# Hydraulic Performance of Wave-Type Flow at a Sill-Controlled Stilling Basin
## 4 Conclusions  
Downstream of the shuce gate or weir, wave-type flows may occur under no tailwater conditions in a stilling basin. Experimental tests were conducted on five different sill configurations, including the sill position and the sill height. Five test unit discharges between 0.154 m\({}^{2}\)/s and 0.230 m\({}^{2}\)/s were conducted. The main findings are summarized as follows:  
1. When a sill is located near the upstream weir flow (i.e., the weir toe in this study), the jump types of the wave flow can be classified as submerged and non-submerged. The submerged wave type flow corresponding to a higher relative sill height was relevant for obtaining a better aeration effect. 2. The ambient pressure head of the wave-type flow (i.e., the bottom pressure of the stilling basin) is strongly influenced by the flow pattern. Pressure fluctuations were more significant in the vicinity of the sill, and these are caused by the movement of the turbulent region of the jump, especially for the change in wave-type flow from a submerged jump to a non-submerged jump. The streamwise mean bottom pressure  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & & & & & & & & & & \\ \cline{2-10}
**Case** & **0.35** & **0.45** & **0.55** & **0.65** & **0.75** & **0.85** & **0.95** & **1.05** & **1.15  
profile revealed the existence of three distinct flow zones: (1) deflection zone, (2) jump zone, and (3) wave impact zone. There were two peak pressure points along the stilling basin, and these values can be distinguished by the upstream Froude number and the position and height of the sill. 3. The air concentrations on the bottom and the sidewall were also affected by the flow pattern. For a given sill-controlled stilling basin, the air concentrations on the bottom and the sidewall decreased with increasing unit discharges. The flow zone within the vicinity of the sill had slight air entrainment and significant pressure fluctuations, which may be prone to cavitation. Thus, this region near the sill should be focused upon in order to provide protection. The findings from this study have the potential to expand the application of sill-controlled stilling basins in hydraulic engineering by establishing new relationships. Additionally, the results can be used to improve the accuracy of CFD models in predicting wave-type flow behavior. Conceptualization, Y.Z. ; methodology, Y.Z. ; validation, H.Z. ; formal analysis, J.H. ; investigation, F.B. ; resources, Y.Z. ; data curation, Y.Z. ; writing--original draft preparation, Y.Z. ; writing--review and editing, H.Z. and Y.Z. ; visualization, J.H. ; funding acquisition, Y.Z. and J.W. All authors have read and agreed to the published version of the manuscript. This research is supported by the Chinese Scholarship Council (CSC), National Natural Science Foundation of China (Grant No. 51809079), the Scientific and Technological Program of Zhejiang Water Resources Department (RB2119, and RC2143), the Joint Funds of the Zhejiang Provincial Natural Science Foundation of China (Grant No. LZJWY23E090002), the Nancun Young Scholar, and the Research Center for Digital Economy and Sustainable Development of Water Resources, Zhejiang University of Water Resources and Electric Power (xrj2022012). Not applicable. All data, models, and code generated or used during the study are available from the corresponding author by request. The authors declare no conflict of interest.