城市街道峡谷内气流运动和颗粒物对流扩散特征的研究

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摘要

随着经济迅速发展，机动车数量的急剧增多，机动车尾气对城市大气环境的

污染已经直接影响人们的生产生活。机动车排放污染物在街道周围的扩散主要由

街道两侧建筑物周围的流场所控制，而流场主要受街道布局的影响。一种典型的

街道布局形式是街道峡谷，街道峡谷内机动车尾气对机动车驾驶员、乘客、行人

以及道路两侧居民的身体健康带来直接危害。由于机动车尾气排放已成为大都市

中空气污染最主要的来源，且机动车拥有量仍持续增长，使得街道峡谷内污染物

对流扩散已成为当前环境工程领域的研究热点。对于街道峡谷内污染物扩散研究，

可采用现场实测、风洞实验和计算流体力学(CFD)数值模拟来开展。随着科学计

算、计算机技术以及空气动力学的发展，CFD 已被愈来愈多的学者用于模拟街道

峡谷内的气流运动和污染物扩散。本文采用数值模拟和风洞实验相结合的方法，

探究了不同建筑布局和结构、不同楔形屋顶下街道峡谷内的气流运动和颗粒物扩

散特征。

基于二维不可压缩流动的 N-S 方程，标准



k

湍流模型和颗粒物扩散运动方

程，构建了模拟街道峡谷内气流运动和颗粒物扩散运动的 CFD 模型，在 FLUENT

平台上，首先数值模拟不同粒径颗粒在理想孤立街谷内的扩散和沉积情况，然后

选取 1µm 粒径的颗粒进行不同建筑结构的孤立街道峡谷内气流运动与颗粒物扩

散研究，接着计算了不同建筑布局下的城市街谷内气流运动和颗粒物扩散情况，

计算得到的气流速度场与颗粒物扩散分布图案表明街谷内气流旋涡结构和颗粒物

分布与颗粒粒径和不同建筑布局和结构密切相关：（1）对不同粒径下颗粒物在街

道峡谷内的扩散情况进行计算模拟，迎风面和背风面颗粒沉积率在 0.01-1µm 粒径

范围内不随颗粒粒径的变化而变化；（2）峡谷内的细颗粒物扩散受控于峡谷内的

气流运动结构，由于气流的顺时针运动使得颗粒物主要富集在街道路面和迎风建

筑物背风侧，背风面颗粒物浓度明显高于迎风面颗粒物浓度；（3）上游建筑物的

宽度改变了来流的气流结构和强度，从而影响了颗粒物的扩散分布和沉积效果，

当上游建筑宽度小于临界宽度（W=2H）时，背风面颗粒物浓度随着上游建筑宽

度的增加而增加，而背风侧屋顶的颗粒物浓度则减少；（4）当上游建筑宽度大于

临界宽度时，背风侧屋顶颗粒物浓度可以小到忽略不计，而且背风侧颗粒物浓度

也几乎不受上游建筑宽度增加的影响；（5）当在街谷上游布置建筑物时，自由来

流附着背风侧建筑屋顶，使得上游建筑屋顶的颗粒物浓度很小，可以忽略。

采用建立的 CFD 模型，同样模拟了不同楔形屋顶的城市街道峡谷内气流运动

和颗粒物扩散，模拟结果表明城市街道峡谷内气流旋涡结果和颗粒物分布与楔形

屋顶密切相关：(1) 在背风建筑物屋顶形状为楔形情况下，迎风建筑物屋顶的上

游拐点位置高度是确定街道峡谷内气流旋涡形状以及颗粒物扩散分布的一个关键

性因素；(2) 峡谷内的颗粒物扩散受控于峡谷内的气流运动，由于不同的楔形屋

顶形成不同的气流旋涡结构，导致峡谷内的颗粒物扩散特征随楔形屋顶结构的变

化而变化；(3) 宽高比是影响街道峡谷内流场和颗粒物扩散的一个重要因素，楔

形屋顶结构的变化相应带来峡谷宽高比的变化；

自行设计制作了线源污染物发放系统，并集成了一套污染物浓度场激光片光

测量系统。在此基础上，选取具有代表性的不同建筑布局和结构下街道峡谷的数

值模拟工况开展风洞实验，得到了每种实验工况下的峡谷内颗粒物污染物分布图。

对比分析颗粒物分布的数值模拟结果和风洞实验得到的颗粒物分布图案，表明数

值模拟结果与风洞实验结果定性一致。

本研究成果可以为环境监测中科学合理布置监测点位置、预测街道峡谷内的

空气质量、优化城市道路建筑布局设计以及构建基于环境容量和交通容量双约束

下的交通配流模型系统提供一定的理论和技术支持。

关键词：街道峡谷不同结构不同布局楔形屋顶风洞实验数值模

拟

ABSTRACT

With the rapid development of economy and vehicle population, vehicle exhaust

pollution becomes a serious problem to urban environment. The dispersion of motor

vehicle emission in street environments depends on the airflow around the buildings on

both sides of the streets, while the airflow is mainly affected by the street configuration.

A typical configuration is the so-called street canyon, within street canyons, the

pollutants emitted from motor vehicles have a direct impact on the health of the drivers,

passengers, pedestrians, and residents nearby. Since traffic is accepted to be a major

emission source of air pollutants in urban areas, and further increase of traffic is

expected, investigations of dispersion processes in street canyons have become a focal

point in environmental research. Field measurements, laboratory-scale physical

modeling and computational fluid dynamics(CFD) techniques are common tools

adopted to study the wind flow and pollutant distributions in urban street canyons.

With the ever-increasing power of computer hardwore, numerous sophisticated CFD

models have been developed to study the flow field and pollutant transport in street

canyons. In order to know the effects of upstream building width, upwind building

arrangement and roof shapes on airflow and particles dispersion in a street canyon

better，this study combined numerical simulation with wind-tunnel experiments.

A two-dimensional computational fluid dynamics (CFD) model for evaluating the

airflow and particles dispersion within a street canyon was built up, which was based

on the incompressible Reynolds Averaged Navier-Stokes equations, standard



k

turbulence model and the particles transportation equation. First, the diffusion and

deposition with different particles diameters within an isolated street canyon were

simulated by using the FLUENT code. Then 1µm particle was selected in the

numerical study of the airflow and particles dispersion under different upstream

building width and upwind building arrangement. The computed air velocity vector

fields and particles concentration contours simulation results indicate that the airflow

vortex structure and particles distribution are highly related to the particle size and

different architectural layout and structure: (1) spherical particles in diameters between

0.01 μm and 10 μm are studied at street level. Capture efficiency varies slightly on the

windward and leeward walls of buildings with different diameters. (2) the diffusion of

fine particles within the canyon controlled by the air flow structure. For the clockwise

vortex the particles mainly concentrated on the leeward and street road, the leeward

particle concentration was significantly higher than the concentration of the windward.

(3) the flow structure and strength are changed by upstream building width. When the

upstream building width is shorter than the critical width(W=2H), increase of the

upstream building width leads to increase of particles concentration on the leeward

wall and to decrease of roof-level concentrations at the upstream building.(4) when the

upstream building width is longer than the critical width, the roof-level concentrations

at the upstream building roof are negligibly small, and the particles concentration on

the leeward wall is almost unaffected by further increasing the upstream building width.

(5) when buildings are placed upwind of the canyon, the flow attaches the upstream

building roof and thus the roof-level concentrations at the upstream building are

negligibly small.

Using established CFD model, kinds of wedge-shaped roof configurations within

urban street canyons are also investigated numerically. The computed air velocity

vector fields and particles concentration contours also indicate that the in-canyon

vortex fields and particles dispersion patterns depend on the wedge-shaped roof

configurations strongly: (1) due to flow separation as synoptic wind passes through the

roof peak, both the heights of upstream and downstream corners of the upwind

building have a significant impact on the in-canyon vertical flow pattern when a

downward wedge-shaped roof is placed on the upwind building of a canyon; (2)

particles dispersion inside an urban street canyon is mostly dominated by the in-canyon

wind flow, and different wedge-shaped roof configurations produce different in-canyon

wind vortex structures, which causes a variety of particles distribution patterns; (3) the

aspect ratio is also an important factor determining the flow field and thus particles

dispersion inside a street canyon.

A line source system attached to the large environmental wind-tunnel was

designed to simulate the emission from motor vehicles，and a system of instantaneous

concentration distribution of pollutant with laser sheet was integrated. On this basis of

that，choose several representative cases to do wind-tunnel experiments. By comparing

the wind-tunnel experiments with the simulated dates, the calculated results agree

reasonablely well with the tunnel experiment.

The result of this study can provide theoretical and technical support to

monitoring point setup in environmental monitoring, air quality forecast inside street

canyons, optimization of urban street configuration and construction of advanced

traffic distribution modeling system based on the double restriction of environmental

and traffic capacity.

Key Word: Street canyon, Upstream building width, Upwind building,

Wedge-shaped roof, Wind-tunnel experiment, Numerical simulation

中文摘要

ABSTRACT

第一章绪论 .................................................................................................................. 1

1.1 引言 .................................................................................................................... 1

1.2 研究背景 ............................................................................................................ 1

1.3 街道峡谷内污染物扩散的研究方法及现状 .................................................... 4

1.4 论文研究的目的、意义及主要内容 ................................................................ 9

1.5 论文的创新点 .................................................................................................. 10

第二章不同结构街道峡谷内气流运动及颗粒物扩散的数值模拟 ......................... 11

2.1 街道峡谷简介 .................................................................................................... 11

2.2 数学模型 ........................................................................................................... 14

2.2.1 气流运动控制方程 ................................................................................ 14

2.2.2 湍流模型方程 ........................................................................................ 15

2.2.3 颗粒物的扩散运动方程 ........................................................................ 18

2.2.4 计算区域及边界条件 ............................................................................ 22

2.2.5 网格划分 ................................................................................................ 26

2.2.6 数值算法 ................................................................................................ 28

2.3 数值模拟结果及其分析 .................................................................................. 28

2.4 本章小结 .......................................................................................................... 37

第三章不同布局城市街道峡谷内气流运动及颗粒物扩散的数值模拟 .................. 39

3.1 计算所采用的城市街道峡谷结构模型 .......................................................... 39

3.2 数学模型 .......................................................................................................... 40

3.2.1 控制方程与湍流模型 ............................................................................. 40

3.2.2 计算区域及边界条件 ............................................................................ 40

3.2.3 网格划分 ................................................................................................ 40

3.2.4 数值算法 ................................................................................................ 40

3.3 数值模拟结果及其分析 .................................................................................. 41

3.4 本章小结 .......................................................................................................... 44

第四章楔形屋顶城市街道峡谷内气流运动与颗粒物扩散的数值模拟 .................. 45

4.1 模拟楔形城市街道峡谷的结构尺寸 ............................................................... 45

4.2 数学模型 .......................................................................................................... 46

4.2.1 控制方程与湍流模型 ............................................................................. 46

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