New Method for Modeling Thin-Walled Orifice Flow under Partially Submerged Conditions
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Volume 138, Issue 10
Abstract
Orifices are often used in stormwater detention facilities for reducing runoff peak flow and achieving extended detention times to improve water quality. Orifices often flow partially full; therefore, accurate and easily implemented methods of modeling basin outflow under such conditions are needed. In this paper we describe two models of partially submerged flow in thin-walled orifices and conduct full-scale testing of these models. The best model (termed the top-width weir approach) treats the orifice as an equivalently sized rectangular weir, where the equivalent weir length equals the top width of flow in the orifice until half-full and the diameter of the orifice when greater than half-full. A single fitting coefficient is required, which is directly proportional to the discharge coefficient for submerged orifice flow. This method provides results that, except for low submergence conditions, are within 2 to 5% of experimental data for steady flow, a significant improvement over the existing circular weir model in which errors are . The model is also shown to closely match transient drainage data, demonstrating its utility for predicting drawdown times for stormwater detention facilities.
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Acknowledgments
We dedicate this paper to the family of the late Bryan C. Hendrickson, Lafayette College class of 2010, who spent many hours in the lab with us during the early stages of this research. Harry Folk and the Engineering Machine Shop staff at Lafayette College constructed the orifices and provided assistance with the flume. Lafayette students Alec Bernstein and Brian Carey assisted with the transient drainage experiments.
References
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© 2012 American Society of Civil Engineers.
History
Received: Jul 26, 2011
Accepted: Apr 19, 2012
Published online: Sep 14, 2012
Published in print: Oct 1, 2012
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