Sharp-crested Weir Research Articles

Flow Rate Capacity Improvement of Triangular Plan Form Sharp Crested Weirs

Flow Rate Capacity Improvement of Triangular Plan Form Sharp Crested Weirs

The stage-discharge relationship of a sharp-crested triangular weir pierced by square orifices

In this paper, the stage-discharge equation of a sharp-crested triangular weir pierced by square orifices is deduced applying both the classical approach of the discharge coefficient Cd and the Π- Theorem of dimensional analysis and the self-similarity theory. At first, using the experimental data by Zeinivand et al. (2024), the applicability of the expression of the discharge coefficient proposed by these authors was verified. Then, applying the dimensional analysis, a new stage-discharge relationship was deduced and calibrated using the available dataset. This theoretical equation is characterized by errors in the discharge estimate that are less than or equal to ±20 % for 98.9 % of cases and ≤ ±10 % for 87.8 % of cases, and the root mean square error is equal to 0.00071 m3 s−1. In conclusion, the stage-discharge relationship deduced by dimensional analysis is characterized by an improvement in the performances in the discharge estimate and also has the advantage of working without the need of estimating the discharge coefficient.

Enhancing rectangular side weir discharge prediction using stacking technique

In this paper, the impact of different variables on discharge coefficients in sharp-crested rectangular side weirs was investigated utilizing 559 experimental data points. Various methodologies, including De Marchi, Traditional weir equation (TWE), Domínguez, adjusted Domínguez, and Schmidt procedures, were employed for the analysis. Novel equations were developed to predict the discharge coefficients with greater accurately, surpassing the predictive capabilities of previous studies' equations. Additionally, three supervised machine learning algorithms, namely extreme gradient boosting (XGBoost), Light gradient boosting machine (LightGBM), and support vector regression (SVR), were employed to enhance the precision of discharge coefficient estimation. Among these algorithms, the XGBoost model exhibited superior performance compared to LightGBM and SVR models for forecasting discharge coefficients. Furthermore, using a stacking technique, hybrid models were constructed by combining XGBoost, LightGBM, and SVR. The hybrid models showed enhanced performance and generalization capacities than the individual models. Notably, the HYBRID5 model, specifically designed for estimated the Schmidt coefficient, achieved outstanding statistical indices (R2 = 0.995, MSE = 1.378, MRPE = 3.73 %) for calculating discharge of rectangular side weirs.

Hydraulic Jump Characteristics Downstream of a Compound Weir consisting of Two Rectangles with a below Semicircular Gate

Weirs are often used in laboratories, industries, and irrigation channels to measure discharge. The discharge capacity of a structure is vital for its safety and plays an important role in the combined gate-weir flow, which is a complicated phenomenon in hydropower. This study carried out experiments on a combined hydraulic structure, which included a compound sharp-crested weir made up of two rectangles along with an inverted semicircular sharp gate. Installed on a straight channel, this structure served as a control instrument. The study aimed to investigate the downstream hydraulic jump characteristics of this combined structure, specifically, the sequent depth ratio (y2/y1), the hydraulic jump height ratio (Hj/y1), the energy loss ratio through the jump (EL/Eu), and the jump length ratio (Lj/y1). The width of the upper rectangle on the weir was set at 20 cm. The width of the lower rectangle (W2) was set at 5, 7, and 9 cm, while its depths (z) were fixed at 6, 9, and 11 cm. The gate's diameters varied between 8, 12, and 15 cm. These measurements were alternated with varying initial Froude numbers (Fn1) ranging between 1.32 and 1.5. The results showed that the dimensions of both the weir and the gate influenced the hydraulic jump characteristics. Empirical formulas were developed to predict y2/y1, Hj/y1, EL/Eu, and Lj/y1 based on the differing dimensions of the combined structure. The findings and analysis of this study are limited to the range of data that were tested.

The calibration of sharp-crested weirs with a horizontal edge used for measuring flows in partially full pipes

This paper presents the results of a laboratory study on the discharge capacity of sharp-crested weirs fitted with a horizontal edge in pipes during open-channel flow conditions and clean water used to measure the outflow. Such sharp-crested weirs are mounted in pipes and are used to control the inflow to separators. The stream profile does not correspond to the profile given by Bazin for sharp crested weirs in channels. A desired location of the water level measurement point for flow rate calculations was provided. Discharge curves were identified for three sharp-crested weirs of 0.0465, 0.0634 and 0.0771 m in height, installed in the pipe of 0.1534 m in diameter and inclinations of 0.5 and 1.0%. The discharge curves for weir flow with free nappe does not show a significant effect of the pipe slope on the weir discharge capacity. The non-dimensional formulas for the discharge capacity of the sharp-crested weir were found as general polynomial regressions. The results indicate that the calibrated sharp-crested weir with a horizontal edge placed in a pipe can be used to control the flow. Due to the scale effect, relationships obtained from the calibration cannot be generalised to other pipe diameters and weirs heights than those analysed.

The discharge coefficient of sharp triangular weir pierced by orifices

Although triangular sharp-crested weirs have less discharge-passing ability compared to rectangular weirs, they have greater accuracy and sensitivity for measuring discharge. In order to enhance the passing-discharge and the discharge coefficient from a sharp-crested-triangular weir, an orifice was created in the weir. In this research, for the first time, several square orifices were created in the weir of the sharp crested triangular weir with different numbers and dimensions. The results of the discharge-passage investigation revealed that by creating one orifice, the discharge passage rose by 41.3%; with the increase of each orifice, the discharge passage increases by 37.2 % on average. It was also observed that upon increasing the relative dimensions (the ratio of the side-square-orifice length to the flume width) by 0.033, the discharge passage grew by 36% in average. Also, the results of discharge-coefficient investigations-showed that with creation of one orifice, it increased by 5.1% in average. But based on the novelty of this research, by increasing one orifice from 2 to 4, the discharge coefficient increases by 1.92 percentage. By upstream velocity measurement in control weir (weir without orifice) and combined weirs (weirs with orifices), a noticeable change in the lateral and depth velocity-profiles was observed, and these changes led to increase in the passing-discharge and also an increase in the discharge coefficient. Finally, an equation was presented to determine the discharge coefficient with high accuracy.

Discharge Coefficient of a Two-Rectangle Compound Weir combined with a Semicircular Gate beneath it under Various Hydraulic and Geometric Conditions

Two-component composite hydraulic structures are commonly employed in irrigation systems. The first component, responsible for managing the overflow, is represented by a weir consisting of two rectangles. The second component, responsible for regulating the underflow, is represented by a semicircular gate. Both components are essential for measuring, directing, and controlling the flow. In this study, we experimentally investigated the flow through a combined two-rectangle sharp-crested weir with a semicircular gate placed across the channel as a control structure. The upper rectangle of the weir has a width of 20 cm, while the lower rectangle has varying widths (W2) of 5, 7, and 9 cm and depths (z) of 6, 9, and 11 cm. Additionally, three different values were considered for the gate diameter (d), namely 8, 12, and 15 cm. These dimensions were tested interchangeably, including a weir without a gate (d = 0), under different water head conditions. The results indicate that the discharge passing through the combined structure of the two rectangles and the gate is significantly affected by the weir and gate dimensions. After analyzing the data, empirical formulas were developed to predict the discharge coefficient (Cd) of the combined structure. It is important to note that the analysis and results presented in this study are limited to the range of data that were tested.

Flow behavior over well-escape weirs

ABSTRACT Weirs play an important role in controlling and managing water in irrigation canal networks through several functions, such as discharge measurements, water distribution, and lowering the water level. Weirs also play a crucial role in protecting canals from flooding, which might cause the earthen banks to collapse, by eliminating surplus water at the ends of the canals. Over the previous decades, the flow over the traditional sharp-crested weirs was extensively investigated by many researchers; however, the well-escape weirs have not received sufficient attention. These types of weirs were mostly constructed in the form of vertical wells that may be circular or rectangular in shape, and water may flow through the entire perimeter of the weir or part of the perimeter. In the present research, the effect of the well-escape-weir shape on the characteristics of flow over the weir was studied. A set of models were constructed in different shapes, circular and square, and the entire perimeter of the weir or part of the perimeter is working as the weir crest length. The discharge passing over the unit length of the weir crest (q) is investigated and compared for the circular and square weirs of various crest lengths and positions. The results indicated that the discharge capacity of the circular weirs increases by a rate ranging between 7.5% and 15% more than that of the square weirs at the same head. Also, results indicated that the discharge coefficient of the circular weirs increases by a rate ranging between 9.3% and 10.3% more than that of the square weirs. This behavior can be attributed to the interference between the orthogonal water nappes at the corners of the square models. In addition, the flow direction has little effect on the discharge coefficient at small discharges, and this effect becomes more obvious at higher discharges. Additionally, the well-escape weirs of the upstream crest have a slightly higher discharge capacity than those of the downstream crest due to the effect of the approach velocity, which increases the water entrance velocity at the upstream crest. The results of flow patterns around the weir showed that the locations of maximum flow velocities (u, v, w) are mostly near the weir crest and depend entirely on the crest length and position.

On the effect of flow regime and slope of the channel bed on the hydraulic performance of the sharp-crested rectangular side weir: a numerical simulation

The aim of this study is to numerically investigate the effect of bed slope on the hydraulic performance of side weirs in supercritical and subcritical flow regimes. Increasing the bed slope decreases the weir efficiency and discharge coefficient in the subcritical flow regime up to 14.54% and in the supercritical flow regime up to 9.26%. By examining the longitudinal velocity distribution, it was observed that in the subcritical flow regime, the maximum longitudinal velocity occurs at the beginning of the upstream of the side weir, and by moving towards the downstream of the weir, the flow velocity decreases and increases again after leaving the length of the weir. In the supercritical flow regime, it has an increasing trend when the flow enters from the upstream of the side weir. The increase in discharge coefficient with the increase of the weir height varied between 4.6% and 7.8%. With increase of the slope of the channel bed, the velocity along the length of the weir increases by 10.88% and 6.17%, respectively, in the subcritical and supercritical regimes, and the transverse velocity along the transverse direction for the subcritical and supercritical flow regimes decreased by 22.23% and 4.80%, respectively.

Discharge formula based on brink depth over sharp-crested weirs

Abstract Weirs are among the most essential hydraulic structures for measuring water discharge in open channels. The prediction of water discharge over weirs should be as precise and straightforward measured as feasible. The experimental investigation of flow prediction over varied heights of a conventional rectangular sharp-crested weir was conducted in the present work. The investigation evaluated five ratios of weir height to length, P/b, of 0.33, 0.4, 0.47, 0.53, and 0.6, different water discharges, Q, of up to 17.25 L/s, and different bed slopes, S, between 0.001 and 0.01. The experiment's findings reveal that a change in the bed slope has no significant effect on the brink depth, hb, for a constant water discharge. However, it influences the head over the weir, h, which is usually measured upstream of the weir location and used to predict water discharge. A simple, accurate formula was developed for predicting water discharge over rectangular sharp-crested weirs depending on the brink depth with mean absolute percent error (MAPE) and root-mean-square error (RMSE) of 1.714% and 0.229, respectively. In addition to having a simple form, the developed formula performs well, is unaffected by the bed slope, and applies to a wide range of h/P values, from 0.158 to 0.945.

Investigation of mesh independence in numerical modeling of sharp-crested weirs at different heights

Mesh independence is a term used in numerical analysis and simulation to refer to a situation where the numerical solution of a problem is insensitive to changes in the size or density of the computational mesh used to discretize the problem domain. In other words, a numerical solution is said to be mesh independent if it remains stable and accurate even when the mesh is refined. This is important because the accuracy and stability of numerical simulations depend on the quality of the mesh used to discretize the problem domain. The shape, size, and number of meshes used while performing numerical modeling in accordance with flow physics in the solution of hydraulic problems significantly affect the result. In this study, a total of 12 experiments were carried out for 4 different discharge values (Q=5 L/s, 10 L/s,15 L/s and 20 L/s) for sharp-crested weirs with three different weir heights (P=20 cm, 30 cm and 40 cm). Numerical models of each experimental setup with four different mesh sizes (m=1.25 mm, 2.50 mm, 5.00 mm and 10.00 mm) were created with the ANSYS-Fluent program. Numerical analyses were performed using the grid resolution method to obtain a mesh size-independent result where the mesh size would not affect the results after the specified error rate.

A comprehensive experimental investigation on discharge formulae of free flow over fully contracted rectangular sharp-crested weirs

In this study, laboratory experiments were conducted to investigate the discharge characteristics of free flow over rectangular sharp-crested weirs under the situation of large discharges and high water heads. By adding the weir plates with contraction ratios which were not considered in the literature, a new division for the rectangular sharp-crested weirs was proposed. The performances of the available discharge coefficient equations from the literature were evaluated and improved. It was found that the water head has significant effect on the accuracy of the proposed discharge coefficient equations. The discharge coefficient is suitable to be described by the Reynolds number at low heads and the contraction ratio at high heads, this is determined by the flow characteristics of the rectangular sharp-crested weir. The work presented in this paper would be useful to enrich and develop the research on the flow discharge of rectangular sharp-crested weirs.

Flow pattern formed over steps at a low-head dam: Salmon River Dam

ABSTRACT Building Stepping way over the low-head dams has been proposed to reduce the risk of drowning in submerged flow conditions. In the Salmon Barrier, adding two steps downstream of weir was previously suggested as an effective method for reducing the risk of drowning downstream of this dam. Given the effect of steps on the flow pattern downstream of the weir, the occurrence of dangerous submerged flows at different tailwaters was predicted, and the flow pattern expected at variable tailwaters was studied in comparison with the flow pattern passing over the sharp crested weir. According to the results, the submerged flow pattern downstream of the dam is a combination of the submerged flow pattern over the abrupt drop at low tailwaters and that over the sharp crested weir at high water levels. Consequently, similar correlations for predicting the flow regime downstream of these structures can be presented to predict the flow pattern at different tailwaters. The flow pattern over the step was compared with that over the abrupt drop, and a few diagrams were presented for predicting the occurrence of different flow patterns based on the submergence ratio of steps. Given the similarity of the flow pattern with those in the literature for sharp crested weirs, the flow pattern was also investigated at higher tailwaters. The comparison of correlations developed in this study indicated that the flow pattern approaches that reported in the literature for sharp crested weirs with increasing discharge.

Application of Simple Crested Weirs to Control Outflows from Tiles Drainage

Triangular sharp-crested weirs are commonly used to measure low-flow measurements in open channels. The flow over such a V-notch is proportional to the height of water above the weir on the upstream side. Therefore, it is relatively easy to calculate the flow from standard equations by using only recordings of water levels. Thus, these types of weirs can provide inexpensive measurements of flow volumes and resulting nutrient loads from subsurface drainage systems and associated conservation practices. The objective of this study was to develop appropriate weir equations for a 22.5° V-notch weir developed for a new tubular water level control structure in a controlled drainage system (CD). Analyses using this weir, with three typical slope angles of 30°, 45°, and 60°, were also conducted. There were no significant differences in the fitted parameters across the three analyzed slope angles. The coefficient of determination (R2) values were 0.9955, 0.9981, and 0.9980, respectively. However, the best-fitted equation for a 22.5° V-notch weir was for a slope angle of 45°. The flow equation was Q = 0.2235H2.4182, with Q in liters per minute and H in centimeters. This equation can be used for measuring flow through tubular-controlled drainage structures.

Evaluating performance of various methods in predicting triangular sharp-crested side weir discharge

This paper investigated the efficiency of the traditional weir equation (TWE), Domínguez, adjusted Domínguez, and Schmidt approaches, as an alternative to the De Marchi procedure, for computing discharge of a sharp-crested triangular side weir. Comprehensive experimental data were used for the analysis, including 342 data from the present study and 140 data from other sources. The effects of approach Froude number Fr1, the ratio of weir height to upstream flow depth p/y1, and weir apex angle θ on the discharge coefficients obtained from different methods were studied. Sensitivity analysis using the partial swarm optimization-support vector regression method indicated that Fr1, p/y1, and θ affect the discharge coefficients. It was found that Fr1 with sensitivity indices equal to 1.89, 3.74, and 4.04 has the most substantial effect on the De Marchi coefficient, TWE coefficient, and adjusted Domínguez coefficient; meanwhile, p/y1 has the most significant impact on Domínguez coefficient and Schmidt coefficient with sensitivity index equal to 1.57. In addition, it was found that θ had the lowest sensitivity indices in estimating discharge coefficients. New equations for forecasting sharp-crested triangular side weir discharge coefficient were presented based on dimensional analysis. The new De Marchi coefficient executed better for calculating triangular side weir discharge than earlier De Marchi coefficients. Moreover, TWE, Domínguez, adjusted Domínguez, and Schmidt methods performed better than the De Marchi procedure (with MSE = 4.581) in calculating sharp-crested triangular side weir discharge. However, considering the simplicity of the TWE approach compared to other methods, this approach with R2 = 0.975, NSE = 0.975, MSE = 3.610, MRE = 0.097, and CP10% = 71.36 was introduced as the superior procedure.

Investigating the process of changing the discharge coefficient of the flow passing through the combined structure of rectangular sharp-crested weir with multiple-gates

To investigate the effect of the number and dimensions of the gates-weir structure, 117 experimental tests were carried out at different flow rates, numbers and dimensions of square gates. The experiments were carried out in a laboratory flume with a length of 12 m. The results showed that with the increase in the number and dimensions of the gates in combined weir-gate structure, the combined discharge coefficient was increased. These changes are such that the combined discharge coefficient is increased by 3.8% with the increase of each gate. The results showed that the lowest and the highest increase in the flow coefficient was observed in the comparison between the single gate and the 5-gate condition compared to the no-gate condition by 16% and 18%, respectively. In the following, a relationship was presented to determine the combined discharge coefficient with RMSE = 0.001.

Utjecaj oblika krune na koeficijent prelijevanja linearnih preljeva

A detailed experimental laboratory analysis of the effect of crest shape on the discharge coefficient of sharp-crested weirs is presented in the paper. The experiments were conducted for four different crest shapes. The experiments and analyses show that discharge capacity, and discharge coefficient in particular, are significantly affected by weir crest height. It is stated in conclusion that rounded crest shape has the highest discharge capacity. In practice, sharp crested weirs are generally preferred to other crest shapes due to construction facility, although the discharge coefficient values of sharp crested weirs are lower compared to rounded crest shape.

Effect of the crest height on the stage-discharge formula of rectangular and triangular sharp-crested weirs under free-flow conditions

Weirs are simple devices widely applied for flow measurements in open channels. These hydraulic structures are characterized by a stage-discharge relationship which mainly depends on their shape and dimensions. In this paper, the outflow process of sharp-crested rectangular and triangular weirs is investigated for the free-flow condition, using dimensional analysis and the incomplete self-similarity theory, in order to test the effect of the crest height. Using a wide database available in the literature for rectangular and triangular weirs, the applicability of a theoretical stage-discharge relationship is tested and then modified to introduce the effect of the crest height. The results showed that the proposed relationships assure good accuracy in the discharge estimate and highlighted the usefulness of considering the effect of the weir height in the relationship.

Determination of flow characteristics over sharp-crested triangular plan form weirs using numerical simulation

ABSTRACT Triangular plan form weirs are one type of long-crested weirs. Therefore, they can pass more discharge capacity than weirs at the given channel width. This study aims to investigate the effects of different number of teeth (3, 4, and 5 teeth), angle of the weir tip (90, 60, 120, and 150 degrees), and the amount of different discharges (0.009–0.0063 m3/s) of sharp-crested triangular plan form weirs on the hydraulic parameters by using the Finite Volume Method (FVM). It was found that, increasing the effective length of the crest, increases the discharge coefficient up to 95% in the case with 5 teeth (L/B = 4.14 and h/W = 0.128), 45% in the case with 4 teeth (L/B = 3.71 and h/W = 0.168) and 39% for 3 teeth (L/B = 3.28 and h/W = 0.188) compared to the simple triangular plan weir (without teeth). Also, Results indicated that the discharge coefficient has an inverse relationship with the h/w ratio. In contrast, the investigations showed that the velocity in the flow jet is affected by the effective length of the triangular plan crest, and the increase in the effective length results in a decrease in the average velocity of the flow jet. So that these disturbances caused the highest dissipation of energy to occur in the triangular plan crest with 5 teeth (27% compared to the upstream section (Section 1) and 37% compared to the downstream section (Section 2)).

Closure to “Application of AI Approaches to Estimate Discharge Coefficient of Novel Kind of Sharp-Crested V-Notch Weirs”

Closure to “Application of AI Approaches to Estimate Discharge Coefficient of Novel Kind of Sharp-Crested V-Notch Weirs”