Air entrainment mechanism of chute bottom aerators in high-speed chute flows

Abstract

In high-head dam projects, chute aerators are commonly applied as artificial aeration devices to prevent cavitation erosion damage in high-speed spillway and tunnel flows. These specific chute air-water flows are generated by jet lower-surface aeration above the bottom cavity and jet impact aeration on the bottom floor. These air entrainment processes determine the total air flux transport downstream of the chute flow. However, the differential air fluxes caused by the two different aeration mechanisms remains unclear. Based on physical model investigations, the two air entrained processes are observed by a high-speed camera, and detailed air flux data are measured in the aerator cavity and impact areas. The effects of the jet lower-surface disintegrating and then instantaneously reattaching to the chute floor are discussed. The measured air flux data indicate that the inertial jet impact entrainment dominates with increasing Froude number, while the air flux proportion of the jet lower-surface aeration increases with the aerator height. A general prediction model for aerator cavity entrainment is proposed, considering the effects of the Froude number and jet lower-surface aeration. The scale effects of the coupling mechanism on chute aerator air entrainment highlight that aerator cavity air entrainment primarily depends on the inertial jet impact, and the main effects of aerator design on entrainment performance are manifested in the air cavity properties.