含淹没柔性水生植被群的弯道水流特性PIV试验研究

PIV Experimental Study on Flow Characteristics of Bend Channel with Submerged Flexible Aquatic Vegetation Group

为了研究淹没柔性水生植被对弯道水流的影响,采用水槽试验的方法,在U形弯道水槽凸岸的25°和45°附近布置相同种类的塑料草模型植被群,设置植被密度分别为密集和稀疏2种工况,采用自动水位测量系统和粒子图像测速仪(PIV)等仪器分别测量了在不同工况下植被附近及U形弯道水槽内水流的流速和水位,研究不同密度(株数/m^(2))的柔性水生植被对水流运动规律的影响。同时,利用测量结果对水位变化、水流流速分布、横比降变化、水头损失、水力坡降等规律进行分析。试验结果表明,弯道凸岸的水流在不同植被密度下各个断面(25°、45°、60°、90°、120°、150°、180°)的流速大小变化均呈先下降后趋于平稳的趋势;凹岸的水流在不同植被密度下各个断面的流速大小变化情况差异较大,在60°断面密集植被的流速小于稀疏植被的流速,同时在150°断面大幅度上升后再下降并在弯道出口处大于稀疏植被的流速;植被群增大水头损失和水力坡降,其中密集植被群影响最大。

The method of flume experiment is adopted to study the influence of submerged flexible aquatic vegetation on bend flow.In experiments,same kind of plastic grass model vegetation group is arranged near 25°and 45°of the convex bank of U-shaped bend flume,the vegetation density is set to be dense and sparse respectively,and the automatic water level measurement system and particle image velocimetry(PIV)are used to measure the flow velocity and water level near the vegetation and in the U-shaped bend flume under different operating conditions respectively.Based on measurement results,the influence of flexible aquatic vegetation with different density(number of plants/m^(2))on water flow is studied,and the water level change,flow velocity distribution,transverse gradient change,head loss and hydraulic gradient are also analyzed.The experimental results show that,(a)the flow velocity of each section(25°,45°,60°,90°,120°,150°,180°)on the convex bank of the bend decreases first and then tends to be stable under different vegetation densities;(b)on the concave bank,the flow velocity of each section varies greatly under different vegetation densities,and among them,the flow velocity of the dense vegetation at the 60°section is smaller than that of the sparse vegetation,while at the 150°section,the flow velocity increases greatly and then decreases,and is larger than that of sparse vegetation at the exit of the bend;and(c)the vegetation groups increase head loss and hydraulic gradient,and the dense vegetation group has the greatest influence.