流场物理特性在脉动风压系数估算中的应用

利用数值模拟技术计算脉动风压需要进行非定常瞬态模拟,计算量过大. 为了提高计算效率,文章根据准定常理论,用预测点高度的入口风速代替参考点高度风速,修正了Paterson、黄本才等人提出的脉动风压估算公式. 通过由CFD 模拟得到的独立柱支撑平板结构的平均风压系数、参考点风速、湍流动能等参数估算了其脉动风压系数,发现大多数工况下与风洞试验结果相吻合. 研究表明,可以利用定常模拟计算结果中获得的参数估算出脉动风压系数.     

体育场阶梯型悬挑屋盖风荷载数值模拟研究

基于CFD数值模拟方法,采用RNG k-ε湍流模型对某体育场阶梯型悬挑屋盖风压进行了模拟研究。分析了屋盖风压分布特性及风向对风压的影响;并且考虑周边建筑对风场的扰动影响,引入风压系数干扰因子IF量化分析了周边建筑对体育场屋盖风压分布的气动干扰效应。结果表明:此类阶梯型大跨屋盖主要受风吸力作用,屋盖檐口、角部区域的风压系数量值较大;0°和180°风向角下平均风压随测点位置变化趋势大致相同,风压在台阶转折处发生突变;屋盖各区域的风载体型系数对风向角的敏感程度存在较大差异;周边建筑对屋盖风压主要起遮挡效应,对屋盖某些局部区域的风压起放大效应。     

本征正交分解技术在屋盖风压场重建与预测中的应用

给出利用本征正交分解(POD)对屋盖风压场进行重建和预测的研究结果.对一个双坡屋盖用同步多点压力扫描系统进行了风洞试验,根据POD技术采用前若干阶本征模态重建屋盖风压场.采用两种方案预测未布置测压点位置的风压时间序列.第一种方案中利用插值技术获得没有测压点位置的本征模态值.第二种方案对参考屋盖和需预测的新屋盖分别进行试验,结合由参考屋盖试验萃取的本征模态和由新屋盖试验的风压数据计算的主坐标,预测出新屋盖未知区域的风压时间序列.文中对风压场重建和预测的效果作了分析,而且比较了根据测量的风压数据和预测的风压数据所计算的屋盖风致响应.     

基于改进的神经网络的大跨度屋盖风压场预测

利用风洞实验测定大跨度屋盖的风压时,由于通常只能通过布置有限测点而获得有限的风压数据,因此采用准确高效的方法预测更多未知点的风压特性具有重要意义。本文在径向基函数神经网络的基础上,结合遗传算法和方差分析对大跨度屋盖的风压场进行了预测。引入整体度量估计作为遗传算法中适应度函数的估计,采用方差分析分解RBF的输出总方差,用求得的均方误差对RBF神经网络模型的权方差进行估计。将本文方法预测得到的大跨度屋盖的风压系数、升力系数等与实验结果和传统RBF方法预测结果进行了对比,并进行了误差统计分析。结果表明:本文方法预测的风压系数与试验结果符合良好,且均方误差小于RBF方法,平均相差约67.21%;在达到同样的收敛精度时,采用本文方法计算所需的时间要比传统RBF模型节省约40%。结合遗传算法和方差分析的RBF神经网络模型是预测大跨度屋盖风压场的有效工具。     

大跨度脊谷式膜屋盖风载分布的实验研究

基于台州某风雨操场脊谷式张拉膜屋盖缩尺模型风洞试验的数据结果,选取典型测点,研究了屋面迎风前缘、过渡区及中轴区的平均风压和脉动风压系数的分布特性。同时,鉴于屋盖的不规则曲面造型,表面风压梯度变化较大,采用单一体型系数反映屋面风载已不能满足要求。文中在结合屋盖自身复杂体型和风压分布特征基础上,按各榀各边片将屋面划分为不同区域,对5个不利风向角下的区域体型系数进行统计分析,并给出各区域体型系数建议取值。最后,针对这类体型屋盖特点和风压分布特性,得出一些结论和建议,为进一步研究该类屋盖的风荷载特性和结构抗风设计提供了依据。     

大跨裙摆屋盖脉动风荷载特性数值模拟研究

以苏州太平金融中心大跨裙摆屋盖为对象,采用LES大涡模拟方法,模拟并分析屋盖表面脉动风压分布特性、脉动风压谱,以及脉动风压空间相干性等。结果表明:屋盖风压能量集中于迎风状态的低频部分,屋盖主体与主楼连接位置的角部区域在锥形涡的作用下会出现脉动风压增大现象;测点间脉动风压相干性随着频率及测点间空间距离的增大而减小,在高频处,其相干函数衰减到0.2以下,可近似认为不相干。     

连拱式大跨悬挑屋盖抗风气动措施研究

本文对连拱式大跨度悬挑屋盖进行了数值风洞试验,分别探讨了在屋盖悬挑前缘增设通风孔、导流板以及同时布设导流板与通风孔这三种气动措施对悬挑屋盖表面风荷载的影响及其作用机理．研究结果表明,同时布设导流板与通风孔的综合气动措施,能显著影响屋盖结构前缘气流的分离,从而减小屋盖的表面风压,并可减弱屋盖的风致振动．在此类屋盖结构设计中,运用综合气动措施可有效降低屋盖整体的升力系数与弯矩系数,对该类屋盖抗风设计较为有利．     

杭州大剧院风压分布的风洞试验研究

杭州大剧院外观造型新颖独特，由一个近似为椭球的双曲面屋盖和一个倒置的圆锥面玻璃幕墙相交形成大剧院的主体建筑的外轮廓．本文结合该主体结构的抗风设计要求，制作了1：200刚性模型进行结构表面脉动风压平均风压分布的风洞试验研究，详细介绍了风洞试验及数据处理方法，讨论了在不同风向角下椭球面屋盖和圆锥面玻璃幕墙的风压分布．为了便于整体结构设计，本文根据结构的实际情况对椭球面和圆锥面进行分块并给出相应的分块风压数据，最后根据各风向角下的风压分布特征给出了整体结构抗风设计的最不利风向角．     

上海世博会气象馆平均风压数值模拟研究

采用数值模拟方法对上海世博会气象馆进行了平均风压数值模拟,比较了4种较适合于结构风工程的RNG k-ε,SST-k-ω,SSG-RSM和BSL-RSM湍流物理模型,包括体型系数、表面合力、合力矩及湍动能结果,同时结合风流动特性分析了其规律性和差别的原因,并得到SST-k-ω,BSL-RSM与SSG-RSM模型各有优势,而RNG k-ε模型稍差的结论.最后研究了有无干扰情况下的场馆表面平均风压系数,分析了风干扰的原因.     

开槽对大跨悬挑平屋盖结构风荷载的影响

本文结合一大跨悬挑平屋盖模型的风洞试验研究，分析了此类结构屋盖的平均局部体型系数和极值局部体型系数的分布特性；并根据其风压的分布特性，提出在悬挑屋盖承受较大负压的屋檐和角点附近这些遇强风易发生破坏的部位采取开槽气动抗风措施，进一步研究了该气动抗风措施对大跨悬挑平屋盖结构风荷载的影响，试验结果显示，它们可以有效地削减屋盖风敏感处的风荷载值，使平均局部体型系数大约降低50％，极值局部体型系数大约降低25％，所得的这些结果对于结构的抗风设计有一定的指导意义。     

Constant Reynolds number turbulence downstream of an orificed perforated plate

Quasi-isotropic turbulence was experimentally produced in a wind tunnel via an orificed, perforated plate (OPP) at 10.5 m/s. The OPP consists of a lattice arrangement of 38.1 mm holes occupying 57% of the plate area. The OPP turbulence was found to be homogeneous over the cross section normal to the mean flow with Gaussian-like turbulence fluctuation. The isotropy of the turbulence field as portrayed by the streamwise/lateral turbulence intensity ratio was found to be approximately 1.1. The OPP turbulence is essentially self-preserving wherein the Taylor microscale Reynolds number remains nearly constant and the lateral velocity correlations collapse into a single curve.     

AN EXTENDED k-ε MODEL FOR NUMERICAL SIMULATION OF WIND FLOW AROUND BUILDINGS

It is assumed in this paper that for a high Reynolds number nearly homogeneouswind flow, the Reynolds stresses are uniquely related to the mean velocity gradientsand the two independent turbulent scaling parameters k and E. By applying dimensionalanalysis and owing to the Cayley-Hamilton theorem for tensors, a new turbulenceenclosure model so-called the axtended k-ε model has been developed. The coefficientsof the model expression were detemined by the wind tunnel experimental data ofhomogeneous shear turbulent flow. The model was compared with the standard k-εmodel in in composition and the prediction of the Reynold’s normal Stresses. Using thenew model the numerical simulation of wind flow around a square cross-section tallbuilding was performed. The results show that the extended k-ε model improves theprediction of wind velocities around the building the building and wind pressures on the buildingenvelope.     

大气边界层流场的模拟与大气边界层风洞

动态风荷载测试数据的可靠性依赖于大气边界层流场的正确模拟。本文根据作者在ＦＤ－４大气边界层风洞中,进行大气边界层流场调试时,就如何准确模拟自然风的四个参数方面所积累经验的总结。     

高层双塔楼绕流风场效应的数值预测

在一高层双塔楼静力风载风洞试验的基础上,采用时均数值模拟的方法,对其绕流风场进行了模拟,获得了风场的绕流特点和塔楼表面风压的分布规律．通过风压的模拟计算值与试验值的比较,表明以数值方法预测气动干扰强烈的绕流风场是准确和可行的．     

Recent improvements of actuator line-large-eddy simulation method for wind turbine wakes

In a large wind farm,the wakes of upstream and downstream wind turbines can interfere with each other,affecting the overall power output of the wind farm.To further improve the numerical accuracy of the turbine wake dynamics under atmosphere turbulence,this work proposes some improvements to the actuator line-large-eddy simulation(AL-LES)method.Based on the dynamic k-equation large-eddy simulation(LES),this method uses a precursor method to generate atmospheric inflow turbulence,models the tower and nacelle wakes,and improves the body force projection method based on an anisotropic Gaussian distribution function.For these three improvements,three wind tunnel experiments are used to validate the numerical accuracy of this method.The results show that the numerical results calculated in the far-wake region can reflect the characteristics of typical onshore and offshore wind conditions compared with the experimental results.After modeling the tower and nacelle wakes,the wake velocity distribution is consistent with the experimental result.The radial migration velocity of the tip vortex calculated by the improved blade body force distribution model is 0.32 m/s,which is about 6%different from the experimental value and improves the prediction accuracy of the tip vortex radial movement.The method proposed in this paper is very helpful for wind turbine wake dynamic analysis and wind farm power prediction.     

The effects of turbulence characteristics on sphere drag

Further results are reported in determining the drag coefficient of spheres in terms of the turbulence characteristics of the flow in which they are immersed. C_D contours are given on plots of turbulence scale versus intensity and show distinct regions where artificially low and high drag can be experienced. The results are shown to be in accordance with theory based on published results for flow conditions upstream and downstream of the spheres.

A Strouhal number (St) based on turbulence macroscale and the r.m.s. value of the fluctuating component of axial velocity is shown to be very appropriate in this application.     

Flutter of hanging roofs and curved membrane roofs

This paper presents the determination method of flutter critical wind velocity of hanging roofs and curved membrane roofs of which outer surface only is exposed to wind, and some numerical results for fundamental shape of the roofs are illustrated to make clear the influences of curvatures, materials, size factors and prestressing on this critical velocity, and the dynamic behavior of the roofs subjected to wind. The procedure to formulate the governing equations is on the basis of classical flow theory with vorticities in the boundary layer and in the wake from the trailing edge, and the solution is obtained with Galerkin's procedure.     

两个角区湍流场及其尾迹的实验研究

绕两个翼型－平面的角区流动及其尾迹的实验是在低湍流度风洞中完成的．在零攻角条件下，对翼型－平面的角区流场内诸参数，如翼型表面和平板面上的压力分布、绕翼型及尾迹区内的平均速度、脉动速度、湍动能、二阶关联量ｕ′ｖ′及ｕ′ｗ′进行了广泛的测量．通过对比，分析了这两种模型与平面所构成的角区及其尾迹区内的流动特性