树冠空间占用对不同高宽比街道行人热环境的影响

在深浅有别的街谷内部，针对树冠大小差异如何影响行人小气候，并在多大程度上产生影响的问题，本文构建了NE-WS和N-S走向的浅、中、深三种不同AR特征的街道，开展了不同大小的树冠对行人气温影响的数值计算，结果表明：（1）无论街谷深浅，植树总是减弱街谷内部行人高度的平均风速，并引起上午行人气温的小幅升高；但是，植树可降低中午和下午的行人气温；（2）树木对行人小气候的影响程度随着街谷深度的增加而减弱，故，行道树绿化差异所致的深街谷行人小气候差异微乎其微；（3）行道树对行人小气候的调节作用很有限，并受来流方向的影响，平行来流下植树阻风而增强的局地湍流有助于树木发挥冷却降温作用。建议NE-WS和N-S走向的街道，种植带有小空隙率（0.125）的行道树，而不是让树冠形成连续树荫，以获得更好的降温和通风。

Effects of canopy space occupation on the thermal environment of pedestrians in the street with various aspect ratios

When comes to the problem of how and to what extent tree crowns of different size affects the pedestrian microclimate. This paper firstly builds different 3D NE-WS and N-S streets models with shallow, medium, and deep. Then perform the CFD (Computational Fluid Dynamics) simulation of the impact of tree crowns of different sizes on the pedestrian temperature. the result shows that:(1) Tree planting always raises air temperature in the morning and reduces the average wind speed at the pedestrian height regardless of any depth of the street canyon, while dropping the pedestrian air temperature at noon and afternoon; (2) As the depth of the street canyon increases, the impact of trees on pedestrian microclimate reduces. Therefore, the difference in pedestrian microclimate induced by street trees'' different greening in the deep street canyon is extremely modest; (3) Street trees have a limited moderating impact on the pedestrian microclimate, which is regulated by the direction of the entering flow. Trees planted in parallel flow increase local turbulence, which is beneficial for trees to play a role in cooling. To provide better cooling and ventilation, we suggest that trees with tiny gaps (0.125) should be placed in the NE-WS and N-S streets instead of forming continuous shade.