| Fishway is both the engineering structure for fish migration and the protection engineering measures of natural fishery resources,biodiversity conservation and sustainable development.On one hand,velocity distribution and flow state of pool room will influence whether or not the fishes can pass through the fishway successfully when they entered the entrance.On the other hand,the stype of clapboard is the decisive factor affecting the flow state in the pool.However,there is no uniform design standards in the design of the type of fishway clapboard nowadays in China,and mostly relies on the engineering experience,which results in the project takes a certain degree of subjectivity and lacks of rigorous scientific demonstration.The flow structure of some fishways’ rest pool is unfavorable,as a result,some fishes can’t pass through the fishways successfully.The research on the improvement measures for the rest pool is also in the preliminary exploration stage.Meanwhile,when fishway pass through roads or bridges near the dam,restricted by topographical condition,it is necessary to place 90°turning section.In view of this,this paper made a preliminary exploration on clapboard type design and analysis the hydraulic characteristics of the fishway in straight and 90°tuming section.Finally,the performance of it was then evaluated in a case study in Laokou fishway,China,and the main contents are as follows:(1)Comparative and quantitative assessment of several types of clapboards based on the indoor model test and numerical simulation.The study found that①the flow of clapboard C in mainstream area is gentle relatively,the trajectory deflection rate is 9%,the attenuation rate of the maximum flow velocity is 18%,and ②the velocity distribution of clapboard C is reasonable at the vertical section,which reflected in the average velocity of 0.95m/s and the ratio of radial velocity(vr)and average velocity(va)of 0.91,and it takes an advantage in project design.(2)Three-dimensional numerical simulation of flow characteristics of clapboard C(proposal type of clapboard for Laokou fishway).The results show that ①the water flow forms a "S" shape and the energy dissipated fully in the pool room,on one hand,② for the mainstream zone located around from the left 1/5～2/5 of pool room along the direction of water flow,the flow is gentle,make a small deflection,and the flow velocity ranges from 0.4m/s to 1.1 m/s,which is suitable for fish to swim upstream,on the other hand,③the recirculation zone is narrow and the value of flow velocity is smaller than 0.4m/s,which is convenient for fish to take a break.(3)Study on the hydraulic characteristics of the resting pool by means of numerical simulation.In view of the adverse flow structure of the resting pool,the improvement measures of the rectifier baffle are put forward.Research shows that①the rectifying baffle is arranged on the left side of the rest pool along the direction of water flow,and the ratio of the length to width of the rectifying baffle is 2.75.In this way,the improvement effect is best;②after the improvement,most of the main area is located in the center of the resting pool,recirculation area approach,and it is an ideal flow pattern.(4)Study the hydraulic characteristics in 90°turning section of Laokou fishway.Research shows that firstly,①the main flow of three pools is explicit and the recirculating region is moderate in 90°turning section.②the turbulent kinetic energy is small and the structure of flow field is rational.Finally,within mainstream region,③the trajectory of maximum velocity distributed from the left about 1/5～2/5 of pool room along the direction of water flow,makes an appropriate deflection,and the attenuation of flow velocity is good,contributing to the energy dissipation. |
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