Abstract
Although spillways have been investigated experimentally by various researchers, only a few studies have been conducted on the comprehensive properties of a self-aerated air-water flow. In this study, new experimental data were recorded and discussed for the distribution of the air concentration, air-water velocity, turbulence intensity and bubble frequency in the completely developed regions for spillways. It was observed that both the turbulence intensity and bubble frequency increased from the bottom and subsequently decreased near the free surface. The positions of maximum air bubble frequency and turbulence intensity gradually approached air concentration to 0.50 in the self-aerated developed region. Self-similar relationships between the turbulence intensity and bubble frequency were proposed.
Highlights
Self-aeration is a phenomenon occurring in high-velocity open channel flows, which is attributed to the strong interactions between the turbulent flows and the atmosphere leading to a strong air-water mixing at the interface
This study focused on high-velocity open channel flows
An accurate measurement technique utilizing conductivity probes provided a comprehensive analysis of the air-water flow properties in the developing and developed regions for the self-aerated flow, including the air-water flow parameters, turbulence intensities and bubble frequencies
Summary
Self-aeration is a phenomenon occurring in high-velocity open channel flows, which is attributed to the strong interactions between the turbulent flows and the atmosphere leading to a strong air-water mixing at the interface. As the air entrainment develops, the completely developed air-water phase flow becomes a result of the equilibrium between the turbulence intensity and buoyancy. The air-water flow properties, such as air concentration, velocity and flow depth, are independent of the flow direction [1,2,3]. Extensive experiments have been conducted on self-aerated flows including studies of the velocity distribution, air concentration and bubble frequency and size [4,5,6,7,8,9]. Chanson [4] focused on the air concentration distribution based on the turbulent diffusion theory for the developed region and predicted the sizes of the entrained bubbles and provided the relationship between the air concentration and bubble frequency
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