Author(s): Bin Li; Chaoqun Li; Jun Lu; Cuixia Chen

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Keywords: Ship-shaped floating-dike; Flow characteristics; Turbulent kinetic energy; Submergence ratio; Length ratio; Arrangement angle

Abstract: Compared with spur dikes, ship-shaped floating-dikes (SSFD) have the characteristics of slowing flow, promoting sedimentation, and ecological suitability. However, there is still gap on the application of SSFD in river regulation. To further reveal the effect of SSFD on flow structure, k-ε model was used to study the three-dimensional flow characteristics and turbulent kinetic energy distribution, in which considered the submergence ratio (draft/depth=D), length ratio (length/river width=K), and arrangement angle (θ>0 means dike tilted downward), and the lateral slope of bed. The results were verified by the results of experiments. The results show that: 1. As D increased from 0.2 to 0.8, the maximum relative stream-wise velocity (local maximum flow velocity/inlet average flow velocity=U/U0max) below the SSFD gradually increases, from 1.52 to 1.69. The length of the back-flow area and U/U0max increase from 1.0L to 3.5L (L is the length of SSFD) and from -0.35 to -0.51, respectively. As D increases, the magnitude of velocity near bed increases, and the turbulence intensity behind the SSFD increases. 2. As K increased, the flow-passed cross-section decreased, resulting in an increase in flow velocity below and outside the SSFD. The area of the back-flow and slow flow zone also increased with K, but the length and intensity of the back-flow unchanged. The turbulent kinetic energy intensity gradually increases and forms core area at the bottom and rear of the SSFD. 3. While the SSFD tilted upwards (θ=-30º), the blocking effect was significant, with U/U0max upstream SSFD attenuation to 0.4, while near the shore and bottom of SSFD, U/U0max=1.53 less than θ=30º with U/U0max=1.63, but both less than θ=0 with U/U0max=1.72; the distribution of the slow-flow zone behind the SSFD was larger when θ=-30º. When θ=30º, the flow state is stable with weak turbulent energy, a local acceleration zone and circulation formed behind the SSFD. When the SSFD was arranged at the deeper side, the water flow was concentrated below the SSFD, and the strength of the back-flow zone increased. The transverse slope of the riverbed enhances the circulation behind the SSFD. The above research results indicated that effect of the slow-flow and sedimentation promotion of SSFD was best when they were arranged on the deeper side, tilted downwards, submerged ratio ≤ 0.4, and length ratio ≤ 0.5. Because the slow-flow area behind the SSFD was stable, circulation developed, and little disturbance to the near-bed flow field, which has good ecological suitability. Our researches provide technical support for practical river regulation projects.

DOI:

Year: 2024