Numerical simulation of optimized flow conditions for tailraces fishway entrance in Xinji Hydropower Station of Hanjiang River

To address the problems of excessive flow velocity at the fishway entrance and large dredging quantities of the tailrace cross-section under multi-unit operation conditions in a hydropower station, this paper took the tailrace of Xinji Hydropower Station as the research object.Aiming at achieving the fish critical flow velocity at the fishway entrance, hydraulic numerical simulation and scheme optimization were carried out on the flow conditions and various unit operation layouts at the entrance for five tailrace dredging schemes (the power generation project transitioning from single-unit operation to simultaneous multi-unit operation with four generators).The results showed that the unit operation condition, tailrace dredging scheme, and fishway entrance layout were all factors affecting the entrance flow conditions.Constructing a low-velocity zone between the tailrace and the separation dike using a longitudinal guide wall, and arranging the fishway entrance in this zone can effectively improve the flow characteristics in the entrance area under high-velocity conditions.The recommended scheme comprehensively adopts appropriate tailrace dredging and a right-angle longitudinal guide wall to ensure a continuous and effective fish passage and fish collection effect under various unit operation conditions.The research results can provide a reference for flow optimization at the fishway entrance of tailrace fishways in similar hydropower stations.