Effect of orifice positions on velocity fluctuations during granular discharge from a Quasi-2D rectangular silo

Abstract

This study examines how orifice position affects velocity fluctuations during gravity-driven discharge from a quasi-2D rectangular silo, combining experiments with Discrete Element Method (DEM) simulations. Experiments used a single 10 × 10 mm² orifice and spherical glass beads (d = 0.9 ± 0.1 mm); high-speed imaging and Digital Particle Image Velocimetry (DPIV) measured front-wall velocity fields for three orifice placements (concentric, mid-eccentric, extreme eccentric). Experimental results show that orifice eccentricity strongly modifies mean flow and fluctuation patterns: extreme eccentric openings produce the largest fluctuations and an asymmetric velocity field adjacent to the sidewall. DEM simulations (front-layer extraction to match DPIV) were first used to validate the experiments, DEM captures average velocities (u_avg and v_avg) and spatial trends (DEM overpredicts v_avg by ≈10% at mid-eccentricity and mass flow by ≈2%), and then to explore parametric effects not varied experimentally. Parametric DEM runs indicate that increasing orifice width and particle diameter generally raise both average discharge velocity and fluctuation magnitudes. Statistical characterization of fluctuations reveals near-Gaussian cores with fat tails close to the outlet. The results show that eccentricity, orifice size, and grain size collectively regulate wall slip, shear localization, and velocity variability, with direct implications for silo design.