بهبود عملكرد هيدروليكي سرريزهاي كليدپيانويي غيرخطي در پلان

در اين پژوهش به بررسي راهكارهايي براي بهبود عملكرد و همچنين افزايش ضريب آبگذري در سرريزهاي كليدپيانويي غير خطي در پلان پرداخته شده است. بدين منظور، تغييراتي در شكل هندسي اين نوع سرريز به­وجود آورده و نتايج اين تغييرات با استفاده از نرم­افزار FLOW3D بررسي شده است. يكي از اين تغييرات، تغيير شكل تاج سرريز مي­باشد. لذا، سه مدل سرريز با تاج­هاي مستطيلي، مثلثي و بيضوي طراحي شد. نتايج نشان داد كه سرريز تاج مثلثي تا حدود 60 درصد نسبت به سرريز تاج بيضوي و تا حدود 65 درصد نسبت به سرريز تاج مستطيلي، از ظرفيت آبگذري بيشتري برخوردار بود. در قسمت دوم اين پژوهش، به تأثير وجود و يا عدم وجود و همچنين شكل هندسي پشت­بند بر عملكرد اين نوع از سرريزها پرداخته شد. بدين منظور، سه مدل سرريز با پشت­بندهاي مكعب مستطيلي ، نيم­استوانه­اي و منشوري طراحي شده و با سرريز بدون پشت­بند مقايسه گرديد. نتايج نشان داد كه در دبي­هاي كم، پشت­بند باعث بهبود عملكرد هيدروليكي سرريز شده و همچنين در بين پشت­بندها نيز پشت­بند نيم­استوانه عملكرد نسبتاً بهتري نسبت به ساير پشت­بندها داشت. ولي با افزايش دبي عبوري، از تأثير عملكرد پشت­بند كاسته شده و به تدريج ضريب دبي سرريزهاي پشت­بند دار و بدون پشت­بند به يكديگر نزديك شدند. در آخر نيز تأثير ديوار جان­پناه بر عملكرد اين نوع سرريزها بررسي گرديد. در اين مورد، ديواره­اي به ارتفاع 3/1 سانتي­متر به تاج سرريز افزوده شد. نتايج نشان داد كه اين عمل تا حدود 7 درصد باعث افزايش ضريب آبگذري مي­گردد. به­طور كلي در هدهاي زياد جريان، عوامل بهبود دهنده اثر محسوسي در عملكرد سرريز ندارند.

Weirs are structures used to measure discharge and flow control in canals and dams. Economically, a significant part of the cost of building a dam is due to weirs. By investigating different types of weirs, researchers have concluded that the piano-key weirs have two major advantages over other weirs. One of the most important advantages of a piano-key weir is that this kind of weir needs less space to run and can have smaller dimensions. Another important advantage of this type of weir is the ability to transmit more water than other weirs, which can safely protect the dam. A review of previous studies suggests that some studies have been carried out in the field of piano-key weirs. But, there are not sufficient studies on the performance of these types of weirs in curved plans as well as their hydraulic performance improvement factors. The main objective of the present research is to investigate the factors that can improve the performance of curvilinear piano-key and increase their hydraulic efficiency. In order to verify the results of the numerical model, the Anderson (2011) laboratory model has been used. Numerical modeling has been done for 5 inflow discharges in FLOW3D software. In order to quantitatively compare the results of the numerical model with laboratory values, some error criteria including R2, MAE and RMSE have been used. The values of these parameters were 0.9985, 0.00804 and 0.009521, respectively. Results showed that numerical model has acceptable adaptation to experimental results. In the next part of the paper, factors that can be effective in increasing the discharge capacity of the curvilinear piano-key weirs are investigated and analyzed based on the discharge coefficient curves and contours. In the first step, effect of crown shape on weir hydraulic performance was investigated and for this purpose three curvilinear piano-key weir models with rectangular, triangular and elliptical shapes were designed. Results showed that the weir with triangular crown had up to 60% higher discharge coefficient than the elliptical-crown weir and up to 65% more than the rectangular-crown weir. According to the general pattern of flow, in weirs with rectangular and elliptical crowns, the flowing flow clinging to trunk weir is discharged to downstream, while in weir with triangular crown, adhesion among flow and trunk of the weir is decreased. This factor increases discharge capacity of the weir with triangular crown in comparison to the other two weir types. In the next section, effect of existence or absence, as well as the geometric shape of the bundle, on the performance of these types of weirs was investigated. For this purpose, three weir models with cubic rectangular, half-cylindrical and prism bundles were designed and compared with a weir without bundle. Results showed that the bundle improved hydraulic performance of the weir. Also, for all the studied range of hydraulic heads, weir with half-cylindrical bundle had higher discharge capacity than the other weirs. The reason is that in the weir with half-cylindrical bundle, the sudden change in the angle of flow lines before collision with the bundle occurred further away from the end of the bundle, which caused flow entrance with less disturbance to the weir keys. Finally, the impact of a parapet wall on the weir operation was investigated. A 1.3 cm high parapet wall was added to the weir crown. Results showed that addition of the parapet wall increased the water level in the weir crown area and resulted in decreasing the velocity of approaching flow to the weir structure. Reduction of the velocity decreases the possibility of flow blockage and the flow has more time to run away from the weir keys. The set of these factors cause the weir with parapet wall to have higher discharge capacity than weir without the parapet wall.