Predicting air concentration in self-aerated skimming flow over stepped chutes of varying slopes and step heights

New physical experiments are presented focusing on air concentration measurement in self-aerated flows running down two stepped chutes of different slope angles 18.4° and 50.8°, each of three step heights 0.025 m, 0.05 m and 0.1 m, covering a range of dimensionless flow rates. Analysis of the stream evolution of air concentration distribution and the equilibrium depth-averaged air concentration in the fully developed aerated region revealed the effects of key influencing factors including the discharge, slope angle and step height. A formula for predicting the equilibrium depth-averaged air concentration is proposed, which can be used to depict the fully developed air concentration distributions. Scale effects of step height on flow aeration are revealed.