Formation of longitudinal structures in granular flows

In the framework of the theory of partially fluidized granular flows we study the formation of longitudinal structures observed experimentally by Forterre and Pouliquen in a flow down a rough inclined plane. We show that the formation of longitudinal structures is related to the positive feedback between the fluidization rate and the lateral stress (side pressure), which leads to a convective instability. Our theory explains main experimental features, such as appearance and amplification of the structure at some distance from the outlet and non-stationary behavior of the structures.