Performance Evaluation of Submerged Vanes by Flow-3D Numerical Model
Reza
Azizi
Department of Water Science and Engineering, Faculty of Agriculture, University of Zanjan, Zanjan, Iran.
author
Mahmood
Shafai Bejestan
Department of Hydraulic Structures, Faculty of Water Science Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran.
author
text
article
2020
per
1- Introduction Submerged vanes are flow-pattern altering structures that are mounted vertically on channel-bed at a small angle of attack to the approach flow. A submerged vane generates a secondary circulation (a spiral flow), due to the vertical pressure gradients on the two sides of the vane, which originates below the top elevation of the vane and extends in the downstream of the vane. The vane-induced vortex redistributes sediment within the channel cross section and changes the alluvial bed profile. However local scour around the vanes is one of the problems in using of submerged vane technique. The extension of local scour hole is related to the shape of the vanes. Primary submerged vanes are generally flat rectangular plates. In the present research, cutting a part of the leading edge of the vanes out is investigated as a countermeasure in reducing the local scour. Studied vanes include a rectangular vane (as the baseline vane), and five other modified vanes with tapered leading edges with angle of = 30°, 45°, 60°, 70°, and 73.3°. The present study aims to evaluate the effect of this modification on the vertical velocity components at the leading edge and strength of the secondary circulation in the downstream of the vanes. In this research, Flow-3D numerical model, version 10, is used to study the flow field around the vanes. 2- Methodology The commercial CFD model Flow-3D was used in this research. Experimental velocity measurements were used for calibration of the model. For this purpose a re-circulating flume (7.30 m long by 0.56 m wide by 0.6 m deep) was used. A centrifugal pump discharged the water into the stilling tank at the entrance of the flume. In order to create a uniform inflow of water, a screen was placed at a distance of 1 m from the flume entrance. A tail gate was used to adjust the depth (do) of water in the flume to a constant value of 0.25 m. The dimensions of the vanes were determined using Odgaard’s (2008) design criteria: a vane height-to-water depth ratio of Ho/do = 0.3 and length of L = 3Ho. A mean flow depth of do = 0.25 m yielded Ho = 0.075 m and L = 0.25 m. velocity measurements carried out using vanes V0 and V3 at a flow Froude number of Fr = 0.16. In each test, the vanes were installed on the centerline of the flume at an angle of 20° to the flow. In order to investigate vane-induced velocity field, 4×4 cm2 grids across the flume were taken at the center of the vanes. At each grid point, three-dimensional components of velocity vector (u, v, w) were measured by means of an electromagnetic velocimeter (EVM). Velocity very close to the walls of the flume was not measured. 3- Results and discussion On the high-pressure side of the vanes, vertical velocity components are upward (positive) and on the low-pressure side are downward (negative). Therefore a clockwise secondary circulation is generated at downstream of the vanes. Downward velocity components at leading edge of primary rectangular vane (vane V0) are obvious. By cutting parts of leading edge out of vane V0 for tapered vanes V1 and V2, the magnitude of negative w-velocity components is reduced by 40% and 69%, respectively. By increasing the taper angle for vanes V3, V4 and V5, downward velocity components are diminished effectively. Moment of momentum (MOM) quantity is used in order to evaluate strength of vane-induced circulation. MOM values are applied for comparison of performance of the vanes. For this purpose, velocity data at two sections at the distances of 2Ho and 4Ho, i.e., 15 cm and 30 cm downstream from center of the vanes was used. In the calculation of MOM, 100 velocity components (50 v-components and 50 w-components) are used. Therefore this quantity is a useful criterion for evaluation of the performance and efficiency of the submerged vanes. 4- Conclusion Velocity distribution and moment of momentum (MOM) of the vanes indicated the reduction of erosive negative velocity components at the leading edge of the tapered vanes. Based on MOM values, cutting the leading edge out of the vanes causes lower performance. In other words, this modification restricts the vane-influenced field of the tapered vanes relative to the rectangular vane (vane V0). Results show that performance of tapered vanes (V1 to V5), relative to the rectangular vane, (at distance of 2Ho) is reduced by 5.8%, 7.3%, 17.8%, 33% and 42.6% respectively; at distance of 4Ho the amount of reduction is 7.4%, 11.9%, 17%, 25.5% and 34.3% respectively. On the contrary, the efficiency of the tapered vanes is increased. The amount of increase at distance of 2Ho from the center of vanes V1 to V5 is 3.2%, 9%, 11%, 14% and 14.8% and at distance of 4Ho is 1.4%, 3.6%, 12.1%, 26.7% and 31.3% respectively. Therefore, if tapered vanes are used to reduce the local scour, big values for the distance between the vanes arrays (δs), according to the design criteria, are not recommended.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
1
no.
2020
1
11
http://jhyd.iha.ir/article_105497_c236468e4d8893bbbe52c96afdd90e07.pdf
dx.doi.org/10.30482/jhyd.2020.105497
Relation of Fractal Dimension and Sinuosity coefficient in Meandering River
Zahra
Ghadampour
Faculty member, Estahban University
author
mehrdad
kashkooli pour
Islamic Azad University, Estahban Branch
author
Mohammad Rafie
Rafiee
Assistant Professor, Deparment of water sciences & engineering, college of agriculture; Jahrom University,
author
text
article
2020
per
Meandering rivers, as prime examples of nature tendency to reach a regular form, have been the focus of many researchers. These rivers contain a series of alternating bends and curves, joined by short straight intervals across their plan and flow over gently sloping channels in which sedimentary load settles as point loads on the inner wall of the bend. River morphology studies the geometrical form of rivers in the plan, longitudinal profile (channel slope), cross section geometry and topography. Morphological analysis of meandering rivers is performed in two stages: determination of independent variables (flow and sedimentary discharge), calculation of geometrical parameters of river morphology through physical or experimental relationships. Such parameters are mostly investigated using Euclidean geometry. Sinuosity, for example, has been calculated with Euclidean attitude in Cartesian coordinates. Quantifying geometrical parameters of meandering rivers morphology in a Euclidean approach arises problems such as inaccuracy or complexity in calculation. Instead, Fractal geometry is widely used in river engineering in recent literature, due to its more detailed perspective of an object and its non-Euclidean properties. In Fractal Geometry, the mathematical space classified into one-, two-, and three-dimensional spaces on the basis of Euclidean geometry, is expressed as is fractal spaces in which the irregularities of the shapes are expressed in terms of fractal dimension (a real dimension and not necessarily a natural number). Single-fractal analyses are mainly carried out using methods such as box counting, variation, scale change, and Brownian motion methods, while multi-fractal analyses include methods such as spectral or wavelet analysis. Box counting is one of the fractal dimension calculation methods, widely used in rivers and shorelines. In this method, the set of points is meshed on a curve or a surface with squares (boxes) and the number of squares covering each part of the curve is calculated. Variation method also is one of the most accurate and popular method that can be used to calculate fractal dimension in various fields, however it is rarly used in river engineering up to now. In the present study, the fractal dimension in the Mond River was calculated over a 15-year period from 2000 to 2015. Mond river, with 685 km length is one of the most important rivers in southern Iran, originating in Fars province and flowing into the Persian Gulf through Bushehr province. Two fractal methods namely, box counting and variational methods were applied to calculate fractal dimensions in I) the whole river II) 3 longest bends III) 13 meanders. The results were then compared with those of sinusoidal coefficient. To calculate the fractal dimension by changes method, the area covered by different characteristic lengths is calculated in fixed intervals. Then, for different characteristic lengths the area covered by meander curve is calculated using code written in Matlab. The correlation coefficient values for the river coordinate data at each of the river intervals are obtained and compared in the bends. In the box counting method, different dimensions of the box and therefore different grids were considered. Then, in order to calculate the fractal dimension, the number of boxes involved was calculated for different widths using codes written in Matlab. Variations in the box width with the number of boxes in logarithmic scale are used to calculate the fractal dimension in the box counting method. The values for fractal dimension ranged between 1.01 to 1.09 and 1.0027 to 1.991 using box counting method and changes method, respectively. Additionally, the calculated fractal dimension values were compared with sinusoidal coefficients in three long meanders and fourteen bends of the river. Results indicated high correlations (R2 = 0.94-0.99) between fractal and sinusoidal coefficients in the meanders. The fractal dimension obtained in 2005 (1.05) was larger than those in other years. The largest fractal dimension was met in the second meander, with a value of 1.06. Highest sinusoidal coefficient was also found in the second meander indicating a direct relationship between these two parameters. There was a high correlation coefficient (close to 1) between the fractal dimension and the sinusoidal coefficient in the long meanders. A considerably high correlation coefficient of 0.96 was obtained between the parameters of the sinusoidal coefficient and the central angle calculated from the morphological analysis, which indicates a direct relationship between these parameters. The correlation coefficient of 0.85 between the fractal dimension parameters and the sinusoidal coefficient as well as the correlation coefficient of 0.86 between the fractal dimension parameters with the central angle indicates that the fractal dimension parameter is an appropriate indicator for expressing the changes and complexity of the meandering rivers.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
1
no.
2020
13
24
http://jhyd.iha.ir/article_105516_e07a73f3bc549b24ed5b4118e9950dc7.pdf
dx.doi.org/10.30482/jhyd.2020.207475.1419
Evaluation of different weighting methods to predict scour depth on grade control structures
Seyed Morteza
seyedian
Hydraulic department, Agriculture school
author
Somaye
Ghaznavi
Hydraulic department, Agriculture school, Gonbad kavoos university
author
Abolhasan
Fathabadi
Hydraulic department, Agriculture school, Gonbad kavoos university
author
Masoome
Farasati
Hydraulic department, Agriculture school, Gonbad kavoos university
author
text
article
2020
per
The scour depth estimation is of great importance. Researchers have provided many empirical relationships based on laboratory and field work, but so far no relationship has been found to be satisfactory in different situations. In this study, the accuracy of different experimental (individual) relationships was evaluated in two stages before and after the correctional correction. The results show that before and after the bias correction, the individual relations of the National Institute and Mason with the mean square error of 0.87 and 0.23 meters are the most accurate. The combination of individual relationships with combined methods models shows that the GRA and EWA methods with a mean square error of 0.25 and 0.23 meters were the most accurate among the direct methods in before and after bias correction stage. The error of the AICA and BICA indirect methods in before and after bias correction is similar to the best single relation and could not improve the results of the individual relationships. The results of local method (KNN) and artificial intelligence (LS-SVM) method before and after bias correction are equal and estimate scour depth more accurately than individual relations. Comparison of different combinational methods in before and after bias correction shows that individual relationships with maximum scour depth using different combinational methods can improve predictive accuracy.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
1
no.
2020
25
43
http://jhyd.iha.ir/article_105686_3718574cd2b2f9f62f06f632c30957b5.pdf
dx.doi.org/10.30482/jhyd.2020.176682.1377
Jet-breaker dimensions effect on drop manhole energy dissipation
Seyedreza
Hasheminejad
PhD Candidate, Hydraulics Structures, Department of Civil Engineering, Faculty of Engineering, Shahid Bahonar University of Kerman, Kerman, Iran
author
Mohammad-Javad
Khanjani
Department of Civil Engineering, Faculty of Engineering, Shahid Bahonar University of Kerman, Kerman, Iran
author
Gholamabbas
Barani
Department of Civil Engineering, Faculty of Engineering, Shahid Bahonar University of Kerman, Kerman, Iran
author
text
article
2020
per
Drop manholes are employed to dissipate energy in steep routes of sewer and drainage systems. The jet-breaker could be used to increase energy dissipation and hydraulic performance of them under Regime R2 and studying the effects of the jet-breaker length, width, sagitta, angle, as well as the inlet pipe filling ratio on drop energy dissipation were among the aims of this research. The modern statistical Design of Experiment (DoE) methodology and dimensional analysis were utilized to design the experiments according to the 2^5 full factorial design. Seventeen jet-breakers were examined and about 350 tests were performed. The statistical analysis of the results revealed that the response variable was significantly improved when the inlet pipe filling ratio was 80% and jet-breaker sagitta was equal to zero, and its angle was at 70˚. Also, effects of jet-breaker length and width ratios were insignificant. Moreover, The use of DoE resulted in straightforward data analysis and unbiased concluding.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
1
no.
2020
45
59
http://jhyd.iha.ir/article_106050_880dfb9820f2cce98dd07ab3bb72c262.pdf
dx.doi.org/10.30482/jhyd.2019.126057.1291
Effect of using single square pile at upstream of the orifice on pressurized flushing
peyman
peykani
M.Sc. Graduate, Faculty of Water Sciences Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran
author
mehdi
daryaee
Assistant Professor, Faculty of Water Sciences Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran
author
Seyed Mahmood
Kashefipour
Hydraulic Structures Department-Shahid Chamran University of Ahvaz- Ahvaz -Iran
author
text
article
2020
per
1- Introduction In pressurized flushing, the removing of sediments is performed under a constant head above the intake. Given the low pressurized flushing efficiency, it is necessary to provide solutions to increase its efficiency. Few studies have been carried out on increasing the efficiency, so far. By applying a group of cylindrical columns in the upstream of the outlet, Madadi et al. (2016) increased the pressurized flushing up to 250 percent, comparing to the control condition. Also, by installing a semi-cylindrical structure in the upstream of the outlet, Madadi et al. (2017) were able to increase the pressurized flushing up to percent, comparing to the control condition. By proposing new methods, this research tries to study the effect of using a single square pile at the upstream of the outlet on the dimensions and volume of the flushing cone in pressurized flushing. 2- Materials and Methods To perform the experiments, three flow rates (Q) of 4.17, 6.39 and 8.34 l/s were considered. In all the experiments, the sediments level (Hs) was considered constant and leveled at the lower edge of the outlet. The water level in the flume to the center of the outlet (Hw) was considered to be 52 centimeters in all the experiments. Also, the output outlet diameter (Do) was considered to be 7 centimeters. The sediment grading used in all the experiments was constant (d50 = 0.5 mm). The experiment duration was considered to be 150 minutes in all the experiments. In order to study the effect of the square pile size (Dp) on the dimensions and efficiency of the pressurized flushing cone, four side sizes of 1.4, 2.1, 2.8 and 3.5 cm were used. The pile installation distance from the outlet (Lp) was considered to be 4.9 cm, through conducting consecutive. In order to study the effect of the pile installation distance (Lp), the pile that had the highest influence of the flushing was installed in different distances from the outlet upstream. These distances were defined as a ratio of the outlet diameter and equal to Lp/Do = 0.7, 1.2, 1.7, 2.2. Subsequently, the desired pile was installed in the determined distances from the upstream of the outlet and experiment stages were carried out. 3- Results and Discussion The results from the experiments related to the installation of the piles suggested that the presence of square pile has a considerable influence in the increasing of the flushing cone volume, so that for the flow rate of 4.17 l/s and installation of the pile with DP =3.5 cm and LP=4.9, the flushing cone volume had a relative increase of 362 percent, comparing to the control condition. Also, in the same condition, comparing to the control condition, the depth, length and width of the flushing cone had a 120, 57 and 42 percent decrease, respectively. Due to the collision of the current lines with the upstream face of the pile when a pile is installed in In front of the flow with sedimentary bed, a series of downward currents are formed, that are called horseshoe vortices, that led to scour phenomenon around the pile. Also, due to the separation of the stream lines in the downstream of the pile, a low-pressure region is formed that leads to the rise and movement of the sediments. Installing the column in the upstream of the outlet causes the eroded sediments due to the presence of a pile exit the outlet in addition to the sediments due to the flushing and the efficiency of the flushing increases. The main influence of installing the pile in all the flow rates is related to the pile relative size of Dp/Do = 0.5. This could be attributed to the fact that by the increase in the size of the pile, more downwards vortices are formed in the upstream of the pile. Also, separation of current lines in this condition is higher and low-pressure region is formed with a larger area in the downstream. Hence, more sediments rise from the upstream of the outlet and exit it. In order to study the influence of pile installation distance on the flushing volume, sediment with the size of Dp/Do = 0.5 which had the highest influence on the abovementioned parameters, was installed at four relative distances of Lp/Do = 0.7, 1.2, 1.7, 2.2 from the upstream of the outlet. By the increasing in the pile installation distance from the outlet upstream, the flushing cone volume decrease an at Lp/Do = 2.2, the influence of pile installation is almost diminished and the cone volume is almost equal to the control condition. It could be said that by the increasing in the distance of the pile from the outlet and the decreasing in the velocity of current collision with the pile, the downward currents power in the upstream of the pile and vortices rise in the downstream decrease and as a result, the influence of the presence of the pile on the increase of the flushing cone decreases. 4- Conclusion Studying the influence of installing square pile on the upstream of the outlet on the pressurized flushing efficiency showed that presence of one pile leads to an increasing in the flushing efficiency. The highest influence of pile installation was related to the largest pile (Dp/Do = 0.5), so that in this condition, the flushing cone volume had 362 percent increasing, comparing to the control condition. In other words, with the same rate of water discharge from the outlet in the condition without installing the pile, the sediment discharge volume could be considerably increased by installing a pile. 5- Keyword Flushing, pile, Flushing cone, Orifice.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
1
no.
2020
61
74
http://jhyd.iha.ir/article_106322_c20a1ddec4a52b831155ea4a8a041749.pdf
dx.doi.org/10.30482/jhyd.2020.210588.1424
Analysis of Sequent Depth Ratio and Length of Sudden Expanding Hydraulic Jump under Symmetrical and Asymmetrical Developments
Hossein
Khalili Shayan
Ph.D. Graduated, Irrigation and Reclamation Eng. Dept., University College of Agriculture and Natural Resources, University of Tehran
author
Javad
Farhoudi
Professor, Irrigation and Reclamation Eng. Dept., University College of Agriculture and Natural Resources, University of Tehran, P.O. Box 4111, Karaj, Iran, 31587-77871.
author
Alireza
Vatankhah
Associate Professor, Irrigation and Reclamation Eng. Dept., University College of Agriculture and Natural Resources, University of Tehran
author
text
article
2020
per
Introduction In practical applications, for instance, at the downstream of hydraulic structures, in some cases the width of the basin may be larger than the upstream supercritical flow (sudden expansion in flow section). In such cases, an expanding hydraulic jump with symmetrical or asymmetrical shape will be developed at the downstream. Under the design of three parallel gates, the operation of the side or middle gate can be lead to the asymmetrical or symmetrical hydraulic jump, respectively. According to the position of jump toe, expanding hydraulic jump can be classified into four types. The present study focuses on a T-shaped hydraulic jump which the toe is established at the beginning of the divergence section. Most of the previous studies are related to the symmetrical expanding hydraulic jump. In this case, the downstream diverging channel is symmetric on the central axis of the channel. However, a systematic study investigating the effect of symmetry and asymmetry on the expanding hydraulic jump was not found in the literature. In this study, using the momentum principle, some theoretical equations were derived to determine the sequent depths ratio of symmetrical and asymmetrical expanding hydraulic jump. Also, some regression relations were proposed to estimate the length of expanding hydraulic jump. The new proposed equations were also extended for the presence of a sill. The equations were calibrated using available experimental data from this study and the literature. This research also considered the characteristics of expanding hydraulic jump under the symmetrical and asymmetrical operation of parallel gates. Methodology To calibrate the new proposed relations and investigate the effects of different parameters on the expanding hydraulic jump characteristics, two experimental data sets were used. In addition to the data set from Bremen (1990), the experimental data from the present study were used. The data were collected from a hydraulic model of three parallel radial gates for operating the side or middle gate which corresponds with the asymmetrical or symmetrical expanding hydraulic jump, respectively. The experiments provided a wide range of different parameters as the approaching Froude number, hydraulic jump length, sequent depths ratio, divergence ratio, sill height and relative length of gate separator wall. Results and discussion Equation (4) was developed to determine the ratio of the sequent depths of expanding hydraulic jump based on the Momentum equation. For the presence of a sill, a combination of Equations (4), (7) and (8) can be used to calculate the ratio of sequent depths under the asymmetric and symmetric developments, respectively. Determining the ratio of the sequent depths requires the calculation of the adjacent water depths of the closed gates. For this purpose, in addition to developing the regression equation (Equation 13), Equation (12) was proposed which based on the calculation of the hydraulic jump profile. It was observed that under the calibration range, the regression equation is more accurate. However, Equation (12) is recommended for the range outside of the experimental observations. The results showed that: As the divergence ratio increases, the ratio of sequent depths approaches to the classic hydraulic jump. By decreasing the relative length of the gate separator wall and decreasing the width of the gate on the downstream channel width, the relative depth at the side gate and consequently the ratio of the sequent depths will decrease. For the lower length of separator wall and under operation of the middle gate, more lengths are needed to develop the jump than the side gate. However, as the length of the separator wall increases, the length and sequent depth of hydraulic jump due to the side gate increases on the middle gate. In the presence of a sill, the relative length of hydraulic jump decreases and the ratio of secondary depths increases. It was observed that the hydraulic jump due to the operation of the middle gate leans toward the left or right side of the channel due to oscillatory behavior. Under operating the middle gate and in the absence of a sill, an asymmetric hydraulic jump is formed in the channel face when the length of the separator wall is less than 38% of the classical hydraulic jump length. For the presence of a sill, the minimum length of the separator wall decreases to about 26%. By decreasing the initial depth of the hydraulic jump on the width of the gate and converting the output jet into a linear jet, the relative development length will increase. As the sill height increases, the difference in the depths attached to the side gates will decrease and the hydraulic jump will develop more symmetrically. As the relative height of the sill decreases, the minimum length of the separator wall to form a symmetrical hydraulic jump in the flanks, increases. Conclusion This research developed a set of theoretical and regression relationships for estimating the length and sequent depth ratio of expanding hydraulic jump. Moreover, the effects of sill height, divergence ratio and the length of the gate separator wall, were investigated. This study compares the effects of side and middle gate operations based on the variation of jump length and sequent depth ratio. The results can be used as a guide for the hydraulic structures operators to reduce the asymmetric severity of the expanding hydraulic jump and achieve the complete development under the minimum length.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
1
no.
2020
75
95
http://jhyd.iha.ir/article_106323_85f3ca881a0b46f4902a315a870a7cdb.pdf
dx.doi.org/10.30482/jhyd.2020.208837.1420
Flow behavior in Non-Prismatic Convergent Compound Channel with Submerged Vegetation on Floodplains
Fatemeh
Vojoudi Mehrabani
PhD Candidate, Department of Civil Eng., Faculty of Civil Eng., Urmia University, Urmia
author
Mirali
Mohammadi
Associate Professor, Hydraulics & River Eng. Mechanics, Department of Civil Eng., Urmia University, Urmia
author
Seyed Ali
Ayyoubzadeh
Professor, Water Structures Engineering Department, Tarbiat Modares University, Tehran
author
João
Fernandes
Civil Eng. PhD, Hydraulics and Environment Department, National Laboratory of Civil Engineering, Lisbon, Portugal
author
Rui
Ferreira
Associate Professor, CERIS, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal
author
text
article
2020
per
Flow behavior in Non-Prismatic Convergent Compound Channel with Submerged Vegetation on Floodplains Introduction Vegetation in compound channels by increasing factors such as roughness in the floodplains rather than main channel, velocity difference and momentum exchange between the sub sections, leads the transverse velocity gradient and apparent shear stress of interface to increase. In natural rivers by changing the cross section, uniform flow converts to non-uniform. In prismatic channels, shear stress in the interface between main channel and floodplains, influences the transfer capacity and velocity distribution pattern significantly. This effect in non-prismatic channels, due to the extra momentum exchange between the sub sections is more intense. In such condition identifying the flow hydraulic is very complex. Although forming the vegetated and non-prismatic floodplains at the same time in natural rivers is highly probable, but there are no specialized studies yet to investigate the hydraulic of flow in such conditions. Therefore in the present study, experimental measurements were conducted in a compound channel with non-prismatic and vegetated floodplains simultaneously and flow behavior is investigated on it. Methodology The experiments were conducted in a 10 m long, 2 m wide compound channel located at the National Laboratory for Civil Engineering (LNEC) in Lisbon, Portugal. The channel cross section consists of two equal rectangular ﬂoodplains (ﬂoodplain width Bfp=0.7 m) and one trapezoidal main channel (bank full height, hb=0.1 m, bottom width bmc = 0.4 m, bank full width Bmc = 0.6 m and side slope of 45°, sy= 1). The channel bed is made of polished concrete and its longitudinal slope is S0= 0.0011 m/m. The vegetated floodplains were obtained by covering their bottoms with a 5 mm hight synthetic grass. For the polished concrete, n= 0.0092 m-1/3s and ks=0.15 mm and for the synthetic grass, n=0.0172 m-1/3s and ks=6.8 mm. Measurements were performed for relative depths of 0.21 and 0.31. The experiments in the non-prismatic channel performed at two convergent angles of floodplains (θ=7.25◦ and θ=11.3◦). In this cases, the mentioned relative depths were set up in the middle sections of convergences by changing the downstream tailgate. The velocity measurements performed for Entrance, Middle and End sections of convergent angles. Results and discussion high velocity distribution pattern’s gradients are observed in non-prismatic rather than prismatic channel for a given relative depths. Comparisons between similar sections indicates by increasing relative depth, the interaction intensity through the main channel and floodplain decreases. Because, presence of vegetation on the floodplain leads to channel transfer capacity decrease and in high values of relative depth, this effect decreases. Except the areas close to wall and interface, the flow on floodplain is two-dimensional while in main channel and especially in low relative depths is three-dimensional. This issue has also been affected by different convergence angles. The maximum velocity generally occurs near the outer wall of the main channel. But, by increasing the relative depth, position of the maximum velocity moves to the floodplain. In the lower relative depth, in vicinity of interface, a bulge is visible in isovel lines that is already reported in previous works. Due to the mass transfer from the floodplain towards the main channel, this bulge occurred more intensively in the middle sections in both the convergent angels. In non-prismatic channel, for all the flow cases, at the interface, the intensity of the secondary flows is more apparent and in the down part main channel flow, a vortex is formed that by increasing the relative depth from 0.21 to 0.31 and convergent angels from 7.25◦ to 11.3◦, moves from the outer wall of the main channel towards the floodplain. Also at the beginning of the floodplain, one vortex is formed that becomes more apparent by increasing the convergence angles. Due to converging floodplains, in the upper layers, a transverse current is directed from the floodplains to the main channel. This transverse current enters the main channel from both sides and, due to symmetry of flow, plunges to the channel bed and as a result, two helical secondary flows are generated in the main channel, rotating in the channel length which is very important in terms of sediment and pollutant transport. By increasing relative depth, velocity gradient between the main channel and floodplains decreases. Conclusion In present study, using an experimental model, flow behavior in a prismatic and non-prismatic compound channel is investigated. Non-prismatic channel consists of two convergence angles; 7.25° and 11.3°. All the experiments are conducted at two relative depths of 0.21 and 0.31. In order to investigate vegetation cover effects, floodplains are covered with synthetic grass and a vecterino (ADV) is used to measure the fluctuations of instantaneous flow velocity. Variations in the streamwise velocity distribution, secondary currents and Reynolds stresses based on proportions of vegetation and non-prismaticity in the flow hydraulic are investigated. Results show for high relative depth, by increasing convergent angles, the floodplains are less involved in discharge carrying and transferring. The maximum velocity values which occur at the main channel center, by increseang the relative depth and extending secondary currents, towards to the floodplains. By increasing the convergent angle, the roughness values in the main channel and floodplains increases. Distribution of flow mean kinetic energy shows that by increasing relative depth, its values in the middle section decreases for both the convergent angles. Key words: Non-prismatic, Compound Channel, Vegetation, Convergent floodplains
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
1
no.
2020
97
111
http://jhyd.iha.ir/article_106434_422846fe15a6ce475c12878189409327.pdf
dx.doi.org/10.30482/jhyd.2020.219798.1442
Laboratory investigation of flow pattern and scour around bridge
with netted unsymmetrical collar
Narges
Raeisi
Hydraulic structures Dept. Faculty of water sciences Engineering, Shahid Chamran University, Ahvaz, IRAN
author
Mehdi
Ghomeshi
Hydraulic structures Dept. Faculty of water sciences Engineering, Shahid Chamran University, Ahvaz, IRAN
author
text
article
2020
per
Abstract – Introduction: Investigation of the scour phenomenon is very important. If it is not possible to control the scour around structures such as bridges or bridge supports. Includes irreparable damages. The scour around the bridge piers causes to instability of them, and without applying an appropriate solution, it eventually leads to demolition of the structure. Therefore, study on the mechanism of the occurrence of the scour and the effective parameters on amount of scour are important. So, already various studies have been done on the mechanism of scour around hydraulic structures especially bridges. In the field of scour around bridges, researches are more focused on scour of piers, but no effective results were obtained on the scour phenomenon around the piers. Bed erosion and transport of sand material from its location by a flow called scour. Local scour is a special type of scour that may occur around the bridge piers or bridge abutments. This type of scour is main reason of many bridge failures in the word. Because of this, supply of methods to control and reduce these phenomena is important. One of the methods of scour reduction around the bridge pier or abutment is installation a thin flat rigid plate (collar) on the pier or abutment. There is no comprehensive study to use this method for protecting the pier against scour so far. Therefore, this topic was considered for this research. Methodology: This study was performed in the flume with a length of 6 m, a width of 0.72 m, a height of 0.6 m and constant bed slope equal to 0 m in Hydraulic Laboratory of Shahid Chamran University. The bed materials were non cohesive sediment with an average diameter equal to 0.73 mm and geometric standard deviation of 1.22. As well as Plexiglas plates with a thickness of 3 mm was used to build the collar. In this study, 27 tests were performed to measured, sediment movement and determine the two-dimensional velocity components. In each section, a series of tests were performed as a control experiment. The tests of sediment were done in the 3 of flow rate equal to 25, 30 and 35 liters per second. In this condition, Froude Number was equal to 0.26, 0.32 and 0.37 respectively. The 3 unsymmetrical collars with different dimensions in four three Numbers were tested. To do so first general non dimensional relationship was developed. Then series of experimental tests were conducted in a physical model using three different Zc (0, 0.25 and 0.5 high). Results and discussion: Dimensionless plots were obtained regarding effect of dimension of both collars on scour reduction around bridge pier. Different positions of installation of collar were investigated. Dimensionless plots were obtained for determination of collar performance in various heights. Different positions of installation of collar were investigated. Dimensionless plots were obtained for determination of collar performance in various heights. In this section, one of the collars had the best performance, and it was called optimum collar. Local scour around a bridge pier results from the flow and pier interaction and separation of the flow at the sides of the pier. One of the methods used as a local scour countermeasure at bridge piers is collar. Then, we have been check about netted unsymmetrical collar. Also two tests were performed to determine three-dimensional components of velocity in different depth. The results show that the performance of collar in unsymmetrical collar improve by increasing its dimension. The collars located on the bed performance are better than the one located above the bed. Conclusion: The results show that the collars have important role in retardation of scour development. In section of determination of three-dimensional components of velocity, the results show that the collar act as a shield against down flow. It can control the horseshoe scour around the pier. Literature review shows that cylinders forms, the maximum scour depth occurs in the case of cylindrical pier. Therefore, in this research cylindrical shape for circular bridge pier was selected and effects of Froude number were investigated on scour development. Result shows, that increasing froude numbers will increase the amount scour. Also, as the height of the collar mounting height is increased, the scour depth and the width of the scour hole increase. Following this research, three-dimensional components of velocities were determined with adv. velocimetry and then use for drawing flow pattern. Also result confirms that, maximum velocity occurs near the bed, because the down flow developed the significant secondary currents, and down flow and generated vortex are effective parameters on bridge scour. Keywords: Flow pattern, Laboratory model, Scour, Bridge pier.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
1
no.
2020
113
128
http://jhyd.iha.ir/article_106638_604fd256e336673383756665eaad8e95.pdf
dx.doi.org/10.30482/jhyd.2020.219351.1441
Declining Separation Zone Dimensions at 90 ° Lateral Intakes by Enhancement of Roughness Coefficient and Drop Implementation
Maryam
Bagheri
M.Sc student, Dept. of Water Sciences Engineering, College of Agriculture, Shiraz University
author
Seyed Mohammad Ali
Zomorrodian
Associate Professor, Dept. of Water Engineering, College of Agriculture, Shiraz University
author
Masih
Zolghadr
Assistant Professor, Dept. of Water Sciences Engineering, College of Agriculture, Jahrom University
author
Jahanshir
Mohammadzadeh-Habili
Assistant Professor, Dept. of Water Sciences Engineering, College of Agriculture, Shiraz University
author
text
article
2020
per
Introduction Studying the flow pattern at lateral intakes where separation occurs is a critical issue. The flow rate and sediment trap is highly dependent on the flow structure in this area. Flow separation occurs due to the detachment of stream lines from the channel side walls. It creates a secondary flow similar to what happens at river bends. Flow separation, reduces the turnout efficiency by decreasing the flow effective area at lateral intakes. It also creates a region with horizontal vortices where is prone to sedimentation. Hence, application of methods to reduce the separation zone dimensions is of important significance. Different techniques have been introduced in the literature such as installation of submerged vanes, deployment of different intake angles to main channel, construction of the entrance part as a part of circles with various radiuses, etc. This study examines the effect of roughness coefficient and drop implementation at the entrance of a 90-degree lateral intake on the dimensions of the separation zone. As far as the knowledge of the authors show, these two variables have not ever been studied as methods to decrease the separation zone dimensions and enhancing the turnout efficiency. Methodology In order to investigate the effect of roughness coefficient and drop implementation on the separation zone dimensions, four different discharges (16, 18, 21, 23 l/s) in subcritical conditions, seven manning roughness coefficients (0.009, 0.011, 0.017, 0.023, 0.030, 0.032) and 3 invert elevation differences between the main channel and lateral intake (0, 5 and 10 cm) at the entrance of the intake were considered. Totally 84 tests were performed in a concrete flume with 15 m length 0.5 m width and 0.4 m depth. The intake structure was made at a 90-degree angle to the main channel with 0.35 m width. The Manning roughness coefficient values were selected based on available and also feasible value for real condition, so that 0.009 is equivalent to galvanized sheet roughness and selected for the baseline tests. 0.011 is for cement with neat surface, 0.017 and 0.023 are for unfinished and gunite concrete respectively. 0.030 and 0.032 values are for concrete on irregular excavated rock. (Chow, 1959). The roughness coefficients were created by gluing sediment particles on a thin galvanized sheet which was installed at the upstream side of the lateral intake. The values of roughness coefficients were calculated based on Srickler’s formula. For this purpose, some uniformly graded sediment samples were prepared and the manning roughness coefficient of each sample was determined with respect to D50 value pasted into the Strickler’s relation. All the experiments were recorded and photographs were taken severally during the experiment and after steady flow conditions were established. The photos were then imported to AutoCAD to measure the separation zone dimensions. The velocity values were also recorded by a one-dimensional velocity meter at 15 cm distance from the intake entrance and in transverse direction (perpendicular to the flow direction). Results and Discussion Negative velocity values were recorded in the separation zone indicating dominant secondary currents at the intake entrance. The velocities were intensified by moving toward the intake midway showing that the effective area is scaled down. The velocity values were almost equal to zero near the side walls as expected. Results were presented as dimensionless separation zone area (ratio of the separation zone area to intake area). Analysis shows that by increasing roughness coefficient alone, separating zone dimensions reduce up to 38%. This technique requires minimal changes in intake geometry and is definitely an inexpensive method to be applied for intakes under operation. Besides roughness coefficient studied were quite accessible. Implementation of drop can decline this area respecting the roughness coefficient value differently. Naturally there is an invert elevation difference between the feeding canal and the areas to be irrigated. This idea was developed base on this issue. A minor part of this difference can be compensated at the intake entrance. This method increases the discharge ratio (ratio of intake to main channel discharge). The results are compatible with literature. Some other researchers reported that intensifying the discharge ratio can scale down the separation zone dimensions (Rumamurty et al., 2007. Keshavarzi and Karami Moghaddam, 2007). However, these scientists employed other methods to enhance the discharge ratio. Employing both techniques simultaneously can decrement the separation zone dimensions up to 41%. A comparison between the new methods introduced in this paper and traditional methods such as installation of submerged vanes, and changing the inlet geometry (angle, radius) was performed. The comparison shows that the new techniques can be highly influential and still practical. Conclusion This study introduces practical and still easy and costly beneficial methods for enhancing intake efficiency by declining the separation zone dimensions. Increasing roughness coefficient and implementation of inlet drop were considered as remedied for reduction separations zone dimensions. Results showed that enhancing roughness coefficient can decline the separation zone dimensions up to 38% while drop implementation effect can scale down this area differently based on roughness coefficient used. Combining both methods can descend the separation zone dimensions up to 41%. It is proposed to investigate the effect of roughness and drop implementation on sedimentation pattern at lateral intakes for further researches.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
1
no.
2020
129
141
http://jhyd.iha.ir/article_107043_e7a9bc335b8fc4a5e2a94228e07fcbaa.pdf
dx.doi.org/10.30482/jhyd.2020.214381.1432
Evaluation of well-balanced form of Weighted Average Flux scheme for simulation of flow in open channels
Ali
Eslamlooian
Department of Civil and Environmental Engineering, Shiraz University
author
Seyed Mehrab
Amiri
Department of Civil and Environmental Engineering, Shiraz University
author
text
article
2020
per
Water is the most strategic liquid in the world. The life of all humankind and animals and plants are relying on the water. The water should supply to the location of demands. One of the most common water transmission ways is open channels. If a sudden change occurs in the channel section, it can affect the whole water flow in the channel. These changes can happen naturally, like aggregation of sediments in a section of the channel. Moreover, the changes may build by humans, like sharp and broad-crested weirs. Thus, it is necessary to simulate open-channel flows to predict possible changes in water surface profile and velocity. Basically, researchers follow three approaches to simulate water flows: the analytic, the experimental, and the numerical approaches. Analytical approach for solving the flow equations is not sufficient due to the complexity and nonlinearity of the equations so there are several restrictions in the modeling. On the other hand, experimental approach is time consuming and expensive. Since the high-performance computers have been developed, researchers attracted to numerical approaches. There are different numerical solutions which are used to solve the water flow equations such as Finite Difference Method, Finite Element Method, Finite Volume Method, etc. The Finite Volume Method is one of the most applicable methods in several computational aspects of engineering, such as computational fluid dynamics and heat transfer problems. In this method, it is necessary to have a strong approximation of numerical flux term for solving flow equations. The Riemann solver provides a reliable approximation for the numerical flux term. The Riemann problem for a set of PDEs is an initial value problem for such PDEs in which the initial condition has a special form. In order to apply numerical solutions, one can use the exact Riemann solver or approximate Riemann solver. The exact Riemann solver uses Newton-Raphson method that takes noticeable cost in time and money and the results rely on the first guess of Newton-Raphson. Therefore, researchers prefer the approximate Riemann solvers such as Harten Lax van Leer (HLL) scheme, Harten Lax van Leer Constant (HLLC) scheme and Weighted Average Flux (WAF) scheme that have acceptable results and running time. WAF scheme can be categorized as a branch of Finite volume method. The scheme was first applied to the Euler equation. This scheme is one of the approximation solution (besides HLL and HLLC methods) of the Riemann problem. Then, Toro used the WAF scheme to simulate two-dimensional shallow water equations. Subsequently, WAF has been utilized to simulate flow over different kinds of open channels. Although the scheme shows reasonable results, it is noticeable that the numerical scheme is not well-balanced essentially. Thus, a well-balanced WAF scheme should be developed to simulate flow in open channels accurately without non-physical fluctuations in flow surface. The aim of this research is using the ability of the WAF scheme to simulate shallow water and applying some consideration on the scheme to prevent non-physical fluctuations in water surfaces. In this paper, a well-balanced form of WAF which is combined with HLL for estimating flux has been employed to simulate one-dimensional flow open channels. MINMOD as an effective slope limiter has been used in order to prevent non-physical oscillations. Moreover, Runge-Kutta has been employed as the time integration method to renew depths and velocities. Several different cases have been used to show that the scheme has an excellent shock-capturing ability and can handle the wet and dry condition of channel bed. Importantly, the linear reconstruction for the scheme has been applied to have second-order accuracy and to prevent the negative depth effect on computations. The scheme is shown to be well-balanced by evaluating stationary solutions at steady state conditions. Besides, the capability and accuracy of the scheme are verified by the comparison of scheme numerical results with literature analytical and experimental results. The numerical results have shown that the scheme can satisfy the continuity equation and prevent negative depth. For real applications of the scheme, the simulations of flow over sharp changes and dam-break show that RMSEs are in acceptable ranges and there is no non-physical fluctuations on the water surface profile. Simulating dam break on wet and dry beds, show that the scheme is capable in shock capturing as well as solving wetting-drying problems. In addition, flow with wide range of Froude number over different forms of broad crested weirs, have been employed to verify the robustness, accuracy and stability of the scheme. Hence all of these results prove that the presented well-balanced scheme is able to simulate different cases of shallow water equation examples accurately.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
1
no.
2020
143
155
http://jhyd.iha.ir/article_107044_19036827ba2c156296cad1aff7543dbd.pdf
dx.doi.org/10.30482/jhyd.2020.219579.1437