Author(s): Ali Shirinzad; Sedem Kumahor; Mark Tachie; Haitham Ghamry; Christos Katopodis

Linked Author(s): Ali Shirinzad, Mark Tachie, Haitham Ghamry, Christos Katopodis

Keywords: PIV; Spillway; Turbulence; Downstream Migration

Abstract: Spillways are anthropogenic obstructions that significantly impact the downstream migration of fish to their spawning grounds. Hence, it is important to understand the influence of spillway geometry on flow hydraulics and fish behavioral responses. The hydraulic environment generated by the commonly used 90° standard spillway designs may provide limited opportunities for timely fish migration. A comprehensive investigation of different spillway geometries, which generate beneficial hydrodynamics for effective fish passage, is lacking. The goal of the present study is to understand the effects of spillway geometry on hydrodynamic fields and relate pertinent characteristics to swimming ability, responses, and safe passage of fish. Three different geometries, including the 90° standard spillway as well as versions with modified angles of inclination of 45° and 30°, were used to examine effects on hydrodynamics. The turbulence characteristics upstream and over the three spillway geometries were experimentally investigated using particle image velocimetry in a recirculating open channel flume with streamwise length, spanwise width, and vertical height of 6.00 m, 0.60 m, and 0.45 m, respectively. The upstream water depth and spillway height were kept constant at D = 0.21 m and h = 0.15 m, while the oncoming flow velocity was set to Ue = 0.162 m/s. This resulted in a Reynolds number based on spillway height (Re = Ue h/ν, where ν is the kinematic viscosity of water at 20℃) of 24300 and a Froude number based on the upstream water depth (Fr = Ue/√gD) of 0.113. The results are analyzed in terms of mean flow topology, Reynolds stresses, and turbulent kinetic energy. Contours of the mean streamwise velocity show that the magnitudes over the spillways increase as the angle of inclination decreases. An elevated region of positive mean vertical velocity is observed upstream of the crest due to the upward deflection of the flow, followed by a sudden change in sign to negative values, which is attributed to the descent of the flow over the crest. The streamwise Reynolds normal stress and vertical Reynolds normal stress also show a reduction in magnitude over the spillway as the angle of inclination decreases. Meanwhile, elevated regions of Reynolds normal stresses are concentrated close to the crest of the spillway. The mean spanwise vorticity is used to examine the orientation of the eddies. Similar to Reynolds stresses, the mean spanwise vorticity shows a decreasing pattern as the angle of inclination decreases. Notably, the upstream vortices become weaker for the modified spillways. In the final paper, the spatial acceleration, turbulent kinetic energy, and strength and size of the large-scale eddies are further examined to highlight the effects of spillway geometry on hydraulics upstream and over spillways.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022923

Year: 2022