نوع مقاله : مقاله پژوهشی
نویسندگان
1 استادیار گروه سازه های آبی، دانشکده مهندسی آب و محیط زیست، دانشگاه شهید چمران اهواز، اهواز، ایران
2 استاد گروه سازه های آبی، دانشکده مهندسی آب و محیط زیست، دانشگاه شهید چمران اهواز، اهواز، ایران
چکیده
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Meanders in rivers are critical areas for studying flow patterns. Flow within river bends is influenced by centrifugal forces and pressure gradients. Given that rivers exhibit various bed slopes, studying the three-dimensional flow pattern in such channels is of significant importance. The objective of this study was to investigate the three-dimensional velocity components of flow in gentle and sharp 90-degree bends with sloped beds. Experiments were conducted in a channel with central curvature radius-to-width ratios of two, four, and six. Velocity measurements were performed using the Vectrino velocity meter, one of the most advanced instruments for measuring flow velocity. The results indicated that due to the effect of the water's weight component along the bed slope, the maximum longitudinal flow velocity in the initial sections of the bend for gentle bends occurs near the outer wall. However, in the later sections, it shifts closer to the middle of the channel width. Across all Froude numbers and all bends, the transverse velocity profile could be divided into two layers: one near the outer wall of the bend with maximum velocity and another near the inner wall of the bend with minimum velocity, located at 25% of the channel width. It was also observed that by doubling the Froude number from 0.05 to 0.1, the location of maximum shear stress extended from the range of up to 30 degrees to the range of up to 50 degrees of the bend section, and was concentrated near the outer wall.
کلیدواژه‌ها [English]
EXTENDED ABSTRACT
In the design of irrigation and drainage networks, it is essential to have a comprehensive understanding of the hydraulic behavior of flow in curved paths. These curved paths, often found in natural rivers and man-made structures, can lead to issues such as erosion and sediment deposition if not carefully considered. To mitigate these issues, a thorough understanding of flow patterns in bends is crucial for effective and economical design. However, the complex interplay of flow and bed topography in bends makes it challenging to achieve a complete understanding of these patterns. Numerous studies have investigated the impact of bend curvature on flow patterns in open channels (Elyasi et al., 2014; Liu et al., 2024; Pradhan et al., 2024; Shaheed et al., 2021). These studies, employing experimental, numerical, and Soft Computing methods, have explored various aspects of flow behavior in bends. Despite extensive research on flow patterns in bends, no studies have specifically investigated the effect of channel bend radius on flow characteristics in sloped surfaces. Therefore, this study aims to experimentally examine the influence of bend radius, ranging from sharp to mild, on flow patterns in sloped channels.
The study was conducted in a rectangular laboratory flume with a width of 20 cm. The flume was designed to create bends with varying centerline radius to width ratios (R/B), specifically 2, 4, and 6, representing sharp, moderate, and mild bends respectively. To ensure controlled flow conditions, the inlet flow rate was regulated using an electromagnetic flow meter, and mesh screens were employed to smooth the incoming flow. The channel bed was covered with a wooden sheet, and a similar sheet was placed over the curved section after each experiment to maintain consistency. Two Froude numbers (Fr), 0.05 and 0.1, were used to represent different flow regimes. The water surface elevation was kept constant at the entrance of the bend.
A 3D Acoustic Doppler Velocimeter (ADV), specifically the Vectrino+, was utilized to measure the three-dimensional velocity components of the flow. The measurement points were distributed along the channel length, width, and depth to capture a comprehensive representation of the flow field. The collected data, initially in polar coordinates, was converted to Cartesian coordinates using mathematical relationships to facilitate visualization and analysis of the velocity components.
The longitudinal velocity distribution in the bend exhibited distinct patterns. As the flow entered the bend, the maximum velocity shifted from the center towards the inner wall due to the sudden change in curvature and the resulting pressure gradient. This shift was consistent with previous studies on horizontal beds. However, in the sloped bed, the maximum velocity shifted towards the outer wall due to the influence of gravity and the added force of the fluid weight in the direction of the slope. This observation suggests that the slope significantly alters the velocity distribution compared to horizontal beds. Secondary flows, characterized by transverse velocity components, play a crucial role in flow patterns within bends. The study revealed that the development and structure of secondary flows are influenced by the curvature ratio of the bend. In milder bends (higher R/B ratios), a single rotational flow formed near the inner wall, gradually expanding to encompass the entire cross-section as the flow progressed along the bend. However, in sharper bends (lower R/B ratios), an additional, smaller rotational flow formed near the inner wall, opposite to the direction of the main secondary flow. Bed shear stress is a critical factor in erosion and sediment transport processes within river bends. These findings suggest that the location and extent of the high shear stress zone are influenced by both the bend sharpness and the flow regime.
The study highlights the significant impact of channel bend radius on flow characteristics in sloped surfaces. The interaction of the slope and the centrifugal force results in a unique velocity distribution that differs from that observed in horizontal beds. The development and structure of secondary flows are also influenced by the bend sharpness, with sharper bends exhibiting more complex flow patterns. The distribution of bed shear stress is crucial for understanding erosion and sediment transport processes. The study identified the location and extent of the high shear stress zone and its dependence on both bend sharpness and flow regime. The findings of this study provide valuable insights for the design of irrigation and drainage networks, as well as for understanding and managing river morphology in natural settings.
For this research article, the individual contributions are as follows: Conceptualization, [Author A] and [Author B]; methodology, [Author B]; software, [Author A]; validation, [Author A], [Author B], and [Author B]; formal analysis, [Author B]; investigation, [Author A]; resources, [Author A]; data curation, [Author B]; writing—original draft preparation, [Author B]; writing—review and editing, [Author B]; visualization, [Author B]; supervision, [Author B]; project administration, [Author B]; funding acquisition, [Author A]. All authors have read and agreed to the published version of the manuscript.
The data that support the findings of this study are available. For further inquiries regarding the data, please contact author’s email.
The authors are grateful for the financial support of the Research Council of Shahid Chamran University of Ahvaz (GN: SCU.WH1403.43525).
The authors avoided data fabrication, falsification, plagiarism, and misconduct.
The author declares no conflict of interest.
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