Abstract: A variety of migratory fish species inhabit China's seas and rivers, and it is difficult for a single fishway to meet the requirements of different swimming behaviors of all the species. Thus far, most previous studies focused on single fishways, while the studies of the combined types were limited to numerical simulations and few experiments were reported. In this work, we design a combined fishway composed of a notch weir, a rectangular central orifice, and a vertical slot, and experimentally study the turbulent structures of its flows. An acoustic Doppler velocimetry (ADV) is used to measure the three-dimensional instantaneous flow velocities at all the gauge points in the combined fishway pool; and various flow characteristics are analyzed–time-averaged flow velocity, turbulence intensity, Reynolds stress, frequency-spectrum characteristics, correlation functions, and turbulence scales. The experimental results show the flow three-dimensionality of the combined fishway is more pronounced than that of a single type. Longitudinal flow velocity exhibits an obvious peak zone on the horizontal plane, and transverse and vertical velocities indicate a vortex occurring at cross sections. In the converging region between the vertical slot wall jet and orifice jet, the turbulence intensities of longitudinal, transverse and vertical velocities take large values and then are decreasing gradually after that. Reynolds stress shows a peak zone largely at the intersection of multiple jets. The dominant frequency of longitudinal fluctuation energy is the highest in central orifice passage, followed by notch weir and vertical slot. Longitudinal velocity fluctuations are correlated with time to a degree of the high-to-low order: notch weir, central orifice, and vertical slot; and their time periods increase along the main flow. The integral and micro scales show vortex structures are related to different flow regions in the combined fishway.

Key words: hydraulics, combined fishway, flow field vectors, three-dimensional velocity, turbulent structures