Segregation forces in dense granular flows: From single intruders to high concentrations

Particle size segregation in dense granular flows has been studied extensively in the context of mixtures and, more recently, single intruder particles. However, the connection between the single intruder limit (i.e., a vanishing concentration) and a mixture with a finite concentration remains unclear. Here we extend the virtual-spring-based force meter approach for single intruder particles to bidisperse mixtures of arbitrary species concentrations to characterize the segregation force as a function of concentration for various particle size ratios in controlled, constant-shear-rate flow simulations. The segregation force on particles exhibits a plateau at low concentrations and varies monotonically above a critical concentration, indicating a transition from non-interacting intruders to cooperative phenomena in mixtures. The segregation force is then used to develop an accurate model of stress partitioning as a function of species concentration, thus bridging the gap between single intruder migration and mixture segregation in dense granular flows.