Bottom and side-wall aeration performance of an offset aerator in a flood discharge chute

Abstract

Building a chute aerator is an efficient measure to protect the chute bottom from cavitation damage in large flood-discharging hydraulic structures, but it sometimes fails to provide sufficient protection to the sidewalls. In this paper, basic air-water flow properties are investigated for discharge flows over an offset chute aerator model, with particular focus on the near-bottom and near-wall regions, for a range of discharge velocities over the offset brink 3.58 m/s < V < 8.02 m/s, Froude numbers 4.8 < Fr < 12.0, and Reynolds numbers 8.0×104 < Re < 9.2×104. Observations indicate little transverse variations in air-water flow properties except near the jet impact perimeter. The bottom air concentration and bubble frequency decrease at different rates downstream the impact point, and the influence of the Reynolds number on the bubble size and density should not be ignored. The shape of the clear-water core between the upper and lower aeration layers is identified with the aid of high-speed imaging and air concentration calibration against the wall. A formula is proposed to predict the narrowing of the jet core until its ending position.