Partially saturated granular flow in a rotating drum: The role of cohesion

Partially saturated granular flows are common in various natural and industrial processes, such as landslides, mineral handling, and food processing. We conduct experiments and apply the discrete element method to study granular flows in rotating drums under partially saturated conditions. We focus on varying the strength of cohesion (surface tension) and rotation rate within the modes of rolling flow and cascading flow. With an increase in surface tension, a rolling mode can possess a steeper slope and correspondingly needs a higher rotation rate to transition to a cascading. The depth of the flowing region increases with increasing cohesion, while the sensitivity is reduced for cases of high cohesion. We propose a dimensionless number C-E that captures the combined effects of rotation, gravity, and cohesion on the dynamic angle of repose and flow depth. In addition, we extract statistical information on the formation of clusters within the flow. We find a power law relation between the cluster size distribution and its probability, which indicates that stronger cohesion can promote the formation of larger clusters, and we discuss how cohesion impact on flows manifested by cluster formation.