Wind-tunnel experiments were carried out on four urban morphologies: two tall canopies with uniform height and two super-tall canopies with a large variation in element heights (where the maximum element height is more than double the average canopy height, \(h_{max}=2.5h_{avg}\)). The average canopy height and packing density are fixed across the surfaces to \(h_{avg} = 80~\hbox {mm}\), and \(\lambda _{p} = 0.44\), respectively. A combination of laser Doppler anemometry and direct-drag measurements are used to calculate and scale the mean velocity profiles with the boundary-layer depth \(\delta \). In the uniform-height experiment, the high packing density results in a ‘skimming flow’ regime with very little flow penetration into the canopy. This leads to a surprisingly shallow roughness sublayer (depth \(\approx 1.15h_{avg}\)), and a well-defined inertial sublayer above it. In the heterogeneous-height canopies, despite the same packing density and average height, the flow features are significantly different. The height heterogeneity enhances mixing, thus encouraging deep flow penetration into the canopy. A deeper roughness sublayer is found to exist extending up to just above the tallest element height (corresponding to \(z/h_{avg} = 2.85\)), which is found to be the dominant length scale controlling the flow behaviour. Results point toward the existence of a constant-stress layer for all surfaces considered herein despite the severity of the surface roughness (\(\delta /h_{avg} = 3 - 6.25\)). This contrasts with the previous literature.

对四种城市形态进行了风洞实验：两个高度均匀的高檐和两个单元高度变化较大的超高檐（其中最大单元高度是平均檐高的两倍以上，\(h_{最大值}=2.5h_{平均}\) )。平均冠层高度和堆积密度在表面上分别固定为\(h_{avg} = 80~\hbox {mm}\)和\(\lambda _{p} = 0.44\)。激光多普勒风速测量和直接阻力测量的组合用于计算和缩放平均速度剖面与边界层深度\(\delta \). 在均匀高度实验中，高填充密度导致“撇渣流”状态，几乎没有流渗透到树冠中。这导致了一个令人惊讶的浅粗糙度子层（深度 \(\approx 1.15h_{avg}\)），以及其上方定义明确的惯性子层。在异高冠层中，尽管堆积密度和平均高度相同，但流动特征却存在显着差异。高度的异质性增强了混合，从而促进了深入到树冠中的流动。发现存在一个更深的粗糙度子层，延伸到最高单元高度的正上方（对应于\(z/h_{avg} = 2.85\))，这是控制流动行为的主要长度尺度。结果表明，尽管表面粗糙度严重 ( \(\delta /h_{avg} = 3 - 6.25\) )，但此处考虑的所有表面都存在恒定应力层。这与之前的文献形成了对比。