شبیه‌سازی عددی اثر هم‌پوشانی پوشش گیاهی صلب در کانال‌ روباز مستقیم با استفاده از OpenFOAM

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری، گروه مهندسی آب و سازه‌های هیدرولیکی، دانشکده مهندسی عمران، دانشگاه سمنان، سمنان، ایران.

2 دانشیار، گروه مهندسی عمران-آب و سازه‌های هیدرولیکی، دانشکده فنی، دانشگاه ارومیه، ارومیه، ایران.

3 دانشیار، گروه مهندسی آب و سازه‌های هیدرولیکی، دانشکده مهندسی عمران، دانشگاه سمنان، سمنان، ایران.

چکیده

در این تحقیق به منظور درک مکانیسم الگوی جریان در کانال‌ها دارای پوشش گیاهی، به بررسی عددی جریان در یک کانال مستطیلی با نرم‌افزار OpenFOAM پرداخته شد. ابتدا از دو حلگر این نرم‌افزار (icoFoam و pimpleFoam) برای محاسبه پروفیل‌های سرعت در هر دو جهت طولی و عرضی برای چهار مقطع منتخب در کانال مستطیلی با یک استوانه مربعی شکل استفاده شد. از مقایسه نتایج شبیه‌سازی‌ با داده‌های موجود، حلگر icoFoam با عملکرد بهتر (خطای شش درصد) برای مدل توسعه‌یافته بعدی انتخاب گشت. سپس مدل جدید با دو استوانه مربعی شکل دوپشته با نسبت فاصله دو و نیم و پنج ایجاد گردید. الگوهای جریان، توزیع سرعت و ویژگی‌های فشار در کانال با سرعت‌های جریان ورودی متفاوت برای این دو مورد بررسی شدند. مشاهده شد که یک اختلال در میدان جریان در تمام شبیه‌سازی‌ها رخ داده و جریان از حالت دایمی به حالت غیردایمی، در یک سرعت بحرانی، تغییر کرد. این حالت ناپایداری در فاصله بین استوانه‌ها برای نسبت فاصله پنج در عدد رینولدز متوسط هشت روی داد، در حالی که برای نسبت فاصله دو و نیم در عدد رینولدز متوسط 32 دیده شد. حداکثر مقادیر جداول زمانی سرعت‌های طولی و عرضی در دوره 200 ثانیه‌ای برای چهار حالت (شامل دو عدد رینولدز و دو نسبت فاصله مختلف) در دو محدوده مکانی ترسیم و به طور کامل بررسی شد. با توجه به نتایج می‌توان گفت که همپوشانی نقش مهمی بر ویژگی‌های -جریان در آرایش‌های دوپشته دارد و با افزایش 55 درصدی نسبت فاصله بین استوانه‌ها، مقدار سرعت بحرانی 74 درصد کاهش می‌یابد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

A numerical simulation of overlay effect of rigid vegetation in a straight open channel by OpenFOAM

نویسندگان [English]

  • Komeil Samet 1
  • Mirali Mohammadi 2
  • Khosrow Hoseini 3
  • Saeed Farzin 3
1 Ph.D. Student, Department of Water Eng., & Hydraulic Structures, Faculty of Civil Engineering, Semnan University, Semnan, Iran.
2 Associate Professor, Department of Civil Engineering (Water and Hydraulic Structures), Faculty of Engineering, Urmia University, Urmia, Iran,
3 Associate Professor, Department of Water Eng., & Hydraulic Structures, Faculty of Civil Engineering, Semnan University, Semnan, Iran.
چکیده [English]

In order to understand the mechanism of flow patterns in vegetated channels, the flow located in a rectangular channel was numerically investigated by using OpenFOAM software. Firstly, two solvers of that software (i.e. icoFoam and pimpleFoam) were used to calculate the velocity profiles in both longitudinal and cross-sectional directions for four selected sections in a rectangular channel with a square cylinder. By comparing the simulation results with the available data, the icoFoam solver with a better performance (six Percent Error) was selected for the next developed model. A new model was then created with two tandem square cylinders with spacing ratios of two and a half and five. Flow patterns, velocity distribution and pressure characteristics in the channel with different inlet flow velocities were investigated for two cases. It was observed that a flow field disturbance occurred in all simulations and the current changed from steady state to unsteady one at a critical velocity. This instability occurred in a distance between the cylinders for the spacing ratio of five at an average Reynolds number of eight, while for the ratio of two and a half it is occurred at an average Reynolds number of 32. The maximum values ​​of longitudinal and transverse velocity timelines in a period of 200 seconds for four states (including two Reynolds numbers and two different spacing ratios) were plotted in two spatial ranges and fully investigated. According to the results, it can be said that the overlap has an important role on the flow characteristics in tandem arrangements and by increasing the distance ratio between the cylinders by 55 percent, the critical velocity value decreases by 74 percent.

کلیدواژه‌ها [English]

  • Critical Velocity
  • Numerical Modelling
  • OpenFOAM
  • Spacing Ratio
  • Straight Channel
  • Tandem Rigid Vegetation
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