Confinement Effects in Shallow-Water Jets
Publication: Journal of Hydraulic Engineering
Volume 137, Issue 3
Abstract
This paper documents measurements of the mean velocity field and turbulence statistics of an isothermal, round jet entering a shallow layer of water. The lower boundary of the jet was a solid wall and the upper boundary a free surface. The jet axis was midway between the solid wall and the free surface in all cases. Experiments were performed at a Reynolds number of 22,500 for water layer depths 15, 10, and 5 times the jet exit diameter (9 mm). Particle image velocimetry measurements were made on vertical and horizontal planes—both containing the axis of the jet. The measurements were taken from 10 to 80 jet diameters downstream. Results showed that, for the highly confined cases at downstream locations, the axial velocity was quite uniform over the depth, with a mild peak below the jet axis. In the horizontal plane, the velocity profiles were slightly narrower than the free jet profile, but in the vertical plane, they were wider. The mean vertical velocity profiles showed that entrainment was suppressed in the vertical direction. At the same time, the lateral velocity profiles indicate that fluid flows from the sides toward the jet centerline. For the shallow cases, the mean vertical velocity becomes negative over most of the depth at downstream locations, indicating that this inflow from the sides is directed downward toward the solid wall. The relative turbulence intensity results were suppressed in the axial and vertical directions and mildly enhanced in the lateral direction. As well, the Reynolds shear stress in the vertical plane was significantly reduced by the vertical confinement, while in the horizontal plane it was only slightly affected by the confinement.
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Acknowledgments
The support of the Natural Sciences and Engineering Research Council (NSERC) of CanadaNSERC is gratefully acknowledged. The assistance of the Bioinformatics Research Laboratory at the University of Saskatchewan with processing the PIV images is also gratefully acknowledged. The authors also thank Prof. David Sumner for the use of his tow tank for these experiments.
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Information & Authors
Information
Published In
Journal of Hydraulic Engineering
Volume 137 • Issue 3 • March 2011
Pages: 300 - 314
Copyright
© 2011 American Society of Civil Engineers.
History
Received: Dec 14, 2009
Accepted: Jul 29, 2010
Published online: Jul 29, 2010
Published in print: Mar 1, 2011
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