depends on the interplay of advection, segregation, and diffusion. The model can be readily adapted to other flow geometries.Key words: Authors should not enter keywords on the manuscript, as these must be chosen by the author during the online submission process and will then be added during the typesetting process (see http://journals.cambridge.org/data/relatedlink/jfm-keywords.pdf for the full list) †

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Section: Introductionmentioning

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Modelling size segregation of granular materials: the roles of segregation, advection and diffusion

et al. 2014

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“…This can sometimes be desirable, such as in mining and stone crushing, and can be exploited to separate the grains [1], but it is often a source of great frustration that can significantly degrade the quality and the safety of a product [2]. A considerable amount of early work was therefore performed by engineers who sought to understand the fundamental size segregation mechanisms and learn how to control their effects [3,4,5]. Geologists and sedimentologists were also early pioneers who were quick to identify inversely (or reverse) graded deposits, in which the grain size population coarsens upwards, and use this as an indicator of ancient granular avalanches on dunes, in dense pyroclastic flows and debris flows [e.g.…”

Section: Introductionmentioning

confidence: 99%

A hierarchy of particle-size segregation models: From polydisperse mixtures to depth-averaged theories

Gray¹

2013

AIP Conference Proceedings

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Numerical study on the axial segregation dynamics of a binary-size granular mixture in a three-dimensional rotating drum Physics of Fluids 29, 103302 (2017) Abstract.Particle size segregation in granular avalanches occurs due to inter-particle percolation and squeeze expulsion. The general theory for a polydisperse mixture yields a segregation equation for each grain size class. For a three constituent mixture of large, small and medium sized particles there are three segregation equations, one of which can be eliminated, since the concentrations of all the species necessarily sums to unity. The remaining two coupled parabolic equations can be solved using a standard Galerkin finite element method. Numerical solutions show that small particles percolate to the base of the avalanche, large particles are squeezed to the surface and the medium sized grains are sandwiched in between. For certain choices of the segregation parameters it is possible to generate instabilities that lead to saw-tooth segregation in the threephase mixture, but these die off as the grains separate into bi-disperse sub-mixtures. In general, all the grains contribute to the segregation process and develop an inversely graded particle size distribution, that coarsens upwards. This is known as reverse distribution grading. Sometimes, however, the fine particles may not segregate readily, leading to reverse coarse tail grading. For a bi-disperse mixture, the general theory yields one independent segregation equation, which always seeks to drive the particles into an inversely graded state. However, when the bulk flow shears small particles over the top of large, a breaking size-segregation wave is created. Such waves are important close to flow fronts, because they allow large particles that are over-run to rise up to the surface again and be recirculated. Computing the evolving particle-size distribution in a three-dimensional flow is still a challenge. However, it is possible to obtain a simplified representation by integrating the segregation equation through the avalanche depth. This fits naturally into the depth-averaged framework of avalanche models and opens the door to fully couple calculations to study levee formation and segregation induced flow fingering.

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Gravel Transport in Granular Perspective

Frey¹,

Church

2012

Gravel‐Bed Rivers

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The mechanisms of free surface segregation

Cited by 196 publications

References 7 publications

Modelling size segregation of granular materials: the roles of segregation, advection and diffusion

Modelling size segregation of granular materials: the roles of segregation, advection and diffusion

A hierarchy of particle-size segregation models: From polydisperse mixtures to depth-averaged theories

Gravel Transport in Granular Perspective

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