Experiments on the evolution process of intermittent air-entraining vortices and its influencing factors

Abstract

Surface vortices are a common hydraulic phenomenon at water intakes that adversely affect safe engineering operations. The complexity of vortex motion, the diversity of influencing factors, and the limitations of research methods make the formation and development mechanisms of vortices unclear. Some analytical and experimental studies on intermittent air-entraining vortices occurring at the horizontal circular intake have been conducted to explore the mechanism of the dynamic characteristics of vortices. Based on experimental observations, the morphologies and dynamic characteristics of intermittent air-entraining vortices at different moments during the entire evolution process were studied, and the velocity field in the vortices was measured using PIV. The evolution processes of intermittent air-entraining vortices comprised inception, rapid development, stability, decay and regeneration, and the collapse and disappearance stages. The tangential velocity, kinetic energy, and vorticity increased over time, reached a maximum, and subsequently decreased. When they decrease to a certain value, they begin to increase before decreasing owing to the decay and regeneration stages. Additionally, we introduced the frequency of intermittent air-entraining vortex occurrence (P) to analyse the direct effect of the Froude number, intake submergence, and rear wall on the occurrence of air-entraining vortices. Based on the analysis of the test results, the effect of intake submergence on P was more significant than that of the intake Froude number in terms of flow conditions. By considering the effects of the flow conditions and rear wall, a method for predicting the possibility of the occurrence of intermittent air-entraining vortices was proposed.