Effect of deflection angle on hydraulics of contraction aerator over stepped chutes

Under high unit discharges, insufficient aeration may lead to cavitation damage on stepped chutes. The previously proposed abrupt-contraction aerator, consisting of two straight walls, demonstrated effective aeration performance but posed potential structural risks due to the perpendicular wall design and the associated high impact pressures. In this study, the configuration of the contraction aerator (CA) was optimized to mitigate flow-induced pressure while maintaining its aeration efficiency. The influence of the deflection angle (θ), the key geometric parameter introduced through optimization, was experimentally investigated on a stepped chute. The results indicate that the optimized CA effectively reduces pressure on both the upstream faces of the aerator and the step bottoms, without compromising aeration performance. With decreasing θ, the maximum jet height decreases and the pile-up water disappears due to the elimination of the local hydraulic jump, indicating smoother flow passage. The persistent lateral cavities were found to play a crucial role in sustaining aeration, suggesting that the optimized design may enhance the unit discharge capacity of stepped chutes.