Broad-crested Weir Research Articles

FEM analysis of water surface profile using VOF Method

The prediction of water surface elevation in open channels is important for evaluation and determination of the heights of side wall of structures in open channel systems. At present empirical equations are basically used for the purpose. In the early half of the 19th century experimental approach was mainly used but it had the drawbacks of laborious data collection and instrument operation limitation. The 3D flow behavior or some complex turbulent structure which is the nature of any open channel flow, cannot be effectively captured through experiments, so in these circumstances, computational approach can be adopted to overcome these obstacles. In comparison to experimental studies computational approach is repeatable, can simulate at full scale, can generate the flow taking all the data points into consideration. The motive of the present work is to use the simple geometry of the rectangular broad crested weir to test the commercial CFD software ANSYS-CFX in order to test its feasibility for implementation in more complex open channel flows. The experimental results of Hager & Schwalt’s are validated and then the analysis has been done for weirs with different slopes.

A novel approach for estimation of discharge coefficient in broad-crested weirs based on Harris Hawks Optimization algorithm

Accurate determination of the discharge coefficient play a very important role in estimating the flow discharge over the weirs. As a result, it is significant to estimate the discharge coefficient correctly. The aim of this study is simulation and estimation the discharge coefficients (Cd) over the broad-crested weirs with cross section rectangular and suppressed. Hence, numerical simulation of hydraulic characteristics of these weirs were performed by ANSYS FLUENT software and results were obtained. Then two intelligent models of ANN, GPR and hybrid both of models namely ANN-HHO, GPR-HHO were used to determine the discharge coefficients using the efficient parameters and the results of these models were compared. Assessment of the results were performed using the statistical metrics: coefficient of determination (R2), root mean square error (RMSE), mean absolute error (MAE), scatter index (SI) and Kling-Gupta efficiency (KGE) and graphical diagrams including violin plot, percent relative error (RE%) plot and probability density function (PDF) plot of residuals. It was found that hybrid artificial neural network and gaussian process regression with Harris Hawks optimization (ANN-HHO and GPR-HHO) could improve ANN and GPR models performance in estimating the Cd in broad-crested weirs. Overall, results indicated that a combination of the HHO with the ANN (ANN-HHO) model performs better than GPR-HHO model for the estimation of the Cd.

Effect of Height and Surface Roughness of a Broad Crested Weir on the Discharge Coefficient: Experimental Study

Weir is usually incorporated as control or regulation devices in hydraulic systems, with flow measurement as their secondary. It is normally intended for use in the field and thus to regulate broad discharges. Broad-Crested weir is among the oldest common weir types. In this paper, the effect of height and surface roughness for different Board Crested weirs models were studied on discharge coefficient (Cd) in a horizontal open channel. In the crest of the weir, certain materials may be combined with concrete (e.g., boulders) or may be used as cladding to minimize the effect of water overflow (e.g. stone). The weir surface should not be considered smooth in this case, and the discharge coefficient (Cd) must be re-estimated. For these purposes, laboratory flume was used to study the effect of height and surface roughness on the discharge coefficients with four of the different weir models dimensions of the concrete blocks. In this study, the flow conditions were considered to be free water flow and the viscosity effect was neglected. In all cases, the weir height effect was directly proportional to the discharge coefficient while the surface roughness effect was found to be inversely proportional to the coefficient Cd of the case study.

Discharge Coefficients for Rectangular Broad-Crested Gabion Weirs: Experimental Study

Weirs are commonly used for making discharge measurements in irrigation canals. There are several types of weirs that are categorized based on their geometric shape or hydraulic properties. A gabion weir is a porous weir that can pass flow through its body in addition to the flow that passes over the weir. This study focuses on determining the discharge coefficients (Cd) for rectangular broad-crested gabion weirs using fabricated physical models. Dimensional analysis was carried out for finding the most effective parameters that govern the flow. Results show that the Cd of gabion weirs is 10.5% greater than that of similar solid weirs. In addition, the Cd for porous weirs in free flow conditions is 17.2% greater than that for submerged flow. For H/L>0.45 (where H is the water depth over the weir crest and L is the weir length) a porous weir acts similar to a solid weir and the effect of porosity (n) nearly vanishes. For a specified value of H/L, the ratio of submergence (Sr) for a solid weir is higher than that for porous weirs. Porous weirs with 50% porosity have lower values of Sr compared with solid weirs and weirs with lower porosities, of 45%, 41%, and 30%. Regression equations for the flow through gabion weirs were generated for free and submerged flow conditions. The derivations of equations were carried out using multivariable nonlinear regression and genetic programming (GP). Finally, a comparison of Cd in the present study with the other studies was carried out.

Critical Water Depth Features over Broad-Crested Weirs.(Dept.C)

The characteristics of flow over suppressed broad-crested weirs have been extensively studied by old and recent investigations, while for contraeled ones, the studies are limited. In the present study, the charaeteristies of the critical water depth over the contracted weirs were investigated. The effects of the different weir geometrical ratios and different flow parameters on the critical water depth locations were discussed. Experiments were conducted on a laboratory flume and the measured data were analyzed. An empirical equation, in terms of the weir and the flow parameters was developed to predict the critical water depth over the broad-crested weirs. Another empirical equation was also developed 10 predict the location of the critical water depth over such weirs. A good agreement was found between the developed equations and the experimental observations of die present study and that of others. Hence, the passing flow discharge becomes easy to be determined using one of the developed empirical equations and applying the discharge equation in terms of the esitical water depth in a rectangular open channel.

Artificial Neural Network Model For Predicting Discharges Over Weirs of Finite Crest Widths .(Dept.C)

Multilayers feedforward Artificial Neural Network (ANN) with back propagation learning algorithm is used to develop a computational model to predict discharge over weirs of finite crest widths. A network of size of 4-6-I is found suitable for this purpose with 3300 iterations and hyperbolic tangent (tansh) activation function The results of the trained, verified and tested ANN model are compared to the experimental measurements. Also, results from previously developed models based on statistical methods are compared to results of ANN model. The effect of using filter applied on the lead over weir on the performance of the ANN model is investigated The sensitivity analysis that conducted using the ANN model indicated that the most contributing variables to flow rate are the head over the weir and the weir width followed by the length of the weir and its height. Results indicated that the prediction of discharge over broad-crested weirs using ANN is more accurate than predictions offered by other previously developed models

Discharge coefficient of flow over Al-Shalalat stepped weir on Al-Khusr River

Many hydraulic structures are constructed in an open channel according to the purposes and the nature of the region. Weir is one of these structures which is used for discharge measurements as well as rising water depth in irrigation channels. According to the crest, there are two different shapes: sharp and broad crested weir. A stepped weir is constructed to reduce scour that happened downstream. There are different studies dealt with discharge coefficient, energy dissipation, and other hydraulic characteristics for flow over the weir. In this study, the coefficient of discharge for the Al-Shalalat stepped weir on the Al-Khusr River has been evaluated. The discharge coefficient equation is predicted, and the result values are compared with previous studies. The percentage error for the predicted discharge equation presented in this study compared with previous studies does not exceed 10%.

CFD simulated model and experimental tests for critical depth and flowrate estimation over a broad-crested weir under the longitudinal slope effect

This work consists of an experimental approach using rectangular broad-crested weirs having varied edge geometries to investigate the longitudinal slope effect on the relationship between the critical depth and the depth at centre of the weir. Based on this relationship, a statistical regression analysis method was used to derive a new and precise formula to estimate the flowrate over square and rounded broad-crested weirs. In all cases, the depth at the centre of the weir was considered as a control section. In general, it was found that the longitudinal slope So has an insignificant effect on the relationship between the critical depth and the depth at the centre of the weir and the suggested new flowrate estimation formula. Also, computational fluid dynamic model using FLUENT ANSYS version 16 was also designed and operated to simulate the problem based on the VOF method and the standard k~e method. The CFD model provided a very good simulation of the problem for the new flowrate formula and the existing pressure head at the centre of the weir. Comparing the results of the new formula with that of the actual experimental tests and the results of the simulation model indicted a very good agreement.

CFD simulated model and experimental tests for critical depth and flowrate estimation over a broad-crested weir under the longitudinal slope effect

CFD simulated model and experimental tests for critical depth and flowrate estimation over a broad-crested weir under the longitudinal slope effect

Experimental Verification And Review Performance of The Modified Triangular Plan Form Weir

Weirs are discharge measurement structures have different geometrical shapes. The performances of the modified triangular plan form weirs were studied under free-flow condition. Three groups of weirs were tested experimentally. The first group has a flat top; the second has one slope and the third has two slopes. Each group has three vertex angles (60o, 90oand 120o) with constant height. The hydraulicperformances of weirs are based on the ability to pass the discharge for certain head flow and on the value of the coefficient of discharge. The values of discharge and the coefficient were compared with earlier studies being carried on conventional normal weir, broad crest, triangular plan-form and different labyrinth weirs. All the groups show better performance than conventional shaped and broad weir. The magnification of the actual discharge to the discharge of broad crested weir is more than one and the best one is the first in the third group, while the vertex angle is (60o) for the second and third group and (120o)for the first. The performance of the third group is better than rectangular labyrinth weirs, and it is compatible with the triangular labyrinth. The discharge coefficient decreases with the increase of relative value of the head to the height of weir except for the first group. Equations for predicting coefficient of discharge are proposed within the limitations of this test.

Free Flow and Discharge Characteristics of Trapezoidal-Shaped Weirs

A number of studies have considered the effects of weir design variations on the free- and submerged-flow characteristics of trapezoidal broad-crested weirs. It appears that the hydraulics of short-crested weir flows have received little attention; thus, the current knowledge is incomplete. By systematically analyzing a large set of experimental data, the present study aims to fill in this knowledge gap and to provide a complete description of the discharge characteristics of trapezoidal-shaped weirs, including the salient features of two-dimensional weir flows. The analysis of the axial free-surface profiles for short-crested weir flows attested that the location of the nearest station for the correct measurement of the overflow depth under free-flow conditions is at η0 from the heel of the weir, where η0 is the upstream free-surface elevation. Additionally, an empirical equation for the free-flow discharge coefficient is proposed as being valid for a trapezoidal-shaped weir with varying upstream- and downstream-face slopes. The results of this investigation reveal that the streamline curvature and the slopes of the upstream and downstream weir faces significantly affect the streamwise flow patterns and, hence, the free-flow discharge.

Discharge coefficient of broad-crested weirs as a function of the relative weir height for different weir lengths

Broad-crested weirs (BCW) are often used in hydraulic engineering and water management. The most complex factor that affects the discharge capacity of BCW is the discharge coefficient. In Ukrainian engineering practice, the flow rate of BCW is defined as a function of the relative height of the spillway wall, while in the most common European methods – as a function of the relative length of the weir. The experimental dependences of the discharge coefficient of rectangular sharp-edged BCW with vertical inlet and outlet walls with the ratio of the weir length and height d/Р = 2; 4 are obtained. A comparison of the obtained results with the values of the discharge coefficient of the same BCW using the methods of Kumin and Hager indicates that this coefficient depends on both the height of the wall and the length of the weir. The corresponding empirical power law dependences are obtained. At the same values of the relative height of the wall, the discharge coefficient for the weir with the ratio d/Р = 4 is significantly lower comparing the weir with d/Р = 2, that can be explained by the more significant effect of friction resistance for the weir with longer threshold.

Modeling of broad crested weirs by using dynamic similarity and CFD

Broad crested weirs and steps are used to regulate the flow in the channel, increase the water level at the upstream side, and measure the discharge. The construction of the broad crested weirs is more practical and also they are more stable compared with the other types of weirs. To serve in accordance with the purpose of their construction, broad crested weirs should be designed and built by considering certain criteria. Before the hydraulic structures are built, model experimental setups are constructed in the laboratory and problems to be encountered are tried to be determined. However, there may be differences between the structure to be built in real life (prototype) and model due to scale effect. These possible differences must be determined and necessary measures must be taken. In this study, the model and prototype of the broad crested weir are constructed in two different open channel systems by using Froude similarity. The geometric similarity between model and prototype is determined as Lr = 4. 44 experimental data were collected from model and prototype. The results obtained from the model and prototype are compared according to hydraulic similarity rules. In addition to the physical experimental setups, numerical models were created using the ANSYS Fluent for the model and prototype separately. By comparing the numerical model and physical experimental setups, optimum mesh size is tried to be determined. According to the results obtained from experimental setups, differences were observed in the position of critical flow depths and downstream water levels due to scale effects.

Experimental study for measuring discharge through compound broad crested weir

This paper deals with a new compound broad crested weir for measurement of discharge. Calibration of broad crested weir is mainly dependent upon the length of the weir crest (L), weir height and upstream water head over weir crest (h). Hence measurement of discharge varies as per change in the flow characteristics due to change in the geometry of weir for a given flume. Based on experimental analysis, past researchers have shown that discharge coefficient (Cd) changes proportionally with h/L ratio, maintaining an average range of Cd for various h/L values. In the present study a novel approach towards design of compound broad crested weir is proposed which can effectively measure wide range of discharges thereby maintaining a constant discharge coefficient irrespective of the head over weir. Experimentation has been carried out in a laboratory horizontal tilting flume 2.5 m long, 20 cm wide and 30 cm deep. The investigation is carried out for discharge ranging from 10 lps to 2 lps. In the earlier experimentation conducted Cd was varying in the range from 0.518 to 0.648, after which the broad crested weir model is modified for suiting best results thereby resulting in the reformed discharge coefficient values of 0.546–0.599 which is in close proximity to the design input value of 0.6.

CFD simulation model and experimental study to implement a new flowrate formula for a rounded broad crested weir considering the end depth as control section

Weirs can be considered as the major types of flow measurement structures which are implemented along open channels to represent a controlling section to estimate the quantity of flowrate. This study depended on considered the control section at the end edge of weir and relate the depth of water at this edge (Ye) as a function of the critical depth flow (Dc). Consequently, a laboratory study was conducted for ten experiments tests of open canal flow with ten different longitudinal slopes ranged from (0 to 0.0495) in order to estimate such a relationship. The statistical regression analysis results illustrated that the relationship for (Dc with Ye) for all experiments is about 1.45831 as an average. As consequence, a new formula for predicting flowrate over weir was derived. Different statistical indexes were used to investigate the precision of the suggested formula where it appeared a very good agreement with all experimental data. A commotional fluid dynamic simulated model CFD with volume of fluid (VOF) method and (k-ɛ) turbulent models was also applied to verify the formula using FLUENT ANSYS ver. 16. The results indicated that the CFD techniques are able to simulate the flow over the weir and satisfactory the results of the suggested formula with less than 10% percentage error for all experimental tests.

Closure to “Hydrodynamics of Rectangular Broad-Crested Porous Weirs” by Akbar Safarzadeh and Seyed Hossein Mohajeri

Closure to “Hydrodynamics of Rectangular Broad-Crested Porous Weirs” by Akbar Safarzadeh and Seyed Hossein Mohajeri

Discussion of “Hydrodynamics of Rectangular Broad-Crested Porous Weirs” by Akbar Safarzadeh and Seyed Hossein Mohajeri

Discussion of “Hydrodynamics of Rectangular Broad-Crested Porous Weirs” by Akbar Safarzadeh and Seyed Hossein Mohajeri

Experimental Study of Cohesive Embankment Dam Breach Formation due to Overtopping

The recurrent floods in recent decades have imposed a challenge of embankment dam breaching, which needs great attention through improved design methods that are based on risk approach, the evacuation plans for people at risk, etc. In this study, based on the small-scale model tests a series of experiments were conducted to determine the breaching process of cohesive embankment dam using a simplified physical based breach model due to overtopping; the breach process observed during tests in the laboratory and the results from analyzed parameters are described. Five dam models, three of which were constructed with homogenous clay soil while two were sandy-clay mixture tested. The heights of the embankments dam were 0.45 m, and the widths at the crest were 0.20 m. The data from these examinations indicated that headcut erosion played an important role in the process of breach development. Initiation of erosion, flow shear erosion, sidewall bottom erosion, and distinct soil mechanical slope mass failure from the headcut vertically and laterally were all observed during these tests. In this physical based experimental model, the initial scouring position calculated by applying a hydraulic method, the broad crested weir formula used for breaching flow discharge and flow velocity computed based on breach flow discharge. The stability of the side slope failures was estimated by comparing the resisting and deriving force. Further, using data from laboratory experiments, the calculated peak breach discharge, breach characteristics times, breach widths, and breach flow velocity generally agreed well with the measured data and also the knowledge acquired from observed breach process at several stages. Finally, the accuracy of model was checked by root-mean-square-error.

Discharge Coefficients for Sluice Gates Set in Weirs at Different Upstream Wall Inclinations

Laboratory experiments and numerical simulations are performed to measure discharge coefficients in the case of a gate located on the upstream wall of a weir for flood storage. The effect of the gate slope and the side contraction have been taken into account. The study was first performed experimentally, when three series of tests were carried out with (and without) a broad crested weir located under the gate, at different values of the inclination angle of the weir upstream wall, and at different values of the shape ratio and the relative opening. In order to provide useful suggestions for those involved in sluice gate construction and management, three equations were obtained based on multiple regression, relating the discharge coefficient to different parameters that characterize the phenomenon at hand, separating the case when the broad-crested weir was present. Then numerical simulations were executed by means of the Reynolds-averaged Navier–Stokes (RANS) equations with the k-ε turbulence closure model and in conjunction with the volume of fluid (VOF) method, to validate the numerical results against the experimental and to possibly investigate phenomena not caught by the experimental measurements. Simulated discharges were very close to the observed ones showing that the proposed three-dimensional numerical procedure is a favorable option to correctly reproduce the phenomenon.

Discharge formula for flows over open-check dams

The present study proposed a discharge prediction model for open-check dams. The open-check dam is composed of a trapezoidal spillway and a rectangular opening located at the bottom of the spillway. The flow conditions, determined using the ratio of water head and dam crest length, for flow over open-check dams were divided into broad-crested and sharp-crested weir flow conditions. For the broad-crested weir flow condition, the discharge equation for rectangular broad-crested weir was proposed to estimate the discharge. For the sharp-crested weir flow condition, a linear combination of discharge equations for rectangular and trapezoidal sharp-crested weirs was proposed to describe the discharge. A series of laboratory experiments were performed in order to calibrate the proposed discharge model. The results showed the discharge coefficient and cross-sectional area ratio (Ar) were highly correlated under two flow conditions. The averaged error between measured and predicted discharge was less than 2%. The previous models displayed averaged errors between 4% and 25% under the present experimental conditions, whereas that of the present model was considerably low. The present model demonstrated favorable accurate and convenient estimation of discharge for flows over open-check dams.