Half-Round Circular Crested Weir: On Hysteresis, Instabilities, and Head–Discharge Relationship
Publication: Journal of Irrigation and Drainage Engineering
Volume 146, Issue 6
Abstract
Waters flowing over rounded weirs experience a rapidly accelerated flow region near the crest. The head-discharge relationship of a half-round crested weir was tested physically under carefully controlled flow conditions for a weir design with a small radius of curvature. The experiments were undertaken for a wide range of discharges, over two orders of magnitude, and the results were compared to the literature on circular weirs. The nappe was not aerated. With increasing discharges, the nappe was initially attached to the weir’s downstream wall, until some nappe detachment occurred. With a further increase in flow rate, the detached nappe reattached at large flow rates. The transitions, i.e., both nappe detachment and reattachment, were characterized by large instabilities, change in flow properties, and sometimes loud noise, and the processes were subject to some hysteresis. The finding demonstrated the complicated features of an unaerated round-crested weir overflow. The importance of careful experimental procedure is discussed.
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Data Availability Statement
Some or all data, models, or code that support the findings of this study are available from the corresponding author upon reasonable request. These include the tabular data corresponding to the data presented in Figs. 5(b).
Acknowledgments
The author thanks Professor Blake Tullis (Utah State University) for helpful discussions. He further thanks Jason Van Der Gevel (University of Queensland) for his technical support. The financial and in-kind support of the School of Civil Engineering at the University of Queensland is acknowledged.
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©2020 American Society of Civil Engineers.
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Received: Oct 14, 2019
Accepted: Jan 7, 2020
Published online: Mar 26, 2020
Published in print: Jun 1, 2020
Discussion open until: Aug 26, 2020
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