Abstract
By means of 2D Contact Dynamics simulations, we investigate the flow properties ofgranular materials composed of elongated grains within a silo of varying orifice size. Thegrains have a rounded-cap rectangular shape described by their aspect ratio parametervarying from 1 for a disk to 7 for a thin or long grain. In order to isolate the effects of grainshape, both the mass and surface of the grains are kept constant as well as the total massof the system and the condition of the discharge. By simulating a large number ofavalanches, the flow rates “Q”, the velocity profiles and the packing fraction profiles closeto the orifice are studied for increasing grain aspect ratio and for various characteristicdimensionless numbers such the orifice size normalized by the grain size, or the systemsize normalized either by the orifice size or by the grain size. A counterintuitive finding ofthis work is that the effect of grain elongation depends on the size of the orifice. Indeed,we find that Q is independent of grain elongation for small (normalized) orifice size. Incontrast, Q increases with grain elongation for intermediate (normalized) orifice size, andit may saturate or continue to increase at larger grain aspect ratio. Based on themethodology proposed by Janda et al. (2012) to deduce the flow rate from the packingfraction and velocity profiles close to the orifice, we show that the nonlinear variation of Qwith grain elongation results from compensation mechanisms between the velocity andthe packing fraction measured at the center of the orifice.