Innovative design approaches for large wind turbine blades

A preliminary design study of an advanced 50 m blade for utility wind turbines is presented and discussed. The effort was part of the Department of Energy WindPACT Blade System Design Study with the goal to investigate and evaluate design and manufacturing issues for wind turbine blades in the 1–10 MW size range. Two different blade designs are considered and compared in this article. The first is a fibreglass design, while the second design selectively incorporates carbon fibre in the main structural elements. The addition of carbon results in modest cost increases and provides significant benefits, particularly with respect to blade deflection. The structural efficiency of both designs was maximized by tailoring the thickness of the blade cross‐sections to simplify the construction of the internal members. Inboard the blades incorporate thick blunt trailing edge aerofoils (flatback aerofoils), while outboard more conventional sharp trailing edge high‐lift aerofoils are used. The outboard section chord lengths were adjusted to yield the least complex and costly internal blade structure. A significant portion of blade weight is related to the root buildup and metal hardware for typical root attachment designs. The results show that increasing the number of studs has a positive effect on total weight, because it reduces the required root laminate thickness. The aerodynamic performance of the blade aerofoils was predicted using computational techniques that properly simulate blunt trailing edge flows. The performance of the rotor was predicted assuming both clean and soiled blade surface conditions. The rotor is shown to provide excellent performance at a weight significantly lower than that of current rotors of this size. Copyright © 2004 John Wiley & Sons, Ltd.     

Design and validation of the high performance and low noise CQU‐DTU‐LN1 airfoils

This paper presents the design and validation of the high performance and low noise Chong Qing University and Technical University of Denmark LN1 (CQU‐DTU‐LN1) series of airfoils for wind turbine applications. The new design method uses target characteristics of wind turbine airfoils in the design objective, such as airfoil lift coefficient, drag coefficient and lift‐drag ratio, and minimizes trailing edge noise as a constraint. To express airfoil shape, an analytical expression is used. One of the main advantages of the present design method is that it produces a highly smooth airfoil shape that can avoid the problem of curvature discontinuity. An airfoil profile with discontinuous curvature can produce a discontinuous pressure gradient (i.e., local flow acceleration or deceleration), which enhances flow separation and thus decreases the airfoil performance. By combining the design method with the blade element momentum theory, the viscous‐inviscid xfoil code and an airfoil self‐noise prediction model, an optimization algorithm has been developed for designing the high performance and low noise CQU‐DTU‐LN1 series of airfoils with targets of maximum power coefficient and low noise emission. To validate the airfoil design, CQU‐DTU‐LN118 airfoil has been tested experimentally in the acoustic wind tunnel located at the Virginia Polytechnic Institute and State University (Virginia Tech), USA. To show the superiority of the CQU‐DTU‐LN1 airfoils, comparisons on aerodynamic performance and noise emission between the CQU‐DTU‐LN118 airfoil and the National Advisory Committee for Aeronautics (NACA) 64618 airfoil, which is used in modern wind turbine blades, are carried out. Copyright © 2013 John Wiley & Sons, Ltd.     

基于多岛遗传算法的钝尾缘翼型多目标优化设计

针对大型水平轴风力机叶片运行工况复杂和结构强度要求高的问题,提出一种钝尾缘翼型的多目标优化方法。基于多岛遗传算法,采用Hicks-Henne型函数和钝尾缘函数对钝尾缘翼型进行参数化拟合,通过Matlab软件自编程序调用XFOIL气动分析软件进行流场分析,对选定翼型进行多工况多目标优化设计。整个优化过程集成在Isight平台中,可实现自动优化。采用上述方法,选用NACA63921翼型作为初始翼型进行多目标优化,利用Fluent转捩模型对得到的钝尾缘翼型进行CFD数值验证,并与几种常见的同厚度翼型进行对比。数值验证表明,优化得到的钝尾缘翼型在多个工况点下的升阻比均高于同厚度的FFA、DU系列等现有风力机翼型,在失速工况区流动分离延后,具有更好的气动稳定性。     

尾随涡对风力机叶片气动性能影响机理研究

以Phase Ⅵ风力机叶片为研究对象,以r/R=30%、63%和95%处叶素为参考,建立与7、9、15 m/s试验风速下该风力机叶片附着涡环量沿展向分布相同的叶片模型,分析尾随涡对风力机当地翼型气动性能的影响机理。采用带转捩效应的SST k-ω湍流模型,对所建立的叶片模型和二维S809翼型的气动特性进行研究和对比分析。结果表明：旋转叶片尾随涡对分离现象产生抑制作用且随攻角的增大减弱;尾随涡的影响表现出多重效应,除了减小当地翼型的攻角,还降低其吸力面负压系数和压力面正压系数。     

USST高性能水平轴风力机翼型族

结合层流翼型与钝尾缘的特性,通过Hicks-Henne型函数对翼型参数化修型,基于多岛遗传算法及Xfoil气动分析,针对大型水平轴风力机翼型进行多目标函数、多设计工况、多约束条件下的优化设计,得到适用于大型风力机的高性能翼型族（USST翼型族）。其升阻比在大多数攻角下均高于同厚度的FFA、DU系列等现有风力机翼型族,且在同样的升力系数下具有更大的升阻比。最后为考核优化设计得到的翼型族,采用数值模拟方法对优化结果进行验证,证明设计得到的新型风力机翼型族具有优越的气动性能。     

V型沟槽对钝尾缘翼型流场分布及气动性能影响的研究

基于k-ωSST湍流模型,利用商业CFD工具ANSYS Fluent 16.0对DU35-17原始翼型、钝尾缘修型翼型及布置V型沟槽钝尾缘翼型进行数值模拟计算,对翼型改进前后的升阻力系数、流场分布和表面压力系数进行对比分析.结果表明,翼型在钝尾缘修型的同时布置V型沟槽,通过改变翼型尾缘处的压力分布和翼型表面的流动分布,...     

YD-大厚度风力机翼型粗糙敏感度试验研究

基于YD-系列3个大厚度钝后缘风力机翼型（相对厚度35%、40%和60%）,在西北工业大学NF-3低速翼型风洞开展粗糙敏感度对翼型性能影响的试验研究。结果表明,前缘粗糙对大厚度翼型的性能影响很大,造成升力线斜率和最大升力系数急剧减小,吸力面后缘流动的提前分离。     

尾缘襟翼对风力机翼型气动特性影响研究

尾缘襟翼(TEF)因其对翼型气动特性的调控能力,被认为是降低叶片疲劳和局部载荷最具可行性的气动控制部件。对TEF进行建模,采用Xfoil和CFD软件分析了TEF对翼型气动特性的影响及其机理,并从叶素理论角度对变化来流下TEF的减载效果进行了验证,结果表明:TEF位于不同摆角时翼型升阻力系数均有不同程度的变化,TEF可有效实现对翼型气动特性的主动控制;TEF摆动改变了翼型表面的静压分布和流动状态,进而对翼型升阻力和失速攻角产生影响;TEF可快速有效降低风速突然增加后的叶素受力,进而控制并减小叶片载荷。     

Computational investigations of blunt trailing‐edge and twist modifications to the inboard region of the NREL 5 MW rotor

The effects of twist and section shape modifications in the inboard region on the aerodynamic characteristics of the NREL 5 MW rotor have been examined using a Reynolds‐averaged Navier–Stokes method OVERFLOW2. The baseline rotor blade was modified by increasing the trailing‐edge thickness over the inboard region by modifying the sections’ thickness distribution aft of the maximum thickness location. Results when compared with the baseline rotor show that a modest increase of trailing‐edge thickness to 10–20%c increased power capture by 1%. Further increases in trailing‐edge thickness decrease in effectiveness to the point of reducing power capture when thicknesses reach 40%c. Increasing trailing‐edge thicknesses also leads to an increase in thrust, but this load is concentrated in the inboard region, resulting in a small increase in root bending moments. The blunt trailing‐edge concept greatly reduces the spanwise extent of inboard flow separation evident in the baseline NREL 5 MW rotor. The low‐pressure region aft of the trailing edge, created by the geometry, acts to reduce the spanwise spreading of the inboard separation. Rotors with modified twist distributions over the inboard 35%R of span are also compared. Inboard twist angles are varied from + 6° to ? 6° from the baseline twist schedule. Increasing inboard blade twist reduces overall rotor power capture but reduces thrust at a faster rate. Power capture remains constant with decreasing inboard geometry twist, whereas thrust increases approximately linearly by 0.75% for a decrease in thrust of 6°. Copyright © 2012 John Wiley & Sons, Ltd.     

垂直轴风力机改进翼型气动及功率特性研究

为提高垂直轴风力机的风能利用率,基于CFD数值模拟技术,分析了常用典型垂直轴风力机翼型的气动及功率特性,并以NACA0012翼型为基础对其进行改进。对比改进前后翼型表明,增大翼型厚度可降低升阻比,增大翼型弯度可增强其失速特性;厚尾缘翼型、升阻互补型翼型可分别降低翼型失速性能、增加启动力矩,其中厚尾缘翼型的H型垂直轴风力机的功率系数较大,可提高风能利用率,为翼型优化设计提供了新思路。     

低雷诺数下凹坑结构对翼型层流分离影响的数值研究

在低雷诺数Re工况下,翼型表面容易发生流动分离,形成的层流分离泡会导致翼型气动性能恶化,且分离泡在尾缘周期性脱落,会诱发振动,影响叶片的结构安全.文章以NACA4415翼型为例,采用大涡模拟(LES)方法,在低Re下,对光滑翼型及布置凹坑结构翼型的层流分离进行了研究.研究结果表明:凹坑结构对翼型在低Re下出现的层流分离...     

增加风力机叶片翼型后缘厚度对气动性能的影响

以FFA-W3翼型族为研究对象,对其系列翼型的后缘作了加厚处理。利用XFOIL软件对修改前后的翼型的气动性能进行了计算,利用Viterna-Corrigan失速后模型将气动性能数据的攻角扩展到了90°。对修改前后的翼型的气动性能数据的改变作了对比分析。利用原翼型和修改后翼型的气动性能数据对同一个风力机进行了气动性能计算,并对计算结果作了对比分析。结论认为,对翼型后缘进行适当加厚处理对气动性能影响不大,为满足工艺要求在叶片的生产中对翼型后缘作加厚处理是可行的。     

高效低载的三维风力机叶片外形优化设计方法

常规风力机叶片的优化设计都是从二维翼型开始的,且翼型总是以升阻比最大为优化目标。然而,二维翼型的升阻比最大和三维叶片的高风能利用率与低气动载荷有本质的不同,采用以往的叶片优化方法常常会在提高风能利用率的同时,使叶片所受的气动载荷也提高。针对这一问题,提出基于多岛遗传算法和动量叶素理论,在给定风况条件下,以加权风能利用率最高与气动载荷最小为目标函数,以叶片各个截面的翼型型线及扭角作为设计变量,对三维叶片开展多目标优化方法设计研究。并对某实际NREL Phase VI叶片进行优化设计,结果表明：在给定风况下相比原叶片,优化叶片在风能利用率提升了3.06%的基础上,叶根弯矩降低了11.68%。在变转速与变风况下,优化叶片的气动效率整体提升,叶根弯矩明显降低。     

风力机翼型尾缘厚度对粗糙敏感性影响的研究

综合应用涡面元和RANS方法,研究DU93-W-210、DU91-W2-250及DU97-W-300这3种常用翼型经尾缘修型后尾缘厚度对粗糙敏感性的影响.在涡面元方法中采用设置固定转捩和在RANS方法中采用设置锯齿形边界条件的方式来模拟翼型前缘污染,研究发现前缘污染造成翼型吸力峰降低,引起翼型气动性能下降,然而随着尾缘...     

Numerical simulation of flatback airfoil aerodynamic noise

The present paper presents a possible path for developing a large eddy simulation (LES) applicable to high Reynolds-number complex turbulent flows and the performance of the coupling of LES with statistical turbulence models around the flow over a blunt trailing edge configuration. The turbulent fluctuations in the boundary layers at the inflow region of the LES domain are generated by a synthesized turbulence method. The hybrid RANS-LES model showed considerable improvement in prediction accuracy even at a moderate grid resolution. The aerodynamic comparison with experimental data shows like results for the pressure distributions surrounding a flatback airfoil. To predict accurately the noise radiation from the blunt trailing edge and to save computational costs, the near-field region is computed by embedded LES while the surrounding region is simultaneously computed by RANS. The Brooks, Pope, and Marcolini (BPM) semi-empirical model is used for noise comparison with the hybrid RANS-LES result and experimental data. The present hybrid RANS-LES method is found to be adequate for predicting aerodynamic noise generation by vortical flow in the vicinity of a blunt trailing edge airfoil over a range of frequencies.     

Design of a new urban wind turbine airfoil using a pressure-load inverse method

This paper presents the design methodology of a new wind turbine airfoil that achieves high performance in urban environment by increasing the maximum lift. For this purpose, an inverse method was applied to obtain a new wind turbine blade section with constant pressure-load along the chord, at the design inlet angle. In comparison with conventional blade section designs, the new airfoil has increased maximum lift, reduced leading edge suction peak and controlled soft-stall behaviour, due to a reduction of the adverse pressure gradient on the suction side. Wind tunnel experimental results confirmed the computational results.     

A Beddoes‐Leishman–type model with an optimization‐based methodology and airfoil shape parameters

Floating offshore wind turbines operate in a highly unsteady environment; thus, many flow transients occur at the blade cross‐sectional level, which affect the rotor aerodynamics. In every rotor aerodynamics modelling technique requiring the blade element theory, the blade cross‐sectional aerodynamics need to be predicted accurately on the basis of the flow conditions. At reduced frequencies of 0.01 and greater, the flow unsteadiness can be considered significant and cannot be treated as quasisteady. Floating offshore wind turbines can be expected to consistently operate in some degree of yaw or pitch, which may result in reduced frequencies greater than 0.01 over most of the blade when operating at rated wind speeds and rotor RPM. The Beddoes‐Leishman model is a comprehensive but complex model for predicting unsteady airfoil aerodynamics, containing 8 dimensionless time constants. In the present study, the Beddoes‐Leishman model was compared with experimental results of 10 different airfoil profiles, each performed under a range of Reynolds numbers, motion frequencies, mean, and amplitudes of angle of attack. An optimization was performed for all time constants in the model, the results of which were used to formulate a simplified model with fewer equations, without any reduction in accuracy. Further, optimizations were performed against the experimental results of each airfoil, and the optimized constants were compared with shape parameters of the airfoils, yielding possible correlations, which were then applied in the simplified Beddoes‐Leishman model to yield improved accuracy, measured as a 5% reduction in accumulated error between experimental and predicted coefficients of lift.     

Extraction of airfoil data using PIV and pressure measurements

A newly developed technique for determining the angle of attack (AOA) on a rotating blade is used to extract AOAs and airfoil data from measurements obtained during the MEXICO (Model rotor EXperiments in COntrolled conditions) rotor experiment. Detailed surface pressure and Particle Image Velocimetry (PIV) flow fields at different rotor azimuth positions are examined for determining sectional airfoil data. The AOA is derived locally by determining the local circulation on the blade from pressure data and subtracting the induction of the bound circulation from the local velocity. The derived airfoil data are compared to 2D data from wind tunnel experiments and XFOIL computations. The comparison suggests that the rotor is subject to severe 3D effects originating from the geometry of the rotor, and explains why the Blade Element Momentum technique with 2D airfoil data over‐predicts the loading of the rotor. The extraction technique is verified by employing the derived airfoil characteristics as input to computations using the BEM technique and comparing the calculated axial and tangential forces to the measured data. The comparison also demonstrates that the used technique of determining the AOA is a reliable tool to extract airfoil data from experimental data. Copyright © 2010 John Wiley & Sons, Ltd.     

Airfoil optimization for wind turbine application

An airfoil optimization method for wind turbine applications that controls the loss in performance due to leading edge contamination is developed and tested. The method uses the class‐shape‐transformation technique to parametrize the airfoil geometry and uses an adjusted version of the panel code XFOIL to calculate the aerodynamic performance. To find optimal airfoil shapes, the derivative‐free Covariance Matrix Adaptation Evolution Strategy is used in combination with an adaptive penalty function. The method is tested for the design of airfoils for the outer part of a megawatt‐class wind turbine rotor blade, and the results are compared with airfoils from Delft University. It is found that the method is able to automatically create airfoils with equal or improved performance compared with the Delft designs. For the tested application, the adjustments performed to the XFOIL code improve the maximum lift, post stall, and the overall drag predictions.     

A solution‐based stall delay model for horizontal‐axis wind turbines

This work proposes a new solution‐based stall delay model to predict rotational effects on horizontal‐axis wind turbines. In contrast to conventional stall delay models that correct sectional airfoil data prior to the solution to account for three‐dimensional and rotational effects, a novel approach is proposed that corrects sectional airfoil data during a blade element momentum solution algorithm by investigating solution‐dependent parameters such as the spanwise circulation distribution and the local flow velocity acting at a section of blade. An iterative process is employed that successively modifies sectional lift and drag data until the blade circulation distribution is converged. Results obtained with the solution‐based stall delay model show consistent good agreement with measured data along the National Renewable Energy Laboratory Phase VI and Model Experiments in Controlled Conditions rotor blades at low and high wind speeds. Copyright © 2014 John Wiley & Sons, Ltd.