Segregation force in dense bidisperse granular mixtures

Granular segregation is typically driven by the combined effects of gravity and shear. Recent studies have characterized the size segregation force on a single intruder with a scaling law that consists of two additive terms: a buoyancy-like gravity-induced pressure gradient term and a shear rate gradient term, both of which depend on the particle size ratio. However, a generalized scaling of the force is still lacking for segregation in finite-concentration mixtures (rather than a single intruder). Here we explore the mixture segregation force, particularly the shear rate gradient term, in DEM simulations of controlled-velocity granular flows where the shear profile is varied. Measuring the mixture segregation force using a modified virtual-spring-based 'force meter' technique reveals that the concentration dependence of the force is well-characterized by a hyperbolic tangent function with no additional free parameters. The extended concentration-dependent scaling law accurately predicts the mixture segregation force in size-bidisperse particle mixtures over a range of pressures, shear rates, and particle size ratios.