نوع مقاله : مقاله پژوهشی

نویسندگان

• کیمیا اخوان ¹
• منوچهر حیدرپور ²

¹ دانشجو دکترای علوم و مهندسی آب، گروه علوم و مهندسی آب، دانشکده کشاورزی، دانشگاه صنعتی اصفهان، اصفهان، ایران

² استاد گروه علوم و مهندسی آب، دانشکده کشاورزی، دانشگاه صنعتی اصفهان، اصفهان، ایران

چکیده

پرش یا جهش هیدرولیکی، از نوع جریان‌های متغیر سریع است که در آن، جریان از فوق بحرانی به زیربحرانی تغییر حالت می‌دهد. گنجاندن بسترهای زبر در کف کانال، به حداکثرسازی اتلاف انرژی منجر می‌شود که نتیجه آن کاهش قابل‌توجه در عمق متوالی و طول غلتاب پرش است. این نتایج پیامدهای مهمی برای طراحی مقرون‌به‌صرفه حوضچه‌های آرامش دارد که معمولاً با پرش‌های هیدرولیکی مواجه می‌شوند. یکی از ویژگی‌هایی که توجه محققان پرش بر بستر زبر را جلب کرده، نیمرخ سرعت پرش است. در این پژوهش اثر آرایش صفحات مستغرق بر روی نیمرخ‌های سرعت پرش هیدرولیکی حوضچه آرامش در دامنه اعداد فرود 4/8 تا 9/14 اندازه‌گیری شده است . نتایج نشان داد مقدار پارامتر بی‌بعد ضخامت لایه مرزی /b ،0.72 بوده است که در آرایش موازی صفحات مستغرق با زاویه برخورد ۷۵ نسبت به زاویه ۴۵ و ۹۰ بیشترین مقدار را داشته است، درحالیکه این مقدار در آرایش پروانه‌ای با زاویه برخورد ۴۵ بدست می‌آید و از 0/56 تا 0/01 نسبت به نتایج سایر پژوهشگران افزایش داشته است. بنابر این بهترین مشخصه پارامتر بی‌بعد ضخامت لایه مرزی، /b بر روی زبری مصنوعی با آرایش پروانه‌ای و زاویه برخورد ۴۵ صفحات مستغرق با یک عامل تاثیرگذاربوده است.

کلیدواژه‌ها

• پرش هیدرولیکی
• نیمرخ‌های سرعت
• آرایش پروانه‌ای

موضوعات

• هیدرولیک

عنوان مقاله [English]

Investigating the Influence of Submerged Block Arrangement and Angle of Incidence to Flow Direction on Boundary Layer Thickness in Stilling Basins

نویسندگان [English]

• Kimia Akhavan ¹
• Manouchehr Heidarpour ²

¹ PhD Student, Department of Water Science and Engineering, Faculty of Agriculture, Isfahan University of Technology, Isfahan, Iran.

² Professor, Department of Water Science and Engineering, Faculty of Agriculture, Isfahan University of Technology, Isfahan, Iran.

چکیده [English]

 Extended Abstract
Introduction
Hydraulic jump is a type of rapidly varied flow in which the flow transitions from supercritical to subcritical. Incorporating rough beds at the channel bottom leads to the maximization of energy dissipation, resulting in a significant reduction in conjugate depth and roller length. These results have important implications for the cost-effective design of stilling basins, which commonly encounter hydraulic jumps.one feature that has attracted the attention of researchers studying jumps on rough beds is the velocity profile of the jump on rough beds. In this research, the effect of the arrangement of submerged vanes on the velocity profiles of the hydraulic jump in a stilling basin was measured for Froude numbers ranging from 4.8 to 9.14.
Methodology
Experiments were conducted in the hydraulic laboratory in a rectangular channel with physical dimensions of length 8 m, width 0.4 m, and height 0.6 m. Submerged vanes were used as roughness elements on the bed of the laboratory channel. These vanes are made of Teflon, and the geometry of a submerged vane, including its width (w), thickness (t), angle of attack (θ), and vane length (L), is one of the parameters affecting the characteristics of the hydraulic jump. For measuring the flow velocity, an instrument called a Pitot tube was used. In the present study, for 12 experimental models, velocity was measured at five cross-sections along the width, and at three points across the width in each cross-section. Measurements were taken at five points along the depth, with equal spacing ratios from the channel bed to the free water surface, and the readings were averaged across three different widths.
Results and Discussion
In general, the maximum velocity value decreases with distance from the beginning of the jump and occurs at a lower depth from the water surface. The bed with submerged vanes causes a reduction in the flow velocity magnitude, and its maximum value occurs at higher points compared to the classical jump. The significance of the non-dimensionalized velocity graphs lies in comparing the growth of the boundary layer across the cross-sections. The average value of δ/b is 0.62 and 0.72, and for 50 < x/D₁, the ratio δ/b lies above the average line. Due to the low effect of turbulence and secondary currents caused by the presence of submerged vanes, the boundary layer thickness is greater in regions of calm flow (  areas with  lower velocity). At values less than 50, the ratio δ/b decreases compared to the average line. The results showed that the value of the non-dimensional boundary layer thickness parameter, δ/b, was 0.72, which was highest in the parallel arrangement of submerged vanes at an attack angle of 75° compared to angles of 45° and 90°. Meanwhile, this value was obtained in the butterfly arrangement with an attack angle of 45° and increased from 0.56 to 0.01 compared to what other researchers have obtained.
Conclusions
 
Therefore, the best characteristic for the non-dimensional boundary layer thickness parameter, δ/b, on artificial roughness was achieved with the butterfly arrangement and a 45° attack angle of the submerged vanes, which proved to be an influential factor. In contemporary hydraulic jump research, the use of advanced techniques, such as machine learning tools and numerical simulations using Computational Fluid Dynamics (CFD), is increasing. Simulating hydraulic jumps with CFD is a complex task and requires careful attention to turbulence modeling, grid accuracy, boundary conditions, and various other factors. It is essential to employ advanced techniques for comprehensive three-dimensional (3D) velocity and bed shear stress measurements. Conducting turbulence analysis will contribute to a more refined understanding of the underlying flow dynamics. Furthermore, the challenge of hydraulic jump stability on adverse slopes persists. Introducing roughness elements and sills can enhance hydraulic jump stability on adverse slopes. Investigating the potential effects of scale in such conditions is necessary. 

کلیدواژه‌ها [English]

• Hydraulic jump
• Velocity Profiles
• Butterfly Arrangement