Jet flow in hydraulic-jump-stepped spillways: experimental study

Abstract A hydraulic-stepped spillway was designed using an aeration basin to provide aerated flow to the stepped spillway utilizing a hydraulic jump. However, the flow through the entrance of the stepped spillway might separate from the first step top and impact the downstream steps at a large unit discharge, causing a so-called jet flow. A new experimental study was conducted to better understand the jet flow in the hydraulic-jump-stepped spillway with comparisons with conventional stepped spillways. The results showed that the critical condition required for the formation of the jet flow was close to the geometric parameters of the upstream aeration basin. Among these parameters, the height of the reverse step had a more significant effect on the local flow pattern, thus lowering the risk of jet flow. The relationships between the critical condition and the geometry of the aeration basin suggested that the Froude number at the entrance of the stepped spillway was the key parameter forming the jet flow. Compared with conventional stepped spillways, the hydraulic-jump-stepped spillway could effectively extend the practical application for large unit discharges by providing a better understanding of jet flow conditions.