Weir Angle Research Articles

Bed configurations downstream combined V-Notch-sharped edged Weir with inverted V-Shaped gate

ABSTRACT Weirs and gates are hydraulic structures installed in canals, mainly for controlling the discharge. Because of their existence, unfavorable influences regarding the downstream bed configurations were recorded. This study experimentally explores the combined effect of simultaneous flow through a hydraulic device consisting of a V-notch sharped weir with an inverted V-shaped gate, aiming to minimize the downstream bed scour. Eighty-one runs were carried out using nine weir-gate models with three different vertex angles. The tests were executed considering three upstream and three downstream water depths. A V-notch weir with an angle of 120º was tested under similar hydraulic conditions and was used for comparison. The results revealed that the length of backflow was increased by the decrease in weir angle under a fixed 120° gate angle. The bed configurations were sensitive to gate angle. The combined device showed a significant decrease in bed disturbances regardless of the angles used compared to the traditional V-notch weir. Simple formulas were developed to predict the scour parameters.

Numerical study of the effect of a V‐shaped weir on turbulence characteristics and velocity in V‐weir fishways

AbstractFishways are used to allow fish to migrate around water infrastructure, whether movements are in the upstream or downstream direction. Hydrodynamic conditions within various fishways, including turbulence levels, are important for successful fish passage. A numerical hydrodynamic study was conducted for V‐weir fishways, which assist species migrating upstream. The variables investigated included, fishway slopes of 4%, 7%, and 10%, relative spacing between weirs of 1.3, 2.6, and 4 (D/L, ratio of distance between weirs to pool width), and weir angles of 22.5°, 40°, and 60°. Turbulence characteristics, including turbulent kinetic energy (TKE), Reynolds shear stress (RSS), turbulent intensity (TI), turbulent dissipation (TD), as well as maximum water velocity, were examined by CFD (computational fluid dynamics) simulation using a re‐normalized group or RNG turbulence model. The CFD was calibrated with flow measurements made in a physical model of the V‐weir fishway in laboratory control experiments. Based on inferences from fish passage literature, the results showed that, in the range of parameters studied, a weir angle of 22.5°, a slope of 10% and relative spacing between weirs of 1.3 and 2.6 were assessed as offering the best potential performance for several species and sizes of fish, while the latter has lower cost as it requires fewer weirs. The V‐weir fishway may be adaptable for smaller fish.

Numerical study of the weir angle on the flow pattern and scour around the submerged weirs

In this study, the flow pattern and scouring around the submerged sharp edge weir, with different slope angles, have been numerically simulated using the Flow-3D model. After validating the results of the numerical model in simulating the flow pattern and scour around the weir with a 90∘ angle, the effect of the weir angles relative to the upstream and downstream on the flow and scour field had been investigated. The results showed upstream and downstream of the weir, vortex flows were formed and by taking an angle of 90∘, the vortex flows were weakened. In addition, the downstream slope of the weir had little effect on the upstream water level and most changes occurred in the downstream flow depth with a 90∘ angle. The downstream scour depth was independent of the upstream slope angle and the upstream scour depth was independent of the downstream slope. When the upstream angle became closer to the horizon, scouring was reduced in this area. The depth of scour downstream was greater than the depth of scouring upstream. Angles of 50∘, 70∘, 110∘ and 130∘ had slight changes in the depth of the downstream scour, but compared to the angle of 90∘, the depth of the downstream scour for these angles decreased significantly.

Hydraulics of combined triangular sharp crested weir with inverted V-shaped gate

The current research investigates experimentally the flow passing through combined hydraulic structure consists of V-notch sharp crested weir and inverted V-shaped sharp gate installed in straight channel as a control structure. Nine structure models were used considering three different vertex angles simultaneously used for the weir and the gate (θ = 60°, 90° and 120°). Eighty-one experimental runs were executed to explore the influence of the combined structure geometry, the upstream head, and the tailwater depth on the conveyed flow, the discharge coefficient and the downstream flow pattern with special emphasize on the hydraulic jump characteristics. The outcomes were analyzed and graphically presented. The results proved that the simultaneous flow through the combined structure regardless the vertex angles conveyed more discharge with less downstream water disturbance on account the classical V-notch weir and the inverted V-shaped gate. The flow discharge increased up to 10 times, and the discharge coefficient increased by around 26% for combined structure of 120° vertex angle under similar hydraulic conditions. The conveyed discharge was influenced by the gate angle than the weir angle. The downstream flow characteristics were more sensitive to the weir angle than the gate angle under similar hydraulic conditions. The measured hydraulic jump lengths were compared to other formulas and showed good agreement. Also, the weir and gate vertex angles effectively influenced the hydraulic jump characteristics. The outcomes were used to develop empirical equations for predicting the discharge coefficient and dimensionless jump length associated to the combined structure. The results and analysis in this research are limited to tested data range.

MODEL OF FALLING POINT AT NAPPE TRAJECTORY FOR CREST GATE TYPE OF RUBBER WEIR

Crest Gate Rubber Weir is a modification of a rubber weir with an installed curved metal plate or crest gate in front of the rubber weir. This crest gate serves as protection for the rubber weir and increases the water level contained by the rubber weir. Although this kind of weir is widely used, the behavior of falling water after passing through or nappe has not been studied adequately. Previous studies of nappe trajectories apply to static weirs with a flat upstream face. The nappe trajectory of this Crest Gate Rubber Weir should be examined differently because it is affected by the curvature of the crest gate and the various angles formed by the weir. This study aims to find the effect of the weir angle with the nappe trajectory by conducting a hydraulic model test of the 18o, 35o, and 53o weir models. The research found that the nappe trajectory of this Crest Gate Rubber Weir is influenced by the design head (Hd) and the weir upstream slope or the ratio of height and length (P/L) of the weir. This finding is applicable for determining which part of the downstream apron is impacted most from nappe and may require special reinforcement.

Flow features in a pooled fishway with V-shaped weir formation

ABSTRACT A pooled fishway is an artificial structure to improve the river flow connectivity and facilitate fish migration. Its conventional layout is characterized by straight weirs and suffers from limited passage rate. To improve its flow behaviors, an alternative design, featuring a V-shaped weir arrangement, is devised. CFD simulations are performed to examine its effects on the flow conditions. The governing geometrical parameters include weir angling, height, and spacing. Depending on weir arm angle, the flow is directed towards either the channel’s central part or the sidewalls, leading to both across- and along-channel differences in flow velocity and turbulent kinetic energy. This offers conducive zones for multiple fish species with distinct swimming preferences. For a given location in a pool, the cross-sectional velocity exhibits a cosine-type variation; a relationship is established to predict the maximum longitudinal velocity. The pressure distribution exhibits a similar pattern, with high-pressure areas residing upstream of the weir. A power law describes the relationship between the energy dissipation rate and unit discharge with an exponent at approximately 2/3. With an increase in either weir spacing or height, the energy dissipation rate declines. A change in weir angle shows however a negligible influence on it.

Minimizing the hydraulic side effects of weirs construction by using labyrinth weirs

It is no doubt that weirs are one of the most important hydraulic structures that play a vital role in irrigation project. So, it is necessary to minimize the hydraulic side effects of weirs. Throughout this paper, experiments were conducted to investigate the suitable dimensions and shape of weir's crest to increase head loss, decrease upstream bank level upstream weir and get the most economic structure. Various crest angles of labyrinth weir were tested under different flow conditions. Also back water curve upstream weir was studied according to different weir crest angles. A case of linear weir crest was also included in the test program. The experimental results indicated that labyrinth weirs have lower operating heads and longer crest length compared with a linear weir having the same lateral space and the same discharge. Results showed that the crest weir angle of 60° is the best angle of weir crest. It reduces water level above crested level and the relative jump depth by 18% and 20%, respectively. In addition, it increase the average values of the dissipated energy and the discharge coefficient by 15% and 14%, respectively. It also gave maximum reduction in backwater curve profile by about 17%. Furthermore, the model was verified using CFD numerical model. The numerical results agreed with the experimental results.

Numerical Investigation of Geometric Parameters Effect of the Labyrinth Weir on the Discharge Coefficient

Weirs, as overflow structures, are extensively applied for the measurement of flow, its diversion, and control in the open canals. Labyrinth weir as a result of more effective length than conventional weirs allows passing more discharge in narrow canals. Determination of the design criteria for the practical application of these weirs needs more examination. Weir angle and its position relative to the flow direction are the most effective parameters on the discharge coefficient. In this article, Fluent software was applied as a virtual laboratory, and extensive experiments were carried out to survey the effect of geometry on the labyrinth weir discharge coefficient. The variables were the height of weir, the angle of the weir, and the discharge. The discharge coefficients acquired from these experiments were then compared with the corresponding values obtained from the usual rectangular sharp-crested weir experiments. Comparison of the results indicated that in all cases with different vertex angle, flow discharge coefficients are in a satisfactory range for relative effective head less than 0.3. The discharge coefficient is reduced for relative effective head more than 0.3 due to the collision of water napes. It revealed that the higher the weir, the more discharge capacity. As a result, the labyrinth weirs have a better performance in comparison with the common sharp-crested.

Rock-weir fishway II: design evaluation and considerations

ABSTRACTThe flow characteristics of a rock-weir type nature-like fishway are determined by the configuration of the stream channel and passage structures. For a fishway to be effective, the rock-weir hydraulics must be compatible with the swimming capabilities of the target fish species. This study optimized the design characteristics of rock-weir fishways by simulating the water depth and velocity for different channel characteristics and geometries, which govern the fish resting zones, volumetric dissipated power and ultimately upstream fish passage performance. This study provided recommendations on effective pool spacing, bed slope, weir height, weir angle and weir arrangements for designing rock-weir fishways. These design recommendations are based on fishway hydraulics and should provide suitable hydraulics for fish migration and sufficient slow velocity areas for fish resting in rock-weir fishways for specific structure geometries and channel characteristics.

Numerical analysis of subcritical flow over two-cycle trapezoidal labyrinth side weir

The side weirs are basic and effective hydraulic structures utilized commonly in irrigation, flood management, drainage and wastewater systems. The labyrinth side weirs have developed in recent years as more effective and efficient mechanism than conventional side weirs. The multi-cycle trapezoidal labyrinth side weirs could increase the side weir performance. The hydrodynamics of these weirs are considerably sophisticated due to the turbulent flow and vortices in the cycles. This paper presents the hydrodynamic behavior of the side weir with two cycles using Computational Fluid Dynamics (CFD) method. The grid convergence index (GCI) was used to demonstrate the mesh sensitivity in the results, and a fine mesh (9mm) selected relatively among the used meshes was applied to computational volume for more accuracy. As the turbulent model, Reynolds Stress Model (RSM) model, which requires more computation effort, was implemented to consider turbulence effects in more detail. Additionally, certain experimental results were used for verification of the numerical results, and the CFD results were considerably consistent with experimental observations. The detailed hydrodynamic results, which were too hard to determine experimentally, were presented to describe the flow properties of this weir. The results indicated that the discharge coefficient decreased with an increase in Froude number. The best performances were obtained with side weir angle, α=30° and weir height, p=20cm among tested values. The results encouraged the use of computational fluid dynamics methods for the further analyses.

Numerical analysis of flow over side weir

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 (30o, 45o, 60o, 75o, and 90o) 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 30o where the percent increase compared with that at 90o was 70%.

Discharge characteristics of skew weirs

Skew weirs are used for reducing afflux while passing a certain discharge. Herein, the discharge characteristics of a sharp-crested skew weir are explored. The concept of elementary discharge coefficient is utilized for predicting the discharge. Based on experimentation, an equation for the discharge coefficient of skew weirs is determined as a function of weir head to weir height and the weir angle relative to the channel axis. The discharge over skew weirs is well predicted.

Hydraulic behaviour of flow over an oblique weir

A comprehensive set of experiments was performed on weirs placed obliquely in a rectangular open channel. The main objectives were to investigate the effect of the weir angle relative to the approach flow direction on the behaviour and the hydraulic flow characteristics and to examine methods such as using upstream guide vanes and inclined aprons to increase the effective oblique weir length. Results indicate that by increasing the oblique angle, the effective length of the oblique weir increases significantly. Relationships are provided for the threshold submergence and the effective length of the oblique weir. Design recommendations are also presented for the use of guide vanes and upstream inclined aprons.

Development of Parabolic Weirs for Simplified Discharge Measurement

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 30°, 45°, 60°, and 90° 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 0·55±0·05. Weir angle specific discharge models (coefficient of determination R 2 ⩾ 0 · 986 ) 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 ⩾ 0 · 993 ), 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.

B231 複断面開水路に設置された斜め堰周辺の流れの可視化

Experimental results on flood flows around oblique weirs in a compound open channel are presented with the emphasis on the effects of weir angle to the main channel and weir shape on flow pattern. Flow visualization is carried out using dye injection and oil film methods together with the measurement of three mean velocity components and water depth. With the increase of the weir angle, flow in the main channel tends to move toward the flood plain in the upstream side of the weir, while flow over the weir is apt to attack the main channel side. Strong upward currents move around the weir on the flood plain with shallow water depth, resulting in an oblique hydraulic jump on the flood plain. A large recirculation zone is generated in the main channel at the downstream side of the weir.

Aeration Performance of Triangular‐Notch Weirs

AbstractHydraulic structures have an impact on the concentration of dissolved oxygen in a river system, even though the water is in contact with the structure for only a short period of time. The same oxygen transfer that would normally occur over several kilometres in a river can occur at a single hydraulic structure, because the flow over a structure is typically highly turbulent, resulting in increased interfacial renewal. Plunging overfall jets from weirs are a good example of this fact, and the aeration properties of such structures have been studied widely in the laboratory and field over a number of years. This technical note (a) describes triangular‐notch weirs having a different weir angle α and how they affect aeration performance, and (b) demonstrates that aeration efficiency decreases with increasing weir angle.

Aeration Performance of Triangular Notch Weirs at Recirculating System

Abstract An adequate supply of dissolved oxygen is essential for the survival of aquatic organisms. Hydraulic structures can increase dissolved oxygen levels by creating turbulent conditions, where small air bubbles are carried into the bulk of the flow. Plunging overfall jets from weirs at recirculating systems are a particular instance of this. This paper seeks triangular notch weirs having different weir angle (α) and how they affect the aeration performance. It is demonstrated that the aeration efficiency of a 90° triangular notch weir is generally better than that of the other weirs.

Production of steel foam by PM : H.H.Eifert et al. (Fraunhofer Resource Centre-Delaware, USA.)

A computer model of flowing foam has been. developed This provides a dynamic, visual simulation of the motion, deformation and coalescence of bubble between the pulp froth interface and either bursting on the surface or overflowing the weir.The model combines the flow model of Murphy et al. [1] based on Laplace's equation and the visualisation techniques of Weaire and Kermode [2]. Murphy et al. [3] verified the prediction of the flow trajectories of bubbles in a rectangular system. Their visualisation was based on elliptical bubbles. Here the method of Weaire and Kermode [2], developed to describe the deformation of bubbles in a diffusing system, has been used. In addition, the model has been extended to allow the simulation of flowing foams in systems of arbitrary dimensions.An experimental system has been developed which allows investigation of bubble motion and coalescence in a flowing foam when changing the weir angle from 30° to 60°. It was found that the model satisfactorily describes bubble trajectories and residence times. Further, the fraction of air leaving the foam as unburst bubbles is a maximum at a specific weir angle.A coalescence criterion has been defined that determines the extent of bubble deformation required to lead to coalescence and which appears to be largely independent of system configuration. Qualitative, visual comparison of experimental and predicted coalescence zones show close agreement.

The effect of weir angle on bubble motion in a flotation froth: Visual modelling and verification

A computer model of flowing foam has been. developed This provides a dynamic, visual simulation of the motion, deformation and coalescence of bubble between the pulp froth interface and either bursting on the surface or overflowing the weir. The model combines the flow model of Murphy et al. [1] based on Laplace's equation and the visualisation techniques of Weaire and Kermode [2]. Murphy et al. [3] verified the prediction of the flow trajectories of bubbles in a rectangular system. Their visualisation was based on elliptical bubbles. Here the method of Weaire and Kermode [2], developed to describe the deformation of bubbles in a diffusing system, has been used. In addition, the model has been extended to allow the simulation of flowing foams in systems of arbitrary dimensions. An experimental system has been developed which allows investigation of bubble motion and coalescence in a flowing foam when changing the weir angle from 30° to 60°. It was found that the model satisfactorily describes bubble trajectories and residence times. Further, the fraction of air leaving the foam as unburst bubbles is a maximum at a specific weir angle. A coalescence criterion has been defined that determines the extent of bubble deformation required to lead to coalescence and which appears to be largely independent of system configuration. Qualitative, visual comparison of experimental and predicted coalescence zones show close agreement.