Flow localization, asymmetry, and velocity fluctuations in eccentric granular discharge from a quasi-two-dimensional silo

The study investigates the combined effects of outlet eccentricity, sidewall friction, and orifice size on flow localization, velocity asymmetry, and fluctuation dynamics during granular discharge from a quasi-two-dimensional rectangular silo using laboratory experiments and discrete element method (DEM) simulations. Experiments were conducted at outlet eccentricities of 0, 0.5, 0.75, and 0.92 under smooth and rough sidewall conditions. The free-surface evolution, discharge rate, and velocity profiles were measured and compared with corresponding DEM predictions. Increasing outlet eccentricity produces increasingly asymmetric and localized wall-guided flow. The normalized discharge rate remains relatively unchanged at lower eccentricities but exhibits a stronger dependence on eccentricity around and above an empirical crossover of 0.75. Flow asymmetry and fluctuation intensity generally increase with eccentricity, while the influence of sidewall friction becomes more apparent at high eccentricity, where increased friction reduces near-wall particle mobility. Velocity fluctuations are concentrated within the active flowing region and increase at high eccentricity, accompanying the corresponding changes in discharge rate and flow asymmetry. Increasing the orifice size influences the mean velocity field, while its influence on fluctuation intensity depends on the degree of flow localization. Contact-network analysis further shows that increasing eccentricity is accompanied by the redistribution of contact connectivity, contact-force intensity, and force-weighted fabric anisotropy, with strong contacts concentrated predominantly away from the localized active flowing region.