大跨度复杂屋盖结构风荷载的大涡模拟

应用一种新的湍流脉动流场产生方法DSRFG(Discretizing and Synthesizing Random Flow Generation)[1]模拟风场实际的湍流边界条件,采用一种新的大涡模拟(Large Eddy Simulation,LES)的亚格子模型[2],基于Linux系统下软件平台Fluent6.3的并行计算技术,对深圳新火车站进行了数值风洞模拟。并将屋盖的平均风压、脉动风压计算结果与风洞试验数据进行了比较,表明数值模拟很好地反映了大跨度屋盖表面风压的分布情况,由其得到的风压系数与风洞试验数据有较好的吻合。表明本文的DSRFG方法以及新的大涡模拟亚格子模型的数值模拟技术是一种很好的预测大型、复杂结构表面风荷载的有效方法。并为进一步发展在复杂湍流环境下大跨度屋盖结构的风荷载数值风洞技术提供参考。     

深圳平安国际金融大厦风致响应大涡模拟分析

运用一种新的湍流脉动流场产生方法模拟了三种风场的湍流边界条件,采用一种新的大涡模拟的亚格子模型,基于Linux系统下软件平台Fluent 6.3的并行计算技术,对深圳平安国际金融大厦进行了全尺寸、高雷诺数（高达10×10⁸量级）的数值风洞模拟。计算了三种风场下建筑表面平均、脉动风压及风荷载时程数据。利用惯性风荷载（IWL）法得到三种风场下深圳平安金融大厦的基底等效静风荷载以及结构顶部峰值加速度响应。分析了不同的湍流来流对结构风压系数、风荷载及加速度响应的影响。分析结果表明：三种来流风场条件下,深圳平安金融大厦周围风场相差较大,来流的湍流强度越高,建筑物前方的脉动风速越高;顺风向等效风荷载主要受平均风速控制,横风向等效风荷载主要受脉动风控制;湍流强度越大,横风向等效风荷载越大;中国规范建议的湍流流场下,深圳平安金融大厦10年重现期顺风向、横风向峰值加速度响应满足居住者舒适度要求。     

Wind effects on a long-span beam string roof structure: Wind tunnel test, field measurement and numerical analysis

The Guangzhou International Convention & Exhibition Center (GICEC) with roof dimensions of 210 m wide and 457 m long is the largest exhibition center in Asia and the 2nd largest of this kind in the world. This paper presents results from a combined study of wind tunnel test, full-scale measurement, and numerical analysis of wind effects on the long-span beam string roof structure. In the wind tunnel test, wind-induced pressures including mean and fluctuating components were measured from the roof of a 1:300 scale GICEC model under suburban boundary layer wind flow configuration. The Proper Orthogonal Decomposition (POD) method and the quasi-steady approach as well as probability analysis were adopted to estimate the characteristics of the fluctuating wind pressures on the roof. On the other hand, full-scale measurements of wind actions and wind-induced structural responses of the roof were conducted during the passage of Typhoon Nuri. The field data such as wind speed, wind direction, and acceleration responses, etc., were continuously and simultaneously monitored from a wind and structural response monitoring system installed on the roof structure during the typhoon. Detailed analysis of the field data was performed to investigate the characteristics of the typhoon-generated wind and the wind-induced vibration of the long-span roof structure under typhoon condition. The dynamic characteristics of the roof were determined from the field measurements and comparisons with those calculated from the finite element model (FEM) of the structure were made. The damping ratios of the roof structure were estimated by means of the random decrement method and the amplitude-dependent damping characteristics were presented and discussed. Finally, the full-scale measurements were compared with the model test results to examine the accuracy of the wind tunnel test results and to identify possible modelling errors in the numerical study. The results presented in this paper are expected to be of considerable interest and of use to researchers and professionals involved in designing long-span roof structures.     

湍流边界层中低矮建筑绕流大涡模拟

通过对平板湍流边界层进行大涡模拟,采用拟周期边界条件维持湍流边界层厚度稳定,提取速度和压力时程作为低矮建筑绕流模拟之脉动入流边界条件,研究脉动入流下的低矮建筑绕流特性。研究结果表明：入流边界特性对网格变化适应性良好,其平均速度剖面、湍流强度、流速频谱特性基本符合空旷地貌风场特性;脉动入流下,建筑表面的平均风压系数、脉动风压系数的计算结果与风洞试验结果基本吻合。受雷诺数及湍流强度的影响,流动分离区负压与试验值存在一定差别;屋盖上分离区风压时程具有非高斯概率特性,尤以气流分离较剧烈的屋盖迎风边缘及屋盖两侧风压的非高斯特性明显,该特征与风洞试验基本一致;受非高斯特性的影响,建议峰值因子g取4.5~5.5。     

高层建筑标准模型脉动风压特性大涡模拟适用方法研究

为提高钝体建筑结构绕流模拟结果的精度,基于两种大涡模拟(large eddy simulation, LES)入口湍流生成方法,分别为NSRFG（narrow band synthesis random flow generation）方法和CDRFG（consistent discretizing random flow generation）方法,进行CAARC(commonwealth advisory aeronautical research concil)高层建筑标准模型绕流的数值模拟比较研究。以风洞试验结果为参照,在对大气边界层湍流风场进行模拟验证的基础上,详细对比分析采用上述两种方法模拟得到的建筑表面平均和脉动风压系数、绕流场湍流结构、风压系数概率密度分布特性等的差异,并着重从脉动风压非高斯特性角度进行探讨,检验采用上述两种方法模拟钝体建筑结构绕流的适用性和准确性。结果显示：在受来流直接作用的建筑迎风面,采用两种方法模拟的脉动风压基本都符合高斯特性;而在受分离流和尾流作用的侧风面和背风面,采用NSRFG方法能更好地反映建筑表面脉动风压的非高斯特性。极值风压分析表明,为了满足99.38%的保证率,CAARC标准模型迎风面极大与极小峰值因子需分别取为3.0和2.5,侧风面和背风面极大和极小峰值因子需分别取为2.5和4.0。     

Study on suitable method to simulate fluctuating wind pressurecharacteristics of standard high-rise building model based on LES

为提高钝体建筑结构绕流模拟结果的精度，基于两种大涡模拟(large eddy simulation, LES)入口湍流生成方法，分别为NSRFG（narrow band synthesis random flow generation）方法和CDRFG（consistent discretizing random flow generation）方法，进行CAARC(commonwealth advisory aeronautical research concil)高层建筑标准模型绕流的数值模拟比较研究。以风洞试验结果为参照，在对大气边界层湍流风场进行模拟验证的基础上，详细对比分析采用上述两种方法模拟得到的建筑表面平均和脉动风压系数、绕流场湍流结构、风压系数概率密度分布特性等的差异，并着重从脉动风压非高斯特性角度进行探讨，检验采用上述两种方法模拟钝体建筑结构绕流的适用性和准确性。结果显示：在受来流直接作用的建筑迎风面，采用两种方法模拟的脉动风压基本都符合高斯特性；而在受分离流和尾流作用的侧风面和背风面，采用NSRFG方法能更好地反映建筑表面脉动风压的非高斯特性。极值风压分析表明，为了满足99.38%的保证率，CAARC标准模型迎风面极大与极小峰值因子需分别取为3.0和2.5，侧风面和背风面极大和极小峰值因子需分别取为2.5和4.0。     

3D experimental and numerical analysis of wind flow around domed-roof buildings with open and closed apertures

This paper presents experimental and numerical study of airflow distribution around a reduced-scale model of a common type of domed-roof building. Measurements are performed in an open loop wind tunnel. A new modified Counihan scheme is developed for constructing a part-depth atmospheric boundary layer (ABL). Measured quantities include: wind velocity profile, turbulence intensity and airflow pattern around the building. To conduct the experiments, a 1:54 scale model of a real domed-roof building with six windows and an aperture on the roof is fabricated and placed in the test section of the wind tunnel. In addition, using a numerical modeling, turbulent airflow around such scale model in the wind tunnel is simulated and airflow field inside and outside the model as well as ventilating discharge coefficient are computed. It is illustrated that, airflow around this type of building contains complex adjacent recirculation flows. The building with open apertures has acceptable discharge coefficient for ventilation, which can be a factor to ensure comfort condition for residents as well as complying with energy-saving considerations.     

A general inflow turbulence generator for large eddy simulation

This paper presents a general inflow turbulence generator for numerical simulation of a spatially correlated turbulent flow field. The novel inflow turbulence generator is developed based on the discretizing and synthesizing random flow generation (DSRFG) technique that is proved to be able to generate a fluctuating turbulent flow field satisfying any given spectrum. Then, the techniques of aligning and remapping are incorporated in the inflow turbulence generator for generation of an inhomogeneous and anisotropic turbulent flow field following arbitrary target spectra in three orthogonal directions. The performance of the present inflow turbulence generator is compared with that of Smirnov’s random flow generation (RFG) method. Detailed numerical studies show that the proposed inflow turbulence generator can strictly guarantee divergence-free condition without any additional improving step and synthetically generate inflows satisfying prescribed spatial anisotropy and correlation conditions. It is demonstrated through numerical examples that the inflow turbulence generator developed in this study is an effective tool for generation of a spatially correlated turbulent flow field for large eddy simulation (LES).     

Numerical evaluation of wind effects on a tall steel building by CFD

A comprehensive numerical study of wind effects on the Commonwealth Advisory Aeronautical Council (CAARC) standard tall building is presented in this paper. The techniques of Computational Fluid Dynamics (CFD), such as Large Eddy Simulation (LES), Reynolds Averaged Navier-Stokes Equations (RANS) Model etc., were adopted in this study to predict wind loads on and wind flows around the building. The main objective of this study is to explore an effective and reliable approach for evaluation of wind effects on tall buildings by CFD techniques. The computed results were compared with extensive experimental data which were obtained at seven wind tunnels. The reasons to cause the discrepancies of the numerical predictions and experimental results were identified and discussed. It was found through the comparison that the LES with a dynamic subgrid-scale (SGS) model can give satisfactory predictions for mean and dynamic wind loads on the tall building, while the RANS model with modifications can yield encouraging results in most cases and has the advantage of providing rapid solutions. Furthermore, it was observed that typical features of the flow fields around such a surface-mounted bluff body standing in atmospheric boundary layers can be captured numerically. It was found that the velocity profile of the approaching wind flow mainly influences the mean pressure coefficients on the building and the incident turbulence intensity profile has a significant effect on the fluctuating wind forces. Therefore, it is necessary to correctly simulate both the incident wind velocity profile and turbulence intensity profile in CFD computations to accurately predict wind effects on tall buildings. The recommended CFD techniques and associated numerical treatments provide an effective way for designers to assess wind effects on a tall building and the need for a detailed wind tunnel test.     

Flow around a cube in a turbulent boundary layer: LES and experiment

We present a numerical simulation of flow around a surface mounted cube placed in a turbulent boundary layer which, although representing a typical wind environment, has been specifically tailored to match a series of wind tunnel observations. The simulations were carried out at a Reynolds number, based on the velocity U at the cube height h, of 20,000—large enough that many aspects of the flow are effectively Reynolds number independent. The turbulence intensity was about 18% at the cube height, and the integral length scale was about 0.8 times the cube height h. The Jenson number Je=h/z₀, based on the approach flow roughness length z₀, was 600, to match the wind tunnel situation. The computational mesh was uniform with a spacing of h/32, aiding rapid convergence of the multigrid solver, and the governing equations were discretised using second-order finite differences within a parallel multiblock environment. The results presented include detailed comparison between measurements and LES computations of both the inflow boundary layer and the flow field around the cube including mean and fluctuating surface pressures. It is concluded that provided properly formulated inflow and surface boundary conditions are used, LES is now a viable tool for use in wind engineering problems concerning flow over isolated bodies. In particular, both mean and fluctuating surface pressures can be obtained with a similar degree of uncertainty as usually associated with wind tunnel modelling.     

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.     

CFD simulations of gas dispersion around high-rise building in non-isothermal boundary layer

Urban heat island phenomena and air pollution become serious problems in weak wind regions such as behind buildings and within street canyons, where buoyancy effect cannot be neglected. In order to apply CFD techniques for estimation of ventilation and thermal and pollutant dispersion in urban areas, it is important to assess the performance of turbulence models adopted to simulate these phenomena. As the first step of this study, we carried out wind tunnel experiments and CFD simulations of gas and thermal dispersion behind a high-rise building in an unstable non-isothermal turbulent flow. The standard k-ε model and a two-equation heat-transfer model as RANS models, and LES, were used for the CFD simulation. One of the important purposes of this study was to clarify the effect of inflow turbulence (both velocity and temperature) on flow field and gas/thermal dispersion for the LES calculation. Thus, LES calculations with/without inflow turbulence were conducted. The inflow turbulence was generated through a separate precursor simulation. The calculated results showed that both RANS models overestimated the size of the recirculation region behind the building and underestimated the lateral dispersion of the gas. Turbulent flow structures of LES with and without inflow turbulence were completely different. The LES result with inflow turbulence achieved better agreement with the experiment.     

复杂型体悬挑屋盖风荷载风洞试验与数值模拟

基于Fluent 6.1软件平台,将Realizablek-ε模型与非平衡壁面函数搭配使用,对位于海岛强台风地区的某海洋文化中心屋盖风压分布进行了计算流体动力学(CFD)数值模拟,同时也对该建筑进行了风洞试验。模拟结果与风洞试验数据的对比显示数值模拟可较准确地反映实际风压。风洞试验和数值模拟均显示悬挑屋盖受到了很大的吸力,对屋盖结构极为不利,对此问题采取在屋盖悬挑部分开洞的减压措施,以改善屋盖悬挑部分的受风特性。对开洞后的建筑进行了CFD建模与计算,结果表明在屋面前缘开洞可有效降低屋盖悬挑部分的最大风压和所受的竖向升力,大大改善屋盖结构的受力状态。     

Large-eddy simulation of wind effects on a super-tall building in urban environment conditions

A combined study of large-eddy simulation (LES), wind tunnel testing and full-scale measurement is conducted for the evaluation of wind effects on a super-tall building in a complex urban area. To validate the numerical simulations, the wind tunnel experiments including synchronous multi-pressure and high-frequency force balance model tests are conducted in a boundary layer wind tunnel laboratory. The numerical predictions are then compared with the experimental results, demonstrating that the LES can provide comparable predictions of the wind effects on the super-tall building. Furthermore, the cross-validation of the predicted displacement responses by the LES against the wind tunnel and full-scale measurements are presented and the agreement among them is reasonably good. The main objective of this study is to explore an effective numerical approach for the accurate estimation of wind effects on tall buildings in urban environment conditions and promote the practical use of the LES in the wind-resistant design of complex structures.     

Simulation of mean flow and turbulence over a 2D building array using high-resolution CFD and a distributed drag force approach

A numerical simulation has been performed of the disturbed flow through and over a two-dimensional array of rectangular buildings immersed in a neutrally stratified deep rough-walled turbulent boundary-layer flow. The model used for the simulation was the steady-state Reynolds-averaged Navier-Stokes equations with linear and non-linear eddy viscosity formulations for the Reynolds stresses. The eddy viscosity was determined using a high-Reynolds number form of the k-ε turbulence-closure model with the boundary conditions at the wall obtained with a standard wall-function approach. The resulting system of partial differential equations was solved using the SIMPLE algorithm in conjunction with a non-orthogonal, colocated, cell-centered, finite volume procedure. The predictive capabilities of the high-resolution computational fluid dynamics (CFD) simulations of urban flow are validated against a very detailed and comprehensive wind tunnel data set. Vertical profiles of the mean streamwise velocity and the turbulence kinetic energy are presented and compared to those measured in the wind tunnel simulation.It is found that the performance of all the turbulence models investigated is generally good—most of the qualitative features in the disturbed turbulent flow field through and over the building array are correctly reproduced. The quantitative agreement is also fairly good (especially for the mean velocity field). Overall, the non-linear k-ε model gave the best performance among four different turbulence closure models examined. The turbulence energy levels within the street canyons and in the exit region downstream of the last building were underestimated by all four turbulence closure models. This appears to contradict the ‘stagnation point anomaly’ associated with the standard k-ε model which is a result of the excessive turbulence energy production due to normal straining. A possible explanation for this is the inability of the present models to account properly for the effects of secondary strains on the turbulence and/or for the effects of large-scale flapping of the strong shear layer at the canopy top.The results of the high-resolution CFD simulations have been used to diagnose values of the drag coefficient to be used in a distributed drag force representation of the obstacles in the array. Comparisons of the measured spatially-averaged time-mean mean velocity and turbulence kinetic energy in the array with predictions of the disturbed flow using the distributed drag force approach have been made.     

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.     

Effects of inflow turbulence intensity on flow and pollutant dispersion in an urban street canyon

The effects of inflow turbulence intensity on flow and pollutant dispersion in an urban street canyon with a street aspect ratio of 1 are examined using a two-dimensional numerical model. As the inflow turbulence intensity increases, turbulent kinetic energy and turbulent diffusivity in the street canyon increases. Also, the mean horizontal velocity near the roof level increases and the street-canyon vortex strengthens. The analyses of the time series and residue ratio of pollutant concentration show that the inflow turbulence intensity significantly affects pollutant concentration in the street canyon. As the inflow turbulence intensity increases, the pollutant concentration in the street canyon becomes low and hence more pollutants escape from the street canyon.     

Parametric study on flutter derivatives of bridge decks

The method for identification of flutter derivatives of bridge decks developed by the authors is first briefly described in this paper. To investigate the effects of dynamic parameters of a bridge deck model on the flutter derivatives a test of the sectional Jiangyin Bridge deck's models with different dynamic parameters was carried out in a boundary layer wind tunnel using the present identification method. In both smooth and simulated turbulent flow conditions, a plate model and the sectional deck model of the Jiangyin Bridge were tested to further survey the effects of turbulence on flutter derivatives. The identified results tend to indicate that the effects of parameters of the model and turbulence on the flutter derivatives are negligible.     

Wind-induced ventilation performances and airflow characteristics in an areaway-attached basement with a single-sided opening

In the present study, we performed both wind tunnel experiments and numerical simulations on a scale model with the focus on wind-driven natural ventilation in an areaway-attached basement with a single-sided opening. In the experiments, the mean value of the effective ventilation rate, purging flow rate (PFR) was measured for nine wind incidence angels based on the homogeneous emission rate method. The experimental results were used to validate two numerical approaches: Reynolds averaged Navier–Stokes (RANS) modeling and large-eddy simulation (LES). The influences of inflow turbulent fluctuations for LES modeling were also examined. The comparisons between the experiment and the numerical simulation indicate that LES can provide more accurate results than RANS and the inflow turbulent fluctuations should be taken into account for LES modeling. Based on LES with the inflow turbulent fluctuations, the mean airflow patterns within and around the areaway-attached basement were further studied for different wind incidence angles to investigate the influence of wind direction on ventilation performance in the areaway space. Furthermore, the relationships between the effective ventilation rate and the kinetic energy in the basement space were analyzed for three wind directions: 0°, 90° and 180°. A close correlation was found between the mean values, whereas the corresponding time variations showed large discrepancies. Finally, we compared the effective ventilation rate obtained using the homogeneous emission rate method and the airflow rates through the opening using two integration procedures. The effective ventilation rates were found lower than the airflow rates through the opening.     

数值模拟大气边界层风洞中湍流模型的比较

风洞模拟试验是风工程研究的一种重要手段,在对大气边界层风洞进行数值模拟的时候,湍流模型的选取是影响模拟计算结果的至关重要的因素之一,本文针对大气边界层的风洞模型为考察对象对湍流模型进行了考察,考虑了各种湍流模型对计算结果的影响,并与实验结果进行了对比,旨在得出大气边界层风洞模拟中比较适合的湍流模型。研究发现在模拟大气边界层的风洞时,一般宜采用RNG k-ε模型,在计算资源和时间允许的情况下,建议使用雷诺应力模型。