Effect of orifice plates on the flow over stepped spillways

The reservoir is an important component of hydraulic projects for supplying water to the city. For guaranteeing reservoir safe operation, stepped spillways are often used to discharge the flood from the reservoir. But under large unit discharges, cavitation erosion and low energy dissipation may occur on stepped spillways, which possibly leads to the hydraulic structures being instable and the reservoir outwork for water supply. Herein, an orifice plate is introduced as a pre-aeration device for the stepped spillways to avoid cavitation damage. To detail the effect of orifice plate on the flow over the stepped spillways, experiments were conducted. The results demonstrate that the orifice plate contracted the flow into a jet. Large amounts of air were entrained, and cavitation damage could be avoided according to the air concentration distributions along the stepped spillways. The orifice plate also significantly increased the energy dissipation of stepped spillways. Further, flow depth before the orifice plate increased because of flow block, and was emphatically discussed for providing a calculation formula to estimate the jet trajectory.