Complexity, segregation, and pattern formation in rotating-drum flows

Rotating-drum flows span a variety of research areas, ranging from physics of granular matter through hydrodynamics of suspensions to pure liquid coating flows. Recent years have seen an intensified scientific activity associated with this unique geometrical configuration, which has contributed to our understanding of related subjects such as avalanches in granules and segregation in suspensions. The existing literature related to rotating-drum flows is reviewed, highlighting similarities and differences between the various flow realizations. Scaling laws expressing the importance of different mechanisms underlying the observed phenomena have been focused on. An emphasis is placed on pattern formation phenomena. Rotating-drum flows exhibit stationary patterns as well as traveling and oscillating patterns; they exhibit reversible transitions as well as hysteresis. Apart from the predominant cylindrical configuration, this review covers recent work done with tumblers having other geometries, such as the sphere and the Hele-Shaw cell.