Air concentration and velocity downstream of an expanding chute aerator

Abstract

ABSTRACTThe mechanisms of air entrainment and velocity distribution at the upper, lower and side air–water interfaces downstream of chute aerators remain unclear. This study reports a series of experiments involving various approach-flow features and geometric parameters of aerators. Analytical solutions are developed for the air concentration profiles in the air–water layers, and it is shown that the solutions agree well with the experiments. Empirical equations are established for the turbulent diffusion of bubbles and the diffusion rate of the aeration layer. The turbulent diffusion coefficient of the lower nappe is found to be approximately 10 times and 1.2–1.8 times larger than those of the upper and side nappes, respectively. The diffusion rate of the aeration layer is the highest at the lower nappe and lowest at the upper nappe, gradually decreasing along the cavity. The velocity distribution indices are found to be different for the upper, lower and side nappes.