城市街道峡谷空间形态及其污染物扩散研究——以杭州市中山路为例

概述了城市街谷污染物的扩散机制及相关研究方法。选择CFD数值模拟法,对杭州市中山路街谷进行试验分析。根据试验结果,从水平断面、纵断面、横断面等对街谷形态及其内部污染物的扩散、分布进行了三维的分析研究,进而总结了街谷形态及其污染物扩散的基本规律,并提出基于促进空气流通和污染物扩散、稀释的相关规划设计策略。     

街区空间形态对于交通污染在街谷相邻街区扩散的影响研究

街区空间是居民活动最活跃的场所,由街谷空间内部交通污染扩散引起的街区空间空气质量的变化是受到广泛关注的问题。研究利用CFD模拟的方法,针对街谷内交通污染物随气流向街谷相邻空间的扩散状况进行模拟分析。通过对18个案例从建筑山墙间距、街谷高宽比及建筑错列式布局三个方面探讨街区空间形态的差异对交通污染在街谷相邻空间内的浓度变化与分布特征的影响。研究结果表明建筑山墙间距、街谷高宽比及建筑错列式布局的差异对街区风环境产生明显影响,从而影响交通污染物在街谷及相邻空间内的扩散,导致街谷上下风向的相邻街区内交通污染浓度有不同程度的升高趋势。     

水平遮阳构件对单侧通风及污染物浓度分布的影响研究

自然通风是改善室内空气质量的有效方法。本文以水平遮阳构件为研究对象,在三种不同高宽比的街谷形态下,研究了5种水平遮阳构件的宽度对临街建筑的单侧自然通风及室外交通污染扩散的影响。笔者通过开源CFD软件OpenFOAM,建立了流场和污染物扩散的三维数值模型。模拟结果表明,水平遮阳构件的宽度与室内换气率的变化率有非常强的相关性,街谷高宽比越小,相关性越强。对于污染物浓度,当街谷高宽比不同时,水平遮阳构件对其影响作用不同。本文通过讨论水平遮阳构件对单侧通风和污染物浓度分布的影响,为设计者在设计水平遮阳时,从风环境及污染扩散的角度提供相关的设计建议与思路。     

三维街道峡谷内气流结构和污染物分布的研究

选取三维街道峡谷为研究对象,采用CFD模拟的方法,从来流风速、来流风向、建筑间距、排布方式四个方面,分析三维街道峡谷内的气流结构和污染物的分布情况,结果表明,增加来流风速对街谷内污染物的扩散是有利的,但街谷内的气流结构和污染物的相对分布则不会改变;来流风向的变化对于街谷内气流结构改变较大,同时也对污染物分布有显著影响;随着建筑间距的增加街谷内污染物浓度呈下降趋势,街道污染物对临街建筑的影响取决于不同间距下街谷内的气流结构;不同建筑排布形式下街谷内的气流结构和污染物分布存在明显差异,交错排布相比对称排布而言更不利于街谷内污染物的扩散。     

秦岭山地古镇街谷空间与物理环境解析

随着经济建设发展,兼具生态和文化特色的秦岭山地古镇新建沿街建筑高度逐渐升高,相对日照、通风等物理环境舒适度逐渐降低,传统街谷空间格局也逐渐丧失。通过对传统街道两侧建筑空间尺度及现状风环境的实测,掌握秦岭古镇传统街谷空间尺度及风环境现状,并结合人的尺度感特征,运用计算流体动力学(CFD)软件模拟及日照软件分析的方法,研究具有舒适日照、通风物理环境的新建街谷空间具体控制指标。希望通过本研究,延续秦岭山地古镇的传统街谷空间格局,营造具有舒适物理环境的街谷空间,对新建沿街建筑空间提供设计依据。     

基于CFD的垃圾中转站总图设计

以厦门地区主导风向、风速为初始条件,结合CFD软件建立理想模型,模拟垃圾中转站恶臭污染物扩散范围。结果表明在以垃圾中转站为起点,沿主导风向60m的区域范围内,恶臭污染物浓度大于允许值,并以此为原则进行总图设计。纳入垃圾中转站周边敏感建筑建立实际模型进行模拟计算验证,模拟结果表明:本项目在夏季、冬季主导风向下垃圾中转站周围部分敏感建筑受到恶臭污染物影响,但污染物浓度很小,符合要求;在对夏季静风模拟中西北、西南方向住宅室外环境恶臭污染物浓度超过规范标准,应采取技术措施降低其恶臭污染物的生成量;采取除臭措施后,西北、西南方向住宅室外环境恶臭污染物显著降低,符合要求。     

城市更新背景下基于CFD模拟的垃圾转运站选址优化策略——以杭州戒坛寺巷为例

以杭州戒坛寺巷垃圾转运站选址对周边影响为研究对象,拟定2个变更选址方案,通过CFD软件Airpak对不同季节下空气污染物H2S的扩散情况进行模拟,通过加权计算全年风频和风速条件,对比原址与变更选址方案的优劣。结果表明,选址1方案能够保证街区得到平均最低空气污染物水平。转运站布置在建筑转角或者庭院中,不利于空气污染物扩散;当布置在长条板式建筑周边时,扩散速度快,有助于降低空气污染物浓度。     

庭院式居住组团平面形态对PM2.5扩散的影响

为缓解目前城市严峻的雾霾这一环境问题,采用实地调研、选点测试与CFD仿真模拟的方法,选取已建成的西安市庭院式居住组团为研究对象。从城市设计角度,提炼具备可比性的各类庭院式居住组团平面布局物理模型,运用实地测试以及CFD模拟建立合理的数值模型,进而对不同庭院式居住组团平面形态进行模拟研究,通过对组团内部及外部空间空气品质的差异分析,定量研究不同平面形态对大气污染物稀释扩散的影响。结果表明:综合考虑垂直方向的湍流特征以及微气候影响下的污染物浓度分布规律,在庭院式组团平面布局中节点式组团空间内部的PM2.5细颗粒扩散最差,最有利的形式为U字式组团,可用的形式为风车式组团和散立式组团。     

某HERMES专营店空调设计研究

本文介绍了某HERMES专营店的空调设计方法。为了使室内获得舒适的温度以及合理的气流组织形式,笔者建立了专营店空调设计的物理几何模型,利用CFD软件对该有限空间的气流场和温度场进行了仿真模拟,并根据仿真结果修正了原有的空调设计方案。专营店的空调正常运行后,笔者又对其运行状况进行了现场测量,并将测量记录的结果与CFD仿真模拟结果进行对比分析,符合性较好。本文的研究可以作为利用CFD软件评估和指导有限空间空调设计的有益尝试。     

人体活动对医院关键科室空气污染控制的影响(1):综述

医院关键科室内应考虑人体活动引起的动态尾流对空气中污染物扩散的影响,通常假设人体静态的模拟方法并不能反映真实情况。对人体动态模拟的研究现状和特殊性及其CFD模拟方法进行了介绍,提出对医院关键科室内污染物扩散的模拟应逐渐从稳态模拟向动态模拟转变。     

街道峡谷内汽车污染物扩散的模拟研究

对街道峡谷污染问题的研究常采用实地测量、物理风洞试验和数值模拟等方法。本文采用数值模拟对城市街道峡谷汽车污染物的扩散规律进行了研究,从描述街道峡谷内空气流动和污染物扩散的控制方程出发,采用数值模拟的方法对街道内部的空气流动和污染物的扩散进行了模拟分析,并将结果与风洞试验结果进行比较,从而获得了城市街道峡谷汽车污染物的扩散规律。研究结果可以为城市街道大气污染监测、评价以及防治提供科学依据。     

Airflow and pollutant transport in street canyons

In this work the dispersion of gaseous and particulate exhaust emissions in different street canyons were studied. For two-dimensional sections of canyon models airflow, pollutant dispersion and deposition patterns in the streets and on the surrounding buildings were analyzed. Effects of building size, street width, and wind velocity on the pollutant transport were examined. While the stress transport turbulence models were used in most of the analysis, the predictions of other turbulence models were also examined. Depending on wind speed, building height, and street width, it was found that large recirculation regions in canyons might form. Under certain conditions, also pollutants emitted from vehicle exhaust may trap inside the street canyon. Variations of transport and deposition of emitted particulate pollutants with particle size and relaxation time were also studied. It was shown that the amount of deposited particles in street canyons reduces when the wind speed increases. The simulation results were compared with the available wind tunnel experiments and favorable agreement was found.     

Wind tunnel simulation studies on dispersion at urban street canyons and intersections—a review

Increased traffic emissions and reduced natural ventilation cause build up of high pollution levels in urban street canyons/intersections. Natural ventilation in urban streets canyons/intersections is restricted because the bulk of flow does not enter inside and pollutants are trapped in the lower region. Wind vortices, low-pressure zones and channeling effects may cause build up of pollutants under adverse meteorological conditions within urban street canyons. The review provides a comprehensive literature on wind tunnel simulation studies in urban street canyons/intersections including the effects of building configurations, canyon geometries, traffic induced turbulence and variable approaching wind directions on flow fields and exhaust dispersion.     

街谷行道树种植对环境热舒适度的影响及适应性设计研究 进展

行道树种植通常被作为改善城市街谷 近地微气候的重要策略,如何发挥行道树对街 谷热舒适度的提升潜力受到诸多学者的广泛关 注。近年来“行道树种植与街谷热舒适度”相关 研究获得了丰硕成果，通过总结梳理可将其归 纳为行道树树木个体形态对热舒适度的调控、 行道树绿带空间配置与街谷热舒适度整体提升 的关联性、适应不同街谷空间形态的行道树种 植设计策略等三个研究主题。在深入分析既有 研究成果基础上，提出了一套改善热舒适度的 街谷行道树种植设计方案技术框架。最后，分 别从建立响应地域气候特征的街谷行道树种植 设计模式、构建街谷环境热舒适度模拟评估导 则、制定街谷环境热舒适度评价标准等方面开展深入讨论，以期为后续城市街谷绿化提升热环境的研究提供思路和借鉴。     

Evaluation of the ventilation potential of courtyards and urban street canyons using RANS and LES

We introduce the ventilation potential (VP) as a statistical, climate-dependent measure to assess the removal of scalars, such as heat and pollutants, from courtyards or urban street canyons. The VP is obtained following a three-step approach. First, the magnitude of the flux through a horizontal surface situated at the top of the courtyard or canyon is determined by means of computational fluid dynamics (CFD) simulations for various courtyard geometries and ambient wind directions. Then, this exchange flux is normalized with the free-stream wind speed and subsequently parameterized as a function of the courtyard’s length-to-width ratio and the incidence angle of the wind flow. Finally, the combination of the parameterization with site-specific wind data yields the VP. This study reveals that the normalized exchange flux is maximal when the angle between the prevailing flow direction and the main courtyard axis is about 15-30°, regardless of the courtyard length. The normalized exchange flux increases with increasing courtyard length, and approaches the optimum for courtyards with a length-to-height ratio of ten. Longer courtyards behave as urban street canyons. Unsteady (LES) simulations lead to a much higher VP and thus favor scalar removal when compared with steady (RANS) simulations. These observations can have a decisive impact on urban planning, human comfort and health.     

A numerical investigation of the impact of low boundary walls on pedestrian exposure to air pollutants in urban street canyons

A previous investigation into methods of exposure reduction for the pedestrian in the urban commuter environment highlighted the impact of a low boundary wall on the dispersion of air pollutants from adjacent traffic sources. The impact of low boundary walls on the dispersion of air pollutants in street canyons has been brought forward in this investigation to examine them, in more generic terms, with a view to highlighting exposure reduction strategies for pedestrians. 3D Computational Fluid Dynamics (CFD) models were used to examine this effect for varying wind speeds and directions in different street canyon geometries. The results of this investigation show that a low boundary wall located at the central median of the street canyon creates a significant reduction in pedestrian exposure on the footpath. Reductions of up to 40% were found for perpendicular wind directions and up to 75% for parallel wind directions, relative to the same canyon with no wall. The magnitude of the exposure reduction was also found to vary according to street canyon geometry and wind speed.     

Effect of uneven building layout on air flow and pollutant dispersion in non-uniform street canyons

Uneven building layouts and non-uniform street canyons are common in actual urban morphology. To study the effects of building layouts on air flow in non-uniform street canyons, various building arrangements are designed in this study. Simulations are carried out under four cases (i.e., a uniform street canyon as Case 1 and three non-uniform canyons as Cases 2–4) with parameter change of the occupying ratio of high buildings (ORHB) in the computational domain and their bilateral allocation as well as the combinations of stepup and/or stepdown notches. In the three non-uniform canyons, stepup and stepdown notches are separating (with ORHB of 25% for Case 2 and 75% for Case 4) or adjoining (with ORHB of 50% for Case 3). The air flow and pollutant dispersion in these street canyons are investigated using Large-eddy Simulation (LES). The air flow structures in the non-uniform street canyons are more complicated than in the uniform street canyon. Inside the non-uniform street canyons, the tilting, horizontal divergence and convergence of wind streamlines are found. Large-scale air exchanges of air mass inside and above the street canyons are found as well. At the pedestrian level, the concentrations of simulated pollutants (e.g., the mean and maximum concentrations) in the non-uniform street canyons are lower than those in the uniform one, suggesting that uneven building layouts are capable of improving the dispersion of pollutants in urban area. Further studies on Case 2–4 show that the separation of stepup and stepdown notches along the street increases the wind velocities in the vicinity of high buildings, while the adjoining of stepup and stepdown notches decreases the wind velocities. Low concentrations of pollutant at the pedestrian level are found in Case 2 compared to Cases 3 and 4. Thus, the separation of stepup and stepdown notches in non-uniform street canyons might be a good choice for uneven building layout arrangements from the point of view of pollutant dispersion and human health.     

A numerical study of reactive pollutant dispersion in street canyons with green roofs

Roof greening is a new technique for improvement of outdoor thermal environment which influences air quality through its impacts on thermal and flow field. In order to examine effects of green roofs on reactive pollutant dispersion within urban street canyons, a computational fluid dynamics (CFD) model was employed which contained NO-NO₂-O₃ photochemistry and energy balance models. Simulations were performed for street canyons with different aspect ratios (H/W) of 0.5, 1.0, and 2.0 such that leaf area density (LAD) of green roofs changed. It was found that roof greening led distribution of pollutants to alter for H/W = 0.5 and 1.0 cases in such a manner that their averaged concentrations had small variations as LAD changed. However, by increasing LAD in H/W = 2.0, ventilation efficiency of nitrogen oxides increased since the flow was enhanced within the canyon. Additionally, averaged concentration of ozone in H/W = 2.0 increased with increasing LAD, owing to downward flux of ozone at roof level. Results show that roof greening is a good strategy which can be used in order to improve air quality and thermal environment, especially within deep street canyons.     

Influence of urban planning regulations on the microclimate in a hot dry climate: The example of Damascus, Syria

Urban planning regulations influence not only the urban form; they also have a great impact on the microclimate in urban areas. This paper deals with the relationship between the urban planning regulations and microclimate in the hot dry city of Damascus. The main purpose is to highlight the shortcomings of the existing urban planning regulations. The microclimatic parameters necessary for the thermal comfort assessment of pedestrians were determined through simulations with the software ENVI-met. It is shown that the street design—as regards aspect ratio, orientation and the presence of trees—has a great influence on ground surface temperatures and thermal comfort. Moreover, the type of buildings—whether detached or attached (street canyons)—has an impact. For deep canyons there is an interactive relationship between aspect ratio, orientation and vegetation. However, for streets with detached buildings, there is only a weak influence of street orientation and aspect ratio but a strong influence of vegetation on surface temperatures and outdoor thermal comfort. The study shows the importance of modifying the planning regulations in Damascus for new areas by allowing smaller setbacks, narrower streets, higher buildings, etc.