Experimental study of turbulent flows over sharp-crested spillways with a circular downstream curvature profile for downstream fish migration
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Date
2022-08-26
Authors
Shirinzad, Ali
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Abstract
This thesis presents experimental investigations of the effects of water depth and upstream face inclination on the turbulence characteristics upstream and over spillways. Spillways are hydraulic structures that regulate the reservoir water level and the flow rate passing through the turbines. Recent studies have focused on using surface spill water as migratory pathways to provide a safe bypass for downstream migrants. Developing an effective passage system through spillways requires both biological knowledge of fish behavior and hydraulic knowledge of spillway flows to provide hydrodynamic conditions that fish may exploit. The goal of this study is to understand the effect of upstream face inclination and water depth on the hydrodynamic characteristics and find the most suitable conditions for the downstream passage of fish.
Particle image velocimetry (PIV) technique was used to conduct nine sets of experiments for a sharp-crested spillway of height ℎ = 0.15m with a circular downstream curvature profile. The examined upstream face inclinations included the 90° standard, 45° modified, and 30° modified angles. For each upstream face inclination, three water depths over the crest (𝐷𝑐), including 𝐷𝑐/ℎ = 0.7, 0.4, and 0.2, were investigated to obtain various configurations of the test parameters. The Reynolds numbers based on the spillway height and oncoming velocity (𝑅𝑒ℎ) were 𝑅𝑒ℎ = 46200, 24300, and 10350 for 𝐷𝑐/ℎ = 0.7, 0.4, and 0.2, respectively.
The results showed a distinct recirculation zone at the heel of the 90° standard spillway at the lowest water depth (𝐷𝑐/ℎ = 0.2) and a secondary recirculation bubble near the crest for all test cases. It was concluded that the upstream recirculation bubble may be suppressed by either increasing the water depth or decreasing the upstream face inclination. Decreasing the upstream face inclination generated a more uniform acceleration and decreased the turbulence levels, which may increase the passage efficiency. Overall, the environment generated by the modified spillways suggested a safer and more appealing hydraulic condition for the downstream migrants. Over the spillway, the flow near the free surface was in rigid-body motion, while the angular momentum varied linearly in the stream-wise direction at a far enough distance from the recirculation zone.
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Keywords
PIV, Downstream migration, Spillway, Turbulent flow