جستجوی مقالات مرتبط با کلیدواژه « Side weir » در نشریات گروه « آب و خاک »

Side weirs are types of hydraulic structures, which are used for different purposes in water transmission systems. In most of the construction operations of irrigation channels and water transfer, based on the topographic conditions of the land, the bottom of the channels is sloped. The purpose of this research is to numerically investigate the changes in the slope of the bottom bed and evaluate the performance of the side weirs in flood conditions and supercritical and subcritical flow regimes. To simulate the flow, CFD method and FLOW-3D® software and RNG turbulence model were used. By examining the surface profile of the flow passing through the weirs at different bed slopes, it was observed that in a fixed slope, in the subcritical flow regime, the surface profile trend is increasing from the beginning to the end of the weir, and decreasing in the supercritical flow regime. As the slope of the main channel bed increases, the level of flow passing over the weir decreases. On average, by changing the regime from subcritical to supercritical, the weir efficiency decreased by 11.21%. Increasing the bed slope decreased 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%. The increase in discharge coefficient with the increase of the weir height varied between 4.6 and 7.8 percent. With the increase of the slope of the channel bed, the velocity along the weir in the subcritical and supercritical flow regimes increased by 10.88 and 6.17%, respectively, and the transverse velocity decreased by 22.23 and 4.8 percent, respectively for the subcritical and supercritical flow regimes.

In this study, the turbulent flow field in rectangular channels with side weir is simulated using the FLOW-3D software. To verify the modeling results, the experimental measurements obtained by Hager (1982) are used. Also, for simulating the flow turbulence the standard k-ε and RNG k-ε turbulence models are used. The numerical modeling results show that the RNG k-ε turbulence model has more accuracy. According to the modeling results, the RMSE and R2 values for the standard k-ε turbulence model are calculated 0.005 and 0.969, respectively. Meanwhile, these values for the RNG k-ε turbulence model are estimated 0.004 and 0.971, respectively. Also, analysis of the numerical results indicates the acceptable accuracy of the numerical model in predicting the experimental results. For example, the RMSE and correlation coefficient values for the mentioned model are calculated 0.004 and 0.971, respectively. Subsequently, the effects of the side weir inlet length on the flow pattern are investigated. For this purpose, three different numerical models with weirs with lengths of 1m, 0.7m and 0.5m are defined. According to the modeling results, by decreasing the inlet length the side Froude number value along the side weir decreases. In contrast, by decreasing the side weir inlet length the maximum value of the flow field pressure for the model with a inlet length of 0.5m is predicted. In other words, the maximum pressure values for the models with side weirs with lengths of 1m, 0.75m and 0.5m are calculated 271pa, 286pa and 317pa, respectively.

A new type of Long-crested weirs is Piano Key weir that allows the reservoir to run at a higher level. The use of a Piano Key weir as side weir allows for more drainage, due to the geometric shape of the channel and the impact of centrifugal force on the flow, in a channel having longitudinal curvature. This research, examine the Changing of flow pattern and discharge coefficient of a Type-B Piano Key weir in 45-degree sector of a channel having longitudinal curvature by Experimental investigation. Experiments were carried out in a certain range of changes in geometric and hydraulic parameters, and the effect of each of the dimensionless parameters on the flow was determined. It is worth noting that all experiments with rectangular sharp-crested weirs have been compared. The result of this study is the high discharge coefficient of Piano Key side weir relative to the rectangular sharp-crested weir. Also, the L/b and Froude number parameters have a significant impact on the performance of the Piano Key side weir in 45-degree sector of a channel having longitudinal curvature. From other results of this research is the flow pattern that from beginning to end of the Piano Key side weir that height of the surface of the flow dropping dramatically at beginning of the weir, and eventually reaching its initial level, which is associated with lower variations in the higher heads. These deformations have been much lower when used with rectangular sharp-crested weirs.

The main application of spillway in rivers and dams reservoirs is control and diversion of flood and protection of their related structures. In this research, a laboratory study was performed to test 16 trapezoid piano key A type weir models with different pillars 10, 15 and 20 cm in a canal with 10 meters length, 0.6 m width and 0.6 m height. The proposed weirs were placed on the main canal wall with two arrangements. The results showed that the maximum overflow rate coefficient was corresponded to weirs with p=15cm in both arranments (1 and 2) and the dimentionless ratio of 0.4 <H/P> 0.2 0.4 and also to weir with dimentionless ratio of 0.5 <H/P and p=20cm. Finally, the trapezoid piano key weir with a p=15cm and a B=50cm identified to pass the most appropriate flow regime.

Generally, side weirs are used for regulating and controlling the flow in the main channels. U-shaped channels are used as transition structure from rectangular to circular cross-section in sewage systems. This study presented a flow field simulation in the U-shaped channels along a side weir using FLOW-3D software, the RNG k-ε turbulence model and volume of fluid (VOF) scheme under the subcritical and supercritical flow conditions. The good agreement was obtained between the results of the numerical simulation and the experimental measurements for both flow regimes. For example, the root mean square error for subcritical and supercritical flow regimes was computed as 2.86% and 2.21%, respectively. In subcritical flow regime, a secondary flow created in the main channel which developed toward the downstream. The lateral flow increased from the beginning of the side weir toward the downstream end of the weir under supercritical flow regime. The effects of the side weirs submergence were investigated on the flow pattern in the main channel too. The maximum transverse velocity almost happened at the middle of the submerged weir length

Side weir is one of the water diversion structures which is widely used for different purposes such as deviation of the excess water in the urban wastewater collection systems, irrigation networks, control of the floods’ elevation, etc. In some conditions, a spatially varied flow over the side weir might include hydraulic jump which has been less studied yet. In present study the hydraulic jump issue was investigated using a Flow-3D software model. The model was validated with experimental data and the results showed that the numerical model was able to simulate the hydraulic jump with reasonable accuracy. Then, the effect of the downstream water depth on the characteristics of the hydrulic jump was investigated. By decreasing the downstream water depth, the location of the hydraulic jump moved toward the weir downstream end while the hydraulic jump was removed by increasing the downstream water depth. By moving towards the end of the weir, the longitudinal velocity distribution became non-uniform due to formation of the separation zone near the main channel bed flow and the areas with negative velocities were formed.

The circular channels with side weirs are widely used to regulate the flow and control the water depth in the urban sewage disposal systems. In this study, the turbulence of flow field and variation of the free surface of supercritical flow in a circular channel with a side weir are simulated using FLOW-3D software, the RNG k-ε turbulence model and VOF scheme. Comparison between the numerical simulation and laboratory measurements shows that the numerical model has simulated the free surface and flow field profile with reasonable accuracy. According to the numerical simulation, the flow depth is decreased along the side weir. In all simulations, a free surface drop has happened at the upstream beginning of the side weir. There is also a surface jump at the downstream end of the side weir. The change of specific energy along the side weir for the supercritical flow regime is almost constant and the energy loss is not significant but by increasing the side weir length the energy difference between the upstream and downstream of the side weir increases. The velocity field analysis indicates that the maximum longitudinal and lateral flow velocities happen at the end and middle of the side weir, respectively. Also in each cross-section, the maximum vertical velocity happens in vicinity of the side weir.

Triangular channel is widely used in irrigation and drainage systems. Also, the triangular channels with alongside weirs are used to control and measure the flow in irrigation and drainage networks and floodwater spreading projects. In this study, the pattern of the spatially-varied flow with decreasing discharge was investigated and compared in subcritical and supercritical flow regimes for triangular channels alongside weirs. Flow pattern in triangular channels alongside weirs is numerically simulated using the FLOW-3D software for both flow regimes. Also, variations of the free surface flow over alongside weirs are modeled by the volume of fluid (VOF) scheme. Furthermore, the turbulence of the flow field in triangular channels alongside weirs is numerically simulated using the RNG k- turbulence model. In the numerical study by these models, the specified amounts of discharge and flow depth are used for the "inlet" boundary condition of the triangular channel. Also, the specified amounts of the flow depth and the pressure are used in the main channel outlet boundary condition and all of the solid walls are defined as the "wall" boundary conditions. Then, the top layer of the air phase is considered as the "symmetry" boundary condition. The whole computational domain is gridded by a non-uniform mesh block consisted of rectangular elements. The distance from the first cell-wall was chosen so that the calculations below the viscous layer are eliminated. For this purpose, the first cell is located where the dimensionless parameter y is greater than 30. The results obtained from the numerical simulation in this study were verified by comparing them to the experimental measurements provided by Uyumaz (1992). A good agreement was obtained between the results of the numerical simulation and the experimental measurements for both flow regimes. The RMSE of the simulated water surface profile for the subcritical and supercritical flow regime was calculated 11.46% and 7.90%, respectively. Also, for free surface flow, the average percent relative error for both flow conditions were computed 10.8% and 6.87%, respectively. The specific energy was measured in the beginning of the side weir which was equal to 0.1661m and 0.2116m in subcritical and supercritical flow condition, respectively. The numerical model predicted the specific energy equal to 0.1565m and 0.2283m for both flow regimes. The specific energy relative error percent was 5.78% and 7.89% which showed suitable accuracy of the numerical model in predicting the specific energy. Generally, the flow depth increases from the upstream end towards the downstream end of the weir in subcritical conditions and decreases from the upstream end towards the downstream end of the side weir in supercritical conditions. A drop in the free surface in the first third of the side weir span and a surface jump in the final third of its length occurs. After this drop, the flow depth increases towards the downstream end of the side weir in subcritical flow regime, while in the supercritical flow condition the water depth gradually decreases towards the downstream end of the weir. The surface jump with a stagnation point occurs at the downstream end of the side weir for both flow regimes. Along the mentioned surface jump the amount of the kinetic energy increases and the potential energy decreases. Also, the water elevation is the highest at the stagnation point location. According to the simulation results, the maximum longitudinal velocity for subcritical regime occurred at the first third of the side weir length and for supercritical flow, almost in the middle of the side weir span. In both subcritical and supercritical flow regimes, the maximum transverse velocity occurred at the last third of the side weir length. According to the numerical simulation, the transverse velocity before the side weir was predicted negligible. In the vicinity of the side weir crest, the transverse velocity increased by flowing toward the span of the side weir. As the flow passed from the plane of the side weir, the amount of the transverse velocity decreased. The angle of the spilling jet was close to 90° at the upstream and downstream of the side weir in both flow regimes. The minimum angle of the spilling jet for subcritical and supercritical flow regimes occurred at the last third and the middle of the side weir length, respectively.

Side weirs are of main hydraulic structures which are widely used in flow diversion systems and drainage networks. Also, circular channels are used as the main channel for flow transmission in sewage disposal systems and irrigation networks. In this study, pattern and field of the passing flow within circular channel along the side weir under supercritical flow regime was simulated using FLOW-3D software. Also, the flow field turbulence and variations of the free surface have been simulated using RNG k-e turbulence model and VOF scheme, respectively. Comparing numerical simulations with experimental results showed the reasonable accuracy of numerical model. In practice, transport channels used in irrigation networks and urban sewage disposal are steep. Therefore, the effect of bed slope variations on the hydraulic characteristics of flow field along the side weir was investigated. By increasing the main channel bed slope the free surface of flow along the side weir was decreased. According to simulation results, by increasing the circular channel bed slope the specific energy was increased.

Side weir is used as a slot in the side of main channel to direct excess flows that are above the weir crest. Such structures are used in control of flow level in irrigation, drainage networks and urban sewage disposal systems. Among these structures, circular channels are extremely important. Considerable length of sewage disposal and transmission pipeline system is made of circular channels. In this study, changes of water surface level, turbulence and flow field passing through a circular channel with side weir is simulated using commercial software. In this numerical simulation for modeling changes of flow free surface, VOF model and for simulating of the flow field turbulence, RNG k-ε turbulence model are used. In this study in order to validate the accuracy of the numerical model, the flow depth changes along the side weir, the discharge coefficient of the side weir, the passing flow over the weir, the Froude number at the upstream of the weir and the specific energy at the beginning of the weir are compared with the laboratory results. Comparison of all mentioned parameters with the experimental results show high accuracy of CFD model in predicting turbulence and flow field of passing through a circular channel with side weir. The main purpose of this simulation is gaining an understanding of behavior of passing flow through circular channels with side weir in order to use in design problems of this type of hydraulic structures.

Side weir is a hydraulic control structure that is widely used in irrigation, drainage and urban sewage purification. In this research, 220 tests were carried out to study discharge coefficient and water surface profile of one-side semi-circular labyrinth side weir under subcritical flow condition. The effects of upstream Froude number, the ratio of length to width of the channel, weir height to upstream water depth, number of cycles and the radius of the Labyrinth on the discharge coefficient of the weir were investigated. The results showed that discharge coefficient of the semi-circular labyrinth side weir was 21 percent higher than rectangular side weir. Using SPSS software, a general equation based on the dimensionless parameters was presented for calculating the discharge coefficient of the semi-circular labyrinth side weir. The determination coefficient and NRMSE of this equation were obtained, 0.93 and 0.28 respectively. The water surface profile along the central axis of the main channel was almost horizontal.

A side weir is being installed as a flow control structure on the side of the main channel. When the water level exceeds the crest level of the side weir, the additional flow will spill over the weir crest and divert into the side channel. This type of structures has wide application in urban sewage disposal, water supply systems, drainage and flood diversion networks. In this study, the free surface of flow and the side weir discharge were simulated using FLOW-3D software. The RNG k- ε turbulence model was used for simulation of the flow field turbulence. Also the volume of fluid (VOF) scheme was applied to predict the variations of flow free surface. Comparing numerical simulations with experimental results showed the acceptable accuracy of numerical model. Next, the discharge coefficient of side weir and the free surface of flow variations were evaluated for different discharges of the main channel. Then the variation of the width of the separating stream surface from bed of the main channel toward the free surface of flow was investigated. Also, the circular channel effects on the pattern and strength of the secondary flow were studied. The effects of the main channel discharge on the stagnation point height and bed shear stress pattern were investigated. According to the subcritical flows pattern, the flow depth was increased from the side weir upstream end towards its downstream end. For all longitudinal profiles with increasing discharges within circular channel, the flow depth was increased along the side weir.

Side weirs are flow diversion and protection devices that are widely used in irrigation, land drainage and urban sewage systems. This study investigates the discharge coefficient of rectangular and triangular sharp crested side weirs and identifies the effective factors on this parameter by using dimensional analysis and statistical approaches. In addition to calculating the discharge coefficient, equations with 5 percent error for rectangular and 3 percent error for triangular shape have been proposed. For checking the effect of factors on this parameter sensitivity analysis is performed. The results demonstrate that the most important effective factors on discharge coefficient of the rectangular and triangular weirs are Froude number and dimensionless ratio of the main channel wide to the depth of flow in the upstream of the weir, respectively. Error of discharge coefficient (Cd) can be increased up to 7 percent for rectangular weir and 4 percent for triangular side weir with ignoring these factors. Also accurate estimation of discharge coefficient, merely with considering the upstream hydraulic condition, is not correct. The geometry of the cross section should be considered as an effective factor for determination of discharge coefficient, and this approach, decreases error of the calculation up to 3 percent.

Side weir is a flow control structure that used extensively in irrigation and drainage networks and sewer networks. In this research, a study with 162 experiments has been done on sharp-crested circular side weir. Since the height of this side weir varies along its length, this feature enables it to control flood better than rectangular side weir in different flood conditions. The governing differential equation of circular side weir has no analytical solution, and thus it is necessary to use numerical methods to solve it. Since numerical methods have computation cost, normal weir equation and linear assumption of water surface profile are used to solve the problem. Lastly, by doing three other experiments under completely different conditions, it was found that the method of considering linear water surface profile has less error in comparison with other methods used in this research.

Sharp crested side weirs are one of the most common hydraulic structures used for flow diversion and control in irrigation, drainage networks, and waste-water channels. Simple side weirs generally have some limitations in flow escape and measurement face with relatively heavy flows from the main channel. The use of combined side weir is one way to solve this problem. Few studies have conducted flow hydraulics in combined side weirs. For this reason, in this study, compound rectangular–triangular sharp crested side weirs were studied experimentally in subcritical flow conditions. Finally, using dimensional analysis, parameters affecting the discharge coefficient of a compound side weir are a function of the upstream Froude number, the ratio of weighted crest height of the weir to upstream water depth and the ratio of weir length to upstream water depth and a relationship for estimating the discharge coefficient was proposed. Comparison of results by using proposed equation with experimental results, shows high accuracy (RMSE=0.00131 and R^2=0.991) in estimation of diverted discharge through compound side weir.

Side weirs are used in drainage systems, flood control, runoff collecting and many water resources and environmental projects. In this study, discharge coefficient in trapezoidal sharp crested side weirs was investigated by designing 18 weirs in subcritical condition and the effective factors on this parameter were studied. Some equations presented for calculating discharge coefficient with 4.3 and 5.4 percent error by using statistical methods and multiple regression. Results demonstrate that considering the side slope of the weir as an effective factor on discharge coefficient, increase accuracy of computations 1.2 up to 2.3 percent. Also, according to the calculations, the most important factor on discharge coefficient in this type of weirs is the ratio of overflow length to the length of the weir and omitting this factor leads to increase the error up to 1.4 percent.Side weirs are used in drainage systems, flood control, runoff collecting and many water resources and environmental projects. In this study, discharge coefficient in trapezoidal sharp crested side weirs was investigated by designing 18 weirs in subcritical condition and the effective factors on this parameter were studied. Some equations presented for calculating discharge coefficient with 4.3 and 5.4 percent error by using statistical methods and multiple regression. Results demonstrate that considering the side slope of the weir as an effective factor on discharge coefficient, increase accuracy of computations 1.2 up to 2.3 percent. Also, according to the calculations, the most important factor on discharge coefficient in this type of weirs is the ratio of overflow length to the length of the weir and omitting this factor leads to increase the error up to 1.4 percent.

Side weir is one of the important structures in irrigation and drainage networks. The main problem to study the hydraulic of flow in this structure is determination of water level profile along the weir and diverted flow discharge. In the present study, discharge coefficient of free flow of side weir located in various parts of the 180 degree channel bend is investigated experimentally. Also with considering the variation of water level along the weir and numerical solution of dynamic equation of spatially varied flow over side weir, the elementary discharge coefficient is related to Froude number, side weir location and the ratio of weir height to head of water. In order to compute the exponents and coefficients of relation, the genetic algorithm was used. The results showed that by using the elementary discharge coefficient, the water level along the weir and diverted flow discharge can be estimated precisely.

Side weir as a hydraulic structure is widely used in water intakes. In addition، this structure is used as a protective structure at the end of the main channels to discharge excess water flow. In some cases a hydraulic jump is possible to occur along the spatially varied flow over the side weir and studies show that a few literatures are available for this condition of flow in the side weirs. This paper discusses water surface profile and discharge coefficient of the side weir under the condition of hydraulic jump occurrence in spatially varied flow. Values of the statistic indices R2 and RMSE between the observed and calculated quantities of discharge coefficient for the side weir were 0. 776 and 0. 005 respectively. A new method called «Calibrated Subramanya Method» was also developed to define the shape of water surface profile of hydraulic jump in side weirs. This method showed a good agreement with the experimental data. Studies show that the hydraulic jump in spatially varied flow has almost a constant shape with oscillations on the water surface.

A side weir is a hydraulic structure with free flow، which is installed at one side and parallel to an open channel. It allows the water to overflow when the surface of the water in the channel rises above the weir crest. This structure affects the depth and the flow rate in the channel. Awareness regarding the effect of this structure on the depth of water and flow rates can affect decision making for the proper hydraulic design of the channel and its side weir. In this research، 36 semi elliptical side weirs were tested in 298 settings، varying in an experimental main channel geometrical characteristics، and subcritical conditions. The range of discharge was varied from 10 to 70 lit/s. The water surface profiles over semi elliptical and rectangular side weirs were investigated and interpreted through velocity profiles. Additionally، the effects of increasing the discharge in the main channel، and varying the height، length and curvature of weir on the water surface profile were examined for this type of weir were studied. Moreover، the result of experimental water surface profiles were compared with the water surface profiles calculated by the Runge-Kutta method over rectangular and semi elliptical side weirs. The results indicated that the accuracy of this method was increased by raising the height and length of the weir، and the reducing the discharge.

Side weir is one of the most common structures for flow control and diversion in hydraulic laboratories, irrigation and drainage networks and water and waste water channels. Side weirs are generally sharp crested and have limitations in measuring discharge, hence in this study, the compound sharp crested side weirs have been suggested, for the first time. Accurate flow measurement in wide range of discharges in comparison with simple side weirs, is one of the main characteristics of these weirs. Some experiments have been carried out in a rectangular-rectangular compound side weir with variable heights and widths. Dimensional analysis of effective parameters on flow discharge of a compound weir illustrates that its discharge coefficient is a function of upstream Froude number, ratio of weighted height of weir crest to upstream water depth and ratio of channel width to upstream water depth. Based on the experimental data and optimization technique, a dimensionless equation has been developed for calculation of the discharge coefficient. Then, a new equation has been proposed for prediction of flow discharge in compound rectangular-rectangular sharp crested side weirs. Through comparison of results of this new equation and experimental data, the determination coefficients of training and testing data were calculated as 0.96 and 0.98, respectively. Also, mean average relative error was 6.4%.