جستجوی مقالات مرتبط با کلیدواژه « hydraulic load » در نشریات گروه « آب و خاک »

Among the regulator structures used in water projects, weirs have remarkable applications like measuring flow, maintaining water level, controlling sediment transport, and managing variable water inflows. Weirs can be classified on the weir axis direction as a normal, side, or a labyrinth weir. labyrinth weirs are hydraulic structures used to regulate water levels and control flow in reservoirs of dams, canals and rivers.The discharge coefficient in the weirs is directly proportional to the crest length of weir. If the width of the channel or reservoir where the weir made is limited, one of the ways to increase the capacity is to increase the crest length of weir by zigzagging the weir in the plan. Due to their complex geometry labyrinth weirs are expensive to build. Therefore, in laboratory studies, high cost is one of the reasons that has made it difficult to investigate this type of weir comprehensively. Numerical methods are a very good option for hydraulic analysis of labyrinth weirs hydraulic. The history of the construction of labyrinth weirs goes back to before the year 1920 (Darvas, 1971). labyrinth weirs were first investigated by Gentellini )1940(. Vahab nezhad (2017) studied the changes in discharge coefficient for the three angles of 15, 18 and 23 degrees. Zamiri, et al. (2016) showed that increasing the thickness of the labyrinth weir wall increases the depth and velocity of the flow and ultimately reduces the discharge coefficient. The results showed that the discharge coefficient increases with increasing the weir angle, because as the weir angle increases, the weir length decreases and the discharge coefficient increase.In this study, the weir performance of a trapezoidal labyrinth with different angles (α) was investigated. For this purpose, labyrinth weir modeling was performed with three angles of 15, 23 and 30 degrees for two crest length of 5 and 7 cm and three heights of 10, 14 and 18 cm. The geometry of the weirs was created in the Inventor software and simulation was performed in Flow3D software. In order to validate the simulation and adjust the software parameters, valid laboratory data were used and the results of the model were in good agreement with the results of the laboratory data. For this purpose, the discharge coefficient of numerical models (Cd (CFD)) and laboratory (Cd (EXP)) for different values of water to overflow ratio (h / p) were compared and the error value was calculated. The highest error rate is 5.88 and the lowest is zero. In fact, with increasing the ratio (h/p) the error rate has increased, but this increase is also acceptable and the results show that Flow3D software has a very good ability to simulate labyrinth weir. Flow field study was performed with different turbulence models in Flow3D software using laboratory data. The RNG model was used in all simulations. To mesh the model, the channel was divided into three parts: initial, middle and end. The dimensions of the cube of the initial and final parts are 1 cm and the middle part is 5 mm.Analysis of the results showed that increasing the weir angle in a fixed crest length, increases the discharge coefficient (cd). The inverse relationship between the relative hydraulic load (h/p) and the discharge coefficient was also determined. Increasing the crest length of the weir by 2 cm, the trend of increasing the discharge coefficient due to increasing the weir angle, decreased by 9%. Also, increasing the angle 15 degrees, the trend of increasing the discharge coefficient due to increasing the crest length, decreased by 5%. This means that at higher angles, the effect of increasing the crest length on the discharge coefficient decreased and during shorter crest length, the effect of increasing the angle on discharge coefficient increased. Due to the direct relationship between the discharge coefficient and the average flow velocity, simultaneous increase crest length and weir angle increased the average flow velocity by 4 times at the beginning of the channel floor impact. In cases where the purpose of the study is to increase the discharge coefficient by increasing the angle and length of the weir crest, it should be noted that the effect of increasing the angle and length of the weir crest is more noticeable at low altitudes, So that with increasing the height of the weir this amount decreases.

Labyrinth weirs are some cost-effective structures, having trapezoidal, triangular and other formats, utilized for increasing the output efficiency in a limited width. Raising the capacity of labyrinth weirs via increasing their width is not always possible. The labyrinth weirs are used due to the increase in their efficient length on a given hydraulic height and width. The present study investigates the weirs having trapezoidal polyhedron format, on the wings of which some new labyrinth have been added so that their spillover discharge rate will be reinforced. The experiments in this study were conducted on 27 laboratory models having 9 different discharge rates, on whose wings double labyrinth have been added, totally through 243 experiment. Besides the spillover simulations were performed using the Flow-3D software. The results obtained from the numerical analysis for the determining the spillovers discharge rate coefficient were validated using laboratory data and it demonstrated a good correspondence between the numerical solutions and laboratory findings. It is also suggested that the Flow-3D software has a high potential in simulating the flow on labyrinth weirs. Laboratory results also indicated that, regarding all the compound polyhedron trapezoidal weirs, the parameter ratio, flow rate coefficient to ratio (Ht: total hydraulic load and P: spillways height) firstly raise and then start to reduce once they reach the maximum level. The spillover discharge rate increases for a given when the effective length of the weirs’ wing is raised. The discharge rate on the weirs having semi-circular compound format is better than this rate of ones having the square format and the ones having compound square format have spillover discharge rates better than the ones having simple trapezoidal format, in a manner that the discharge rate of the current flow is increased 15 percent more than the trapezoidal dam labyrinth spillways and flow rate coefficient interval increases from 0.4 percent of dam labyrinth spillways to 0.65 on the compound spillways.

Nonlinear weirs are regarded as important hydraulic structures for water level adjustment and flow control in channels, rivers and dam reservoirs. One example of non-linear weirs is shaped as curved-zigzag. The crest axis of these weirs is non-linear. At a given width, the crest length is greater than that of the conventional linear weirs. Thus, they achieve a higher flow rate for an identical hydraulic load. This research experimentally focused on the discharge coefficient and flow rate of curved weirs with three different curve radii in two triangular linear and zigzag shapes. The discharge coefficients of these weirs were comparatively explored in terms of the hydraulic performance as a function of the total hydraulic load to weir crest height ratio (hd/P) and curvature angle (θ) (or curve radius). The results indicated that for the same hydraulic load, the increase of θ (the decrease in curve radius) led to a lower discharge coefficient; this was first because of the increased topical rise of water level, and then the more indirect path with a greater curvature through which the flow had to transport. Both factors could negatively affect the water discharge coefficient. In practice, the runoff coefficient at a weir with a curve radius of R/w=1.25 was approximately 8.5% greater than that of a weir with a curve radius of R/w=0.75 under a hydraulic load of 0.2.

Labyrinth weirs are the economic structures to increase the weir output efficiency in limited widths, which can be seen in the plane f trapezoidal and triangular forms. These weirs with a hydraulic load and fixed width pass the more discharge in comparison to other type of weirs. In this study, labyrinth weirs trapezoidal in plane form were investigated. The experiments were performed on 27 laboratory models with 9 different discharge rates and a total of 243 tests. The results showed that, in all of the composite trapezoidal labyrinth weirs, the ratio of discharge coefficient to Ht/p (Ht: Total hydraulic load and p: weir length) weir length was increased at first; after reaching the maximum rate, it started to decrease. According to the suggested general relation, the utmost impact on discharge coefficient resulted from the cycle number and  Ht/p relation. Creating new labyrinth on the wing of the weir led to the increase of the effective length; as a result of it, the discharge rate increased in a specific amount of Ht/p. Also, the discharge through a trapezoidal labyrinth weir with the semicircular planform was better than the square; the square, in turn, was better than the simple trapezoidal weirs.