Influence of Aeration Threshold on Performance of Stepped Spillway

Abstract

【Background and Objective】 Flood control is a primary task in water conservancy hubs, especially hydropower stations. Many hydropower projects in western China are characterized by high water head, large discharge, and narrow river valleys. Ensuring smooth energy dissipation during discharge is crucial to their safe operation. Stepped spillways have become a popular flood discharge structure due to its high energy dissipation rate and ability to effectively reduce the size of downstream damping. One challenge to the stepped spillways operated in large single-width flow conditions is the cavitation erosion it could create. Extensive efforts have been made to understand the flow pattern and enhance the performance of stepped spillways by improving their design. Among the various stepped spillways proposed, the aerated candy-type stepped spillway appears to be superior in mitigating cavitation erosion. However, there is limited research on the optimal height and position of the aerator. This paper aims to bridge this technology gap. 【Method】 Nine different stepped spillway configurations with varying aerator positions were numerically simulated to calculate the velocity vectors, spillway surface characteristics, and aeration consistency. These results were used to evaluate the hydraulic performance of each configuration. 【Result】 It was found that the sigma (σ) value of the aerated candy-type stepped spillway significantly influenced the performance of the spillway. The closer the aerator was positioned to the downstream end, the higher and more stable the energy dissipation rate of the stepped spillway would be, and less impact of the σ is. A smaller σ resulted in more cavities in front of the aerator, while a larger σ generated more cavities behind the aerator. The vertical plane of the lifting step resulted in a concentrated aeration flow and demonstrated the advantage of cavities after the aeration barrier. Aerator proximity to the downstream end led to higher aeration concentration; higher aeration thresholds resulted in increased aeration concentration. 【Conclusion】 Numerical simulations revealed that location of the aerator and sigma value of the candy-type stepped spillway have significant impacts on performance of the spillway.

Keywords

• stepped spillway
• the aerated candy
• energy dissipation rate
• numerical simulation