Phase transition and bistable phenomenon of granular flows down a chute with successive turnings

This paper studies the granular flow down a chute with two successive turnings, which play the role of bottlenecks for the granular flow system and determine the granular flow state in main section between them. With the increase of main section width D, phase transition from dilute to dense granular flow is observed: When the main section width D is small (large), the granular flow at upper (lower) bottleneck is dense and the granular flow is dilute (dense) in the main section. More interestingly, a bistable region is exhibited, in which either dilute flow or dense flow may occur and continue for the entire run. In this region, the packing in the reservoir will affect initial flow rate and then affect the flow pattern. This study can be viewed as a paradigm for the jamming and unjamming transitions under shear due to gravity.