Huai Wenxin, Li Chengguang
State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China E-mail:
Water Sci Technol. 2016;74(3):722-8. doi: 10.2166/wst.2016.236.
Suspended canopies can cause flow disturbances such as reducing velocities within the canopy, and increasing flow beneath the canopy. Flow modifications by canopies dramatically affect the fate and transport of sediment, nutrients, contaminants, dissolved oxygen, and fauna in aquatic systems. A three-zone model is presented here to predict the longitudinal dispersion coefficient by simplifying Chikwendu's N-zone model. To validate the model, both flow field and tracer experiments were conducted using a straight rectangular Plexiglas flume, with rigid circular rods as the modeled suspended canopies. The result shows that velocities increased above the flume bed and maximized at a point between the canopies and flume bed. Above that point, streamwise velocities decreased into and within the canopies. Reynolds shear stresses were largest at the canopy interface and smallest (zero) at the velocity maximum point. Good agreement between the modeled results and experimental data shows that the model can effectively predict the longitudinal dispersion coefficient in open channels with suspended canopies.
悬浮冠层会导致水流扰动，例如降低冠层内部的流速，并增加冠层下方的水流速度。冠层对水流的改变会极大地影响水生系统中沉积物、营养物质、污染物、溶解氧和动物群的归宿与迁移。本文提出了一个三区模型，通过简化奇克温杜的N区模型来预测纵向扩散系数。为了验证该模型，使用了一个直的矩形有机玻璃水槽进行流场和示踪剂实验，其中刚性圆形杆作为模拟的悬浮冠层。结果表明，水槽底部上方的流速增加，并在冠层与水槽底部之间的某一点达到最大值。在该点之上，流向流速在冠层内部及进入冠层时降低。雷诺切应力在冠层界面处最大，在流速最大值点最小（为零）。模拟结果与实验数据之间的良好一致性表明，该模型能够有效地预测具有悬浮冠层的明渠中的纵向扩散系数。
