The effects of obstacle-height variability on spatial characteristics of turbulent organized structures were investigated with the use of a large-eddy simulation technique for airflows over roughness obstacles. Two-types simulation cases were considered: one is uniform-height case in which uniform-height obstacles are aligned in streamwise direction, the other is height-variability case with staggered higher-height obstacles. Streaky structures were observed above the roughness sublayer (RSL) regardless of obstacle-height variability. When obstacles are uniform, flow fields within the RSL contain low- and high-speed regions along the streamwise streets. When obstacle heights vary, airflow within the RSL collides with the front-facing surfaces of taller obstacles. The statistical features of low- and high-speed structures were examined using the spatial correlations of flow fields centering on strong ejection and sweep, respectively. The ejection– and sweep–center spatial correlations extend forward and backward in the streamwise direction, respectively. Length scales were obtained from the ejection–center and sweep–center spatial correlations. The streamwise lengths vary significantly below the canopy height when obstacles are uniform. In contrast, the streamwise length scales remain nearly constant when obstacle heights vary. The horizontal aspect ratios below the canopy heights indicate that turbulent organized structures over obstacles with variable heights are more isotropic than those over uniform obstacles. The inclination angles of the organized structures were also deduced using the spatial correlations. The angles of sweep–center structures are steeper than those of the ejection–center structures. The angles of the ejection–center structures at the RSL heights become larger with obstacle-height variability.

障碍物高度变化对湍流有组织结构空间特征的影响，通过使用大涡模拟技术对粗糙障碍物上的气流进行了研究。考虑了两种类型的模拟情况：一种是均匀高度的情况，其中均匀高度的障碍物沿流向对齐，另一种是高度可变的情况，其中高度障碍物交错。不管障碍物高度的可变性如何，在粗糙度子层（RSL）上方都可以看到条纹结构。当障碍物均匀时，RSL内的流场包含沿河道的低速和高速区域。当障碍物高度变化时，RSL中的气流会与较高障碍物的前表面碰撞。利用分别以强射流和掠射为中心的流场的空间相关性，研究了低速和高速结构的统计特征。射血中心和波及中心的空间相关性分别沿河流方向向前和向后延伸。长度尺度是从射出中心和扫掠中心的空间相关性获得的。当障碍物均匀时，沿河的长度在顶篷高度以下变化很大。相反，当障碍物高度变化时，沿流的长度比例几乎保持恒定。冠层高度以下的水平长宽比表明，高度可变的障碍物上方的湍流有组织结构比均匀障碍物上的湍流组织结构各向同性。还使用空间相关性推导了有组织结构的倾斜角度。后掠中心结构的角度比弹射中心结构的角度陡。RSL高度处的弹射中心结构的角度随着障碍物高度的变化而变大。