DEM modelling of the influence of initial stress state on the discharge rate of spherical particles from a model silo

Formulation of a proper physical law describing the dynamics of discharge of granular solids has been undertaken by researchers for decades. A frequently expressed opinion is the existence of the free-fall arch region and independence of the discharge rate on pressure. The objective of this study was to explore the impact of dynamic particle–particle contact interactions in the vicinity of the orifice on the discharge flow rate from a model silo by means of DEM simulations with special attention paid to the impact of the bedding height and bottom pressure. The DEM simulations were performed with an assembly of spherical particles poured on a flat bottom of the cylindrical model silo with a height-to-diameter ratio of 1.14. The bottom pressure was changed by changing the height of the bedding deposit and depositing an additional layer of very dense particles on the top of the bedding of primary particles. The results indicate that the discharge rate was affected by both the orifice diameter and mean bottom pressure during storage. The correction coefficient derived from the integral of the dimensionless acceleration of particles along the dimensionless movement path allowed obtaining very good approximation of the discharge rate using the well known Beverloo equation in the entire range of change of the orifice size and bottom pressure.