植被作用下复式渠道的三维湍流数值模拟

3D Turbulent Numerical Simulation in Compound Open Channel with Vegetation

针对浅水植被作用下的渠道流动特征,建立了三维标准的k-ε双方程湍流数学模型,模型考虑了植物拖曳力对水流的影响,植物阻力作为源项被加入到各方程中.曲线网格被应用模拟复杂边界的区域,变量采用部分交错网格布置,利用控制体积法离散控制方程,采用由二维深度平均方程演化而来的2D泊松方程计算三维自由水面,应用SIMPLEC程式求解离散的方程.通过实验室局部带有刚性植被的顺直矩形水槽和滩地种植植物的复式顺直水槽进行了数值模拟研究,给出了测量断面带有植被和未带有植被的速度对比结果及速度、湍流动能等值线图,计算结果和测量结果符合得较好.通过对比分析发现,未种植植被的水槽主流分布在整个渠道断面,种植植被后,由于植被拖曳力的影响,使得主流流速分布发生了改变,主槽流速增大,滩地流速降低,滩地上计算的纵向流速出现了S型的分布,在植物顶部和临近主槽一侧水流的交界面湍动能最大.

Based on the hydrodynamic characteristic of turbulent flow in open channel with a domain of vegetation, a 3 D standard k-8 turbulence model has been set up in this paper, the vegetation resistance is considered as an internal source of resistant force and added to the equations. The Boundary-fitted grids are used to approximate closely the complex boundary geometries of watercourses, the partly staggered grid is used. The governing equations are discretized by using the finite volume method, the water level of this model is determined from 2D Poisson equation derived from 2D depth averaged momentum equations. The equations are solved by using SIMPLEC algorithm. The numerical model is tested against two laboratory experiments from straight flume and compound open channel without vegetation and with vegetation, the vegetation partially covered the cross-section in the flumes. The calculated velocities and the contours of velocity and turbulent kinetic energy for measured section are presented, the agreement with measurements is generally good. By contrasting and analyzing, the streamwise velocity distributes at all the whole channel section in nonvegetated case, the velocity in main flume increases while that in floodplain floodplain. The velocity of the floodplains decreases owing to the vegetation resistance in presents the distribution of S type. The maximum turbulent kinetic energy is generated at the top region of the vegetated and non-vegetated interfacial zones near the main channel.