Scaling particle-size segregation in wide-ranging sheared granular flows

Scaling relationships have been proposed to describe shear-driven size segregation based on intruder experiments and simulations [Trewhela et al., “An experimental scaling law for particle-size segregation in dense granular flows,” J. Fluid Mech. 916, A55 (2021); Jing et al., “A unified description of gravity-and kinematics-induced segregation forces in dense granular flows,” J. Fluid Mech. 925, A29 (2021)]. While these models have shown agreement with experimental and numerical results under uniform shear rate, their validity across varying shear-rate conditions remains uncertain. Here, we employ Discrete Element Method simulations to investigate particle size segregation in sheared granular flows under wide-ranging shear-rate conditions. We find that the scaling between segregation velocity and local rheological conditions holds only within a moderate inertial number range (0.01<I<0.1) and breaks down in both quasi-static and collisional regimes. Furthermore, we show that this discrepancy leads continuum models to mispredict segregation rates in bidisperse mixtures. These findings emphasize the need for more generalized scaling laws capable of capturing segregation dynamics across a broader spectrum of shear-rate conditions and regimes.