Effect of orifice plates on the flow over stepped spillways

Abstract

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. HIGHLIGHTS The orifice plate generates a jet to entrain air, which can avoid cavitation damage for stepped spillways with large unit discharges.; The orifice plate increases the energy dissipation of the stepped spillway.; The relationship of take-off flow depth and hydraulic as well as structure parameters of the orifice plate are revealed.; This paper presents the formula of jet trajectory based on the corrected take-off flow depth.;

Keywords

• air entrainment
• energy dissipation
• jet trajectory
• orifice plate
• stepped spillway