岸坡植被对复式河道水动力特性影响的数值模拟

广泛分布于天然河道岸坡的植被能够改变河道水流特性，进而影响坡脚淘刷、河岸稳定及河道形态演变趋势。为精细揭示岸坡植被对复式河道水动力特性的影响，提出植被固壁边界处理方法，利用雷诺应力模型封闭紊流控制方程构建了复式河道三维水动力数学模型，并对复式河道水流特性进行了模型验证，模拟结果与实测结果吻合较好。将该模型应用于岸坡有植被的复式河道水流特性研究，对比非淹没刚性植被、淹没刚性植被、淹没与非淹没刚性植被交替和无植被情况下流速、流量、河床剪应力、雷诺应力以及紊动能分布的差异。结果表明：岸坡植被加剧了滩槽间横向动量交换，引起二次流涡旋数量、强度和范围的增加，同时使得横断面流速、流量分配、河床剪应力、雷诺应力及紊动能在滩槽交界区显著减小，紊动交换在临近植被的周边区域明显增加。其中岸坡种植非淹没刚性植被时效果最为显著，相比无植被情况，二次流涡旋数量增加了一对，岸坡植被区流速、流量分配、河床剪应力、雷诺应力及紊动能大幅减小，甚至趋近于零，而临近植被的周围区域紊动交换剧烈，无量纲化的紊动能值可达到20。

Numerical Simulation of the Influence of Riparian Vegetation on Hydrodynamic Characteristics of a Compound River

The riparian vegetation can change the characteristics of the river flow, thereby affecting the bank erosion, bank stability and the river evolution trends. In order to clarify the influence of riparian vegetation on the hydrodynamic characteristics, the method of the vegetation treated as a solid wall boundary was proposed. Using the Reynolds stress model to close the turbulence control equation, a three-dimensional hydrodynamic numerical model of the compound channel was constructed. The flow characteristics model of the compound channel under the condition of no vegetation was verified well. The model was applied to the study of the water flow characteristics of a compound river with vegetation on the bank slope. And the differences in the distribution of velocity, flow, river bed shear stress, Reynolds stress, and turbulent kinetic energy under emerged rigid vegetation, submerged rigid vegetation, alternating emerged and submerged rigid vegetation, and no vegetation were compared. The results show that vegetation intensifies the momentum exchange between the main channel of the floodplain, causing the increase in the number, intensity and range of secondary current vortexes. At the same time, the cross-sectional flow velocity, flow, river bed shear stress, Reynolds stress and turbulent kinetic energy are significantly reduced in the beach-trough junction area, and the turbulence exchange was significantly increased in the area around the vegetation. The effect is most significant when non-submerged rigid vegetation is planted on the bank slope. Compared with the case of no vegetation, the number of secondary flow vortices increases by one pair, and the velocity, flow distribution, river bed shear stress, Reynolds stress and turbulent kinetic energy of the bank slope vegetation area are greatly reduced and even close to zero. The turbulent exchange in the surrounding area near the vegetation is intense, and the dimensionless turbulent kinetic energy value can be increased to 20.