水平轴风力机尾迹流场试验

在水平轴风力机模型不同尖速比条件下,利用旋转单斜丝热线在风轮下游进行尾迹流场速度测量。采用周期性采样和锁相平均技术热线测量技术,获得了风轮下游尾迹三维流场的定量信息,为准确计算风力机的流场、载荷和气动特性等提供了依据。试验结果表明:风轮下游尾迹区内气流存在明显的三维性。尾迹在向风轮下游的发展传播过程中,尾迹中心形成的运动轨迹是与风轮叶片旋转方向相反的螺旋线。尾迹区内的速度亏损随风轮下游轴向位置的增加而减弱,在气流向下游流动的过程中尾迹速度亏损值逐渐衰减,尾迹区的宽度不断扩大,并逐渐与主流掺混融合。尾迹区内相同轴向位置上不同叶高处的速度型相似。在叶片的尾迹区内,流动的紊流强度大大高于周围的非尾迹区,其中紊流强度径向、切向分量较大,轴向分量最小,尾迹区内的紊流具有高度不均匀性。     

水平轴风力机尾迹的测量与分析

在水平轴风力机模型不同尖速比条件下，利用旋转单斜丝热线在风轮下游进行尾迹流场速度测量。采用周期性采样和锁相平均热线测量技术，获得了风轮下游尾迹三维流场的定量信息。实验结果表明：风轮下游尾迹区内气流存在明显的三维性。尾迹在向风轮下游的发展传播过程中，尾迹中心形成的运动轨迹是与风轮叶片旋转方向相反的螺旋线。尾迹区内在气流向下游流动的过程中尾迹速度亏损逐渐衰减，尾迹区的宽度不断扩大，并逐渐与主流掺混融合。在叶片的尾迹区内，流动的紊流强度大大高于周围的非尾迹区，其中径向、切向紊流强度分量较大，而轴向分量紊流强度最小，尾迹区内的紊流具有高度不均匀性。最后，利用CFD软件Fluent6．0对实验风力机的三维流场进行了数值模拟，实验与数值模拟得到了较为一致的结果。图11参10     

水平轴风力机近尾迹流场结构的实验研究

在风洞开口实验段,应用PIV锁相周期采样技术测试风力机近尾迹速度场,通过分析速度场和涡量场,得到近尾迹流场结构特征。近尾迹中存在具有形态特征强烈的叶尖涡结构向下游不断传播。由风轮旋转轴向外,近尾迹的结构组成依次为中央尾迹区、叶尖涡诱导效应区和外部主流区。在叶尖涡诱导效应区内,涡流诱导效应使流场中存在明显的速度增益区和速度亏损区,且增益区和亏损区关于叶尖涡核中心对称。在研究区域内,叶尖涡向下游运动的轴向位移与尖速比成反比,径向位移与尖速比成正比,使叶尖涡诱导效应区影响范围随尖速比的增加径向扩展、轴向缩小。     

水平轴风力机塔筒近尾迹流场PIV实验研究

应用PIV粒子图像测速技术,在风洞中测量水平轴风力机模型塔筒的近尾迹流场。通过对模型风力机在不同运行尖速比下、不同叶高平面内的塔筒近尾迹速度场和涡量场的分析,得到了塔筒近尾迹流场的结构特征,为水平轴风力机气动设计、性能预测及CFD数值模拟提供了依据。实验结果表明,受到风轮旋转效应的影响,在水平轴风力机塔筒下游轴向距离6倍当地弦长范围内,近尾迹在水平面内向一侧明显偏转,近尾迹流场相对塔筒中心轴面呈非对称分布。随着尖速比的减小,塔筒下游轴向距离6倍当地弦长范围内,近尾迹涡流宽度逐渐增大,且尾迹向一侧偏转的程度也越大。风力机叶片对塔筒近尾迹涡流的影响,在叶根部位高度平面内尤为显著,随着叶片高度的增加,叶片对塔筒近尾迹涡流的影响逐渐减弱。     

水平轴风力机尾迹三维流场的热线测量

利用单斜丝热线旋转进行水平轴风力机模型的尾迹流场测量。热线测量过程中采用了周期性采样和锁相平均技术,获得了风轮下游尾迹三维流场的定量信息,并利用自行编制的MATLAB程序求出尾迹流场的三维平均速度。试验结果表明：采用旋转单斜丝热线结合周期性多点采样技术构成的热线测量系统,能够获得风轮流场速度分布等准确的定量信息,是一种比较有效的风力机三维流场动态测试方法。风轮下游的尾迹区内存在速度亏损,速度亏损随着风轮下游轴向位置的增加而减弱。风轮下游4倍弦长外,尾迹区的速度就已经基本恢复到主流速度。在气流向下游流动的过程中尾迹的轴向速度亏损形成的波谷曲线渐趋平缓,尾迹区的宽度不断扩大,2倍弦长以后尾迹宽度基本不再扩大,并逐渐与主流掺混融合。     

水平轴风力机风轮子午面流场结构的实验研究

利用线式互相关PIV系统,采用轴编码器定位周期采样技术,在不同尖速比下对旋转水平轴风力机风轮不同子午面下游流场结构进行测量.分析得到不同条件下的瞬时图、时均图,重点对叶尖涡诱导效应区进行研究.实验结果表明:在风轮下游尾迹中可清晰看到叶轮近尾迹流场中的外部主流区、叶尖涡诱导效应区和中心尾迹区.其中风轮下游尾迹流管廓线是锥形螺旋体;叶尖涡核直径随轴向距离的增加而增大,随着测试方位角的增加,尾迹中各叶片产生的叶尖涡沿螺旋锥形廓线有序地向下游扩散流动;随着尖速比的增加,内部中心尾迹区轴向速度亏损值逐渐增加,并且中心尾迹区的范围逐渐扩大.     

叶片旋向对风力机尾流特性影响的试验研究

采用一种简单、有效的方法来改善风力机尾流效应,提升下游风力机功率。进行叶片旋向对风力机尾流特性的试验研究,利用低频粒子图像测速（PIV）系统对NACA4415翼型的叶片进行扰流流场测试并采集风力机的尾流数据。当2台串列排布的风力机旋向不同时,首先在下游风力机前1D(D为风轮直径)处,叶尖涡涡核位置向中央尾迹区偏移,而外部主流区的流体在叶尖涡诱导区的输运和卷吸作用下持续进入中央尾迹区并与之掺混使得轴向速度恢复得更佳;进而分析下游风力机后1D的流场数据,结果显示：虽然下游风力机叶尖涡几何结构被“打碎”,但涡核能量却未降低;最后探讨影响风力机功率特性的因素,下游风力机入流角的增大促使下游风力机捕获更多风能,在风轮间距为2D时,逆向旋转的功率比比同向旋转时高4.70%,且功率比随间距增加其增幅逐渐减小。     

水平轴风力机尾流特性的数值研究

对600kW单风轮和7倍风轮直径(7D)间距的两风轮水平轴风力机在不同来流风速条件进行三维流场数值模拟.结果显示:风力机下游流场存在三维速度流动,轴向速度在尾迹区存在明显亏损,且随尾迹向下游的发展,轴向速度亏损逐渐减少.不同来流风速条件下风轮尾迹流的发展有一定区别,在来流风速较低的条件下尾流风速恢复较快.风场在布置风力机时应考虑当地的风速条件,若多数情况在额定风速或超过额定风速工况下运行,则前后风轮间距应大于7倍风轮直径;否则可考虑缩短前后风轮间距.     

垂直轴风力机气动特性与涡脱落模态分析

垂直轴风力机运行过程中,叶片上下表面边界层与剪切层的相互作用使风力机下游尾迹形成周期性涡结构,这种尾迹涡结构对风力机空气动力学特性具有重要影响。基于此,该文采用计算流体力学方法对不同工况下垂直轴风力机尾迹涡结构展开研究,利用快速傅里叶变换与相空间轨迹分析不同尖速比下风力机叶片涡脱落现象和尾迹涡结构,并通过分形维数研究转矩与尾迹流场速度变化。结果表明：风力机尾迹涡结构随尖速比变化呈现不同特征,当尖速比为3.6时,风力机尾迹两侧呈规则性反向脱落涡模态;低尖速比垂直轴风力机尾迹具有明显的混沌特性,且随尖速比的增加混沌特性逐渐减弱;随着尖速比的增加,风力机转矩与下游速度分形维数不断降低,且当尖速比为3.6时,风力机下游速度分形维数仅为1.07。     

基于预定涡尾迹法的风力机性能研究

以三叶片水平轴风力机为研究对象,建立了尾迹扩张模型,研究了叶片尾迹流动结构。涡面模型叶片无量纲环量的计算结果与经典环量数据对比,结果吻合较好。计算了根尖涡模型风轮面诱导速度随尾迹扩张系数的变化关系,得出了尖速比对气动性能的影响:推力系数与环量及尖速比成正比;对于不同环量,功率系数存在最佳尖速比。分析了尾迹扩张模型对气动性能的影响:推力系数和功率系数与尾迹扩张系数成正比,尾迹收敛参数对其影响甚微。     

HAWT near‐wake aerodynamics,Part I: axial flow conditions

An improved physical understanding of the rotor aerodynamics of a horizontal axis wind turbine (HAWT) is required to reduce the uncertainties associated with today's design codes. Wind tunnel experiments contribute to increased knowledge and enable validation and construction of models. The present study focuses on the near‐wake of a model HAWT in both axial and yawed flow conditions. At three downstream planes parallel to the rotor plane, single‐sensor hot‐film traverses are made. The phase‐locked unsteady three‐dimensional flow velocity vector is determined by a novel data reduction method. A series of two papers discusses the near‐wake aerodynamics of a model HAWT. The main goals are to obtain a detailed understanding of the near‐wake development and to arrive at a base for model construction and validation. The first paper presents the experimental setup, data reduction and the results for the baseline case (axial flow conditions). In the second paper, the results for the yawed flow cases are presented and the effect of yaw misalignment on the near‐wake development is discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

尾流激振对转子叶片振动应力影响试验研究

利用一台单级风扇试验件,通过对零级导叶尾流参数和转子叶片振动应力的测量,研究了尾流激振强度及叶片振动应力的变化特性,分析了零导安装角和零导与转子之间的轴向间距对转子叶片振动应力的影响。试验结果表明:等转速线上随工况点向失速边界移动时,零导总压损失系数急剧上升,转子叶片振动应力不断增大;打开零导安装角或减小零导与转子之间的轴向间距均能增大下游转子叶片的振动应力。     

Numerical Investigation of the Superimposed Effects on Stator Wake Oscillation in an Axial-radial Combined Compressor ZHAO Ben,YANG Ce,HU Liangjun,ZHOU Mi and ZHANG Jizhong简

The superimposed influences of the blade rows in a multistage compressor are important because different matches of upstream and downstream blades can result in significant differences in the stator wake oscillation. Numerical inves- tigation of the axial stator wake oscillation, which is affected upstream by the axial rotor and downstream by the radial rotor, was performed in an axial-radial combined compressor. Many configurations with different blade numbers and locations, which influence axial stator wake oscillation were investigated. When rotors have equal blade numbers, the axial stator wake oscillates periodically versus time within time T （moving blade passing 1/3 revolution）. In contrast, stator wake oscillates irregularly within T when rotors have different blade numbers. A model-split subtraction method is presented in order to separate the influences of the individual blade rows on the wake oscillation of the axial stator. Analysis from the rotor-stator configuration showed that the unsteady flow angle fluctuation response is caused by the upstream rotor. For the rotor-stator-rotor configuration, the unsteady flow angle fluctuations are influenced by up- and downstream blade rows. With the model-split subtraction method, the up- and downstream influences on the flow angle fluctuation could be clearly separated and quantified. Low amplitudes could be observed when the influences from up- and downstream moving rows were superimposed with the ＂positive peak- negative peak＂ type wave. Clocking investi- gations were carried out to change the relative superimposed phase of influences from the surrounding blade rows in or- der to modulate the amplitudes of the axial stator wake oscillation. However, the amplitudes did not reach the maximum when they were superimposed with ＂positive peak-positive peak＂ type wave due to the impact of the interaction between the two moving blade rows.     

Performance and near wake measurements of a model horizontal axis wind turbine

The performance characteristics and the near wake of a model wind turbine were investigated experimentally. The model tested is a three‐bladed horizontal axis type wind turbine with an upstream rotor of 0.90 m diameter. The performance measurements were conducted at various yaw angles, a freestream speed of about 10 m s ^?1, and the tip speed ratio was varied from 0.5 to 12. The time‐averaged streamwise velocity field in the near wake of the turbine was measured at different tip speed ratios and downstream locations. As expected, it was found that power and thrust coefficients decrease with increasing yaw angle. The power loss is about 3% when the yaw angle is less than 10° and increases to more than 30% when the yaw angle is greater than 30°. The velocity distribution in the near wake was found to be strongly influenced by the tip speed ratio and the yaw angle. At the optimum tip speed ratio, the axial velocity was almost uniform within the midsection of the rotor wake, whereas two strong peaks are observed for high tip speed ratios when the yaw angle is 0°. As the yaw angle increases, the wake width was found to be reduced and skewed towards the yawed direction. With increasing downstream distance, the wake velocity field was observed to depend on the tip speed ratio and more pronounced at high tip speed ratio. Copyright © 2011 John Wiley & Sons, Ltd.     

沿海滩涂风力机近尾流风速分布特性研究

为获得风力机近尾流风速在垂直方向和水平方向的变化规律,提出一种测量风力机近尾流区风速的实测方法。针对某沿海滩涂风电场,采用2台搭载风速仪的无人机对近尾流区进行测量。结果表明：垂直方向,尾流和来流风速比值在1.0D~2.5D处（D为风轮直径）随着高度的增加呈先减小后增大的趋势,在轮毂中轴线处存在最小值0.53~0.68;风速比值沿轮毂中轴线呈非对称分布。0.5D处风速比值分别在上下风轮处存在2个极小值0.56和0.50。水平方向,风速比值在1.0D~3.0D处沿径向距离从左向右呈先减小后增大的趋势,在轮毂中轴线处存在最小值（0.54~0.78）;风速比值沿轮毂中轴线呈对称分布,随着风轮下游距离的增加呈扩张趋势。最后给出用于A类风场风力机下游尾流风速剖面的预测公式。     

Effects of a kind of non-smooth blade on the unsteady flow field at the exit of an axial fan

An experimental investigation of effects of a kind of streamwise-grooved blade on the unsteady flow field at an exit of an axial-flow fan was performed. The flow field at 25% chord downstream from the trailing edge at hub was measured using a fast-response five-hole pressure probe at different mass-flow conditions. The unsteady flow of the grooved blades was compared with that of the smooth blades. The measurement results indicate that： （1） the grooved blades restrain the velocity fluctuation and the pressure fluctuation by modulating the blade boundary layers, which contributes to the flow loss reduction in the hub region and in the rotor wake region at the design condition; （2） the stream-wise grooves play an important role in restraining the radial migration in the blade boundary layer and abating the tip flow mixing, which contributes to the flow loss reduction in the tip region at the design condition; （3） at the near stall condition, the grooved surface can not reduce the flow loss, even increase the loss nearby when the separation happens in the blade boundary layer.     

Comparing rotor plane induction determined from full‐scale measurements and CFD simulations

This paper investigates the flow field in the rotor plane of a full‐scale operating wind turbine using full‐scale light detection and ranging (LiDAR) measurements for the first time. Comparison of the measured flow field with results from large eddy simulations (LES) combined with an actuator line approach is also presented for in‐depth study of the induction field in the rotor plane. The measurements include data from two synchronized LiDAR systems—one scanning the undisturbed upstream inflow field and one measuring in the rotor plane. The standard deviation of the mean of velocity time series are and presented as a measure of reliability. The method for calculating the axial velocity based on the line‐of‐sight velocity is explained and the uncertainty of such method is presented. The process of calculating the yaw misalignment is described. The time‐averaged and phase‐averaged axial velocity and induction factors are presented relative to radius and azimuth, and the general behavior is described relative to the flow regimes around the blades, tower and nacelle. Simulations and measurements are compared with special emphasis on the flow structures in the vicinity of the individual rotor blades. A convincing agreement between measurements and simulations is demonstrated. The uncertainties originated from the imprecise positions and angles of the measurement instruments are shown. The uncertainties are limited to the middle parts of the blades between 15 m to 25 m from the root. In addition, longer selected time series show smaller uncertainties. This proves the reliability of the application of the methodology for even longer time series.