Abstract Floating-leaved vegetation alters the flow structure through the combined action of floating leaves, stems, and the channel bed. This study investigated the vertical distribution of streamwise velocity and the turbulence structure of an open channel flow with floating-leaved vegetation through theoretical analysis and laboratory experiments. Bionic lotus leaves fixed on circular wooden cylinders were used to imitate floating-leaved vegetation, and the 3D velocity field was measured by using an acoustic Doppler velocimeter. The measured data showed that with the presence of the channel bed and vegetation cover, strong velocity gradients appear at the bottom and top layers, whereas the velocity is almost uniformly distributed in the internal layer. On the basis of the modified mixing length hypothesis, the vertical distribution of streamwise velocity was numerically predicted, and the prediction results agreed well with the experimental data. The model parameters were then determined, and the effect of mixing length was analyzed. Spectral analysis showed that the peak frequency in the streamwise velocity spectra is within the range of 0.1 Hz to 0.2 Hz and that the vortices are mainly affected by stem-scale turbulence. Quadrant analysis showed that the ejections and sweeps are the major contributors to Reynolds stress in the bottom layer, inward and outward interactions are prominent in the top layer, and the contribution of sweeps and ejections are approximately equivalent to those of outward and inward interactions in the internal layer. Different to open channel flow featured with emergent rigid vegetation, the velocity and wake production decrease while the Reynolds stress and shear production increase towards the floating leaf. The effect of stem diameter, vegetation density, stem flexibility and boundary roughness on flow structure of open channel flow with floating-leaved vegetation need to be examined in future research.

中文翻译：

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浮叶植被明渠流速度分布及湍流结构

摘要 浮叶植被通过浮叶、茎和河床的共同作用改变水流结构。本研究通过理论分析和实验室实验研究了流向速度的垂直分布和带有浮叶植被的明渠流的湍流结构。采用固定在圆形木柱上的仿生荷叶模拟浮叶植被，使用声学多普勒测速仪测量3D速度场。实测数据表明，随着河床和植被覆盖的存在，底层和顶层出现强烈的速度梯度，而内层的速度几乎均匀分布。在修正混合长度假设的基础上，对流向速度的垂直分布进行了数值预测，预测结果与实验数据吻合较好。然后确定模型参数，并分析混合长度的影响。谱分析表明，流向速度谱中的峰值频率在 0.1 Hz 至 0.2 Hz 范围内，涡流主要受茎尺度湍流的影响。象限分析表明，射出和扫掠是底层雷诺应力的主要贡献者，上层内向和向外相互作用突出，扫射和射出的贡献与外向和向内相互作用的贡献近似相等。内层。不同于以突现刚性植被为特征的明渠流，速度和尾流产生减少，而雷诺应力和剪切产生向浮叶方向增加。茎粗、植被密度、茎柔韧性和边界粗糙度对浮叶植被明渠流流动结构的影响需要在未来的研究中进行研究。