基于CFD的城市绿地空间格局热环境效应分析

运用CFD数值模拟方法,结合RS技术,对城市中五类常见的绿地空间格局在垂直和水平方向上进行温度场和风速场数值模拟,以探讨绿地空间格局对城市热环境的影响程度及方式。在绿地的垂直结构上,灌木层对流场的影响要大于乔木层;而乔木层对绿地内部的降温作用更为明显。在绿地的水平布局形式中,在绿地率相当的情况下,楔状格局具有较好的热环境效应,即该格局在城市中的降温效果最为明显;放射状和条带状的次之,点状格局对周边环境的降温效果要弱些,但各"绿点"(即组成该格局的各块绿地)在小范围内降温效果比较明显,可以作为改善局部小气候的手段;环状格局热环境效应最弱。将CFD技术引入城市热环境研究,利用遥感技术对其进行参数修正,使热环境研究更加准确完整,具有经济高效方便等优点。

Urban green space landscape patterns and thermal environment investigations based on computational fluid dynamics

The temperature and velocity fields of five common forms for urban green space patterns in the vertical and horizontal directions have been simulated by computational fluid dynamics (CFD) and remote sensing (RS), in order to study the influence and extent of green space patterns on an urban thermal environment. Based on Thematic Mapper remote sensing images (resolution 30 m) of Taiyuan (111°30' to 113°09'E, 37°27' to 38°25'N) acquired on September 16, 2008, numerical models of plant cover were used within a traditional CFD framework. A typical mathematical model of green space distribution patterns was established. CFD model parameters were modified to improve the accuracy of the simulation using RS technology related to the parameters and results. The results show that the shrub layer has a greater influence than the tree layer in the flow field for the vertical structure of a green space. In order to form good local circulation within the green space, importance is attached to the choice and configuration of the shrub layer. Nevertheless, the cooling effect for the tree layer is more apparent. For appropriate rates of change of green space, the following results can be obtained. A wedge-shaped pattern of green space had the most significant cooling effect in the city, followed by radial and banded patterns. The cooling effect of a green space point pattern was insignificant on the surrounding environment. However, local vorticity in its velocity field was obvious, showing that a green space point pattern had a significant cooling effect within a small area and therefore could be used to improve local microclimates. The cooling effect of a ring-shaped pattern was the weakest. We conclude that it is possible to use CFD numerical simulation technology in the study of urban thermal environments, and additionally, remote sensing technology can be used to modify the parameters needed for CFD. CFD has the advantages of saving time, effort and monetary expense. Also, the complementary application of CFD and remote sensing to thermal environment studies will make the results more accurate and complete. Based on the study results, some corresponding proposals for urban green space planning and construction are posed.