Numerical simulation of flow over rectangular broad-crested weirs including various upstream and downstream sloping faces

Abstract

A weir is one of the oldest man-made hydraulic structures, which is used to measure and regulate water flow. The flow passing over a weir is turbulent and is accompanied by mixing of water and air. In this study, the flow passing over two types of broad-crested weirs, i.e., ARB and BRA with downstream and upstream sloping faces is simulated in two dimensions. The standard K-ε model is used to predict free flow surface with volume of fluid (VOF) method. The results of the numerical model for the hydraulic parameters like discharge coefficient, flow velocity and boundary layer development are compared with experimental results and existing relations. The results showed that the standard K-ε turbulence model and the VOF method are suitable for predicting the water surface profile on broad-crested weirs for estimating the discharge coefficient (Cd) and velocity profiles at different distances on the crest. The maximum relative error for the hydraulic head (h1) and Cd is 4.06% and 6.54%, respectively, which is acceptable.

Keywords

• Fluid volume fraction
• broad-crested weir
• discharge coefficient
• fluent
• K-ε turbulence model

References

1. [1] Samadi, A., Salmasi, F., Arvanaghi, H., Mousaviraad, M., (2022), Effects of Geometrical Parameters on Labyrinth Weir Hydraulics. Journal Of Irrigation and Drainage Engineering, 148(10), 06022006. https://doi.org/10.1061/(ASCE)IR.1943-4774.0001695.
2. [2] Hager, W. H., Schwalt, M., (1994), Broad-crested Weir. Journal of Irrigation and Drainage Engineering, 120(1), 13–26.
3. [3] Fitz, H. M., Hager, W. H., (1998), Hydraulics of Embankment Weirs. Journal of Hydraulic Engineering, 124(9), 963–971.
4. [4] Johnson, M. C., (2000), Discharge Coefficient Analysis for Flat-Topped and Sharp-Crested Weirs. Irrigation Science, 19, 133–137.
5. [5] Gogus, M., Defne, Z., Ozkandemir, V., (2006), Broad-Crested Weirs with Rectangular Compound Cross Sections. Journal of Irrigation and Drainage Engineering, 132(3), 272–280.
6. [6] Salmasi, F., Poorescandar, S., Hosseinzadeh Dalir, A., Farsadizadeh, D., (2012), Discharge Relations for Rectangular Broad-Crested Weirs. Journal of Agricultural Sciences (Tarım Bilimleri Dergisi), 17(4), 324–336. https://doi.org/10.1501/Tarimbil_0000001184
7. [7] Malekzadeh, F., Salmasi, F., Abraham, J., Arvanaghi, H., (2022), 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(5), 22–34. https://doi.org/10.1007/s13201-022-01631-5
8. [8] Felder, S., Chanson, H., (2012), Velocity and Pressure Measurements on Broad-Crested Weir: Physical Measurement. 4th IAHR International Symposium on Hydraulic Structures, Porto, Portugal.

9. [9] Liu, C. R., Ma, W. J., Hu, He, A.D., (2002), Numerical Investigation of Flow Over a Weir. Acta Mechanica Sinica, 18, 594–602.
10. [10] Hargreaves, D. M., Morvan, H. P., Wright, N. G., (2007), Validation of the Volume of Fluid Method for Free Surface Calculation: The Broad-Crested Weir. Engineering Applications of Computational Fluid Mechanics, 1(2), 136–146.
11. [11] Haun, S., Reidar, B. N., Feurich, O., Feurich, R., (2011), Numerical Modeling of Flow Over Trapezoidal Broad-Crested Weir. Engineering Applications of Computational Fluid Mechanics, 5(3), 327–405.
12. [12] Sargison, J. E., Percy, A., (2009), Hydraulics of Broad-Crested Weirs with Varying Side Slopes. Journal of Irrigation and Drainage Engineering, ASCE, 115–118.
13. [13] Salmasi, F., Abraham, J., (2023), Hydraulic Characteristics of Flow Over Stepped and Chute Spillways (case study: Zirdan Dam). Water Supply, 23(2), 851–866. https://doi.org/10.2166/ws.2023.011.
14. [14] Taheri, Aghdam, A., Hosseinzadeh, Dalir, A., Salmasi, F., Abbaspour, A., Abraham, J., (2023), Numerical and Experimental Study of Trajectory for Free-Falling Jets. Iranian Journal of Science and Technology, Transactions of Civil Engineering, 9(5), 62–70. https://doi.org/10.1007/s40996-023-01043-8
15. [15] Papageorgakis, G. C., Assanis, D.N., (1999), Comparison of Linear and Nonlinear RNG-Based Models for Incompressible Turbulent Flows, Numerical Heat Transfer, 35, 1–22.
16. [16] Daneshfaraz, R., Aminvash, E., Omidvar, R., Süme, V., Marangoz, H. O., Yılmaz, E., (2025), Investigating The Effect of Grooves on The Hydraulic Parameters of a Sharp-Crested Trapezoidal Side Weir. Journal of Applied Fluid Mechanics, 18(10), 2465–2475.
17. [17] Daneshfaraz, R., Norouzi, R., Akhondi, B., Süme, V., Marangoz, H. O., Yılmaz, E., (2025), Experimental İnvestigation of The Effect of Perforated Sill And Orifice on Sluice Gate Discharge Coefficient. Water Science, 40(1), 1–30.