Dense, rapid flows of inelastic grains under gravity.
Abstract: We address the regime of rapid flows of densely packed collections of grains under gravity. First, we present experimental results obtained in inclined channels in two dimensions (with free surface) and we recall results obtained in three dimensions. We show that with a non-sliding condition at the bottom, the velocity profile appears as linear in the stationary regime, for moderate slopes. This result cannot be accounted for by standard hydrodynamic descriptions; the deep reason is that collisions are multicontact, in the case of dense packings, unlike the starting assumption of kinetic theories. Emphasizing the role of inelastic losses and collapse, we propose a new approach relying on a long range dissipation scheme. Our model succeeds in accounting qualitatively and quantitatively for the linear profile of velocity found in experiments on dense gravity-driven flows (1).
(1) Phys. Rev. Lett. 90, 144302 (2003).