چكيده به لاتين
Natural channels and rivers rarely follow a straight path, often exhibiting meandering shapes. Due to the natural meanders that shape the river channels, understanding the flow characteristics is essential. Additionally, the presence of vegetation in the bed and banks of rivers and its interaction with the bends has a significant impact on the ecosystem and flow structure, as it alters the flow pattern and the distribution of hydraulic parameters. Moreover, the flow passing through open meandering channels, due to secondary and rotational flows, changes the water surface and flow pattern compared to straight channels, affecting flow characteristics such as velocity distribution and turbulence components, and influencing downstream flow as well. This research was conducted in the Hydraulic Laboratory at the Iran University of Science and Technology, in a curved channel with a concrete bed, 8 meters long, covered with sandy bed and a median particle diameter of 15.1, and varying aspect ratios (width-to-depth ratios). The aim of this study is to analyze the impact of submerged flexible and rigid reeds vegetation on the internal and external walls of a reconstructed natural meandering channel with a sandy bed and fixed slope on velocity distribution, turbulence, and drag coefficient. To investigate the effect of vegetation on the flow in the bend, submerged flexible and rigid plastic reeds, 4 cm in height, were used over the sandy bed with a 2% slope. To examine turbulent flow structures, three-dimensional Acoustic Doppler Velocimeter (ADV) velocity data were employed. The experiments consisted of three series: one series with a bare bed and two series with flexible and rigid vegetation, with a flow depth of 13 cm. Parameters such as velocity, Reynolds shear stress, turbulence intensity, turbulence degree, TKE, and drag coefficient were measured, calculated, and analyzed. The results showed that the maximum velocity in the bare bed condition occurred at sections 1, 2, and 3 in the middle of the bend, near the inner bend, and near the outer bend, respectively. With the presence of rigid vegetation, the maximum velocity was observed in the middle of the channel in the first two sections and near the inner bend in the third section. For the flexible vegetation case, the maximum velocity occurred first near the inner bend, then in the middle of the channel, and finally again near the inner bend at the end of the curve. The presence of vegetation increased the turbulence intensity, with the maximum observed near the bed. The highest drag coefficient for the bare bed was found in section 2 and the center of the bend, while for the vegetated bed, it was observed near the outer bend. In other parts of the bend, flexible vegetation increased the drag coefficient, while rigid vegetation decreased it.
