The influence of the wind speed profile on wind turbine performance measurements

To identify the influence of wind shear and turbulence on wind turbine performance, flat terrain wind profiles are analysed up to a height of 160 m. The profiles' shapes are found to extend from no shear to high wind shear, and on many occasions, local maxima within the profiles are also observed. Assuming a certain turbine hub height, the profiles with hub‐height wind speeds between 6 m s^?1 and 8 m s^?1 are normalized at 7 m s^?1 and grouped to a number of mean shear profiles. The energy in the profiles varies considerably for the same hub‐height wind speed. These profiles are then used as input to a Blade Element Momentum model that simulates the Siemens 3.6 MW wind turbine. The analysis is carried out as time series simulations where the electrical power is the primary characterization parameter. The results of the simulations indicate that wind speed measurements at different heights over the swept rotor area would allow the determination of the electrical power as a function of an ‘equivalent wind speed’ where wind shear and turbulence intensity are taken into account. Electrical power is found to correlate significantly better to the equivalent wind speed than to the single point hub‐height wind speed. Copyright © 2008 John Wiley & Sons, Ltd.     

Measurements and modelling of the power performance of a model floating wind turbine under controlled conditions

This paper describes power performance measurements undertaken on a model floating wind turbine installed on a tension‐leg platform (TLP) in a wind/wave generator facility. Initially, the surge of the platform was measured under different rotor and wave conditions. The surge behaviour depended considerably on the rotor tip speed ratio and the wave frequency and amplitude. High‐frequency data sampling techniques were then used to derive the instantaneous power coefficient and tip speed ratio directly from the measurements, together with the surge velocity of the floating system. The power measurements were compared with those predicted by three independent numerical models, two of which are based on the blade element momentum approach and the third involving a lifting‐line free‐wake vortex model. The fluctuations of the power coefficient with time predicted by the three models were in close agreement; however, these were all significantly larger than those derived from the rotor shaft torque measurements. This was found to be due to the limitations of the torque measurement technique. Although being accurate in measuring the time‐averaged torque, the sensor was incapable of measuring the high‐frequency low‐amplitude fluctuations in the rotor shaft torque induced by the TLP surge. This was confirmed using an alternative experimental technique involving hot‐wire near‐wake measurements. The study also investigated the influence of the platform surge motion on the time‐averaged power coefficients. Both the measurements and the free‐wake vortex model revealed marginal deviations in the time‐averaged power coefficients when compared with those obtained for a fixed, non‐surging rotor. Copyright © 2014 John Wiley & Sons, Ltd.     

Redefinition power curve for more accurate performance assessment of wind farms

The lack of accurate methods for assessment of the productive capacity of wind power plants is becoming a bottleneck in an increasingly commercialized wind power industry. In this article the inherent components of performance assessment are identified and analysed and ways of minimizing uncertainties on the components are investigated. The main components are identified as ‘site calibration’, ‘wind turbine sensitivity to flow variables’, ‘plant blockage effects’ and ‘uncertainty analysis’. Site calibration is the action of estimating the flow variables at the wind turbine position from measurements of these quantities at another (reference) position. The purpose of sensitivity analysis is to clarify which and how flow variables influence power output. Plant blockage effects refer to the power plant's influence on the reference measurements of flow variables. Finally, the component uncertainties and in turn the integrated uncertainty on the average productive capacity of the wind power plant are investigated. It is found that uncertainties can be reduced (1) by including several more flow variables in addition to hub‐height wind speed, (2) by carrying out site calibration with utmost care and by inclusion of more variables, (3) by taking plant blockage into consideration, (4) by aiming at ‘plant‐average’ power instead of looking only at individual machines and, possibly, (5) by introduction of remote‐sensing anemometer techniques. Copyright © 2000 John Wiley & Sons, Ltd.     

Modelling and measurements of power losses and turbulence intensity in wind turbine wakes at Middelgrunden offshore wind farm

Understanding of power losses and turbulence increase due to wind turbine wake interactions in large offshore wind farms is crucial to optimizing wind farm design. Power losses and turbulence increase due to wakes are quantified based on observations from Middelgrunden and state‐of‐the‐art models. Observed power losses due solely to wakes are approximately 10% on average. These are relatively high for a single line of wind turbines due in part to the close spacing of the wind farm. The wind farm model Wind Analysis and Application Program (WAsP) is shown to capture wake losses despite operating beyond its specifications for turbine spacing. The paper describes two methods of estimating turbulence intensity: one based on the mean and standard deviation (SD) of wind speed from the nacelle anemometer, the other from mean power output and its SD. Observations from the nacelle anemometer indicate turbulence intensity which is around 9% higher in absolute terms than those derived from the power measurements. For comparison, turbulence intensity is also derived from wind speed and SD from a meteorological mast at the same site prior to wind farm construction. Despite differences in the measurement height and period, overall agreement is better between the turbulence intensity derived from power measurements and the meteorological mast than with those derived from data from the nacelle anemometers. The turbulence in wind farm model indicates turbulence increase of the order 20% in absolute terms for flow directly along the row which is in good agreement with the observations. Copyright © 2007 John Wiley & Sons, Ltd.     

具有较强气动性能的风力发电机叶片研究

利用流体分析软件Fluent对NACA4415与SD7043两种常见翼型进行流场模拟,从外形特征分析两者的气动性能差异,进一步利用翼型分析软件profili的翼型设计功能,结合两种翼型的长处,设计出新的翼型,并对新翼型与原有翼型在升阻特性上的差异进行分析,对比发现新翼型气动性能更优。最后利用新翼型基于Solidworks设计出一款小型风力发电机叶片。     

湍流对风力发电机组发电性能评价的影响研究

风力发电机组的发电量通过功率曲线和对应风频分布计算得出,功率曲线通过功率曲线测试获得,风频分布通过长期测风数据获得.然而功率曲线在测试过程中,由于环境因素不同以及测试周期有限等原因,称为特定环境条件下的功率曲线,与理论功率曲线有所偏差.通过研究湍流强度对功率曲线的影响,利用理论方法修正测试功率曲线到特定湍流强度,以达到...     

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。     

An assessment of the impact of reduced averaging time on small wind turbine power curves,energy capture predictions and turbulence intensity measurements

The effect of varying the averaging time of measured data used to calculate wind turbine power curves is examined. The effects of reducing the averaging time from 10 to 1 min, as recommended for small wind turbines, are investigated using power performance data recorded using a 15 kW wind turbine. Test site data have been processed according to the relevant international standard, IEC 61400‐12‐1, to provide power curves and annual energy yield predictions. A number of issues are explored: the systematic distortion of the power curve that occurs as averaging time is decreased, the errors introduced by the use of 1 min averaged power curves to calculate energy yield and the reduction of turbulence intensity as averaging time is reduced. Recommendations for improved small wind turbine testing and energy yield calculation are given. Copyright © 2012 John Wiley & Sons, Ltd.     

基于IEC标准的小型风力发电机功率特性测试数据处理方法的研究

基于IEC标准的虚拟式小型风力发电机功率特性测试系统,采用Matlab软件对输出电流、输出电压、输出功率、大气温度、大气压力、风速等现场试验数据进行了bin法的分析和处理,获得了满足IEC61400-12-1标准的功率特性曲线、功率输出散点图、Cp曲线和年发电量的估算值,在风场测试中也获得了满意的结果,为评估和改进风力机性能提供了技术支持。     

Numerical study of turbulent flow around a wind turbine nacelle

This article presents a numerical method for the simulation of turbulent flow around the nacelle of a horizontal axis wind turbine. The flow field around the turbine and nacelle is described by the Reynolds‐averaged Navier–Stokes equations. The k–? model has been chosen for closure of the time‐averaged turbulent flow equations. The rotor disc is modelled using the actuator disc concept. The main purpose of this article is to assess the impacts of the variation of some operational parameters (e.g. blade pitch angle changes) and atmospheric turbulence upon the relationship between wind speed measured near the nacelle and freestream wind speed established for an isolated turbine. Simulation results were compared with experimental data (from a typical stall‐controlled, commercially available wind turbine rated higher than 600 kW). In general, good qualitative agreements have been found that validate the proposed method. It has been shown that a level of accuracy sufficient for use in power performance testing can be obtained only when a proper aerodynamic analysis of the inboard non‐lifting cylindrical sections of the blade is included. Furthermore, the numerical method has proven to be a useful tool for locating nacelle anemometers. Copyright © 2005 John Wiley & Sons, Ltd.     

The field performance of a remote 10 kW wind turbine

The collection and analysis of 15 months of continuously recorded field data from a small remote wind–diesel power system at a coastal farm site are reported. The paper focuses on the available wind data and the performance of the 10 kW Bergey wind turbine.     

Empirical and numerical analysis of small wind turbine aerodynamic performance at a plateau terrain in Kenya

Kenya's energy depends on fossil fuels and the country is yet to embrace alternative sources that are environmentally friendly. In this paper, empirical and computational approaches are presented to investigate aerodynamic performance of Small Wind Turbine (SWT) operation at arid rural Mwingi-Kitui plateau region, Kenya. We used empirical statistics to represent wind resource, and Computational Fluid Dynamics (CFD) to address SWT aerodynamic performance at the site. The numerical simulations, employing Transition Shear Stress Transport (SST) model and fully mesh resolved rotor, were performed and results obtained compared with empirical methods. From the Wind Power Density (WPD) values, 44.50–85.48 W/m² between turbine hub heights 20 and 60 m, the site corresponds to wind class ≈1; hence unsuitable for grid-connected power generation. In addition, the numerical findings give useful insights to SWT aerodynamic performance with respect to empirical approach at a plateau terrain wind regime.     

Prediction of aerodynamic performance of NREL offshore 5-MW baseline wind turbine considering power loss at varying wind speeds

In this study, a computational fluid dynamics (CFD) model was developed to simulate the aerodynamic performance of the National Renewable Energy Laboratory (NREL) offshore 5-MW baseline wind turbine with single rotor and full wind turbine. Using statistical methods, the relation between pitch angle and performance when the speed is above the rated wind speed was analyzed; furthermore, other published data were compiled to establish the functional equations of power, thrust with various inflow wind speeds, and pitch angles. In addition, according to shape optimization based on parametric modeling, the two-dimensional cross-section of the wind turbine blade can be defined through a metasurface approach, and the three-dimensional surface modeling of the wind turbine blade, nacelle, and tower is completed using the nonuniform rational B-splines (NURBS) interpolator. In terms of aerodynamic simulation, the unstructured polygon mesh was used herein to discretize the space and simulate the highly curved and twisted surfaces of the blade. In this study, the compact and accurate mesh form obtained through a grid independence test will be used to analyze the distribution of the pressure coefficient, shear stress coefficient, and limited streamline on the blade surface at various inflow wind speeds and pitch angles to understand the differences between different turbulence models and the causes of power and thrust attenuation at high inflow wind speeds. In addition, the phenomena of blade-tip vortices, dynamic stall, blade loading, and the interaction between nacelle and tower were collectively explored.     

Effects of leading edge erosion on wind turbine blade performance

This paper presents results of a study to investigate the effect of leading edge erosion on the aerodynamic performance of a wind turbine airfoil. The tests were conducted on the DU 96‐W‐180 wind turbine airfoil at three Reynolds numbers between 1 million and 1.85 million, and angles of attack spanning the nominal low drag range of the airfoil. The airfoil was tested with simulated leading edge erosion by varying both the type and severity of the erosion to investigate the loss in performance due to an eroded leading edge. Tests were also run with simulated bugs on the airfoil to assess the impact of insect accretion on airfoil performance. The objective was to develop a baseline understanding of the aerodynamic effects of varying levels of leading edge erosion and to quantify their relative impact on airfoil performance. Results show that leading edge erosion can produce substantial airfoil performance degradation, yielding a large increase in drag coupled with a significant loss in lift near the upper corner of the drag polar, which is key to maximizing wind turbine energy production. Copyright © 2013 John Wiley & Sons, Ltd.     

基于输出功率波动性的风电机组性能分析方法

输出功率特性是反映风电机组性能的主要指标之一,利用中央监控系统记录的运行数据,提出了3种不同的基于输出功率波动性机组性能分析方法。针对不同型号的机组,在测量机组动态功率曲线的基础上,构建基于功率曲线变异的输出性能分析模型;针对单台机组提出了基于风速和功率方差系数相关性的性能分析模型;针对单台机组运行在不同风速下,提出了基于分段风速的输出性能的分析方法。最后,以2个风电场的机组8个月的运行数据,对提出的机组分析性能方法进行验证,结果表明,文章提出的方法能够有效的分析风电机组的性能。     

Accounting for the speed shear in wind turbine power performance measurement

The current IEC standard for wind turbine power performance measurement only requires measurement of the wind speed at hub height assuming this wind speed to be representative for the whole rotor swept area. However, the power output of a wind turbine depends on the kinetic energy flux, which itself depends on the wind speed profile, especially for large turbines. Therefore, it is important to characterize the wind profile in front of the turbine, and this should be preferably achieved by measuring the wind speed over the vertical range between lower and higher rotor tips. In this paper, we describe an experiment in which wind speed profiles were measured in front of a multimegawatt turbine using a ground–based pulsed lidar. Ignoring the vertical shear was shown to overestimate the kinetic energy flux of these profiles, in particular for those deviating significantly from a power law profile. As a consequence, the power curve obtained for these deviant profiles was different from that obtained for the ‘near power law’ profiles. An equivalent wind speed based on the kinetic energy derived from the measured wind speed profile was then used to plot the performance curves. The curves obtained for the two kinds of profiles were very similar, corresponding to a significant reduction of the scatter for an undivided data set. This new method for power curve measurement results in a power curve less sensitive to shear. It is therefore expected to eventually reduce the power curve measurement uncertainty and improve the annual energy production estimation. Copyright © 2011 John Wiley & Sons, Ltd.     

Horizontal axis wind turbine working at maximum power coefficient continuously

The performance of a horizontal axis wind turbine continuously operating at its maximum power coefficient was evaluated by a calculation code based on Blade Element Momentum (BEM) theory. It was then evaluated for performance and Annual Energy Production (AEP) at a constant standard rotational velocity as well as at a variable velocity but at its maximum power coefficient.The mathematical code produced a power coefficiency curve which showed that notwithstanding further increases in rotational velocity a constant maximum power value was reached even as wind velocity increased.This means that as wind velocity varies there will always be a rotational velocity of the turbine which maximises its coefficient. It would be sufficient therefore to formulate the law governing the variation in rotational velocity as it varied with wind velocity to arrive at a power coefficient that is always the same and its maximum.This work demonstrates the methodology for determining the law governing the rotational velocity of the rotor and it highlights the advantages of a wind turbine whose power coefficient is always at maximum rather than very variable in line with the variation of wind velocity.     

Dynamic wind turbine output power reduction under varying wind speed conditions due to inertia

The inertia of wind turbines causes a reduction in their output power due to their inability to operate at the turbine maximum co‐efficient of performance point under dynamic wind conditions. In this paper, this dynamic power reduction is studied analytically and using simulations, assuming that a steady‐state optimal torque control strategy is used. The concepts of the natural and actual turbine time‐constant are introduced, and typical values for these parameters are examined. It is shown that for the typical turbine co‐efficient of performance curve used, the average turbine speed can be assumed to be determined by the average wind speed. With this assumption, analytical expressions for the power reduction with infinite and then finite turbine inertia are determined for sine‐wave wind speed variations. The results are then generalized for arbitrary wind speed profiles. A numerical wind turbine system simulation model is used to validate the analytical results for step and sine‐wave wind speed variations. Finally, it is used with real wind speed data to compare with the analytical predictions. Copyright © 2012 John Wiley & Sons, Ltd.     

The performance of Wells turbine under bi-directional airflow

This paper presents the performance of a Wells turbine operating under unsteady bi-directional airflow conditions. In this study, four kinds of blade profile were selected, NACA0020, NACA0015, CA9 and HSIM 15-262123-1576. The experiments have been carried out for two solidities under sinusoidal and irregular unsteady flow conditions based on Irish waves (Site2). It was found that for a Wells turbine operating under bi-directional air flow, the rotor geometry preferred is the blade profile of CA9 with rotor solidity σ=0.64. In addition, the efficiency curve of the Wells turbine under unidirectional flow conditions fails to present the rapid rise in the instantaneous efficiency which occurs at low flow coefficient of bi-directional flow condition. A comparative analysis between the numerical simulation results and experimental results was carried out. As a result, an excellent agreement was found between the numerical and experimental results. In addition, the effect of blade profile and rotor solidity on hysteretic characteristics of the turbine has been clarified experimentally under bi-directional airflow.     

风力机叶片翼型气动性能数值模拟

采用数值模拟方法对NACA23012,NACA4412,S809,S810等4种常用风力机叶片翼型进行了研究,分析了翼型静止与振荡时的气动性能.随着攻角的增加,静止翼型的升力系数先增大后减小,其阻力系数一直增大,显示出NACA4412翼型具有较好的低风速启动性能;振荡翼型的升力系数随着攻角的变化呈现一个闭合迟滞环曲线,显示出振荡翼型S809的动态失速迟滞效应最为明显.文章参照模拟结果和对比试验数据,验证了数值模拟的可靠性.