Three-dimensional direct numerical simulation is carried out to investigate the effects of the yaw angle and spanning length on the vortex structures and hydrodynamics of flow crossing a near-wall cylindrical structure. Two yaw angles (α = 0°, 45°), and three spanning length ratios (L* = 25, 50, 100) are investigated at Re = 500. Under the normal cylinder condition (α = 0°), a parallel vortex shedding pattern is observed in the wake. The vortex formation lengths are identical for all L*, whereas the spanwise correlation of the vortex shedding declines with the increasing L*, indicating the intensified three-dimensionality. A single dominant peak is found in the lift frequency spectra for each L* case. Under the yawed condition (α = 45°), the flow characteristics are fundamentally changed with negatively-yawed linear vortex shedding tubes being observed in the wake. Different from the normal cases, the vortex formation length for L* = 25 is larger than that of L* = 50 and 100, while the oblique angle of the vortex tube decreases with the increasing L*. It is shown that, at α = 45°, the three-dimensional flow features are fully developed when L* ≥ 50. The lift frequency spectra show multiple peaks while the magnitudes of the secondary peaks are significantly reduced by extending the spanning length. By comparing the results between α = 0° and α = 45°, it is found the Independence Principle (IP) is applicable for predicting the first-order statistics of the hydrodynamic forces and vortex shedding frequency, but fails in predicting the second-order force statistics. The effects of the yaw angle on the pressure and shear stress distributions of the bottom wall are also discussed.

通过三维直接数值模拟研究偏航角和跨距对涡流结构和流经近壁圆柱结构的流体动力学的影响。在 Re = 500 时研究了两个偏航角 ( α  = 0°, 45°) 和三个跨度比 ( L * = 25, 50, 100)。 在正常圆柱体条件 ( α  = 0°) 下，平行涡在尾流中观察到脱落模式。所有L *的涡旋形成长度都相同，而涡旋脱落的展向相关性随着L *的增加而下降，表明三维度增强。在每个L的提升频谱中发现一个单一的主峰* 案件。在偏航条件下（α  = 45°），流动特性发生了根本性的变化，尾流中观察到负偏航线性涡流脱落管。与正常情况不同的是，L * = 25 时的涡流形成长度大于L * = 50 和 100 时的涡流形成长度，而涡管的斜角随着L *的增加而减小。结果表明，在α  =45°时，当L *≥50时，三维流动特征充分发展。升力频谱呈现多峰，而次峰的幅度随着跨距的延长而显着降低。通过比较α  = 0° 和α  = 45°，发现独立原理（IP）适用于预测水动力和涡旋脱落频率的一阶统计量，但无法预测二阶力统计量。还讨论了偏航角对底壁压力和剪应力分布的影响。