应用BEM理论与嵌套网格技术的风力机性能预测对比研究

分别采用BEM理论和基于嵌套网格技术的CFD方法,以两叶片NREL Phase VI风力机为研究对象,对不同风速下的风力机性能预测进行研究。将两种方法得到的预测结果与实验结果进行对比。结果显示,BEM方法在全风速范围内与实验值吻合良好,嵌套网格技术方法在低风速区能准确地对风力机性能进行预测,并能显示出叶片绕流流场的流动细节,但在高风速区对风力机的性能预测有较大偏差。     

偏航和风切变下风力机气动特性的研究

采用基于滑移网格技术的三维非定常CFD方法,以TJ?REBORG和NREL Phase VI风力机为例,数值模拟轴向均匀来流条件下风力机气动性能的变化规律并与实验值进行比较,确定该方法的可靠性。在此基础上探讨风切变以及偏航条件下水平轴风力机风轮的气动特性,分析其影响规律、叶片旋转平面附近流场中的流动细节及尾迹的变化。     

小翼对风力机气动性能的影响

采用升力面法作为风力机气动性能预测模型对以美国国家新能源实验室NREL Phase VI风力机叶片为原型加装相应小翼的风力机进行气动性能预测与分析。结果表明加装小翼可在提高风力机功率输出的同时有效控制叶片载荷,降低风力机各部件的强度要求从而有效控制风力机各部件成本。     

风剪切来流下风力机叶片表面压力的分布规律

以某33 kW两叶片水平轴风力机的风轮和NREL PhaseⅥ风力机叶片为研究对象,数值模拟得到均匀来流条件下NREL PhaseⅥ风力机叶片表面压力系数的分布规律并与实验值进行对比,验证数值计算方法的有效性。在此基础研究不同风剪切来流对风力机叶片表面压力的影响及风剪切来流下叶片表面压力随方位角的变化规律。结果表明:当风剪切指数由0.3增至0.5时,叶片表面压力在不同方位角下发生不同的变化;剪切来流下,在叶片压力面和吸力面未发生流动分离的区域,压力随方位角呈现正余弦的变化趋势,越靠近尾缘,压力的波动幅度越小;在吸力面压力最小值的位置压力随方位角的波动幅度最大;在叶片吸力面发生流动分离的区域,压力随方位角的波动不稳定;无论是压力面还是吸力面,压力随方位角的变化均存在相位滞后现象,越靠近叶根,滞后现象越明显。     

锯齿尾缘风力机叶片气动及噪声性能研究

为理解锯齿尾缘风力机的气动噪声原理和气动性能,以NREL Phase VI风力机的锯齿尾缘仿生叶片为研究对象,在7 m/s风速工况下,采用分离涡和FW-H方程模拟相结合的方法进行仿真,获得并对比5个叶片展向位置的压力系数和声信号声压指向性。研究表明,在叶片吸力面靠近叶尖的尾缘区域,风力机原型相比于锯齿型出现了明显的分离现象;锯齿型叶片声压级在前缘处较大,尾缘处次之;锯齿结构改变了壁面分离模式,使流场得到改善,降低了风力机噪声的声压级,提高了叶片的气动性能,同时也说明了风力机叶片前缘与尾缘是噪声集中产生的位置。研究结果能够为风力机降噪提供重要的理论依据。     

风力机叶片三维数值计算方法确认研究

采用CFD软件包FINETM/TURBO,以两叶片NREL PhaseⅥ风力机的风轮为对象,进行了风力机风轮叶片三维绕流的定常粘性数值模拟研究。通过详细对比计算结果与实验数据(包括功率、叶片展向5个截面压力系数分布及沿叶展方向载荷系数分布),确认在大部分风速条件下数值模拟可以很好的预计风力机气动性能。然后分析了计算域尺度、边界条件和湍流模型等对数值模拟结果的影响,为采用CFD技术对实际风力机叶片三维气动性能进行精确数值模拟提供参考。     

基于混合笛卡尔网格的风力机问题数值模拟

基于混合笛卡尔网格方法,对S809翼型和Phase VI叶片的绕流问题进行数值模拟研究。计算网格物面附近生成贴体结构网格,其余部分使用笛卡尔网格进行填充,两者之间通过查找"贡献单元"的方法来进行流场信息的传递。计算方法采用低速预处理方法消除可压缩方程在处理低速问题时的刚性,同时结合旋转坐标系方法考虑风力机旋转效应,进行风力机低速问题数值模拟研究。另外,在Phase VI叶片的计算中,通过笛卡尔网格的局部加密来捕捉尾涡。通过与实验数据及他人数值计算的结果进行对比分析,结果表明该文开发的这套基于混合笛卡尔网格的低速求解器能较为准确模拟风力机叶片轴流状态的流场,并能准确捕捉叶尖涡和叶根涡在风力机下游的发展。     

基于尾缘分离模型的风力机独立变桨性能优化

为准确研究风力机高风速非定常气动特性,以NREL Phase VI实验叶片为算例,考虑三维旋转效应和尾缘流动分离现象,建立了Du-Selig三维失速延迟模型与Kirchhoff-Helmholz尾缘分离预估模型耦合的三维尾缘分离预估模型,并与升力面自由涡尾迹法结合,分析了叶片升力面弦向不同涡格数对模拟准确性的影响;基于尾缘分离因子的周向分布规律,通过独立变桨引入风轮旋转半周期的正弦波桨距角增量,抵消相对来流速度变化引起的攻角增大,以优化风力机气动性能.结果表明:升力面弦向采用2涡格的三维尾缘分离预估模型来模拟叶片法向力系数和弦向力系数最为精确;在每个旋转周期内,叶片尾缘分离因子在180°~360°方位角内较大,且在270°达到最大;经独立变桨后,尾缘分离因子得到减小,减小幅度与变桨幅值成正比,且变桨幅值为5°时,叶片主轴扭矩和挥舞力矩达到最佳优化效果.     

基于烟线法的直线翼垂直轴风力机静态流场可视化试验

为探明直线翼垂直轴风力机自起动性能与风力机叶片迎风角度的关系,设计制作了一台具有3枚NACA0018翼型叶片的直线翼垂直轴风力机模型.通过风洞试验测试了直线翼垂直轴风力机在不同风速下自起动性与叶片迎风角度的关系;利用烟线法对风力机的静态流场进行了可视化试验,获得了不同叶片迎风角度下风力机周围流场的流迹线图像;分析了风力机自起动性与叶片翼型、叶片个数、叶片受力情况和周围流场的关系.     

基于改进型升力面自由涡尾迹法的风力机性能研究

为准确模拟风力机高风速偏航工况下的气动特性,以NREL Phase VI实验叶片为算例,考虑叶片旋转导致的失速延迟现象,通过Kirchhoff-Helmholz尾缘分离预估模型与Du-Selig失速延迟模型建立三维尾缘分离预估模型,并与升力面自由涡尾迹法耦合。以更精确预测分离点位置和附着涡诱导速度,讨论叶片弦向布置的涡格数量对计算准确性的影响。对比改进前后的升力面模型模拟叶片在高风速下不同偏航角工况的气动性能,结果表明:改进后升力面模型可大幅提高高风速气动性能预测的准确度,两涡格三维尾缘分离预估模型对法向力系数和弦向力系数的模拟最为精确。     

前缘结节对风力机气动性能影响的数值研究

基于座头鲸的鱼鳍前缘结节的流动特性,开展前缘结节对改造的Phase Ⅵ仿生风力机叶片性能及流动特性影响的数值研究。结果表明：在设计工况下（V_∞=10 m/s）,结节放置在叶片展向81%位置时,叶片根部的回流区域消除,但结节处的旋涡扰动会破坏叶片稳定流动,使叶片性能相对较低。在高风速下（V_∞=15、20、25 m/s）,由于前缘结节的结构特征,叶片表面产生旋涡,发生阻塞作用,叶片吸力侧压力减小,叶片正背面压差增大,升力增大,进而使仿生叶片的性能得到提升。     

高效低载的三维风力机叶片外形优化设计方法

常规风力机叶片的优化设计都是从二维翼型开始的,且翼型总是以升阻比最大为优化目标。然而,二维翼型的升阻比最大和三维叶片的高风能利用率与低气动载荷有本质的不同,采用以往的叶片优化方法常常会在提高风能利用率的同时,使叶片所受的气动载荷也提高。针对这一问题,提出基于多岛遗传算法和动量叶素理论,在给定风况条件下,以加权风能利用率最高与气动载荷最小为目标函数,以叶片各个截面的翼型型线及扭角作为设计变量,对三维叶片开展多目标优化方法设计研究。并对某实际NREL Phase VI叶片进行优化设计,结果表明：在给定风况下相比原叶片,优化叶片在风能利用率提升了3.06%的基础上,叶根弯矩降低了11.68%。在变转速与变风况下,优化叶片的气动效率整体提升,叶根弯矩明显降低。     

Computational aerodynamic analysis of a blunt trailing‐edge airfoil modification to the NREL Phase VI rotor

The effects of modifying the inboard portion of the experimental NREL Phase VI rotor using a thickened, blunt trailing‐edge (or flatback) version of the S809 design airfoil are studied using a compressible, three‐dimensional, Reynolds‐averaged Navier–Stokes method. A motivation for using such a thicker airfoil design coupled with a blunt trailing edge is to alleviate structural constraints while reducing blade weight and maintaining the power performance of the rotor. The numerical results for the baseline Phase VI rotor are benchmarked against wind tunnel measurements obtained at freestream velocities of 5, 7 and 10ms^?1. The calculated results for the modified rotor are compared against those of the baseline rotor. The results of this study demonstrate that a thick, blunt trailing‐edge blade profile is viable as a bridge to connect structural requirements with aerodynamic performance in designing future wind turbine rotors. Copyright © 2007 John Wiley & Sons, Ltd.     

大粗糙度弦向分布对风力机气动性能影响

针对5 mm大尺度蚊虫尸体在叶片上的附积问题,采用带转捩的k-ω SST湍流模型,以NERL Phase VI风力机为研究对象,从不同弦向覆盖位置入手,对大粗糙度下风力机气动性能进行数值模拟。研究结果表明,粗糙度对风力机整体做功具有较大影响,粗糙度越大效率降低越显著;粗糙度使在叶片靠近叶尖位置的吸力面促成小型低压涡,转捩提前;该效应在大尺度粗糙条件下表现明显,附着涡强度也更大;在叶片压力面添加75%c粗糙度会使翼型产生的气动损失最大。     

风力机叶片制造误差对功率和推力影响的量化研究

为量化叶片制造误差对风力机功率和推力的影响,以NREL Phase VI S809风力机叶轮为研究对象,基于区间分析法和修正叶素动量理论,建立风力机不确定气动响应模型,量化弦长扭角制造误差对功率和推力影响的相对波动幅度,采用极差分析法进行敏感性分析,获得不确定影响敏感位置。结果表明,叶片扭角误差对性能影响更为显著;当弦长误差和扭角误差为±0.02c和±0.6°时,功率和推力最大相对波动达到3.26%和8.09%;弦长误差影响敏感位置为叶根,而扭角误差敏感位置为叶尖,可在此部位施加质量参数要求以控制性能偏差。     

风力机叶片三维效应翼型气动参数修正研究

以NREL Phase VI风力机为研究对象,对低雷诺数下叶片三维效应翼型气动参数修正进行研究。通过三维CFD数值模拟与二维翼型风洞实验,比较和检验现有的Snel、Lindenburg、Du&Selig、Chaviaropoulos&Hansen这4种修正公式。结果显示修正效果明显不同,以Du&Selig修正公式效果最佳,但它在叶尖和叶根部位的修正误差较大,而且随着尖速比的减小,叶片上的修正值与三维CFD结果吻合的区域减小,尤其不适合负攻角流动的修正。     

Influence of microcylinders with different vibration laws on the flow control effect of a horizontal axis wind turbine

Due to the flow separation on the blade of the NREL Phase VI wind turbine, a new flow control technique involving installation of an off‐surface vibrating small structure is proposed. By considering the actual flow condition, fluid‐solid coupling is applied in which two kinds of microcylinder vibration modes are set up, and the aerodynamic performance is numerically studied. The influence of the vibration modes, amplitude, and frequency of the off‐surface vibrating small structure on the aerodynamic performance is explored. For various stall conditions, the flow separation can be well suppressed by utilizing a suitable vibrating microcylinder rather than a static microcylinder. In addition, the vibrating microcylinder shows a noticeable suppression effect on large flow separation. Both the vibration direction and vibration amplitude play leading roles in the improvement of the aerodynamic performance, and a microcylinder with a high vibration frequency can more quickly suppress surface flow separation to achieve an optimum aerodynamic performance than a microcylinder with a low vibration frequency. By setting microcylinders with suitable vibration rules close to the blade surface, the wind energy coefficient can be obviously increased compared with those obtained when adding a static microcylinder or without microcylinder addition.     

Estimating the angle of attack from blade pressure measurements on the NREL Phase VI rotor using a free wake vortex model: axial conditions

Blade element momentum (BEM) methods are still the most common methods used for predicting the aerodynamic loads during the aeroelastic design of wind turbine blades. However, their accuracy is limited by the availability of reliable aerofoil data. Owing to the 3D nature of the flow over wind turbine blades, the aerofoil characteristics will vary considerably from the 2D aerofoil characteristics, especially at the inboard sections of the blades. Detailed surface pressure measurements on the blade surfaces may be used to derive more realistic aerofoil data. However, in doing so, knowledge of the angle of attack distributions is required. This study presents a method in which a free wake vortex model is used to derive such distributions for the NREL Phase VI wind turbine under different operating conditions. The derived free wake geometry solutions are plotted together with the corresponding wake circulation distribution. These plots provide better insight into how circulation formed at the blades is eventually diffused into the wake. The free wake model is described and its numerical behaviour is examined. Copyright © 2006 John Wiley &Sons, Ltd.     

Investigating the influence of dimensional scaling on aerodynamic characteristics of wind turbine using CFD simulation

Wind turbines are used in a variety of applications with different performance requirements. Investigating the influence of scaling on wind turbine characteristics can pave the way to utilize the experience gained from a smaller turbine for a larger one. In this paper, the effects of wind turbine size on aerodynamic characteristics of a rotor blade are examined using CFD simulation. NREL phase VI wind turbine rotor was simulated in order to validate the results and ensure the accuracy of the CFD model. A 2 MW wind turbine was then chosen as a large turbine and a scaled down model of its rotor was simulated numerically. The results of the simulation were introduced to Similarity Theory relations in order to predict the aerodynamic characteristics of the 2 MW wind turbine. The 2 MW turbine was also simulated and the results of the simulation were compared to predictions of Similarity Theory. It was observed that the results of the simulation completely follow the values predicted by Similarity Theory. Both Similarity Theory predictions and simulation results demonstrated that the torque increases with the cube of change in rotor diameter whereas the thrust value and aerodynamic forces grow with the square of change in diameter.