Temporal and spatial vortex shedding evolution for flow around a circular cylinder near a plane boundary is investigated using three-dimensional direct numerical simulation, with a parameter space of boundary layer thickness-to-diameter δ/D = 0–1.4, gap-to-diameter G/D = 0.4 and Re = 350. For each δ/D, three consecutive wake stages are divided with time based on the dominated flow structures – mode A and mode B, of which spanwise wavelength is quantitatively measured by the autocorrelation function (ACF). In the first stage, mode A structures spread from two spanwise ends to the middle region and from upstream to downstream wake simultaneously. This stage is only dominated by ordered mode A structures and shows a weak three-dimensionality. In the second stage, mode B structures start to propagate in the same spanwise but opposite streamwise direction as mode A, and squeeze the mode A region until its disappearance. A mixture of mode A and mode B structures dominate the second stage and the flow is in the strongest three-dimensionality. In the third stage, the wake transits from a symmetric distribution of ordered mode B structure to an asymmetric distribution of disordered mode B structure, showing a relatively strong three-dimensionality. The typical vortex shedding patterns are analyzed by dynamic mode decomposition (DMD). When δ/D > 0, the dominant mode frequency (f₀) of vortex shedding, larger than that of an isolated cylinder, decreases with the increase of δ/D. Due to suppression of the lower-surface vortex shedding, the flow structures with f₀ are greatly reduced both in size and regularity with the increase of δ/D. Scattered mode components are reduced and the energy of each mode is more concentrated with increasing δ/D.

利用三维直接数值模拟研究了绕平面边界的圆柱体绕圆柱绕流的时空涡流演化，参数空间为边界层厚度-直径δ / D  = 0-1.4，间隙-直径直径G / D  = 0.4，Re =350。对于每个δ/ D，三个连续的唤醒阶段根据主导的流动结构-模式A和模式B按时间划分，其中跨度波长由自相关函数（ACF）定量测量。在第一阶段，模式A的结构从两个翼展方向的两端延伸到中间区域，同时从上游尾流扩展到下游尾流。该阶段仅受有序模式A结构支配，并且显示出较弱的三维性。在第二阶段中，模式B结构开始沿与模式A相同的跨度但沿逆流方向传播，并挤压模式A区域直至消失。模式A和模式B结构的混合体在第二阶段占主导地位，并且流动具有最强的三维性。在第三阶段 尾波从有序模式B结构的对称分布转变为无序模式B结构的不对称分布，表现出相对较强的三维性。通过动态模式分解（DMD）分析典型的涡旋脱落模式。什么时候δ / D  > 0时，涡旋脱落的主模频率（f ₀）大于孤立圆柱的主模频率（f ₀），随δ / D的增加而减小。由于抑制了下表面涡旋脱落，随着δ / D的增加，f ₀的流动结构在大小和规则性上都大大减小。随着δ / D的增加，散射模式的成分减少，每个模式的能量更加集中。