Streak patterns in binary granular media in a rotating drum

The Discrete Element Method (DEM) is used to understand the formation of radial streak patterns produced when binary granular material (which may differ either in size, density or shape) segregate in a slowly rotating drum. Our simulations show that initial streak formation requires temporal fluctuations in the particle bed’s strength. This, in turn, creates fluctuations in the slope and shape of the upper surface of the bed which control the particle avalanches down the free surface. These ultimately lead to streak formation. We conjecture that growth and stabilisation of a regular streak pattern requires the two sets of particles to have significantly different angles of repose.