Particle Dynamics of Irregular Sand Particles Flow within a Rotating Drum

Rotating drums are important due to their industrial application but also as a simple model system for studying transient avalanche process. The speckle visibility spectroscopy (SVS), spatial filtering velocimetry (SFV), and alongside simple imaging techniques were used to measure the time-resolved dynamics of sand particles in a rotating drum operating in discrete and continual avalanching regime. The SVS measurement of discrete avalanching shows that the fluctuation velocity, so called granular temperature, increased sharply before plateauing then decreases sharply to zero values 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 visually observed flowing mound down the avalanching surface so there are more characteristics peaks in plateau region of the signal for measurement point in lower part of the bed. The SFV measurement of continual avalanching shows that there are two velocity peaks in the velocity curve of irregular glass sand at a relatively lower rotating speed. Furthermore, with the increase of the drum speed, the middle valley gradually moves to the upper right and merges with the second peak and there is only one peak in the velocity profile along stream wise direction of the bed surface consequently. And the variation of the velocity distribution of irregular particles with particle sizes, and drum diameters are also studied as well.