High speed granular flows down inclines

We investigate numerically high speed granular flows down inclines. Recent numerical works have
highlighted that the presence of lateral frictional walls allows to produce novel Steady and Fully
Developed (SFD) flow regimes at high angle of inclination where accelerated regimes are usually
expected (Brodu et al., 2015). These SFD regimes present non-trivial features, including secondary flows
with longitudinal vortices and “supported“ flows characterized by a central and dense core supported by
a very agitated dilute layer.
We present a review of these new regimes and provide their domain of existence in the parameter space
including the mass hold-up M, the inclination angle θ and the gap width between the lateral walls. We
also investigate the sensitivity of these states to the mechanical parameters of particles such as the
restitution coefficient e for binary collisions.
We emphasize two salient outcomes. (I) First, our simulations reveal that the emergence of the
supported flows is favored by low restitution coefficient (i.e., high dissipation). Surprisingly, increasing
the dissipation leads to faster flows. This is explained by a contraction of the flow, resulting in a lower
contribution of the side-wall friction. (ii) Second, despite the diversity of the supported flow regimes, the
simulations bring to the light that the mass flow rate Q obeys a simple scaling law with the mass hold-up
and the gap width: Q~M3/4W1/4.
Bibliography
Brodu et al., 2015, Journal of Fluid Mechanics, 2015, 769, 218-228