Velocity measurements from experiments performed downstream of patches of submerged aquatic vegetation were analysed. Two patches of different species, i.e., P crispus and M. spicatum, were characterised by the same size. Measurement points covered the water depth in the centre and at the sides of the patches from 0.1 m to 0.85 m downstream. Conditional quadrant analysis was modified and applied to the data to study turbulence structures propagating from the mixing layer formed at the interface between the vegetation canopy and flow above. These structures were responsible for the majority of momentum transport and tended to vary with patch distance, height and plant physical characteristics. The stiffer plant, i.e., M. spicatum, produced a higher difference between the contributions of even events, i.e., sweeps and ejections, and odd events, i.e., outward and inward interactions. The changes in the detected strong bursting events across measurement profiles indicated that two main kinds of organised motions occurred immediately behind the plant patches. Strong sweep motions carried water flow into the low-velocity region below the vegetation height. Strong ejections, which had the longest time of the occurrence and had the highest contributions to the $\overline{u^{\prime }{w}^{\prime }}$ Reynolds stress, pushed flow towards the water surface. Both kinds of extreme events produced the same Reynolds stress in an instant, but ejections had a higher frequency of occurrence. The presented results show how the observed changes in ejection and sweeps distribution reflect the model where vegetation canopy-induced vortices transform into the dual-head hairpin vortices downstream of the inflection point.

分析了来自水下水生植物斑块下游进行的实验的速度测量值。两个不同物种的斑块，即P crispus和M. spicatum，具有相同的大小。测量点覆盖了补丁中心和两侧的水深，从下游的0.1 m到0.85 m。修改了条件象限分析并将其应用于数据，以研究从植被冠层与上方流之间的界面处形成的混合层传播的湍流结构。这些结构负责大部分动量传递，并且往往会随着斑块距离，高度和植物物理特性而变化。较硬的植物，即M. spicatum在偶数事件（即扫掠和弹射）与奇数事件（即向外和向内的相互作用）的贡献之间产生了更高的差异。整个测量曲线中检测到的强烈爆发事件的变化表明，两种主要的有组织的运动直接发生在植物斑块的后面。强烈的扫掠运动使水流入植被高度以下的低速区域。强弹射，发生时间最长，对弹射的贡献最大$\overline{{ü}^{\prime }{w}^{\prime }}$雷诺应力，将水流推向水面。两种极端事件都会在瞬间产生相同的雷诺应力，但弹射的发生频率更高。呈现的结果表明，观测到的射血和扫掠分布变化如何反映了模型，在该模型中，植被冠层诱发的涡流转变为拐点下游的双头发夹形涡流。