نوع مقاله : مقاله پژوهشی

نویسندگان

• صائب الغزی ¹
• جواد مظفری ²

¹ گروه علوم و مهندسی آب دانشگاه اراک، ایران

² دانشیار گروه علوم و مهندسی آب دانشگاه اراک، ایران

چکیده

سرریزهای کنگره‌ای، نسبت به سرریزهای خطی، دارای طول بیشتری دارند و دبی بیشتری را در هد ثابت آب از خود عبور می‌دهند. در این پژوهش به بررسی ضریب آبگذری در سرریز کنگره‌ای مثلثی و ذوزنقه‌ای با استفاده از نرم افزار FLOW 3D و مدل k-ε RNG پرداخته شد. بررسی‌ها نشان داد که با افزایش هد نسبی (H_T⁄P) و نیز با افزایش نسبت بزرگنمایی، استغراق موضعی و تداخل تیغه‌های ریزشی افزایش می‌یابد و سبب کاهش ضریب دبی در سرریز کنگره‌ای مثلثی و ذوزنقه‌ای می‌شود. نتایج نشان داد با افزایش نسبت راس، تا 12/7 درصد ضریب دبی کاهش می‌یابد. با افزایش عرض راس، تا 20 سانتی‌متر در سرریزکنگره‌ای ذوزنقه‌ای، منطقه‏ ای بزرگتر در بالادست راس سرریز با سرعت کمتر ایجاد می‌شود و آشفتگی بیشتری در جریان نزدیک به راس به وجود می آید. از طرفی، ایجاد سرعت کمتر در راس سبب حرکت جریان به سمت کناره‌ها می‌شود که حرکت جریان به سمت کناره‌ها سبب ایجاد آشفتگی بیشتری در کناره‌ها شده و ضریب دبی را کاهش خواهد داد. نتایج نشان داد همچنین که سرریزکنگره‌ای ذوزنقه‌ای با عرض راس در کناره‌ها، عملکرد کمتری را نشان می‌دهد زیرا میزان تداخل تیغه‌های ریزشی و استغراق موضعی در راس آن بیشتر است.

کلیدواژه‌ها

• استغراق موضعی
• تداخل تیغه ریزشی
• سرریز کنگره‌ای ذوزنقه‌ای
• سرریز کنگره‌ای مثلثی

موضوعات

• مهندسی رودخانه

عنوان مقاله [English]

Simulating the effect of trapezoidal labyrinth weir apex ratio on discharge coefficient using Flow-3D software

نویسندگان [English]

• Saeb Alghezi ¹
• Javad Mozaffari ²

¹ Water science & engineering department, Arak University, Iran

² Associate Professor, Water Science & Engineering, Arak University, Iran

چکیده [English]

Introduction
Labyrinth weirs have a longer length than linear weirs and therefore pass more flow in the fixed width of the channel. Investigating a labyrinth weir with the highest efficiency at a fixed width can help reduce construction costs and also allow flow to pass at a lower height. However, investigating physical models to determine a labyrinth weir with a more appropriate efficiency will be costly. While using simulation software,
in addition to reducing costs, allows for the creation of different labyrinth weir shapes in the software. The discharge coefficient of a labyrinth weir is affected by various parameters, one of which is the apex ratio. These parameters can be effective on the  nappe interference, local submergence, and the creation of turbulence in the flow. In this study, the effect of different apex ratios in a labyrinth weir will be investigated.
 Methodology
In this research, the flow in triangular and trapezoidal Labyrinth weir was investigated using FLOW 3D software and RNG k-ε model.To investigate the effect of the apex ratio, nine labyrith weir models were simulated with magnification ratios L⁄W=2, L⁄W=3, and L⁄W=4. Three triangular labyrith weir models with an apex ratio of zero, three trapezoidal labyrith weir models with an apex ratio of 0.125, and three trapezoidal labyrith weir models with an apex ratio of 0.250 were simulated. Also, to investigate the effect of the weir wall angle with the channel wall, a trapezoidal labyrith weir model with an apex ratio of 0.25 on the side was investigated.
 Results and Discussion
Investigations showed that with an increase in the water head ratio (H_T⁄P) and also with an increase in the magnification ratio, the local submergence and the nappe interference increases and causes a decrease in the discharge coefficient in the triangular and trapezoidal labyrinth weir. Although it seems that the greater distance between the two sides of the trapezoidal labyrinth weir at the apex compared to each other, caused a decrease in local submergence and an increase in the discharge coefficient, but the results showed that the triangular labyrinth weir had a better performance. By increasing the apex width up to 20 cm in a trapezoidal weir, a larger area will be created upstream of the weir apex with a lower velocity and more turbulence will be created in the flow near the apex. On the other hand, creating a lower velocity at the apex will cause the flow to move to the sides, which will cause the flow to move to the sides and create more turbulence on the sides and will reduce the discharge coefficient. Also, the results showed that trapezoidal labyrinth weir with apex width on the sides had lower performance because the amount of nappe interference and local submergence at the apex will be higher.
Conclusions
The study of the k-ε RNG turbulence model and comparison with laboratory data showed that the model used had acceptable accuracy in simulation. Increasing the water head ratio has caused a decrease in the discharge coefficient in the weir in all models. The reason is the increase in local submergence and napee interference. Local submergence causes the effective length of the labyrinet weir to decrease. Also, the nappe interference causes resistance to the flow and reduces the discharge coefficient. Increasing the magnification ratio causes more nappe interference and local submergence at downstream of weir and causes transverse curvature in the flow and collision of transverse jets and creates turbulence at upstream of weir. As a result, these factors will cause a decrease in the discharge coefficient. At the same magnification ratios, the trapezoidal labyrinth weir has a lower efficiency than the triangular labyrinth weir. It seems that although the nappe interference and local submergence at the apex of the trapezoidal labyrinet weir has decreased, the perpendicularity of the flow at the apex to the weir wall will cause more turbulence and reduce performance.

کلیدواژه‌ها [English]

• Local submergene
• Nappe interference
• Trapezoidal labyrinth weir
• Triangular labyrinth weir