Abstract
Overfall spillways are important hydraulic structures for the release of overtopping water flows downstream of a dam. To reduce the effects of the impact of falling water in plunge pools, an overfall spillway outlet design that produces a longitudinally spreading jet is required. This study examined the effects of a triangular wedge placed at the end of an overfall spillway to deflect the water flow in the lateral direction, making the jet longitudinally diffuse before reaching the plunge pool. Laboratory data on the mean pressure coefficient were used to analyse the effects of various design parameters. An increase in the deflection ratio and a decrease in the weir crest length reduced the jet impact pressure. Compared with the impact of a rectangular jet falling into a plunge pool, an appropriate triangular wedge structure was found to improve the spreading of the impingement jet and reduce the mean dynamic pressure coefficient. By optimising the geometric design to accomplish jet impact control, the results of the present investigation may help engineers to design overfall spillways in high-head dam projects.
Highlights
In recent decades, technological advances in hydraulics have promoted the development of high-head dams
This study examined the effects of a triangular wedge placed at the end of an overfall spillway to deflect the water flow in the lateral direction, making the jet longitudinally diffuse before reaching the plunge pool
The findings presented may help engineers in designing overfall spillway outlets and improving the energy dissipation performance in high-head dams
Summary
Technological advances in hydraulics have promoted the development of high-head dams. One of the most important aspects of dam protection is the transfer of reservoir water downstream. The overfall spillway is used as the flood discharge structure in many high-arch dams (reaching 200–300 m), such as Jinping-I dam (China, 305 m high), Xiaowan dam (China, 292 m), Xiluodu dam (China, 285.5 m high) and Ertan dam (China, 240 m). High-velocity plunging jets (40–50 m/s) transfer water from the reservoir level to the plunge pool downstream, generating high demand on hydraulic structures. Overfall spillways have received considerable attention due to their massive energy dissipation and potential for failure during large flood discharge operations
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