Experimental study of air-water turbulent flow structures on stepped spillways

Stepped chute flows are characterized by intense turbulence and strong flow aeration, but most studies did not investigate the turbulence characteristics. In this study, highly turbulent air-water flows skimming down a large-size stepped chute were systematically investigated. An experimental study of detailed air-water flow properties measurements were introduced in different types of flow regimes on a stepped chute (θ = 21.8°, h = 0.04 m, l = 0.10 m) model to investigate the location and the flow depth at inception point of air entrainment and velocity profiles distributions. Detailed velocity and turbulence intensity measurements in flow direction were performed by use of a phase detection conductivity probe which was designed, developed and calibrated by writers. The results showed that the turbulence characteristics vary in different regions. The study showed further that the turbulence intensity increases rapidly close to the step bottom at the viscous sub layer and maximized for 0.4 ≤ y/dc ≤ 0.5 at intermediate region then decreases gradually in the upper region. It is hypothesized that the high turbulence levels in the intermediate region were caused by the continuous deformations and modification of the air-water interfacial structure.