Abstract
ABSTRACTImproved particle tracking velocimetry (improved PTV) is proposed for experimental study of very slow dense pebble flow in a silo bed by combining the relaxation method and Voronoï diagram. The improved PTV method is validated by comparison with DEM (discrete element method) simulation and experimental result. Velocity and fluctuation characteristics on different streamlines are investigated to show the macroscopic kinematics of pebble flow. Bulk arches on different locations of the pebble bed are identified. Two local arching characteristics including size distribution and horizontal span are analyzed, and their effects on whole flow regime are discussed. It is found that the arch size distribution follows second-order polynomial distribution in semi-logarithmic scale. The horizontal span of arches provides evidence for transition between the ordered and disordered regimes. The probability distribution of successive angles between the neighbors of arching particles is a good indicator of arch stability. The relation between arch breakdown and contact network change is demonstrated by correlation analysis. High correlation between arching structure and mean velocity in targeted regions is indicated. The characteristic lifetime of arches and autocorrelation time of fluctuation velocity present positive correlation. The bulk arching dynamics is the main reason for fluctuations of particle velocities.
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