Normal Weirs Research Articles

Numerical Simulation And Experimental Study of Hydraulic Performance of Circular Crested Normal Weirs

Weirs are simple control structures usually built across channels for water storage and measurementof flow rates. The main target of the present study is to numerically simulate and experimentally study thehydraulic performance of circular crested normal weirs. For numerical simulation, the commercialpackage ANSYS CFX is utilized adopting tetrahedrons mesh with a maximum total number of 1932301elements, while, for the experimental study nine physical models are manufactured and tested havingdifferent crest diameters and various weir heights. Numerical simulation results demonstrated that theANSYS CFX software is highly capable for simulating circular crested normal weirs showing quite goodagreements in water surface profiles and 4.3% mean percentage error in upstream head above crest,while, the software showed 6.8% mean percentage error in estimating discharge coefficient. A simpleempirical expression is obtained for the estimation of coefficient of discharge in terms of ratio of upstreamhead to weir height and the ratio of upstream head to crest diameter with a coefficient of correlation =0.88. The flow rate magnification is found increasing with the increase of upstream relative head and thebest performance of the weir is found when the ratio of crest diameter to weir height = 0.33 at which thehighest increase in flow rate is observed ranging between 25.41% and 32.14% compared with sharpcrested weirs having the same height and the same length of crest

Development of ANN model for discharge prediction and optimal design of sharp-crested triangular plan form weir for maximum discharge using linked ANN–optimization model

Abstract Triangular plan form weirs are advantageous over a normal weir in two ways. Within the limited channel width, use of such a weir increases the crest length and hence for a given head, increases the discharge and for a given discharge, reduces the head in comparison with a normal weir. In a previous study, researchers proposed an empirical equation to compute the discharge coefficient of a triangular plan form weir. The prediction error on the discharge coefficient was ±7% from the line of agreement. In the present study, an ANN model has been utilized to train randomly selected 70% data, with 15% tested and validation made for the remaining 15% data. The model predicts the discharge coefficient with a prediction error in the range of ±2.5% from the line of agreement, thereby decreasing the prediction error in Cd by 64%. Also, the sensitivity analysis of the developed ANN model has been performed for all the parameters (weir height, skew weir length and flow depth) involved in the study and the weir height was found to be the most sensitive parameter. Furthermore, the linked ANN–optimization model has been developed to find the optimal values of design parameters of a triangular plan form weir for maximum discharge.

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.

Hydraulic performance of circular crested oblique weirs

Abstract The present study attempted to improve the discharge capacity of oblique weirs by rounding their crests. Twenty-four oblique weir models have been tested in which oblique angle (α), weir height (P) and crest diameter (D) were changed. Analysis of the results shows that the discharge (QOC) increases with the increase of effective head above crest (He). Values of discharge coefficient (CD) are found decreasing slightly with the increase of (He/P) and (He/D) values and weirs of small oblique angles give lower values of CD. An empirical expression is presented to determine CD in terms of He/P, He/D and α (in radian) with a correlation coefficient of 0.90 and a standard error of 0.01. The highest discharge capacity is obtained from a weir having α = 20°, P = 20 cm, D = 4 cm and D/P ratio = 0.2 in which the percentage increase in discharge is ranging between 147% and 175% compared to sharp crested normal weir. Comparison of the present study results with those of other investigations shows that circular crested oblique weirs offer higher discharge capacity compared with some other weir shapes. A simple design method is recommended through which the lasting dimensions and the head-discharge relationship of the weir can be predicted.

Flow simulation over a triangular labyrinth side weir in a rectangular channel

Labyrinth side weirs are used as regulator outlets in river diversion structures , water conveyance systems and sewer networks . Herein , the flow around triangular labyrinth side weir with three different included angles (θ = 45 , 60 and 90°) were numerically studied . The 3D RANS equations were solved and VOF method was implemented for free-surface tracking . Different boundary conditions and geometric dimensions were examined and their results were compared with experimental data. Different two-equation turbulence models were implemented. The water depth profiles and overflow discharge were compared with experimental results. The root mean square error of simulated water depth profile using standard k-e model was less than 1 mm. The diverted water discharge was computed with relative error less than 0.7%. The discharge of the labyrinth side weir was 1.7, 1.33 and 1.25 times the discharge of an equivalent normal side weir for θ = 45 , 60 and 90°, respectively.

Flow Characteristics of Triangular Plan Form Weir

Weirs are used for discharge measurement and flow diversion in the open channels. However, modified weirs such as plan form weirs, Labyrinth weir, oblique weir and piano key weir, etc. having larger crest length compared to normal weir having same lateral space assist in enhancing discharging capacity for a given upstream head, without creating much afflux. An experimental study was carried out to understand the effect of the geometry of a triangular plan form weir on discharge coefficient under free and submerged flow conditions. In this paper attempts are made to investigate working of triangular plan form weir of vertex angle 45° with three heights 10, 20 and 30 cm under free and submerged flow conditions. The discharge coefficients were calculated under free & submerged flow conditions and the results were compared with normal weirs as well. Further, triangular plan form weir is quite simple device/geometry and easy to install & quite useful for discharge measurement in open channels.

Modeling discharge coefficient of normal and inverted orientation labyrinth weirs using machine learning techniques

A labyrinth weir is a polygonal overflow weir that is characterized by its hydraulic performance and distinct geometric shape (triangular, trapezoidal or rectangular cycles). The present study provides new knowledge and design information on the performance and operation of adaptive neuro-fuzzy inference system (ANFIS) and gene expression programming (GEP) techniques for predicting discharge coefficient of labyrinth weirs in a flume. Discharge coefficient, Cd, was considered as a function of headwater ratio, upstream Froude number, magnification ratio, sidewall angle, apex ratio, and cycle width ratio (dimensionless parameters). The records obtained through 300 laboratory data sets were used to determine the Cd of labyrinth weirs. The results showed that the best GEP model determined the Cd values of the normal and inverted orientation labyrinth weir with a RMSE of 0.0139, 0.590, DC of 0.977, 0.852 and R of 0.996, 0.923, respectively by using the four dimensionless parameters of Fr, HT/P, Lc/W and A/w as input variables. The best ANFIS model determined the Cd value of the normal orientation labyrinth weir by using all six dimensionless parameters (RMSE = 0.0110, DC = 0.964, R = 0.987) and inverted orientation labyrinth weir by using three dimensionless parameters of HT/P, α, and w/p as input variables (RMSE = 0.0290, DC = 0.952, R = 0.987). The results of sensitivity analysis showed that Fr in the GEP model and Fr and HT/P in the ANFIS model are the most effective variables for determining Cd for normal and inverted orientation labyrinth weirs, respectively. It was found that when low headwater ratios were eliminated from analysis, performance accuracy of the models was improved.

A combined adaptive neuro-fuzzy inference system–firefly algorithm model for predicting the roller length of a hydraulic jump on a rough channel bed

Hydraulic jumps can occur downstream of hydraulic structures, such as normal weirs, gates and ogee spillways. The roller length is one of the most important parameters of hydraulic jumps in open channels. In this study, the roller length of a hydraulic jump on a rough bed is predicted using a hybrid of adaptive neuro-fuzzy inference systems and the firefly algorithm (ANFIS–FA). First, the effect of parameters including the Froude number (Fr), sequent depth (h 2/h 1) and relative roughness (ks/h 1) upstream of a hydraulic jump is studied. Following the modeling result analysis, ANFIS–FA is introduced as the superior model for estimating the roller length of a hydraulic jump on a rough bed according to Fr, h 2/h 1 and ks/h 1. The calculated MAPE, RMSE and correlation coefficient values for the superior model are 7.606, 1.771 and 0.970, respectively. ANFIS–FA predicted approximately 40 % of the results with less than 5 % error, and only 36 % of data had more than 10 % error.

A Comparison on Discharge Coefficients of Side and Normal Weirs with Suspended Flow Load using FLOW3D

Normal 0 MicrosoftInternetExplorer4 Weirs and gates are structures which are used to measure water flow in open channels. Entering rivers’ sediments into channels is considered as one of the main problems in irrigation and water transmission networks. The relations presented based on laboratory results for gates, weirs and apertures’ discharge coefficients have been extracted and developed based on the conditions of sediment free water flow. Therefore, applying these relations in natural conditions requires investigating the effect of suspended load on hydraulic coefficients which are highly effective to technically and economically design and select these structures. The purpose of the present paper was to determine the amount of flow discharge and the type of effective parameters using different geometrical and hydraulic conditions such as overflow height. It was also attempted to present the relation of discharge coefficient at the presence of suspended load. To this end, three-dimensional FLOW 3D model was employed. This numerical model can simulate the flow containing suspended sediments and sediments’ deposition in various parts of channel. In numerical simulation, based on landing number of flow, C d has a determination coefficient (R 2 ) relatively better and higher than laboratory results. It can be attributed to the lack of suspended load thickness distribution in laboratory and difficult conditions of such action in laboratory modeling. In laboratory model, suspended load cannot be fully injected with appropriate ratio to the entire fluid. However, in numerical model, flow thickness amount can be easily added an injected to the model from input boundary on cubic meter unit of flow. This significant point is considered as one of the advantages of numerical model to simulate such problems. In the present study, total relation of flow discharge (C d ) was presented as a combination of values of flow landing (F r ), flow thickness amount (S) and relative low depth (y d /P) in side weirs. st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:Table Normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Calibri; mso-bidi-font-family:Calibri;}

Behavior of the Discharge Coefficient for the Overflow Characteristics of Oblique Circular Weirs

This paper presents an experimental study and analysis for effect of the geometrical characteristics, of the oblique cylindrical weir on discharge coefficient, wherefrom three sizes used for the weir and two angles for the deviation.From the results, it was found that the coefficient of discharge is affected by geometrical characteristics represented by radius of the weir and the angle of inclination with the wall of the channel. It was noticed that the increase in the radius of the weir lead to a low discharge coefficient of the cylindrical weir. And found that discharge coefficient of the oblique weir is higher than the discharge coefficient of the normal weir. And the value of discharge coefficient is directly proportional with the weir inclination.

A new approach to improve the discharging capacity of sharp-crested triangular plan form weirs

Conventional weirs are inherited with afflux and submergence of area upstream of the weir. Various weirs of modified plan form have been suggested in the past to enhance their discharging capacity and to restrict the afflux. Presented in this paper are results of the experimental study carried out to investigate the discharging capacity of a sharp-crested triangular plan form weir under free flow conditions in a rectangular channel. The efficiency of the triangular plan form weirs is better than the normal weir and also high for low vertex angle and decreases with the increase of ratio of head over the crest of the weir and crest height due to interference of the water jets downstream. The computed discharge using the proposed equation is within ±5% of the observed ones. Sensitivity of the weir, i.e., change of discharge due to unit change in head is also carried out which indicates that the weir is more sensitive at the low head and low vertex angle.

USE OF INCLINED COMPOUND TRIANGULAR NOTCH-WEIR TO IMPROVE DISCHARGE RANGE

ABSTRACT The notch-weir having simple geometric shapes is unable to measure small as well as occasional large flows. In such situation compound weirs find application. In the present paper authors have reported their study on the use inclined compound notch-weir consisting of two triangular sections with different vertex angles. The notch plane is placed inclined to the general flow surface in the channel. The general discharge equation has been evolved through the semi analytical cum experimental procedure. Results show a significant improvement in discharging rate compared to normal weir. The lower triangular portion of the notch-weir handles the smaller flow whereas the upper part helps to measures the occasional high flows. Further advantages of the inclined compound weir in reducing afflux near the structure are also discussed.

STUDY ON DISCHARGE CHARACTERISTICS OF SHARP CREST INCLINED TRAPEZOIDAL NOTCH

ABSTRACT The various sharp crested weirs have been in use as normal weirs, for flow measurement and control in the field as well as laboratory. The characteristics of these weirs have been extensively studied by researchers. Majority of these investigators have expressed discharge coefficient of weirs in terms of flow and fluid properties. However, the study on inclined weirs has attracted very little attention of the researchers. This paper is concerned with the experimental study and theoretical analysis conducted by the authors on inclined trapezoidal weir. The general discharge equation for the inclined trapezoidal weir in terms of the angle of inclination of the plane of the weir with respect to the plane normal to the flow axis (vertical plane) has been developed. Further, an advantage of inclination in reducing the free board requirement on upstream of the weir in the channel is also highlighted.

Subcritical Flow over Rectangular Side Weir

Side weirs are flow‐diversion devices widely used in irrigation, land drainage, urban sewage systems, and so forth. For computation of side‐weir discharge, the de Marchi equation is widely used. Using de Marchi's equation, various investigators have related the weir discharge coefficient with the main channel's upstream Froude number. Thus, the dominant variable ratio of head to weir height has not been considered in previous investigations. Presented herein is a concept of elementary discharge coefficient for the discharge of an elementary rectangular strip along the weir crest. Like that of a normal weir, this elementary discharge coefficient has been related to the head weir height ratio only. Using this relation, a methodology for determination of the weir discharge is described.

Relations between discharge coefficients in formulas of the capacity of straight rectangular spillways

1. Approximate formulas (5) and (6) determine the relations between the discharge coefficient m1, m, and m0 with the necessary accuracy only for values ν<1/2–2/3, i.e., for relatively small approach velocities of the flow. In the entire range 0≤ν≤1, rigorous relations between these coefficients are determined by formula (7) and by the formulas derived in this article. 2. With consideration of the formulas derived here for calculating the coefficient m0 on the basis of known m1 and m, it is expedient to calculate the capacity of all rectangular spillways by formula (4). 3. The coefficient m1 for a sharp-crested spillway in the entire range 0≤ν≤1 is determined by formula (28) and with some approximation by formula (31). 4. For normal weirs the dependence of the discharge coefficient on the ratio of ν is represented by graphs.