﻿ 架空建筑街谷内流动与污染物扩散的数值模拟研究
 上海理工大学学报  2021, Vol. 43 Issue (4): 368-377 PDF

Numerical simulation studies on airflow and pollutant dispersion in street canyons with void decks
REN Suqi, HUANG Yuandong, CUI Pengyi
School of Environment and Architecture, University of Shanghai for Science and Technology, Shanghai 200093, China
Abstract: To explore the influence of the structure of buildings with void decks on the airflow and pollutant dispersion in street canyons, CFD (computational fluid dynamics) numerical models validated by the wind-tunnel tests were employed by considering four aspect ratios (H/W) and three configurations of buildings with void decks. The results show that the increase of H/W is not conducive to the dispersion of pollutants in the street canyon without any void decks. Compared with the street canyon without any void decks, the structures of building with void decks observable improves the air quality in street canyons. The structure of buildings with void decks on both sides is more propitious to the dispersion of pollutants in the street canyon than the structure of building with a void deck on one side, and the dilution effect of the structure of upstream building with a void deck on the pollutants in the street canyon is better than that of the structure of downstream building with a void deck. The pollutant concentration in the street canyon with void decks at buildings on both sides is reduced by more than 90%. Therefore, the structures of buildings with void decks significantly enhances the airflow in the area near the ground and improves the air quality in street canyons.
Key words: street canyon     numerical simulation     void deck     aspect ratio     airflow     pollutant dispersion

1 研究方法 1.1 物理模型

 图 1 二维街谷模型 Fig. 1 Two-dimensional street canyon model

 $Re = {U_{{\rm{ref}}}}H/\nu$ (1)

1.2 数值模型 1.2.1 控制方程

RANS（Reynolds Averaged Navier Stokes）模型是计算街谷内流场最常用的模型，在RANS模型中，标准 $k - \varepsilon$ 模型可以很好地再现完全湍流的一般结构，因此，本文采用标准 $k - \varepsilon$ 模型对湍流的二维流动进行求解。控制方程：

 $\frac{{\partial {u_j}}}{{\partial {x_j}}} = 0$ (2)
 ${u_j}\frac{{\partial {u_j}}}{{\partial {x_j}}} = - \frac{1}{\rho }\frac{{\partial p}}{{\partial {x_i}}} - \frac{\partial }{{\partial {x_j}}}\left( {\overline {{u'_i}{u'_j}} } \right) + \nu {\nabla ^2}{u_i} + {g_i}$ (3)
 ${u_j}\frac{{\partial k}}{{\partial {x_j}}} = \frac{\partial }{{\partial {x_j}}}\left( {\frac{{{\nu _{\rm t}}}}{{{\sigma _k}}}\frac{{\partial k}}{{\partial {x_j}}}} \right) + {\nu _t}\left( {\frac{{\partial {u_i}}}{{\partial {x_j}}} + \frac{{\partial {u_j}}}{{\partial {x_i}}}} \right)\frac{{\partial {u_i}}}{{\partial {x_j}}} - \varepsilon$ (4)
 $\begin{split}{u_j}\frac{{\partial \varepsilon }}{{\partial {x_j}}} =& \frac{\partial }{{\partial {x_j}}}\left( {\frac{{{\nu _{\rm t}}}}{{{\sigma _\varepsilon }}}\frac{{\partial \varepsilon }}{{\partial {x_j}}}} \right) +\\ &\frac{\varepsilon }{k}\left[ {{C_{\varepsilon 1}}{\nu _{\rm t}}\left( {\frac{{\partial {u_i}}}{{\partial {x_j}}} + \frac{{\partial {u_j}}}{{\partial {x_i}}}} \right)\frac{{\partial {u_i}}}{{\partial {x_j}}} - {C_{\varepsilon 2}}\varepsilon } \right]\end{split}$ (5)

 $\qquad\quad{u_j}\frac{{\partial {C_\alpha }}}{{\partial {x_j}}} = \frac{\partial }{{\partial {x_j}}}\left( {\left( {{D_{\alpha ,{\rm m}}} + \frac{{{\nu _{\rm t}}}}{{S{c_{\rm t}}}}} \right)\frac{{\partial {C_\alpha }}}{{\partial {x_j}}}} \right) + {S_{\alpha ,p}}$ (6)

1.2.2 计算域、边界条件与计算方法

 图 2 计算域示意图 Fig. 2 Computational domain

1.3 模型验证与网格独立性分析 1.3.1 风洞实验概况

 图 3 风洞实验二维街谷模型 Fig. 3 Two-dimensional street canyon model of wind-tunnel experiment
 $K = \frac{{C{U_{{\rm{ref}}}}HL}}{{{Q_{\rm e}}}}$ (7)

 $\frac{u}{{{U_{{\rm{ref}}}}}} = {\left( {\frac{{z - {d_0}}}{{{z_{{\rm{ref}}}} - {d_0}}}} \right)^{{\rm{0}}{\rm{.23}}}}$ (8)
 $k\left( z \right) = \frac{{{u_*}^2}}{{\sqrt {{C_u}} }}$ (9)
 $\varepsilon = \frac{{{u_ * }^3}}{{\kappa z}}$ (10)

1.3.2 网格敏感性与模型参数验证

 图 4 数值模拟结果与风洞实验数据对比 Fig. 4 Comparison of numerical simulation results and wind tunnel experiment data
2 结果与讨论 2.1 不同架空结构街谷内流场变化与分析

 图 5 H/W = 1时不同底层架空结构的街谷流场 Fig. 5 Flow fields inside street canyons with void decks when H/W = 1

 图 6 H/W = 4/3时不同底层架空结构的街谷流场 Fig. 6 Flow fields inside street canyons with void decks when H/W = 4/3

 图 7 H/W = 5/3时不同底层架空结构的街谷流场 Fig. 7 Flow fields inside street canyons with void decks when H/W = 5/3

 图 8 H/W = 2时不同底层架空结构的街谷流场 Fig. 8 Flow fields inside street canyons with void decks when H/W = 2
2.2 不同架空结构街谷内污染物浓度分布特点及分析

 图 9 H/W = 1下不同底层架空结构的街谷内无量纲浓度分布 Fig. 9 Dimensionless concentration distributions inside street canyons with void decks when H/W = 1

 图 10 H/W = 4/3时不同底层架空结构的街谷内无量纲浓度分布 Fig. 10 Dimensionless concentration distributions inside street canyons with void decks when H/W = 4/3

 图 11 H/W = 5/3时不同底层架空结构的街谷内无量纲浓度分布 Fig. 11 Dimensionless concentration distributions inside street canyons with void decks when H/W = 5/3

 图 12 H/W = 2时不同底层架空结构的街谷内无量纲浓度分布 Fig. 12 Dimensionless concentration distributions inside street canyons with void decks when H/W = 2
2.3 街谷内平均污染水平评价分析

 图 13 研究工况街谷内不同位置的平均污染物浓度 Fig. 13 Mean concentrations at different locations for all studied cases

3 结　论

a. 架空结构增强了街道峡谷内的平均通风能力，且随着H/W的增加，对街谷内流动结构的影响逐渐增大。当H/W < 2时，架空建筑街谷内的主涡逐渐变大，涡心上移，上方涡变小。当 H/W = 2时，架空建筑街谷内流动结构与污染物扩散发生显著变化，街谷内仅有一个涡，屋顶上方对流作用减弱。

b. 不同建筑架空结构对街谷两侧污染物分布的影响不同。两侧建筑架空和上游建筑架空显著降低了背风面污染物的浓度，背风面的污染物平均浓度为0。下游建筑架空结构有利于迎风面污染物的扩散。

c. 与无架空街谷相比，架空结构显著改善了街谷内的空气质量。两侧建筑架空结构比单侧建筑架空更有利于街谷内污染扩散，两侧建筑架空街谷内的污染物浓度降低了91%～98%。而在单侧建筑架空街谷内，上游建筑架空街谷内的污染物浓度可降低71%～90%。下游建筑架空结构对街谷内污染物的扩散作用随着H/W的增加逐渐增强，当H/W = 2时，街谷内平均污染物浓度可降低69%。

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