Steady and unsteady fluidised granular flows down slopes

David Jessop, Andrew Hogg, Mark Gilbertson, Christian Schoof

Research output: Contribution to journalArticle (Academic Journal)peer-review

1 Citation (Scopus)
311 Downloads (Pure)

Abstract

Fluidisation is the process by which the weight of a bed of particles is supported by a gas flow passing through it from below. When fluidised materials flow down an incline, the dynamics of the motion differ from their non-fluidised counterparts because the granular agitation is no longer required to support the weight of the flowing layer. Instead, the weight is borne by the imposed gas flow and this leads to a greatly increased flow mobility. In this paper, a framework is developed to model this two phase motion by incorporating a kinetic theory description for the particulate stresses generated by the flow. In addition to calculating numerical solutions for fully developed flows, it is shown that for sufficiently thick flows there is often a local balance between the production and dissipation of the granular temperature. This phenomenon permits an asymptotic reduction of the full governing equations and the identification of a simple state in which the volume fraction of the flow is uniform. The results of the model are compared with new experimental measurements of the internal velocity profiles of steady granular flows down slopes. The distance covered with time by unsteady granular flows down slopes and along horizontal surfaces and their shapes are also measured and compared with theoretical predictions developed for flows that are thin relative to their streamwise extent. For the horizontal flows, it was found that resistance from the sidewalls was required in addition to basal resistance to capture accurately the unsteady evolution of the front position and the depth of the current and for situations in which side-wall drag dominates, similarity solutions are found for the experimentally-measured motion.
Original languageEnglish
Pages (from-to)67-120
Number of pages53
JournalJournal of Fluid Mechanics
Volume827
Early online date18 Aug 2017
DOIs
Publication statusPublished - 25 Sep 2017

Keywords

  • fluidized beds
  • particle/fluid flow
  • multiphase flow

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