جستجوی مقالات مرتبط با کلیدواژه « کانال مستطیلی » در نشریات گروه « آب و خاک »

The study of fluid motion using experimental and analytical methods is one of the scientific fields that has been considered today. With the advent of computer methods, humans have been able to study more complex phenomena. One of the scientific fields in which many advances have been made is computational fluid dynamics. In fact, computational fluid dynamics studies fluid behavior using new technologies and computational capabilities. In fluid dynamics, stagnation pressure (Pitot pressure) is the static pressure at a stable point in the fluid flow at a stable point, the fluid velocity is zero. In the present study, the stagnant pressure at the edge of the flow separating blade in rectangular channels was investigated in 18 models with different opening angles, baffle shapes and baffle arrangements. The modeling results show that the lowest stagnant pressure in the channel is created with an opening angle of 45 degrees and with convergent mode,and the maximum pressure was created in the channel with an opening angle of 60 degrees with the zigzag arrangement type.

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.

Side weirs are installed on the side wall of main channels. By reaching the flow to the side weir, the exceeded flow falls from the side weir crest and is directs to the side channel. The flow within the channels with side weirs is considered as spatially varied flow. In this study, the three-dimensional flow in a rectangular channel with side weir was simulated by the FLOW-3D software. For simulating the turbulence of the flow, the standard and RNG turbulence models were used. According to the modeling results, the accuracy of the RNG turbulence model was higher than that of the standard model. Furthermore, the Volume of Fluid (VOF) model was used for estimating the variations of the flow free surface. In the study, the velocity was predicted with an acceptable accuracy. Also, the MARE values for the longitudinal, transverse and vertical components were estimated 0.480, 0.468 and 3.519 percent, respectively. Then, the effects of sharp and broad crested weirs on the characteristics of the flow field in the main channel along the side weir for three different models with width of 0.01, 0.05 and 0.15 m were investigated. According to the numerical modeling results, by increasing the width of the side weir crest the shear stress value in the vicinity of the side weir crest increase significantly.

Generally, intakes are used for conveying and diverting the flow within main channels and rivers. In this study, a flow field was simulated using FLOW-3D software. In addition, the flow free-surface variations were predicted using the Volume of Fluid (VOF) scheme. The flow turbulence was estimated by standard k-ε and RNG k-ε turbulence models. For instance, the MAE values for standard k-ε and RNG k-ε models to simulate the free surface profile were computed 0.166 and 0.201, respectively. The modeling results showed that the numerical model simulated the flow field with an acceptable accuracy. For example, the RMSE, MAE and R values for the simulated flow free-surface variations were calculated 0.164, 0.158 and 0.997 percent, respectively. Then, the effects of four flow division angles (30, 45, 75 and 90 degrees) on flow field pattern were considered. Regarding the modeling results, the highest depth-averaged velocity was obtained for the model with 45-degree. Among the models with division angles of 30, 45 and 75 degrees, the maximum shear stress was predicted for the model with 45-degree.

In order to precise design, the determination of flow behavior in open channels have always been subjected by the hydraulic researchers. The traditional Manning-Strickler, Keulegan, and Colebrook-White equations provide inaccurate estimations for resistance coefficients in roughened rectangular channels. In this research, flow resistance coefficients both in smooth and rough rectangular channel sections were investigated by using experimental models and three types of river materials. The results show that the revised Strickler formula estimates Manning's n with an average error about 2.56%; and the revised Keulegan equation for smooth and Colebrook-White equation for roughened channels give some good agreements with the experimental measurements by an error of less than 4.91% and a correlation coefficient of 0.983. Some empirical derived equations are also presented which gives the value of Nikuradse sand equivalent roughness, ks, as a function of roughness diameter size. A new explicit formula presented for friction factor, f, using gene expression programming (GEP) for uniformly roughened rectangular channels with an average relative error 5.1% and the corresponding correlation coefficient, 0.981.

Side weirs are hydraulic structures installing on the side walls of the channels to divert excess water of main channel. Labyrinth weirs are broken in their plans; so, they have more effective length and in some conditions have more discharge coefficient than that of simple ones. In this research, the effects of piles with different arrangements on discharge coefficient of semi-circular labyrinth side weir have been studied. The experiments were carried out in a rectangular channel with subcritical flow with Froude number range equal to 0.1-0.37. Three diameters were considered for semi-circular labyrinth side weirs with constant height. The piles used in the study were cylindrical and the same height of the side weir. The number of piles varied from 1 to 3, and fourteen arrangements were considered for them. First of all, the effects of dimensionless parameters, obtained from the Buckingham method, on side weir discharge coefficient were studied and then a relationship, with acceptable accuracy, between these parameters was obtained to predict the discharge coefficient of semi-circular labyrinth side weir with piles.. The results,  compared with semi-circular labyrinth side weir without piles, showed that semi-circular labyrinth side weir with arrangements of piles have higher discharge coefficient. In fact, piles proved an improvement in the performance of semi-circular side weirs, so that within the range of the studied Froude number, the discharge coefficient faced an increase up to 15% and specific energy changes faced a decrease up to 34%. The most increase in discharge coefficient and the most decrease in specific energy changes occurd when three piles were installed at the downstream end of weirs.

In order to precise design, the determination of flow behavior in open channels have always been subjected by the hydraulic researchers. The traditional Manning-Strickler, Keulegan, and Colebrook-White equations provide inaccurate estimations for resistance coefficients in roughened rectangular channels. In this research, flow resistance coefficients both in smooth and rough rectangular channel sections were investigated by using experimental models and three types of river materials. The results show that the revised Strickler formula estimates Manning's n with an average error about 2.56%; and the revised Keulegan equation for smooth and Colebrook-White equation for roughened channels give some good agreements with the experimental measurements by an error of less than 4.91% and a correlation coefficient of 0.983. Some empirical derived equations are also presented which gives the value of Nikuradse sand equivalent roughness, ks, as a function of roughness diameter size. A new explicit formula presented for friction factor, f, using gene expression programming (GEP) for uniformly roughened rectangular channels with an average relative error 5.1% and the corresponding correlation coefficient, 0.981.

Flap gates are used to measure the flow in canal and are considered as a hydraulic engineering topic, which lacks enough attention so far. Use of flap gate as a measuring tool requires extended studies in order to be recommends as a measuring device for different types of gates. The structures could provide an acceptable economic condition in flow measurement applications where, low costs of manufacturing, installation, and operation could be achieved. This paper presents the discharge estimation from flap gates in rectangular canals under free and submerged flow conditions by using regression and analytical techniques. The derived discharge equations are resulted from the combination of energy and momentum equations. The suggested equations were validated by means of experimental observations, which showed an average error of 1.06% to 1.91% at free flow and 2.28% to 5.26% for submerged flow conditions. The paper also presents some diagrams for estimating the discharge coefficient of flap gates in both flow conditions.

In this study, the depth spreading coefficient in surface discharge of dense jet flow from convergent and inclined rectangular channels into deep and stagnant ambient have been investigated. Therefore, the experiments were done in the hydraulic laboratory of Shahid Chamran University on a flume with 3.2-meter length, 0.6-meter width and 0.9-meter depth. For purposes of this research, the jet flow was injected with three different flow rates and concentrations. Also, for surface discharge of the jet flow, a rectangular channel with floor width of 6 cm and four different convergence angles of 12.5, 25, 45 and 90 degrees was used. The discharge channel was installed in three slopes of 0, 4 and 8 percent in order to be the surface discharge of the jet fluid tangent to the ambient water surface. After conducting the tests, the data were analyzed using the routing process of the prepared images. Then, the coefficients of depth spreading were calculated and the results were extracted. The results showed that increasing the channel slope, reducing the convergence angle and increasing densimetric Froude number increased the depth spreading coefficient. Quantitatively, the results showed that change of channel slope from 0 to 8 percent caused an increase in the spreading coefficient up to 34 percent and the change of convergence angle from 90 to 12.5 degrees caused an increase up to 27 percent. Finally, a statistical relationship between spreading coefficient and the other relevant parameters was extracted that its root mean square error was obtained 0.024.

The study of flow diversion in open channels which has been, since long, under consideration by hydraulic engineers, is much used to divert flow from a main channel or from a river into an irrigation or hydropower channel. When a water intake with an angle is installed at one side of the channel, the streamlines of the flow deflect towards the intake. As a result, a separation zone is produced in the lateral channel. The separation zone develops in the lateral channel and reduces the discharge capacity and efficiency of water intake by delimiting the channel width available for the flow. Therefore, determination of water intake geometry and flow conditions to produce minimum separation zone is very important and they are the focus of this study. The majority of previous studies was conducted on sharp edged water intake entrances. Therefore, in this study, to find the optimum radius for a round edged entrance water intake, a comprehensive experimental program was carried out in a laboratory flume and the separation zone dimensions and Alpha and Beta coefficients were measured.
The experimental model was built in hydraulics laboratory. The water intake was installed at 55 degrees to the main channel. The main channel consisted of a rectangular cross-section with a base width of 0.5 m, height of 0.4 m and a length of 15.80 m. The lateral diversion channel was 0.25 m wide, 0.40 m high. According to previous experiments that performed by Keshavarzi and Habibi (2005), radii of 10, 15 and 20 cm were selected for the edges of the intakes, upstream of the 55 degree water intake. The velocities of the flow in transverse and flow directions were measured using an electromagnetic velocity meter at three distances Z= 3 cm, 6 cm and 12 cm, in which Z is the distance from the bed. Then the size of the separation zone, Alpha and Beta coefficients were determined.
To find a relationship between the radius of the round edge entrance in the 55 degree water intake and the size of separation, the geometry of the separation zone must be determined. To find the geometry and pattern of separation zone for different flow conditions, the particle traces technique was employed using Tec plot Software version 8.0. In open end flow condition, for discharge ratios of 0.2, 0.4, 0.6 and 0.8, and for the radii of 10, 15 and 20 cm, flow separation occurs at 3 cm and 12 cm distance and only upstream of the intake inlet. The separation size in r=20 cm is less than for other radii. Also, the separation size for Qr = 0.8 is minimized and for Qr =0.2 is the maximum and for r/Wb=0.8, the length and width of separation are minimum. In close end flow condition and for radii of 10, 15 and 20 cm, the size of separation zone at upstream of water intake is much larger than that in downstream. Comparing with the separation length downstream of the intake it can be concluded that with increasing the inlet radius, the separation length upstream of the intake inlet decreases. Therefore, in close end conditions, rounding of the intake inlet is effective to decrease separation length at upstream side of water intake. Also, in close end conditions, flow separation occurs at downstream side of water intake. Furthermore, the separation size for r=20 cm is less than for other radii, therefore, r/Wb=0.8 is the optimum radius ratio with a minimum separation size at the 55 degree water intake.
When a water intake with an angle is installed at one side of the channel, the streamlines of the flow deflect towards the intake. As a result, a separation zone is produced in the lateral channel. The separation zone development in the lateral channel and reduces the discharge capacity and efficiency of water intake by delimiting the channel width available for the flow. In this study, to find the optimum round inlet radius, the experimental tests were carried out at a water intake installed in a rectangular channel with rounded edge with 10, 15 and 20 cm inlet radius. Then separation zone dimensions and alpha and beta coefficients determined. These experiments were carried out in close end and open end flow conditions for diversion flow ratio 0.2, 0.4, 0.6 and 0.8. Using particle trace plot for different flow pattern, the values of length and width of flow separation upstream and downstream of the intake were determined. The result showed that the separation size for Qr = 0.8 is minimized, whereas it is maximum for Qr =0.2. Furthermore, the separation size for r=20 cm is less than for other radius, therefore, r/Wb=0.8 with a minimum separation size was selected as the optimum radius ratio.

In this paper flow pattern at 90o, rectangular channel junctions have been studied. Flow pattern in open channel junctions was studied both experimentally and numerically. Velocity measurements were taken using an acoustic doppler velocimeter and depth measurements were made using a point gauge over a grid defined throughout the junction channel region. Velocity distribution in various plates for six discharges ratio Q* was investigated. Results showed that there is a good agreement between the model simulation and the experimental measurements. Both experiments and numerical model showed that by combining two flows in the main and lateral channel, producing a helical flow in the main channel affecting flow pattern. This helical flow formed a separation zone at downstream of lateral channel and this separation zone affecting by discharge ratio. This zone has an inclination to the main right wall at upper layer and in lower layer has an inclination to the left wall. When decreasing Q* separation zone is also decreased in width and length. Longitudinal and vertical velocity vectors in the main channel have small magnitude at upstream main channel. By combining the lateral flow and main flow increasing the magnitude of transversal velocities results also indicate that maximum transversal velocities occur at maximum contraction of flow.