大型冷却塔表面脉动风压原型实测与分布准则

我国冷却塔规范风荷载条款仍源自20世纪80年代原型冷却塔（约90m高）实测资料,且仅规定了塔筒表面静态风压分布。事实上,超大型冷却塔（高度≥165m）风振问题与风荷载脉动作用关系更加密切,由此导致了冷却塔数学和物理试验模型雷诺数效应模拟准则的不完整性,难于准确再现冷却塔表面动态风荷载与来流条件、塔群组合状况等参数间的合理关系,已成为制约大型冷却塔抗风性能研究和结构设计的瓶颈。为此,采用全天候动态风压采集设备,对某电厂冷却塔（约166m高）进行通风筒表面动、静态风压长期现场观测,量化表面脉动压力与来流紊流度之间的影响关系,提出具有原创性的冷却塔超高雷诺数条件（Re≥6E7）脉动风压雷诺数效应模拟准则。     

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。     

风力机叶片周边瞬态风场的混合数值模拟

本文根据已有的三维瞬态风场混合数值模拟方法,首先利用k-ε湍流模型对风力发电机叶片周边的时均湍流场进行CFD数值模拟,用ESDU推荐的方法计算了叶片附近的Reynolds应力张量,并修正叶片周边风场的脉动风功率谱密度函数。基于随机流场生成方法逐点模拟了叶片周边的三维脉动风速场,为今后进行叶片脉动荷载的求解奠定了基础。     

Wind tunnel tests on scale models of a large power station chimney

This work is aimed at providing a better understanding of the parameters required for the wind-tunnel simulation of the wind loads on large power station chimneys. Measurements of mean and fluctuating pressure distributions have been made on scale models of Fawley power station chimney, for comparison with the full-scale measurements of Tunstall. The measurements have been made in a simulated atmospheric boundary layer of height 1.2 m (nominal scale 1:500), using the method developed by Counihan.Initial measurements of mean pressure distribution were made on a 1:250 scale model chimney in the 1:500 scale boundary layer, in order to obtain as high a Reynolds number as possible in the wind tunnel available. No fluctuating pressure measurements were made owing to the limited tunnel time available. Following the good agreement between mean pressure distributions obtained on the 1:250 model and full-scale measurements, a 1:500 scale model chimney was tested in the same simulated atmospheric boundary layer. Mean pressure measurements gave good agreement with full-scale measurements at a Reynolds number of 2.3 × 10⁷, for model Reynolds numbers above 1.5 × 10⁵, and with a smooth or slightly rough model surface. Good agreement was obtained between model and full scale for the distribution of fluctuating pressure coefficients, when the difference in turbulence intensity between the simulated and full-scale flow was considered. No coherent vortex shedding was found on the model, in agreement with full-scale measurements.     

Characteristic of wind loads on a hemispherical dome in smooth flow and turbulent boundary layer flow

A series of wind tunnel tests was performed to investigate the effects of Reynolds number on the aerodynamic characteristics of hemispherical dome in smooth and turbulent boundary layer flows. Reynolds number of this study varies from 5.3×10⁴ to 2.0×10⁶. Instantaneous pressures were measured through high frequency electronic scanner system. Mean and RMS pressure coefficients on the center meridian and the overall pressure patterns of domes were calculated for comparative study. The results indicate that, in smooth flow, the transition of separation flow occurs in-between Re=1.8×10⁵–3.0×10⁵ and pressure distributions become relatively stable after Re>3.0×10⁵. In turbulent flow, the transition of separation flow occurs at lower Reynolds number, Re<1.1×10⁵, while the pressure distributions become Reynolds number independent at Re=1.0–2.0×10⁵.     

Prediction of the pressure distribution on a cubical building with implicit LES

This paper presents a numerical study of the flow around a cubical building in an atmospheric boundary layer. The Reynolds number of the flow is Re=4×10⁶. Different types of turbulence models, steady state RANS, hybrid RANS/LES and LES, are used and the simulation results are compared to field measurement data of the mean pressure distribution. The objective is to build an approach to perform simulations on coarse grids with low computational cost. The outcome is that the Implicit LES (ILES) method is the most accurate for coarse grid simulations. In order to verify the sensitivity of the results to the Reynolds number, also simulations of a wind tunnel experiment at Reynolds number 4×10⁴ are performed. We demonstrate that also for lower Reynolds numbers, although not optimal, the ILES approach leads to quite good results.     

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。     

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.     

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。     

A hybrid RANS and kinematic simulation of wind load effects on full-scale tall buildings

Up till recent years, predicting wind loads on full-scale tall buildings using Large Eddy Simulation (LES) is still impractical due to a prohibitively large amount of meshes required, especially in the vicinity of the near-wall layers of the turbulent flow. A hybrid approach is proposed for solving pressure fluctuations of wind flows around tall buildings based on the Reynolds Averaged Navier-Stokes (RANS) simulation, which requires coarse meshes, and the mesh-free Kinematic Simulation (KS). While RANS is commonly used to provide mean flow characteristics of turbulent airflows, KS is able to generate an artificial fluctuating velocity field that satisfies both the flow continuity condition and the specific energy spectra of atmospheric turbulence. The kinetic energy is split along three orthogonal directions to account for anisotropic effects in atmospheric boundary layer. The periodic vortex shedding effects can partially be incorporated by the use of an energy density function peaked at a Strouhal wave number. The pressure fluctuations can then be obtained by solving the Poisson equation corresponding to the generated velocity fluctuation field by the KS. An example of the CAARC building demonstrates the efficiency of the synthesized approach and shows good agreements with the results of LES and wind tunnel measurements.     

圆形截面冷却塔不同表面粗糙度时绕流特性的试验研究

以双曲型圆截面冷却塔的风荷载模型为背景,探讨了高雷诺数模拟的途径,采用改变模型表面粗糙度和调整风速的手段,获得了在较低雷诺数条件下模拟高雷诺数流态特性的试验条件。研究了不同粗糙度表面的截面绕流特性,得到了一些宝贵的试验数据和有益的结论。     

Flow structure around a 3-D rectangular prism in a turbulent boundary layer

Flow around a three-dimensional (3-D) rectangular prism has been investigated by using a particle image velocimetry technique. The prism was immersed in a thick turbulent boundary layer. The ratio of the boundary layer thickness and the model height was about 0.06. Measurements were made at Reynolds number of 7.9×10³ which is based on free stream velocity and model height. Detailed flow structures and characteristics including three circulation zones were obtained by averaging over a large number of instantaneous velocity maps. The 3-D structure in a wake zone is clearly seen from mean flow streamline topology. Turbulent kinetic energy distribution is also obtained approximately. Maximum turbulent kinetic energy was found at the separated layer in the upper boundary of the separation bubble near the leading edge of a roof. The magnitude of the maximum energy is about 2.5 times that in the wake region.     

3D flow around a rectangular cylinder: A computational study

The aim of this paper is to provide a contribution to the analysis of the 3D, high Reynolds number, turbulent, separated and reattached flow around a fixed sharp-edged rectangular cylinder with a chord-to-depth ratio equal to 5. The work is developed in the perspective of the benchmark on the aerodynamics of a rectangular cylinder (BARC), in terms of an exploratory computational study. First, the adopted flow modelling and computational approach are shortly described. Second, the obtained main aerodynamic integral parameters are compared with other results proposed in the literature. Hence, the 3D flow features around the nominally 2D cylinder are investigated by means of both proper orthogonal decomposition and coherence function of the side-surface fluctuating pressure field. Once the main 2D nature of the flow has been pointed out, some of the 2D mechanisms that are responsible for the variation of the fluctuating aerodynamic forces are scrutinised: the computational approach post-processing facilities are employed to look for significant relationships between the flow structures, the pressure field and the aerodynamic force components.     

基于RNG κ-ε模型的竖板绕流数值模拟

作为薄矩形柱类高层建筑绕穿流动的基础研究之一,采用简化的直通道内置竖板二维平面空气绕流模型为研究对象.基于有限体积法和RNGk-ε湍流模型,对不同风级作用下的长宽比D/B=0.1的竖板流动进行非定常数值模拟.计算结果揭示了竖板空气绕流尾涡的形成、脱落及消失的周期性过程.在Re =4.42×104和Re=4.62×104区间尾涡无明显脱落,当雷诺数大于或等于4.62×104时,出现尾涡的生成及脱落消失过程.计算并分析了竖板表面不同位置的压力分布和风载体型系数,计算结果与相关文献结论进行了对比.     

On the aerodynamic and aeroelastic response of a bridge tower

This work is concerned with the aerodynamic characterization of a cable-stayed bridge tower in free-standing configuration; experimental tests were performed at Politecnico di Milano Wind Tunnel under smooth and turbulent flow conditions. The aerodynamic behavior of the tower was investigated through static and dynamic tests on a 1:30 scale sectional model; the whole structure response has been studied using a 1:100 scale full aeroelastic model in stand-alone configuration. Aim of this paper is to compare wind tunnel test results obtained on the two models for different wind exposures, discussing the problems related to scale effects in scale model testing. Some inconsistencies found during the experimental campaign confirm that scale effects in wind tunnel testing represent a serious issue especially for bluff body structures whose vortex shedding response is strongly affected by Reynolds number.     

Interaction of square prisms in two flow fields

A single square prism was tested at several angles of attack in a wind tunnel in smooth and in turbulent flow. A second square prism of equal size was placed upstream with various separation distances and orientations. Proper combination of signals from sensitive pressure transducers yielded the fluctuating aerodynamic forces and moments. The mean forces and moments were determined using conventional piezometer openings in conjunction with a liquid manometer. Some error is inevitable since only three transducers were used to a side. Comparisons with available information show reasonable correspondence with the mean and fluctuating forces. Little information appears available for moments.Although the upstream prism effectively shields the downstream prism in many cases, particularly for the mean forces and moments, there are in all cases, significant values for the coefficients of fluctuating force and moment. When the two objects are offset both vertically and horizontally, particularly large mean moments occur.Use of a turbulent flow field is to be recommended for testing. Consideration of moment measurement should be of prime importance in wind sensitive structures.     

Flow and pressure field characteristics around pyramidal buildings

An experimental investigation of the flow and pressure characteristics around pyramidal buildings is presented. The experiments were conducted in a boundary layer wind tunnel. The velocities of the flow around the pyramids and the pressure distribution on the pyramid surfaces were measured using 2D laser Doppler anemometry (LDA) and standard pressure tapping technique, respectively. Eight different pyramids (model scale, 1:200) with varying base angles were investigated. The mean and fluctuating characteristics of the flow and pressure field around pyramids surfaces are described. The basic flow characteristics that distinguish pyramids from rectangular buildings are also discussed in this study. The influence of two parameters, base angle and wind direction, was investigated. The results show that base angle and wind direction characteristically influence the flow and pressure field around pyramids yielding differences in flow characteristics and in wind loads on the structure.