Elham Roshani; ali hossienzade dalir; Davoud Farsadi; farzin salmasi
Abstract
Introduction: In alluvial streams, water flow affects the sediment and transports them to the downstream constantly. In the meantime, bed forms will be created on stream bed with various dimensions and in different conditions. In this paper experiments have been done to study the influences of width ...
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Introduction: In alluvial streams, water flow affects the sediment and transports them to the downstream constantly. In the meantime, bed forms will be created on stream bed with various dimensions and in different conditions. In this paper experiments have been done to study the influences of width reduced transitions on the height of ripple forms. These transitions are made with different angel 5, 10 and 15 degrees. Based on Van Rijn (7), when the sediment particles are smaller than 500 μm, if the flow velocity exceeds about 10 to 20 percent of critical velocity for starting the particle movement, small ripples grow on the bed surface. Ripple profiles have an asymmetric shape which has steep slope at the upstream and mild slope at the downstream. If the particles are bigger, flow velocity should be higher too in order to create taller ripples and in this situation a variety of bed form height and length will occur. There is a lot of research associated to bed form formation in alluvial beds like Van Rijn (4 and 7), Karim (2009), Omid and et al (2010), Chegini and Pender (2012) and Esmaili and et al (2009). But in none of them a width reduced transition has applied. The mail part of this research is specified to the effects of width reduced transitions on the dimension of ripple bed form.
Methods and Materials: Experiments were done in the hydraulic laboratory of water engineering faculty of Tabriz University. The flume had a 6 m long, 50 cm height and 50 cm wide flume. The α (angle of transition at the beginning) was different. The sediment particles had D_50=0.86 mm and ρ_s=2300gr.〖cm〗^(-3). The sediment flow was directly injected to the main flow from the upstream carefully. Water level was measured with scales installed on the glass wall of the flume and sediments were collected with the help of a sand trap located at the end of the flume. Experiments were classified in three discharges of 10, 12 and 14 L.S-1and in 0, 0.006, 0.009, 0.012 and 0.015 slopes of the channel. π Buckingham method was used to obtain a dimensionless relationship such as ∆/y=f(F_r,α). In which the ∆ is the bed form height, y is the flow depth, Fr is the Froud number and the α is the transition angle at the beginning part of it. To compare the situation of having transitions with the absence of any transition, was studied as a witness type. Totally, 136 experiments were done.
Results and Discussion:The changes in the bed form height based on different Froud Numbers, are exhibited in a series of curves. Basically, transitions which shortened the flow width, in low discharges, the initial walls of these transitions act like a barrier and absorb a significant amount of flow intensity. Therefore, when there is no such a transition, it is accepted that the flow has more freedom and as a result bed form height will grow bigger. Naturally, if the reduction of the channel width was milder, the barrier effect on the flow would be smaller slight. In study of bed form shaping and its height, in low discharges (e. 10 L.S-1) the flow intensity is not strong enough to conquer the barrier role of the transitions and however with increasing angle of the transition, the bed forms height in the transition area decreased. For the 12 L.S-1discharge the flow intensity is more and the power of entering flow to the transition is higher and ripples with taller height exist. But the point is that the 12 lit.s^(-1) is still a transition stage, it means that when the discharge reaches to 14 L.S-1, the bed form height has increased about 10 to 12 percent, comparing with no transitions. Another important issue is that, in any situation, transitions with α=15° have a strong barrier role against the flow and they always reduce the bed form height.
Conclusions: It can conclude that width reduced transitions can decrease scours slightly and therefore sediment transitions was reduced about 15 to 20 percent, compared with no transitions installed on the flume. The results show that if the discharge exceeds 14 L.S-1 or if steeper angles for the initial part of the transitions are used, the transition loses the barrier role and even they increases turbulences at the beginning and much more sediment would pass through the transition area due to higher velocities.
Mohammad Reza Nikpour; Davoud Farsadi
Abstract
Formation of shock waves has an important role in supercritical flows studies. These waves are often occurring during passage of supercritical flow in the non-prismatic channels. In the present study, the effect of length and convergence of contraction wall of open-channel was investigated on hydraulic ...
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Formation of shock waves has an important role in supercritical flows studies. These waves are often occurring during passage of supercritical flow in the non-prismatic channels. In the present study, the effect of length and convergence of contraction wall of open-channel was investigated on hydraulic parameters of shock waves using experimental model. For achieving to this goal, values of depth and instantaneous velocity were measured in various points of shock waves observed in contractions for four Froude Numbers. The results showed that for 63% decreasing the length of contraction, the values of maximum velocity and waves height averagely increased to the amount of 23.6% and 2.77×102%, respectively. Also for the fixed length of contraction, by changing the form of walls from straight-wall to convex-wall the mentioned values averagely decreased to 6.9% and 35.2%, respectively.
P. Varjavand; A. Hosseinzadeh Dalir; M. Ghomeshi; Davoud Farsadi
Abstract
Instantaneous velocity fluctuations are very important insuspended sediment load transportation. In this study experiments were performed toinvestigate the effects of artificial bed roughness on the instantaneous velocity fluctuations of saline density currents. Conic and cylindrical shapes of roughness ...
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Instantaneous velocity fluctuations are very important insuspended sediment load transportation. In this study experiments were performed toinvestigate the effects of artificial bed roughness on the instantaneous velocity fluctuations of saline density currents. Conic and cylindrical shapes of roughness with three heights were used. Velocity profiles were measured with an acoustic profiler velocity meter. Velocity and concentrationprofiles were measured in 3 and 4 cross-sections, respectively. The results show that increasing inrelative roughness height has a little impact on instantaneous velocity fluctuations in the entrainment region of the body of current. Also results of theinstantaneous velocity fluctuations profile on the rough bed show that turbulence intensity at the boundary of the ambient fluid and body of the current for cylindrical and conic roughness were 48 and 32 percent of shear velocity, respectively.
P. Parsamehr; Davoud Farsadi; A. Hosseinzadeh Dalir
Abstract
Hydraulic jump plays a significant role in dissipation of kinetic energy downstream of hydraulic structures in a stilling basin. In the present research, hydraulic jump characteristics on roughened bed with half cylindrical shape bars and rectangular bed sill on two adverse slopes of 1 and 1.5 % and ...
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Hydraulic jump plays a significant role in dissipation of kinetic energy downstream of hydraulic structures in a stilling basin. In the present research, hydraulic jump characteristics on roughened bed with half cylindrical shape bars and rectangular bed sill on two adverse slopes of 1 and 1.5 % and horizontal bed were investigated. In total 338 experiments were performed for Froude numbers ranging from 4.6 to 7.4. The results indicated that the length of the hydraulic jump on the adverse slope of 1.5% decreased 46% with sill and 49% on rough bed. Also maximum reduction of sequent depth on the adverse slope of 1.5 % with sill and on rough bed was 24.4% and 44%, respectively, compared with the classic jump. Furthermore, application of a continuous sill on adverse slope to stabilize hydraulic jump with decreasing its length will be economical.
F. Sahebi Vayghan; Davoud Farsadi; M. Esmaeili Varaki; A. Abbaspour; Ali hosseinzadeh
Abstract
Stilling basins are one of the most common structures for energy dissipation of flow with high velocity and among different sections and types of these basins, diverging basins have better performance and lower constructional costs. In this research, the feasibility of 3D numerical simulation of diverging ...
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Stilling basins are one of the most common structures for energy dissipation of flow with high velocity and among different sections and types of these basins, diverging basins have better performance and lower constructional costs. In this research, the feasibility of 3D numerical simulation of diverging hydraulic jump in rectangular basins was investigated using standard and RNG turbulence models using Fluent software. The free surface was determined using the VOF method. The outputs of numerical model in comparison with the results of physical model of hydraulic jump in diverging rectangular basins with diverging angels of and showed that the standard turbulence model evaluated the free surface of water, jump length and maximum velocity in defined sections better than RNG turbulence model. this model show that the efficiency of diverging basins in decreasing length of jump is more better than the classic basins. So this model is recommended for simulating hydraulic jump in diverging sections. Results showed that the mean relative error of water surface obtained from numerical model and measured values is about 7 percent. Modeled Velocity profiles were in good agreement with measured data. Also the numerical model showed the vortices that were accrued because of diverging walls as well as experiment investigations. These vortices accrued near the right side of diverging wall in high Froude numbers and in lower values of Froude numbers, accrued in both two sides of walls. The intensity of vortices was increased by increasing the angle of diverging walls.
M.R. Madadi; Davoud Farsadi; A. Hosseinzadeh Dalir
Abstract
Undular flow on broad-crested weirs is a phenomenon occurs under certain hydraulic conditions. In this case the flow surface on the weir transforms to a sinusoidal wave and the number of waves may vary from one to over 10. Forming of this phenomenon leads to error in measurement of flow discharge by ...
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Undular flow on broad-crested weirs is a phenomenon occurs under certain hydraulic conditions. In this case the flow surface on the weir transforms to a sinusoidal wave and the number of waves may vary from one to over 10. Forming of this phenomenon leads to error in measurement of flow discharge by weirs. In this study in addition to introduction of the most effective parameters on undular flow formation, effect of geometric properties of rectangular broad-crested weirs was also investigated when only one wave formed. The results show that reducing the upstream slope from standard angle to 21 degree, decreases the relative wave height by 78 percent and increases the relative wave length by 55 percent. The position of undular wave also displaced toward the downstream. With changing in upstream edge shape from sharp edge to a relative radius of curvature equal to 0.5, the relative height of wave decreased up to 80 percent. Roughening the surface of the weir crest led to attenuation and elimination of undular wave, depending on the position of roughness surface.
S. Razi; A. Hosseinzadeh Dalir; F. Salmasi; D. Farsadi
Abstract
In this paper the effectiveness combination of bed sill and collar in reduction of local scour depth at cylindrical piers under clear water flow condition was investigated (V/Vc=0.9). In the first of experiments, the bed sill was located in downstream and different distances from the piers. Results indicated ...
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In this paper the effectiveness combination of bed sill and collar in reduction of local scour depth at cylindrical piers under clear water flow condition was investigated (V/Vc=0.9). In the first of experiments, the bed sill was located in downstream and different distances from the piers. Results indicated that minimum distance of the bed sill from the piers in downstream has maximum reduction of scour depth in front of the piers. The percent reduction of scour depth is about 30% in this case. In continuing the tests, used the collar and bed sill simultaneous. When using the combined of collar (2D) and bed sill (L=0), the percent reduction of scour depth in front of piers is about 42% and more than 98% when using the combined of collar (3D) and bed sill (L=0). The results show that using combined of collar and bed sill have more effect in reduction of local scour around bridge piers.
H.R. Jalili; A. Hosseinzadeh Dalir; D. Farsadizadeh
Abstract
Abstract
One of the most important sources of drinking and agricultural water needs is rivers. One of the oldest methods of getting water from rivers that still has the greatest use is the gravity intake. In this type of intake, due to the disproportionate velocity at the upstream and downstream mouth ...
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Abstract
One of the most important sources of drinking and agricultural water needs is rivers. One of the oldest methods of getting water from rivers that still has the greatest use is the gravity intake. In this type of intake, due to the disproportionate velocity at the upstream and downstream mouth of intake, occur flow separation and following sedimentation at the upstream mouth. In this study, by use of a numerical model (SSIIM 2.0) optimized hydraulic mode of intake, so that the minimum flow separation at the upstream mouth occurs, then similar models was performed in the physical model. Results indicated that the optimum model of numerical model and the optimum of physical model (based on sedimentation data) is the same. The optimal model is 7 in 63 cm combined arc at the upstream mouth.
Keywords: Vertical lateral intake, Flow separation, Secondary flows, Numerical model, SSIIM 2
