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Characteristics of siphon flow under submerged discharge conditions


Characteristics of siphon flow under submerged discharge conditions

Ahmed, warda Mansour (2021) Characteristics of siphon flow under submerged discharge conditions. PhD thesis, Concordia University.

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Characteristics of siphon flow under submerged discharge conditions

Water reservoirs serve such essential purposes as water supply, irrigation, and hydroelectric power developments. Their effective and safe operations need reliable hydraulic structures for flow control. Siphon spillways are a flow control structure, with two main advantages: 1) no moving parts required and thus less susceptible to breakdown; 2) the ability to pass full discharge with a minimal increase of reservoir water level. The second advantage makes it easier to maintain target water levels as water resources while to ensure safe operations. The design of a siphon spillway uses one discharge head only, termed the design head, which is derived from statistical analysis of hydrological data for the reservoir region. However, under climate change, most existing siphons have been or are expected to be subject to actual discharge heads larger than their design heads. In other words, climate change results in submerged exit condition for siphon flow.
Previous studies of siphons focus on their hydraulic performance under free discharge condition. How submergence affects the flow is a question, not addressed previously. The flow over the crest of a siphon is highly curved. It is a challenge to deal with the curved boundary surface of the crest in siphon analysis. Streamline curvatures, three-dimensional vorticities and other subtle characteristics of the velocity and pressure fields remain to be discovered. Existing studies limit to a qualitative description of siphon flow and oversimplify flow mechanisms. The purpose of this research is to improve our understanding of siphon flow characteristics in a range of submerged exit conditions; to reveal any changes in the hydraulic performance of siphons, compared to free discharge conditions; and ultimately to contribute to an improved design of siphons.This research took the approach of combining laboratory experiments with mathematical modelling. The experiments used a scaled model siphon. It was fabricated and tested in the Hydraulics Laboratory at Concordia University. A series of experiments were conducted to determine the discharge coefficient in a range of flow rates. A three‐dimensional computational fluid dynamics (CFD) model was established for predicting the velocity and pressure fields as well as turbulence quantities. The CFD model used mesh refinement for regions close to solid boundaries and computed two-phase flow. The free surface of reservoir was tracked using the volume-of-fluid (VOF) method. Turbulence closure was obtained using the RNG k‐ε model.
The CFD model predicted detailed distributions of the flow field, including curvilinear flow features in the crest region. The flow characteristics corresponded to various conditions of submergence at the downstream exit of the siphon conduit, and included primary flow velocity, secondary flow velocity, turbulence kinetic energy, and pressure. The predicted discharge coefficient compared well with experimental data. The predicted mean-flow velocities were validated using estimates from the potential flow theory.
The experimental and computational results lead to the following findings: 1) The flow in the upstream reservoir is relatively uniform, with smooth movement toward the siphon entrance. At the entrance, the flow contracts, causing the pressure to drop below the hydrostatic pressure level in the upper corner of the entrance. Under the impact of centrifugal forces, the flow at the crest is forced to move in the extrados direction, causing secondary flow and an increased velocity above the crest. 2) The velocity rapidly increases near the crest, and reaches the maximum at a very small height from the crest surface. In the zone above the boundary layer, the velocity decreases gradually before it starts to rapidly decrease near the crown surface. 3) Flow separation occurs just a short distance downstream of the crest. Eddies start to form on the crest and develop along the lower leg of the siphon. Further downstream, the flow contracts by a deflector, creating flow separation on the downstream side. 4) The pressures differ along the siphon conduit, with negative values in the crest region. The pressure decrease is proportional to the increase of velocity. Negative pressures at the crest surface may drop to water vapour pressure at the prototype scale. 5) The discharge coefficient is a parameter of practical importance. It allows one-to-one determination of siphon discharge from the head which is simple to measure. Values of the discharge coefficient range from 0.62 to 0.68 under submerged exit conditions. These values are larger than those under free discharge conditions.
This study has contributed to a better understanding of flow behaviours in a region bounded by curved boundaries. The CFD modelling strategies discussed in this research can be applied to analyse complex flows in similar hydraulic structures. The pressure data reported can possibly be used to access risks of cavitation in siphon spillways. In conclusion, the siphon flow is a complex flow, with curvatures, three dimensionality and turbulence. Through laboratory experiments and mathematical modelling, this research sheds lights on the flow characteristics such as discharge performance, velocity distribution, and pressure distribution.

Divisions:Concordia University > Gina Cody School of Engineering and Computer Science > Building, Civil and Environmental Engineering
Item Type:Thesis (PhD)
Authors:Ahmed, warda Mansour
Institution:Concordia University
Degree Name:Ph. D.
Program:Civil Engineering
Date:3 March 2021
Thesis Supervisor(s):Li, Samuel and Ramamurthy, Amruthur
Keywords:Spillway, siphon, velocity distribution, pressure distribution, CFD, turbulence and cavitation .
ID Code:988438
Deposited By: Warda Ahmed
Deposited On:29 Nov 2021 16:18
Last Modified:29 Nov 2021 16:18
Related URLs:


Ali, K.H.M. and Pateman, D., 1980. Theoretical and experimental investigations of air-regulated siphons. Proceedings of the Institution of Civil Engineers, 69(1), pp. 111-138.
Babaeyan-Koopaei, K., Valentine, E.M. and Ervine, D.A., 2002. Case study on hydraulic performance of Brent Reservoir siphon spillway. Journal of Hydraulic Engineering, 128(6), pp. 562-567.
Bos, M.G., 1976. Discharge measurement structures. Publication No. 161, Delft Hydraulic Laboratry, Delft, the Nederlands.
Cassidy, J.J., 1965. Irrotational flow over spillways of finite height. Journal of the Engineering Mechanics Division, 91(6), pp. 155-173.
Cassidy, J.J., 1970. Designing spillway crests for high-head operation. Journal of the Hydraulics Division, 96(3), pp. 745-753.
Castro-Orgaz, O., 2008. Curvilinear flow over round-crested weirs. Journal of Hydraulic Research, 46(4), pp. 543-547.
Chow, V.T., 1959. Open-channel hydraulics. McGraw-Hill, Caldwell, New Jersey.
Coleman, H.W., Wei, C.Y. and Lindell, J.E., 2004. Hydraulic design of spillways. Hydraulic design handbook, pp.17-41. McGraw-Hill
Dressler, R.F., 1978. New nonlinear shallow-flow equations with curvature. Journal of Hydraulic Research, 16(3), pp. 205-222.
Ervine, D.A. and Oliver, G.C.S., 1980. The full-scale behaviour of air-regulated siphon spillways. Proceedings of the Institution of Civil Engineers, 69(3), pp. 687-706.
Falvey, H.T., 1990. Cavitation in chutes and spillways. Denver: US Department of the Interior, Bureau of Reclamation.

Ferziger, J.H., Perić, M. and Street, R.L., 2002. Computational methods for fluid dynamics (Vol. 3, pp. 196-200). Springer, Berlin
Foerster, K.E. and Anderson, A.G., 1969. Model Study of the Spillway of the Reza Shah Kabir Project Khuzestan Water and Power Authority Ministry of Water and Power-Government of Iran.
Frizell, K.W., Renna, F.M. and Matos, J., 2013. Cavitation potential of flow on stepped spillways. Journal of Hydraulic Engineering, 139(6), pp.630-636.
Gribbin, J.E., 2013. Introduction to Hydraulics & Hydrology: With Applications for Stormwater Management. Nelson Education. Hager, W.H. and Bremen, R., 1988. Plane gate on standard spillway. Journal of Hydraulic Engineering, 114(11), pp. 1390-1397.
Head, C.R., 1971. A self-regulating river siphon. Journal of Institution of Water Engineers, 25(1), pp. 63-72.
Head, C.R., 1975. Low-Head Air Regulated Siphons. Journal of the Hydraulics Division, 101(3), pp. 329-345.
Hirt, C.W. and Nichols, B.D., 1981. Volume of fluid (VOF) method for the dynamics of free boundaries. Journal of Computational Physics, 39(1), pp. 201-225.
Houghtalen, R.J., Osman, A. and Hwang, N.H., 2017. Fundamentals of hydraulic engineering systems. Fifth edition. Prentice Hall, Hoboken, New Jersey.
Jones, W.P. and Launder, B.E., 1972. The prediction of laminarization with a two-equation model of turbulence. International Journal of Heat and Mass Transfer, 15(2), pp. 301-314.
Kermani, E.F., Barani, G.A. and Hessaroeyeh, M.G., 2018. Cavitation damage prediction on dam spillways using Fuzzy-KNN modeling. J Appl Fluid Mech, 11(2), pp.323-329.
Khatsuria, R.M., 2004. Hydraulics of spillways and energy dissipators. CRC Press, Boca Raton, Florida.
Launder, B.E. and Spalding, D.B., 1974. The numerical computation of turbulent flows. Computer Methods in Applied Mechanics and Engineering, 3(2), pp. 269-289.
Lee, W. and Hoopes, J.A., 1996. Prediction of cavitation damage for spillways. Journal of Hydraulic Engineering, 122(9), pp.481-488.
Linsley, R.K. and Franzini, J.B., 1964. Water-resources engineering. McGraw-Hill, Highstown, New Jersey 08520
Liuzzo, L. and Freni, G., 2015. Analysis of extreme rainfall trends in sicily for the evaluation of depth-duration-frequency curves in climate change scenarios. Journal of Hydrologic Engineering, 20(12), p.04015036.
Mailhot, A. and Duchesne, S., 2010. Design criteria of urban drainage infrastructures under climate change. Journal of Water Resources Planning and Management, 136(2), pp.201-208.
Nie, M.X., 2001. Cavitation prevention with roughened surface. Journal of Hydraulic engineering, 127(10), pp.878-880.
Peltier, Y., Dewals, B., Archambeau, P., Pirotton, M. and Erpicum, S., 2018. Pressure and velocity on an ogee spillway crest operating at high head ratio: experimental measurements and validation. Journal of Hydro-environment Research, 19, pp. 128-136
Pope, S.B., 2001. Turbulent flows. Cambridge University Press, Cambridge, U.K.
Rahmeyer, W.J., 1981. Cavitation damage to hydraulic structures. Journal‐American Water Works Association, 73(5), pp.270-274.
Ramamurthy, A.S. and Vo, N.D., 1993. Application of Dressler theory to weir flow. Journal of Applied Mechanics, 60, pp. 163-166.
Ramamurthy, A.S., Vo, N.D. and Balachandar, R., 1994. A note on irrotational curvilinear flow past a weir. Journal of Fluids Engineering, 116(2), pp. 378-381.
Johnson, N. K. and Richardson, L. F., 1922. Weather Prediction by Numerical Process. The Mathematical Gazette, 11(159), pp. 125–125. Doi: 10.2307/3603284.
Savage, B.M. and Johnson, M.C., 2001. Flow over ogee spillway: Physical and numerical model case study. Journal of Hydraulic Engineering, 127(8), pp. 640-649.
Shih, T.H., Liou, W.W., Shabbir, A., Yang, Z. and Zhu, J., 1995. A new k-ϵ eddy viscosity model for high Reynolds number turbulent flows. Computers & Fluids, 24(3), pp. 227-238.
Schlichting, H. and Gersten, K., 2000. Boundary-Layer Theory. Springer, Berlin
Tadayon, R. and Ramamurthy, A.S., 2013. Discharge coefficient for siphon spillways. Journal of Irrigation and Drainage Engineering, 139(3), pp. 267-270.
Tennekes, H. and Wyngaard, J.C., 1972. The intermittent small-scale structure of turbulence: data-processing hazards. Journal of Fluid Mechanics, 55(1), pp. 93-103.
Tullis, B.P., 2011. Behavior of submerged ogee crest weir discharge coefficients. Journal of Irrigation and Drainage Engineering, 137(10), pp. 677-681.
USACE, 1990. Hydraulic design of dpillways. Department of the Army Corps of Engineers, Washington, D.C. EM 1110‐2‐1603.
USBR, 1977. Design of small dams. U.S. Government Printing Office. Washington, D.C.
Vermeyen, T.B., Merritt, D.H. and Taylor, G.M., 1991. Design of high capacity spillways for Ritschard Dam, Colorado. In Hydraulic Engineering (pp. 394-399). ASCE.
Vermeyen, T.B., 1992. Uncontrolled ogee crest research. PAP-0609, U.S. Bureau of Reclamation.
Wan, W., Liu, B. and Raza, A., 2018. Numerical prediction and risk analysis of hydraulic cavitation damage in a High-Speed-Flow spillway. Shock and Vibration, 2018.
Wilcox, D.C., 1998. Turbulence modeling for CFD. DCW Industries, La Canada, CA.
Yakhot, V. and Orszag, S.A., 1986. Renormalization group analysis of turbulence. I. Basic theory. Journal of Scientific Computing, 1(1), pp. 3-51.
Yusuf, F. and Micovic, Z., 2020. Prototype-scale investigation of spillway cavitation damage and numerical modeling of mitigation options. Journal of Hydraulic Engineering, 146(2), p.04019057.
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