MICROSTRUCTURAL SIMULATION AND IMAGING OF GRANULAR FLOWS IN 2-DIMENSIONAL AND 3-DIMENSIONAL HOPPERS

Distinct element simulations of granular flows in two-and three-dimens ional hoppers are compared with imaging data from conventional photogr aphy and gamma-ray tomography where information of the order of the pa rticle size can be extracted. A novel feature of these comparisons is that both particle and vessel dimensions are matched exactly between t he experiments and the computer simulations, thereby leaving little sc ope for speculation regarding 'scale effects' which are often used to justify scepticism over the validity of simulation predictions. Anothe r novel feature of the work is that quantitative comparisons are provi ded during the entire period of filling and discharge events rather th an selecting an arbitrary 'snapshot' in time, as is often the case in such simulation studies. Microstructural inspection of two-dimensional photographs of systems with large disc particles provides quantitativ e information which shows good agreement with simulation in terms of p acking height, static and flowing voidage, stagnant/flow boundaries in funnel flow and heap/repose angles. Three-dimensional solids fraction data from packed beds of 7 mm diameter maple peas obtained by transmi ssion gamma-ray tomography show encouraging agreement with simulation. An important result of these investigations is the degree of correlat ion between the flowing voidage and flow velocity of particles which a re individually both affected by variations in particle size and shape but are mutually compensating in their effects on the simulated and m easured discharge rates. In general, the simulations produce a less di lated assembly moving at smaller velocities. (C) 1997 Elsevier Science S.A.