The evolution and characteristics of large-scale vortices are critical for understanding temporal and spatial exchange of mass and momentum. Using a validated depth-averaged large-eddy simulation (DA-LES) model, this paper visualizes the vortex processes in a partly-obstructed canopy channel, and analyzes associated hydrodynamics. Particular interests are focused on the effect of canopy blocking ratio (canopy-to-channel width ratio) reflecting vegetation lateral colonization extent, which is poorly addressed by current knowledge. We find that two vortex evolution patterns including sequent sole along-canopy vortices (SCVs) and alternating hybrid along-canopy and along-wall paired vortices (HCWVs) correspond to small and large blocking ratios, respectively. Particularly for the latter, the outer length of along-canopy vortices decreases once along-wall vortices arise, with the vortex fields characterized by pronounced decreased wavelength and increased wave number. Hyperbolic tangent velocity profiles typically for shear layer flows with SCVs shift to parabolic ones as HCWVs dominate. The simulations imply that the key mechanism of SCVs shifting to HCWVs is that along-canopy vortices touch the main-channel sidewall when canopy width continuously increases, triggering vortices shedding off the sidewall. New insights into sediment deposition in the main channel are achieved as the hydrodynamics and vortex fields alter under different canopy blocking extents.

大尺度涡旋的演化和特征对于理解质量和动量的时空交换至关重要。使用经过验证的深度平均大涡模拟 (DA-LES) 模型，本文可视化了部分阻塞的冠层通道中的涡流过程，并分析了相关的流体动力学。特别的兴趣集中在反映植被横向定植程度的冠层阻塞率（冠层与通道宽度比）的影响上，目前的知识很难解决这一问题。我们发现两种涡旋演化模式，包括连续的单一沿冠层涡（SCVs）和交替混合的沿冠层和沿壁成对涡旋（HCWVs），分别对应于小的和大的阻塞比。特别是对于后者，一旦沿壁涡出现，沿冠层涡的外部长度就会减小，涡场的特征是波长明显减小，波数增加。当 HCWV 占主导地位时，通常用于具有 SCV 的剪切层流的双曲线切线速度分布转变为抛物线速度分布。模拟表明，SCVs 向 HCWVs 转变的关键机制是，当冠层宽度不断增加时，沿冠层涡流接触主通道侧壁，触发涡流从侧壁脱落。随着不同冠层阻塞程度下的流体动力学和涡流场发生变化，对主河道沉积物沉积有了新的认识。当 HCWV 占主导地位时，通常用于具有 SCV 的剪切层流的双曲线切线速度分布转变为抛物线速度分布。模拟表明，SCVs 向 HCWVs 转变的关键机制是，当冠层宽度不断增加时，沿冠层涡流接触主通道侧壁，触发涡流从侧壁脱落。随着不同冠层阻塞程度下的流体动力学和涡流场发生变化，对主河道沉积物沉积有了新的认识。当 HCWV 占主导地位时，通常用于具有 SCV 的剪切层流的双曲线切线速度分布转变为抛物线速度分布。模拟表明，SCVs 向 HCWVs 转变的关键机制是，当冠层宽度不断增加时，沿冠层涡流接触主通道侧壁，触发涡流从侧壁脱落。随着不同冠层阻塞程度下的流体动力学和涡流场发生变化，对主河道沉积物沉积有了新的认识。