大型风力发电机旋转叶片结构动力特性分析

大型风力发电机叶片的结构动力特性是叶片结构设计时考虑的重要方面,其固有自振频率对于整个风力机的安全运行具有重要意义。文章基于现代柔性多体动力学理论和有限元数值分析相结合的方法,对5MW风力发电机叶片的固有振动特性进行分析。结合复合材料叶片结构特性及结构参数,建立了5 MW风机复合材料叶片有限元模型,计算了考虑动力刚化及阻尼效应影响下的固有频率和振型,揭示了动力刚化效应对叶片固有频率的影响规律;并结合坎贝尔图,对叶片进行了共振分析,为叶片的结构设计及优化提供了参考依据。     

拉索式小型风力发电机塔架结构吸振器的研发

风力发电机塔架结构的自然频率与风轮的工作频率(风叶的通过频率)相近时,将发生共振,导致风力发电机无法正常工作。文章基于动力吸振原理,建立了拉索式小型风力发电机塔架结构等效振动模型,再以6kW级拉索式小型风力发电机塔架结构的缩小模型为对象制作吸振器,用理论与试验验证吸振器的有效性。试验结果表明,吸振器能够有效减少塔架结构共振频域内的振动。     

某燃气轮机压气机叶片振动特性研究

针对某燃气轮机压气机叶片断裂故障,通过理论计算和试验方法,对故障级叶片在与轮盘耦合条件下的振动特性进行了研究分析。理论计算叶片动频时考虑了旋转离心力和温度载荷的影响,利用有限元计算程序ANSYS WORKBENCH循环对称分析功能和接触分析功能,完成了压气机叶片振动分析,通过坎贝尔图得到叶片1阶弯曲共振转速为6 900 r/min。随后,在整机状态下,利用非接触式微波测量方法,对该级动叶进行了振动测试,获得的叶片1阶弯曲共振转速为6 988 r/min,实测得到的共振转速与理论计算结果吻合,为故障的进一步排查提供有利的理论和试验依据。     

某燃气轮机压气机叶片振动特性研究

针对某燃气轮机压气机叶片断裂故障,通过理论计算和试验方法,对故障级叶片在与轮盘耦合条件下的振动特性进行了研究分析。理论计算叶片动频时考虑了旋转离心力和温度载荷的影响,利用有限元计算程序ANSYS WORKBENCH循环对称分析功能和接触分析功能,完成了压气机叶片振动分析,通过坎贝尔图得到叶片1阶弯曲共振转速为6 900 r/min。随后,在整机状态下,利用非接触式微波测量方法,对该级动叶进行了振动测试,获得的叶片1阶弯曲共振转速为6 988 r/min,实测得到的共振转速与理论计算结果吻合,为故障的进一步排查提供有利的理论和试验依据。     

基于CFD的旋转风轮气动性能分析

采用Fluent6．3软件,并结合SSTκ-ω模型对1．2MW风力发电机旋转风轮流场进行了数值模拟,对设计转速为18．44r／min工况下三叶片风轮与相同叶片单叶片、双叶片以及四叶片风轮流场的输出功率与湍动能进行了比较,并分析了风轮旋转对叶片间流动的影响．结果表明：旋转上游叶片在转动过程中会发生附着涡的脱落,导致旋转下游叶片周围流场的环境发生变化,对叶片转矩及输出功率造成较大影响．在翼型优化中,考虑叶片间作用可以提高风力发电机的效率．     

小型风力发电机叶片模态特性分析

以800W水平轴风力发电机叶片为对象,研究其叶片的模态特性．从理论上介绍了应力刚化和旋转软化对叶片固有频率的影响,并给出了考虑应力刚化和旋转软化效应的振动方程;利用ANSYS软件建立了有限元模型,分别对风力发电机叶片在仅考虑应力刚化或旋转软化时,以及同时考虑应力刚化和旋转软化时的模态特性进行了计算分析．计算结果表明：应力刚化对固有频率的影响比旋转软化大;仅考虑旋转软化时,叶片的固有频率比零旋转角速度时低;而综合两者的影响时,叶片的固有频率比零旋转角速度时高．     

水平轴风力机叶片的截面与动力特性分析

风力机叶片在旋转过程中受重力和离心力作用,产生动力刚化导致固有频率增加。文章以NRELPhase VI风力机叶片为对象,在其内部分别添加圆形腹板、单腹板和双腹板,建立3种不同截面的叶片三维模型,并结合复合材料对叶片铺层进行动力学分析。结果表明,叶片采用的铺层方案能有效避免共振,并且3种叶片模型的重量均接近叶片的真实值。在额定转速下,3种腹板叶片的一阶频率增量随腹板的厚度增加而增加,但在两倍额定转速时,单腹板和圆形腹板的一阶频率增量随腹板厚度增加而减少;同时,腹板中的双轴向玻璃布材料以±45°铺设时,一阶固有频率最大,而由动力刚化引起的一阶频率增量较其他角度小。     

风力发电机组传动链振动特性研究及试验

建立风力发电机组主传动链振动特性全实物仿真分析模型。模型包括叶片、轮毂、主轴、齿轮箱、连轴器和发电机等,其中叶片、轮毂、主轴、齿轮箱内的行星架、各级旋转轴等以超单元模型的型式导入总模型。根据风力机设计参数计算得到风力机的激励频率,分别在切入、额定和切出的3种动平衡状态基础上计算风力机运行时的特征频率,并结合激励频率和特征频率绘制坎贝尔图及能量分布图,找出风力机的潜在共振点,最后对风力机进行时域扫频分析,结合三维坎贝尔图、傅里叶变换对潜在共振点进行排除或确认。分析结果表明:该款自主设计的风力发电机组具有良好的振动特性,可避免共振,并得到试验结果的验证。     

叶轮质量不平衡故障下双馈风力发电机特性分析

针对双馈风力发电机组叶轮质量不平衡故障展开研究,综合考虑机组最大风能追踪控制策略(MPPT)以及转子侧矢量控制策略,分析叶轮质量不平衡故障对双馈风力发电机电气特性的影响,推导转子电流的解析表达式,并得出定子电流和功率的变化特性。然后在Matlab/Simulink平台进行仿真,并通过实验进行验证。仿真和实验表明,叶轮质量不平衡故障时双馈风力发电机功率发生波动,频率为叶轮转频及其倍频;定、转子电流中除基波外还包含调制谐波,调制频率为叶轮转频及其倍频。     

基于压气机动静叶干涉的共振研究

燃气轮机压气机叶片在设计时需要进行共振考核,但由于激振力复杂,叶片产生共振的条件也不相同。考虑了动静叶的干涉扰动,得到一般气流压力脉动模型,然后在压力脉动作用下推导下游动叶受迫响应的解析解,从受迫响应的解中得出基于压力脉动特性的共振条件。最后利用某燃气轮机压气机叶片轮盘模型进行了验证,得到了与理论推导一致的结果。该共振条件基于动静叶数量和动叶轮盘模态特性关系,揭示了阶次激励作用下叶片轮盘耦合振动存在更多可能出现的共振点,在设计阶段需要注意避开这些共振点,控制叶片振动,保证叶片安全运行。     

基于几何精确梁的风力机叶片动力学建模及动态特性分析

基于几何精确梁理论,结合广义-α时间预测法的迭代算法,考虑叶片复合铺层材料的各向异性特性,建立了大型风力机叶片的几何非线性动力学模型并导出了相应的特征方程,编制了数值仿真程序。通过对几何非线性梁标准算例和某10 MW柔性风力机叶片动力特性的模拟分析,验证了动力学模型的正确性,以及几何精确梁模型对分析叶片几何非线性大变形及其所导致的非线性动力学效应的有效性。叶片在静止和转动工况下的模态分析结果表明,在动力刚化效应作用下,叶片的固有频率会随着转速的增加而增大,动力刚化效应在挥舞方向比在摆振方向更明显,在低阶模态比在高阶模态更明显。     

New vortex‐lift and tangential‐force models for HAWT aerodynamic load prediction

Horizontal axis wind turbines (HAWTs) experience three‐dimensional rotational and unsteady aerodynamic phenomena at the rotor blades sections. These highly unsteady three‐dimensional effects have a dramatic impact on the aerodynamic load distributions on the blades, in particular, when they occur at high angles of attack due to stall delay and dynamic stall. Unfortunately, there is no complete understanding of the flow physics yet at these unsteady 3D flow conditions, and hence, the existing published theoretical models are often incapable of modelling the impact on the turbine response realistically. The purpose of this paper is to provide an insight on the combined influence of the stall delay and dynamic stall on the blade load history of wind turbines in controlled and uncontrolled conditions. New dynamic stall vortex and nonlinear tangential force coefficient modules, which integrally take into account the three dimensional rotational effect, are also proposed in this paper. This module along with the unsteady influence of turbulent wind speed and tower shadow is implemented in a blade element momentum (BEM) model to estimate the aerodynamic loads on a rotating blade more accurately. This work presents an important step to help modelling the combined influence of the stall delay and dynamic stall on the load history of the rotating wind turbine blades which is vital to have lighter turbine blades and improved wind turbine design systems.     

Discharge path observation and the statistical characteristics of discharge paths for long–air gap discharge for in‐operation wind turbines

When a wind turbine is in normal operation, the blades are rotating, and this blade rotation may affect the process of lightning striking the wind turbine. To investigate this problem, long‐gap discharge tests are performed in this study. Moreover, a multiple physical parameter synchronous observation platform is designed for a scaled wind turbine. Long‐gap discharge tests of a static and rotary‐scaled wind turbine with blade tip‐electrode gap distances of 1 to 8 m are conducted, and the discharge paths under different gaps and wind turbine operating conditions are obtained. The characteristic parameters—arc shape upon discharge, lengths of the downward and upward leaders, blade angle at the moment of discharge, and angle of upward leader initiation—are statistically analyzed. The analysis of the aforementioned data indicates that rotation has opposite effects on the discharge characteristic parameters under short and long gap distances. According to the analysis, blade rotation reduces the space charge density of the corona discharge near the tip, which leads to an increase in the field strength near the blade tip and a decrease in the field strength away from the blade tip. Short and long gaps have different degrees of influence on discharge, which changes the difficulty of upward leader initiation at the blade tip and consequently alters the entire discharge process. The obtained results can provide a reference for the lightning protection of wind turbines.     

Influence of blade rotation on the lightning stroke characteristic of a wind turbine

The blades of a wind turbine rotate during normal operation. To investigate the influence of blade rotation on the lightning‐attracting ability of a wind turbine, a discharge test platform is designed for scaled wind turbines. The 50% impulse voltages and flash probabilities of the scaled wind turbines with gap distances of 1 to 8 m in the static and rotary conditions are determined by using the discharge test and selective discharge test. The discharge test for a single wind turbine with a gap of 1 to 2 m indicates that the breakdown voltages of the gap between the scaled turbine and electrodes increases with an increase in the blade rotation speed. However, the discharge test with a gap distance of 4 to 8 m indicates that the breakdown voltage of the fan decreases with an increase in the blade rotation speed. The test results of the scaled dual wind turbines experiment have the same rules. To explain this phenomenon, the influence of wind speed on the space‐charge distribution and electrical field intensity of corona discharge is simulated in the background of a target thundercloud. The rotation of the fan reduces the space‐charge density near the area of the blade tip, which leads to an increase in the field strength near the blade tip of the wind turbine and a decrease in the field strength away from the blade tip. This influence varies in short and long air gap, resulting in opposite relationships between discharge voltage and distance from the tip of the turbine. The results can provide a reference for the lightning protection of wind turbines.     

The spectrum of wind speed fluctuations encountered by a rotating blade of a wind energy conversion system

A point on a rotating wind turbine blade encounters turbulence whose characteristics are quite different from turbulence measured by a stationary anemometer. This is true for vertical as well as horizontal axis wind turbines. The spectrum of the observed turbulence is distored in several subranges of frequency in characteristic ways. The midfrequency region is depleted and the removed energy is distributed into the high frequency end of the spectrum. The resulting two-peaked continuous spectrum also contains narrow-band spikes of turbulence energy centered on the frequency of rotor rotation and multiples of that frequency. The statistics of gusts are expected to be distorted also.The rotational sampling effect is quantified using measurements of wind velocity at circular arrays of anemometers and measurements by laser and hotwire anemometers traversing crosswind circular paths. A simple theoretical model of the spectrum of turbulence which is rotationally sampled is developed. The model, which assumes homogeneous, isotropic turbulence, reproduces the observed spectral features and provides an analytic verification and extension of scaling relations using turbine and atmospheric length and time scales. All known theoretical models of the spectrum of a rotationally sampled turbulence field are compared with the spectra which are derived from rotationally measured turbulence.Implications for turbine design, siting and control are drawn. A nondimensional parametric analysis of the rotational turbulence effect suggests criteria for selecting rotor height above ground and rotor rotation rate and provides guidelines for optimizing a design once the preliminary turbine configuration has been established.     

不同类型漂浮式风电场内机组塔基载荷研究

构建基于NREL 5 MW 风电机组的海上固定式风电场和不同类型的漂浮式风电场,考虑不同类型风电机组尾流特性、平台漂浮特性的差异,在不同工况下对风电场内机组动力学响应进行仿真计算。通过时域分析与箱线图分析,对风电场内各位置处机组在风、浪、尾流联合作用下的塔基载荷进行对比研究。结果表明：在相同工况下,Spar式风电场内机组风轮与平台位移值、塔基载荷在来流方向上最大;在中低风速下,风电场内机组塔基载荷相差较大;高风速时,塔基载荷相近;随着风速的增大,漂浮式机组塔基载荷呈先增大后减小的规律。     

预弯外形对风力机叶片气弹稳定性的影响

为了研究预弯外形对风力机气弹稳定性的影响,以某2 MW低风速风电叶片为研究对象,采用外形参数化表达方法构造叶尖预弯量分别为3、4和5 m的叶片.基于SIMPACK软件建立并验证气-弹-控耦合的风力机整机模型,对配装不同预弯叶片的风力机进行仿真分析.结果显示,在湍流风况下,随着叶尖预弯量的增大,叶根载荷、叶尖附近截面的气...     

Analysis of throw distances of detached objects from horizontal‐axis wind turbines

This paper aims at predicting trajectories of the detached fragments from wind turbines, in order to better quantify consequences of wind turbine failures. The trajectories of thrown objects are attained using the solution to equations of motion and rotation, with the external loads and moments obtained using blade element approach. We have extended an earlier work by taking into account dynamic stall and wind variations due to shear, and investigated different scenarios of throw including throw of the entire or a part of blade, as well as throw of accumulated ice on the blade. Trajectories are simulated for modern wind turbines ranging in size from 2 to 20 MW using upscaling laws. Extensive parametric analyses are performed against initial release angle, tip speed ratio, detachment geometry, and blade pitch setting. It is found that, while at tip speeds of about 70 m/s (normal operating conditions), pieces of blade (with weights in the range of approximately 7‐16 ton) would be thrown out less than 700 m for the entire range of wind turbines, and turbines operating at the extreme tip speed of 150 m/s may be subject to blade throw of up to 2 km from the turbine. For the ice throw cases, maximum distances of approximately 100 and 600 m are obtained for standstill and normal operating conditions of the wind turbine, respectively, with the ice pieces weighting from 0.4 to 6.5 kg. The simulations can be useful for revision of wind turbine setback standards, especially when combined with risk assessment studies. Copyright © 2015 John Wiley & Sons, Ltd.     

Modeling turbine wakes and power losses within a wind farm using LES: An application to the Horns Rev offshore wind farm

A modeling framework is proposed and validated to simulate turbine wakes and associated power losses in wind farms. It combines the large-eddy simulation (LES) technique with blade element theory and a turbine-model-specific relationship between shaft torque and rotational speed. In the LES, the turbulent subgrid-scale stresses are parameterized with a tuning-free Lagrangian scale-dependent dynamic model. The turbine-induced forces and turbine-generated power are modeled using a recently developed actuator-disk model with rotation (ADM-R), which adopts blade element theory to calculate the lift and drag forces (that produce thrust, rotor shaft torque and power) based on the local simulated flow and the blade characteristics. In order to predict simultaneously the turbine angular velocity and the turbine-induced forces (and thus the power output), a new iterative dynamic procedure is developed to couple the ADM-R turbine model with a relationship between shaft torque and rotational speed. This relationship, which is unique for a given turbine model and independent of the inflow condition, is derived from simulations of a stand-alone wind turbine in conditions for which the thrust coefficient can be validated. Comparison with observed power data from the Horns Rev wind farm shows that better power predictions are obtained with the dynamic ADM-R than with the standard ADM, which assumes a uniform thrust distribution and ignores the torque effect on the turbine wakes and rotor power. The results are also compared with the power predictions obtained using two commercial wind-farm design tools (WindSim and WAsP). These models are found to underestimate the power output compared with the results from the proposed LES framework.     

旋转对风力涡轮叶片三维边界层影响的数值计算

由于旋转的影响,基于经典二维叶素理论设计的水平轴风力涡轮叶片,在高风速工况下不能可靠运行,即存在失速延迟现象,采用不可压缩三维边界层积分方程揭示产生这种失速延迟现象的机理,分析旋转对风力涡轮边界层的影响,通过积分边界层方程的求解（包括层流,转捩及紊流）,得到一些关键的影响参数（如失速点位置,动量厚度等）。并在相同的运行条件下,比较二维工况与三维旋转工况下各关键参数的差别,得到由于旋转的影响,边界层