نوع مقاله : مقاله پژوهشی
نویسندگان
1 دانشجوی کارشناسی ارشد مهندسی آب و سازه های هیدرولیکی، واحد اصفهان (خوراسگان)، دانشگاه آزاد اسلامی، اصفهان، ایران
2 گروه مهندسی عمران، واحد اصفهان (خوراسگان)، دانشگاه آزاد اسلامی، اصفهان، ایران
چکیده
سرریزهای کلیدپیانویی شکل جدیدی از سرریزهای منقاری هستند که ظرفیت عبور جریان بیشتری از روی خود دارند؛ لذا بررسی اتلاف انرژی در این سرریزها، دارای اهمیت است. در این تحقیق از سرریزهای کلیدپیانویی ذوزنقه‌ای نوع C با ارتفاع 0/2 و 0/18 متر در یک فلوم آزمایشگاهی، استفاده شد. برای اولین بار از سه هندسه‌ی متفاوت بلوک در کلیدهای خروجی جهت بررسی اتلاف انرژی جریان در سرریز کلیدپیانویی ذوزنقه‌ای نوع C استفاده شد. بلوک‌ها بر اساس سرریزهای مجهز به بارشکن طراحی شدند. بلوک‌های اول مکعب مستطیل، بلوک‌های دوم استوانه‌ای و بلوک‌های سوم با مقطع ذوزنقه‌ای هستند. همچنین از چهار دبی0/025، 0/03، 0/035 و 0/04 متر مکعب بر ثانیه نیز استفاده شد. نتایج نشان داد که با افزایش دبی جریان، اتلاف انرژی جریان کاهش می‌یابد. همچنین با افزایش 10 درصدی ارتفاع سرریز، اتلاف انرژی جریان حدود 19/3 درصد افزایش می‌یابد. بیشترین اتلاف انرژی در سرریز با بلوک مستطیلی مشاهده شد. اتلاف انرژی در سرریزهای با بلوک مستطیلی، دایره‌ای و ذوزنقه‌ای نسبت به سرریز بدون بلوک و با ارتفاع 0/2 متر، حدود 16/8، 10/9 و 14/1 درصد افزایش می‌یابد. در انتها رابطه‌ای با ضریب همبستگی 98/83 درصد برای تعداد 20 آزمایش جهت بررسی اتلاف انرژی جریان در سرریزهای ذوزنقه‌ای نوع C با دو ارتفاع متفاوت و با و بدون بلوک در کلیدهای خروجی، ارائه شد.
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
Different Block Geometry in Piano Key Weir and its Effect on Energy Loss
نویسندگان [English]
- Negin Hafizi 1
- Ali Khoshfetrat 2
1 Faculty of Civil Engineering, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran
2 Civil Engineering Department, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran
چکیده [English]
Since ancient times, humans have built barriers before the flow to increase the depth upstream of the barrier for drinking and agriculture. Weirs are among the most widely used hydraulic structures in water transmission systems. Labyrinth weirs are a non-linear weir that, with a longer length in a limited width, passes more discharge. Labyrinth weirs are used to regulate the water level and control it in dams and irrigation canals (Kabiri-Samani and Javaheri, 2012). Another type of non-linear and long crest weir is the Piano key weir (PKW). Piano key weirs are an evolution of labyrinth weirs. The difference between labyrinth weirs and piano key weirs is the presence of slope in the inlet and outlet keys and hanging edges in piano key weirs. PKW is capable of passing more discharge (up to 3 to 4 times) (Safarzadeh and Noroozi, 2014). Piano key weirs in the plan have triangular, trapezoidal, and rectangular shapes and have four types A, B, C, and D. These weirs have inlet and outlet keys, with inlet keys having a negative slope and outlet keys having a positive slope. According to the conducted research, the lack of investigation of energy loss in the weir of a C-type Piano key and the effect of different geometry of the block on its output keys can be seen.
The experiments were conducted in a flume with a length, width, and height of 10, 0.60, and 1.10 meters, respectively. The floor of the flume was galvanized and the walls were made of thick glass. After turning on the pump, the flow passed through flow straighteners made of large gravel grains and metal screens, and after traveling 5.50 meters, it entered the weir. The pump pumped the flow from a tank through a 0.1-meter-diameter pipe with a maximum flow rate of 55 liters per second into the flume. The flow depth was measured by three sensors installed at the top of the flume. The pump and sensors provided the flow rate and flow depth with very little error. The elevation changes of the 10-meter laboratory flume were less than 4 mm, and the temperature of the water flowing in the flume varied between 7 and 13 centigrade degrees. Two trapezoidal type C piano key weirs with constant geometric specifications were used. The width of the weirs (W) was 0.6 meters, the length of the crest of the weirs (L) was 2.58 meters, the width of the inlet keys (Wi) and outlet keys (Wo) of the weirs were 0.215 and 0.075 meters, respectively, the length of the side walls of the weirs (B) was 0.50 meters, the length of the inlet side walls (Bi) was 0 meters, the length of the outlet side walls (Bo) was 0.13 meters, and the thickness of the weirs (Ts) was 0.01 meters. The only non-constant geometric component of the weirs was their height. The height of the first weir was 0.20 meters and the height of the second weir was 0.18 meters. The weirs have two cycles. The weirs are made of iron sheets.
The current flowed from the input keys and as a free jet to the downstream and output keys. Also, the flow was transferred downstream by the outlet keys in the form of an inclined jet. The output current from the output keys hit the blocks and its speed was reduced. Also, after hitting the blocks, the current was separated and hit the block of the second row. In the second row, the flow separated from each block was mixed and hit the block of the third row. This action continued until the end of the output keys. The local submerged area of the flow passed over the first block and hit the blocks of the third row. By increasing the flow rate and weir height, the amount of energy loss decreases. By increasing the ratio of the total head to the height of the weir, the amount of energy loss decreases. By reducing the weir height by 10%, the amount of energy loss is reduced by 19.3%. The block in the weir output keys causes more energy loss. The highest amount of energy loss was observed in the block weir with a rectangular section. The amount of energy loss in weirs with rectangular, circular, and trapezoidal blocks increases by about 16.8, 10.9, and 14.1% compared to the weirs without blocks. In the end, a relationship with a relatively high correlation coefficient was presented to calculate energy loss.
کلیدواژه‌ها [English]
- Blocks
- Energy dissipation
- Experimental investigation
- PKWs
- Output keys
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