行列式街区风场和污染物浓度场分布特征

Distribution characteristics of wind and pollutant concentration fields in a parallel urban block

为了探讨街区风场和污染物的传输特性,本文基于计算流体力学软件FLUENT数值模拟了行列式街区的风场和污染物浓度,采用RNGκ-ε湍流模型,以接近实况并在街道中央设置了线性污染源的非孤立三维行列式街区作为研究对象,经过风洞实验验证数值方案可行,研究分析了微尺度范围内的三维街区下游及其内部流场与污染物浓度的分布特征,并对流场和污染物浓度的分布特征进行了解释。结果表明:由于建筑群的阻挡作用,导致建筑群下风方向产生风速的低值涡旋区,并聚集了大量来自街区内部的污染物;在街区两个主干道风速入口处附近,受狭管效应作用形成风速最大值区,相应的污染物浓度最低。与以往研究结果一致,在高宽比为1:1的街道峡谷内均产生了一个顺时针涡旋,且污染物主要聚集在背风面底层;污染物的扩散与湍流强度和风速密切关系,在高湍流区域和风速较大的迎风面表现为污染物浓度较低,反之,背风面污染物浓度较高。本文研究结果可以为合理设计街区布局和利用自然风缓解城市高密度地区空气污染提供科学依据。

In order to study the characteristics of wind field and pollutant transportation in a block,the wind field and pollutant concentration were simulated based on the computational fluid dynamics(CFD)software FLUENT using the RNGκεturbulence model.A non isolated three dimensional(3D)parallel block with a linear pollution source in the center of the street was taken as the research object,which was close to the real.The numerical scheme was validated by a wind tunnel experiment,and then the distribution characteristics of flow field and pollutant concentration in the inner and downstream areas of the3D block on a micro scale were analyzed and demonstrated.The results show that the blocking effect of building group results in vortex area with low wind speed in the downwind direction and leads to high loads of pollutants from the inner block.The area of maximum wind speed exists nearby the entrances of two main roads due to the narrow tunnel effect,corresponding to the lowest pollutant concentration.A clockwise rotated vortex appears in the street canyon with a ratio of height to width of1∶1,and pollutants mostly accumulates in the bottom of leeward,which is consistent with previous studies.The diffusion of pollutants is closely related to turbulence intensity and wind speed.Low pollutant concentration usually appears at the windward with intense turbulence and strong wind speed,while high pollutant concentration exists at the leeward.This work can provide a scientific basis for the city planning and alleviate the air pollution in populated urban areas using natural wind.