نوع مقاله : مقاله پژوهشی
نویسندگان
1 استادیار گروه عمران، دانشکده فنی مهندسی، دانشگاه بوعلی سینا، همدان، ایران
2 دانشجوی کارشناسی ارشد آب و سازه‌های هیدرولیکی، دانشگاه بوعلی سینا، همدان، ایران.
چکیده
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Sloped piano key weirs, by adjusting the inclination of their sidewalls, enable improved hydraulic performance under various conditions. These weirs, with appropriate slopes, demonstrate better performance than non-sloped weirs by storing more water during low-flow conditions and providing more effective discharge during floods. The flow discharge in sloped piano key weirs is proportional to the upstream head, which contributes to increased efficiency and safety of dams. Trapezoidal piano key weirs, given their high efficiency, are well-suited for complex hydraulic conditions such as floods and variable flows. This study examines the performance of trapezoidal piano key weirs in both sloped and non-sloped configurations. The experiments were conducted in a 15-meter-long channel with a width and height of 60 cm. The laboratory models included trapezoidal piano key weirs of type A with slopes of 0, 5, 7.5, and 10 degrees. To investigate the effect of slope direction, the piano key weirs were inclined both in the flow direction and against the flow direction and were tested under 9 different discharges. The results showed that sloped trapezoidal piano key weirs inclined against the flow, with over 75% of the weir crest length engaged, have a higher discharge coefficient compared to other models. The discharge coefficient in the weir with a 5-degree slope against the flow direction is on average 7% higher than that of the non-sloped weir. The results of this study indicate that a trapezoidal piano key weir with a 5-degree slope against the flow direction performs better under flood and low-flow conditions compared to a non-sloped trapezoidal piano key weir.
کلیدواژه‌ها [English]
EXTENDED ABSTRACT
The construction of dams as a cost-effective method for preserving freshwater is of great importance. One of the critical components in dam construction is spillways, which are essential for preventing dam failure and controlling floods. Spillways raise the water level upstream of the dam, increase the flow velocity over the weir crest, and transfer excess water to the downstream side of the dam. According to studies, Piano Key Weirs (PKWs) experience a decrease in efficiency due to increased water load from submergence at the inlet keys. According to ICOLD reports, one-third of dam failures occur due to inadequate spillway capacity, making proper spillway design vital.
This research investigates the impact of sidewall slopes on the discharge coefficient of trapezoidal PKWs, to optimize design to enhance efficiency and performance under various hydraulic conditions. One notable feature of sloped PKWs is their ability to store more water without the need to increase dam height, making them an economically advantageous design. Additionally, irrigation and drainage networks can maintain the required water level for upstream intakes during low-flow seasons. Overall, sloped PKWs play a crucial role in water resource conservation and flood control by discharging flow proportionate to the upstream head.
The experiments were conducted in the Hydraulics Laboratory of the Faculty of Engineering at Bu-Ali Sina University, which features a glass-sided and glass-bottomed flume 15 meters in length, with a width and height of 60 centimeters. In the final 1 meter of the channel, the width increased to 97 centimeters using a diverging section made of iron sheets, where the models were installed. Water flow was regulated by a control valve, allowing flow rates ranging from 3.25 to 72.62 liters per second. The water, supplied from a reservoir located beneath the channel, flowed through the channel and over the weir, then returned to the reservoir.
To construct the trapezoidal type-A PKW with a thickness of 5 mm and in 4 cycles, the necessary components for the weir and those required to slope the weir were first designed using AutoCAD software. The parts were then fabricated from 5 mm PVC sheets using laser cutting and assembled with 1-2-3 glue to produce the models. The experimental models included type-A PKWs with sidewall slopes of 0, 5, 7.5, and 10 degrees. To examine the effect of weir slope orientation, these PKWs were inclined once in the direction of flow and once against the direction of flow.
After installing and sealing the weir in the channel, the flow depth was measured using a point gauge with an accuracy of ±0.1 mm at a distance of twice the height of the weir due to minimal water curvature. Additionally, the effective length of the weir was measured using a ruler with an accuracy of ±1 mm.
Flow discharge in trapezoidal Piano Key Weirs (PKWs) with sloped sidewalls corresponds to the upstream head of the weir. In other words, at lower discharges, only half of the keys are involved in passing the flow, which leads to increased head and water storage upstream of the weir. As the discharge increases, the full capacity of the sloped PKW is utilized for flow passage (Figure 7). The results indicate that trapezoidal PKWs sloped in the direction of flow result in a decrease in the discharge coefficient and weir efficiency. Conversely, PKWs sloped against the flow direction exhibit a smaller reduction in the discharge coefficient and efficiency.
The analysis of the data reveals that the discharge coefficient and efficiency of trapezoidal PKWs sloped against the flow direction increase once over 75% of the weir becomes active in passing the flow, compared to a non-sloped PKW, thus enhancing the weir's performance. Additionally, the results show that increasing the weir slope reduces the effective length of the weir, thereby decreasing the discharge coefficient and efficiency (Figure 8).
Therefore, with an increase in the ratio to above 0.12, resulting in more than 75% activation of the trapezoidal PKW with a 5-degree slope against the flow direction, the discharge coefficient and efficiency improve compared to a non-sloped trapezoidal PKW (Figure 12). The discharge coefficient and efficiency of the trapezoidal piano key weir with a 5-degree slope against the flow direction are, on average, 7% higher than those of the non-sloped weir, making it the best-performing model among the constructed models.
Ultimately, after analyzing the experimental data, Equation 7 was developed to estimate the discharge coefficient for both sloped and non-sloped trapezoidal Piano Key Weirs.
The use of trapezoidal Piano Key Weirs (PKWs) with sidewall slopes against the flow direction appears to be an effective option for increasing water storage during low-flow periods and enhancing discharge during flood events. Based on previous research and the present study, the PKW with a 5-degree slope against the flow direction exhibits the best performance. It provides suitable water storage during low-flow conditions and offers high discharge capacity during floods. The findings of this study can serve as a guideline for the optimal design of PKWs in water resource management and hydraulic structure projects.
All authors have read and agreed to the published version of the manuscript.
All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.
Data available on request from the authors
The authors avoided data fabrication, falsification, plagiarism, and misconduct.
The author declares no conflict of interest.
)