Air Entrainment of Chute Aerators Under Different Atmospheric Pressures

In high-altitude regions, the influence of atmospheric pressure on the air entrainment capacity of chute aerators remains inadequately quantified. This study characterizes aerator efficiency through the air entrainment coefficient under variable atmospheric pressures. Systematic physical modeling was employed to investigate air transport downstream of chute aerators. The results demonstrate that the air entrainment coefficient decreases with reduced atmospheric pressure, manifested by declining air concentrations, particularly in the bottom flow layer. Downstream of the aerator, both the average and bottom air concentrations exhibit diminished streamwise development under lower pressures. Specifically, a 100 hPa reduction in atmospheric pressure corresponds to a 0.69–0.93% decrease in the air entrainment coefficient, accompanied by a 3.16% reduction in the regionally averaged air concentration downstream of the impact zone. For the first time, a comprehensive formula of the air entrainment coefficient expressed by basic parameters and an empirical formula of the bottom air concentration under different atmospheric pressures was established based on extensive tests, with results in good agreement. Based on the present experimental results, the atmospheric pressure can significantly affect the air intake of the aerator. Consequently, the atmospheric pressure should be considered as an important parameter in hydraulic aeration design.