Microscopic Air–Water Properties in Non-Uniform Self-Aerated Flows

Supercritical open channel flows contribute substantially to the air–water transfer process in spillways, rivers, and streams. They are characterized by strong turbulent mixing and a substantial amount of air entrainment. The microscopic air–water properties in non-uniform self-aerated flows are investigated experimentally with various chute slopes, including air chord size and air–water transfer frequency. Microscopic air–water structures are primarily affected by chute slope, whereas the approach flow Reynolds number hardly influences them, resulting in self-similarity of the probability distribution of air chord length and air–water transfer frequency distribution in the self-aerated region. The distribution of bubble chord length is more continuous from the small to large scale in the high-air-concentration region for a greater chute slope, and the position of maximum air frequency moves to the higher-aeration zone and gets closely to the free surface. Moreover, empirical relationships are provided to predict the microscopic air–water properties in non-uniform self-aerated flows.