Résumé
Three-dimensional contact dynamics simulations are used to study the flow properties of elongated grains in a silo. The grains have a sphero-cylinder shape described by their aspect ratio, which varies from 1 (sphere) to 5 for a thin elongated grain. To ensure accurate statistics, a "perpetual" discharge is simulated for different orifice sizes by 1) reintroducing the exiting grains at the top of the silo and 2) implementing a procedure to break arches when the flow comes to rest, especially for small orifice sizes. As a general observation, when the flow rate Q is plotted as a function of orifice size, it follows a Beverloo-like curve for all shapes. In contrast, for a given orifice size, the flow rate Q is found to vary non-linearly with grain elongation: It first increases to a maximum and then decreases with increasing elongation. Both the packing fraction and velocity profiles are found to be self-similar near the orifice when normalised to the maximum packing fraction and velocity measured at the center of the orifice, respectively. From these profiles, a 3D theoretical expression, inspired by the work of Janda et al [Phys. Rev. Lett. 108, 248001], for the evolution of the flow rate with grain shape is derived, proving that the non-linear variation of Q has its origin in the non-linear variation of the packing fraction with grain shape measured at the centre of the orifice.