Study of variations in discharge coefficients for broad-crested weirs with sloped upstream and downstream faces using numerical simulation

Document Type : Research Article

Authors

Department of Water Engineering, Faculty of Agriculture, University of Tabriz

Abstract

Weirs are structures that are important for measuring flow and controlling water levels. Research has shown that the discharge coefficient is not constant and depends on the crest length, the height of the weir, the upstream head, and the upstream and downstream slopes. In this study, the effect of these parameters on the discharge coefficient (Cd) is investigated by numerical simulation. The current study presents numerical simulation using the ANSYS FLUENT software. The total number of simulations is 432 which includes: 4 upstream slopes, 4 downstream slopes, 3 weir heights, 3 upstream heads (h1) and 3 weir crest lengths. It was found that the downstream face slope has little effect on Cd. For 0.1<H1/w<0.4 by decreasing the upstream slope, Cd increases, where H1 is the water head on the weir crest and w is the length of the crest. Also, for the same range, by decreasing the height of the weir (p), the Cd increases. For 0.16<H1/p<2, as the length of the crest decreases, the Cd increases. By comparing the numerical simulation results to physical measurements, multi-variable regression equations for estimating Cd are presented. In addition to Cd, extraction of other more detailed information such as water level profiles and velocity profiles at different locations are provided.

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Main Subjects


[1] M.G. Bos, Discharge measurement structures. International Institute for Land Reclamation and Improvement (ILRI) Publication 20 (1989) 3rd Revised Edition Wageningen.
[2] F.M. Henderson, Open-Channel Flow, Macmillan, New York, (1966).
[3] J.E. Sargison, A. Percy, Hydraulic of broad-crested weirs with varying side slopes. J. Irrig. Drain. Eng., 135(1) (2009) 115-118.
[4] N.S. Govinda Rao, D. Muralidhar, Discharge characteristics of weirs of finite-crest width. Houille Blanche, 18(5), (1963) 537-545.
[5] J. Singer, Square-edged broad-crested weir as a flow measuring device. Water and Water Eng., 68(820), (1964) 229-235
[6] W.H. Hager, M. Schwalt, Broad-crested weir. J. Irrig. Drain. Eng., 120(1), (1994) 13-26.
[7] H.M. Fritz, H.W. Hager, Hydraulics of embankment weirs. J. Hydraul. Eng., 124(9), (1998) 963-971.
[8] M. Johnson, Discharge coefficient analysis for flat-topped and sharp-crested weirs. Irrig Sci 19, (2000) 133–137
[9] J. Farhoudi, H. Shah Alami, Slope Effect on Discharge Efficiency in Rectangular Broad Crested Weir with Sloped Upstream Face, International Journal of Civil Engineering, 3(1), (2005) 58-65.
[10] M. Gogus, Z. Defne, V. Ozkandemir, Broad-crested weirs with rectangular compound cross sections, Irrig. Drain. Eng., 132(3), (2006) 272-280
[11] F. Salmasi, G. Yıldırım, A. Masoodi P. Parsamehr, Predicting discharge coefficient of compound broad- crested weir by using genetic programming (GP) and artificial neural network (ANN) techniques. Arabian Journal of Geosciences. (6), (2013) 2709–2717.
[12] J. Farhoudi, N. Shokri, Flow from broad crested rectangular weirs with sloped downstream face. 32nd IAHR Congress, Venice, Italy (2007).
[13] C.A. Gonzalez, H. Chanson, Experimental measurements of velocity and pressure distributions on a large broad-crested weir, J.  Flow Measurement and Instrumentation. 18 (3), (2007) 107–113.
[14] M. Bijankhan, C. Di Stefano, S. Kouchakzadeh, New stage-discharge relationship for weirs of finite crest length, J. Irrig. Drain. Eng., 06013006(8), (2013) 0733-9437
[15] S.H. Hosseini H. Afshar, Experimental and 3-D numerical simulation of flow over a rectangular broad- crested weir. Int J Eng Adv Tech 2(6), (2014) 2249–8958
[16] M.R. Madadi  A. Hosseinzadeh Dalir, D. Farsadizadeh, Investigation of flow characteristics above trapezoidal broad-crested weirs, Flow Measurement and Instrumentation 38, (2014)
[17] L. Jiang, M. Diao, H. Snu, Y. Ren, Numerical modeling of flow over a rectangular broad-crested weir with a sloped upstream face. Water, 10 (11), (2018) 1663
[18] C.W. Hirt, B.D. Nichols, Volume of fluid (VOF) method for the dynamics of free boundaries. J. Comput. Phys. 39, (1981) 201–225.
[19] M. Moradi, M. Fathi Moghadam, L. Davoudi, Experimental investigation of submerged flow over porous embankment weirs with up and downstream slopes. J. Irrig. Sci. and Eng., 42(2), (2020) 187-199, (In Persian).
[20] F. Salmasi, N. Sabahi, J. Abraham, Discharge coefficients for rectangular broad crested gabion weirs: An experimental study. J. Irrig. Drain. Eng., (2021a)
[21] A. David, K. James, Free flow and discharge characteristics of trapezoidal-shaped weirs. J. Fluids, 5, (2020) 238-242.
[22] F. Salmasi, F. Nahrain, J. Abraham, A. Taheri Aghdam, Prediction of discharge coefficients for broad- crested weirs using expert systems, ISH Journal of Hydraulic Engineering, (2021b)
[23] F. Salmasi, J. Abraham, Discharge coefficients for ogee spillways, Water Supply, ws2022129, (2022)
[24] Y.T. Zerihun, Free flow and discharge characteristics of trapezoidal-shaped weirs. Fluids, 5(4), (2020) 238
[25] M. Akbari, F. Salmasi, H. Arvanaghi, M. Karbasi, D. Farsadizadeh, Application of Gaussian Process Regression Model to Predict Discharge Coefficient of Gated Piano Key Weir, Water Resources Management, 33 (11), (2019) 3929–3947
[26] F. Malekzadeh, F. Salmasi, J. Abraham, H. Arvanaghi, Numerical investigation of the effect of geometric parameters on discharge coefficients for broad-crested weirs with sloped upstream and downstream faces, Applied Water Science, 12, (2022) 110