Flows over flip-bucket aerators, physical and CFD modeling with prototype tests

The paper deals with a unique spillway structure, in which an aerator is incorporated in each flip bucket to aerate the flow jet and avoid sub-pressure in the air cavity below. In terms of jet breakup and stability, the physical models and the prototype lead to contradicting conclusions. CFD is performed to help seek the reason for the discrepancy. With sealed aerators, the model studies exhibit intact flow jets featuring negative cavity air pressure and oscillations, suggesting the need for jet aeration. Both the field observations and CFD indicate that the jets break up, allowing air to penetrate into the air cavities. The resulting cavity air pressure drops are small. The discrepancy is due to the effect of surface tension in the physical models leading to the formation of the enclosed air cavities with negative air pressure, which together with air entrainment in the tail-water gives rise to the jet oscillations. It is suggested, for similar flow phenomena, that compound modelling be performed so as to make amends for physical model test results. QC 20170224