Particle dynamics in avalanche flow of irregular sand particles in the slumping regime of a rotating drum

Slowly rotating drums are important due to their industrial application, but also as a simple model system for studying transient avalanche processes. A speckle visibility spectroscopy (SVS) alongside a simple imaging technique was used to measure the time-resolved avalanching of 1.3mm diameter sand particles in a 35% full rotating drum operating in the slumping regime. The major difference from spherical particle dynamics is visual observation of granular compaction in the upper part of the drum at the beginning of the avalanching process which is not present in experiments with spherical particles. The SVS measurement of avalanching shows that the fluctuation velocity, so called granular temperature, increased sharply before plateauing then decreases sharply to zero during a typical avalanche event which is different to spherical particle behavior where these transitions are more gradual. Furthermore, the granular dynamics of avalanching flow is influenced by a visually observed flowing mound down the avalanching surface so there are more characteristic peaks in the plateau region of the signal for measurement point in the lower part of the bed. Overall, the observed plastic deformation is influencing the dynamics of the system in several ways indicating the importance of considering particle shape in the study of granular flow dynamics. [Display omitted] •Granular dynamics of irregular sand particles in rotating drums is studied by SVS.•Granular compaction in upper part of bed was observed at the beginning of avalanching.•Subsequent formation of mound on flowing surface during avalanches was also observed.•The granular temperature sharply transitions to plateau during surface avalanching.•The granular temperature temporal profile was greatly influenced by compaction.