Turbulent flows are investigated in the bypass of a bar rack system to understand the effects of weirs placed at the bypass entrance on hydraulic conditions used to guide fish moving downstream. Three test cases were studied: (a) no weir (reference case), (b) arc-shaped weir and (c) triangular weir. A stereo particle image velocimetry system was employed to acquire the three velocity components in the mid-plane of the bypass and examine various statistics including mean velocities, Reynolds stresses, turbulent kinetic energy as well as turbulence eddies and swirling strength. The weirs deflect the flow away from the channel bed due to the blockage effect and increase the bypass velocity significantly, though remains under the suggested critical value of 1 m s when the approach velocity was 0.38 m s. In the wake region of the triangular weir, a distinct recirculation bubble forms which may negatively affect fish migration. There is an increase in the level of Reynolds stresses and turbulent kinetic energy in the upstream vicinity of the weirs and the shear layers issuing from their tips. It is shown that the topology of the turbulence eddies is greatly modified by the weirs which can more readily assist fish guidance toward the bypass. Also, the swirling strength of the turbulence eddies behind the triangular weir is more pronounced compared to the arc-shaped weir. For the reference case, the swirling strength of the eddies is the weakest.

中文翻译：

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综合研究拦杆系统旁路设置堰的水动力效应，更好地引导下游洄游鱼类

研究了栅栏系统旁路中的湍流，以了解放置在旁路入口处的堰对用于引导鱼向下游移动的水力条件的影响。研究了三个测试案例：(a) 无堰（参考案例）、(b) 弧形堰和 (c) 三角形堰。采用立体粒子图像测速系统来获取旁路中平面的三个速度分量，并检查各种统计数据，包括平均速度、雷诺应力、湍流动能以及湍流涡流和旋转强度。由于堵塞效应，堰使水流偏转离开河床，并显着增加旁路速度，但当接近速度为 0.38 m s 时，旁路速度仍低于建议的临界值 1 m s。在三角堰的尾流区域，形成明显的再循环气泡，这可能会对鱼类洄游产生负面影响。在堰的上游附近以及从其尖端发出的剪切层中，雷诺应力和湍流动能水平增加。结果表明，湍流涡流的拓扑结构被堰极大地改变，可以更容易地帮助鱼引导到旁路。而且，与弧形堰相比，三角形堰后面的湍流漩涡的旋流强度更加明显。对于参考案例，涡流的旋转强度最弱。