Hydraulics of the Developing Flow Region of Stepped Spillways. I: Physical Modeling and Boundary Layer Development
Publication: Journal of Hydraulic Engineering
Volume 142, Issue 7
Abstract
On a stepped spillway, the steps act as macroroughness elements, contributing to enhanced energy dissipation and significant aeration. In a skimming flow, the upstream flow motion is nonaerated, and the free surface appears smooth and glossy up to the inception point of free-surface aeration. In this developing flow region, a turbulent boundary layer grows until the outer edge of the boundary layer interacts with the free surface and air entrainment takes place. The flow properties in the developing flow region were documented carefully in a large stepped spillway model (1V:1H; ). The upstream flow was controlled by a broad-crested weir and critical flow conditions were observed along most of the weir crest, although the pressure distributions were not hydrostatic at the upstream and downstream ends. Downstream of the broad crest and upstream of the inception point, the free surface was smooth, although some significant free-surface curvature was observed for all discharges. The boundary layer growth was faster than on a smooth chute for identical flow conditions. The inception point of free-surface aeration was observed when the boundary layer thickness reached 80% of the flow depth: . The location of the inception point of free-surface aeration and the flow depth at inception were compared successfully to previous laboratory and prototype results.
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Acknowledgments
The authors thank Professor Fabian Bombardelli (University of California Davis, in the United States) and Professor Jorge Matos (IST Lisbon, Portugal) for their valuable comments. They also thank Dr. John Macintosh (Water Solutions, Brisbane, Australia) for his comments and supervisory involvement. The authors acknowledge the technical assistance provided by Jason Van de Gevel and Stewart Matthews, at the University of Queensland (Australia). The financial support of the Australian Research Council (Grant DP120100481) is acknowledged.
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Published In
Journal of Hydraulic Engineering
Volume 142 • Issue 7 • July 2016
Copyright
© 2016 American Society of Civil Engineers.
History
Received: May 28, 2015
Accepted: Dec 21, 2015
Published online: Mar 22, 2016
Published in print: Jul 1, 2016
Discussion open until: Aug 22, 2016
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