南水北调中线工程典型倒虹吸进口上游垂向流速分布

倒虹吸是输水工程中常见的水工建筑物，研究倒虹吸进口上游的垂向流速分布是明晰其水力学性能的重要内容之一。以南水北调中线工程典型的唐河倒虹吸为研究对象，通过水力学概化模型试验，运用声学多普勒流速仪，实测不同水深和流量组合工况下倒虹吸进口上游的垂向流速分布。试验结果表明，受倒虹吸进口结构的影响，上游垂向流速分布呈现出明显的顶部流速降低和底部流速增加的现象，且淹没度越大、距离倒虹吸进口越近，上述趋势越显著；采用明渠对数型流速分布描述上述垂向流速分布时，其计算误差呈抛物线型分布，采用指数项修正后，新的修正公式可用于计算倒虹吸进口上游垂向流速分布。

Distribution of vertical flow velocity upstream of an inverted siphon in the Middle Route of South-to-North Water Diversion Project

The inverted siphon is a commonly used hydraulic structure in water diversion projects.Therefore, research on the vertical flow velocity distribution in the upstream of the inverted siphon inlet is important to elucidating its hydraulic performance.The typical inverted siphon of the Tanghe River in the Middle Route of the South-to-North Water Diversion Project was taken as the research object.Generalized hydraulic model experiments were carried out, and measurements were performed to obtain the vertical velocity distribution in the upstream of the inverted siphon inlet under different combinations of water depth and flow discharge, using an acoustic doppler velocimeter.The experimental results demonstrated that owing to the influence of the inverted siphon inlet structure, the upstream vertical velocity distribution largely exhibited lower velocity at the top and higher velocity at the bottom.Moreover, for greater submergence and closer to the inverted siphon inlet, the aforementioned trend was more evident.Further, when the above vertical velocity distribution was represented using the open-channel logarithmic velocity distribution approach, its computing error exhibited a parabolic distribution.When the open-channel logarithmic velocity distribution formula was improved using exponential terms, a new modified formula was obtained, which can be employed to compute the vertical velocity distribution in the upstream of the inverted siphon inlet.