Physical Modeling of Unsteady Turbulence in Breaking Tidal Bores
Publication: Journal of Hydraulic Engineering
Volume 138, Issue 5
Abstract
A tidal bore is an unsteady flow motion generated by the rapid water level rise at the river mouth during the early flood tide under macrotidal and appropriate bathymetric conditions. This paper presents a study that physically investigates the turbulent properties of tidal bores. Results from some experimental measurements of free-surface fluctuations and turbulent velocities conducted on smooth and rough beds are reported. The free-surface measurements were conducted with Froude numbers of 1–1.7. Both undular and breaking bores were observed. Using an ensemble-averaging technique, the free-surface fluctuations of breaking tidal bores are characterized. Immediately before the roller, the free-surface curves gradually upwards. The passage of the bore roller is associated with some large water elevation fluctuations; the largest free-surface fluctuations are observed during the first half of the bore roller. The turbulent velocity measurements were performed at several vertical elevations during and shortly after the passage of breaking bores. Both the instantaneous and ensemble-averaged velocity data highlight a strong flow deceleration at all elevations during the bore passage. Close to the bed, the longitudinal velocity component becomes negative immediately after the roller passage, implying the existence of a transient recirculation. The height and duration of the transient are a function of the bed roughness, with a higher and longer recirculation region above the rough bed. The vertical velocity data presented some positive, upward motion beneath the front with increasing maximum vertical velocity with increasing distance from the bed. The transverse velocity data show some large fluctuations with nonzero ensemble average after the roller passage that highlight some intense secondary motion advected behind the bore front.
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Acknowledgments
The authors thank Graham Illidge and Clive Booth (University of Queensland, Australia) for their technical assistance. They thank further Prof. Colin Apelt (University of Queensland, Australia), Prof. Laurent David (University of Poitiers, France), and Dr David Reungoat (University of Bordeaux, France) for their valuable comments.
References
Andersen, V. M. (1978). “Undular hydraulic jump.” J. Hydraul. Div.JYCEAJ, 104(8), 1185–1188.
Boussinesq, J. V. (1871). “Théorie de l’intumescence appelée onde solitaire ou de translation se propageant dans un canal rectangulaire.” Comptes-Rendus de l'Académie des Sciences, Vol. 72, Paris, 755–759 (in French).
Chanson, H. (1999). The hydraulics of open channel flow: An introduction, Edward Arnold, London.
Chanson, H. (2010). “Unsteady turbulence in tidal bores: Effects of bed roughness.” J. Waterway, Port, Coastal, Ocean Eng.JWPED5, 136(5), 247–256,.
Chanson, H. (2011). Tidal bores, aegir, eagre, mascaret, pororoca: Theory and observations, World Scientific, Singapore.
Chanson, H. (2012). “Momentum considerations in hydraulic jumps and bores.” J. Irrig. Drain. Eng.JIDEDH, 138(3),.
Docherty, N. J., and Chanson, H. (2010). “Characterisation of unsteady turbulence in breaking tidal bores including the effects of bed roughness.” Hydraulic Model Rep. No. CH76/10, School of Civil Engineering, Univ. of Queensland, Brisbane, Australia.
Henderson, F. M. (1966). Open channel flow, MacMillan Company, New York.
Hornung, H. G., Willert, C., and Turner, S. (1995). “The flow field downstream of a hydraulic jump.” J. Fluid Mech.JFLSA7, 287, 299–316.
Koch, C., and Chanson, H. (2009). “Turbulence measurements in positive surges and bores.” J. Hydraul. Res.JHYRAF, 47(1), 29–40.
Lemoine, R. (1948). “Sur les ondes positives de translation dans les canaux et sur le ressaut ondulé de.aible amplitude.” Houille BlancheHOBLAB, 2, 183–185 (in French).
Liggett, J. A. (1994). Fluid mechanics, McGraw-Hill, New York.
Lighthill, J. (1978). Waves in fluids, Cambridge University Press, Cambridge, U.K.
Montes, J. S. (1998). Hydraulics of open channel flow, ASCE Press, New York.
Mouaze, D., Murzyn, F., and Chaplin, J. R. (2005). “Free surface length scale estimation in hydraulic jumps.” J. Fluids Eng.JFEGA4, 127(6), 1191–1193.
Murzyn, F., and Chanson, H. (2009). “Free-surface fluctuations in hydraulic jumps: Experimental observations.” Exp. Therm. Fluid. Sci.ETFSEO, 33(7), 1055–1064,.
Rayleigh, L. (1908). “Note on tidal bores.” Proc. R. Soc. London, Ser. A, 81(541), 448–449.
Treske, A. (1994). “Undular bores (favre-waves) in open channels-experimental studies.” J. Hydraul. Res.JHYRAF, 32(3), 355–370.
Information & Authors
Information
Published In
Journal of Hydraulic Engineering
Volume 138 • Issue 5 • May 2012
Pages: 412 - 419
Copyright
© 2012. American Society of Civil Engineers.
History
Received: Jul 27, 2010
Accepted: Dec 6, 2011
Published online: Dec 8, 2011
Published in print: May 1, 2012
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