LHE on the cover page of the Journal of Fluid Mechanics

Natural flows such as avalanches and debris flows can travel over long distances. One of the mechanisms explaining this high mobility is self-channelization: part of the largest blocks are trapped within the leading edge, then deposited laterally and form levees that confine the flow. This limits lateral spreading and reduces power dissipation. In this paper, fruit of a collaboration between EPFL, the University of Manchester and the University of Twente, we present a diffusion model that describes how coarse particles segregrate. The theoretical model is compared with experimental data (including those that serve to illustrate the cover page) and numerical simulations by discrete element. One of the key findings is that contrary to what has been initially anticipated and according to the flow conditions, not all coarse particles are trapped in the leading edge, some successfully escape it and join the flow tail.