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1.
Side weirs are frequently used in many water projects. Due to their position with respect to the flow direction, side weirs are categorized as plain, oblique and labyrinth. One of the advantages of an oblique side weir is the increase in the effective length of the weir for overflowing and, therefore, diverting more discharge with the same channel opening, weir height and flow properties (i.e., upstream discharge, upstream Froude number and so on). In this paper, an experimental set-up of a new design of an oblique side weir with asymmetric geometry has been studied. The hydraulic behavior of this kind of oblique side weir, with a constant opening length, different weir heights and asymmetric oblique angle, has been investigated in a subcritical situation. The results from over 200 test measurements show that this kind of weir is up to 2.33 times more efficient with respect to the conventional side weir in a rectangular channel among the tested conditions. Finally, the discharge coefficient as a function of geometrical and flow variables are presented for design engineers. In addition, a more precise relation has been obtained for flow with Froude numbers less than 0.4. 相似文献
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In this paper, the inclined side weir discharge coefficient was studied using a side weir with three different crest angles (θ=4°,8°,12°) fixed either against and in the flow direction, and the results are compared with those from a horizontal side weir crest (θ=0°). In total there were seven models.The results show that the De Marchi assumption of constant energy for all side weir crested angles is acceptable, and thus that the calculated weir discharge value can therefore be undertaken.An equation for the discharge coefficient was obtained for an inclined side weir, so the value of Cd for crest angle θ=12° increased by 13.6% with respect to the value for θ=8°, by 29% with respect to that for θ=4°, and by 39% with respect to that for the horizontal case (θ=0°), for a crest inclined against the flow direction, while when the crest was inclined in the flow direction all those values exceed, to 14.5%, 31.0%, and 40.7%, respectively. This means that the discharge increases with increasing side weir crest angle, so when we want uniformity in the flow direction and exceed discharge we need to make the side weir crest incline against the flow direction while when we want furthermore discharge we need to make the side weir crest incline in the flow direction. 相似文献
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Piano key weirs are high performance labyrinth weirs particularly at lower heads (water height over the weir). These weirs are considered a recent development in terms of application and research. This study was conducted to numerically and experimentally investigate the hydraulic performance of arced trapezoidal piano key weirs ATPKW under different hydraulic and geometric conditions. The main purpose was to investigate the effect of the planform arc angle on the weir's hydraulic performance. To this end, four LRPKW models as well as four ATPKW models were studied. Due to the complexities associated with flow over piano key weirs, numerical models were used to simulate the flow pattern over the weir. Comparison of the results obtained for the ATPKW and LRPKW models indicated that, at upper heads, the ATPKW models offered a higher hydraulic performance than the LRPKW models. On the other hand, LRPKW model indicated better performance at lower heads. In addition, it was found that reducing the planform arc angle from 90° to 45° caused an initial reduction in the discharge coefficient, after which it dramatically increased. Also, LRPKW models indicated a more effective length and a more appropriate performance. 相似文献
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Arced labyrinth weir is a certain type of nonlinear weirs with a very high discharge capacity. Thanks to the increased effective length and the ensuing increased discharge capacity of these weirs, they can be used in dam spillways and water regulating structures. This study focused on trapezoidal Arced labyrinth weirs (TALW) of widened middle cycle. Various experiments were performed to evaluate the effect on discharge coefficient of various geometric parameters, including the ratio of inside apex width of the end cycles to that of the middle cycle (w2/w1) and the ratio of the length of labyrinth weir (Apron) in flow direction to the width of the middle cycle (B/w1). Results of this study showed that with a decrease in w2/w1 from 0.42 to 0.30, discharge coefficient (Cd) would increase by 13–33%. 相似文献
7.
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. 相似文献
8.
Parapet walls on the crown of piano key weirs (PKW) are employed in the channels to regulate or increase water levels of the upstream. They are also used in the reservoirs to increase water storage. Most recent surveys concerning discharge coefficient and parapet walls have been conducted on the rectangular piano key weirs (RPKW) while not many of them devoted to trapezoidal piano key weirs (TPKW). Also, the effects of its parapet wall and crest shape are rarely investigated in this regard. The aim of this research was to study the impacts of height (R), installation arrangements (S), and crest shape of parapet walls (flat, triangular, and semicircular) on changes of the upstream water level and discharge coefficient of TPKW. The weir height (P) was 15 cm. The parapet walls were installed on the crest of weir with three different arrangements: S1 (on the crest overall), S2 (on the sidewalls and inlet key), and S3 (on the sidewalls). The results indicated that the influence of installation arrangement on changes of water level increased with the growth of parapet walls height. In the case of a flat parapet walls, maximum and minimum increase rates of total head were recorded for S1 and S3 arrangements, respectively. There was also a direct relationship between discharge coefficient (C) and the heights of parapet walls in a constant water level at upstream. When installing flat parapet walls with R/P = 0.3, the value of C for S2 exceeded those for S1 and S3. 相似文献
9.
Piano Key Weirs (PKW) have been invented in the last decade to increase discharge capacity of hydraulic structures. Despite extensive studies on this type of weir with a rectangular plan form (RPKW), there are only a few pieces of research addressing trapezoidal piano key weirs (TPKW). In this experimental study, geometrical parameters of TPKW models were varied under different flow conditions and effects on discharge coefficient (Cd) were investigated. The Cd values were found to be mostly influenced by L/W whereas Wi/Wo had the least effect. Results also showed that TPKW has higher discharge efficiency in comparison with RPKW. This was believed to be related to formation of an “interference wedge” over the TPKW. Finally, quantitative values for distinguishing three flow regimes (i.e. nappe, transition and submergence) as well as criteria for design of TPKW are proposed. 相似文献
10.
A simple model is proposed for predicting the dimensionless isovel contours in straight ducts and open channels. It is assumed that each element of the boundary influences the velocity at an arbitrary point in the cross section. Then, the total effect of the boundary can be obtained using integration along the wetted perimeter. In this paper, power and logarithmic laws are used, while any velocity profile can be applied in the model. The model is applied to calculate the normalized isovel contours in rectangular channels. Then they are used, in combination with a single-point velocity measurement at a cross section of the uniform flow, to estimate the discharge. The kinetic energy and momentum correction factors, and the ratio of maximum to mean velocity, are also calculated from isovel patterns. Calibration and validation of the model are carried out by comparing the results obtained with measurements of the velocity in the main flow direction along the centerline of a rectangular flume as well as in the transverse direction. Each point of measurement can be used to estimate the discharge. Then, the estimated discharge is compared with the actual measured one. Depending on the position of the measurement, the deviation of the calculated and measured discharges will be altered. Model predictions are well correlated with experimental data for rectangular open channels. 相似文献
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Thin-plate weirs are the simplest and least expensive devices, which frequently have been employed in many water projects. In this research, a unique type of Sharp-Crested V-notch weir, entitled SCVW, has been introduced. The hydraulic characteristics of the present weir were investigated theoretically and experimentally under free aerated and non-aerated flow conditions in an open channel for large physical models. To investigate the variations of the discharge coefficient of SCVW versus weir height and vertex angle, a comprehensive laboratory experiments were conducted by measuring the discharge and the water head over the crest of weir. Possibility of different formulations for the head- discharge relationship of SCVW was examined and suitable analytical equation was proposed. The computed discharge using the suggested equation was within 0–10% of the observed ones. According to the experimental observations, the SCVW showed better performance in comparison with normal wire. 相似文献
13.
A side weir is a hydraulic control structure used in irrigation and drainage systems and combined sewer systems. A comprehensive laboratory study, including 843 tests for the discharge coefficient of a sharp-crested rectangular side weir in a straight channel, was conducted in a large physical model under subcritical flow conditions. The discharge coefficient is a function of the upstream Froude number, the ratios of weir length to channel width, weir length to flow depth, and weir height to flow depth. An equation was developed considering all dimensional parameters for discharge coefficient of the sharp-crested rectangular side weir. The average error of the proposed equation is 4.54%. The present study data were compared with ten different discharge coefficient equations developed by several researchers. The study also presents water surface profile and surface velocity streamlines. 相似文献
14.
One of the practical and economical ways to enhance the discharge capacity is to use labyrinth weirs. The longer crest length in labyrinth weirs than in linear weirs has caused these weirs to have both a higher discharge coefficient and water discharge capacity than a linear weir. In the present study, the discharge coefficient of trapezoidal and triangular labyrinth weirs was investigated by creating an additional cycle along the lateral crest of the weir. By constructing 10 physical models of labyrinth weirs, tests were performed in the hydraulic and sediment laboratory of the Khuzestan Water and Power Authority (KWPA). Dimensional analysis by the Buckingham method revealed the discharge coefficient (Cd) as a function of variable parameters such as the total hydraulic head to weir height ratio (Ht/P) and weir shape factor (Sf). The results of experimental tests showed that at the hydraulic head ratio (Ht/P) of 0.1, the TP weir had a higher discharge coefficient of 3.5% than the TPTPO weir and 2.5% than the TPTRO weir. However, at a hydraulic head ratio of 0.12, the TR weir had a lower discharge coefficient of 4.6% than the TRTPO weir and 6.9% compared to the TRTRO weir. For the hydraulic head ratio of 0.14, the TRTPI weir was 5.8% and the TRTRI weir was 9.4% higher than the TR weir. Statistical analysis using SPSS indicated that TRTPO and TPTRO weirs had the highest correlation with the cubic model. 相似文献
15.
The flow through a triangular plan labyrinth weir is studied for both free and submerged flow conditions experimentally and theoretically. The free flow condition is studied using a new experimental data set collected in this study. For the submerged flow condition, the threshold between free and submerged flow regimes is studied experimentally. Then Buckingham analysis is employed to determine the submerged head-discharge formula of the triangular plan labyrinth weir. Finally, a step by step calibration method is proposed to find the unified discharge coefficient. The proposed discharge coefficient can be used for both free and submerged flow conditions continuously and within the transition zone. 相似文献
16.
Experimental and numerical investigation of self-priming siphon side weir on a straight open channel
Siphons are basic and powerful hydraulic instruments which can be used as dam spillway or weir. In a siphon, atmospheric pressure pushes the water into the region of vacuum at the crest of the siphon, and then water falls towards the outlet of siphon. In this study, the siphon used as a side weir was investigated to determine hydrodynamic characteristics experimentally, theoretically and numerically. First, the flow properties of main channel were examined for subcritical flow condition. Then, the velocity and pressures distributions inside the siphon; finally the discharge performance of siphon side weir was determined comparatively, and the results were discussed. 相似文献
17.
Side weir is placed at the channel bank as a head regulator or a diversion device. Flow over a side weir has been the subject of many research studies considering its three dimensional and complicated characteristics. However, the labyrinth side weirs warrant further research due to their higher efficiency compared to linear side weirs. In this paper, subcritical flow characteristics and discharge coefficient for both symmetric and asymmetric triangular labyrinth side weirs were studied experimentally. The results show that asymmetric labyrinth side weirs have higher discharge coefficient compared to symmetric labyrinth side weirs; since a larger portion of the crest is orthogonal to the flow. Using the present laboratory data, general equations were proposed for the estimation of discharge coefficient of both symmetric and asymmetric triangular labyrinth side weirs. The results of this study can be useful to design side weirs with high hydraulic performance. 相似文献
18.
Flumes with either width contractions or raised beds to force modular flow conditions (i.e. a transition from sub- to super-critical flow) are a widely used instrument for the measurement of flow rate. The conservation of mass, written as the continuity equation, and the conservation of energy are combined with the existence of a critical depth point to derive a theoretical equation for the discharge as a function of the upstream water depth. This derivation requires a number of assumptions regarding the flow both upstream and in the throat of the contraction. The international standard covering the use of such flumes, ISO4359, places restrictions on the upstream position at which the water depth should be measured, which this work shows to be unnecessary, at least for the small (100 mm throat width) flumes examined. The assumption that critical depth occurs at the end of the flume throat is also shown to be incorrect, but has negligible effect on discharge calculation using the ISO4359 method. 相似文献
19.
Accurate determination of the discharge coefficient play a very important role in estimating the flow discharge over the weirs. As a result, it is significant to estimate the discharge coefficient correctly. The aim of this study is simulation and estimation the discharge coefficients (Cd) over the broad-crested weirs with cross section rectangular and suppressed. Hence, numerical simulation of hydraulic characteristics of these weirs were performed by ANSYS FLUENT software and results were obtained. Then two intelligent models of ANN, GPR and hybrid both of models namely ANN-HHO, GPR-HHO were used to determine the discharge coefficients using the efficient parameters and the results of these models were compared. Assessment of the results were performed using the statistical metrics: coefficient of determination (R2), root mean square error (RMSE), mean absolute error (MAE), scatter index (SI) and Kling-Gupta efficiency (KGE) and graphical diagrams including violin plot, percent relative error (RE%) plot and probability density function (PDF) plot of residuals. It was found that hybrid artificial neural network and gaussian process regression with Harris Hawks optimization (ANN-HHO and GPR-HHO) could improve ANN and GPR models performance in estimating the Cd in broad-crested weirs. Overall, results indicated that a combination of the HHO with the ANN (ANN-HHO) model performs better than GPR-HHO model for the estimation of the Cd. 相似文献
20.
A sharp-crested weir with power-law sides is a general form, which reduces to the wildly used rectangular, parabolic, and triangular weirs. This general form allows modeling the weirs with different shapes. Up to now, the hydraulic performance of the power-law weirs with the exponent n in the range of 1 ≤ n ≤ 2 has not been studied. In this study, the triangular (n = 1) and curved-edge triangular (n > 1) weirs are studied experimentally and theoretically. For this, weir and critical flow theories along with Buckingham's theorem of dimensional analysis are used to deduce the stage-discharge relationship of the triangular and curved-edge triangular weirs. A series of laboratory experiments (464 runs) were conducted to calibrate the deduced theoretical stage-discharge relationships under free outflow condition. The proposed general stage-discharge relationship using the weir theory has a mean absolute relative error of 2.51% for 1 ≤ n ≤ 2. For this relationship, the mean absolute relative errors for n = 1, n = 1.5 and n = 2 are respectively as 1.96%, 2.64% and 3.08% whilst for the proposed stage-discharge relationship using the critical flow theory they are as 1.96%, 2.75% and 3.82%, respectively. Thus, the proposed stage-discharge relationship using the weir theory may be preferable due to its accuracy and generality. 相似文献