Periodic Oscillation Caused by a Flow over a Vertical Drop Pool
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VIEW THE REPLYPublication: Journal of Hydraulic Engineering
Volume 134, Issue 7
Abstract
The flow patterns of various dropping flows were investigated and classified experimentally for subcritical approach flows passing a vertical drop pool. A wave gauge was used to measure the free surface fluctuations in the pool. A flow visualization technique was employed to reveal the flow structure of the dropping flows qualitatively. It was discovered that, under certain conditions, the dropping flow forms a switching jet that oscillates up and down periodically and impinges on the bed and the downstream pool wall alternately. The switching jet switches between an impinging jet (a napped flow) and a sliding jet (a skimming flow), causing it to oscillate periodically with a unique period. The primary frequency of the periodic oscillation was determined by applying spectral analysis to the time series of the gauge measurements. Since a large number of air bubbles was entrained in the oscillatory flow, particle image velocimetry, and bubble image velocimetry were used for quantitative velocity determination in the liquid region and the aerated region, respectively. The mechanism causing the periodic oscillation in the pool was elucidated, and variables affecting the oscillation frequency were identified. An empirical relation between a weighted Strouhal number and a grouped dimensionless parameter was proposed to predict the primary frequency of the periodic oscillatory flow.
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Acknowledgments
The writers are grateful for the financial support from the Directorate General of Highways, Ministry of Transportation and Communications of Taiwan, and the National Science Council of Taiwan (under Grant Nos. NSCTNSC94-2611-E-005-002 and NSCTNSC95-2611-E-005-157).
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Information & Authors
Information
Published In
Journal of Hydraulic Engineering
Volume 134 • Issue 7 • July 2008
Pages: 948 - 960
Copyright
© 2008 ASCE.
History
Received: Sep 19, 2006
Accepted: Nov 2, 2007
Published online: Jul 1, 2008
Published in print: Jul 2008
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