风力机叶片挥舞摆振气弹失稳分析

为避免风机叶片在强风作用下发生破坏,需对其采取停机保护措施。该文研究叶片处于非旋转状态时的挥舞摆振气弹失稳现象发生的条件。基于风力机叶片简化模型,采用迭代法求解叶片的自振频率及振型,建立了非旋转叶片挥舞摆振气弹效应响应的振型叠加法,该方法可以便捷地进行叶片多工况气动弹性响应分析。计算了在不同风速不同攻角条件下叶片的挥舞摆振气弹效应响应,得到了叶片挥舞摆振响应随风速和风攻角的变化规律以及不稳定风攻角的分布特征。结果表明:在某些风攻角下,风机叶片挥舞摆振失稳现象在风速较低的情况就有可能发生,其响应幅值与结构阻尼联系紧密。另外,挥舞摆振失稳会大大增加作用于叶片上的风荷载,并进一步造成叶片结构的损伤破坏。     

考虑叶片离心刚化效应的风力机塔架风振反应分析

为分析风轮作用力和叶片刚化对风力机塔架风振反应的影响,研究了考虑叶片刚化效应时风力机塔架的风振反应。采用谐波叠加法模拟了风力机塔架和叶片的脉动风速时程,在理论上推导了考虑离心刚化效应的叶片振动方程。该文分3种工况计算了叶片与塔架在风荷载作用下的动力反应,并对比了3种工况的塔架顶点位移及其相对误差。结果分析表明:叶片剪力对塔架的动力反应影响较大,叶片刚化效应减小了塔架的风振反应,在动力计算过程中应考虑刚化效应的影响。     

考虑风速分布的叶片MPC气弹控制

作为叶片失效的重要原因,颤振一直是风电领域研究重点。以抑制叶片工作过程中的颤振为目的,建立分析模型时应充分考虑实际风速分布特别是风切变和塔影效应对叶片振动的影响,并在离散化后求取平均输入风速。针对小型风力机叶片气动弹性稳定性问题进行综合分析,根据实体结构建立叶片气弹模型,考虑非线性气动力作用时叶片大攻角、大风速工况下产生的高频、高幅失速颤振,模拟典型截面仿真振动位移。通过模型预测控制的滚动优化和误差矫正控制叶片挥舞、摆振两个运动方向的振动频率和幅值,结果表明振动形式实现控制后可在短时间内达到稳定且静差可接受。     

A computational procedure for prebending of wind turbine blades

Prebending of wind turbine blades constitutes a viable engineering solution to the problem of tower clearance, that is, ensuring that during wind turbine operation there is sufficient distance between the rotor blades and the tower to avoid collision. The prebent shape of the blade must be such that when the turbine rotor is subjected to wind and inertial loads, the blades are straightened into their design configuration. In this paper, we propose a method for accurate prediction of the prebent shape of wind turbine blades. The method relies on a stand‐alone aerodynamics simulation that provides the wind loads on a rigidly spinning rotor, followed by a series of structural mechanics simulations to determine the stress‐free prebent shape of the blade. This procedure involves only one‐way coupling between the fluid and structural mechanics, which avoids the challenges of solving the coupled fluid–structure interaction problem. The proposed methodology, which has no limitations on the blade geometry and structural modeling, is successfully applied to prebending of a 63‐m offshore wind turbine blade. Copyright © 2011 John Wiley & Sons, Ltd.     

叶片局部损伤对大型水平轴风力机静动态特性影响的仿真分析

基于参数化整机模型研究风力机的静态和动态特性,以及叶片局部损伤对单叶片和整机的静动态特性影响规律,揭示叶片局部损伤与这些特性的关系。使用ANSYS的APDL语言,实现MW级水平轴风力机复合材料叶片的参数化建模;采用公共几何元素、连接单元和自由度耦合等方法,组建包含叶片、轮毂、塔架等部件的整机有限元模型。计算分析了重力、离心力和风压力共同作用下正常整机和包含叶片局部损伤的整机在迎风位置时的静态响应。比较了正常和损伤状态下根部固定单叶片和装入整机中叶片的动态应变响应。研究表明:对根部固定的单叶片,风轮面内的动态应变响应随迎风面损伤程度的增大而减小;对整机中的叶片,垂直风轮面的动态应变响应随迎风面损伤程度的增大而增大。研究方法和结论对大型水平轴风力机叶片损伤的在线监测具有重要 意义。     

Aerodynamic design and analysis of a 10 kW horizontal-axis wind turbine for Tainan,Taiwan

The purpose of the present study is to develop a small-scale horizontal-axis wind turbine (HAWT) suitable for the local wind conditions of Tainan, Taiwan. The wind energy potential was first determined through the Weibull wind speed distribution and then was adapted to the design of the turbine blade. Two numerical approaches were adopted in the design and analysis of the HAWT turbine blades. The blade element momentum theory (BEMT) was used to lay out the shape of the turbine blades (S822 and S823 airfoils). The geometry of the root region of the turbine blade was then modified to facilitate integration with a pitch control system. A mathematical model for the prediction of aerodynamic performance of the S822 and S823 airfoils, in which the lift and drag coefficients are calculated using BEMT equations, was then developed. Finally, computational fluid dynamics (CFD) was used to examine the aerodynamic characteristics of the resulting turbine blades. The resulting aerodynamic performance curves obtained from CFD simulation are in agreement with those obtained using BEMT. It is also observed that separation flow occurred at the turbine blade root at the tip speed ratios of 5 and 7.     

In Situ Detection of Turbine Blade Vibration and Prevention

Turbine blades are the most critical components in any power plant. Failure in even one rogue blade out of hundreds of blades fixed on the rotor leads to colossal damage to the machine. Statistics have shown that low-pressure turbine blades in steam power plants are generally more susceptible to failure compared to high- or intermediate-pressure blades. The mechanism of failures is different in each case and is generally very complex. As a result, a large number of blade failures are not fully understood. Two primary forces acting on the blades are the steady centrifugal force due to rotation and the fluctuating steam bending force. In view of no direct access to monitor the health of the blades through vibration or other means, indirect method using non-contacting probes have been attempted and some are in use in special cases. Largely these methods are expensive and intrusive in nature. They involve placing of sensors in the narrow space inside the turbine casing, routing special signal cables with sealing arrangement and involves difficulties in analyzing shot duration signals from each rotating blades. Unless a diagnostic technique is made simple to implement and whose reliability is proven, power plants will not find it attractive to invest on upgrade for safe operation of the machine. This article is about an innovative method of detecting the presence of blade vibration in operating turbine through vibration signal analysis and prevention through process control. The method is based on vibration analysis of the turbine casing. The casing vibration includes signals associated with the blades of different stages called as blade passing frequency (BPF). When the rotating blades vibrate, the analysis of changes in the BPF is a novel way of diagnosing blade vibrations. Signals captured from operating plants have been analyzed and blade vibrations have been detected and verified with Campbell diagram. Laboratory experiments were carried out on a rotating fan to demonstrate robustness of the diagnostics tool for turbine blades.     

混流式水轮机转轮叶片流激振动分析

结合小变形弹性理论和不可压缩粘性流体的最大功率耗散原理构造流体-叶片系统的功率泛函,通过广义变分原理建立了混流式水轮机转轮叶片在非定常湍流场中考虑流体-结构相互作用(FSI)的有限元模型,计算叶片在FSI情况下的流激振动。数值计算采用分离迭代格式,流动用大涡模拟(LES),叶片振动用直接积分法。试验模型以某型水轮机为原型设计制作,在一片叶片的正面和负面上分别装有5只Kulite的压力传感器,在另一片叶片上装有3只微加速度传感器。计算得到的叶片自振频率、频谱曲线以及加速度时程与试验实测结果是吻合的。     

Non-linear dynamic analysis of a wind turbine blade

ABSTRACT

Wind turbine blades’ dynamic behavior must be well investigated during the design process in order to avoid resonance. Modal analysis and nonlinear dynamic analysis of a rotating wind turbine blade are presented in this paper to study the effects of rotation speed on the natural frequencies and displacements. Accordingly, an enhanced finite element formulation based on uncoupled translational and rotational displacements’ kinetic energy was developed. A twisted wind turbine blade was discretized using beam elements with different cross sections; each has six degrees of freedom per node. At rest, the model results were validated using ABAQUS software. Furthermore, the effects of geometrically non-linear phenomena produced by blade displacement on the vibration characteristics of the rotating blade have been discussed. The blade non-linear problem was solved by applying the Newmark method combined with the Newton-Raphson schema. Results show that the blade natural frequencies and displacements increase under angular rotation speed augmentation. This work highlights the significant sensitivity of the blade vibration characteristics to the geometric non-linearity. Accordingly, a modal and a linear analysis are insufficient to precisely estimate the dynamic behavior of a rotating turbine blade.     

预应力装配式风机叶片连接段结构模拟分析

随着风力发电机功率提高,其叶片越来越长,叶片的运输难度和风险增大,成本增高,特别是在山区风场建设中愈发明显。将长叶片分段制造、运输并现场组装是解决此问题的有效途径。该文提出了一种全新的基于高强预应力螺栓连接的装配式风力发电机叶片结构方案。以某兆瓦级玻璃纤维叶片为对象,确定了在离叶根16 m处进行分段时的预应力连接结构方案,利用大型有限元分析软件ABAQUS建立了连接段的精细化有限元模型,对模型在预应力以及挥舞和摆振方向4种设计荷载作用下的应力进行了分析。结果表明:在4种工况下的叶片玻璃纤维材料以及预应力连接螺栓强度均满足要求,验证了该文所提出的基于高强预应力螺栓连接的装配式风机叶片结构方案可行,该研究为解决传统风力发电机叶片的运输难题提供具有应用前景的新方法。     

Finite element analysis with an improved failure criterion for composite wind turbine blades

Some interesting studies are made in this paper on the life management of a composite wind turbine blade. It presents the details of finite element modeling and validation, blade response under service loading conditions, power coefficient evaluation for the optimum design parameters of the blade configuration, development of failure envelope and fatigue life estimations. Finite element analysis results are found to be in good agreement with existing test results on a typical composite blade configuration. The failure envelope generated from the present modified failure criterion correlates well with the test results on different composite materials. The procedure adopted in this paper can be utilized for optimum design of large size composite wind turbine blades.     

复合材料风电叶片避雷防护研究进展

复合材料风电叶片作为风力发电机组的一个重要组成部件,一旦受雷击损坏,经济损失巨大。因此对风力叶片避雷防护的研究越来越受到人们的关注。本文主要分析了风力叶片受雷击后的几种损伤形式和损伤机理,还总结了目前常用的几种避雷接收器的形式,并对国外在叶片避雷防护方面的研究进展进行了介绍。     

风力机叶片挥舞—摆振气弹稳定性分析

根据Euler-Bernoulli梁理论和粘弹性材料的Kelvin-Voigt理论建立风力机叶片挥舞—摆振耦合非线性动力学方程。将位移视为静态位移和动态位移的叠加,进而将非线性动力学方程线性化为动态位移的线性方程,得到叶片耦合振动特征方程。使用基于加权残值的Galerkin方法求解特征方程,分析叶片气弹稳定性,讨论风速、安装角、耦合效应和材料阻尼对叶片颤振稳定性和非线性自激振动行为的影响。结果表明:摆振方向易出现不稳定振动,通过设置安装角,利用挥舞—摆振耦合可以控制不稳定振动,但当安装角太大时,挥舞—摆振耦合会引起不稳定振动。     

Vibration based damage detection of rotor blades in a gas turbine engine

This paper describes the problems concerning turbine rotor blade vibration that seriously impact the structural integrity of a developmental aero gas turbine. Experimental determination of vibration characteristics of rotor blades in an engine is very important from fatigue failure considerations. The blades under investigation are fabricated from nickel base super alloy through directionally solidified investment casting process. The blade surfaces are coated with platinum aluminide for oxidation protection. A three dimensional finite element modal analysis on a bladed disk was performed to know the likely blade resonances for a particular design in the speed range of operation. Experiments were conducted to assess vibration characteristics of bladed disk rotor during engine tests. Rotor blade vibrations were measured using non-intrusive stress measurement system, an indirect method of blade vibration measurement utilizing blade tip timing technique. Abnormalities observed in the vibration characteristics of the blade tip timing data measured during engine tests were used to detect the blade damage. Upon disassembly of the engine and subsequent fluorescent penetrant inspection, it was observed that three blades of the rotor assembly were identified to have damaged. These are the blades that exhibited vibration abnormalities as a result of large resonant vibration response while engine tests. Further, fractographic analysis performed on the blades revealed the mechanism of blade failures as fatigue related. The root cause of blade failure is established to be high cycle fatigue from the engine run data history although the blades were put into service for just 6 h of engine operation.     

风电机组塔筒模态的环境脉动实测与数值模拟研究

摘 要：基于随机振动及系统识别理论,对内蒙古京能乌兰伊利更风电场中三座风电机组塔筒进行了环境脉动实测,提出了 “桨叶—轮毂—机舱—塔筒”耦合的整体建模的方法,数值模拟与实测结果表明,风电机组塔筒可以有效地避免共振,满足GL规范的设计要求;塔筒主要振动形式为侧向弯曲振动、前后弯曲振动和扭转振动;塔筒一阶平动阻尼比为1.78%左右,一阶扭转阻尼比为0.6%左右。采用整体建模方法建立的模型与实测结果有较好的一致性,可以指导风力发电塔系统的风致动力响应分析和振动控制分析。     

中小尺度嵌套下考虑停机位置的大型风力机体系风振响应分析

国内外风工程界采用的风力机体系风效应分析方法通常基于良态气候模式,而台风边界层风特性不同于良态气候模式,台风作用过程中会表现出明显的时空变异性和多尺度涡结构。针对现存土木工程台风模型理论体系过度简化的问题,引入考虑真实台风场强变异性和衰减效应的中尺度天气预报模式(WRF)对“鹦鹉”台风进行高时空分辨率模拟,重点对比台风登陆前、登陆时和登陆后台风风向和风强特征,并结合模拟台风中心路径与实测路径的对比结果验证了中尺度台风“鹦鹉”模拟的有效性。以中国东南沿海地区某风电厂5 MW水平轴风力机为对象,基于WRF模拟获得近地面三维风场数据,并结合小尺度CFD大涡模拟技术分别对叶片单个旋转周期不同停机位置工况进行三维非定常数值模拟。在此基础上,结合有限元完全瞬态法对不同停机工况进行了风振响应动力时程分析,提炼出停机位置对体系风振响应和风振系数的影响规律,最终归纳总结了台风作用下大型风力机体系最不利停机位置。结果表明:采用WRF模式可以有效模拟近地面台风风场,拟合的台风剖面指数为0.076;台风下塔架内力和风振系数显著增大,尤其是与塔架相对位置最近的叶片风振响应最为不利,内力最大增幅达35%。分析发现:当台风作用下大型风力机处于停机状态,下叶片与塔架完全重合(工况1)时为最不利,旋转至上叶片完全重合(工况5)时安全余度最大。     

考虑不同截面翼型选取的风电机组叶片优化设计方法

传统叶片优化设计中缺乏对截面翼型的考虑,导致叶片设计难以达到最优效果。为解决此问题,提出了考虑不同截面翼型的风电机组叶片优化设计方法,以截面翼型、弦长和扭角为设计变量,以年发电量最大化为目标,兼顾考虑相对厚度和相对弯度限制,建立了叶片参数设计遗传算法优化模型。以某1.5 MW风电机组为例,验证所提出优化设计方法的有效性。结果表明：考虑截面翼型等参数优化后的叶片功率系数明显增大;机组特性曲线在较大范围内均能保持在最佳功率系数附近,更易控制在最大风能捕捉效率点运行,从而提升了年发电量;同时,增加考虑相对厚度和相对弯度限制以更贴近实际工程应用。     

风力机风轮低频振动特性的实验模态研究

利用国际上先进的PULSE16.1结构振动分析系统,对4个风力机风轮进行模态测试,发现风轮在挂机状态下,低频时存在轴向窜动效应和圆盘效应两种普遍存在的振动方式。振动发生时叶根处分别伴随着往复式和回转式剪切应力,影响到风力机的安全稳定运行和寿命。同时,利用挂机实验对比证明了通常采取的风轮通过夹具安装后在平面上进行模态实验的方法,对风轮振动特性的完整和准确获得均存在一定的影响。初探性分析,轴向窜动效应的产生因主要与塔架的弹性有关;圆盘效应的产生因主要与风轮的安装方式有关。本文相关研究成果有可能为很多风力机叶片在远短于设计寿命期频繁发生疲劳损伤事故的分析提供新的思路和理论支撑。     

On Advanced Control Methods toward Power Capture and Load Mitigation in Wind Turbines

This article provides a survey of recently emerged methods for wind turbine control. Multivariate control approaches to the optimization of power capture and the reduction of loads in components under time-varying turbulent wind fields have been under extensive investigation in recent years. We divide the related research activities into three categories: modeling and dynamics of wind turbines, active control of wind turbines, and passive control of wind turbines. Regarding turbine dynamics, we discuss the physical fundamentals and present the aeroelastic analysis tools. Regarding active control, we review pitch control, torque control, and yaw control strategies encompassing mathematical formulations as well as their applications toward different objectives. Our survey mostly focuses on blade pitch control, which is considered one of the key elements in facilitating load reduction while maintaining power capture performance. Regarding passive control, we review techniques such as tuned mass dampers, smart rotors, and microtabs. Possible future directions are suggested.     

汽轮机叶片动频的转子调频非接触测量法

叶片的共振断裂是叶片损伤的主要形式,为了避免叶片共振,如何准确地测得叶片的动频是保证叶片安全工作的关键。本文提出采用转子调频非接触测量法测量汽轮机叶片的动频。采用该方法只需要在叶片顶部固定支架上安装两只光学传感器及在转子的适当位置安装一只转子旋转同步传感器,就可以测量工作轮上所有叶片的动步,从而克服了传统接触应变片法仅能测量某几个叶片动频、应变片寿命短等缺点,同时也避免了安装多只传感器工艺复杂、费用较高等问题。本文通过实验验证了该方法的可行性。