Air–Water Flow Patterns and Shockwave Formation in Low-Level Outlets
Publication: Journal of Hydraulic Engineering
Volume 149, Issue 6
Abstract
Reservoir dams play a significant role in society and the economy. Low-level outlets (LLOs) are key safety devices providing reservoir drawdown for maintenance and emergency purposes, sediment flushing, and release of environmental flow. High velocities and turbulence levels of the free-surface flow lead to air entrainment and air transport along the LLO tunnel, resulting in subatmospheric air pressures. In addition, shockwaves formed downstream of the gate may lead to a complete filling of the tunnel cross section, possibly resulting in slug flow and flow pulsations, which should be avoided for operational safety. In this study, physical model tests were performed to investigate the effects of gate opening and hydraulic head on shockwave patterns. Especially for large contraction Froude numbers, the shockwaves were strongly aerated, resulting in a complex air–water flow pattern. The results provide insights into the formation and propagation of shockwaves, contributing to an improved design of LLO tunnels.
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Data Availability Statement
All data that support the findings of this study are available from the corresponding author upon reasonable request.
Acknowledgments
The project was supported by the Swiss National Science Foundation (SNSF) under Grant 197208 (https://data.snf.ch/grants/grant/197208).
References
Barenblatt, G. I. 1996. Scaling, self-similarity, and intermediate asymptotics. Cambridge, UK: Cambridge University Press.
Bollrich, G. 2007. Technische Hydromechanik Band 1 [Technical Hydraulics, Vol. 1]. [In German.] Berlin: Huss-Medien.
Felder, S., B. Hohermuth, and R. M. Boes. 2019. “High-velocity air-water flows downstream of sluice gates including selection of optimum phase-detection probe.” Int. J. Multiphase Flow 116 (Jul): 203–220. https://doi.org/10.1016/j.ijmultiphaseflow.2019.04.015.
Hager, W. H. 2010. Wastewater hydraulics: Theory and practice. Berlin: Springer Science & Business Media.
Hager, W. H., A. J. Schleiss, R. M. Boes, and M. Pfister. 2020. Hydraulic engineering of dams. Boca Raton: CRC Press.
Heller, V. 2011. “Scale effects in physical hydraulic engineering models.” J. Hydraul. Res. 49 (3): 293–306. https://doi.org/10.1080/00221686.2011.578914.
Heller, V. 2017. “Self-similarity and Reynolds number invariance in Froude modelling.” J. Hydraul. Res. 55 (3): 293–309. https://doi.org/10.1080/00221686.2016.1250832.
Hohermuth, B. 2019. “Aeration and two-phase flow characteristics of low-level outlets.” Doctoral dissertation, Laboratory of Hydraulics, Hydrology, Glaciology, Dept. of Civil, Environmental and Geomatic Engineering, Eidgenössische Technische Hochschule Zurich.
Hohermuth, B., M. Kramer, S. Felder, and D. Valero. 2021. “Velocity bias in intrusive gas-liquid flow measurements.” Nat. Commun. 12 (1): 1–9. https://doi.org/10.1038/s41467-021-24231-4.
Hohermuth, B., L. Schmocker, and R. M. Boes. 2020. “Air demand of low-level outlets for large dams.” J. Hydraul. Eng. 146 (8): 04020055. https://doi.org/10.1061/(ASCE)HY.1943-7900.0001775.
Hohermuth, B., D. F. Vetsch, L. Schmocker, S. Felder, and R. M. Boes. 2019. “Air-water flow downstream of high-head sluice gates: Experimental and numerical investigations.” In Proc., 38th IAHR World Congress, 6187–6197. Madrid, Spain: International Association for Hydro-Environment Engineering and Research.
ICOLD (International Commission on Large Dams). 2022. “France.” Accessed March 1, 2022. https://www.icold-cigb.org/GB/dams/role_of_dams.asp.
Lian, J., X. Wang, and D. Liu. 2021. “Air demand prediction and air duct design optimization method for spillway tunnel.” J. Hydraul. Res. 59 (3): 448–461. https://doi.org/10.1080/00221686.2020.1780499.
Mazumder, S. K., and W. H. Hager. 1993. “Supercritical expansion flow in Rouse modified and reversed transitions.” J. Hydraul. Eng. 119 (2): 201–219. https://doi.org/10.1061/(ASCE)0733-9429(1993)119:2(201).
Montes, J. S. 1997. “Irrotational flow and real fluid effects under planar sluice gates.” J. Hydraul. Eng. 123 (3): 219–232. https://doi.org/10.1061/(ASCE)0733-9429(1997)123:3(219).
Rabben, S. L. 1984. Investigation of aeration of high-head gates with special consideration of scale effects. Aachen, Germany: Institut für Wasserbau und Wasserwirtschaft, RWTH Aachen.
Roth, A., and W. H. Hager. 1999. “Underflow of standard sluice gate.” Exp. Fluids 27 (4): 339–350. https://doi.org/10.1007/s003480050358.
Sharma, H. R. 1976. “Air-entrainment in high head gated conduits.” J. Hydraul. Div. 102 (11): 1629–1646. https://doi.org/10.1061/JYCEAJ.0004650.
Speerli, J., and W. H. Hager. 1999. “Discussions and closure: Irrotational flow and real fluid effects under planar sluice gates.” J. Hydraul. Eng. 125 (2): 208–213. https://doi.org/10.1061/(ASCE)0733-9429(1999)125:2(208).
Speerli, J., and W. H. Hager. 2000. “Air-water flow in bottom outlets.” Can. J. Civ. Eng. 27 (3): 454–462. https://doi.org/10.1139/l99-087.
Tregnaghi, M., A. Marion, and R. Gaudio. 2007. “Affinity and similarity of local scour holes at bed sills.” Water Resour. Res. 43 (11): W11417. https://doi.org/10.1029/2006WR005559.
Wisner, P. 1967. “Air entrainment in high speed flows.” In Proc., 9th ICOLD Congress, Istanbul, 495–507. Paris: International Commission on Large Dams.
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Published In
Journal of Hydraulic Engineering
Volume 149 • Issue 6 • June 2023
Copyright
© 2023 American Society of Civil Engineers.
History
Received: May 24, 2022
Accepted: Feb 10, 2023
Published online: Apr 6, 2023
Published in print: Jun 1, 2023
Discussion open until: Sep 6, 2023
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