Air entrainment scale effects in chute aerator flows

Abstract

Physical study of air–water flow in a spillway aerator is usually conducted using a downscaled Froude-similar model. The Reynolds number much smaller than that in a prototype structure may adversely affect the understanding and correct interpretation of many physical processes, including air entrainment and turbulence development. In this paper, the similarity and scale effects in the aeration process of flows in chute aerators were systematically investigated by using physical models of three different geometric scales. Air–water flow properties related to the air entrainment, turbulence and bubble characteristics were measured for inflow Froude numbers from 4.9 to 12 and Reynolds numbers from 8.26 × 104 to 9.23 × 105. The experimental results showed that the parameters of air concentration and bubble count rate were scale-sensitive, while the velocity and turbulence intensity were almost free of scale effects. The Reynolds number seemed to have a significant effect on bubble size which was observed to increase with increasing Reynolds number.