Discharge Relations for Rectangular Broad-Crested Weirs

Year 2011, Volume: 17 Issue: 4, 324 - 336, 04.12.2011

Farzin Salmasi

https://doi.org/10.1501/Tarimbil_0000001184

Cited By: 2

Abstract

Compound broad-crested weirs have a small inner rectangular section for measuring low flows and then, they
broaden to a wide rectangular section at higher flow depths. It can be used as a water measurement device in
irrigation canals. This paper presents data that will be of use in the design of hydraulic structures for flow control
and measurement. A series of laboratory experiments were performed in order to investigate the effects of width of
the lower weir crest and step height of broad-crested weirs with rectangular compound cross section on the values
of the discharge coefficient (Cd) and the approach velocity coefficient. For this purpose, 15 different broad-crested
weir models with rectangular compound cross sections for a wide range of discharges were tested. The sillreferenced heads at the approach channel and at the tail water channel were measured in each experiment. The
dependence of the discharge coefficient and approach velocity coefficient on model parameters was investigated.
Results show that a discontinuity occurs in head-discharge ratings because the section width suddenly changes
shape, experiencing a break in slope when the flow enters the outer section. Values of Cd obtained from the
experiments on compound broad-crested weirs are lower than those of a broad crested weir with a rectangular cross
section because of it’s contraction effects. 

Keywords

Broad-crested weir, Compound, Discharge coefficient, Velocity coefficient

Bileşik Geniş tepeli Savaklar hidroliği

Abstract

Bileşik geniş tepeli savak, düşük akım ölçme ve ardından küçük bir iç dikdörtgen bölüm var, onlar daha yüksek akış derinliklerde geniş bir dikdörtgen bölümüne genişletmek. Sulama kanallarında su ölçüm cihazı olarak kullanılabilir. Bu yazıda akış kontrolü ve ölçümü için hidrolik yapıların tasarımında faydalı olacaktır verilerini sunmaktadır. laboratuvar deneyleri bir dizi sipariş katsayısı deşarj değerleri üzerine dikdörtgen bileşik kesitli geniş tepeli savaklar alt savak kret ve basamak yüksekliği ve genişliğinin etkisini araştırmak için, yaklaşım hızı katsayısı ve modüler limit yapıldı . Bu amaçla, deşarj geniş bir yelpazede için dikdörtgen bileşik kesitli 15 farklı geniş tepeli savak modelleri test edildi. yaklaşım kanalı ve kuyruk su kanalında eşik referansı başları her deney ölçüldü. deşarj katsayısı ve yaklaşım hız modeli parametreleri üzerine katsayısı bağımlılık araştırıldı

Keywords

Kalın eşikli savak, Bileşik, Debi katsayısı, Hız katsayısı

References

• Azimi A H & Rajaratnam N (2009). Discharge characteristics of weirs of finite crest length. Journal of Hydraulic Engineering 135(12):120-125
• Boiten W & Pitlo H R (1982). The V-shaped broadcrested weir. Journal of Irrigation and Drainage Engineering 108(2): 142-160
• Bos M G (1976). Discharge measurement structures, 2nd Ed., International Institute for Land Reclamation and Improvement, Wageningen, The Netherlands
• Clemmens A J, Bos M G & Replogle J A (1984). RBC broad-crested weirs for circular sewers and pipes. Journal of Hydrology 68: 349-368
• Crabbe A D (1974). Some hydraulic features of the square-edged broad-crested weir. Water and Water Engineering 78(10): 354-358
• French R H (1987). Open-channel hydraulics. McGrawHill, New York Gogus M & Oskandemir V (2006). Broad-crested weirs with rectangular compound cross section. Journal of Irrigation and Drainage Engineering 132(3): 272-280
• Gonzalez C A & Chanson H (2007). Experimental measurements of velocity and pressure distributions on a large broad-crested weir. Flow Measurement and Instrumentation 18:107-113
• Hager W H & Schwalt M (1994). Broad-crested weir. Journal of Irrigation and Drainage Engineering 120(1): 13-26
• Harrison A J M (1967). The streamlined broad-crested weir. Proceedings of the Institution of Civil Engineers 38: 657-678
• Horton R E (1907). Weir experiments, coefficients, and formulas. Dept. of the Interior, U.S. Geological Survey, Water-Supply and Irrigation Paper 200. Government Printing Office, Washington, D.C
• Keutner C (1934). Strrmungsvorginge an breitkronigen Wehrkrpern und an Einlaufbauwerken. Bauingenieur, 15(37/38), 366-371; 15(39/40), 389- 392 (in German)
• Jan C D, Chang C J & Kuo F H (2009). Experiments on discharge equations of compound broad-crested weirs. Journal of Irrigation and Drainage Engineering 135(4): 61-73
• Jan C D, Chang C J & Lee M H (2006). Discussion of ‘Design and calibration of compound sharp-crested weir, by J. Martinez et al. Journal of Hydraulic Engineering 132(8): 868-871
• Martinez J, Reca J, Morillas M T, & López J G (2005). Design and calibration of a compound sharp-crested weir. Journal of Hydraulic Engineering 131(2): 112-116
• Moss W D (1972). Flow separation at the upstream edge of a square-edged broadcrested weir. Journal of Fluid Mechanics 52(2): 307-320
• Ramamurty A S, Udoyara S T, & Rao M V J (1987). Characteristic of square-edged and round-nosed broad-crested weirs. Journal of Irrigation and Drainage Engineering 114(1): 61-73
• Ranga Raju K G 1993. Flow through open channel, McGraw-Hill, New York Ranga Raju K G & Ahmad I (1973). Discharge characteristics of suppressed and contacted broadcrested weirs. Journal of Irrigation and Power (India) 30(4): 157-166
• Sarker M A & Rhodes D G (2004). Calculation of freesurface profile over a rectangular broad-crested weir. Flow Measurement and Instrumentation 15(4) 215-219
• Singer J (1964). Square-edged broad-crested weir as a flow measurement device. Water and Water Engineering 68(6): 229-235
• Tracy H J (1957). Discharge characteristics of broadcrested weirs. U.S. Dept. of Interior, Geological Survey Circular 397, Washington D.C