Vertical slot fish passes have been applied as a solution to mitigate fish migration problems in running waters, for over two decades. They are commonly used to enable target fish to ascend through obstacles in rivers. However, small species are rarely considered in such fishways, of which the performance for small fish still remains unknown. This experiment was to study the turbulence structure in a vertical slot fish pass concerning two different pool length/width ratios of 9 and 6.67 as well as the effect of instal領(lǐng) a cylinder behind the slot in affecting the characteristics of instationary flow. Cylinders are considered an effective solution to modify the flow structure and to reduce velocity and turbulent energy in order to adapt the flow for the passage of small fish species. Flow visualization and particle image velocimetry were used to study the characteristics of mean flow and turbulence and particular emphasis on the unsteady flow. The results show that flow patterns consist of a water jet and one or two recirculation zones depending on the length/width ratio of the pool. The direction of the jet was strongly affected by the vertical cylinders. The frequencies and spatio-temporal evolutions of the main jet beats were analyzed. Combining with the previous studies of fish migration experiments, the results provide hydraulic evidence on the biological performance. 德國LaVision PIV/PLIF粒子成像測速場儀