Flow rate in 2D silo discharge of binary granular mixtures: The role of ordering in monosized systems

A long-standing debate regarding the dynamics of silo discharge revolves around the use of mono-dispersed grains in simplified models. It is well-known that granular systems composed of particles of the same size can generate crystal or quasi-crystal domains with specific structural and dynamic behaviors. In this work, we present 2D simulations of the discharge of silos filled with binary mixtures of circular grains that, crucially, conserve the same mean particle size in order to isolate the effect of dispersity on flow rate. We address the question of how the size ratio affects the mass flow rate, in particular considering the limit of mono-sized systems. We observe that the flow rate depends only weakly but non-monotonically on bidispersity -- slightly bidisperse systems exhibit a maximum flow rate in comparison with purely monodisperse or more strongly bidisperse mixtures -- and that spatial ordering in the vicinity of the orifice is not strongly influenced by dispersity of grains.