论文标题
城市边界层在茂密和高大的檐篷上
Urban boundary layers over dense and tall canopies
论文作者
论文摘要
在四个城市形态上进行了风隧道实验：两个高高的高高的檐篷和两个超高的檐篷，元素高度变化很大（其中最大元素高度是平均冠层高度的两倍以上，$ h_ {max} $ = 2.5 $ = 2.5 $ h_ {avg} $）。 {The average canopy height and packing density were fixed across the surfaces to $h_{avg} = 80$ mm, and $λ_{p} = 0.44$, respectively.} A combination of laser doppler anemometry and direct drag measurements were used to calculate and scale the mean velocity profiles {within the boundary layer depth, $δ$}.在统一的高度实验中，高堆积密度导致了“撇流流”状态，而流入冠层的流动很少。这导致了令人惊讶的浅色粗糙度子层（$ z \ of1.15h_ {avg} $），在其上方有一个明确定义的惯性sublayer。 {在异质高度檐篷中，尽管填料密度相同和平均高度，但流量特征显着不同。} {高度异质性增强了混合，从而鼓励了深层流入冠层。发现存在更深的粗糙度子层，并延伸到最高的元素高度（对应于$ z/h_ {avg} = 2.85 $）}，这被认为是控制流动行为的主要长度。 {尽管表面粗糙度严重（$Δ/h_ {avg} = 3-6.25 $），但结果指向本在本文考虑的所有表面的惯性子层的存在。这与以前的文献形成鲜明对比。
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, $h_{max}$=2.5 $h_{avg}$). {The average canopy height and packing density were fixed across the surfaces to $h_{avg} = 80$ mm, and $λ_{p} = 0.44$, respectively.} A combination of laser doppler anemometry and direct drag measurements were used to calculate and scale the mean velocity profiles {within the boundary layer depth, $δ$}. In the uniform-height experiment, the high packing density resulted in a `skimming flow' regime with very little flow penetration into the canopy. This led to a surprisingly shallow roughness sublayer ($z\approx1.15h_{avg}$), and a well-defined inertial sublayer above it. {In the heterogeneous-height canopies, despite the same packing density and average height, the flow features were significantly different.} {The height heterogeneity enhanced mixing thus encouraging deep flow penetration into the canopy. A deeper roughness sublayer was found to exist and extend up to just above the tallest element height (corresponding to $z/h_{avg} = 2.85$)}, which was found to be the dominant lengthscale controlling the flow behaviour. {Results points toward the existence of an inertial sublayer for all surfaces considered herein despite the severity of the surface roughness ($δ/h_{avg} = 3 - 6.25$)}. This contrasts with previous literature.
