نوع مقاله : مقاله پژوهشی

نویسندگان

• سارا احمدی عدلی ¹
• اکرم عباسپور ¹
• علی حسین زاده دلیر ¹
• جواد پارسا ²

¹ گروه علوم و مهندسی آب، دانشکده کشاورزی، دانشگاه تبریز، ایران

² گروه علوم ومهندسی آب، دانشکده کشاورزی، دانشگاه تبریز، ایران

چکیده

بهبود شرایط زیستمحیطی رودخانه‌ها یکی از جنبه‌های اصلی مهندسی رودخانه در دهه‌های گذشته بوده است. سازه‌های زیست‌محیطی عموما با هدف کنترل بستر رودخانه‌ها، تثبیت سواحل و بهبود شرایط اکوسیستم رودخانه‌ها طراحی و اجرا می‌شوند. صفحات متصل به ساحل یکی از انواع سازه‌های زیست‌محیطی می‌باشند که در تحقیق حاضر تاثیر حالت‌های مختلف هندسی و نفوذپذیری این سازه‌ها بر الگوی جریان متلاطم مورد بررسی قرار گرفته است. با استفاده از نرم‌افزار فلوئنت و مدل گرداب‌های بزرگ، میدان جریان حول صفحات متصل به ساحل در یک کانال مستقیم شبیه‌سازی شده است. دقت و قابلیت مدل گرداب‌های بزرگ، با مقایسه مقادیر پروفیل سطح آب به دست آمده از مدل عددی با نتایج آزمایشگاهی، مورد ارزیابی قرار گرفته است. نتایج برآیند سرعت حول صفحات متصل به ساحل، نشان‌دهنده وجود دو ناحیه در اطراف این سازه‌ها می‌باشد که ناشی از اثرات موضعی صفحات متصل به ساحل و تنگ‌شدگی کانال تشکیل شده‌اند. پارامترهایی هم‌چون سرعت دماغه، سرعت بیشینه و زاویه انحراف جریان تحت تاثیر اندرکنش گردابه‌های مختلف، شرایط هندسی و ساختاری صفحات متصل به ساحل دچار تغییر می‌شوند. به طور کلی با افزایش نفوذپذیری، صفحات متصل به ساحل تاثیر قابل توجهی بر الگوی جریان ندارند. هم‌چنین با افزایش نفوذپذیری، بیشینه تنش برشی بستر به محور مرکزی کانال منتقل می‌شود.

کلیدواژه‌ها

• سازه‌های زیست‌محیطی
• فلوئنت
• مدل گرداب‌های بزرگ
• نفوذپذیری
• هندسه

موضوعات

• مهندسی رودخانه

عنوان مقاله [English]

Turbulent Flow Characteristics Around Bank-Attached Vanes

نویسندگان [English]

• Sara Ahmadi Adli ¹
• Akram Abbaspour ¹
• Ali Hosseinzadeh Dalir ¹
• Javad Parsa ²

¹ Dept. Water Science and Engineering, Faculty of Agriculture, University of Tabriz, Iran

² Dept. Water Science and Engineering, Faculty of Agriculture, University of Tabriz, Iran

چکیده [English]

Introduction:

Regarding the growing awareness of the environmental issues over the past decades, the main aspect of river engineering has been the environmental improvement of the rivers. River restoration refers to the environmental and ecological aspects of river engineering. New eco-friendly river restoration techniques such as vanes, deflectors, W-weir, U-weir, cross vane and J-hook vanes are generally designed and implemented in accordance with different hydraulic conditions to control the river bed, stabilize the banks, improve the river ecosystem conditions and to overcome the negative effects of the conventional structures on river natural functioning. These structures performance has been evaluated in many studies. Bank-attached vanes are one of the eco-friendly structures. In the present paper, the effect of the different geometry and permeability rates of these structures on turbulent flow pattern has been investigated.



Methods:

Turbulent flows are simulated by solving the Navier-Stokes equations. FLUENT software and large eddy simulation (LES) mathematical model were used to solve the Navier-Stokes equations and simulate the turbulent flow field around bank-attached vanes in a straight channel. Smagorinsky-Lilly subgrid-scale model was used to model unclosed residual stress tensor (τ_ij) in the governing equations. It must be noted that subgrid-scale turbulence models in FLUENT employ the Boussinesq hypothesis to calculate subgrid-scale stresses (τ_kk). To simulate the flow field affected by different bank-attached vanes, boundary conditions, flow depth and approach flow velocity were determined. Streamwise measured and simulated free surface profiles around 30% permeable rectangular vane at different Y/L positions were compared to evaluate the numerical model accuracy. Numerical and experimental results agreed well since relative average error values were 4-5% in all cases. Furthermore, a mesh composed of approximately 150000 elements was considered as an optimum mesh for all created models to resolve flow characteristics. However, due to the different permeability rates, generating the optimum mesh for all cases it is not possible.



Results:

Velocity magnitude results around bank-attached vanes revealed the presence of two flow zones which are the main flow field, upstream and downstream separation region formed due to the local effects of the bank-attached vanes and channel constriction. These zones are separated by a fully turbulent and dynamic flow, named the detached shear layer. In general high velocity zones near the vanes tip region and channel bed effect the local scour hole characteristics, thus tip velocity and maximum velocity variations are investigated at the near bed horizontal plane. Moreover, parameters such as tip velocity, maximum velocity and flow separation angle are affected by the interaction of different eddies, varying geometry and permeability conditions. Results showed that tip velocity and maximum velocity ratios have declining trend with increasing permeability rate. Generally by increasing the permeability rate, bank-attached vanes do not have a significant effect on flow pattern. Bed shear stress is considered as one of the primary parameters that affect the main flow field and downstream separation zone, results showed that due to the local effects of the bank-attached vanes, channel constriction and interaction of the horseshoe vortices downstream of the simulated vanes, maximum bed shear stress values mainly occurred at X⁄L= 2.4 section. Furthermore, by increasing the permeability rate, maximum bed shear stress values shifted towards the channel centerline. In general, due to the triangular vanes cross-sectional opening (geometry), these structures effect on flow characteristics is smaller in comparison to the rectangular vanes.

کلیدواژه‌ها [English]

• Eco-Friendly Structures
• FLUENT
• Geometry
• Large Eddy Simulation
• Permeability