Unsteady Hydrodynamic Behavior at Piano Key Weirs
Publication: Journal of Hydraulic Engineering
Volume 146, Issue 5
Abstract
Piano key weirs (PKWs) are nonlinear hydraulic structures that exhibit unsteady hydraulic phenomena. A study incorporating both physical and numerical modeling was undertaken to identify instabilities that are generated by flow. Several excitations were identified and a portion of their nature is characterized in this paper. These include a system of vortices in the inlet key induced by the breakdown of a free shear layer, oscillations of the overflow nappe, and surging of the air cavity underneath the nappe. Of these, the inlet key vortices were found to be of the most significance as they were observed to occur at nearly all modeled flows () and exposed the sidewall separating the inlet and outlet keys to periodic pressure fluctuations. These fluctuating pressure forces, although small ( of the total pressure oscillating at ), are persistent and may cause structural vibrations. Reinforced concrete PKWs are sufficiently stiff to limit the amplitude of any deflections caused by these vibrations; however, thin, steel-plate PKWs may remain susceptible.
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Data Availability Statement
Some or all data, models, or codes generated or used during this study are available from the corresponding author by request.
Acknowledgments
This research was conducted at the Civil Engineering Department at Stellenbosch University, South Africa. Funding was provided by South African National Committee on Large Dams (SANCOLD). We are grateful for their support.
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Information & Authors
Information
Published In
Journal of Hydraulic Engineering
Volume 146 • Issue 5 • May 2020
Copyright
©2020 American Society of Civil Engineers.
History
Received: Jan 20, 2019
Accepted: Oct 4, 2019
Published online: Feb 21, 2020
Published in print: May 1, 2020
Discussion open until: Jul 21, 2020
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