Scalar Fluxes from Urban Street Canyons Part II: Model
Scalar Fluxes from Urban Street Canyons Part II: Model
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DOI：
10.1007/s10546-004-6205-7
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发表时间：
2004-12
影响因子：
4.3
通讯作者：
I. Harman;J. Barlow;S. Belcher
中科院分区：
文献类型：
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作者：
I. Harman;J. Barlow;S. Belcher
一个实用的模型，如热量，从城市街道峡谷，占流量和湍流的变化与峡谷的几何形状的垂直通量。该模型给出了城市街道峡谷每个面的通量的大小和几何依赖关系，并与第一部分中描述的风洞测量结果一致。城市街道峡谷通量的几何依赖性由两个物理过程决定。首先，随着街道峡谷高宽比的增大，地表的粗糙长度和位移高度也随之增大。这种增加导致街道峡谷上方惯性子层中的风速降低。由于街道中环流的速度与该惯性下层风速成比例，因此通量随惯性下层风速而减小。该过程在低高宽比时占主导地位。第二，街道峡谷内的环流特征也随高宽比的增大而变化。街道内的流动被划分为回流区和通风区。当街道峡谷具有高宽比时，回流区占据整个街道峡谷，并且街道内的风速较低。这种趋势在高宽比下降低了通量。当与来自相同材料的水平表面的通量密度相比时，这些过程倾向于降低来自街道峡谷的各个刻面的通量密度。但是街道峡谷具有增加的总表面积，这意味着来自街道峡谷的总通量大于来自水平表面的总通量。从城市街道峡谷与几何形状的标量通量的变化是超过两个因素，这意味着负责的物理机制应纳入城市地区的能量平衡模型。
A practical model is developed for the vertical flux of a scalar, such as heat, from an urban street canyon that accounts for variations of the flow and turbulence with canyon geometry. The model gives the magnitude and geometric dependence of the flux from each facet of the urban street canyon, and is shown to agree well with wind-tunnel measurements described in Part I. The geometric dependence of the flux from an urban street canyon is shown to be determined by two physical processes. Firstly, as the height-to-width ratio of the street canyon increases, so does the roughness length and displacement height of the surface. This increase leads to a reduction in the wind speed in the inertial sublayer above the street canyons. Since the speed of the circulations in the street are proportional to this inertial sublayer wind speed, the flux then reduces with the inertial sublayer wind speed. This process is dominant at low height-to-width ratios. Secondly, the character of the circulations within the street canyon also varies as the height-to-width ratio increases. The flow in the street is partitioned into a recirculation region and a ventilated region. When the street canyon has high height-to-width ratios the recirculation region occupies the whole street canyon and the wind speeds within the street are low. This tendency decreases the flux at high height-to-width ratios. These processes tend to reduce the flux density from the individual facets of the street canyon, when compared to the flux density from a horizontal surface of the same material. But the street canyon has an increased total surface area, which means that the total flux from the street canyon is larger than from a horizontal surface. The variations in scalar flux from an urban street canyon with geometry is over a factor of two, which means that the physical mechanisms responsible should be incorporated into energy balance models for urban areas.