Flow through sharp-crested rectangular side orifices under free flow condition in open channels (original) (raw)
Related papers
Effects of side orifice dimensions on characteristics of flow field in rectangular channels
Journal of Applied Research in Water and Wastewater, 2022
In this paper, the flow in the vicinity of rectangular side orifices placed in main channels is estimated by means of the FLOW-3D model. To reconstruct the flow free surface, the volume of fluid (VOF) approach is utilized. In addition, the standard k-ε and RNG k-ε turbulence models are employed to predict turbulence flow. According to the results obtained from the numerical modeling, the RNG k-ε turbulence model has higher accuracy than the standard k-ε. The analysis of the numerical modeling results proved that this model forecasts the discharge coefficient of side weirs with suitable accuracy. On the other hand, the mean absolute percent error (MAPE) is calculated equal to 12.204%. Also, the maximum pressure is simulated near the main channel bed. Moreover, the minimum pressure is estimated near the flow free surface. Regarding the numerical simulations, the maximum turbulence energy state occurs near the inlet of the side orifice and by increasing the side orifice dimensions the flow field turbulence energy value increases.
2013
An unsteady experimental study was completed with the intention of identifying a transition region between partially full weir flow and fully developed orifice flow for a circular sharpedged orifice. Three orifices of different diameter were tested. The head-discharge relationships were obtained by pressure recordings and directly compared by using dimensional analysis. The presence of true weir and orifice flow behaviour was evaluated by an original technique where the head exponent in the head-discharge relationship is considered. The study found that true orifice behaviour was achieved in the experiments. Correspondingly, based on the head exponent, no evidence was obtained to support the existence of a different flow behaviour within the transition. Nevertheless, the experimental data have indicated that corrections are required to be applied to the discharge coefficient in the transition domain. A set of steady state experiments verified the unsteady data results in the orifice flow regime. Discharge coefficients were calculated and predicted by a fitted equation for a circular sharp-edged orifice across the entire range of head. Comparisons to the commonly used orifice equation validate its use for design.
Discharge coefficient of a broad crested side weir in an earthen channel
Water Supply, 2012
Side weirs are widely used to divert flows from rivers and channels. However, the hydraulic behavior of this type of weir is complex and difficult to predict accurately. Previous studies on side weirs have generally focused on side weirs in rectangular channels with a smooth bed. However, one of the applications of side weirs is in irrigation systems which have trapezoidal cross sections and significant bed roughness. The present study investigates the hydraulic behavior of a broad crested side weir in an earthen channel with a rough bed under subcritical flow. These investigations showed that the side weir discharge coefficient is influenced by four main parameters which are upstream Froude number, ratio of the main channel width to the upstream flow depth, ratio of the length of the side weir to the main channel width and ratio of side weir height to the upstream flow depth. The results showed that the discharge coefficient of the side weir gives a lower coefficient value compared...
THE EFFECT OF CHARACTERISTICS OF FLOW ON DISCHARGE COEFFICIENT FOR OBLIQUE 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.
Performance Evaluation of Flow Through Triangular Weirs with Bottom Orifices
FUDMA JOURNAL OF SCIENCES, 2022
This study attempted to evaluate the performance capacity of Triangular weirs with bottom orifices by varying the crest angles, diameters and number of orifices. Forty- Eight (48) triangular weirs with bottom orifices with crest angles of degrees 450, 600, and 900 with varying orifice sizes of diameters 6.5 mm, 7.5 mm and 8.5 mm and the number of orifices ranging from one to five. The analysis of the results indicates that, the discharge (Q) increases with an increase in effective head above crest (Ha) while the discharge coefficients (Cd) are found increasing steadily as the number of orifices and diameter increases with a minimum and maximum Cd of 0.3128 and 1.7986 respectively while the hydraulic performance of the models increasing as the number of orifices increases with the best hydraulic performance of the weirs determined to be 1.7630 at the model of angle 900 with five orifices of diameter 8.5 mm
Effect of Varying Orifice Thickness on the Discharge Coefficient for Different Orifices Shapes
Engineering Research Journal - Faculty of Engineering (Shoubra)
One of the most important factors to be studied carefully is the discharge coefficient "Cd" through the orifices, which reflects the efficiency of the flow and plays an important role in the design of hydraulic units. The purpose of this paper is to investigate experimentally the effect of changing orifice thickness on the discharge coefficient for water flow through different orifice shapes and comparing each other. To achieve this goal, four orifices shapes were used: circular, square, equilateral triangle and rectangular, five different thicknesses (9.25, 7.5, 6.75, 4 and 2 mm) were tested. It should be noted that the tests were conducted on four different values of the pressure heads affecting the center of the hole: (35, 40, 45 and 50 cm). Bernoulli's equation was used as a theoretical basis for calculating the discharge coefficient. The results of the study demonstrated that the changing in the thickness of the orifice affects the coefficient of discharge. The coefficient of discharge gradually decreases when the ratio (orifice thickness "t"/orifice equivalent diameter "d") increases, with the fixity of both the orifice area and the vertical pressure head located above the center of the orifice. In all the analytical comparisons made in this study it was observed that circular orifices give the highest values of the coefficient of discharge compared to all other shapes followed by equilateral triangular orifices and then square orifices and finally it was observed that rectangular orifices give the lowest values of the coefficient of discharge.
Discharge Coefficients for Orifices Cut into Round Pipes
Journal of Irrigation and Drainage Engineering, 2013
This study focuses on the discharge coefficient (C d) for flow into orifices cut with a circular bit perpendicular to and along the centerline of a round pipe, a common configuration on perforated risers installed as the principal outlets for stormwater detention or sediment basins. When predicting flow, the orifice area is generally defined as the area of the bit used to cut the hole, but the true orifice area is larger than the bit due to the curvature of the riser pipe. Four different descriptions for orifice area were tested while attempting to fit C d to measured discharge experiments. The tests showed that C d decreases as the orifice diameter approaches the diameter of the riser. Photographic imagery shows that the reduced C d is due to lateral flow from the riser's curved sides decreasing the vena contracta area more than what normally occurs during flow through an orifice in a flat plate. In contrast, but to a lesser extent, C d increases as the water surface approaches the top of the orifice. Best fit equations to model C d were developed to better estimate flow, with the most applicable having an R 2 of 88.8% and a root-mean squared error of 0.028. Orifice elevation above the tank floor was measured and initially modeled but was ultimately not included in the C d model because the R 2 improved by only 0.6%.
Flow Measurement and Instrumentation, 2020
A side orifice is an important type of hydraulic structure which is used widely in irrigation and waste management systems to divert desired discharges from a main channel or to distribute the flow within the basins. Circular pipes flowing partially full are often used in these systems, but existing predictive relations developed for rectangular channels result in significant error. In the present study, the flow through a side orifice in a circular open-channel is numerically simulated and validated to test the effect of different parameters on the discharge coefficient and propose an appropriate predictive equation. To minimize the number of required simulations and validations, a Response Surface Method-Central Composite Design (RSM-CCD) is employed. Results showed that the discharge coefficient is inversely related to the Froude number (Fr) and the ratio of the side orifice length to the approaching flow water depth. However, any increase in either the ratio of the orifice length to the main channel diameter or the ratio of the lower crest level to the orifice length will increase the discharge coefficient. A new equation is presented to determine the discharge coefficient of side orifice in a circular open-channel using RSM-CCD. The sensitivity analysis showed that all linear terms must considered in the equation but that the interaction terms can be dropped. The maximum error of the equation to predict the training and validation data are 1% and 2% respectively.
Determination of Orifice Coefficients for Flow Through Circular and Rectangular Orifices
ATBU Journal of Science, Technology and Education, 2018
Circular and rectangular orifices are among the types of orifices being classified according to geometrical shapes. They are among others widely used as flow meters. Knowledge about the orifice coefficients and discharges through circular and rectangular orifice is very important, when selection for use is based on the requirement of low or high discharges as well as high or low orifice coefficients. So, this research work experimentally determined the orifice coefficients and discharges through circular and rectangular orifices having the same area of 0.00015m 2 under a constant head of water of 0.9m. The experimental results revealed that under a constant head of water of 0.9m, circular orifice has average coefficient of discharge, coefficient of velocity, coefficient of contraction, theoretical and actual discharges as 0.62, 0.94, 0.66, 5.52x 10 -4 m 3 /s and 3.42x 10 -4 m 3 /s respectively. More so, that rectangular orifice under the same constant head of water of 0.9m, has a...