While convective flows are implicated in many granular segregation processes, the associated particle-scale rearrangements are not well understood. A three-dimensional bidisperse mixture segregates under steady shear, but the cyclically driven system either remains mixed or segregates slowly. Individual grain motion shows no signs of particle-scale segregation dynamics that precede bulk segregation. Instead, we find that the transition from nonsegregating to segregating flow is accompanied by significantly less reversible particle trajectories and the emergence of a convective flow field.
Harrington, M., Weijs, J. H., & Losert, W. (2013). Suppression and emergence of granular segregation under cyclic shear. Physical review letters, 111(7), . https://doi.org/10.1103/PhysRevLett.111.078001