上游阻挡建筑间距对街谷内空气环境的影响

发布时间：2019-03-22 20:38

【摘要】：城市人口膨胀,使得住宅用地紧张,进而导致建筑密度大大增加;同时,城市机动车持续增多,也在某种程度上使城市空气环境污染问题日益严重。街谷(street canyon)是城市区域的重要组成元素,街谷微环境直接影响着城市空气质量。因此,近几十年来学者们对街谷微环境的各种特性进行了研究。然而,已有研究大多数都是针对孤立街谷进行的,仅有少数研究是针对街谷上游的阻挡建筑对街谷环境的影响进行的。由于城市中的大部分街谷都在上风向存在阻挡建筑(以下简称上游阻挡建筑),因此,研究不同特征的上游阻挡建筑对街谷内空气品质的影响,对减小交通污染物对街谷内行人的影响,改善城市空气质量是非常必要的。本文采用CFD数值模拟方法,研究了四种典型建筑布局下,上游阻挡建筑物与街谷建筑的间距对街谷气体流动特性和污染物分布规律的影响,为改善街谷微环境和合理的城市规划提供设计原则和理论基础。本文分析讨论了街谷内不同典型位置、典型高度处的流场和污染物垂直与水平分布规律。同时将街谷划分成迎风区、中心区和背风区等三个区域,统计了各区域在建筑高度以下空间范围及2 m以下空间内的气体流速、湍流强度和污染物无量纲浓度的平均值。研究结果表明,上游阻挡建筑与街谷间距的改变影响了街谷空间的流场,进而影响了街谷内污染物浓度的分布规律。对于行列式街谷,不论上游阻挡建筑与上风建筑的相对布局如何,随着上游阻挡建筑与街谷间距的增加,街谷内污染物上部空间平均浓度都会呈现先增后减的趋势,存在对应着平均浓度最大值的间距,在本文计算的常规街谷中,该对应街谷最大平均浓度的间距为90 m,即上游阻挡建筑与街谷上风建筑的间距小于90 m时,街谷内上部空间平均浓度反而随该间距的增大而升高,这将影响到临街建筑室内空气环境,而同时街谷内2 m以下人员空间的浓度呈相反的变化趋势;当建筑间距D90 m时,行人活动空间污染物浓度亦会随该间距的增大而升高,因此建议在城市建筑规划布局设计中,行列式街谷临街建筑与上游阻挡建筑的间距不必过大;对于错列式街谷,不论上游阻挡建筑与上风建筑对齐或错列布局,街谷内污染物平均浓度都呈现波动式变化,没有表现出行列式街谷类似的规律。另外,研究结果还表明,四种典型布局下,无上游阻挡建筑时,街谷内污染物整体平均浓度最小,但是2 m以下空间范围内的污染物平均浓度反而最高,这说明上游阻挡建筑的存在形成了利于近地面的污染物扩散的气流形态,利于街谷内行人呼吸环境的改善。
[Abstract]:The expansion of urban population makes residential land tense and leads to a great increase in building density. At the same time, urban motor vehicles continue to increase, to some extent, the urban air pollution problem is becoming more and more serious. Street valley (street canyon) is an important element of urban area. Street valley microenvironment directly affects the air quality of city. Therefore, in recent decades, scholars have studied the characteristics of street valley microenvironment. However, most of the studies have been carried out on isolated streets and valleys, and only a few studies have been carried out on the impact of blocking buildings in the upper reaches of the valley on the environment of the streets and valleys. Since most of the streets and valleys in the city are blocking buildings in the upwind direction (hereinafter referred to as upstream blocking buildings), the impact of upstream blocking buildings with different characteristics on the air quality in the street valleys is studied. It is necessary to reduce the influence of traffic pollutants on pedestrians in the street valley and to improve the air quality of the city. In this paper, the CFD numerical simulation method is used to study the influence of the distance between upstream barrier building and street valley building on gas flow characteristics and pollutant distribution in street valley under four typical building layouts. To improve the street and valley micro-environment and rational urban planning to provide design principles and theoretical basis. In this paper, the flow field and the vertical and horizontal distribution of pollutants at different typical positions and typical heights in street valleys are analyzed and discussed. At the same time, the street valley is divided into three areas: upwind area, central area and leeward area. The average values of gas velocity, turbulence intensity and dimensionless concentration of pollutants in the space below building height and below 2 m in each area are calculated. The results show that the change of the distance between the upstream barrier building and the street valley affects the flow field in the street valley space, and then affects the distribution of the pollutant concentration in the street valley. For street valleys, regardless of the relative layout of upstream barrier buildings and upwind buildings, as the distance between upstream barrier buildings and street valleys increases, the average concentration of pollutants in the upper space of street valleys tends to increase first and then decrease. There is a space corresponding to the maximum of the average concentration. In the conventional street valley calculated in this paper, the spacing of the maximum average concentration of the corresponding street valley is 90 m, that is, when the distance between the upstream barrier building and the upwind building in the street valley is less than 90 m, On the contrary, the average concentration of the upper space in the valley increases with the increase of the distance, which will affect the indoor air environment of the street-facing building, while the concentration of the people below 2 m in the valley has the opposite trend. When the space between buildings is D90 m, the concentration of pollutants in pedestrian moving space will also increase with the increase of the spacing. Therefore, it is suggested that in the layout design of urban architecture, the spacing between street-facing buildings and upstream barrier buildings should not be too large. For staggered street valley, no matter the upstream blocking building aligned with the upper wind building or the staggered layout, the average concentration of pollutants in the street valley is fluctuating, and there is no similar rule as the trip type street valley. In addition, the results also show that the average concentration of pollutants in street valley is the smallest when there is no upstream barrier in the four typical layouts, but the average concentration of pollutants in the space below 2 m is the highest. This shows that the presence of upstream barrier building forms the air flow pattern which is conducive to the diffusion of pollutants near the ground and to the improvement of the breathing environment of pedestrians in the street valley.
【学位授予单位】：东华大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU-023;X51

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