基于振动性能优化的风力机叶片设计

风轮是风力机最重要的部件之一,设计良好的风轮是风力机获得较高风能利用系数和较大经济效益的基础.本文应用Wilson气动理论设计了 100 W 水平轴风力机叶片,并兼顾振动性能对设计参数进行修正.对设计的风轮进行了模态实验和气动外特性实验,实验结果表明,所设计的风力机在低风速时基本能够达到设计的风能利用系数,并使得风力机在运行时避开转速共振区,延长风轮寿命,从而降低设计成本.     

Cable connected active tuned mass dampers for control of in-plane vibrations of wind turbine blades

In-plane vibrations of wind turbine blades are of concern in modern multi-megawatt wind turbines. Today?s turbines with capacities of up to 7.5 MW have very large, flexible blades. As blades have grown longer the increasing flexibility has led to vibration problems. Vibration of blades can reduce the power produced by the turbine and decrease the fatigue life of the turbine. In this paper a new active control strategy is designed and implemented to control the in-plane vibration of large wind turbine blades which in general is not aerodynamically damped. A cable connected active tuned mass damper (CCATMD) system is proposed for the mitigation of in-plane blade vibration. An Euler–Lagrangian wind turbine model based on energy formulation has been developed for this purpose which considers the structural dynamics of the system and the interaction between in-plane and out-of-plane vibrations and also the interaction between the blades and the tower including the CCATMDs. The CCATMDs are located inside the blades and are controlled by an LQR controller. The turbine is subject to turbulent aerodynamic loading simulated using a modification to the classic Blade Element Momentum (BEM) theory with turbulence generated from rotationally sampled spectra. The turbine is also subject to gravity loading. The effect of centrifugal stiffening of the rotating blades has also been considered. Results show that the use of the proposed new active control scheme significantly reduces the in-plane vibration of large, flexible wind turbine blades.     

Dynamic Modeling and Analysis of Wind Turbine Blade of Piezoelectric Plate Shell

This paper presents a theoretical analysis of vibration control technology of wind turbine blades made of piezoelectric intelligent structures. The design of the blade structure, which is made from piezoelectric material, is approximately equivalent to a flat shell structure. The differential equations of piezoelectric shallow shells for vibration control are derived based on piezoelectric laminated shell theory. On this basis, wind turbine blades are simplified as elastic piezoelectric laminated shells. We establish the electromechanical coupling system dynamic model of intelligent structures and the dynamic equation of composite piezoelectric flat shell structures by analyzing simulations of active vibration control. Simulation results show that, under wind load, blade vibration is reduced upon applying the control voltage.     

小型风机叶片结构损伤识别实验模拟研究

搭建小型风机叶片振动检测实验平台,采集风机叶片振动响应数据,利用自互功率谱法辨别叶片损伤前后的模态参数,通过实验数据对比风机叶片损伤前后固有频率的变化,当风机叶片发生损伤时,其各阶固有频率会下降,且随着损伤程度的增加,各阶固有频率的下降幅度越大,并利用轴向振型差法对叶片损伤进行了定位,在实验室条件下完成了风机叶片结构损伤的识别。     

Dynamic analysis of horizontal axis wind turbine by thin-walled beam theory

A mixed flexible-rigid multi-body mathematical model is applied to predict the dynamic performance of a wind turbine system. Since the tower and rotor are both flexible thin-walled structures, a consistent expression for their deformations is applied, which employs a successive series of transformations to locate any point on the blade and tower relative to an inertial coordinate system. The kinetic and potential energy terms of each flexible body and rigid body are derived for use in the Lagrange approach to formulate the wind turbine system's governing equation. The mode shapes are then obtained from the free vibration solution, while the distributions of dynamic stress and displacement of the tower and rotor are computed from the forced vibration response analysis. Using this dynamic model, the influence of the tower's stiffness on the blade tip deformation is studied. From the analysis, it is evident that the proposed model not only inherits the simplicity of the traditional 1-D beam element, but also able to provide detailed information about the tower and rotor response due to the incorporation of the flexible thin-walled beam theory.     

Numerical simulation and experimental validation of ultrasonic de-icing system for wind turbine blade

It is widely accepted that wind energy is clean and renewable. However, icing on the blade surfaces of wind turbines is a serious problem in cold regions, which greatly affects its performance. Therefore, it is important to prevent ice accumulation on the surface of wind turbine blade and remove it whenever necessary. In this paper, a new non-thermal method–ultrasonic de-icing for wind turbine blade is proposed. Firstly, baced on the theory of ultrasonic de-icing, the harmonic analysis of the structure of the composite plate-ice layered system is investigated using the finite element method. The simulation results showed that ultrasonic de-icing method is feasible for wind turbine blade de-icing purposes. Secondly, the de-icing experiment of wind turbine blades using piezoelectric actuators is carried out in the freezer at a temperature of −15 °C, results showed that the ice layer can be debonded from the surface of wind turbine blade by the commonly used piezoelectric transducers made by PZT-5. The optimal frequency of ultrasonic de-icing of wind turbine blade is also given; finally, the installation way of ultrasonic transducers on the inner surface of wind turbine blade is given.     

Tactile Response Characterization of a Dynamic System Using Craig-Bampton Method

Vibrational characteristics in small horizontal axis wind turbine system are presented in this study with a system concept called tactile response and substructuring. The main focus is on managing the dynamic properties like vibration, noise, and harshness that occur during the operational mode. Tactile response is defined as the response of subsystem which is induced when a human body touches a vibrating system. Sub structuring is a computational method used to reduce the dynamic behavior of a large complex system with a smaller number of degrees of freedom without disturbing the mesh size of the model. Sub structuring has the ability to combine numerical results along with the experimental results. Combination of substructuring and tactile response is applied in this study. Mode shapes of the system are analyzed and results obtained are correlated within this study to provide better optimization of the results. Wind turbine excited with wind energy depends on wind speed. Torsional vibration has a significant role in determining dynamic properties. Torsional vibration is caused as a result of the rotation of the turbine blade and depends on wind speed. The study gives importance to investigating the ability to simulate the numerical method and tactile response to predict and improve dynamic properties.     

海上风电叶片智能控制实验系统研制及控制效果分析

随着风力机大型化发展,叶片尾缘襟翼控制技术,作为叶片流场主动控制的一种有效手段,能够有效、快速、灵活地降低叶片载荷,提高风力机,特别是大型风力机的可靠性、经济性,该技术受到国内外的广泛关注。为深入了解叶片襟翼实际作用效果及降载机制,在大量数值仿真计算工作基础上,需进一步开展带有襟翼控制的模型风力机风洞实验工作。本文在相似准则基础上,引入叶片展向环量、Polar线相似条件,对NREL 5 MW风力机叶片按1:105进行缩比设计,采用伺服电机驱动襟翼的结构方案对叶片参数进行修正,并根据BEM理论优化带有襟翼叶片的气动性能,最终确定带有襟翼控制的风力机叶片设计方案。最后利用气弹耦合仿真计算平台对带有襟翼控制的模型风力机进行性能计算,确定理想实验工况点及对应的降载效果。本文所开展的工作不仅能够为叶片缩比设计提供新思路,更有意义的是为襟翼控制系统在叶片中的实现提供有效借鉴。     

Long distance laser ultrasonic propagation imaging system for damage visualization

Wind turbine blade failure is the most prominent and common type of damage occurring in operating wind turbine systems. Conventional nondestructive testing systems are not available for in situ wind turbine blades. We propose a portable long distance ultrasonic propagation imaging (LUPI) system that uses a laser beam targeting and scanning system to excite, from a long distance, acoustic emission sensors installed in the blade. An examination of the beam collimation effect using geometric parameters of a commercial 2 MW wind turbine provided Lamb wave amplitude increases of 41.5 and 23.1 dB at a distance of 40 m for symmetrical and asymmetrical modes, respectively, in a 2 mm-thick stainless steel plate. With this improvement in signal-to-noise ratio, a feasibility study of damage detection was conducted with a 5 mm-thick composite leading edge specimen. To develop a reliable damage evaluation system, the excitation/sensing technology and the associated damage visualization algorithm are equally important. Hence, our results provide a new platform based on anomalous wave propagation imaging (AWPI) methods with adjacent wave subtraction, reference wave subtraction, reference image subtraction, and the variable time window amplitude mapping method. The advantages and disadvantages of AWPI algorithms are reported in terms of reference data requirements, signal-to-noise ratios, and damage evaluation accuracy. The compactness and portability of the proposed UPI system are also important for in-field applications at wind farms.     

Optical system design and experimental evaluation of a coherent Doppler wind Lidar system for the predictive control of wind turbine

The control of wind turbine blade pitch systems by Lidar assisted wind speed prediction has been proposed to increase the electric power generation and reduce the mechanical fatigue load on wind turbines. However, the sticking point of such Lidar systems is the price. Hence, our objective is to develop a more cost efficient Lidar system to support the pitch control of horizontal axis wind turbines and therefore to reduce the material requirement, lower the operation and maintenance costs and decrease the cost of wind energy in the long term. Compared to the state of the art Lidar systems, a laser with a shorter coherence length and a corresponding fiber delay line is introduced for reducing the costs. In this paper we present the experimental evaluation of different sending and receiving optics designs for such a system from a free space laboratory setup.     

Dynamic response of a horizontal axis wind turbine blade under aerodynamic,gravity and gyroscopic effects

This work presents analytical and numerical dynamics studies of a horizontal axis wind turbine blade subjected to aerodynamic, centrifugal, gravity, and gyroscopic loads. The blade, assimilated to a long beam of variable cross section, is composed of homogeneous and isotropic material. It is discretized with blade elements of constant sections. Using Finite Element Method (FEM), the assembly of these elements constitutes an approximate model of the blade. The analytical study consists on defining the elementary matrices of rigidity, mass, and gyroscopic coupling between vibration and the blade rotation, as well as the elementary vector of the external loads. The numerical study deals with the resolution of the linear system of equations of the blade motion. Then, it will be possible to calculate its static and dynamic responses for a practical case. The numerical results show that the blade presents cyclic deformations under the considered loadings. These sustained vibrations directly affect the fatigue life of the blade, leading to a significant reduction in the operational efficiency of the wind turbine.     

Wind turbine noise measurement using a compact microphone array with advanced deconvolution algorithms

This paper experimentally investigates the noise from a large wind turbine (GE 1.5 MW) with a compact microphone array (OptiNav 24) using advanced deconvolution based beamforming methods, such as DAMAS and CLEAN-SC beamforming algorithms, for data reduction. Our study focuses on the ability of a compact microphone array to successfully locate both mechanical and aerodynamic noise sources on the wind turbine. Several interesting results have emerged from this study: (i) A compact microphone array is sufficient to perform a detailed study on wind turbine noise if advanced deconvolution methods are applied. (ii) Noise sources on the blade and on the nacelle can clearly be separated. (iii) Noise of the blades is dominated by trailing edge noise which is frequency dependent and is distributed along the length of the blade with the dominant noise source closer to the tip of the blade. (iv) The LP and DAMAS algorithms represent the distributed trailing edge noise source better than CLEAN-SC and classical beamforming. (v) Additional tonal noise produced during yawing operation is believed to be radiating from the tower of the wind turbine that acts like a resonator. (vi) Ground reflection is not believed to have a significant effect on noise source location estimates in this study.     

基于面元法的水平轴风力机数值模拟

使用基于速度面元法的势流数值模拟方法,以NREL PhaseⅥ为例进行了叶片气动载荷和风轮近尾流场的数值模拟。将势流数值模拟、叶素动量理论和计算流体力学CFD方法的计算结果与实验数据进行了对比分析。结果表明使用速度面元法计算风轮绕流场具有较高的计算精度和求解效率,为大规模风力机群的流场计算和出力预报提供支撑。     

谱分析法测量叶尖小翼对风轮旋转时固有频率的影响

风力机叶尖加小翼,在一定范围内可以增加风力发电机的输出功率,提高功率系数.本文通过应用谱分析法测量风力机风轮旋转时机头的振动谱,通过分析得到了风轮动频,应用动频曲线研究了风力机叶尖小翼对风轮固有频率的影响.实验表明,叶尖小翼虽然降低了风轮静频但通过增大离心力和气动力提高了动频.叶尖小翼可以改善旋转风轮的结构动态特性.     

叶片扰流器对风力机性能影响的数值研究

风力发电机组不断向大型化发展,风力机叶片的长度越来越长,为满足其结构要求,需要在叶片内侧采用厚翼型,而厚翼型在大攻角下容易导致流动分离,影响功率输出。本文通过对某一风力机叶片进行数值模拟,分析其近叶根处的流场,发现存在较大的流动分离现象。针对两种工况,在叶片内侧最大弦长位置增加环形扰流器后进行数值模拟,与原始叶片进行比较。结果表明:扰流器可以有效减小叶片内侧的流动分离区域,风速为11 m/s和15 m/s时功率都得到一定程度的提高,扰流器附近截面上的压力分布也有所改善。     

Remote monitoring of ice loading on wind turbine blades based on total internal reflection

The paper presents an optical method for monitoring of transparent icing, which is applicable for remote monitoring of wind turbine blade icing. The method is based on the effect of total internal reflection of light. A point light source is formed on a wind turbine blade. When icing appears on the blade, a light circle is formed around the light source at the ice–air interface as a result of refraction and reflection of light beams; the observed size of the beam depends on the icing thickness. Using several light sources, the method enables field monitoring of icing on the wind turbine blades.     

Detecting salt deposition on a wind turbine blade using laser induced breakdown spectroscopy technique

The study of pollution performance on a wind turbine blade due to lightning is important, as it can cause major damage to wind turbine blades. In the present work, optical emission spectroscopy (OES) technique is used to understand the influence of pollutant deposited on a wind turbine blade in an off-shore environment. A methodical experimental study was carried out by adopting IEC 60507 standards, and it was observed that the lightning discharge propagates at the interface between the pollutant and the glass fiber reinforced plastic (Material used in manufacturing of wind turbine blades). In addition, as a diagnostic condition monitoring technique, laser-induced breakdown spectroscopy (LIBS) is proposed and demonstrated to rank the severity of pollutant on the wind turbine blades from a remote area. Optical emission spectra observed during surface discharge process induced by lightning impulse voltage is in agreement with the spectra observed during LIBS.     

基于数字图像相关技术的风电叶片静态特性试验研究

进行了风电叶片双轴静载试验,全程采用数字图像相关技术监测其全场三维变形。结果表明,在各工况荷载作用下,风电叶片的三维位移分布具有良好规律,而应变分布则无明显规律。3个方向位移中,平面外位移远大于平面内位移。双轴荷载作用下,风电叶片挥舞方向位移与摆振方向位移均随加载等级增大而增大。在风电叶片全场范围内,挥舞方向位移沿叶片展向逐渐增大,直至叶尖达到最大值。叶片各点的摆振方向位移均为负位移,负位移最大值出现在叶片中部。在叶根至41%叶长(55 cm)区域内,叶片各工况下的展向位移几乎接近于0;而在41%叶长至叶尖区域,当荷载较小时,叶片迎风面纤维的受拉伸长量大于平面外弯曲的展向位移分量而产生正位移;随着荷载增大,叶片平面外弯曲变形的展向位移分量大于迎风面纤维的受拉伸长量而产生负位移。     

一种改进的诱导因子计算方法

本文利用开发的程序,对BEM计算模型中诱导因子的计算方法进行研究.比较分析了已有几种计算方法的优劣,在此基础上提出一种改进的计算方法,并以美国可再生能源实验室(NREL)直径为10 m水平轴风力机叶片气动试验数据为依据,验证了本文算法的准确性和优越性.