جستجوی مقالات مرتبط با کلیدواژه "spillway" در نشریات گروه "عمران"

Introduction :

Spillways are simple and widely used hydraulic structures in water transfer and irrigation, and drainage systems. They are used in dams to pass excess water caused by floods and control the reservoir water level, as well as in irrigation and drainage canals to regulate the water level and measure the flow rate. Piano key weirs are the newest type of nonlinear weirs are piano key weir (PK weir), which this type of weir can increase the capacity of discharge coefficient 3-4 times to a linear spillway. However, the discharge coefficient of PK weirs decreases with increasing the head over the weir.

This study aims to check the discontinuous wall over the crest of the piano key weir to improve the discharge coefficient of the piano key weir in the high heads. To achieve this goal, Two weirs with a ratio of W/B = 2/3 have been used (Figures 1 to 3). The desired weirs were installed and carried out in a rotating flume in the Tarbiat Modares University of Tehran (Figure 4). The range of testing was from Q = 55 lit/sec to Q = 180 lit/sec ; and with steps of 5 lit/sec. To conduct the tests, first, the tests were performed on the Rec-Base model, and then the tests were performed on the Rec-B1 model. The geometric features of these two models are presented in Table 1.In order to extend the results of the prototype to the real sample, the dimensional analysis of the weir has been done. For this purpose, the effective parameters are shown in Eq. 2, and then, after performing the dimensional analysis techniques, it can be seen in the form of Eq. 3. By removing the constant values, the discharge coefficient will depend on the parameters of Eq. 4.

Figure 5 shows the Q-Ht curve of two Rec-Base and Rec-B1 models. According to this figure, the upstream head of the weir of the Rec-B1 model has increased by an average of 8.35% compared to the Rec-Base model. Also, regarding the behavior of the flowing blade, in the model (Re-Base) in the range of Ht<8 cm, air penetrates under the flow blades, and the flow becomes aerated. In the interval (Ht < 12 Cm < 8 Cm), with the increase of water head, the flow under the blade goes to the free air, and the blade takes an oscillating state. At higher values (Ht < 12 cm), The flow passes over the weir crest in the form of a thick blade. In this condition, fluctuations are observed on the flowing blade. Equation 5 has been used to calculate the discharge coefficient of the Rec-Base model. This issue is while Eq.12 has been used to calculate the water discharge coefficient of the Rec-B1 model. In this regard, QT is obtained from Eq. 10, and QE is the laboratory discharge. Figure 8 shows the discharge coefficient of the two models. According to this figure and the numbers in Table 2, the discharge coefficient has increased by 6.7% in the Rec-B1 model compared to the Rec-Base model. Figure 11 also shows a 7.22% increase in efficiency of the Rec-B1 model compared to the Rec-Base model. Also, coefficient C was calculated using equation 13 and its curve was drawn in figure 9. Figure 10 is also calculated according to Figure 14. Finally, Eq. 16 to estimate the water discharge coefficient has been presented. Also, the coefficients of this equation are presented in Table 3. Figure 12 shows the comparison between the estimated water discharge coefficient of equation 10 with the actual value of the discharge coefficient, which indicates the high accuracy of the presented equations. Table 4 indicates the equation proposed by other researchers to calculate the discharge coefficient of the PKW as well.

In conclusion, it can be mentioned that although the slope over part of the weir crest increases the upstream head of the piano key weir, however the efficiency of the weir increase by 7.33%. Also, the discharge coefficient in the Rec-B1 model increases by 6.7% compared to the Rec-Base model. Considering that in the Rec-Base model, with the increase of the head, interference of the flow increase, it is possible to reduce the decreasing rate of efficiency in higher discharge by modifying the weir crest.

Overflows are generally installed to drain excess water or floods that the volume of the tank can not store. In diversion dams, overflow is used to bypass or divert current in excess of system capacity. Demolition of many dams occurs due to incorrect design or insufficient overflow capacity. Proper spill design is more important in gravel earthen dams than in concrete dams. because the probability of destruction of earthen and gravel dams due to water passage is much higher than concrete dams. In the present study, a comprehensive review of the types of applied overflows based on effective dynamic and kinematic parameters was performed. Also, definitions and summaries of different types of free overflows were shot, siphon, stepped, congressional, lateral, tunnel, circular crown, peak, lotus or tulip. Then, the mechanism of vortex formation was introduced and an overflow appropriate to this phenomenon was introduced. The results of these cases showed that the application of lotus or tulip overflow in flood areas with high discharge has better performance.

Run-of-river hydropower dams almost have a small reservoir and therefore, the spillway starts with the smallest flood in simultaneous with operation of power intakes. In the present study, by forming 16 vortex in different classes using Flow-3D software, the effect of simultaneous operation of spillway and power intakes in Masjed Soleyman dam and power plant was investigated. VOF method and LES model were used for simulating free surface and turbulence, respectively. Regarding the cost of calculations and the amount of error, the network size of 5 mm was selected as the appropriate mesh size. In Class A vortices when the spillway flow is at its peak, the strength of formed vortices reduced about 23%, 36%, and 68% in different intake submerged depths. The results showed that by increasing the discharge of spillway, the formed vortices were weaker. Moreover, spillway flow in Class A formed vortices did not eliminate the vortex, But it caused to change the vortex class to B and C in some cases; However, in the formed vortex of Class B and C, with simultaneous operation of the spillway and power intakes, the vortex disappear completely and rotation was not observed on the surface of the reservoir.

Cavitation is one of the hydraulic phenomena that its occurrence caucus destroying the hydraulic structures. Chute spillway is an example of hydraulic structures that cavitation may be occurred. In this work, cavitation in chute spillway of Surk dam, which it have a rapidly change slope in chute path, has been studied using physical modeling. The physical model was made by plexiglass with scale of 1:50 and dynamic similarity between the model and the prototype was considered based on Froude number. The experiments were conducted in 5 different flow rates and pressure, velocity and flow depth were measured in the central axis and side of the wall. In this study, Falvey criterion (1990) was used for commenting of cavitation index. The results showed that the calculated cavitation index was in range of 0.25 to 1.8. In this range Falvey recommended to prevent the risk of cavitation, it is required the concrete surface of the chute spillway should be lining with a smooth materials.

Gabion stepped weir is a simple hydraulic and environment friendly structure that can be used to dissipate flow energy in different dams or to control downstream erosion of various structures. Most researches have been related to concrete and rigid stepped spillways, so studies on gabion stepped weirs are very small. In this research using the experimental method and physical model various components that affect the energy loss in gabion stepped weirs have been studied and comparisons with other studies by researchers have also been made. The flow passes in gabion stepped weir was carried out both in overflow and inflow (both simultaneously) and the amount of energy dissipation along the structure was calculated based on the energy relation. In this study, completely uniform particles with three diameters ( ) of 10, 25 and 40 mm were used. The height and width of physical models made of gabion stepped weirs were 60 cm and 40 cm respectively, with stairs of 3, 6 and 12 and height of stairs 5, 10 and 20 cm and the slope of the weirs are 1:1, 1:2 and 1:3 (2 and 3 horizontals, 1 vertical). In the gabion stepped weirs, the downward slope of the weir has a negligible impact on the energy dissipation. As the number of steps increases (for constant ), the energy loss decreases. The average diameter of the particles of 10 mm for and the average diameter of the particles of 40 mm for has the highest of relative energy loss.

One of the important issues in the design of chute spillway is to study the flow characteristics in the chute path because the flow is supercritical. In this study, the hydraulic characteristic of flow in the chute spillway of Surk dam has been investigated using both physical and numerical modeling. The plexiglass physical model was made with a geometry scale of 1:50 and FLUENT software was used for mathematical modeling. The experiments were carried out at 5 different discharges and the parameters of pressure, velocity and depth of flow were measured in the central axis and at the side of the wall. The results showed that among the measured parameters of FLUENT model, the velocity parameter was simulated with the lowest average error rate (4.3%) and the depth parameter with the highest average error rate (16.9%). Also, the Nash-Sutcliff coefficient and the correlation coefficient for the parameters, indicated that FLUENT software has a good ability to simulate flow characteristics over the chute spillway with a suddenly change slope. Regarding the RMSE and NRMSE criteria, FLUENT model have had the highest accuracy in calculating the flow parameters by using finite volume numerical method, turbulent model k-e, RNG, SIMPLE pressure correction method and VOF two-phase method.

In this research the effects of installed blades on the combined model of ogee spillway with lower bypass on energy loss of structure and downstream hydraulic jump characteristics has been experimentally investigated. In order to achieve the goal of this study, a physical model of ogee spillway with lower bypass was built, in which the output jet from the lower bypass (bottom outlet) was set to be at the angle of 30 degrees to the overflow of spillway. Installation of blades at the upstream of the lower bypass slit makes flow separation and more turbulence on spillway and as a result more energy dissipation on structure. In this research, two blades relative thickness including tb/ y1d= 0.07 and 0.14 were used and the results showed that the blades with the higher relative thickness (i.e. tb/ y1d=0.14) was found to be more effective in energy dissipation on structure and less values for the downstream hydraulic jump parameters. The measured values showed that the average energy loss on spillway, and the reduction length and secondary relative depth of hydraulic jump were 47.6%, 40% and 23.2%, respectively. According to the results obtained in this research study, the use of this structure is recommended for economical stilling basin construction at the downstream of small dams and spillways.

Fuse gate is one of the spillway types that according to the plan view have two models of straight and labyrinth crest. Labyrinth crest fuse gates with increasing crest length, discharge capacity and storage of water in reservoir, can prevent flooding of upstream land by reducing water level above the structure. They have three different types: Narrow Low Head (NLH), Wide Low Head (WLH), and Wide High Head (WHH). In this study, the effect of increasing canal slope on discharge coefficient in 3 models of fuse gate: WLH, Straight, and Straight with Inclined Side view was investigated. These models were made of Plexiglas with a bucket height of 16.7 cm. Tests were made in a sloping experimental canal with a length of 12 m, width of 0.5 m, and height of 0.8 m. The results showed that the discharge coefficient of fuse gate spillway depends on h/H. In WLH model of fuse gate, the discharge coefficient reduces as parabolic with increasing discharge and in Straight Fuse gates, the discharge coefficient in the form of linear has increasing, constant and decreasing depending on the slopes. In all 3 models with increasing slope, the downstream water depth of spillway reduces and discharge coefficient value increases. Model comparison showed that in a constant h/H, the Straight spillway with Inclined Side view has higher discharge coefficient and stores the maximum volume of water in the reservoir. It was also found that at a constant discharge, the WLH model has lower upstream water level. Finally, the discharge coefficient equation for straight and labyrinth fuse gates were obtained in the form of linear and power functions. The statistical analysis indicated high accuracy of the equations.