State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan, 430072, China.
Environ Sci Pollut Res Int. 2019 May;26(14):14583-14597. doi: 10.1007/s11356-019-04709-x. Epub 2019 Mar 15.
Dead-water zones (DWZs) in natural open channels, formed by embayment or consecutive groins, can provide favorable growth conditions for aquatic organisms. Although flow hydrodynamics in side-cavity zones have been well studied, the impact of vegetation on recirculating flow is rarely considered. This study adopts large eddy simulation (LES) to examine the flow field in a rectangular embayment zone with different population densities of vegetation. The numerical model is validated by mean streamwise velocity data collected near mid-depth in the physical experiment. Vegetation rearranges the circulation structure in the DWZ and weakens the velocity and turbulent kinetic energy. This negative effect increases with increasing population density. With the development of the shedding vortex induced in the front edge of the channel-embayment interface, the large-scale coherent structure forms in the mixing layer and is hardly affected by the variation of population density. As the population density increases, the mean retention time first decreases and then increases as a result of the combined action of three factors, namely, the large-scale coherent structure, the plant-induced Karman vortex street, and the blocking effect of dense vegetation.
死水区（DWZ）在自然明渠中，由湾口或连续的突堤形成，可以为水生生物提供有利的生长条件。尽管侧腔区的水流动力学已经得到了很好的研究，但植被对回流的影响很少被考虑。本研究采用大涡模拟（LES）来研究不同植被密度的矩形湾口区域的流场。数值模型通过在物理实验中近中深度收集的平均流向速度数据进行验证。植被改变了 DWZ 的循环结构，并削弱了速度和湍流动能。这种负面影响随着种群密度的增加而增加。随着在通道-湾口界面前缘诱导的脱落涡的发展，在混合层中形成了大尺度相干结构，并且几乎不受种群密度变化的影响。随着种群密度的增加，平均停留时间首先减小，然后由于三个因素的共同作用而增大，即大尺度相干结构、植物诱导的卡门涡街和密集植被的阻挡效应。
