Effect of Inter-Orifice Spacing on Granular Flow Discharge Rate: The Role of an Inter-Orifice Quasi-Solid Region

The discharge behavior of granular materials from double-orifice silos is strongly affected by the inter-orifice spacing, yet the mechanical role of the inter-orifice region remains unclear. In this study, discrete element method (DEM) simulations are combined with experiments to investigate the formation, stability, and collapse of an inter-orifice quasi-solid region and its impact on the discharge rate. The results show that increasing the inter-orifice spacing progressively weakens shear transmission between adjacent outlets, promoting the development of a low-velocity, load-bearing quasi-solid region. Based on μ(I) rheology and a nonlocal granular fluidity framework, the quasi-solid region is shown to be controlled by local shear activation rather than by geometric separation alone. Once the inter-orifice quasi-solid region is formed, this region restricts the spatial extension of shear bands near the outlets, leading to a reduction in the effective shear area and a corresponding decrease in the discharge rate. A critical inter-orifice spacing is identified, beyond which the two outlets discharge independently. These findings provide a mechanistic understanding of flow-rate regulation in multi-orifice silos, offering guidance for the design of granular discharge systems.