含淹没植物明渠近床面区紊流特征高度试验研究

为研究含淹没植物明渠紊流统计参数垂向分布突变位置、理论床面和渗透高度的关系,进行了含淹没刚性植物明渠水流试验,使用圆柱铝棒模拟刚性植物,采用激光多普勒流速仪(LDV)测量流场,对由纵向流速、雷诺应力、局部阻力系数分布确定的特征高度和渗透高度进行研究,比较各类紊流特征高度的相对位置,分析植物密度与淹没度对其的影响。试验结果表明,在植物密度较大的情况下,近床面区流速沿垂向保持常数,雷诺应力梯度较小,一定高度处分布规律发生明显变化,能够较容易地确定流速梯度和雷诺应力梯度突变位置,淹没度对由3种方法确定的特征高度影响不明显;各种方法确定的特征高度中,雷诺应力特征高度与渗透高度更加接近;渗透高度随植物密度与淹没度的增大而增大;渗透高度与理论床面高度存在一定的线性关系。

Experimental study on turbulence characteristic height near bed area in open channel flow with submerged vegetation

In order to investigate the relationships among the sudden variation positions of vertical distributions of turbulent statistical parameters, the zero-plane displacement, and the penetration height, laboratory flume experiments with submerged rigid vegetation were carried out. Aluminum cylinders were used to simulate rigid vegetation and laser Doppler velocimetry(LDV)was utilized to measure the flow fields. The characteristic heights, determined by longitudinal velocity, Reynolds stress, local drag coefficient distribution, respectively, and the penetration height are discussed to compare their relative positions and analyze the effects of vegetation density and submergence on them. Experimental results show that, under high-density conditions, velocity along the vertical direction nearly remains constant, the gradient of Reynolds stress is low near the bed, and the sudden increase positions of the gradients of velocity and Reynolds stress distribution can be easily determined because distinct variations of their distribution patterns exist at certain heights. The influence of submergence on these characteristic heights is not obvious. Compared with other characteristic heights, the one determined by Reynolds stress is most approximate to the penetration height. Moreover, penetration height increases with the increase of vegetation density and submergence. Penetration height has a linear relationship with the zero-plane displacement.