Radial segregation in a two-dimensional rotating drum

We simulate the size segregation of a binary mixture of granular material in a half filled two-dimensional rotating drum using the discrete elements method with linear contact forces. The dynamics of the segregation process is studied in detail as function of the angular velocity of the drum. We propose an order parameter to characterize the final amount of segregation and the segregation speed which allows to compare systems of different sizes and with different material properties. We demonstrate its usefulness by investigating its time dependence as function of the angular velocity of the drum and discuss the interplay between the thickness of the flowing layer and the mean particle velocity.