Author(s): Xingjun Fang; Mark F. Tachie; Christos Katopodis; Haitham Ghamry

Linked Author(s): Haitham Ghamry, Christos Katopodis

Keywords: Bar rack; Fish guidance; Particle image velocimetry; Turbulent statistics; Turbulent eddy

Abstract: Particle image velocimetry (PIV) was used to investigate the statistical and structural characteristics of turbulent flows induced by a bar rack, with an objective of improving guidance of downstream migrating fish. The configuration of the investigated bar rack was recommended by previous studies for optimum fish guidance efficiency. Two different incoming velocities were tested, resulting in two Reynolds numbers of 4000 and 6000 (based on incoming velocity and bar thickness). Two-dimensional two-component PIV was used to measure the flow field in the streamwise-spanwise plane at half height of the bottom overlay, while two-dimensional threecomponent PIV was used to measure the flow field in the streamwise-vertical plane at the channel mid-span. The results indicate that mean flow accelerates while being deflected towards the bypass. During the process, the normal velocity perpendicular to the bottom overlay becomes larger than the sweep velocity parallel to the bottom overlay near the bypass. This implies that near the rear part of the bar rack, fish may impinge on the bars resulting in low fish guidance at this location. As fish approach the bottom overlay near the wall, they experience elevated Reynolds stresses but smaller turbulent eddies. In the streamwise-vertical plane at the channel mid-span, the spanwise velocity is high below the bottom overlay height. This underscores the positive effects of the bottom overlay on fish guidance efficiency. As fish approach the bars in the region of the bottom overlay, they are exposed to strong and abrupt switching of mean velocity acceleration and deceleration, that may deter fish from contacting the bars. Additionally, turbulent eddies vary in orientation, size and topology as the bottom overlay is approached. These conditions may help fish to avoid contact with the bottom overlay and improve fish guidance.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p0406-cd

Year: 2023