Modeling and Prototype Testing of Flows over Flip-Bucket Aerators
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Volume 144, Issue 12
Abstract
The paper deals with a unique spillway which incorporates an aerator in each flip bucket with the intention to aerate the flow and avoid subatmospheric air cavities enclosed by the jets. In terms of jet breakup and stability, the physical models and the prototype lead to contradicting conclusions. With sealed aerators, the models exhibit intact air cavities featuring negative air pressure, suggesting the aeration need. Computational fluid dynamics (CFD) is performed to determine the reason for the discrepancy. Both the prototype observations and CFD indicate that the jets break up as a result of air entrainment; the resulting cavity air-pressure drops are insignificantly small. The discrepancy is due to the small model scale, in which the threshold flow velocity for air entrainment is not met and the prerequisite for jet breakup does not exist. To correctly reproduce similar water–air flow phenomena, the model should be large enough to meet the air-entrainment criterion. When questioning a small-scale model with air-cavity formation, CFD simulations should be performed to check the model results and make corrections, if needed.
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Acknowledgments
Both the physical model tests and prototype flood discharge studies were performed by the power producer Vattenfall. The numerical computations presented here were carried out as part of the research project entitled Hydraulic Design of Spillway Aerators funded by the Swedish Hydropower Centre (SVC). Vattenfall R&D also provided partial funding. Together with the Royal Institute of Technology (KTH), Luleå University of Technology (LTU), Chalmers University of Technology (CTH), and Uppsala University (UU), SVC was established by the Swedish Energy Agency, Energiforsk, and Swedish National Grid, www.svc.nu. James Yang is indebted to Sara Sandberg of SVC for project co-ordination and to Håkan Bond of WSP, Stockholm, for kindly providing photos and videos from the prototype flood studies.
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Journal of Hydraulic Engineering
Volume 144 • Issue 12 • December 2018
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©2018 American Society of Civil Engineers.
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Received: Aug 3, 2016
Accepted: May 15, 2018
Published online: Sep 17, 2018
Published in print: Dec 1, 2018
Discussion open until: Feb 17, 2019
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