热力作用对城市冠层内流场及湍流扩散影响的数值研究

项目名称： 热力作用对城市冠层内流场及湍流扩散影响的数值研究

项目编号： No.40805004

项目类型： 青年科学基金项目

立项/批准年度： 2009

项目学科： 建筑科学

项目作者： 李磊

作者单位： 北京市气象局

项目金额： 20万元

中文摘要： 利用数值模拟方法研究了热力作用对城市冠层内复杂流场和湍流扩散的影响，获得了一系列有意义的成果：（1）揭示了由地表加热诱发冠层内街谷热力环流的物理过程，指出静风条件下纯热力作用激发的环流速度尺度可达1m/s量级，有助于驱散街谷内的污染物；（2）研究了不同背景风速条件下地表加热作用对城市冠层内街谷流场的影响，得出结论认为对于特定高宽比街谷和特定地表加热强度，存在一个临界的背景风速值，当背景风速小于该临界值时，地表加热对街谷流场的影响比较明显；（3）研究了建筑壁面加热强度和加热位置对冠层内街谷环流的影响，得出结论认为壁面的加热会显著地提升街谷上空的风速，而街谷内下风侧壁面的加热会显著影响流场结构；（4）逆温层结对冠层内的扩散有抑制作用，但是当地面存在加热时，逆温的影响在冠层内不再明显。

中文关键词： 城市冠层;热力作用;流场;湍流扩散;建筑物

英文摘要： Based on the numerical simulation method, the influence of thermal effect on the complex flow and diffusion process in the urban canopy layer was studied, and a series of valuable results were obtained, which include: (1) The development process of the thermal induced circulation in street canyon under calm condition was revealed and the simulation results indicate that the wind speed of the circulation purely induced by thermal effect can reach 1.0 m/s, which is helpful to disperse the pollutant. (2) The impacts of the ground heating on the flow in the urban canopy layer under different ambient wind speeds were studied and the results show that an ambient wind speed threshold exists for a street canyon with a certain H/W ratio. When ambient wind speed is lower than the threshold, the impact of the thermal effect on the flow field is obvious. When the ambient wind speed is higher than the threshold, the circulation is basically driven by dynamic effect. (3) The influences of the wall heating on the flow in street canyon is determined by the location and the intensity of the heating, and a stronger heating will obviously improve the wind speed above the street canyon. The results also show that the heating from the wall on the downwind side of the street canyon will obviously influence the pattern of the flow field within the urban canopy layer. (4) A stable stratification will suppress the diffusion in the urban canopy layer. However, when the ground heating exists in the street canyon, the impact of the stable stratification is no more obvious.

英文关键词： urban canopy layer; thermal effect; flow field; turbulent diffusion; building