极端台风下停机姿态对海上风力机叶片气动载荷影响

基于计算流体力学(CFD)方法,选取美国可再生能源实验室(NREL)5 MW风力机叶片主要设计参数,重点研究台风风速大于切出风速(风力机停机)时,不同台风入射风向及不同叶片停机桨矩角对风力机叶片气动载荷的影响特征,揭示最不利叶片停机姿态及对应风载系数;进一步对比分析可能出现的最不利叶片变桨故障停机工况与正常顺桨矩停机工况下的风力机气动载荷的特征,提出2种停机姿态下海上风力机最大安全设计风速的对应建议值。     

风力机变桨故障叶片载荷特征及仿生分形与原始结构对比研究

为探究切出风速下风力机变桨故障叶片的载荷及动力学特征,利用FAST软件进行数值计算,发现载荷及叶尖位移分别为变桨成功叶片的13.6和14.2倍,可知变桨故障叶片极可能发生结构失效断裂事故。为改善结构力学性能,提出结合仿生方法及分形理论的新构型叶片,并通过有限元分析与原始叶片进行对比,其中载荷边界条件来自以数据库方式存储FAST计算结果的叶片17段载荷数据。结果表明：仿生分形叶片重量及叶尖位移分别比原始叶片减少23.4%和19.7%;同时,结构屈曲分析显示,仿生分形叶片一阶屈曲因子为1.858,比原始叶片提高33.6%,极大增加了叶片结构安全性。     

垂直轴风力机流场主动控制方法研究

针对垂直轴风力机叶片攻角连续性变化导致的非稳定流动,提出一种改善叶片攻角的主动变桨控制方法。首先通过实验验证数值模拟方法的可行性及有效性,其次对变桨控制前后风力机流场进行二维数值模拟,得到风力机在不同变桨条件下的气动特性及流场结构,计算结果表明:变桨控制可使叶片在不同方位角下处于更合适的攻角,进而获得较优的气动性能,变桨控制后的风能利用系数有所增加。随着最大变桨角度的增加,风能利用系数先增大后减小,最大可提高33.2%,同时主动变桨可抑制叶片尾缘流动分离,使得叶片尾涡耗散轨迹更贴合风轮旋转圆周。从而降低转矩系数波动幅值,提高风力机运行寿命。     

减小风力机1P气动载荷和3P气动转矩脉动的独立变桨距控制策略研究

为研究风切变和塔影效应对三叶片风力机气动载荷、气动转矩以及输出功率的影响,根据风切变和塔影效应的风速模型,引入等效风速模型,推导分析风力机1P(P为风轮旋转频率)气动载荷和3P气动转矩脉动的形成机理,并基于GH Bladed仿真平台验证这2种脉动的存在性。为减小这2种脉动对风力机产生的影响,基于变桨控制,设计带通滤波器过滤出风力机输出功率的3P脉动分量,并结合方位角信号将其转换为每支叶片的桨距角调节信号,与统一变桨控制的桨距角参考信号叠加,实现基于输出功率和方位角联合反馈的独立变桨距控制。仿真结果表明,所提独立变桨距控制策略不仅能有效缓解风力机1P叶根挥舞载荷脉动,还能明显减小气动转矩和输出功率的3P分量,从而在减小风轮疲劳载荷的同时提高风电机组输出电能质量。     

新型随动变桨垂直轴风力机气动性能的数值分析

文中研究目的是开发一种使垂直轴风力机自启动能力强、风能利用率高的随动变桨技术,此变桨技术的原理是在不需添加任何外加动力的情况下,利用风力机主轴旋转的同时带动风力机叶片的旋转,且保持主轴的旋转角速度是叶片旋转角速度的2倍。通过运用数值模拟的方法,得到了该新型随动变桨垂直轴风力机的气动参数值及特点;并分别将其与传统垂直轴风力机、理想直叶片垂直轴风力机的气动参数进行了对比分析,分析结果表明:新型随动变桨垂直轴风力机的气动性能优于其它两种类型风力机。     

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.     

台风作用下近海风力机叶片的空气动力载荷研究

结合2005年0518号台风"Damrey"的实测时程数据,参考美国可再生能源实验室5 MW风力机主要设计参数,重点研究台风作用下近海风力机叶片的空气动力载荷特征。首先,鉴于完整台风实测数据跨越时间较长,且风速和风向变化具有显著的时段特征,因此科学截取一段具有代表性的3 h台风风速-风向时程数据。其次,综合考虑5 MW风力机叶片主要截面翼型设计参数和变速变桨控制系统,基于叶素动量(BEM)理论模拟分析代表性台风时程下风力机叶片的空气动力载荷特征,并将该数值模拟结果与相关简化计算结果进行对比分析,揭示风力机变速变桨控制系统的时滞性对台风作用下叶片空气动力载荷的重要影响。最后,进一步研究风力机停机状态下的叶片台风载荷特征,建议在台风作用下采用主动顺桨叶停机策略,以实现降低叶片气动载荷保证风力机主体结构安全的目的。     

低空急流条件下水平轴风力机风轮气动特性的研究

为阐明低空急流条件下风力机风轮的气动特性,基于工程化的边界层风速模型和Von Karman谱模型建立不同来流的脉动风场,对比研究低空急流条件下NREL 5 MW风力机风轮的输出功率和气动载荷的变化规律。结果表明:如果仅以轮毂高度处的风速作为风力机变桨控制的依据,与均匀来流和剪切来流相比较,低空急流条件下,虽然来流风功率明显增大,但风轮的输出功率在较高风速时反而减小;风轮所受的不平衡气动载荷,包括横向力、纵向力、偏航力矩和倾覆力矩在较高风速时小于剪切来流的结果;且仅以轮毂高度处的风速预测得到的风轮输出功率高于实际结果,其最大相对误差为89.4%。因此,低空急流条件下,为提高风能利用率和风轮输出功率的预测精度,应考虑不同高度位置处的风速大小对风力机进行变桨控制和功率预测。     

新型变桨立轴风力机涡效应分析

该文旨在通过变桨来改善升力型立轴风力机叶片气动特性,提高风力机最大运行效率。针对设计尖速比下风能利用系数较低的问题,提出减小叶片小攻角范围,增大叶片大攻角工作范围,以重点改善叶片低性能区域的气动特性为出发点,提高风能利用系数新变桨思路。以采用NACA0012翼型、2 m高和2 m旋转直径的两叶片H型风力机为研究对象,从涡理论来分析和比较在最佳尖速比为5的条件下,附着涡、尾随涡、脱体涡和桨距角对攻角、切向力和功率输出的影响规律。研究结果表明:变桨后,叶片的攻角、切向力和输出功率在原最大值两侧均有明显提高,拓宽了叶片高性能的工作区域;涡系中脱体涡对叶片气动特性影响最大,其中在上盘面影响较小,在下盘面影响较大;变桨前后涡系对上盘面的差异较小,对下盘面的影响差异较明显;变桨后,下盘面的叶片的涡尾迹弯曲程度在加大。     

基于ONERA模型的柔性叶片气弹稳定性研究北大核心CSCD

为了探究大型风力机柔性叶片在挥舞-摆振耦合作用下的气弹稳定性,文章基于ONERA非线性气动模型建立了包括二维翼型非线性气动升阻力方程及其挥舞-摆振耦合运动方程的气弹模型。利用该气弹模型计算得到NREL 5 MW风力机叶中段DU35-A17翼型在叶片变桨前后的挥舞、摆振变形量变化曲线,并与FAST计算结果进行比较,以验证气弹模型的准确性。结果表明:在额定工况时,叶片出现z轴正方向、y轴负方向的弯曲变形;风力机未变桨时,挥舞、摆振变形量会随风速增大而增大;叶片变桨后,挥舞、摆振变形量会比额定工况下的变形量有所减少。由于计算得到的挥舞、摆振变形量曲线是收敛的,故叶片是气弹稳定的。该气弹模型为评估大型风力机柔性叶片气弹稳定性提供了新方法,计算得到的挥舞摆振位移数据为优化风力机结构参数、提升叶片气弹稳定性提供了数据参考。     

Localization of wind turbine noise using a microphone array in wind tunnel measurements

An experimental investigation on scaled wind turbine models in a wind tunnel with a microphone array is presented. Our study focuses on the localization and quantification of aerodynamic noise sources on rotating wind turbine blades with the aim of identifying the contributing factors that have an impact on the source spectra. Therefore, wind tunnel measurements were conducted for three different blade geometries (NACA 4412 shape, Clark-Y shape, and sickle shape), five pitch angles between ?2° and +8° and five wind velocities between 5 and 13 ms^??1. For the localization of rotating sound sources with a microphone array, a rotating beamforming method based on the acoustic ray method is used. The Clean-SC deconvolution method was used to improve the resolution of the acoustic sources, and integrated spectra were calculated for the individual blades. The sound sources were localized at the wind turbine blades and assigned to the leading edge and trailing edge subregions. The results show a high dependency on the sound source distribution and the source strength with regard to the observed one-third octave bands, wind velocity, and blade geometry. Hence, the localization of rotating sound sources with a microphone array is a suitable method for the development of wind turbine blades that emit less noise.     

Dynamic response analysis of wind turbines under blade pitch system fault,grid loss,and shutdown events

This study focuses on the dynamic responses of land‐based and floating wind turbines under blade pitch system fault and emergency shutdown conditions. The NREL 5 MW turbine is studied. A hydraulic pitch system is considered, and the faults under study are events with a seized blade or a blade running out of control. Emergency shutdown is defined as a fast pitch‐to‐feather maneuver of the blades. Load cases with power production and grid fault with ensuing shutdown are also analysed for comparison. The fault scenarios and the blades' fast pitching activity are simulated using HAWC2 through external Dynamic Link Libraries. On the basis of the time‐domain simulations, the response characteristics of the land‐based and the floating turbines in the four design load cases are compared. The load effects from the fault conditions are compared with the operational cases. Strong system dynamics and resonant responses, such as the tower elastic mode and the yaw resonant response, are elicited during shutdown. If the pitch system has a fault and one blade is hindered from normal pitching, the uneven load distribution of the blades leads to large structural and motion responses. For both turbines, the response maxima vary cyclically with the instantaneous azimuth when the blades start pitching to feather. For the floating wind turbine, the interaction of waves and wind also affects the results. The effect of the pitch rate during shutdown is analysed. The responses of the land‐based turbine in grid loss and shutdown conditions are proportional to the pitch rate, whereas decreased sensitivity is found in the cases with pitch system faults. For the floating turbine, the effect of the pitch rate is small, and reduced pitch and yaw motion extremes are observed as the pitch rate increases. Copyright © 2013 John Wiley & Sons, Ltd.     

风力机叶片覆冰状态监测基准值与分级诊断标准研究

以2 MW风力机为研究对象,基于实际风力机状态(SCADA)系统大数据,选取叶片正常状态和覆冰状态下的风速、功率、桨距角和偏航角数据,采用核密度-均值数据处理方法,得到叶片覆冰状态监测基准值及其定量表达式。同时,根据叶片不同覆冰时期桨距角和功率值随风速的变化情况,提出叶片覆冰状态分级诊断标准。应用结果表明,根据桨距角随风速的变化情况可判断在叶片覆冰过程中机组最大功率追踪情况以及气动性能损失情况,根据风速-功率值分布情况可较准确地判别叶片的覆冰状态。     

Modelling the aerodynamics of vertical‐axis wind turbines in unsteady wind conditions

Most numerical and experimental studies of the performance of vertical‐axis wind turbines have been conducted with the rotors in steady, and thus somewhat artificial, wind conditions—with the result that turbine aerodynamics, under varying wind conditions, are still poorly understood. The vorticity transport model has been used to investigate the aerodynamic performance and wake dynamics, both in steady and unsteady wind conditions, of three different vertical‐axis wind turbines: one with a straight‐bladed configuration, another with a curved‐bladed configuration and another with a helically twisted configuration. The turbines with non‐twisted blades are shown to be somewhat less efficient than the turbine with helically twisted blades when the rotors are operated at constant rotational speed in unsteady wind conditions. In steady wind conditions, the power coefficients that are produced by both the straight‐bladed and curved‐bladed turbines vary considerably within one rotor revolution because of the continuously varying angle of attack on the blades and, thus, the inherent unsteadiness in the blade aerodynamic loading. These variations are much larger, and thus far more significant, than those that are induced by the unsteadiness in the wind conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

风力机叶片动态气弹变形及其对整机性能的影响

基于风力机整机刚柔耦合模型,文章提出了一种叶片动态气弹扭转变形分析的新方法。该方法采用SIMPACK和AeroDyn软件联合数值仿真对风力机在几种恶劣风况下进行动力学分析,通过对分析结果的变换处理,进而得到叶片在复杂工况下的动态气弹变形数据。采用该方法,重点分析了叶片气弹扭转变形对风力机气动功率及气弹稳定性的影响。该方法为大型风电叶片的气弹特性评价以及气弹剪裁设计提供了一种新的技术手段。     

垂直轴风力机两种翼型气动性能比较研究

叶片是风力机最重要的组成部分,在不同的风能资源情况下,翼型的选择对垂直轴风力机气动特性有着重要的影响。文章分别以NACA0018翼型(对称翼型)和NACA4418翼型(非对称翼型)建立3叶片H型垂直轴风力机二维仿真模型。应用数值模拟的研究方法,从功率系数、单个叶片切向力系数等方面比较两种风力机模型在不同叶尖速比下的气动特性,并采用风洞实验数据验证了流场计算的准确性。CFD计算结果表明:在低叶尖速比下,NACA4418翼型风力机气动特性优于NACA0018翼型风力机,适用于低风速区域;在高叶尖速比下,NACA0018翼型风力机气动特性较好,适用于高风速地区。而且在高叶尖速比时,NACA0018翼型在上风区时,切向力系数平均值要高于NACA4418翼型,在下风区时,NACA418翼型切向力系数平均值高。该研究可为小型垂直轴风力机翼型的选择提供参考。     

小型变桨距风力机的气动优化设计

基于叶素动量理论分析了小型风力机的气动性能分析模型,并提出了叶片的气动优化设计方法.结合叶片制造和应用中的实际要求,设计了10 kW小型变桨距风力机叶片的气动外形.计算结果表明,设计叶片具有良好的气动性能,验证了该设计方法有效实用.     

Aerodynamic characteristics of wind turbine blades with a sinusoidal leading edge

The aerodynamic characteristics of a kind of bionic wind turbine blades with a sinusoidal leading edge have been investigated in this paper based on a three‐dimensional Reynolds‐averaged Navier–Stokes simulation. The calculated results show that compared with a straight leading‐edge blade, the new‐type blade has a great improvement in shaft torque at high wind speeds. The localized vortices shedding from the leading‐edge tubercles, which can generate a much greater peak of the leading‐edge suction pressure than that from the straight leading‐edge case, are the physical essentials to enhance the wavy blade's aerodynamic performances as the blade goes into stall. In particular, the outboard segment from the 60%R station to the blade tip is the key region for wavy leading‐edge blades to improve the aerodynamic characteristics at high‐speed inflows. In this key region, a wavy blade can obtain a greater power output as the wavelength l and the waveheight δ increase. The present numerical results also show that the wavy leading‐edge shape is unfavorable for a wind turbine blade under the design conditions (e.g., at the rated wind speed). At these conditions, an early boundary‐layer separation as a result of the geometric disturbances of the leading‐edge tubercles will inevitably result in a visible shaft‐torque reduction in the wavy‐blade cases. Anyway, the wavy blades still tend to generate a more robust power output as a whole from 10 to 20 m s ^?1 than the original NREL phase‐VI blade. Copyright © 2011 John Wiley & Sons, Ltd.     

Simulating the aerodynamic performance and wake dynamics of a vertical‐axis wind turbine

The accurate prediction of the aerodynamics and performance of vertical‐axis wind turbines is essential if their design is to be improved but poses a significant challenge to numerical simulation tools. The cyclic motion of the blades induces large variations in the angle of attack of the blades that can manifest as dynamic stall. In addition, predicting the interaction between the blades and the wake developed by the rotor requires a high‐fidelity representation of the vortical structures within the flow field in which the turbine operates. The aerodynamic performance and wake dynamics of a Darrieus‐type vertical‐axis wind turbine consisting of two straight blades is simulated using Brown's Vorticity Transport Model. The predicted variation with azimuth of the normal and tangential force on the turbine blades compares well with experimental measurements. The interaction between the blades and the vortices that are shed and trailed in previous revolutions of the turbine is shown to have a significant effect on the distribution of aerodynamic loading on the blades. Furthermore, it is suggested that the disagreement between experimental and numerical data that has been presented in previous studies arises because the blade–vortex interactions on the rotor were not modelled with sufficient fidelity. Copyright © 2010 John Wiley & Sons, Ltd.