M. F. Maghrebi; B. Mirzendehdel
Abstract
Introduction: The hydraulic jump happens when flow transfers from supercritical regime to subcritical regime. The hydraulic jump on smooth bed is called the classic hydraulic jump. One way to increase the energy dissipation in a hydraulic jump is to roughen the bed. Elements including stabilizers and ...
Read More
Introduction: The hydraulic jump happens when flow transfers from supercritical regime to subcritical regime. The hydraulic jump on smooth bed is called the classic hydraulic jump. One way to increase the energy dissipation in a hydraulic jump is to roughen the bed. Elements including stabilizers and baffle blocks are commonly used as the energy dissipators in stilling basins to stabilize the location and decrease the length and conjugate depths of the hydraulic jumps. If roughness elements are placed uniformly on the bed and orthogonal to the flow direction, the formed jump is addressed as the hydraulic jump on rough bed. Recently, implementing short energy dissipaters and environment friendly rough beds have attracted attention and justify more research in these fields. Recent studies have addressed hydraulic jump on rough beds ([14], [5], and [12]). Relative roughness parameter first defined by Rajaratnam to investigate the jump characteristics and other researchers then used this parameter to investigate the characteristics of jump on rough bed. In this research, similar experiments to Pagliara et al (5) are designed to study continuous and natural rough beds.
Materials and Methods: All the experiments have been arranged and carried out in the hydraulic laboratory of Ferdowsi University, Mashhad Iran. Hydraulic jump characteristicswere measured in a horizontal rectangular flume, 0.30 m wide, 0.50 m deep, and 11 m long, with smooth glass side walls.The rough bed was simulated by gluing a layer of uniform gravel material with middle diameter 3.5mm and 11mm on a glass plate which was placed on the flume, throughout its length .In the physical model, to simulate a supercritical flow with three constant initial depths including , 1.5 and ,a steel sluice gate is installed. Furthermore, to stabilize the location ofhydraulic jump and create a free-surface jump, a sharp-crested weir with the same width as the channel width is installed at the end of the flume. Water contraction usually occurs after the sluice gate is avoided by a steel plate welded on the sluice gate. So, the initial depth equals the gate opening. According to the experimental procedure, after placing theuniform roughness heights on channel bed, the pump runs and water flows slowly into the flume. Then, discharge increases to reach the desired value and the sluice gate opening is set up to have the hydraulic jump formed at a distance of ahead of the gate. These circumstances maintain enough for data recording. The parameter of gravel particles considered as the most sensible characteristic. The subcritical depth y2 was measured from the profile survey, where the water surface began to be essentially level.
Results and discussions: In the smooth and rough beds experiments show that variation in initial depth does not have any effect on decreasing the conjugate depths ratio. The conjugate depths ratio decreases as the roughness increases. The difference between conjugate depths ratio of rough beds with middle diameter 3.5mm (B) and 11mm (C) appears when the Froude number exceeds 7.5 and for Froude numbers greater than 10, a significant drop can be observed in the conjugate depths ratio diagrams from rough bed B to C. The horizontal distance between the beginning and end point of a hydraulic jump is considered as the length of the hydraulic jump. Dimensionless length of the hydraulic jump is presented as which is usually considered as a function of . For Froude number greater than 10, the dimensionless length of the hydraulic jump is nearly constant. Then, the ratio of for Froude numbers greater than 10 seems to be independent of supercritical Froude number and is just a function of roughness. In all experiments the length of the hydraulic jump decreases compared with the smooth bed under conditions that bed roughness is not subjected to water jet.
Conclusions: Experiments demonstrated that in the rough bed by increasing roughness, the conjugated depths ratio decreased compared with the classical hydraulic jump. The variation of initial depth of flow does not have any effect on reducing conjugate depths ratio and dimensionless length of the hydraulic jump. The length of the hydraulic jump in rough beds on average reduced between 28.5% and 47% with respect to the classical hydraulic jump which causes reduction in length of the stilling basin without bed roughness.
S. Pouresmaeil; M.F. Maghrebi
Abstract
Bottom intakes are hydraulic structures widely adopted for diverting water in steep rivers. The problems of vibration, corrosion, deformity, and clogging of the bottom racks by sediment, freezing and foliage inspire a new system of bottom intake in which a filled trench of porous media replaces the bottom ...
Read More
Bottom intakes are hydraulic structures widely adopted for diverting water in steep rivers. The problems of vibration, corrosion, deformity, and clogging of the bottom racks by sediment, freezing and foliage inspire a new system of bottom intake in which a filled trench of porous media replaces the bottom racks. In the present paper we have analyzed the data obtained from a systematic series of experiments carried out in a laboratory two-story flume. Measurements of the diverted discharge were performed for different rates of flow, grain size distributions, surface slopes and dimensions of intake as well as important factors. Also the relationships presented in previous studies, are compared with the results of new experiments and the characteristics of the physical behavior of these equations are investigated. Due to lack of the validity in previous models, a new equation for estimating discharge coefficient and flow diversion in porous bottom intake is presented, by using dimensional analysis and multivariate regression with experimental observations. The robustness of the proposed relationship is confirmed by the principles of hydraulic behavior of this intake and the comparison between the calculated discharges through the proposed relationship and those measured in an extensive series of experiments, characterized by ranges of the relevant flow parameters much larger than those investigated in the present contribution.
R. Badizadegan; K. Esmaili; M. Faghfour Maghrebi; M. Saneie
Abstract
Abstract
One of the most frequently encountered cases of rapid varied flow is the hydraulic jump. It occurs when a supercritical open channel flow changes into sub critical flow. In the present research, the experimental study of the hydraulic jump on seven sinusoidal corrugated beds with different ...
Read More
Abstract
One of the most frequently encountered cases of rapid varied flow is the hydraulic jump. It occurs when a supercritical open channel flow changes into sub critical flow. In the present research, the experimental study of the hydraulic jump on seven sinusoidal corrugated beds with different wave steepness. The wave steepness of sinusoidal corrugated beds is in the range of 0.1667 to 0.75 and Froude number was in the range of 4.5 to 12.26. The results showed that the tail water depth of a jump on a corrugated bed is about 20% smaller than that on smooth bed in Froude number 12 and the length of jump on corrugated beds is about 35% less than that for smooth bed.
Keywords: Hydraulic jump, Corrugated bed, Wave steepness
F. Koorosh Vahid; K. Esmaili; M. Faghfur Maghrebi; A. Alizadeh; B. Naghavi
Abstract
Abstract
Bottom intake is one of the most appropriate systems for diverting discharge in steep rivers. Bottom intake with porous media is a new system of diverting discharge which can be replaced by bottom rack intakes. To investigate the hydraulic flow characteristics on diverted discharge of this ...
Read More
Abstract
Bottom intake is one of the most appropriate systems for diverting discharge in steep rivers. Bottom intake with porous media is a new system of diverting discharge which can be replaced by bottom rack intakes. To investigate the hydraulic flow characteristics on diverted discharge of this intake, an experimental model was designed in which the inflow, diverted discharge and remained flow of porous media intake can be measured. In the present research, measurements of the diverted discharge were performed for different rates of flow, grain size distributions as well as surface slopes of intake with clear water. According to the obtained results, by increasing the inflow discharge, the rate of diverted discharge increases gradually and then reaches to a constant value. Any increment of the surface slope above the intake also decrease the relation diverted flow. It is found that the grain size of the porous media has a great influence on the diverted flow. By increasing the grain size diverted flow increases, too. Dimensional analysis and experimental results were used to estimate the discharge coefficient of porous media. Analytical analysis on experimental data shows that the discharge coefficient of porous media intake is about 0.1. Also an empirical-theoretical relation is proposed to evaluate the diverted discharge of this kind of bottom intakes.
Keywords: Bottom intake, Porous media, Discharge coefficient, Free surface flow
B. Naghavi; M. Faghfour Maghrebi; K. Esmaili; S.R. Khodshenas; F. Koorosh Vahid
Abstract
Abstract
Bottom rack intake is one of the most appropriate structures for diverting water in steep rivers. The problems of corrosion, deformity and clogging of the bottom racks in long term, inspires a new system of bottom intake in which a filled trench of porous media is replaced by the bottom racks. ...
Read More
Abstract
Bottom rack intake is one of the most appropriate structures for diverting water in steep rivers. The problems of corrosion, deformity and clogging of the bottom racks in long term, inspires a new system of bottom intake in which a filled trench of porous media is replaced by the bottom racks. Diversion of a specified amount of discharge through the porous media when void space in the granular material are filled with fine sediment in comparison to the bottom racks, requires much larger structure. However, for the new system of water intake, lower cost of construction and maintenance and higher compatibility with the river morphology in long term are considered as major advantages. The present research deals with an experimental model with two-storey channel, the lower one is used to divert water through the porous media and the upper one is used to convey the remained flow. Measurements of the diverted discharge were performed for different rates of flow, grain size distributions as well as surface slopes of intake with clear water and sediment flow. The influence of clogging phenomena on diverted discharge is also examined. The experimental results show that the effect of clogging in sediment flow in comparison to the clear water is decreased as the surface slope of the porous media is increased. It is revealed that the discharge coefficient of bottom intake when clear water is passed through the channel is varied in the range of 0.06 to 0.13. When sediment flow is passed over the bottom intake, due to clogging phenomena discharge coefficient is reduced up to 5 to 35% in comparison to the clear water. Experimental equations prepared for the discharge coefficients show that the significant factors affecting the efficiency of the water intakes are grain size distribution and surface slope of the bottom intake. The results show that the discharge coefficients for the water intake with the clear water and sediment flow when the above mentioned factors are selected appropriately are close to each other.
Key words: Bottom intake, Porous media, Discharge coefficient, Clear water flow, Sediment flow, Clogging
B. Naghavi; S.R. Khodshenas; M. Faghfour Maghrebi; K. Esmaili; F. Koorosh Vahid
Abstract
Abstract
Bottom rack intake is one of the most popular structures used for diverting water in mountain region. Corrosion and rotten problems of bottom racks inspire the introduction of a new system of bottom intake in which a porous media is replaced by the bottom rack. Obviously, clogging and reduction ...
Read More
Abstract
Bottom rack intake is one of the most popular structures used for diverting water in mountain region. Corrosion and rotten problems of bottom racks inspire the introduction of a new system of bottom intake in which a porous media is replaced by the bottom rack. Obviously, clogging and reduction of diverted discharge are the most important problems in this new system, too. In this paper, the effects of different media grain size, longitudinal slope, sediment grain size and flow discharge are investigated. Results show that despite of clogging role of suspended sediments in porous media, using appropriate grain size and slope for the porous media, would attenuate the side effects of the problem. Compare with clear water flow, the discharge reduction induced by clogging is not significant and efficiency of system in long time and no operation effort are confirmed. To recognize the effective parameters on infiltration resistance in porous medium intake an empirical theoretical formulation has been diverted from the Darcy’s law in surface infiltration. The equation is found to be dependent on size ratio, Reynolds number and hydraulic gradient. The theoretical predictions have been compared with experimental results, with good agreement.
Key words: Bottom intake, Porous media, clogging, Discharge reduction, Infiltration resistance
