弯道对植被群河道水流结构影响的试验研究北大核心CSCD

为了解弯道对含植被群河道水流结构的影响,本文在180°U型弯道水槽中进行试验,采用圆形竹筷模拟低密度植被群,圆柱体模拟高密度植被群,运用声学多普勒流速仪测量三维流速,不同密度植被群放置于水槽相同位置,对比分析弯道的影响。试验结果发现,植被群上游调整长度及其稳定尾流区长度受弯道影响发生了明显调整,植被群密度的影响仅作用于植被群尾流结构,包括其中垂向湍动能的差异。植被群后出现植被群直径尺度的涡,使纵向湍动能分布出现波峰,峰值大小受弯道影响;植被群在弯道中所处位置越后,峰值越小。湍流谱分析中验证了此现象,并发现弯道作用使得植被群后小尺度涡增多,从而使得植被群后较小湍动能峰值的大小不随植被群放置位置改变。

Effect of curved channel on flow structure with vegetation patch

To understand the changes in the characteristics of flow structure caused by an emergent vegetation patch over a curved channel, laboratory experiments were conducted on a 180-degree U-shaped flume. Wooden cylinders were used to simulate a sparse vegetation patch and solid cylinders mimicked a dense vegetation patch; in each case, the patch position in the U-bend was the same to clarify the bend effect. An acoustic Doppler velocimeter (ADV) was used to measure the three-dimensional velocity. Experimental results show that the adjustment length upstream from the patch and the length of the stable wake region are adjusted significantly by the curved channel. And both the vegetation density and curved channel work together on the wake structure behind the patch, including but not limited to the difference in vertical turbulent kinetic energy (TKE), while the upstream adjustment length is not affected by vegetation density. Behind the vegetation patch, turbulence structure changes significantly, and large vortices appear on a scale comparable to the patch size, resulting in an obvious peak of the longitudinal TKE distribution. The peak value is also affected by the curve. However, it becomes smaller once the vegetation patch is moved to a position closer to the bend outlet. This trend is also found in turbulence spectrum analysis, showing the channel bend increases the number of small-scale turbulent eddies behind the patch. Therefore, small peak values caused by small-scale turbulent eddies do not depend on the relative patch position in the curved channel.