建筑密度对城市热岛影响的多孔介质数值模拟

Numerical Simulation on Impact of Building Density on Urban Heat Island with an Urban Porous Media Model

根据城市空间结构与多孔介质的相似性,在城市热岛效应的研究中引入了多孔介质理论,采用体积平均技术和雷诺时均方程法建立了适用于城市湍流流动与换热的多孔介质数学模型,并利用微尺度数值模拟计算结果的空间体积平均对模型的有效性进行了验证.采用建立的城市多孔介质数学模型,合理地考虑城市热源在城市冠层内的空间分布,研究了建筑密度对城市热岛强度的影响.结果表明:城市区域热岛强度随着地面孔隙率的增大而减弱,地面孔隙率每增加0.1,就会引起城市热岛强度减小0.36K;在城市下游的乡村地区,随着离开城市距离的增加,热岛强度逐渐消失;城市冠层底部的热岛强度要显著高于上部,热岛强度随高度的增加几乎呈线性减小;城市对上空气流的影响可以延伸至5倍的城市冠层高度.

According to the urban spatial structure and the similarity of the porous media, a two- dimensional model for the turbulent flow and heat transfer in a city was derived from the porous media theory. The urban porous media model was verified by comparing the numerical results with the volume-averaged results of the micro-scale CFD model. Moreover, the urban porous media model was applied to examine the effects of building density on the spatial UHI of the ur- ban area and the leeward rural area. The results show that an increase in ground porosity by 0.1 leads to an increase in UHI intensity by 0.36 K and the UHI intensity decreases rapidly as the airflow enters the leeward rural area. The UHI intensity decreases linearly as the height increases and the UHI almost vanishes as the height reaches five times the height of the urban canopy.