含挺水植物和沉水植物水流紊动特性

Turbulent characteristics in open-channel flow with emergent and submerged macrophytes

在一定的水动力条件下,不同水生植物对水流结构改变的程度及对底泥再悬浮的影响由于其形态结构的差异有所不同。在玻璃水槽中铺设太湖底泥并种植天然沉水植物(水蕨)和挺水植物(菖蒲),通过水槽实验,用三维声学多普勒流速仪ADV对植物段紊流特性进行测量研究,分析含水生植物明渠水流的水力特性及底泥再悬浮规律。结果表明:含沉水植物和挺水植物明渠水流的垂向流速分布各自遵循不同的规律;其紊动强度和雷诺应力具有明显的各向异性特性;在沉水植物冠层交界处及挺水植物的茎杆和枝叶分叉处,紊流强度及雷诺应力均出现最大值;在一定条件下沉水植物和挺水植物均能抑制底泥再悬浮,但当雷诺数达到一定数值时,水生植物的存在反而加剧了底泥的再悬浮,与挺水植物相比,沉水植物对底泥再悬浮的抑制效果要更好。

Under certain hydrodynamic conditions, different species of aquatic plants will have different impacts on the flow structure and sediment re-suspension due to the differences in plant morphology. In this study, the sediment collected from the Taihu Lake is placed in a glass tank planting with emergent and submerged macrophytes calamus and water fern. Using the flume experiments, the turbulent flow in the open channel with macrophytes is measured by a three-dimensional Acoustic Doppler Velocimeter (ADV). The analysis of flow turbulence and sediment re-suspension is conducted. The results show that the vertical velocity distribution has different regularities in open-channel flow with emergent and submerged mcrophytes. Both turbulence intensity and Reynolds Number exhibit obvious anisotropy, and their maximum values are found to be at the junction of submerged plant canopy and at the bifurcation of emergent plant stems and branches, respectively. The sediment re-suspension process can be inhibited by the presence of emergent and submerged macrophytes under certain conditions. However, when the Reynolds Number reaches a certain value, the presence of these macrophytes can actually exacerbate the sediment re-suspension process. In comparison with emergent plants, submerged mcrophytes would be more effective in inhibiting sediment re-suspension.