Stripes in sheared non-Brownian suspensions with a free surface

The experiments of Tirumkudulu et al. (Phys. Fluids 11 (1999) 507; Phys. Fluids 12 (2000) 1615) showed spontaneous segregation and stripe formation in neutrally buoyant suspensions of particles in a partially filled, horizontal, rotating cylinder. Here, we propose a mechanism for this phenomenon, using two well-known properties of suspensions—shear-induced diffusion of particles and the concentration dependence of the viscosity.