Abstract: By using the RNG k-ε model, we examined the impact of arranging cylindrical obstacles in the pool chamber of vertical slot fishway on the hydraulic characteristics. We comprehensively analyzed the alterations in flow pattern, flow velocity, turbulent kinetic energy (TKE), and volumetric energy dissipation rate (E) in the presence of cylindrical obstacles arranged at different positions. Our findings manifest that the placement of the cylinder at x=1.5b₀ and y=3.1b₀ (where we designate the intersection between the upstream face of the short baffle and the guide wall as the origin and b₀ as the cylinder’s diameter or the vertical slot’s width) does not effectively reduce the maximum velocity in the vertical slot area but decreases the area of low-velocity recirculation, which would possibly reduce fish passing efficiency. When the cylinder is positioned at x=2.2b₀ and y=3.1b₀, the maximum flow velocity decreases by 12% compared to the conventional layout, creating an “Ω” shaped flow pattern and elongates the streamline in the chamber, conducive for fish migration. However, upon moving the cylinder downstream to x=3.0b₀, its positive influence on the hydraulic characteristics within the pool weakens. Although cylinders could effectively lower the maximum TKE and promote a more even distribution of TKE within the pool, the position of cylinders greatly influences the E distribution, and an inappropriate location increases E and thus decreases fish migration efficiency.

Key words: vertical slot fishway, pool chamber structure, velocity distribution, hydraulic characteristics, turbulent kinetic energy