Turbulence and energy dissipation in the developing non-aerated and the fully-developed aerated flows on a stepped spillway

Stepped spillways are characterised by highly turbulent air-water flows and a large rate of energy dissipation compared to smooth chutes. Herein, detailed measurements were performed in both the developing non-aerated and fully-developed air-water flow regions on a large 1V:1H stepped spillway model. In the developing flow region, large total pressure fluctuations and turbulence intensities were recorded next to the pseudo-bottom. Downstream of the inception point, large total pressure fluctuations were recorded, which were mainly induced by density fluctuations. The water turbulence intensities in the air-water flow region did not differ significantly from those in the developing flow region. The steps generated significant form loss, amounting to about 50% of the upstream total energy regardless of discharge. Similar rates of energy dissipation and friction factors were found between the developing non-aerated and fully-developed air-water flow regions. The energy dissipation on stepped chutes was found to be sensitive to the chute slope and relatively little affected by the air-bubble diffusion