Broad-crested Weir Research Articles

Experimental investigation of turbulent flow upstream of the broad-crested weir

Broad crested weirs (BCW) are widely used hydraulic structures in streams and irrigation canals to control the flow and to measure the discharge. In this study, turbulent flow structure at the upstream of the sharp edged broad crested weir is investigated by means of Acoustic Doppler Velocimetry (ADV) measurements at different stations. Vertical distributions of velocity and turbulence stresses revealed that, while fully developed velocity distributions are observed at stations far from the weir, turbulence effects significantly alter the flow structure as the flow approaches to the weir. High-resolution photographs are digitized to extract water surface profiles of the flow through the weir for different flow rates. Comparison of the experimental results with the theoretical results shows that the accuracy of the theoretical solutions decreases for low flow rates, in which boundary-layer effects are calculated based on the power law.

Air entrainment and free surface modeling of fully turbulent flow near the broad-crested weirs

Abstract The research was carried out at the Department of Hydraulic Engineering, Faculty of Civil Engineering, Slovak University of Technology in Bratislava with close cooperation with Institute o...

Performance of a shallow-water model for simulating flow over trapezoidal broad-crested weirs

Abstract Shallow-water models are standard for simulating flow in river systems during floods, including in the near-field of sudden changes in the topography, where vertical flow contraction occurs such as in case of channel overbanking, side spillways or levee overtopping. In the case of stagnant inundation and for frontal flow, the flow configurations are close to the flow over a broad-crested weir with the trapezoidal profile in the flow direction (i.e. inclined upstream and downstream slopes). In this study, results of shallow-water numerical modelling were compared with seven sets of previous experimental observations of flow over a frontal broad-crested weir, to assess the effect of vertical contraction and surface roughness on the accuracy of the computational results. Three different upstream slopes of the broad-crested weir (V:H = 1:Z 1 = 1:1, 1:2, 1:3) and three roughness scenarios were tested. The results indicate that, for smooth surface, numerical simulations overestimate by about 2 to 5% the weir discharge coefficient. In case of a rough surface, the difference between computations and observations reach up to 10%, for high relative roughness. When taking into account mentioned the differences, the shallow-water model may be applied for a range of engineering purposes.

Submergence coefficient of full-width sharp-edged broad-crested rectangular weirs

Abstract Full-width sharp-edged broad-crested rectangular weirs in the range 0.1 < h/L ≤ 0.3 situated in rectangular channels are frequently used in submerged flow conditions. To determine the discharge for the submerged flow, submergence coefficient and modular limit shall be known. This article deals with their determination upon a theoretic derivation and experimental research. The equation for modular limit has been determined from energy balance with simplifications. To validate it, extensive experimental research was carried out. However, the derived equation is too complicated for practical use which is why it was approximated by a simple equation applicable for the limited range. The equation for submergence coefficient was derived by modifying Villemonte’s application of the principle of superposition and its coefficients were determined using the data from experimental research of many authors. The new system of equations computes the discharge more accurately than other authors’ equations, with the error of approximately ±10% in full range of the measured data.

Unsteady draining of reservoirs over weirs and through constrictions

The gravitationally driven flow of fluid from a reservoir following the partial collapse of its confining dam, or the partial opening of its confining lock, is modelled using the nonlinear shallow water equations, coupled to outflow conditions, in which the drainage is modelled as flow over a constricted, broad-crested weir. The resulting unsteady motion reveals systematic draining, on which strong and relatively rapid oscillations are imposed. The oscillations propagate between the outflow and the impermeable back wall of the reservoir. This dynamics is investigated utilising three methods: hodograph techniques to yield quasi-analytical solutions, asymptotic analysis at relatively late times after initiation and numerical integration of the governing equations. The hodograph transformation is used to find exact solutions at early times, revealing that from initially quiescent conditions the fluid drains and yet repeatedly generates intervals during which there are regions of constant depth and velocity adjacent to the boundaries. A novel modified multiscale asymptotic analysis designed for late times is employed to determine the limiting rate of draining and wave structure. It is shown that the excess height drains as and, when the obstacle has finite height, the velocity field decays as , and exhibits a wave structure that tends towards a constant and relatively rapid phase speed. In the case of a pure constriction, for which all the fluid ultimately drains out of the reservoir, the motion adjusts to a self-similar state in which the velocity field decays as . Oscillations around this state have an exponentially increasing period. Numerical simulations with a novel implementation of boundary conditions are performed; they confirm the hodograph solution and provide data for the asymptotic results.

Determining the Maximum Discharge of Blackwater in the Treatment Using Wetland System

This study aimed to improve irrigation efficiency by simplify discharge distribution mechanism on, tertiary, sub tertiary, quarter and secondary level where all this time its operation was unreliable. Physical model that being tested was in the form of broad crested weir (channel 2), pipe in diameter 3” (channel 1) and pipe in diameter 4” (channel 3) they will going to distribute discharge to the left, frontal and to the right. Stream flow phenomenon that occurred was used to plan the determining design of new irrigation construction. Measure instrument of discharge in this experiment was calibrated before the experiment took place, in order to decrease the experiment relative error smaller than 5%. Physical model of distribution box has ratio 1 : 1 in prototype and it has used verification in order to get result carefulness that fulfils the prerequisite. There are three conditions in this testing, that is one channel operations, three channels operation and three channels operation with discharge plan on two channels (right and left) and one gate operation to frontal side. This study used six variations discharge testing to stream flow type respectively on distribution box in order to get discharge distribution pattern. One channel has gotten the same headwaters discharge and downstream discharge. Three channels has gotten discharge coefficient (Cd) 0.56 and friction coefficient (f) 0.046, whereas discharge distribution has gotten ratio 11.44%, 71.24% and 18.35% (no gate). Three channels that using gate has gotten discharge distribution in ratio 12.68%, 65.89%, and 21.05% (a = 4 cm, frontal) and 11.77%, 68.90% and 19.33% (a = 8 cm, frontal) on discharge plan has gotten equation on pipe one y = 0.1097 (h) 1.4901 and on pipe three y = 0.1017 (h) 1.566, with the result that discharge that happen is reasonable to pipe diameter, discharge variation and high variation of opening gate (a).

Assessment of CFD turbulence models for free surface flow simulation and 1-D modelling for water level calculations over a broad-crested weir floodway

Floodways, where a road embankment is permitted to be overtopped by flood water, are usually designed as broad-crested weirs. Determination of the water level above the floodway is crucial and related to road safety. Hydraulic performance of floodways can be assessed numerically using 1-D modelling or 3-D simulation using computational fluid dynamics (CFD) packages. Turbulence modelling is one of the key elements in CFD simulations. A wide variety of turbulence models are utilized in CFD packages; in order to identify the most relevant turbulence model for the case in question, 96 3-D CFD simulations were conducted using Flow-3D package, for 24 broad-crested weir configurations selected based on experimental data from a previous study. Four turbulence models (one-equation, k-ε, RNG k-ε, and k-ω) ere examined for each configuration. The volume of fluid (VOF) algorithm was adopted for free water surface determination. In addition, 24 1-D simulations using HEC-RAS-1-D were conducted for comparison with CFD results and experimental data. Validation of the simulated water free surface profiles versus the experimental measurements was carried out by the evaluation of the mean absolute error, the mean relative error percentage, and the root mean square error. It was concluded that the minimum error in simulating the full upstream to downstream free surface profile is achieved by using one-equation turbulence model with mixing length equal to 7% of the smallest domain dimension. Nevertheless, for the broad-crested weir upstream section, no significant difference in accuracy was found between all turbulence models and the one-dimensional analysis results, due to the low turbulence intensity at this part. For engineering design purposes, in which the water level is the main concern at the location of the flood way, the one-dimensional analysis has sufficient accuracy to determine the water level.

Experimental study on flow over sinusoidal and semicircular labyrinth weirs

ABSTRACT For a given width, a labyrinth weir has a developed crest length, thereby increasing the flow capacity for a given upstream headwater. This paper experimentally studies the flow over labyrinth weirs with semicircular and sinusoidal configurations in a rectangular channel under a wide range of flow discharges. The effects of headwater ratio (HT/P), length of weir (L/P), arc radius ratio (R/P) and the number of cycles (N) on the discharge coefficient of semicircular and sinusoidal labyrinth weirs are investigated. Experimental results indicated the decreasing trend of Cd for HT/P>0.35 which is probably related to the progressive development of local submergence. Despite the effects of local submergence, the labyrinth weirs have nearly the same discharge coefficient as broad-crested weirs, and the flow discharge exceeded the linear weirs efficiency by ∼30. Additionally, reliable equations for estimating the discharge coefficient of labyrinth weirs with semicircular and sinusoidal configurations are presented.

Investigating the effect of a parapet wall on the hydraulic performance of an arced piano key weir

ABSTRACT Piano key weirs (PKWs) are classified as broad-crested weirs offering a high hydraulic performance. In this experimental study, the hydraulic performance of PKWs (of curved plan-form) under different hydraulic and geometric conditions was studied. A total of 16 experimental models with four different arc radii (35, 49, 70 and 90 cm) and central angles (90°, 65°, 50°, 45°) with a parapet wall of 4.5 cm height were considered. The results showed that by increasing the angle of the curved plan-form, the hydraulic performance of the weir was further affected by the parapet wall. Moreover, the parapet wall increased the hydraulic performance by 10% at most. In addition, the arced PKW with a parapet wall increased the performance by 2.98 and 3.82 times compared to the arced sharp-crested weir and the linear sharp-crested weir, respectively.

Estimates of Discharge Coefficient in Levee Breach Under Two Different Approach Flow Types

The amount of released water (discharge) in a levee breach is a primary input variable to establish an emergency action plan for the area next to the levee. However, although several studies have been conducted, there is still no widely applicable discharge coefficient formula; this needs to be known to estimate discharge amount through an opening caused by a levee breach. Sometimes, the discharge coefficient developed for a sharp crested side weir is used to rate the discharge, but, in case of a levee breach, the resulting geometry and flow types are similar to that over a broad crested weir. Thus, in this study, two different openings—rectangular and trapezoidal shape—are constructed in the center of a levee at a height of 0.6m to replicate levee breach scenarios, and the effect of two different approach flow types—the river type approach and reservoir type approach—are explored to suggest a discharge coefficient formula applicable for discharge rating for a levee breach. The results show that the ratio of head above the bottom of an opening and the opening width is a key variable for calculating the discharge coefficient of a reservoir type, but the approach Froude number should also be considered for a river type approach. The measured data are used to improve rating equations and will be useful in the future to validate computational fluid dynamics simulations of wave propagation during levee failure into the inundation area.

Experimental and CFD Modeling of Hydraulic Jumps Forming at Submerged Weir

Broad-crested weirs are defined as structures where the streamlines are parallel to each other and the pressure is hydrostatic over the horizontal crest. The water surface profile for submerged flow over weir was estimated through flume experimentation and compared with numerical model results. The numerical model was developed using ANSYS FLUENT version 15 in three dimensions (3D) with a standard k–e turbulent model. The Volume of Fluid (VOF) method was used to estimate the water level in each cell and includes tail water influence acting on a broad-crested weir. The agreement between the FLUENT model and the experimental results for water depth was good. Such conditions are often difficult to predict, particularly at onset of the hydraulic jump. The numerically derived pressure and velocity distributions over the weir are simulated in 3D. Good agreement was achieved between numerical and experimental discharge with a relative error of 6.6%. The relative error between the numerical and experimental coefficient of discharge was 7.7%.

Numerical and Experimental Modeling of Flow Over a Broad-Crested Weir

Broad-crested weirs are hydraulic structures installed in open-channels used to control the flow of water and measure the discharge. In this study, the flow over a broad-crested weir in open-channel was experimentally and numerically modeled. Experiments were carried out in a channel with a length of 1.5 m and a width of 0.055 m under five different flow rates. In each experiment, water depth and flow velocity in flow direction were measured using a pitot tube. Numerical model was developed using SimFlow software. The velocities and pressure fields were computed numerically. The water depths and velocities in flow direction obtained from the numerical model were compared to experimental values. There is generally a good agreement between experimental and numerical results. Relatively small errors in velocity profiles are observed in higher discharges.

3-D Numerical simulation of water flow over a broad-crested weir with openings

ABSTRACT The creation of an opening in a broad-crested weir body increases the discharge coefficient and reduces the water elevation behind the weir. In this study, three-dimensional numerical modeling is applied to investigate the water behavior, free-surface profiles, and velocity distributions over a broad-crested weir with one opening, two vertically arranged openings, and two horizontally arranged openings. The present study is limited to the above-described weir-opening arrangements. To determinate the most accurate turbulence model, results from the numerical simulation were compared with experimental data. Based on this comparison, the RNG turbulence model was chosen. The behavior of two horizontally arranged openings and the no-opening model were similar and critical flow occurred in two other models (one opening and two vertically arranged openings), downstream of the weir. Also, the maximum velocity in the models without openings was higher than in the other cases.

Numerical Modeling of Flow Over a Rectangular Broad-Crested Weir with a Sloped Upstream Face

The objective of this study was to evaluate the effect of the upstream angle on flow over a trapezoidal broad-crested weir based on numerical simulations using the open-source toolbox OpenFOAM. Eight trapezoidal broad-crested weir configurations with different upstream face angles (θ = 10°, 15°, 22.5°, 30°, 45°, 60°, 75°, 90°) were investigated under free-flow conditions. The volume-of-fluid (VOF) method and two turbulence models (the standard k-ε model and the SST k-w model) were employed in the numerical simulations. The numerical results were compared with the experimental results obtained from published papers. The root mean square error (RMSE) and the mean absolute percent error (MAPE) were used to evaluate the accuracy of the numerical results. The statistical results show that RMSE and MAPE values of the standard k-ε model are 0.35–0.67% and 0.50–1.48%, respectively; the RMSE and MAPE values of the SST k-w model are 0.25–0.66% and 0.55–1.41%, respectively. Additionally, the effects of the upstream face angle on the flow features, including the discharge coefficient and the flow separation zone, were also discussed in the present study.

Comparison of Flow over Broad Crested Weir in Laboratory and by a Numerical Method

The main purpose of this study is to test the ability of competition fluid dynamic (CFD) model which (FLUENT) program to simulate the flow over broad crested weir with lower cost and lesser time. This purpose is done by operating an experimental model in the laboratory and then validating this model in the GAMBIT program and FLUENT (ANSYS R 15.0), by comparing the results. The FLUENT can solve Navier- Stokes equations of the flow numerically, the volume of fluid method (VOF) and Standard k– ε turbulence equation is depended to simulate water level. Generally, it can be established that the experimental results of flow have a good agreement with the numerical results. The percentage of error (RE %) between numerical and experimental discharge is 2.94%, while the maximum RE % for water level is 6.25%. The numerical results of flow over broad crested weir showed in counter and vector results, and the streamlines of flow was clear than that of the experimental model. Finally, the FLUENT proved that can it be relied upon in future by designing weirs without needing to work experimentally.

The Coefficient of Broad-Crested Weir in Natural Channels

Weirs have been designed and used extensively in hydraulic structures to control the flow depth and discharge. To estimate the discharge over the weir, a weir coefficient is required. The discharge coefficient can be obtained experimentally as a function of the dimensionless total head of the approaching flow or as a function of various parameters. However, a universally acceptable discharge coefficient does not exist. Beside the man-made weirs that have been constructed by hydraulic engineers, some natural channel characteristics and slopes can be simulated as broad-crested weirs that are clearly noticeable in examining water surface profiles. The study area is Centralia watershed in Central Florida, which contains several cascades of step like waterfalls that can be selected for transecting. Cross-section data from 5 transects and detailed hydraulic data was obtained using the Digital terrain model (DTM) and the Triangular Irregular Network (TIN). The Hydrologic Engineering Center-River Analysis System (HEC-RAS) stepbackwater technique was used to calculate water surface profiles for natural channels that are likely used for storm water drainage. The results show that these channels have chains of steps that dissipate the momentum of falling water in steep areas and maintain a steady rate of flow. The weir coefficients were determined by comparing the steady state discharges to the equivalent weir discharges. The results indicate that the weir coefficient can be expressed as a function of weir height and channel cross-section area. The relationship between this function and the weir coefficient showed a high correlation with R2 = 0.991. The results of this study can be used to estimate the discharge in similar reaches in any water surface profile.

Hydrodynamics of Rectangular Broad-Crested Porous Weirs

AbstractIn this study, the hydrodynamics of rectangular broad-crested porous weirs were numerically simulated using a nonlinear model between the pressure gradient and flow velocity through the por...

Numerical simulation of the hydraulic performance of triangular and trapezoidal gabion weirs in free flow condition

During the recent years, gabion weirs have attracted the attention of many researchers due to their compatibility with the environment, positive effects on river's water quality and simple design and implementation. In this research, the hydraulic parameters of flow around the triangular and broad-crested gabion weirs with various side slopes were numerically investigated. The numerical results were validated using the data obtained from laboratory experiments. Overall, a number of 256 different models were studied numerically. Results indicated that decreasing the average diameter of particles may result in the reduction of the discharge coefficient (Cd), through flow discharge and the energy dissipation of flow over the models up to 27%, 34%, and 8% respectively. Also, it was concluded that the upstream slope of triangular weirs and downstream slope of broad-crested gabion weirs have more significant impact on the performance of gabion weirs. Finally, mathematical relationships are correlated using Nonlinear Multivariate regression analysis in order to estimate the discharge coefficient and through flow discharge of these structures.

A simplified physically-based model for core dam overtopping breach

Abstract Based on the breach mechanism of the core dam due to overtopping failure, a simplified physically-based model has been proposed in this study. A hydraulic method was used to predict the initial scour position for high dam. A time averaged erosion equation was adopted to simulate the backward erosion of dam's shoulder. The broad-crested weir equation was adopted to calculate the breach flow discharge. Furthermore, the sliding or overturning failure was adopted as the key mechanism for the core, which was judged based upon numerical analysis. The results showed that the model allowed for one-side and two-side erosions, as well as for the dam base erosion. An iterative method is developed to simulate the coupling process of soil and water at each time step. The failure of Banqiao dam was used as an illustrative example, as detailed data about its failure is available in literature. Nine core dam breach cases, caused by overtopping, were studied to verify the model. Meanwhile, three typical parametric breach models were chosen to compare the results with those obtained from the proposed model. The back analysis and comparison results demonstrated that the proposed physically-based model not only provided satisfactory results, but also performed better and produced more detailed results than the parametric model. Moreover, the calculated results indicated that the overturning failure was the dominating failure mode for the core failure.

The effect of weir crest width and discharge on passage performance of a potamodromous cyprinid

Contrary to the vast literature on dams, much less is known about the effects of small weirs on fish movements. This study aims to evaluate the upstream and downstream passage of the Iberian barbel (Luciobarbus bocagei), when facing a small broad-crested experimental weir with varying widths of the weir crest (W) and discharges (Q). Nine configurations (W×Q) were tested. Fish were released downstream of the weir and upstream and downstream passages were monitored. Hydrodynamics were characterised with a flow probe and a three-dimensional acoustic Doppler velocimeter (ADV). Fish negotiated all configurations, registering a total of 273 upstream passages and 192 downstream passages. The number of fish that approached, attempted and successfully ascended and descended the weir varied among configurations, emphasising the complex influence of factors on passage performance. Discharge was preponderant on both passages, proving that fish movements may be hampered by increasing discharges. However, the width of the weir crest only significantly influenced downstream passages, showing that strong velocity gradients experienced on narrower widths of the weir crest may discourage downstream movements. Results from the present study are expected to be useful to identify potential migration obstacles and may be applicable to other cyprinid species.