Radial segregation patterns in rotating granular mixtures: Waviness selection

Abstract

We model the radial segregation patterns that form in a thin rotating drum partially filled with beads of two sizes. We predict that the waviness (or amplitude-to-wavelength ratio, denoted w) of a pattern should be subjected to low-pass filtering with a cut-off waviness wc that depends strongly on the fill level of the drum. Then we perform experiments and find that w < wc for all patterns, in accord with our prediction. We also find that w = wc for (and only for) steady patterns, and conclude that the waviness of a steady pattern is selected by the low-pass filtering.