بررسی آزمایشگاهی هیدرودینامیک جریان در آبراهه‌های مرکب پیچان با دیواره سیلاب‌دشت هم‌راستا

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه علوم و مهندسی آب، دانشکده کشاورزی، دانشگاه فردوسی مشهد، مشهد، ایران

2 گروه علوم و مهندسی آب، دانشکده کشاورزی، دانشگاه فردوسی مشهد، مشهد، ایران.

چکیده

پیش­بینی رفتار جریان در قوس رودخانه­های مرکب پیچانی در برنامه­های حفاظت سواحل (الگوی انتقال و ته­نشست رسوبات)، انتشار آلودگی و کنترل سیلاب کاربردی و دارای اهمیت زیادی می­باشد. ازاین‌رو؛ هیدرودینامیک جریان در آبراهة مرکب - پیچان با ضریب خمیدگی ثابت 3/1، و هم­راستایی دیوارة سیلاب­دشت با کانال اصلی در دو عمق نسبی 3/0 و 55/0 با استفاده از مدل آزمایشگاهی بررسی شد. به دلیل ساختار سه­بعدی جریان در قوس آبراهه، تجزیه‌وتحلیل داده­ها در هفت مقطع عرضی با زوایای صفر، 30 و 60 درجه نسبت به رئوس قوس با استفاده از سرعت­سنج ADV در صفحه­های مشبک با ابعاد cm2 3×3 و عمود بر جریان انجام گرفت. نتایج نشان داد؛ گرادیان هر سه مؤلفه سرعت در عمق نسبی 3/0 بیش­تر از 55/0 است که نشان از قدرت بیشتر گرداب­ها و شدت آشفتگی در عمق نسبی کمتر دارد. نسبت سرعت متوسط در ساحل خارجی سیلاب­دشت به‌سرعت متوسط کل مقطع، مشابه ساحل داخلی، تابع عمق نسبی جریان بوده و به ترتیب کمتر و بیشتر از یک است. به همین علت، جریان در سیلاب­دشت خارجی بر خلاف سیلاب­دشت داخلی اثر کاهنده بر سرعت جریان در آبراهه اصلی دارد. همچنین نسبت سرعت متوسط جریان در آبراهه اصلی به‌سرعت متوسط کل به­ازای افزایش عمق نسبی تقریبی از 3/0 به 55/0 کاهش‌یافته و به یک نزدیک می­گردد. تنش رینولدز  در نزدیک بستر آبراهه اصلی، دارای مقادیر بیشینه و مثبت بوده و با فاصله گرفتن از بستر، با روندی کاهشی، به مقدار منفی رسیده و کمینه خود را در نزدیکی سطح جریان نشان می­دهد. همچنین در لبه دشت­های سیلابی نیز مقدار این پارامتر موضعی افزایش می­یابد.

کلیدواژه‌ها


عنوان مقاله [English]

Experimental Study of Flow Hydrodynamics in Meandering Compound Channels with Parallel Floodplain Wall

نویسندگان [English]

  • sobhan moradi 1
  • kazem esmaili 2
  • saeed reza khodashenas 2
1 Department of Water Science and Engineering, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran.
2 Department of Water Science and Engineering, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran.
چکیده [English]

Predicting the flow behavior in the arch of meandering compound channels has a great importance in coastal protection programs (sediment transport and deposit pattern), pollution propagation and flood control. Therefore; the hydrodynamics of the flow in the composite-meander channel with a constant sinuosity factor 1.3, and at two relative depths 0.3 and 0.55 were investigated using a laboratory model. Due to the three-dimensional structure of the flow in the channel bend, the data were analyzed in seven cross sections with angles of zero, 30 and 60 degrees to the vertices of the bending apex using an ADV velocity-meter in lattice plates with dimensions 3*3 cm2 and perpendicular to the flow. The results showed that the gradient of three components of velocity at relative depths 0.3 are greater than 0.55 which shows more vortex power and intensity of turbulence in less amount of relative depth. average velocity ratio on the outer beach of the floodplain to the average velocity of the whole section, similar to the inner beach, has been a function of the relative depth of the flow, and is less and more than one, respectively. For this reason, the flow in the outer floodplain, unlike the inner floodplain, has a reducing effect on the flow velocity in the main channel. Also, as the relative depth increases from 0.3 to 0.55, the ratio of the average flow velocity in the main channel to the total average velocity decreases and approaches one. Reynolds stress () had maximum and positive values near the main channel bed, and by moving away from the bed, it has reached a negative value and it shows its minimum amount near the flow surface. The value of this local parameter also increases at the edge of floodplains.

کلیدواژه‌ها [English]

  • River bend
  • Momentum Transmission
  • Turbulent Flow
  • Compound Meander Channel
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