A New Type of Pre-Aeration Stepped Spillway

Aiming to increase energy dissipation and prevent the cavitation potential of a traditional stepped spillway (TSS) at large unit discharges, a kind of pre-aeration stepped spillway, called a hydraulic-jump-stepped spillway (HJSS), is introduced in this paper. Unlike a TSS, a basin added upstream of the stepped chute in the HJSS plays a vital role in the hydraulic performance owing to the formation of a hydraulic jump in the basin. This paper presents experimental research on the hydraulic performance of the HJSS in comparison to a TSS with the same chute slope (theta = 39.3 degrees) for a wide range of unit discharges, including the flow pattern, energy dissipation, pre-aeration effect, and maximum splash height. The results showed that the HJSS corresponded to a large energy dissipation rate, the air was effectively entrained at the inlet of the stepped chute, and there was an observation of splash formation in the foregoing and downstream steps. Under large unit discharges, the HJSS maintained an energy dissipation rate exceeding 80%. Additionally, at the inlet, the air concentrations reached 4.5% on the bottom and 11.2% on the sidewall. The findings of this research could be used as a general guideline for stepped spillway design with large unit discharges.