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.     

A wind tunnel experiment and CFD analysis on airflow performance of enclosed-arcade markets in Korea

Many traditional markets, which had previously formed along the streets, have been remodeled into arcade-type malls in Korea to reduce the inconveniences due to rain. The markets that used to be exposed to outside air have become a semi-open space. Therefore sufficient natural ventilation has become an important environmental factor to make the marketplace more comfortable and healthy.     

被上游建筑遮挡的下游建筑表面风压CFD模拟的可靠性研究

研究城市通风或建筑风环境的主要目的是探索建筑之间和建筑内外的气流运动及污染物扩散规律,主要手段有风洞实验和计算流体动力学（CFD）模拟,后者相对前者的优点是易操作且成本低,但由于流体运动的高度不确定性,其结果的准确性存疑。在城市中,建筑之间的互相遮挡是主要特征之一,提取其中最基本单元,把两个建筑之间的遮挡问题分为上游建筑有孔（如穿堂风）与无孔两种情况,运用CFD中的雷诺平均模型（RANS）模拟下游建筑表面的风压,并与风洞实验进行严格对比,以讨论CFD方法在这一基本单元问题中的可靠性。网格敏感性分析显示,建筑表面最小网格为建筑高度的2%时,可获得可靠的结果。5种常用RANS模型的结果与风洞实验严格对比表明：RANS模型对模拟上游有孔遮挡的可靠性明显高于模拟无孔遮挡;RANS模型对于建筑上部的风压模拟结果普遍好于建筑下部;其中,SST k-ω模型准确性最高,在上游有孔时,平均误差11%,上游无孔遮挡时,则为16%。     

Effect of inclined roof on the airflow associated with a wind driven turbine ventilator

Rotating wind driven turbine ventilator has been used as cost-effective environmental friendly natural ventilation device. Rotating wind driven turbine ventilator type of device is usually installed on the rooftop to extract air extract air flow from a building to improve air quality and comfort. Performance investigations carried thus far on turbine ventilator have ignored the effect of the inclination on rooftop. An experimental program was, therefore, formulated at the aerodynamic laboratory of the University of New South Wales to study such effect on a simulated rooftop. The results obtained from the measured forces and rotational speeds on different configurations indicate that the effect is minimal in extracting air from a building at low wind speed. The static pressure and skin friction distributions on the simulated roof further supports this finding. Two important conclusions can be drawn from the present investigation: firstly, the presence of the inclined roof may extend the safety margin in the operation of a turbine ventilator at high wind speed by reducing the magnitude of the total force that acts on the ventilator; secondly the dependency of the total fore on low Reynolds number suggests that the efficiency and reliability of operation of such ventilator should be boosted through the provision of other power source such as solar power at low wind speed.     

Simulation of honeycomb-screen combinations for turbulence management in a subsonic wind tunnel

Honeycomb and screens, mainly used for turbulence reduction, are the key elements of a subsonic wind tunnel. In this paper, design aspects of these elements are addressed for an open-circuit wind tunnel, installed at Indian Institute of Technology Guwahati (IITG), India. The effectiveness of honeycomb and honeycomb-screen combinations, in reducing swirl and turbulence level in the test section, is studied by simulating the flowfield using commercial computational fluid dynamics (CFD) package ANSYS-CFX. RNG k−ε turbulence model, with scalable wall functions, is used for modeling turbulence. Results of these simulations for turbulence management, using honeycombs of different lengths, cell shapes and screens of different open area ratios, are found to be in good agreement with experimental and theoretical results available in open literature. These simulations have confirmed the methodology to be adopted for design of wind tunnel subsections. Thus validated design parameters have been used for fabricating the honeycomb and screens for the IITG wind tunnel.     

基于风洞试验的双塔楼超高层建筑风荷载与风致响应

当超高层建筑的高度和间距都比较接近的时候,相互的干扰效应对结构的表面风荷载与结构的风致响应都会产生较大影响。基于刚性模型表面测压风洞试验,得到了双塔楼超高层建筑表面各测点的风压时程。在此基础上,通过数据处理,得到结构的三维动力风荷载模型,进而分别采用频域法进行结构动力响应分析。最后,通过分析结构表面风荷载与风致响应,研究了塔楼之间的干扰对结构风荷载的影响以及对结构风致响应的影响,结果表明:当双塔连线与来流方向平行时,三维风荷载和风致响应都会明显增大,干扰效应影响十分明显。     

杭州萧山国际机场T4航站楼主楼屋盖风荷载的风洞试验与数值模拟研究

综合采用风洞试验和计算流体动力学(简称CFD)数值模拟方法,对萧山国际机场T4航站楼主楼屋盖表面风荷载进行了分析研究.首先,分析了屋盖表面典型位置的平均风压系数和脉动风压系数随风向角的变化规律,进而研究了具有较大平均和脉动风压系数的75°和270°风向角下,屋盖短轴中心位置和边缘位置截面测点平均风压系数随位置的变化情况;然后,研究了典型风向角下屋盖表面体型系数等值线云图,并给出了用于屋盖结构抗风设计的分块体型系数;最后,结合CFD数值模拟所得屋盖周围流场,分析了屋盖风荷载作用机理.结果 表明,来流在屋盖迎风边缘位置存在较为明显的流动分离现象,屋盖总体上处于流动分离区,导致屋盖总体表现为受到向上的风吸力作用;屋盖迎风边缘位置流动分离更为显著,因此该位置的风吸力也最大,比较容易引起屋盖的局部受风破坏.     

大跨屋盖结构风洞试验模型的设计方法讨论

通过理论分析及风洞试验研究大跨屋盖结构风洞试验的模型设计问题。以气承刚度理论为主线阐述了内压传播方程及赫姆霍兹频率、四周封闭屋盖结构及墙面开孔屋盖结构的频移特性和气承刚度的相似性模拟准则,考虑了墙体柔度在理论分析中的关键作用。设计制作了大跨平屋盖刚性模型和气弹模型进行墙面开孔前后的风洞试验,试验结果与理论分析较为吻合。研究结果证明了气承刚度相似性模拟在大跨屋盖结构风洞试验中的基础性作用,并指出在模型设计中调整结构内部容积是模拟气承刚度最有效的措施,而保证刚度比的一致性则是试验成功的关键。     

Smoke spreading characteristics during a fire in a shallow urban road tunnel with roof openings under a longitudinal external wind blowing

A series of fire experiments was conducted using a 1:12 scale model of a shallow urban road tunnel with roof openings to clarify the flow structure of smoke and fresh air during a fire with a longitudinal external wind blowing above the roof openings. The model tunnel consisted of two road tubes separated by a pillar-type median structure. Five fire test cases were conducted by changing the heat release rate as the experimental parameter. When the smoke produced by a fire in the tunnel tube was exhausted by natural ventilation through the roof openings of the tunnel tube, fresh air was sucked in from the roof openings of the opposite tunnel tube. The flow of exhausted smoke and sucked-in fresh air created a complex three-dimensional flow structure inside the tunnel tubes. Stratified smoke that had formed under the ceiling of the tunnel tube was disturbed by the flow of sucked-in fresh air and was diffused on the upstream side of the fire. Compared to the condition without a longitudinal external wind, when a longitudinal external wind blew over the tunnel with the pillar median structure, the smoke spreading distance on the upstream side was longer than that without the external wind due to the diffusion of smoke. On the other hand, the smoke spreading distance on the downstream side of the fire was shorter than that without the external wind due to the improved smoke extraction performance by the Venturi effect of the longitudinal external wind. Furthermore, the smoke spreading distance on the downstream side was nearly constant and independent of the heat release rate of the fire, within the scope of our experimental conditions.     

CFD modeling of snowdrift around a building: An overview of models and evaluation of a new approach

The first part of this paper provides an overview of Computational Fluid Dynamics (CFD) modeling of snowdrift around a building by reviewing previous research including the authors’ in order to clarify its applicability and limitations. It is clarified that a quantitative validation study in particular by predicting snow depth distribution near a building is not enough, even though many models have been proposed. The latter part presents the results of CFD prediction of snowdrift around a cubic building model using a new approach of a snowdrift model based on experimental and numerical studies by the authors. The numerical results are compared with data obtained from detailed field measurements and previous CFD in order to confirm the accuracy of the new model. This new approach shows good correspondence with results obtained from field measurements and wind tunnel experiments in terms of not only snowdrift patterns but also quantitative distribution of snow depth.     

CFD investigation of turbulence models for mechanical agitation of non-Newtonian fluids in anaerobic digesters

This study evaluates six turbulence models for mechanical agitation of non-Newtonian fluids in a lab-scale anaerobic digestion tank with a pitched blade turbine (PBT) impeller. The models studied are: (1) the standard k-? model, (2) the RNG k-? model, (3) the realizable k-? model, (4) the standard k-ω model, (5) the SST k-ω model, and (6) the Reynolds stress model. Through comparing power and flow numbers for the PBT impeller obtained from computational fluid dynamics (CFD) with those from the lab specifications, the realizable k-? and the standard k-ω models are found to be more appropriate than the other turbulence models. An alternative method to calculate the Reynolds number for the moving zone that characterizes the impeller rotation is proposed to judge the flow regime. To check the effect of the model setup on the predictive accuracy, both discretization scheme and numerical approach are investigated. The model validation is conducted by comparing the simulated velocities with experimental data in a lab-scale digester from literature. Moreover, CFD simulation of mixing in a full-scale digester with two side-entry impellers is performed to optimize the installation.     

罩棚式低矮房屋屋面风荷载特性及气动抗风措施研究

采用模型的风洞试验详细研究了矩形和圆形罩棚屋面结构的平均风压和峰值风压分布特征,分析了屋面风致破坏的主要原因,在此基础上实施了7种不同的屋面局部修改方案的对比试验,从中筛选出可以有效消减屋面风荷载的抗风措施。两种平顶矩形和圆形罩棚屋面结构均以负压为主,试验测得两结构屋面的最高平均负压系数分别为-1.83和-0.97,相应最高极值负压系数为-5.41和-3.11,结果远高于GB 50009-2001《建筑荷载规范》推荐的平均风压乘以阵风系数的方法,这显示规范中的阵风系数方法并不适合于计算该类屋面结构的风压值。根据分析结果给出了平顶矩形和圆形罩棚屋面结构风压体型系数取值的建议值,采用斜切角形式的屋檐或在屋面板和侧面围板交界处开贯通透风槽方式可以使屋面风敏感区域的极值负压削减25%~35%。     

Integrating neural network models with computational fluid dynamics (CFD) for site-specific wind condition

Most building energy simulations tend to neglect microclimates in building and system design, concentrating instead on building and system efficiency. Energy simulations utilize various outdoor variables from weather data, typically from the average weather record of the nearest weather station that is located in an open field, near airports and parks. The weather data may not accurately represent the physical microclimate of the site, and may therefore reduce the accuracy of simulation results. For this reason, this paper investigates utilizing computational fluid dynamics (CFD) with neural network (NN) model to predict site-specific wind parameters for energy simulation. The CFD simulation is used to find selected samples of site-specific wind conditions. Findings from CFD simulation are used as training data for NN. A trained NN predicts site-specific hourly wind conditions for a typical year. The outcome of the site-specific wind condition from the neural network is used as wind condition input for the energy simulation. The results of energy simulation using typical weather station data and site-specific weather data are compared in this paper, in order to find the possibility of using site-specific weather condition by NN with CFD to yield more realistic and robust ES results.     

Pedestrian-level wind conditions around buildings:Review of wind-tunnel and CFD techniques and their accuracy for wind comfort assessment

Information on pedestrian-level wind(PLW)speed for wind comfort assessment can be obtained by wind-tunnel measurements or Computational Fluid Dynamics(CFD)simulations.Wind-tunnel measurements for PLW are routinely performed with low-cost techniques such as hot-wire or hot-film anemometers,Irwin probes or sand erosion,while Laser-Doppler Anemometry(LDA)and Particle-Image Velocimetry(PIV)are less often used because they are more expensive.CFD simulations are routinely performed by the relatively low-cost steady Reynolds-AveragedNavier-Stokes(RANS)approach.Large-Eddy Simulation(LES)is less often used because of its larger complexity and cost.This paper reviews wind-tunnel and CFD techniques to determine PLW speeds expressed generally in terms of amplification factors defined as the ratio of local mean wind speed to mean wind speed at the same position without buildings present.Some comparative studies systematically indicate that the low-cost wind-tunnel techniques and steady RANS simulations can provide accurate results(~10%)at high amplification factors(1)while their accuracy can deteriorate at lower amplification factors(1).This does not necessarily compromise the accuracy of PLW comfort assessment,because the higher amplification factors provide the largest contribution to the discomfort exceedance probability in the comfort criterion.Although LDA,PIV and LES are inherently more accurate techniques,this paper supports the continued use of faster and less expensive techniques for PLW studies.Extrapolating a previous saying,we argue that pedestrian-level wind comfort is one of the few topics in wind engineering where nature is kind to us concerning turbulent flows.     

双幕墙长矩形建筑风荷载特性的试验研究

以节能、生态为理念的双幕墙围护体系已逐步应用于高层办公建筑中。由于双幕墙之间存在通风廊道,因此对于双幕墙建筑有三个受风表面,即外层幕墙的内表面和外表面以及内幕墙的外表面,这使得风载取值变得复杂,目前也无规范可依。本文通过对杭州市某双幕墙办公楼的风洞试验研究,探讨了双幕墙建筑内、外层幕墙的风载取值问题;研究了门厅大跨挑篷风压分布特征,当风从侧面吹向挑篷时,挑篷上、下表面风载与普通屋盖挑篷相同,而当风从正面吹向挑篷时,挑篷上表面出现正风压,并对此现象进行了分析;文中针对该建筑物长宽比较大的特点,比较了大长宽比矩形建筑风载体型系数与规范给出的正方形建筑风载体型系数:当风沿建筑物长向流动时,采用规范给出的正方形建筑风载体型系数是可行的,当风沿建筑物进深方向流动时,其两侧及背风面的负压比正方形的大。     

应县木塔风压分布的风洞试验与CFD模拟研究

风荷载作用下高耸古木塔的结构安全在建筑遗产保护领域备受关注.为了研究古木塔风压分布特性,开展了应县木塔的1:50刚性模型风洞试验,并进行了计算流体动力学(CFD)数值模拟分析.提出复杂中式高耸古木塔的几何建模与网格尺寸划分策略,并使用雷诺平均Navier-Stokes (RANS)方法对木塔的表面风压进行预测,分析木塔...     

Effect of building length on wind loads on low-rise buildings with a steep roof pitch

A wind tunnel model study was carried out on long, low-rise buildings with a steep roof pitch to determine the effect of the length-to-span aspect ratio on the external wind pressure distributions. The study showed a significant increase in the magnitude of the negative pressure coefficients on the leeward roof and wall, with an increase in aspect ratio, for oblique approach winds. These large suction pressures also generate large design wind load effects on the frames near the gable-end. The 1989 edition of the Australian standard for wind loads, AS 1170.2-1989 was found to underestimate the wind loads on steep pitch gable-roof buildings of aspect ratio greater than 3, on areas near the windward gable-end, and hence the critical bending moments in the supporting structural frames. The current Australian/New Zealand wind load standard, AS/NZS 1170.2-2002 specifies increased negative pressure coefficients on the leeward half of high pitch roof buildings, and critical bending moments in the supporting frames calculated from these distributions agree quite well with values obtained from the wind tunnel study. However, other major standards severely underestimate the critical bending moments, and the effective pressure coefficients producing those bending moments, especially on the leeward roof slope.     

Time domain formulation of self-excited forces on bridge deck for wind tunnel experiment

Time domain formulation of the self-excited wind forces on bridge decks employs indicial functions. In bridge aeroelasticity, these functions are obtained by transforming the flutter derivative model to time domain. Studies have suggested, however, that the relative amplitude effect, i.e. the effect of structural oscillation amplitude relative to the amplitude of response to ambient wind, on flutter derivatives needs to be considered. This effect indicates the difference between the two cases, where the pulse response of an elastically supported body is smooth and where the motion is significantly affected by ambient wind forces. The non-linearity may affect the transformation of flutter derivative model to time domain. An alternative to obtaining the time domain formulation for the self-excited force is to treat the self-excited force as a separate dynamic system, so that the relative amplitude effect can be evaluated in more detail. In this paper, a self-excited force generation system coupled with the rigid bridge deck system is proposed to overcome the difficulties in the measurement and derivation of the time domain representation of self-excited force on bridge decks. This expression can be linked to a flutter derivative model, and a transform relationship between the two models is suggested.     

从风环境试验看建筑群对自身风环境的影响：深圳福田同城建筑风洞风 …

本文作者从建筑风环境的试验目的和评价标准出发,以试验原始数据为基础,对自成一个建筑群的深圳福田商城的风洞风环境试验结果进行了分析。