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

Building a chute aerator is an efficient way of protecting the chute bottom from cavitation damage in large flood-discharging hydraulic structures, but it sometimes fails to provide sufficient protection to the side-walls. In this study, basic air–water flow properties were 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 × 10⁵). The results indicated little transverse variations in air–water flow properties except near the jet impact perimeter. The bottom air concentration and bubble frequency decreased at different rates downstream of the impact point; the influence of 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 was identified with the aid of high-speed imaging and air concentration calibration against the wall. A formula to predict narrowing of the jet core until its end position was developed.