Air-water flows and free-surface profiles on a non-uniform stepped chute

Comparative experiments were conducted between uniform and non-uniform stepped spillway profiles in a large-size laboratory facility. For each stepped configuration, the air concentration distributions matched the advective diffusion equation and the interfacial velocity was well correlated with a power law. A comparison of the air-water flow properties showed small differences in terms of number of entrained air bubbles, chord sizes and turbulence characteristics between the different configurations. For the non-uniform steps, larger flow instabilities and stronger variation in the air-water flow properties were observed. Further some nonintrusive measurements were performed with acoustic displacement meters to characterise the free-surface profiles, free-surface fluctuations and free-surface wave celerity in both non-aerated and aerated flow regions. The experiments highlighted a close agreement between experimental data and theoretical predictions in the non-aerated flows and with conductivity probe data in the aerated flows. The non-intrusive technique was suitable for measuring the free-surface characteristics on stepped chutes, especially in the non-aerated flow region.