Air infiltration induced inter-unit dispersion and infectious risk assessment in a high-rise residential building

Identifying possible airborne transmission routes and assessing the associated infectious risks are essential for implementing effective control measures. This study focuses on the infiltration-induced inter-unit pollutant dispersion in a high-rise residential (HRR) building. The outdoor wind pressure distribution on the building facades was obtained from the wind tunnel experiments. And the inter-household infiltration and tracer gas transmission were simulated using multi-zone model. The risk levels along building height and under different wind directions were examined, and influence of component leakage area was analysed. It is found that, the cross-infection risk can be over 20% because of the low air infiltration rate below 0.7 ACH, which is significantly higher than the risk of 9% obtained in our previous on-site measurement with air change rate over 3 ACH. As the air infiltration rate increases along building height, cross-infection risk is generally higher on the lower floors. The effect of wind direction on inter-unit dispersion level is significant, and the presence of a contaminant source in the windward side results in the highest cross-infection risks in other adjacent units on the same floor. Properly improving internal components tightness and increasing air change via external components are beneficial to the control of internal inter-unit transmission induced by infiltration. However, this approach may increase the cross-infection via the external transmission, and effective control measures should be further explored considering multiple transmission routes.     

Evaluation of RANS turbulence models for simulating wind-induced mean pressures and dispersions around a complex-shaped high-rise building

Re-ingestion of the contaminated exhaust air from the same building is a concern in high-rise residential buildings, and can be serious depending on wind conditions and contaminant source locations. In this paper, we aim to assess the prediction accuracy of three k-? turbulence models, in numerically simulating the wind-induced pressure and indoor-originated air pollutant dispersion around a complex-shaped high-rise building, by comparing with our earlier wind tunnel test results. The building modeled is a typical, 33-story tower-like building consisting of 8-household units on each floor, and 4 semi-open, vertical re-entrant spaces are formed, with opposite household units facing each other in very close proximity. It was found that the predicted surface pressure distributions by the two revised k-? models, namely the renormalized and realizable k-? models agree reasonably with experimental data. However, with regard to the vertical pollutant concentration distribution in the windward re-entrance space, obvious differences were found between the three turbulence models, and the simulation result using the realizable k-? model agreed the best with the experiment. On the other hand, with regard to the vertical pollutant concentration distribution in the re-entrant space oblique to the wind, all the three models gave acceptable predictions at the concentration level above the source location, but severely underestimated the downward dispersion. The effects of modifying the value of the turbulent Schmidt number in the realizable k-? model were also examined for oblique-wind case. It was confirmed that the numerical results, especially the downward dispersion, are quite sensitive to the value of turbulent Schmidt number.     

Experimental and numerical investigation on the distribution characteristics of wind pressure coefficient of airflow around enclosed and open-window buildings

In the present paper, the distribution characteristics of the wind pressure coefficient of the air flow around enclosed and open-window buildings were studied by using wind tunnel model tests and numerical analyses. A typical high-rise building model was designed and wind tunnel tests were performed for the airflow around the building for an enclosed and an open-window condition. The experimental findings were complemented by the numerical analysis. This study shows that the opening windows of a building has little influence on the wind pressure coefficients in the area around the window of adjacent area from window edge; the wind pressure coefficient increases slightly after opening the windows of the buildings. Opening the windows in the rooms adjacent to this window decreases the ventilation efficiency of the room although the influence is small. The time-average value of the wind pressure coefficient can effectively represent the magnitude of the instantaneous wind pressure coefficient. The wind pressure coefficient is independent of the wind velocity of inflow. Furthermore, this study also proposed the distribution characteristics of wind pressure coefficients with different incident angles of wind.     

基于风洞试验的高层建筑钢结构风致加速度研究

对钢结构高层建筑群中的典型狭长形建筑进行了表面风压的风洞模型试验,分别考虑了建筑为单体和群体的情况。利用试验获得的风荷载时程对该高层结构进行风振响应的动力时程分析,并着重对得到的与风致舒适度关联的加速度响应进行分析和讨论,对比群体效应对顺风向、横风向和扭转向峰值加速度的不同影响。结果表明,对于平面为狭长形的住宅钢结构高层建筑,扭转效应引起的风致峰值加速度不容忽略;而群体效应一般对结构的加速度呈增大趋势,而且对横风向及扭转向的增大程度通常大于对顺风向的程度。     

An experimental investigation of the wind environment and air quality within a densely populated urban street canyon

This paper presents an experimental investigation of wind flow characteristics and air quality along a street canyon located within a dense urban area. Four typical models of a highly populated urban area are studied and wind tunnel experiments are carried out over an extended range of the applied wind directions. The building patterns are represented by 1:100 scale models, where wind velocity and tracer gas concentrations are measured along the two sides of the street. The study results provide evidence that building configurations and wind directions are very important factors in determining both wind flow and pollutant dispersion characteristics within urban domains. Also, the results demonstrate that gaps between buildings are a very important factor to be considered by urban planners and designers, because, for a given building height, larger gaps induce more wind in urban canyons, thus improving the ventilation process.     

Numerical simulation of inter-flat air cross-contamination under the condition of single-sided natural ventilation

The objective of this study is to investigate the mechanism of inter-flat airborne disease transmission under the condition of single-sided natural ventilation. The focus is on one of the typical designs in residential buildings with a rectangular plan layout and having a common corridor separating the two sides, each of which has a flat façade with openable windows. When the wind speed is extremely low, with doors closed and windows opened, the flats become single-sided naturally ventilated driven by buoyancy effects. The air pollutants can travel from a lower flat to a vertically adjacent upper flat through open windows, caused by indoor/outdoor temperature-difference induced buoyancy. Computational fluid dynamics is employed to explore the characteristics of this process. Based on the comparison with experimental data about the air flow distribution in and around a single-sided naturally ventilated room, the renormalization group based k?ε model, together with carbon dioxide used as a tracer, is chosen to reveal this air cross-contamination. The simulation results are in agreement with our prior on-site tracer-gas measurements, revealing that the windows flush with a flat façade can be a major route of the air cross-contamination in high-rise residential buildings. Finally, an assessment index is proposed to evaluate the potential infection risks associated with this inter-flat air flow occurring in high-rise residential buildings.     

某超高层建筑风洞测压试验

依据某超高层建筑,着重介绍了风洞试验的方法,描述了在考虑有、无环境建筑影响下,该高层建筑一些典型的表面风压特性以及一些测点风压随风向角的变化规律。结果表明:迎风面中上部风压系数较大,接近1.0;底部部分风压系数达到1.0;侧风面和背风面风压系数大多为负值,特别是靠近角落处由于涡旋脱落,其值可达到-2。环境建筑对该高层建筑表面风压的影响较大,特别在建筑中下部。为其进行结构设计提出一些参考。     

Wind tunnel experiments on wind-induced natural ventilation rate in residential basements with areaway space

In residential building design, areaways can act as an open subsurface space to help improve the living environment in adjacent basements for residential purposes, mainly by wind-induced natural ventilation. The accurate prediction of effective air change rate is quite important; nevertheless so far little is known about this kind of ventilation issue. In order to acquire more knowledge in this field and make accurate ventilation predictions, direct measurement of ventilation rate was performed in this study using small-scale wind tunnel models. In the experiment, considering ventilation induced only by the exterior wind, we applied the constant tracer gas flow technique to measure the time-averaged ventilation rate for nine wind directions for each case. Furthermore, the relationships between the ventilation rate and a variety of parameters including wind direction, opening type, plan area of the areaway space and building coverage ratio, etc. were investigated and analyzed in detail. The findings of the present study can provide fundamental data for the design of areaway space in the urban residential buildings.     

高层建筑水平悬挑遮阳板风荷载的风洞试验研究

高层建筑悬挑遮阳板等小尺寸构件直接承受风荷载作用,在强风作用下的安全性备受关注。相对于建筑的整体尺寸,悬挑遮阳板很小,难以在缩尺模型上直接模拟,因此在实际工程的风洞试验研究中常常被简化或者忽略。研究中利用3D打印技术制作了精细化的有悬挑遮阳板的高层建筑风洞试验模型,并在打印遮阳板模型时直接预留测压管道,分析了水平悬挑遮阳板的风压分布规律及遮阳板对建筑立面风压的影响,并对基于建筑立面风压的悬挑遮阳板风压估计方法的估算误差进行了评估。研究结果表明：高层建筑水平悬挑遮阳板的最不利净风压的最大值出现在顶层遮阳板处;水平悬挑遮阳板的存在能较大程度地削弱建筑立面上的最不利负风压;悬挑遮阳板最不利风压可利用其上下两侧附近建筑立面测点的风压差近似估计,但对于建筑立面边缘附近的悬挑遮阳板端部以及建筑底部附近的最底层悬挑遮阳板上的最不利风压,这种方法的估算误差较大。     

Temperature- and wind-induced air flow patterns in a staircase. Computer modelling and experimental verification

The typical infiltration load for a residential building has been found to range from one-third to one-half of the total space conditioning load. However, most infiltration measurements have been made on single-family houses. Information about the role of infiltration in the energy consumption of large buildings is limited. Furthermore, the prediction of infiltration rates in high-rise buildings is a complex problem. The forces that drive this flow result from the superposition of wind pressure on the faces of the building and the stack effect across the height of the building. Infiltration models have shown the latter effect to be significant in single-family residences, particular in colder climates and, consequently, the stack effect is even greater in high-rise buildings. For this work, we performed tracer gas and fan pressurization measurements on a 30 m tall University of California dormitory in order to determine the importance of both wind and stack effect upon infiltration. Measured pressure and tracer gas distributions were compared with those from a predictive infiltration computer model for high-rise buildings. To study the influence of the air flow pattern around the building, this model uses various wind velocity profiles characteristic of urban areas and different sets of surface pressure coefficients derived from wind tunnel experiments.     

周边高层建筑对大跨度曲面屋盖的气动干扰

结合无锡新区科技交流中心的风洞试验,分析了有无周边建筑两种情况下的风压分布,并对梅花形屋盖的花蕊、花瓣凹弧面和花瓣凸弧面3个典型部位的风荷载体型系数进行了研究,获得周边高层建筑对大跨度曲面屋盖气动干扰的相关结论:虽然受扰建筑的最不利风向角和风压发生很大变化,但是最危险部位始终处于檐口附近,而且是负风压为主;在"兜风效应"的作用下,受扰建筑的风压会急剧增大;在"阻挡效应"的作用下,受扰建筑的风压存在由负压向正压变化的趋势;屋盖凹弧面的槽向与风向角一致时,存在涡流作用与"兜风效应"叠加的现象,受"吸"破坏力极大,在曲面屋盖设计中应予以重视。     

单重和多重调谐质量惯容阻尼器控制连体超高层建筑风振响应比较研究

连体超高层建筑因存在强烈的气动干扰,在强风下可能会出现大幅相对振动,调谐质量惯容阻尼器(TMDI)是一种振动控制装置,其惯容器两端的相对加速度较大时,TMDI振动控制效果较好。结合两者各自的特点提出了多重调谐质量惯容阻尼器(MTMDI)控制连体超高层建筑的风振响应,两个TMDI分别控制两栋建筑各自的一阶自振频率。首先建立了MTMDI控制连体超高层建筑风致响应数学模型,然后开展了某连体超高层建筑的刚性模型同步测压风洞试验;最后,基于该数学模型和测压风洞试验结果分析了该连体建筑在分别安装两个和单个TMDI对风振加速度和位移响应的减振效果。研究结果表明：虽然两个TMDI的总质量和总惯容量比单个TMDI相应的参数小,但两者的减振效果基本相同,两者都能有效地减小两栋建筑在各个风向角下的加速度响应,如在270°风向角下,安装TMDI后两栋建筑顶层加速度响应分别减小了37.5%和50.0%;对于位移响应,两者都可以减小高栋建筑的响应,其对低栋建筑在少部分风向角下的减振效果并不理想。     

Assessment of pollutant dispersion from rooftop stacks: ASHRAE,ADMS and wind tunnel simulation

The prediction of downwind concentration of effluents from stack located on top of buildings is important. Most current dispersion models assess the pollutant concentration at distances away from the building. It is important to study pollutant dispersion within the recirculation zone of the building, since studies have shown that effluents released from rooftop stacks have a tendency to re-enter the building through intakes located on the roof. These effects get more pronounced with the influence of RoofTop Structures (RTS). This paper presents a comparative study of the Atmospheric Dispersion Modelling System (ADMS), American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE 2003 and 2007 versions) and wind tunnel results. Four different cases involving a low-rise and high-rise building for stack heights (h_s) ranging from 1 m to 7 m, exhaust momentum ratios (M) ranging from 1 to 5 and wind direction (θ) of 0° and 45°, have been studied for neutral atmospheric stability conditions. In this regard the effect of RTS has also been examined by using wind tunnel, ADMS and ASHRAE models. ADMS yields higher dilutions near the stack at θ = 0° and cannot model the effect of RTS. Wind tunnel data compare well with ASHRAE 2003 at M = 5 for the low-rise building, but generally predict higher dilutions for the high-rise building. ASHRAE 2003 predicts lower dilutions than ADMS for the high-rise building, while ASHRAE 2007 yields very low dilutions for all cases, suggesting a need to reassess its suitability for practical design.     

外凸式矩形高层建筑风压研究

针对外凸式矩形高层建筑结构外形复杂且其风荷载值无法通过建筑荷载规范直接获得的情况,以丝绸之路世界贸易中心外凸式矩形高层建筑为研究对象,通过风洞试验获得其风荷载值,并与规范给出的矩形结构体型系数进行对比,总结外凸式矩形建筑结构风荷载规律。基于Fluent软件,选用不同湍流模型,对外凸式矩形高层建筑进行数值模拟,并将计算结果与风洞试验结果进行比较,验证数值模拟方法的可行性。结果表明:该高层建筑迎风面的体型系数与规范接近; 背风面底部区域的体型系数比规范值大约70%,其他区域与规范值接近; 侧面体型系数均大于规范值,且最大负压出现在侧面; 对于外凸式矩形高层建筑结构,外凸结构风压较相邻区域增大,凹进结构的风压较相邻区域减小; 体型系数沿高度方向变化较大,凸出结构为迎风面时,其下方相邻区域体型系数比规范值小近50%; 数值计算结果与试验数据整体趋势基本一致; Realizable k-ε模型的数值模拟结果要优于Standard k-ε模型; 对于矩形高层建筑,凸出结构为迎风面时,其相邻上部区域和背风面下部区域风荷载不仅受凸出结构的影响,而且还受到凸出结构宽度的影响,其对体型系数的影响幅度为±20%之间。     

高层建筑群绕流风场的数值计算

高层建筑物及其群体周围所引起的风环境问题正日益受到人们的重视。在人们日益关心人居环境的今天,有必要对高层建筑物绕流风场进行全方面系统的研究。本文采用标准k-ε模型的湍流模型对相邻高层建筑物之间的绕流流场进行计算,分析了相邻两建筑物之间的风速、风压等流场特征,讨论了建筑物间距等因素对风环境特性的影响,为城市高层建筑住宅小区设计提供了一定的理论参考和依据。     

A transient transport model for gaseous pollutants in naturally-ventilated partitioned buildings

Natural ventilation is one of the most commonly used methods to remove air pollutants and to improve indoor air quality. This study integrates a resistance model to predict the ventilation rate and a transport model to compute the pollutant concentration in partitioned buildings. The model predictions are validated by a series of wind tunnel experiments with scale-down building models. The concentration variations of tracer gas inside the models were measured by a gas chromatography, and the external and internal pressures were determined by a multi-channel pressure scanner. The verified transport model was then applied to evaluate the influences of external wind speed, initial concentration, opening areas and interior volume on the transient concentration and dispersion time of gaseous pollutants within a two-room buildings. Results of the parametric study indicate that the dispersion time and the ratio of the maximum concentration in the adjacent room to the initial concentration of the room with the pollutant source was about 0.50–0.60, depending on the ventilation rate and interior volume.     

Dispersion characteristics of vehicle emission in an urban street canyon

The dispersion of vehicle emission is limited by various factors existing in an urban environment, which may produce a poor air quality in an urban street canyon environment. This poor air quality has a high potential to be easily delivered into indoor air environment through building ventilation. In this study, the dispersion of vehicle emission was characterized by conducting wind tunnel tests and applying tracer gas techniques. The aspect ratio of a street canyon (i.e. the ratio of the width of a street and the average height of buildings) and the direction of external wind are the major test parameters. In addition to the simple data analysis of the results, a series of statistical analysis was also introduced to formulate the complex effects on the dispersion of vehicle emission. The updated result is presented in this article.     

高层矩形建筑横风向风力特性试验研究

在边界层风洞中对10个典型超高层建筑模型进行测压试验,获得了测点层的顺风向、横风向和扭转方向的风荷载,整理了横风向风荷载的功率谱、相关系数和水平、竖向相干函数,分析了流场绕流的特点,总结了横风向风力对扭转的贡献。得到如下结论:选取分离点作为参考点时,横风向水平相关性随厚宽比增加变化较大,通过确定其零点位置可以定量确定再附点位置;横风向风力竖向相关性受所选基点位置影响程度较小;竖向相干性随厚宽比增大而降低;模型厚宽比大于1.5时,结构扭矩谱几乎全部由横风向贡献。     

设有外镂空装饰结构的扭转体型高层建筑风荷载研究

对设有外镂空装饰结构的扭转体型高层建筑的风荷载采用风洞试验方法进行研究,分析扭转体型高层建筑风压和风荷载合力的分布特征,研究装饰结构对主体结构风压分布的影响、装饰结构自身内外表面的风压分布特点,比较有无装饰结构的扭转体型高层建筑风荷载合力。结果表明：扭转体型对主体结构的局部风压和扭矩产生较大的影响,但对主体结构X向和Y向风荷载合力的影响不大;装饰结构对主体结构迎风面和背风面的风压影响较小,但能明显减小主体结构侧风面风压的平均值和脉动效应,使得主体结构的极值负压得到降低,有利于围护结构的抗风设计;装饰结构上同一位置内外表面的平均风压非常接近,合成的净压值很小;装饰结构对于主体结构的平均风荷载影响较小,但降低了主体结构风荷载的脉动效应,对主体结构的抗风有利。     

住宅小区风环境数值模拟

建立了某典型住宅小区风环境的物理和数学模型,并应用计算流体动力学方法求解了三种来流角度下的稳态三维湍流流场,给出了速度、压力、湍流度参数的分布;分析了街区涡流、巷道风及活塞风等效应,研究了风压作用下建筑群的迎风及背压区,讨论了湍流入流边界对合理湍流分布的作用;比较了不同来流角度下五个观测点位置的风环境参数。