ارزیابی روش تعادل مومنتم در تعیین تنش برشی آبراهه های سیلاب دشتی پیچانی

نوع مقاله : پژوهشی

نویسندگان

1 گروه علوم ومهندسی آب دانشگاه فردوسی مشهد

2 گروه علوم و مهندسی آب دانشگاه فردوسی مشهد

چکیده

با ‌توجه به ماهیت سه‌بُعدی و پیچیده‌ی جریان در آبراهه‌های سیلاب دشتی پیچانی و به‌ویژه بر‌اساس نقش مؤثر جریان‌های ثانویه و انتقال مومنتم در قوس‌ها، محاسبه‌ی پارامتر تنش برشی توسط روش-های ارائه‌شده برای کانال‌های مستقیم با چالش‌هایی مواجه است. روش تعادل مومنتم، که براساس حل معادله‌ی تعادل مومنتم برای نقاط جریان کار می‌کند، می‌تواند در تعیین پارامتر تنش برشی در کانال-های پیچانی استفاده شود. در یک مدل فیزیکی، شامل یک آبراهه‌ی آزمایشگاهی مستطیلی، مجرای پیچانی همراه با دو سیلاب‌دشت، تنش برشی در طول جریان با استفاده از روش تعادل مومنتم محاسبه و نتایج با روش توزیع لگاریتمی سرعت و تنش برشی رینولدز مقایسه شد. مقادیر بیشینه‌ی تنش برشی نسبی در روش‌های MBM، RSM، و LLM به‌ترتیب 43/5 و 24/7 در مقطع چهارم و 05/6 در مقطع اول بوده است. با‌توجه به بررسی نتایج، روش MBM می‌تواند به‌عنوان روشی کاربردی در ارزیابی مقادیر تنش برشی در پیچان‌رودها معرفی شود.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Assessment of the Momentum Balance Method for Determination of Shear Stress in Compound Meandering Channels

نویسندگان [English]

  • V. Moratzavi Amiri 1
  • K. Esmaili 2
1 Department of Water Science and Engineering, Ferdowsi University of Mashhad, Mashhad, Iran
2 Department of Water Science and Engineering, Ferdowsi University of Mashhad, Mashhad, Iran
چکیده [English]

Shear stress is one of the most essential factors in the flow dynamics of open channels. The hydraulics of sediment transport in channels are affected by how and the amount of this factor. Considering the three-dimensional and complex nature of the flow in meandering compound channels, and based on the effective role of secondary flows and momentum transfer, especially in curves, calculating this parameter using the methods provided for straight channels is challenging. The Momentum Balance Method, introduced as one of the shear stress determination methods in straight channels, can be used to determine the shear stress in meandering channels. In this research, using the 3-D flow velocity component data measured by ADV, the distribution of shear stress along the flow path in a meandering compound channel was investigated. The transverse distribution of streamwise velocity was investigated in a physical model, including a rectangular concrete channel, a meandering main channel, and two floodplains. Then, the transverse distribution of shear stress in five sections along the flow was calculated using the momentum balance method, and the results were compared using the logarithmic distribution method of velocity and Reynolds shear stress in these sections. Also, the amount of shear stress at four depths of the main channel is illustrated. Since the determination of maximum shear stress areas can be effective in flow and sediment studies, and issues related to river maintenance, such as bed erosion, especially in arches, the maximum values of relative shear stress in MBM, RSM, and LLM methods were determined as 5.43 and 7.24 in the fourth section and 6.05 in the first section, respectively. The minimum amounts of shear stress were observed in section 5 in both RSM and MBM methods. According to the reviewed results, the MBM method can be introduced as a practical method for evaluating shear stress values in meandering rivers.

کلیدواژه‌ها [English]

  • Momentum exchange
  • Reynolds shear stress
  • RSM
  • MBM
  • Meandering compound channels
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