Effect of Middle Vertical Slot Width on the Hydraulic Characteristics of Vertical-Slot Double-Chamber Fishways

The hydraulic characteristics of vertical-slot double-chamber fishways are critical determinants of fish passage efficiency. Various geometric dimensions and hydraulic operating parameters jointly determine the internal flow characteristics of vertical-slot double-chamber fishways, such as chamber aspect ratio, side slot width, bed slope and inlet discharge. Focusing on the relative width of the middle vertical slot (b0/B), this study employs computational fluid dynamics (CFD) simulations to investigate its regulatory mechanism on hydraulic performance. The evolution of the flow-field structure in a double-chamber fishway was analyzed under 12 groups of relative slot-width conditions, and the influence of b0/B on key hydraulic parameters was quantitatively evaluated, including flow velocity distribution, vortex structure, mainstream attenuation, and water exchange between chambers. The results indicate that the impact of b0/B on hydraulic characteristics exhibits a distinct phased behavior. By modifying the momentum distribution between the vertical slot and the pool, b0/B regulates the formation, development, and interaction of the dominant vortex system. When b0/B ranges from 0.13 to 0.16, the flow-field structure is optimal, characterized by a high effective utilization rate of the mainstream, a stable along-course energy attenuation rate of approximately 40%, a relatively uniform flow velocity distribution at the vertical-slot section, and a turbulence kinetic energy level in the chamber that falls within the literature-based reference range for fish-passage hydraulics. This study characterizes the internal evolution mechanism of fishway hydraulic characteristics regulated by the relative width of the vertical slot, providing a robust theoretical basis and practical parameter-selection guidance for the refined design and performance optimization of vertical-slot double-chamber fishways.