بررسی آزمایشگاهی ضریب دبی سرریز جانبی کلید پیانویی ذوزنقه‌ای

سرریزها سازه‌های هیدرولیکی هستند که برای عبور آب‌های اضافی و سیلاب‌ها در سدها استفاده می‌شوند. سرریزهای جانبی نوعی خاص از سرریزها هستند که به‌ موازات جریان اصلی در دیوارۀ مجاری انتقال آب، مانند کانال‌ها یا رودخانه‌ها، جانمایی می‌شوند و هنگامی‌که سطح آب بالا می‌آید تنظیم دبی و کنترل سطح آب را به‌عهده دارند. کنترل و انحراف سیلاب در مخازن سدها، انحراف جریان و محافظت سازه در برابر سیلاب در رودخانه‌ها از دیگر موارد کاربرد سرریزهای جانبی است. این تحقیق، در شرایط آزمایشگاهی و با 16 مدل سرریز کلید پیانویی ذوزنقه‌ای تیپ a با سه ارتفاع متفاوت 10، 15 و 20 سانتی‌متر اجرا ‌شده است. نتایج بررسی هانشان می‌دهد که سرریز با p=15cm در نسبت بی‌بعد 0/4 > h/p> 0/2 دارای بیشترین میزان ضریب دبی عبوری  است و در نسبت بی‌بعد 0/5 < h/p سرریز با p=20cm بیشترین ضریب دبی عبوری cm را دارد. در مقایسۀ ضریب دبی عبوری از سرریز جانبی کلید پیانویی ذوزنقه‌ای با سرریز جانبی کنگره‌ای ذوزنقه‌ای 12 درجه و 6 درجه به‌ترتیب 1/2 و 1/87 برابر و از سرریز جانبی کنگره‌ای مثلثی 1/5 برابر دبی بیشتری آب از خود عبور می‌دهد.

Laboratory Investigation on Discharge Coefficient of Trapezoidal Piano Key Side Weirs

Introduction The flow passing through a side weir, one of the varieties of water diversion structures, is a variable flow with decreasing flow rate. Labyrinth weir is the basis for piano key weirs. They are often constructed with vertical walls and are much more efficient than the linear weirs. Nevertheless, the flow, especially the bottom flow, enters this type of weirs and passes through two vertical walls of the side crests. Then it becomes squeezed and therefore the upstream and downstream crests come up with inappropriate hydraulic behavior. Also, the most outstanding disadvantage of this type of weirs is the large foundation area needed to be constructed on the concrete dams. The piano key weirs are a modern type of the nonlinear weirs which have been developed by Hydro Coop Institute of France and the Hydraulic and Environmental laboratory of the Biskara University of Algeria. In general, these weirs comprise of 4 different types, the differences of which lie in the presence or the absence of slopes created for them. Type A is sloped both upstream and downstream, Type B is sloped upstream, Type C is sloped downstream and Type D lacks any slope. The present study conducted show the effective geometrical parameters on the hydraulic performance and discharge coefficient (CM) of the trapezoidal piano key side weirs (TPKSW). The type of flow and its variations in a side weir can be considered as the C_M of the side weir, using simplifications and assumptions suggested by DeMarchi in 1934 to obtain suitable equivalents for side weirs.   Methodology All tests have been conducted in a closedloop rectangular Plexiglas flume in Soil Conservation and Watershed Management Research Institute (SCWMRI), Tehran, Iran. The study canal  was10m long, 0.6m wide and 0.6m high. All tests have been carried out on the 0.6m wide canal. To prevent flow turbulence upstream of the canal, tranquilizing racks were used at the upstream. A calibrated triangular weir was also applied to measure the flow at upstream. Also, a calibrated rectangular sharpcrested weir was used downstream. The water surface profiles were measured longitudinally. For this purpose, a digital depth profiler with 0.1 mm precision was used. The profiler accuracy was valid for almost stable water surface but it could be decreased in highly turbulent flows. An electromagnetic velocity meter with 0.001 m/s precision was used to determine velocity components to obtain parallel (𝑉𝑥) and perpendicular (𝑉𝑌)to the side weir. The profiler and the velocity meter could move on a rail in both X and Y directions. Flow rates at the main and the collection canal were measured by a calibrated 90° Vnotched and a rectangular weir, respectively. Figure 6 shows a general view of the laboratory. In this research, 16 models of TypeA trapezoidal weirs have been studied in two cases of 1 and 2. The weirs had 3mm thickness made of Plexiglas. The tests were carried out preventing the effects of viscosity and surface tension over the weir and considering the height of more than 3 cm.   Results and Discussion In this research, for investigating the effects of a number of inlet cycles, the weirs were tested at two different directions of the side weirs located in the main canal. The results showed that the weirs with 15cm and 20cm had the highest discharge coefficient CM in dimensionless ratios of 0.2> H/P> 0.4 and H/P>0.5 respectively. Having reviewed previous studies, it could be concluded that the trapezoidal piano key side weir was capable of releasing a flow 1.2 times more than that of the linear trapezoidal labyrinth weir with 12 degrees angle and 1.87 times more than the one with 6 degrees angle, and 1.5 times more than that of the triangular labyrinth weir.   Conclusions The result of the present study has shown that trapezoidal piano key weir can perform well on the side of trapezoidal and triangular labyrinth weir. In the comparisons made in this study, in comparison with the discharge coefficient of the side weir overflow, the trapezoidal piano key with the lateral overflow of the 12degree Congress and the 6degree trapezoidal labyrinth is equal to 1.2 and 1.87, respectively, and 1.5 times the lateral overflow of the triangular labyrinth weir. Although, the trapezoidal piano key weir in both lateral and direct modes is 1.55 times higher than the rectangular overflow of the direct piano key of the discharge coefficient. The trapezoidal piano key side weir in the dimensionless ratio of 0.4> H / P> 0.2 has the highest discharge coefficient flow. Keywords:Discharge, Flow, Water Diversion Structure