Flow discharge computation over compound sharp-crested side weirs

Journal of Irrigation and Drainage Engineering, 1994

Side weirs are flow-diversion devices widely used in irrigation, land drainage, urban sewage systems, and so forth. For computation of side-weir discharge, the de Marchi equation is widely used. Using de Marchi's equation, various investigators have related the weir discharge coefficient with the main channel's upstream Froude number. Thus, the dominant variable ratio of head to weir height has not been considered in previous investigations. Presented herein is a concept of elementary discharge coefficient for the discharge of an elementary rectangular strip along the weir crest. Like that of a normal weir, this elementary discharge coefficient has been related to the head weir height ratio only. Using this relation, a methodology for determination of the weir discharge is described.

Journal of Hydrology and Hydromechanics, 2014

This paper is concerned with the determination of the relationship for the calculation of the discharge coefficient at free overflow over a rectangular sharp-edged broad-crested weir without lateral contraction. The determination was made on the basis of new measurement in a range of the relative thickness of the weir from 0.12 to 0.30 and newly in a large range of relative height of the weir extremely from 0.24 to 6.8 which greatly expands the application possibilities of low weirs. In addition, the effects of friction and surface tension on the value of the discharge coefficient were evaluated as well as the effect of the relative thickness of the weir. The new equation for discharge coefficient, expressed using the relative height of the weir, was subjected to verification made by an independent laboratory which confirmed its accuracy.

Triangular weirs are commonly used to measure discharge in open channel flow, representing an inexpensive, reliable methodology to monitor water allocation. In this work, a low-speed photographic technique was used to characterize the upper and lower nappe profiles of flow over fully aerated triangular weirs. A total of 112 experiments were performed covering a range of weir vertex angles (from 30°to 90°), crest elevations (8 or 10 cm), and discharges (0.01-7.82 l s −1 ). The experimental nappe profiles were mathematically modeled and combined with elements of free-vortex theory to derive a predictive equation for the weir discharge coefficient. Comparisons were established between measured C d , the proposed discharge coefficient equation, and discharge coefficient equations identified in the literature. The proposed equation predicts C d with a mean estimation error (MEE) of 0.001, a root-mean square error (RMSE) of 0.004, and an index of agreement (IA) of 0.984. In the experimental conditions of this study, this performance slightly improves that of the equation proposed by Greve in 1932, and showed the same absolute value of MEE but lower values of RMSE and IA.

PriMera Scientific Engineering, 2022

More than eighty years ago, De-Marchi indicated an assumption for hydraulics of flow-through side weir. Many researchers who study side weir depended on this assumption in their studies. Many studies for side weir were carried out in different channels, and numerical studies supported the results. This study deal with a comprehensive review of discharge coefficient for side weir.

Any flow taking place over a hydraulic structure under the free surface condition is analyzed with the weirs formula because is good advice and easy measured. Experimentally using a laboratory flume for compound crested weir models were investigated. The crests weir for models divided two parts; the first part is a quarter rounds shape in upstream. The second part is sharp crested in downstream. Series of experiments were used for weir crest radius of R = 1.5 cm, and angles of weir inclination (α = 10, 15°, 25 and 90°) to the direction of flow with a different weir height (P = 15 cm, 20cm, and 25cm) to measure discharges and water heads over the weir models. This kind of weir can used to increase the efficiency by increased the length weir and discharge for same head and width of channel. By the eddy and hydraulic jump in downstream is aerating automatically. Finally, this paper used three formulas for discharge coefficient related for each height weir included oblique angles tested and the equations gave a good correction.

Applied Water Science

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 present 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

Flow Measurement and Instrumentation, 2015

Biosystems Engineering, 2007

Discharge equations of all existing sharp crested flow measurement weirs involve some fractions such as exponents of flow depth, which make manual calculations difficult. In the present research work, weirs with a simplified discharge equation were designed by manipulating the weir profile so that the flow depth exponent was a whole number. A parabolic weir profile gave the simplified discharge equation with two as the flow depth exponent. A relationship for obtaining the parabolic weir profile with any weir angle was developed. The theoretical discharge of flow across the parabolic weir was derived using a geometric constant based on the weir profile. Four parabolic weirs with 301, 451, 601, and 901 weir angles were developed and evaluated in laboratory hydraulic flume. The flow regime across weirs was turbulent and the average coefficient of discharge was estimated as 0Á5570Á05. Weir angle specific discharge models (coefficient of determination R 2 X0Á986) were developed based on two approaches; the first based on the product of geometric constant and the mean coefficient of discharge, and the second on a non-linear regression model constant. Weir constant linear regression prediction equations (R 2 X0Á993), capable of predicting discharge characteristics in combination with discharge models at any intermediate weir angle, were fitted. Parabolic weirs have the merits of both rectangular and triangular weirs, and may find application in field irrigation, industrial flow, and automated control systems measurements.

In the present work the alternative concept of an elementary discharge coefficient along the longitudinal side weir was studied using an oblique weir. Five different angles (30 o , 45 o , 60 o , 75 o , and 90 o) in the flow direction (inclined to the left) with respect to the branch channel wall were examined. A numerical solution of two ordinary differential equations was proposed for discharge and flow depth conducted with program using Euler's method and compared with experimental values. Results referred to the possibility of correlating water surface profile (W.S.P), water depth, and flow discharge numerically as well as the possibility of increasing flow discharge passing through the branch channel by an oblique side weir installation. Thus flow discharge can be increased with side weir angle. Maximum discharge occurred at an angle of 30 o where the percent increase compared with that at 90 o was 70%.

Journal of Engineering

An experimental study is made here to investigate the discharge coefficient for contracted rectangular Sharp crested weirs. Three Models are used, each with different weir width to flume width ratios (0.333, 0.5, and 0.666). The experimental work is conducted in a standard flume with high-precision head and flow measuring devices. Results are used to find a dimensionless equation for the discharge coefficient variation with geometrical, flow, and fluid properties. These are the ratio of the total head to the weir height, the ratio of the contracted weir width to the flume width, the ratio of the total head to the contracted width, and Reynolds and Weber numbers. Results show that the relationship between the discharge coefficient and these variables is a non-linear power function with a determination coefficient of 0.97. The importance and normalized importance analysis show that 56.3 % of the discharge coefficient variation is explained by the head-to-contracted width of the weir r...