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Street-canyon pollution with respect to urban-array complexity: The role of lateral and mean pollution fluxes

机译：关于城市阵列复杂性的街峡谷污染：横向和平均污染通量的作用

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摘要

The prediction of pollution within street canyons remains challenging due to the complexity of turbulent flows in urban environments. To improve our understanding of these flows and their relation to the ventilation of street-canyons, we studied pollution fluxes through all street-canyon openings and their balance with respect to urban-array complexity using large-eddy simulations (LES). We validated the LES with wind-tunnel measurements using mean velocities and concentrations and the mean total and turbulent pollution fluxes at the top and lateral openings of the street canyons with either uniform or nonuniform heights and pitched roofs. The LES confirm and extend recent findings about the importance of mean horizontal pollution fluxes for pollutant transport within a street network. The mean fluxes have at least the same dominance as the turbulent ones in case of lateral openings. In case of top openings, the mean fluxes clearly dominate if openings at the roof eaves are selected. While pollutant removal and entrainment through lateral openings are negligible in case of uniform canyons, they are notable in case of nonuniform canyons. We demonstrate that urban roof height nonuniformity does not necessarily enhance the street-canyon ventilation because it worsens (by a factor of 1.1) or improves (by a factor of 1.5) the ventilation compared with the urban uniform height.
机译：由于城市环境中湍流的复杂性，对街道峡谷内污染的预测仍然具有挑战性。为了更好地理解这些流量及其与街道峡谷通风的关系，我们使用大涡模拟（LES）研究了所有街道峡谷开口处的污染通量及其在城市阵列复杂度方面的平衡。我们使用平均速度和浓度以及平均高度和不均匀高度以及倾斜屋顶的街道峡谷的顶部和侧面开口处的平均总和湍流污染通量，通过风洞测量验证了LES。 LES证实并扩展了有关平均水平污染通量对街道网络内污染物运输的重要性的最新发现。在横向开口的情况下，平均通量至少具有与湍流相同的优势。在顶部开口的情况下，如果选择屋檐处的开口，则平均通量显然占主导地位。尽管在均匀峡谷的情况下，通过侧向开口进行的污染物去除和夹带可以忽略不计，但在不均匀峡谷的情况下，这些污染物的清除和引人注目。我们证明，与城市统一高度相比，城市屋顶高度不均匀性并不一定会增强街道峡谷通风，因为它会使通风变差（系数为1.1）或改善（系数为1.5）。

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