Although chute aerators have been investigated experimentally by many researchers, only a few studies have been conducted on the comprehensive air–water flow properties of the lower jet downstream chute aerators. In this study, after eliminating the upper aeration of the jet, a complete characterization was recorded and presented for the distributions of air concentration, air–water velocity, and bubble frequency. Based on these extensive tests, a comprehensive equation to compute the air concentration distributions of each zone was presented. The velocity distribution had a shape similar to that of shear air–water flows; however, the quantitative parameters differ in each zone. In the cavity zone, the position of the maximum air bubble frequency was largely within a region of relatively high air concentration and gradually approached an equal air concentration of 0.50. The location of the maximum air bubble frequency was approximately the same as that of the section maximum air concentration at a section in the impact zone, but lower than that in the equilibrium zone. Self-similar relationships between the air concentration and bubble frequency were proposed for each zone.

Prototype hydraulic jump experiments were conducted at the Pei-bridge Gates in the Bao River, China. Two D-jumps formed on the 14° slope downstream one of the 5-m-wide sluice gates, followed by a sudden expansion of flow cross-section in the stilling basin. With the Froude numbers Fr = 7.47 and 3.18, the Reynolds numbers reached Re = 1.16 × 10⁶ and 1.88 × 10⁶, respectively. The fluctuating jump toe and free-surface characteristics were analysed and compared with existing model tests of classic and D-type jumps. The air–water flow properties were measured intrusively with phase-detection probes and compared to the laboratory data. The prototype jumps exhibited three-dimensional roller motions with shorter roller lengths than classic hydraulic jumps in prismatic channels. Scale effects were noted for the bubble frequency and bubble size distributions among the influences of other measuring factors, implying the need to revisit the model-based prediction relationship at prototype conditions.

Although stepped chute flows have been studied for a variety of chute geometries and flow conditions, reports on air–water flow development in the fully developed aerated region are not as comprehensive as those in the nonaerated and developing aerated regions. In this paper, skimming air–water flows in a large stepped chute (1V:2.5H) were studied comparatively for two step heights, showing different stages for velocity and aeration development downstream the inception point. The mean air concentration reached a constant level while the bubble frequency kept increasing slowly in the fully developed region. The developed mean air concentration was related to the sloping angle, step height and flow discharge. The results provided possible prediction of maximum bubble frequency and its longitudinal evolution, and a glance at the scale effect on it. The free-surface fluctuations and splash height were presented, with particular attention to the effects of step height on the turbulence and aeration modification.