تحلیل عملکرد شکاف کنترل مرکب ذوزنقه‌ای تحت جریان هیدرولیکی زیربحرانی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه آب و محیط زیست، دانشکده مهندسی عمران، دانشگاه علم و صنعت ایران، تهران، ایران

2 گروه مهندسی عمران، دانشکده فنی و مهندسی، دانشگاه ارومیه، ارومیه، ایران

چکیده

در محل اتصال کانال‌های انتقال آب حامل جریان زیربحرانی با سازه‌های هیدرولیکی نظیر سیفون‌های معکوس و تندآب‌ها، می‌توان از شکاف‌های کنترل برای ایجاد جریان با شرایط بحرانی و جلوگیری از افت سطح آب یا پس زدن آن در کانال بالادست بهره گرفت. در تحقیق حاضر، عملکرد شکاف کنترل مرکب ذوزنقه‌ای برای اولین بار مورد بررسی قرار گرفته و نحوه تعیین بهینه ابعاد آن به‌ازاء وقوع دبی‌های مختلف در بازه دبی طراحی کانال ارائه می‌شود. به‌این‌منظور، با استفاده از معادلات انرژی مخصوص و در نظر گرفتن شرایط بحرانی جریان بر روی این سازه، روابط موردنیاز استخراج شده و با حل هم‌زمان معادلات غیرخطی با استفاده از روش گرادیان کاهش‌یافته، ابعاد بهینه سازه برای سه حالت هیدرولیکی مختلف (دبی‌های 10، 25 و 50 درصد دبی طراحی) محاسبه می‌گردد. سپس، نتایج حاصل با استفاده از مدلسازی در نرم‌افزار Flow3D نیز صحت‌سنجی می‌شود. با استفاده از این نرم‌افزار، مشخصات جریان از جمله عمق، انرژی مخصوص، توزیع سرعت و مسیر خطوط جریان بر روی شکاف کنترل پیشنهادی مورد ارزیابی قرار می‌گیرد. نتایج بررسی‌ها نشان داد سازه یادشده قادر است شرایط جریان بحرانی را در بازه‌ی گسترده‌ای از دبی‌ها با دقت مناسبی حفظ نماید. مقایسه داده‌های نظری و نتایج عددی حاکی از تطابق قابل‌توجه با میانگین خطای کمتر از 5 درصد بود. به‌طور خاص، در حالت‌های مختلف هیدرولیکی، خطای محاسبه عمق جریان بین 9/2 تا 5/4 درصد و خطای محاسبه انرژی مخصوص بین 2/3 تا 8/4 درصد مشاهده شد. از پژوهش حاضر می‌توان دریافت که استفاده از شکاف کنترل مرکب ذوزنقه‌ای موجب ایجاد شرایط بحرانی در جریان شده و از پایین افتادن سطح آب و یا پس زدن جریان در کانال بالادست به‌ازاء وقوع حالات هیدرولیکی گوناگون جلوگیری می‌نماید.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Performance analysis of combined trapezoidal control notch in the sub-critical flow

نویسندگان [English]

  • Amirhossein Mahmoudi Rahmani 1
  • Roohollah Zanganeh 1
  • Amir Ghaderi 2
1 School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran
2 Department of Civil Engineering, Faculty of Engineering, Urmia University, Urmia, Iran
چکیده [English]

At the connection point of water conveyance canals carrying sub-critical flow with hydraulic structures such as inverted siphons and chutes, control notches can be used to create critical flow conditions and prevent water level drop in the downstream section or backwater flow in the upstream channel. In the present study, the performance of a combined trapezoidal control notch is investigated for the first time, and a method to determine its optimal dimensions for various discharges within the channel’s design discharge range is presented. For this purpose, the required equations are derived using specific energy equations and considering critical flow conditions over the notch and the non-linear equations are simultaneously solved using GRG method for discharges of 10, 25 and 50% of the design discharge. The obtained results are also validated through modeling in Flow3D software. Using this software, the flow characteristics including flow depth, specific energy, velocity profiles and stream lines over the proposed notch are evaluated. The results showed that the proposed structure is able to keep the flow in critical condition over different design discharges. The comparison between analytical results and the numerical method resulted in the proper compliance of these two methods with errors of less than 5%. Errors in flow depth ranged between 2.9% to 4.5%, and in specific energy 3.2% to 4.8%. The findings show that the use of a combined trapezoidal control notch creates critical flow conditions and prevents water level drop or backwater flow in the upstream channel under various hydraulic conditions.

کلیدواژه‌ها [English]

  • Combined Trapezoidal Control Notch
  • Critical Depth
  • Specific Energy
  • Specific Force
  • Sub-critical Flow

Introduction

The existence of hydraulic structures such as chutes and spillways in water conveyance canals carrying sub-critical flow, sometimes leads to occurrence of high energy flow and excessive shear stress in the downstream section or backwater flow in the upstream section. Therefore, the presence of a water level regulator seems crucial. Typically, a trapezoidal weir with a crest level aligned with channel bed, which is called a trapezoidal control notch, is used to prevent water level drop or any erosion in canal. In some areas with variable hydraulic and hydrologic conditions, it is recommended to use combined sections to be able to handle very low flows to very high flows within the design discharge range. In this study, the specific energy method for designing control notches is used to design a combined trapezoidal control notch under various hydraulic conditions and its performance is investigated using Flow3D modeling software.

Method

In this study, a combined trapezoidal control notch is designed using the specific energy balance method under three different hydraulic conditions to regulate sub-critical flow in open channels. The structure consists of lower and upper sections with dimensions derived from critical flow equations. Numerical modeling was performed using Flow3D to investigate the performance of the structure. In other words, simulations validated water depth and specific energy against theoretical calculations. Design equations were solved using generalized reduced gradient method and the corresponding geometry was created in AutoCAD. This approach ensured critical flow maintenance without any backwater flow in the upstream section of the cannel.

Results

The combined trapezoidal control notch effectively maintained critical flow conditions across the tested discharge range (20–100% of design flow) for every hydraulic condition. Also, Flow3D simulations confirmed stable water depths upstream and specific energy, with less than 5% deviation from calculations. The structure prevented backflow and minimized water level fluctuations. The design demonstrated robustness in maintaining hydraulic efficiency under variable flow conditions.

Conclusions

This study indicated that the combined trapezoidal control notch effectively regulates subcritical flow while maintaining critical conditions across varying discharges. Numerical simulations validated the theoretical approach, showing desirable agreement with predicted hydraulic performance. These findings support the notch's practical application in water management systems requiring flow control.

Author Contributions

Conceptualization, R.Z. and A.M.; methodology, R.Z. and A.M.; software, A.M. and A.GH.; validation, A.M., R.Z. and A.GH.; formal analysis, A.M., R.Z. and A.GH.; investigation, A.M., R.Z. and A.GH.; writing—original draft preparation, A.M.; writing—review and editing, R.Z. and A.GH; visualization, A.M.; supervision, R.Z.

All authors have read and agreed to the published version of the manuscript

Data Availability Statement

Data is available on reasonable request from the authors.

Acknowledgements

The authors would like to thank all participants of the present study.

Ethical considerations

The authors avoided data fabrication, falsification, plagiarism, and misconduct.

Conflict of interest

 The authors declare no conflict of interest.

 

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تحقیقات آب و خاک ایران
دوره 56، شماره 8
آبان 1404
صفحه 2119-2136

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