Mitigation Techniques for Nappe Oscillations on Free-Overfall Structures
Publication: Journal of Hydraulic Engineering
Volume 145, Issue 2
Abstract
Nappe oscillation is a phenomenon that can have an undesirable impact to the local environment (e.g., nearby residences, and parks) as the phenomenon has been observed to produce a significant level of noise caused by acoustic pressure waves. As a result, a detailed investigation was undertaken to identify practical and effective mitigation solutions to address these effects for free-overfall structures. Nappe oscillations were studied using a prototype-scale linear weir (weir length of 3.5 m and fall height of 3 m), a high-speed camera, and audio equipment. The effectiveness of various crest modifications to reduce nappe oscillation and any corresponding impacts to hydraulic efficiency were evaluated. The test matrix included the optimization (position and spacing of elements) of three mitigation solutions: 12 configurations with projecting elements, 5 configurations with deflectors, and 1 configuration with a step. These three countermeasures proved to be effective after the optimization of their characteristics. In particular, deflectors or a step produced the maximum noise reduction while decreasing the discharge coefficient by less than 3% over the range of experimental conditions.
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Acknowledgments
Funding for this research was provided by the University de Liège and Schnabel Engineering.
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Published In
Journal of Hydraulic Engineering
Volume 145 • Issue 2 • February 2019
Copyright
©2018 American Society of Civil Engineers.
History
Received: Feb 21, 2018
Accepted: Jul 25, 2018
Published online: Dec 12, 2018
Published in print: Feb 1, 2019
Discussion open until: May 12, 2019
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