Aerodynamic effects of trees on pollutant concentration in street canyons

This paper deals with aerodynamic effects of avenue-like tree planting on flow and traffic-originated pollutant dispersion in urban street canyons by means of wind tunnel experiments and numerical simulations. Several parameters affecting pedestrian level concentration are investigated, namely plant morphology, positioning and arrangement. We extend our previous work in this novel aspect of research to new configurations which comprise tree planting of different crown porosity and stand density, planted in two rows within a canyon of street width to building height ratio W/H = 2 with perpendicular approaching wind. Sulfur hexafluoride was used as tracer gas to model the traffic emissions. Complementary to wind tunnel experiments, 3D numerical simulations were performed with the Computational Fluid Dynamics (CFD) code FLUENT™ using a Reynolds Stress turbulence closure for flow and the advection-diffusion method for concentration calculations. In the presence of trees, both measurements and simulations showed considerable larger pollutant concentrations near the leeward wall and slightly lower concentrations near the windward wall in comparison with the tree-less case. Tree stand density and crown porosity were found to be of minor importance in affecting pollutant concentration. On the other hand, the analysis indicated that W/H is a more crucial parameter. The larger the value of W/H the smaller is the effect of trees on pedestrian level concentration regardless of tree morphology and arrangement. A preliminary analysis of approaching flow velocities showed that at low wind speed the effect of trees on concentrations is worst than at higher speed. The investigations carried out in this work allowed us to set up an appropriate CFD modelling methodology for the study of the aerodynamic effects of tree planting in street canyons. The results obtained can be used by city planners for the design of tree planting in the urban environment with regard to air quality issues.     

Numerical study on the effects of aspect ratio and orientation of an urban street canyon on outdoor thermal comfort in hot and dry climate

This paper discusses the contribution of street design, i.e. aspect ratio (or height-to-width ratio, H/W) and solar orientation, towards the development of a comfortable microclimate at street level for pedestrians. The investigation is carried out by using the three-dimensional numerical model ENVI-met, which simulates the microclimatic changes within urban environments in a high spatial and temporal resolution. Model calculations are run for a typical summer day in Ghardaia, Algeria (32.40°N, 3.80°E, 469 m a.s.l.), a region characterized by a hot and dry climate. Symmetrical urban canyons, with various height-to-width ratios (i.e. H/W=0.5, 1, 2 and 4) and different solar orientations (i.e. E–W, N–S, NE–SW and NW–SE), have been studied. Special emphasis is placed on a human bio-meteorological assessment of these microclimates by using the physiologically equivalent temperature (PET).     

On the numerical study of contaminant particle concentration in indoor airflow

The application of three turbulence models—standard k–ε, re-normalization group (RNG) k–ε and RNG-based large eddy simulation (LES) model—to simulate indoor contaminant particle dispersion and concentration distribution in a model room has been investigated. The measured air phase velocity data obtained by Posner et al. [Energy and Buildings 2003;35:515–26], are used to validate the simulation results. All the three turbulence model predictions have shown to be in good agreement with the experimental data. The RNG-based LES model has shown to yield the best agreement. The flow of contaminant particles (with diameters of 1 and 10 μm) is simulated within the indoor airflow environment of the model room. Comparing the three turbulence models for particle flow predictions, the RNG-based LES model through better accommodating unsteady low-Reynolds-number (LRN) turbulent flow structure has shown to provide more realistic particle dispersion and concentration distribution than the other two conventional turbulence models. As the experimental approach to access indoor contaminant particle concentration can be rather expensive and unable to provide the required detailed information, the LES prediction can be effectively employed to validate the widely used k–ε models that are commonly applied in many building simulation investigations.     

室外风对火焰特征影响的数值模拟研究

为研究高层建筑或超高层建筑中室外风在玻璃破碎后对火焰特征的影响,运用FDS数值模拟方法,对风速为0～24m/s的17个自由燃烧算例进行了模拟研究,拟合了适用于较大室外风速条件下的火焰长度及其倾角计算公式,并与Dfaveri模型、Drysdale模型进行了对比分析。结果表明:室外风速增大会使火焰长度及其向上风向倾斜的角度减小,但会使火焰向下风向倾斜的角度增大。     

颗粒浓度对固液泵工作性能影响分析

为了揭示离心泵内部固液两相流动的规律,采用数值模拟方法,应用FLUENT软件对离心泵固液两相流进行模拟。研究结果表明:在同一粒径下,随着固相体积分数的增加,泵的扬程、效率降低越来越明显;固相体积分数越大,效率下降越快,但是下降的幅值越来越小;在不同的体积分数下,离心泵内部的压力分布规律基本一致,在叶片的压力面上,从进口到出口压力值逐渐增大,压力值在出口处达到了最大值。     

CFS夯扩桩复合地基作用机理的颗粒流数值模拟初探

对竖向载荷作用下的CFS夯扩桩-土作用机理进行颗粒流数值模拟研究.应用PFC2D程序模拟了夯扩桩-土相互作用过程.通过对加载过程中土的颗粒位移图、量测圈的考察,分析夯扩桩复合地基在不同荷载作用下的土体颗粒位移变化及土体孔隙度的变化规律,探讨桩-土相互作用土的细观力学特征和宏观力学行为之间的相互联系.同时,数值试验观测到的结果可为物理模型试验提供指导作用.     

太阳能烟囱结构对通风效果影响的数值研究

采用Realizable K-ε湍流模型和DO辐射模型对太阳能烟囱内部的流场和温度场进行了数值模拟,计算结果与文献中实验值吻合得较好。对太阳能烟囱高度和宽度等结构因素对通风效果的影响进行了模拟分析,结果表明,诱导风量随烟囱高度增大而增大,随宽度增大先增大后减小;Gr可作为设计太阳能烟囱高度时的参考;渐缩型通道能有效防止通道内回流的产生。     

棉纺车间颗粒物浓度及粒径分布特征研究

通过实地监测,针对不同车间的棉尘颗粒物的浓度及粒径分布特征进行了对比分析,监测结果表明:清花,梳棉及细纱车间的平均总颗粒物浓度分别为3.65 mg/m 3、2.87 mg/m 3、1.75 mg/m 3,均大于棉尘接触限值.由前纺工艺至后纺工艺,总颗粒物浓度呈逐渐减小的趋势,清花车间总颗粒物浓度是细纱车间浓度的2.08...     

地下水流动对埋地换热器影响的模拟研究

通过求解含水层中地下水流动的二维能量方程,分析了地下水流动对U型埋地换热器与周围土壤换热的影响,并与非含水层情况进行了比较。模拟结果表明,地下水流动显著影响埋地换热器周围的土壤温度场。与粘土层相比,埋地换热器在含水层内土壤温度变化较小,到达稳态时间较短。埋地换热器周围热作用半径,沿上游方向较小且很快达到稳态,而沿下游方向上的热作用半径基本与运行时间成正比关系。地下水流速越大,埋地换热器周围介质的平均温度越低,这有利于夏季排热工况。     

生物安全实验室气流组织效果的数值模拟研究

对上送上排和上送下排气流组织形式下生物安全实验室内的污染物浓度场和气流速度场进行了数值模拟,结果表明上送下排在室内污染物排除效果上明显优于上送上排。将数值模拟结果与模型实验结果进行了对比,二者基本一致。     

双塔建筑风荷载狭缝效应的数值研究

对双塔建筑进行了风荷载和风场的数值模拟,计算得出了建筑周围的流场分布和建筑表面各测点的风压,并着重讨论了双塔建筑物之间的狭缝效应,结果表明,并列布置时,干扰作用只发生在相邻建筑物的侧风面,对相邻建筑物的迎风面影响很小,干扰作用的大小与建筑物的间距有关。     

邯郸市高层居住区室外风环境数值模拟研究

以邯郸市某小区为研究对象,结合Phoenics 2015软件模拟的方法,对小区室外风环境进行模拟分析,并对其优劣状况进行评价,为高层居住区室外风环境的分析提供参考。     

建筑布局对小区热环境影响的数值分析

介绍了适合实际三维建筑小区热环境模拟的方法,并利用改进的CTTC(建筑群热时间常数)模型分析了不同类型建筑布局对小区热环境的影响。结果表明：建筑面积对建筑群热环境影响较大;在小区面积一定、建筑面积一定的情况下,增加绿化率可以明显地改善小区的热环境。     

Multi-zone simulation of outdoor particle penetration and transport in a multi-story building

In areas with poor ambient air quality, indoor particle concentrations can be significantly affected by particulate matter originating outdoors. The indoor environments of multi-zone and multi-story buildings are affected differently by outdoor particles compared with single-family houses, because of the buildings’ more complicated airflow characteristics. The objective of this study is to analyze outdoor particle penetration and transport, and their impact on indoor air, in a multi-zone and multi-story building using a CONTAMW simulation. For the airflow and particle transport analysis, the building leakage, penetration coefficients, and deposition rates were determined by on-site experiments. The results of airflow simulations for cold winters show that outdoor air infiltrates through the lower part of building and exfiltrates from the upper part. The results of the particle simulation also indicated that the airflow characteristics, combined with deposition rates, cause the lower floors of a multi-story building to be exposed to higher fine particle concentrations compared with the upper floors of the building. The study demonstrated that the CONTAMW simulation can be useful in analyzing the impact of outdoor particles on indoor environments through the identification of key particle transport parameters and validated airflow simulations.     

室外风对高层建筑竖井内烟气运动影响的数值模拟

采用火灾模拟专业软件FDS对不同火源位置、不同风向条件下火灾烟气的运动进行模拟,测定典型位置处温度、速度、CO及CO2体积分数变化情况。实验结果表明:在近地风场中,风向对竖井内烟气蔓延的影响大小顺序为迎风>背风>侧风,竖井开口位于迎风面时,外界风对竖井内烟气运动影响最大:火源位于中性面以上时,烟气通过竖井与前室的开口向竖井内蔓延,并向下运动;而火源位于中性面以下时,前室内烟气向外部运动,竖井内无烟气流入。     

浅谈室外排水管道的施工控制要点

建筑物(小区)的室外排水系统是其服务区内其他工程设施得以正常使用的重要设施之一,确保其施工质量至关重要。本文重点阐述了室外排水管道在施工全过程中的施工管理方法及其控制要点。     

Indoor/outdoor relationships of size-resolved particle concentrations in naturally ventilated school environments

Assessment of indoor air quality in typical classrooms is vital to students’ health and their performance. The present study was designed to monitor indoor and outdoor size-resolved particle concentrations in a naturally ventilated classroom and investigate factors influencing their levels and relationships. The experiments were performed, at normal ventilation condition with doors and windows opened, on the top floor of a public school building near a busy commercial area of Chiang Mai, Thailand. The particle number concentrations were measured using an optical counter with four size intervals between 0.3 and 5.0 μm. The dataset was collected during weekdays and weekends with a 24 h sampling period over November and December 2005. It was observed that the median indoor particle number concentrations during daytime for 0.3–0.5, 0.5–1.0, 1.0–2.5, and 2.5–5.0 μm size intervals were about 1.6×10⁸, 1.7×10⁷, 1.2×10⁶, and 4.1×10⁵ particles/m³, respectively. It was also found that concentrations at weekends were slightly higher those measured on weekdays, and at night, appeared to be higher than daytime. Indoor particles were observed to exhibit similar temporal variation pattern with outdoor particles. Results suggested that a significant contribution to indoor particles was from penetration of outdoor particles, whereas indoor sources generated from occupant activity did not show strong evidence. High outdoor particle loading and high air exchange rate were thought to be predominant causes. Ratios of indoor-to-outdoor (I/O) particle concentrations varied in a relatively narrow range from 0.69 to 0.88 with average values well below 1. The I/O ratios were in the range from 0.74 to 0.88 for submicrometer particles and from 0.69 to 0.80 for supermicrometer particles.     

生物洁净室尘埃浓度与细菌浓度的计算方法

本文根据洁净手术室的有关检测标准，提出了基于静态又兼顾动态的尘埃浓度和浮游菌浓度计算方法，在设计计算中以自净换气次数限定合理的自净时间，并以例题说明了该方法的使用。     

Modeling the effects of outdoor gasoline powered generator use on indoor carbon monoxide exposures

The U.S. Centers for Disease Control and Prevention (CDC) has reported that up to half of non-fatal CO poisoning incidents during the hurricane seasons in 2004 and 2005 involved generators operated outdoors but within seven feet of the home. The guidance provided on the safe operating distance of a generator is often neither specific nor consistent. Furthermore, some generator manufacturers recommend the use of extension cords to be “as short as possible to prevent voltage drop and possible overheating of wires”. This study modeled multiple scenarios of a portable generator operated outdoors using the CONTAM indoor air quality model coupled with a computational fluid dynamics (CFD) model to predict CO concentrations near and within a home. The simulation cases included both human-controllable factors (e.g., generator location and exhaust direction and window opening size) and non-controllable factors (e.g., wind, temperature, and house dimensions). For the house modeled in this study, a generator positioned 4.6 m (15 feet) away from open windows may not be far enough to limit CO entry into the house. It was also found that winds perpendicular to the open window resulted in more CO infiltration than winds at an angle, and lower wind speed generally led to more CO entry. To reduce CO entry, the generator should ideally be positioned outside of airflow recirculation region near the open windows.