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.