Fingering in granular flows

Pouliquen, Olivier; Delour, J.; Savage, Stuart B.

doi:10.1038/386816a0

Cited by 198 publications

(208 citation statements)

References 17 publications

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“…In contrast, few studies concern the stability of granular flows along slopes which are the paradigm for geophysical situations. The formation of roll waves has been reported [9] and a fingering instability observed during the propagation of a granular front has been described [10]. In this Letter we present a new instability that spontaneously generates longitudinal vortices (i.e., with axes parallel to flow) in rapid granular flows down rough inclined planes.…”

Section: Longitudinal Vortices In Granular Flowsmentioning

confidence: 76%

Longitudinal Vortices in Granular Flows

2001

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We present a new instability observed in rapid granular flows down rough inclined planes. For high inclinations and flow rates, the free surface of the flow experiences a regular deformation in the transverse direction. Measurements of the surface velocities imply that this instability is associated with the formation of longitudinal vortices in the granular flow. From the experimental observations, we propose a mechanism for the longitudinal vortex formation based on the concept of granular temperature.Comment: 4 pages, 4 figure

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Section: Longitudinal Vortices In Granular Flowsmentioning

confidence: 76%

Longitudinal Vortices in Granular Flows

2001

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“…This opens up the possibility of coupling the bulk motion to the local size distribution through the modification of the pore-pressure or the basal friction to investigate the instabilities that these can generate (e.g. Pouliquen, Delour & Savage 1997;Pouliquen & Vallance 1999;Iverson & Vallance 2001;Iverson 2003).…”

Section: Discussionmentioning

confidence: 99%

Particle-size segregation and diffusive remixing in shallow granular avalanches

2006

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Segregation and mixing of dissimilar grains is a problem in many industrial and pharmaceutical processes, as well as in hazardous geophysical flows, where the sizedistribution can have a major impact on the local rheology and the overall run-out. In this paper, a simple binary mixture theory is used to formulate a model for particlesize segregation and diffusive remixing of large and small particles in shallow gravitydriven free-surface flows. This builds on a recent theory for the process of kinetic sieving, which is the dominant mechanism for segregation in granular avalanches provided the density-ratio and the size-ratio of the particles are not too large. The resulting nonlinear parabolic segregation-remixing equation reduces to a quasi-linear hyperbolic equation in the no-remixing limit. It assumes that the bulk velocity is incompressible and that the bulk pressure is lithostatic, making it compatible with most theories used to compute the motion of shallow granular free-surface flows. In steady-state, the segregation-remixing equation reduces to a logistic type equation and the 'S'-shaped solutions are in very good agreement with existing particle dynamics simulations for both size and density segregation. Laterally uniform time-dependent solutions are constructed by mapping the segregation-remixing equation to Burgers equation and using the Cole-Hopf transformation to linearize the problem. It is then shown how solutions for arbitrary initial conditions can be constructed using standard methods. Three examples are investigated in which the initial concentration is (i) homogeneous, (ii) reverse graded with the coarse grains above the fines, and, (iii) normally graded with the fines above the coarse grains. Time-dependent twodimensional solutions are also constructed for plug-flow in a semi-infinite chute.

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“…The first two below occur in both dry and fluid media. The basic physics of these and many other similar processes are discussed and reviewed by Aranson and Tsimring (2009; see also the review by Ottino and Khakhar 2000; see also Al-Naafa and Selim 1992; Davis and Acrivos 1985;Greenspan and Ungarish 1982;Jaeger et al 1996;Kynch 1952;Pouliquen et al 1997). …”

Section: Granular Processesmentioning

confidence: 99%

On some fundamentals of igneous petrology

Marsh

2013

Contrib Mineral Petrol

135

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The age-old process of crystal fractionation leading to the diversity of the igneous rocks and Earth itself is an exceedingly well-understood chemical process in magmatism and physical chemistry. But the broader physical aspects of this and related processes have proven elusive on many fronts, especially in its relation to the spatial variations in rock composition, texture, and macroscopic features like layering. Magmatic systems, be they volcanic, dikes, sills, or plutons, are generally analyzed with a problem at hand and an end result in mind. The processes invoked to solve these problems, which are most often purely chemical, are often unique to each problem with few if any general principles emerging that are central to understanding the wider perspective of magmatic processes and problems. An attempt is made at the outset to provide a list of inviolate Magmatic First Principles that are relevant to analyzing most magmatic problems. These involve: initial conditions; critical crystallinity; solidification fronts; transport and emplacement fluxes; phenocrysts, xenocrysts, primocrysts; crystal size; layering and crystal sorting; thermal convection; magmatic processes are physical. Along with these principles, two reference magmatic systems are suggested where the initial conditions and outcome are unequivocal: the Sudbury impact melt sheet and the Hawaiian lava lakes. Sudbury formed in *5 min by superheated magma crystallized to a near uniform sequence, while the tiny lava lakes, formed of crystal-laden slurries, form a highly differentiated layered sequence. The major difference is in the initial conditions of formation, especially the nature of the input materials. The challenge is to construct and analyze magmatic systems (i.e., magma chambers, sills, dikes, and lavas) using these reference end members and the suggested principles. The Hawaiian 500,000 year volcanic record exhibits what can be expected as input materials, namely a highly varied output of magma of an overall composition reflecting the abundance of entrained olivine primocrysts. The provenance of these crystals is varied, and within any single sample, the population may be highly heterogeneous in composition from crystal to crystal, yet the overall pattern of chemical fractionation is exceedingly regular and well defined. If similar inputs go to form large intrusions, these systems will undoubtedly be dominated by crystal-rich slurries, which provide a vast set of physical processes promoting exotic layering and, at the same time, given the effects of annealing and continued crystal growth, a final chemical record adhering to all the time-honored effects of crystal fractionation. The long assumed initial condition of instantaneously emplaced crystal-free magmas cannot reasonably produce the observed rock records.

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Fingering in granular flows

Cited by 198 publications

References 17 publications

Longitudinal Vortices in Granular Flows

Longitudinal Vortices in Granular Flows

Particle-size segregation and diffusive remixing in shallow granular avalanches

On some fundamentals of igneous petrology

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