Experimental investigations of the indoor natural ventilation for different building configurations and incidences

This paper presents an experimental investigation of the indoor natural ventilation in terms of wind pressures on the surfaces of cubic buildings of a street located within a high density urban area. Wind tunnel tests over 1:100 scale models for four typical building patterns of a highly populated urban area have been carried out. The variables of the experiments were the building configurations and the incident wind direction. The experimental data are presented in terms of wind pressure coefficient measured on the surfaces of the buildings. The study results gave the evidence that buildings configuration and wind direction are very important factors in determining the induced natural ventilation within urban domains since they characteristically influence the flow yielding differences in wind pressures.     

Crosswind action on rail vehicles: Wind tunnel experimental analyses

Extensive wind tunnel tests have been carried out on train scale models. The experimental tests have been performed on three types of rail vehicles, in different configurations. The wind tunnel tests allowed to point out the most critical wind conditions with respect to running safety and to perform a sensitivity analysis on the principal parameters that can influence the aerodynamic behaviour of rail vehicles. In particular, the effects of the turbulence intensity and of the train motion on the aerodynamic coefficients have been studied.     

Numerical simulation of the wind field around different building arrangements

A numerical model with the RNG κ−ε turbulence closure model and a pressure correction algorithm of SIMPLEC is used to examine three different building configuration effects on wind flow. Comparisons of computational results with experimental data have been carried out for the vertical velocity profiles at some measurement points. For the experimental study, the building arrangements were presented by 1:150 scale models and tested in a low-speed wind tunnel. It was found that the wind environment for two improved arrangements with lower interval-to-height ratio is better than that for the reference layout with higher aspect ratio in terms of the natural ventilation. The interference effect is more obvious for two improved arrangements than the reference one. The numerical results also show that changing wind direction from perpendicular to the building facades to a 45°-incidence angle has significant effect on the flow field for different configurations.     

Wind tunnel study of a cone-like shaped roof: Reynolds number effects

This paper describes the results of wind tunnel tests performed on a cone-like shaped roof characterised by multiple curved surfaces. Surface pressure measurements were carried out by high-frequency scanners. In particular, Reynolds number and surface roughness effects on the mean pressure distribution and on its unsteady components have been analysed. Methodologies were found in order to validate the wind tunnel wind load measures performed on scale models having the typology of building roofs with curved surfaces.     

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.     

Wind pressures and buckling of cylindrical steel tanks with a dome roof

An experimental/computational strategy is used in this paper to evaluate the buckling behavior of steel tanks with a dome roof under exposure to wind. First, wind tunnel experiments using small scale rigid models were carried out, from which pressure distributions due to wind on the cylindrical part and on the roof were obtained. Second, a computational model of the structure (using the pressures obtained in the experiments) was used to evaluate buckling loads and modes and to study the imperfection sensitivity of the tanks. The computational tools used were bifurcation buckling analysis (eigenvalue analysis) and geometrical nonlinear analysis (step-by-step incremental analysis). Geometric imperfections and changes in the buckling results due to reductions in the thickness were also included in the study to investigate reductions in the buckling strength of the shell. For the geometries considered, the results show low imperfection sensitivity of the tanks and buckling loads associated with wind speeds 45% higher than those specified by the ASCE 7-02 standard.     

Wind effects on the world’s longest spatial lattice structure: Loading characteristics and numerical prediction

The 486-m long roof structure of Shenzhen Citizens’ Centre is the world’s longest spatial lattice structure. This paper presents some selected results from a combined wind tunnel and numerical simulation study of wind effects on the extra-long-span roof structure. In this study, simultaneous pressure measurements on its entire roof are made in a boundary layer wind tunnel, and the measured wind pressures, such as mean, root-mean-square (rms) and peak pressure coefficient distributions on the roof are presented and discussed. Based on the measured data from a number of pressure taps, a numerical simulation approach using backpropagation neural networks (BPNN) is developed for the predictions of wind-induced pressure time series at other roof locations which are not covered in the wind tunnel measurements. The BPNN is trained with the pressure data time series measured from adjacent pressure taps. The good performance of the developed neural network is demonstrated by comparing the predictions with the model test results, illustrating that the BPNN approach can serve as an effective tool for the design and analysis of wind effects on large roof structures in conjunction with wind tunnel tests.     

BLWT tests and design loads on the roof of the new olympic stadium in Piraeus

The paper introduces some peculiar and innovative aspects by the experimental tests carried out in a boundary-layer wind tunnel (BLWT) for the design of the roof of the new Olympic soccer stadium in Piraeus, Greece, using simultaneous pressure measurements and state-of-the-art processing techniques. The wind tunnel data are then used for the numerical simulation of the quasi-static response of the structure in the time domain, so obtaining the time histories of the structural response. The extreme values of the wind effects are evaluated directly from the statistical analysis of the corresponding time histories and are compared with those from dead loads. Finally the uniform pressure distributions are identified which produce the same extreme values of wind effects.     

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.     

球面壳体表面风压分布特性风洞试验研究

球面壳体是工程中一种常用的屋面结构形式。本文通过刚性模型风洞试验,对不同场地类别下球面壳体表面风压分布进行了同步测量。根据测到的同步风压分布数据,对壳体表面风压场特性进行了分析,包括平均风压系数及脉动风压系数分布、脉动风压的自功率谱及互功率谱分布、风压场的本征正交分解特性、雷诺数对壳体表面风压分布的影响等。结果表明,球面壳体模型表面风压分布受雷诺数的影响明显,且模型的曲面特性使得由风场本征正交分解得到的前几阶特征模态对整个风压分布的贡献增大。该研究为这类结构在抗风分析中风荷载的确定及数值模拟提供试验依据。     

Wind tunnel evaluation of mean wind pressure on a frame-type signboard

In the context of the growing concern for the wind effects and the wind design of “street architecture” (bill-boards, traffic signs, traffic lights, etc.), wind tunnel tests have been carried out on a model of a frame-type signboard, placed within a regular array of buildings. The first experimental results, reported here, help to clarify the relationship between the wind loading on the signboard and the characteristics of the wind acting on the surrounding buildings.     

Compensation of high-frequency components of wind load by wind tunnel testing

To analyze the wind-induced response of structures, wind tunnel tests are often carried out to determine the wind loads on structures. However, due to the influence of similarity requirements in wind tunnel tests, the resulting data from the model test still needs to be translated by similarity rules for predicting the real loads on prototype structures. During this process, an inevitable result is that the high-frequency components of fluctuating wind loads get lost, which leads to some unexpected errors in the subsequent wind-induced response analysis. To solve this problem, a frequency compensation method is put forward. The purpose of this method is to reconstruct the high-frequency part of fluctuating wind loads based on experimental data and some basic principles of the aerodynamics of bluff bodies. The causes and effects of the frequency compensation problem are discussed first, then a practical method of frequency compensation is proposed by combining the fluctuating wind energy spectrum theory and the Proper Orthogonal Decomposition technique. Based on this method, the wind-induced response of a single-layer reticulated shell is analyzed to show the validity and necessity of this method.     

External flow effects on the discharge coefficients of two types of ventilation opening

Envelope flow models are commonly used in the design of naturally ventilated buildings. Such models rely on specification of the discharge coefficient, C_z, of ventilation openings, such as air vents and chimneys (stacks). Current practice is to make use of values obtained from laboratory tests under still-air conditions. These values may not be appropriate when the ventilation is due to wind, due to the external flow around the opening which is characterized by unsteadiness of both the velocity and pressure fields. Experimental tests have been carried out in a wind tunnel on two types of openings, namely a sharp-edged orifice (flush to the wall) and a long opening (chimney). Using an analytic result for the still-air case and simple dimensional analysis it is argued that the local crossflow velocity ratio, V/u, is an important parameter for the orifice and the experimental results support this (as do some simple CFD calculations). The experimental results for the sharp-edged opening are similar to earlier work on generally larger openings. For the long opening the effects of external flow are smaller. In particular, the effects are negligible when the outlet of the opening lies in the external flow. Estimates are made of the consequential uncertainties arising in envelope flow calculations for natural ventilation design.     

一大跨度悬挑雨篷的风荷载及开洞比较

对一座将建于强风区的悬挑屋盖(雨篷)结构模型进行了风洞试验,研究了大跨度悬挑屋盖上的风荷载特性。不同工况下屋盖表面的风压分布特性表明,周边建筑对所测建筑的风荷载有较大的干扰影响。还研究了在顶部开洞情况下屋盖表面的风压分布特性,结果表明开洞后屋盖上的风压有一定程度的降低。     

Facade flame height ejected from an opening of fire compartment under external wind

This paper presents an experimental study and analysis on the facade flame height ejected from an opening of fire compartment under external wind. Experiments are carried out in a reduced-scale model consisting of a cubic fire compartment with a vertical facade wall. An opening is designed at the center of one sidewall of the fire compartment at the facade side and subjected to external wind (normal to the opening) provided by a wind tunnel. The facade flame heights are measured by a CCD camera for five different openings at various fuel supply heat release rates and wind speeds. It is found that the facade flame height decreases with increasing external wind speed. A scaling analysis is performed to interpret this behavior based on the change of air entrainment into the flame from both the facing-facade and parallel-facade directions caused by the external wind flow. A global model incorporating the external wind speed, the two characteristic length scales of the opening as well as the dimensionless excess heat release rate is developed for describing the facade flame height of various conditions. The proposed model correlates the experimental data well.     

安装过程中风吸力对大跨加劲钢桁桥的影响

在大跨钢桁桥的安装过程中,为缩短工期,桥面板和钢桁梁常同时施工,这将导致风吸力对桥面板产生影响,从而影响安装过程中含大跨悬臂梁的加劲钢桁桥的抗风性能,因为风吸力与自重共同作用会增大结构响应。然而,现有规范和研究都没有考虑这种影响,故需研究风吸力对安装过程中加劲钢桁桥的抗风静力性能的影响。以世界最长的拱加劲钢桁桥为模型,进行2个风洞试验:高频底座天平试验和同步多点压力传感系统试验。基于试验结果,建立2个净压力系数以确定风吸力。通过确定安装过程中风吸力对桥梁的影响,建立了考虑风吸力的有限元模型。     

Large eddy simulation of wind effects on a long-span complex roof structure

This paper presents a combined study of numerical simulations and wind tunnel tests for the determinations of wind effects on a long-span complex roof of the Shenzhen New Railway Station Building. The main objective of this study is to present an effective approach for the estimations of wind effects on a complex roof by computational fluid dynamics (CFD) techniques. A new inflow turbulence generator called the discretizing and synthesizing random flow generation (DSRFG) approach was applied to simulate inflow boundary conditions of a turbulent flow field. A new one-equation dynamic subgrid scale (SGS) model was adopted for the large eddy simulations (LES) of wind effects on the station building. The wind-induced pressures on the roof and turbulent flow fields around the station building were thus calculated based upon the DSRFG approach and the new SGS model integrated with the FLUENT software. In parallel with the numerical investigation, simultaneous pressure measurements on the entire station building were made in a boundary layer wind tunnel to determine the mean, fluctuating, and peak pressure coefficient distributions. The numerically predicted results were found to be consistent with the wind tunnel test data. The comparative study demonstrated that the recommended inflow turbulence generation technique and the new SGS model as well as the associated numerical treatments are useful tools for structural engineers to assess wind effects on long-span complex roofs and irregularly shaped buildings at the design stage.     

体育场悬挑屋盖结构的风荷载及干扰影响的风洞试验研究

本文结合 1座将建于强风区的大型体育场的实际建设情况 ,在风洞中对该体育场的 1、2期工程分别进行了试验 ,仔细分析了其主看台悬挑屋盖上的风压分布 ,并对干扰影响进行了讨论 ,得出的一些结论对建立此类体育场悬挑屋盖的风振分析方法有参考作用     

单个周边建筑对工业厂房屋面平均风压的气动干扰效应

工业厂房通常处于工业厂区内,受周边建筑的干扰,其表面风压分布与单个独立厂房不同,相邻建筑会对风荷载产生影响。基于单个厂房与两个串列厂房刚性模型风洞试验,给出了不同工况下屋面的平均风压,分析了屋盖横向、纵向端部与中部测点的平均风压分布规律,对比了不同串列距离条件下受扰厂房与独立厂房屋盖表面平均风压分布,探讨了平均风压系数干扰因子随风向角及干扰距离的变化规律。试验结果表明：不同风向角时,干扰效应截然不同;干扰效应存在临界风向角。临界风向角一般保持在 30°~50°范围内,小于临界风向角时,干扰起放大效应;大于临界风向角时,干扰为遮挡效应。此外,运用最小二乘法拟合了干扰因子设计值实用计算式,为受扰厂房建筑屋盖表面风压的修正提供依据。     

大跨双层屋盖结构风洞试验与风振响应研究

对南太湖湿地奥体公园复杂体型体育场双层屋盖结构进行了风荷载的风洞试验与风致动力响应研究。屋盖由高低两个开口椭圆屋面叠合而成,两屋面之间设置观光走廊。利用风洞模型试验测定了双层屋盖上下表面的平均和脉动风压时程数据。通过计算分析得到了屋盖结构局部测点的极值风压以及平均风荷载整体合力与最不利风向角。然后基于有限元方法对该屋盖进行了风振响应的动力时程分析,获得了结构风振系数、等效静力风荷载的分布图以及考虑风振效应的最不利风向等数据和结论。