Weir Geometry Research Articles

SPH Analysis of Free Surface Flow over Pivot Weirs

Pivot weirs have been proved efficient to measure, control and stabilize open channel flows in an easy-to-use manner. This work presents a numerical investigation of free surface overflow from full-width rectangular pivot weirs based on the hydrostatic-corrected smoothed particle hydrodynamics (SPH). In verification stage, the draining process of a reservoir-vertical weir system is separately analyzed by activating and deactivating the hydrostatic correction. The SPH results are benchmarked against a simplified analytical solution derived herein. It is shown that the declining reservoir head is more accurately predicted by activating the correction term. The SPH simulations are then validated for five weir inclination angles, ranging from a very mild to vertical configurations. Comparison with relevant experimental data demonstrates satisfactory agreement in each case. It is observed that the location of vena contracta in the overtopping jet shifts further downstream at steeper inclination angles. Moreover, a simple relation among discharge coefficient and weir inclination angle is proposed based on the curve-fitting of SPH results. These two parameters appeared to be negatively correlated so that an increase in the inclination angle poses a decrease in the discharge coefficient and vice-versa. The present analysis can be useful for estimating flow discharge if a simple head measurement is available for a given geometry of the pivot weir.

Discharge characteristics and structure of flow in labyrinth weirs with a downstream pool

A new design of a labyrinth weir is introduced in this study by adding a square pool to the vertex of a one-cycle triangular labyrinth weir with a sidewall angle of 45°. The addition of the square pool increased weir length without causing an excessive nappe interaction, and as a result, reduced the head water over the weir with the same discharge. Laboratory experiments were carried out to investigate the hydraulic performance of the new design with a potential application in pool-weir fishways. Mean and turbulence characteristics of flow for different weir geometries and in both free and submerged flow regimes were measured to be used for prediction of fish behaviour in the upstream of the proposed weir models. Discharge coefficients based on channel width and weir length were calculated. It was found that the new design can significantly increase the capacity of triangular labyrinth weirs and provide financial advantages in construction over triangular labyrinth weirs without pools in low discharges. In submerged flow conditions, the proposed model performed better than sharp-crested linear weirs in low discharges. Contour plots of the three-dimensional velocity components showed a region of strong mean flow around the neck of the new weir model. Turbulent characteristics such as turbulent kinetic energy, power spectra, exuberance ratio, and joint probability distribution functions of velocity fluctuations were extracted from instantaneous three dimensional velocities for different weir depths and flow regimes. Two vertical planes were identified based on the highest turbulent mixing in free and submerged flow regimes. The depths contributing the most to turbulent mixing were identified; active depths decreased as the flow regime changed from free to submerge flow regime.

Equivalent Discharge Coefficient of Side Weirs in Circular Channel—A Lazy Machine Learning Approach

Side weirs have been widely used since ancient times in many hydraulic works. Their operation can be analyzed following different approaches. However, almost all possible analysis approaches require knowledge of the discharge coefficient, which depends on several geometric and hydraulic parameters. An effective methodology for predicting discharge coefficient can be based on machine learning algorithms. In this research, experimental data obtained from tests carried out on a side weir in a circular channel and supercritical flow have been used to build predictive models of the equivalent discharge coefficient, by which the lateral outflow can be estimated by referring only to the flow depth upstream of the side weir. Four models, different in the input variables, have been developed. Each model has been proposed in 5 variants, depending on the applied algorithm. The focus is mainly on two lazy machine learning algorithms: k Nearest Neighbor and K-Star. The 5-input variables Model 1 and the 4-input variables Model 2 noticeably outperform the 3-input variables Model 3 and Model 4, showing that a suitable characterization of the side weir geometry is essential for a good accuracy of the prediction model. In addition, under models 1 and 2, k Nearest Neighbor and K-Star, despite the simpler structure, provide comparable or better performance than more complex algorithms such as Random Forest and Support Vector Regression.

Mean velocity and turbulent characteristics of flow over half-cycle cosine sharp-crested weirs

The classical sharp-crested weirs are not suitable to implement in irrigation canals with high suspended sediment flow. Over the time, sediment deposition occurs in the upstream of sharp-crested weirs and causes a time variant water level raise in the upstream and consequently variable discharge coefficients. A series of laboratory experiments was carried out to test the hypothesis of strong turbulent formation and three-dimensional flow in the upstream of half-cosine sharp-crested weirs to prevent sediment deposition. To verify this hypothesis, a series of laboratory experiment was carried out for different weir heights and top widths in free and submerged flow conditions. Mean flow structure and turbulent characteristics of half-cosine and rectangular sharp-crested weirs were measured using a micro-Acoustic Doppler Velocimeter (ADV) probe. It was found that the streamwise velocities of half-cosine weirs were higher than the corresponding rectangular weirs, however, the velocity fluctuations in this direction were similar for both types of weirs. Velocity fluctuations in vertical and transverse directions were found to be significant in half-cosine weirs. The results showed higher turbulent kinetic energy below the crest level for half-cosine weirs which made them capable of sediment resuspension and sediment removal. In was found that the introduced weir model are suitable structures for passage of small floating debris and sediments. A head-discharge formulation was also developed based on the geometry of half-cosine weir in free flow and a constant discharge coefficient was obtained by solving the Fresnel integrals. For practical purposes, semi-empirical formulations were also developed to estimate flow discharge in both free and submerged flow conditions.

Computational fluid dynamics characterization of a novel mixed cell raceway design

Computational fluid dynamics (CFD) analysis was performed on a new type of mixed cell raceway (MCR) that incorporates longitudinal plug flow using inlet and outlet weirs for the primary fraction of the total flow. As opposed to conventional MCR’s wherein vortices are entirely characterized by the boundary conditions at inlet nozzles and outlet center drains in the center of each cell, the new MCR design can develop a wider variety of fluid behaviors due to the additional boundary conditions at the inlet and outlet walls where the weirs are placed. In this study, we investigated how the primary longitudinal flow would affect vortex formations in the cells by designing three different MCR models and simulating three major cases for each model. Through this process, performances of two numerical CFD models (transition k-kl-ω vs. k-ε) were compared, along with two vortex quantification methods (Q-criterion vs. a proposed method). We found that the k-kl-ω CFD model more accurately predicted vortex formation than the k-ε model. The three MCR models differed only by weir geometry or drain size, in order to see their individual influence on cell vortex formation. Each case had its own unique weir flow rate and center drain loading rate values that combined to a total flow rate resulting in 15-min hydraulic retention time (HRT) for the MCR. The ratio of (expressed as percentage) of center drain loading rate to total flow rate (R = 7.5%, 12.5%, and 20.1%.) was defined to establish a relationship between R and vortex strength or size. Simulations demonstrated that inlet weir aspect ratio impacted cell vortex formation and strength. Unlike weir geometry effects, the drain size had non-significant impacts on fluid behavior other than the velocity very near the drains. While R did have positive correlations with vortex strength, vortex size, and self-cleaning performance, an R of 20.1% was sufficient to create uninterrupted vortex formations. Too low of a center drain rate or R value can result in lack of any meaningful cell vortex formation which then obviates any self-cleaning action in an MCR. Our key finding through extensive computational analysis was that an R value of 20% was required in order to maintain effective vortex formation. Expressed more explicitly, this can be described as maintaining a center drain loading rate of 0.010094 m3/s per cell (160 gpm), which correspond to unit loading rates of 16.3 lpm/m2 per cell (0.40 gpm/ft2 per cell).

Free-flow discharge estimation method for Piano Key weir geometries

Currently, many existing spillways located throughout the globe require rehabilitation due to dam safety issues. Consequently, there is an increasing need for design tools that facilitate better, more economical spillway designs. Piano Key weirs (PK weirs), the focus of this study, represent one option to address spillway deficiencies. Two design approaches used by practitioners for estimating PK weir discharge were examined: (1) empirical prediction methods ranging from simple to sophisticated and (2) computational fluid dynamics. This evaluation included five published empirical design methods and CFD simulations featuring two different turbulence models (i.e., LES and RNG k-ε). The results indicate that, depending on geometry, differences exceeding 30% can exist between predictive method and experimental results. Also, CFD discharge results were relatively independent of turbulence closure schemes and showed very good agreement with experimental data (mean relative errors of 3–4%). Finally, recommendations are presented to designers that include a new empirical equation for Type-A PK weir geometries and rectangular labyrinth weirs.

Physical modelling of pool and weir fishways with rock weirs

AbstractThe flow characteristics of pool and weir fishways with rock weirs were studied through physical modelling. Detailed flow measurements were obtained using an acoustic Doppler velocimeter to understand how weir geometry, discharge, and bed slope affect flow patterns, velocity, turbulence kinetic energy, turbulence intensity, and Reynolds shear stresses in the fishway. The weir geometries used in this study are similar to those typically used for river restoration projects. The use of a V‐shaped rock weir was found to reduce the mean streamwise velocity in the pools by about 20% but more than double the maximum velocity magnitude. Two stage–discharge relationships were developed using the standard weir equation and a modified discharge coefficient to account for both flow over the weir and orifice flow through the base of the weir. The use of V‐shaped rock weirs has the potential to offer significant advantages in assisting multispecies fish migration. The results of this study can be applied to the hydrotechnical design of pool and weir fishways with rock weirs and for river restoration projects.

Study of flow and hydraulic jump along side weirs

Side weirs are widely used for flow control and diversion. Although many studies on sub- and supercritical flows along these weirs have been conducted, only a few research studies have considered the generation of a hydraulic jump along the side weir. Spatially varied flow including a hydraulic jump along the rectangular side weir is studied in this paper. Experimental data for different weir geometries and hydraulic conditions are analysed. Based on the experimental results, new equations for estimating the jump length, the ratio of the conjugate depths and the discharge coefficient are presented. Also, the head loss due to the presence of a hydraulic jump is studied. Furthermore, a numerical model is developed for coupling the water surface profile with a hydraulic jump along the side weir. In this model the lateral outflow momentum is considered, which has been mostly ignored in previous works. The model predicts the location of the hydraulic jump. A comparison of the numerical and experimental results indicates good agreement.

An Experimental and Numerical Comparison of Flow Hydraulic Parameters in Circular Crested Weir Using Flow3D

Circular crested weirs consist of a circular crested of upstream and downstream walls. These weirs are widely used in hydraulic engineering as water discharge structures and can be used to control water level in channels and tanks. In the present study, using Flow3D software, hydraulic properties were investigated to find weir geometry optimization through CFD method. Also, this study attempted to investigate flow on some sections of circular crested weirs in 3 groups and 11 models. Upstream and downstream slope changes as well as the height of the weir were also studied. To validate the model, laboratory models were used. In the research, flow depth parameters on crest, pressure distribution, velocity distribution, energy loss on circular crested weirs, as well as the height and changes of upstream and downstream slope were evaluated. Flow depth on the body of circular crest in this state is about 0.71 (H1). Upstream slope changes on flow depth on the weir’s crest revealed that increasing upstream slope causes to the increase of flow relative depth (H1/R) on the crest about 62%. Downstream changes in H1/R values less than 0.7 have no significant effect on discharge coefficient; however, increasing H1/R values seems to cause more change in slope.

Numerical simulation of sediment transport and bedmorphology around Gangjeong Weir on Nakdong River

In this study, we modified and applied an open source CFD software package, the TELEMAC, to simulate sediment transport and bed morphology around Gangjeong Weir on Nakdong River in Korea. The simulations have been carried out with the real river bathymetry and the weir geometry, and for different operation scenarios of the weir. The hydrodynamic parameters and bed evolutions obtained from the numerical results have been validated against field observation data. Particularly, the scour depth has been verified against the results obtained from a well-known empirical formula. Agreement between numerical computations, observed data and empirical formulas is judged to be satisfactory on all major comparisons. This study is not only to point out the locations where deposition and erosion taken place due to the weir gate operation, but also to analyze the mechanism of formation and evolution of scour holes after the weir gates.

Weir velocity formulation for sharp-crested rectangular weirs

Discharge in open channels can be measured by sharp-crested rectangular weirs. Generally, measured head over the weir crest is substituted into an empirical formula derived from energy considerations to calculate the discharge. Assumptions made on the derivation are taken into account by defining a discharge coefficient that fits into the experimental data. In this study, a physical quantity, the average velocity over the weir section defined as ‘weir velocity’ is directly formulated as function of weir geometry and head over the weir. Weir velocity plotted against the weir head has a universal behavior for constant weir width to channel width ratio independent of the weir size. This unique behavior is described in terms of weir parameters to calculate the discharge without involving a discharge coefficient. Combining weir velocity data for variable weir widths provides a basis for direct formulation of discharge. The weir velocity exhibits simpler functional dependency on weir parameters in contrast to the discharge coefficient.

Neuro-fuzzy GMDH based particle swarm optimization for prediction of scour depth at downstream of grade control structures

Abstracts In the present study, neuro-fuzzy based-group method of data handling (NF-GMDH) as an adaptive learning network was utilized to predict the maximum scour depth at the downstream of grade-control structures. The NF-GMDH network was developed using particle swarm optimization (PSO). Effective parameters on the scour depth include sediment size, geometry of weir, and flow characteristics in the upstream and downstream of structure. Training and testing of performances were carried out using non-dimensional variables. Datasets were divided into three series of dataset (DS). The testing results of performances were compared with the gene-expression programming (GEP), evolutionary polynomial regression (EPR) model, and conventional techniques. The NF-GMDH-PSO network produced lower error of the scour depth prediction than those obtained using the other models. Also, the effective input parameter on the maximum scour depth was determined through a sensitivity analysis.

Discharge coefficient of subsurface weirs

Experimental and numerical studies were performed to examine the relationship between the hydraulic properties and physical dimensions of a subsurface weir system and the discharge over it under steady-state conditions. Experimental modelling was based on a laboratory-scale physical sand-tank model, within which a subsurface dam and weir structure was constructed. To evaluate the effect of the dominant parameters on the discharge coefficient, numerical modelling was also carried out. A number of physical and numerical models of subsurface dams and weirs were constructed and the effect of each parameter on the discharge coefficient was studied. The results indicate that the hydraulic conductivity of the aquifer, the head above the weir and the effective width of the aquifer, in addition to the geometry of the subsurface weir, significantly affect discharge efficiency. It was also shown that the Reynolds and Weber numbers only have a small effect on the discharge coefficient. Based on the experimental results, a threshold value is suggested for the subsurface weir submergence. Finally, according to the results of both experimental and numerical models, an equation is derived to estimate the discharge coefficient of subsurface weirs.

Control of undular weir flow by changing of weir geometry

Undular flow above the broad-crested weirs is an open channel flow phenomenon which occurs under certain hydraulic conditions. The flow surface on the weir transforms to sinusoidal waves and the number of waves may vary from one to over 10. Hence weir cannot be utilized to measure the flow discharge due to the formation of surface undulations above its crest. Propagated waves can be disturbed remarkably to the channel downstream. In this study, effects of upstream face slope of rectangular broad-crested weirs on the undular weir flow were investigated. The results obtained indicated when the weir upstream slope reduced from standard angle 90° to 40°, the relative wave height decreased up to 78% and the relative wave length increased up to 55%. The experimental results showed that wave was not generated above the weir with 21° upstream face. Furthermore, effects of the radius of curvature of weir upstream corner on the undular wave characteristics were studied. This study established that curvature and slope has similar effects on the wave elimination.

Debris-Blocking Sensitivity of Piano Key Weirs under Reservoir-Type Approach Flow

The collection of floating woody debris at flow control structures, such as spillways and weirs, can potentially result in reduced discharge efficiency (higher upstream head for a given weir discharge). Compared to less hydraulically-efficient control structures, piano key weirs have higher discharge efficiency (lower upstream heads for a given discharge), which may increase the likelihood of woody debris collection. A systematic laboratory study was conducted to evaluate the interaction between various piano key weir geometries and woody debris types and sizes. The results of individual (noncumulative) debris tests indicated that floating debris blockage probability is highly influenced by trunk diameter and upstream head. The effects of debris accumulation on the upstream head varied with the value of the debrisfree reference upstream head condition. At lower upstream reference head values, the cumulative debris tests indicated a relative increase of the debris-associated upstream head of approximately 70%; higher upstream reference head values produced upstream head increases limited to approximately 20%.

Discharge coefficient of a rectangular labyrinth weir

A rectangular labyrinth weir has a very good flood release capacity as well as strong economical and structural advantages. In this study, combined analytical and experimental investigations were undertaken for a rectangular labyrinth weir. The analytical model is based on the synthesis of general weir equations and spatially varied flow dynamic equations. A comprehensive set of experiments led to characterisation of the flow behaviour for low and high heads over the weir and indicated the influences of weir geometry on the release capacity. The results show that this type of weir represents an effective weir alternative and could be five times more efficient than a corresponding traditional broad-crested weir. These types of weirs may thus find great use in water and dam engineering projects. An equation for the free-flow discharge coefficient of a rectangular labyrinth weir is presented.

Method for the preliminary design of Piano Key Weirs

The Piano Key Weir (PKW) is a particular geometry of weir associating to a labyrinth shape the use of overhangs to reduce the basis length. The PKW could thus be directly placed on a dam crest. Together with its important discharge capacity for low heads, this geometric feature makes the PKW an interesting solution for dam rehabilitation. However, its hydraulic design remains problematic, even at a preliminary stage.This paper presents a preliminary design method based on results of experimental tests. The method enables to design project models by extrapolation of characteristics of existing idealized scale models.A practical application is presented to illustrate the method.

Experiments on hydraulic relations for flow over a compound sharp-crested weir

Basic experiments were conducted in a near full-scale compound sharp-crested weir. The compound sharp-crested weir composed of a trapezoidal weir, sloping crests and a rectangular weir. Detailed velocity measurements were performed for the effects of the compound weir geometry on the flow velocity distributions and the kinetic energy correction factors. Furthermore, a theoretical discharge equation for the proposed compound weir was derived and experimentally validated. The results showed that the kinetic energy correction factors decreased with increasing the head of the weir. The weir behaves as uniform flows passing over the weir under the conditions of the . The proposed compound weir provided a good estimation of the discharge without discontinuities. Consequently, an equation for the discharge coefficient was introduced. The experimental data indicated that the discharge coefficient could be simplified in the form of the relative head . Key words: Compound sharp-crested weir, velocity distributions, water discharge.

Labyrinth Weirs: Nappe Interference and Local Submergence

AbstractThe interaction of nappes from adjacent weir walls near an upstream apex can cause local submergence, which reduces labyrinth weir discharge efficiency. Local submergence effects can cause the head-discharge relationships for labyrinth weirs of equivalent lengths but different cycle numbers to differ. Empirical labyrinth weir discharge coefficients implicitly account for apex effects and local submergence; however, the uncertainty associated with applying hydraulic design data developed from specific weir geometries to comparable but different labyrinth weir geometries is not well understood. This study investigates the concept of labyrinth weir nappe interference and identifies labyrinth weir flow characteristics that decrease discharge efficiency, including local submergence. Parametric methods for quantifying nappe interference region size as a function of weir geometry (e.g., sidewall angle and crest shape) and flow conditions (e.g., headwater and nappe aeration) are presented. A comparison be...

Piano Key Weir: Reservoir versus Channel Application

The piano key (PK) weir is a relatively new nonlinear weir geometry that can be used to increase spillway discharge capacity over linear weir geometries, particularly when the weir footprint area is restricted (e.g., spillways on the crest of a concrete dam). The majority of the published PK weir research (e.g., head-discharge curves) has been based on channelized applications (sectional PK weir models in laboratory flumes). The head-discharge characteristics of crest-of-dam PK weir applications are influenced by the approach flow conditions. Using a laboratory-scale physical model, the hydraulic efficiency of a PK weir design was tested with varying approach flow depths, upstream apron slopes, and abutment details. In general, discharge efficiency increased with increasing approach flow depth, steeper approach aprons, and improved abutment geometries that reduced the effects of flow separation.