جستجوی مقالات مرتبط با کلیدواژه « flow coefficient » در نشریات گروه « آب و خاک »

Weirs of the labyrinth have some advantages including the high coefficient of the irrigation of weir and the low fluctuation of water when the flow passes over the crest of the weir. In this research, the flow rate coefficient has been investigated by changing the weir geometry in terms of wall slope, arc cycle angle, and nose length change in the upstream and downstream of each cycle of the trapezoidal arc labyrinth weir. A total of 240 tests have been performed on 16 different physical models in a channel with a width of 120 cm and a narrowing of 20 cm from each wall. All models have been compared with the control model (normal labyrinth weir) (80A). The results showed that the 80B weir with an arc cycle angle of 20 degrees and without wall slope has a better performance than other weirs. Also, the weir with an arc cycle angle and a wall slope of 20 degrees in a divergent form (D20B) in the area (Ht/P) <0.31 has a better performance than other weirs with an arc cycle angle of 20 degrees, and after this area, the weir with a wall slope of 10 degrees has performed better in divergent form (D10B). In weirs with different cycles at an arc cycle angle of 20 degrees, the labyrinth weir with 5 cycles (N5) has performed better up to the point (Ht/P)=0.36. Also, at the maximum point, the difference is 13 and 17%, respectively, compared to the 4-cycle and 3-cycle weirs.

Non-linear weirs have more passing length than linear ones for a certain value of flow width, so they have more utilization for water surface adjustment, flow control in channels, rivers, and dam reservoir purposes. Labyrinth weir is a common type of non-linear weir that has been considered by researchers in recent decades. The effect of some geometric and hydraulic characteristics appears as discharge coefficient in the head-discharge relationship. For the same conditions, the higher the discharge coefficient, the more flow will pass over the weir. The experimental study is one of the methods to determine the effect of parameters on the discharge coefficient value. Due to the occurrence of complex phenomena that can not be measured or the existence of physical limitations in the laboratory, the use of intelligent artificial methods has become a growing trend in recent decades. The GEP and the SVM are two algorithms with train and test base phases that are used to extract the hidden and complex relationships among dependent and independent variables. In this research work, in addition to the experimental assessment of different geometric and hydraulic parameters on discharge coefficient, the outputs of the two mentioned algorithms have been considered and compared with laboratory results.

One of these types of weir is the sharp edges overflow, which is widely used due to the current flow pattern and ease of flow pass. In the present study, the flow characteristics of the proposed horizontal sharp edge triangular overflow with different angles of 30, 60, 90, 120, 150 and 180 degrees at downstream are simulated for 10 different discharges using the FLOW-3D numerical model. In this regard, after validation of the amount of the flow depth over the weir with valid experimental results, parameters of the discharge coefficient, pressure profile, velocity in transverse section and flow pattern have been calculated and analyzed. The results indicated the high accuracy of RNG turbulence model compared with other turbulence models with correlation coefficient R2 = 0.9996. Other results showed that discharge coefficient of proposed weir increases with 6% in compared with experimental weir model (with vertex at upstream). Weir with 150-degree angle has the highest increment of discharge coefficient with about 8.5%. As the angle rises from 30 to 150 degrees, the minimum pressure range progresses from the tip of the weir and goes downwards. The maximum amount of pressure in the downstream of overflow was observed for weir with 120-degree angle with a value of 1100 Pascal. The minimum pressure of 10 pascal was obtained in a small range of 150-degree weir. As the flow approach to tip of the overflow, the flow passing from the side and tip of the overflow and has high velocity values. The maximum longitudinal velocity was observed with a value of 1.53 meter on second in a 90-degree overflow.

Weirs are one of important hydraulic structures that are constructed to regulate water surface, flow measurement and flood discharge in canals, rivers and reservoirs. According to the shape of crest across river, weirs are divided to two direct and indirect groups. Using labyrinth weir is an effective and economical way to increase discharge capacity. Main goal of labyrinth design of weirs is increase the length of weir by making the shape of it nonlinear. Effective factors on labyrinth weir’s discharge coefficient are important which should be considered. Different parameters affect this characteristic of flow and any change in one of these factors affect the flow condition and discharge coefficient. One of these parameters is downstream and upstream ramps slope of labyrinth weir. This study is concentrated on experimental investigation of simultaneous slope of downstream and upstream ramps’ effect on hydraulic performance of rectangular labyrinth weir.
In this study 5 models of rectangular labyrinth weir in 4 different ramp slopes were investigated in hydraulic laboratory. Effective parameters on system were obtained by dimensionless indexes using Buckingham theory. Experiments are carried out in flume with rectangular profile, it’s length, width and height are 12, 0.5 and 0.8 meters, respectively and discharge range of 10 to 70 l/s. Weirs under experiments were made of Plexiglas with 10 mm thickness and 2 cycles. Weirs including different heights of 15, 20, 25 cm and different crest’s length of 1.075, 1.275 and 1.675 cm were investigated. In this study 4 different slopes were considered for rectangular labyrinth weir including without slope, 15, 30 and 45 degrees.
Results indicated that in the case of upstream and downstream ramp's simultaneous slope, discharge coefficient decreased up to 7 percent compared to without slope condition. Increasing dimensionless parameter Ht/P leads to decrease discharge coefficient reduction. In the high discharge range, rectangular labyrinth discharge coefficient with upstream and downstream ramp's simultaneous slope is more than without slope condition. Furthermore, results showed that increase of weir height in rectangular labyrinth weir with upstream and downstream ramp's simultaneous slope results in discharge coefficient increase up to 13%. Increase of weir's effective length reduces the discharge coefficient up to 9% in Ht/P ratios that are more than 0.3.
With regard to the conclusion of this study, upstream and downstream ramps simultaneous slope plays an important role in efficiency of rectangular labyrinth weir. So, two ramps simultaneous slope can be used for high discharge in order to improvement of rectangular labyrinth weir's hydraulic efficiency.