Chute Aerators. I: Air Transport Characteristics

Abstract

Chutes with flow velocities in excess of some 20 to 30 m/s are usually prone to cavitation damage. Therefore, these flows are aerated using chute aerators. The current literature describes the aerator efficiency mainly in terms of the air entrainment coefficient as the ratio of the entrained air and the water discharges. However, this global coefficient neither specifies the air distribution nor its detrainment rate. The present investigation focuses on the flow structure and the air transport downstream of chute aerators. Systematic hydraulic model tests were conducted including a data analysis of the spatial air concentration distribution in both the near and the far aerator fields. Based on these, three flow zones were introduced, namely: (1) jet zone; (2) reattachment and spray zone; and (3) far-field zone. It was further found that aerators have primarily an effect on the average air concentration, whereas the increase of the bottom air concentration is typically small.