Developing Flow Region and Pressure Fluctuations on Steeply Sloping Stepped Spillways
Publication: Journal of Hydraulic Engineering
Volume 135, Issue 12
Abstract
The hydrodynamic pressure field is important for the design and safety of steeply sloping stepped spillways, which are typically designed for considerably lower maximum specific discharges than smooth spillways. The hydraulic performance of stepped spillways at high velocities may compromise its use due to major concern with safety against cavitation damage. Hydraulic model investigations were conducted in different large-size stepped chutes to characterize the nonaerated flow region which is potentially prone to cavitation damage and the pressure field acting on the step faces. The clear water depths and energy dissipation in the developing flow region are described in terms of integral measures of the turbulent boundary layer. Expressions for the location of and the flow depth at the inception point of air entrainment are derived. Pressure distributions on the horizontal and vertical faces of the step along the spillway are presented. Measurements indicated a different behavior of the pressure field in the aerated and nonaerated flow region. The mean and fluctuating pressure coefficients along the spillway are approximated by a regression function. The vertical face near the outer step edge close to the inception point of air entrainment is identified as a critical region for predicting cavitation inception in flow over stepped spillways. From the analysis of the pressure fluctuations in that region a maximum velocity of 15 m/s is proposed as a criterion to avoid extreme negative pressures in typical prototype steeply sloping stepped spillways, eventually leading to the occurrence of cavitation in the nonaerated flow.
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Acknowledgments
The writers would like to acknowledge Centro de Innovación Tecnoloxica en Edificación e Enxeneria Civil (CITEEC) and Professor Jerónimo Puertas from A Coruña University for giving the conditions for the realization of the experimental work. The first writer acknowledges the financial support of the Fundação para a Ciência e Tecnologia (Portugal, Praxis XXI, Grant No. UNSPECIFIEDBD/3056/2000).
References
Amador, A. (2005). “Comportamiento Hidráulico de los Aliviaderos Escalonados en Presas de Hormigón Compactado.” Ph.D. thesis, Universitat Politècnica de Catalunya (UPC), Barcelona, Spain (in Spanish).
Amador, A., Sánchez-Juny, M., and Dolz, J. (2005). “Discussion: Two-phase flow characteristics of stepped spillways by Boes, R. and Hager, W.” J. Hydraul. Eng., 131(5), 419–429.
Amador, A., Sánchez-Juny, M., and Dolz, J. (2006). “Characterization of the nonaerated flow region in a stepped spillway by PIV.” J. Fluids Eng., 128(6), 1266–1273.
André, S. (2004). “High velocity aerated flows over stepped chutes with macro-roughness elements.” Ph.D. thesis, EPFL, Lausanne, Switzerland.
Boes, R. M., and Hager, W. (2003a). “Two-phase flow characteristics of stepped spillways.” J. Hydraul. Eng., 129(9), 661–670.
Boes, R. M., and Hager, W. (2003b). “Hydraulic design of stepped spillways.” J. Hydraul. Eng., 129(9), 671–679.
Chanson, H. (1994). “Hydraulics of skimming flows over stepped channels and spillways.” J. Hydraul. Res., 32(3), 445–460.
Chanson, H. (1995). Hydraulic design of stepped cascades channels weirs and spillways, Pergamon, Oxford, U.K.
Chanson, H. (2001). The hydraulics of stepped chutes and spillways, Swets & Zeitlinger, Lisse, The Netherlands.
Chanson, H. (2006). “Hydraulics of skimming flows on stepped chutes: The effects of inflow conditions.” J. Hydraul. Res., 44(1), 51–60.
Frizell, K. (2006). “Research state of the art and needs for hydraulic design of stepped spillways.” Hydraulic Laboratory Rep. No. HL-2005-06, USBR, Denver.
Frizell, K., and Mefford, B. (1991). “Designing spillways to prevent cavitation damage.” Concr. Int., 13(5), 58–64.
Gomes, J. (2006). “Estudo do campo de pressões em soleiras de vertedouros em degraus com declividade 1V:0,75H.” Ph.D. thesis, Federal Univ. of Rio Grande do Sul, Brazil (in Portuguese).
Gomes, J., Amador, A., Marques, M., Matos, J., and Sánchez-Juny, M. (2006). “Hydrodynamic pressure field on steeply sloping stepped spillways.” Proc., of the Int. Junior Researcher and Engineer Workshop on Hydraulic Structures (IJREWHS'06).” J. Matos and H. Chanson, eds., APRH, Montemor-o-Novo, 71–80.
Gonzalez, C. (2005). “An experimental study of free surface aeration on embankment stepped chutes.” Ph.D. thesis, Univ. of Queensland, Brisbane, Australia.
Lopardo, R. (2002). “Contribution of hydraulic models on the safe design of large dams stilling basins.” Proc., IAHR Symp. on Hydraulic and Hydrological Aspects of Reliability and Safety Assessment of Hydraulic Structures, IAHR, S. Petersbourg.
Mateos, C., and Elviro, V. (2000). “Stepped spillways studies at CEDEX.” Proc., Int. Workshop on Hydraulics of Stepped Spillways, H. E. Minor and W. Hager, eds., Balkema, Rotterdam, The Netherlands, 87–93.
Matos, J. (1999). “Emulsionamento de ar e dissipação de energia do escoamento em descarregadores em degraus.” Research Rep. (in Portuguese).
Matos, J. (2000). “Hydraulic design of stepped spillways over RCC dams.” Proc., Int. Workshop on Hydraulics of Stepped Spillways, H. E. Minor and W. Hager, eds., Balkema, Rotterdam, The Netherlands, 187–194.
Matos, J., Quintela, A. C., and Ramos, C. M. (2001). “Sobre a protecção contra a erosão por cavitação em descarregadores em degraus.” Recursos Hídricos, 23(1) (in Portuguese).
Ohtsu, I., Yasuda, Y., and Takahashi, M. (2004). “Flow characteristic of skimming flow in stepped channels.” J. Hydraul. Eng., 130(9), 860–869.
Peterka, A. (1953). “The effect of entrained air on cavitation pitting.” Proc., Joint Meeting Paper, 507–518.
Rajaratnam, N. (1990). “Skimming flow in stepped spillways.” J. Hydraul. Eng., 116(4), 587–591.
Sánchez-Juny, M. (2001). “Comportamiento hidraulico de los aliviaderos escalonados en presas de hormigón compactado. Analisis del campo de presiones.” Ph.D. thesis, Universitat Politécnica de Catalunya, Spain (in Spanish).
Sánchez-Juny, M., and Dolz, J. (2005). “Experimental study of transition and skimming flows on stepped spillways in RCC dams. Qualitative analysis and pressure measurements.” J. Hydraul. Res., 43(5), 540–548.
Sorensen, R. (1985). “Stepped spillway hydraulic model investigation.” J. Hydraul. Eng., 111(12), 1461–1472.
Toso, J., and Bowers, C. (1988). “Extreme pressures in hydraulic jump stilling basins.” J. Hydraul. Eng., 114(8), 829–843.
Information & Authors
Information
Published In
Journal of Hydraulic Engineering
Volume 135 • Issue 12 • December 2009
Pages: 1092 - 1100
Copyright
© 2009 ASCE.
History
Received: Oct 5, 2007
Accepted: Jun 16, 2009
Published online: Jun 24, 2009
Published in print: Dec 2009
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