Scalar fluxes from urban street canyons. Part I: Laboratory simulation
Scalar fluxes from urban street canyons. Part I: Laboratory simulation
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DOI：
10.1007/s10546-004-6204-8
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发表时间：
2004-12-01
影响因子：
4.3
通讯作者：
Belcher, SE
中科院分区：
文献类型：
--
作者：
Barlow, JF;Harman, IN;Belcher, SE
城市表面的流量取决于表面形态以及与上方边界层的相互作用。然而，流动对标量通量的影响很难量化。萘升华技术用于量化中性条件下从街道峡谷流出的标量垂直通量。对于纵横比 H/W=0.75 的八个峡谷阵列（这里，H 是建筑物高度，W 是街道宽度），在上游中度和低粗糙度的前两个或三个峡谷中观察到通量增加。这与城市冠层流量初步调整的长度尺度的预测是一致的。在初始调整区域之后通量是恒定的，因此仅取决于局部几何形状。对于阵列“平衡”部分的街道峡谷，街道峡谷的每个面都涂有萘，以模拟街道、墙壁和屋顶的标量释放，以评估街道峡谷几何形状对 H/W=0.25、0.6、1 和 2 通量的影响。来自屋顶和下游墙壁的通量远大于来自街道和上游墙壁的通量，并且只有来自下游墙壁的通量随硬件/W。对于每个 H/W，下游墙、街道和上游墙转移之间存在单调递减。这表明流在上游建筑物背风处的再循环区域周围减速，即再循环射流而不是对称涡流。由于峡谷空气中萘浓度增加，在街道峡谷内添加第二个源导致 H/W>0.25 时每个面的通量减少。
Flow over urban surfaces depends on surface morphology and interaction with the boundary layer above. However, the effect of the flow on scalar fluxes is hard to quantify. The naphthalene sublimation technique was used to quantify scalar vertical fluxes out of a street canyon under neutral conditions. For an array of eight canyons with aspect ratio H/W=0.75 (here, H is building height and W is the street width), increased flux was observed in the first two or three canyons for moderate and low roughness upstream. This is consistent with predictions of the length scale for initial adjustment of flow to an urban canopy. The flux was constant after the initial adjustment region and thus dependent only on local geometry. For a street canyon in the 'equilibrium' part of the array, each facet of the street canyon was coated with naphthalene to simulate scalar release from street, walls and roof, to evaluate the effect of street canyon geometry on fluxes for H/W=0.25, 0.6, 1 and 2. Fluxes from the roof and downstream wall were considerably larger than fluxes from the street and upstream wall, and only the flux from the downstream wall exhibited a simple decrease with H/W. For each H/W there was a monotonic decrease between downstream wall, street and upstream wall transfer. This suggests that flow decelerates around the recirculation region in the lee of the upstream building, i.e. a recirculating jet rather than a symmetrical vortex. The addition of a second source within the street canyon resulted in reduced fluxes from each facet for H/W>0.25, due to increased concentration of naphthalene in the canyon air.