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下出现的层流分离现象有较好的抑制作用,凹坑结构翼型在尾缘的分离流更加贴近翼型表面,凹坑结构翼型尾缘附近的分离涡明显减少;凹坑结构改善了低Re工况下翼型的气动性能,深径比h/d为0.25时,翼型升、阻比达到最大18.23。     

Design of high-efficiency turbomachinery blades for energy conversion devices with the three-dimensional prescribed surface curvature distribution blade design (CIRCLE) method

The purpose of this paper is to present the advantages of the direct presCrIbed suRface Curvature distribution bLade dEsign (CIRCLE) method for the design of high-efficiency turbomachinery blades. These advantages are illustrated by redesigning several examples of axial turbomachinery blades of interest to energy conversion devices, and discussing in detail the aerodynamic performance and efficiency improvements of the redesigned blades over the original geometries. The two-dimensional (2D) method, originally proposed for turbine blades, has been extended for use with 2D and three-dimensional (3D) turbine, compressor and fan blades, and isolated airfoils. By specification, the method allows joining line segments between the leading edge (LE) and trailing edge (TE) circles or ellipses so that the streamwise distribution of surface curvature and slope of curvature are continuous everywhere from the LE stagnation point to the TE stagnation point. The form of the line segments to prevent the “wiggles” of higher order lines is presented. Also by specification, the CIRCLE method can be integrated with multi-objective heuristic or evolutionary-algorithm optimization methods. The efficacy of the method is examined by: redesigning two 2D turbine blades, one 2D compressor blade, and one 2D isolated airfoil; and by designing one 3D compressor blade row and one 3D turbine blade row. The aerodynamic performance improvements between the original and the sample redesigned blades are discussed in detail, resulting in higher-efficiency blades than the original geometries. Further extension of the method for centrifugal and mixed-flow impeller geometries is a coordinate transformation. It is concluded that the CIRCLE method is a new design environment enabling the original design (or redesign) of high-efficiency 2D and 3D turbomachine blades, with direct applications in a variety of energy conversion devices.     

Aerodynamic characteristics of wind turbine blades with a sinusoidal leading edge

The aerodynamic characteristics of a kind of bionic wind turbine blades with a sinusoidal leading edge have been investigated in this paper based on a three‐dimensional Reynolds‐averaged Navier–Stokes simulation. The calculated results show that compared with a straight leading‐edge blade, the new‐type blade has a great improvement in shaft torque at high wind speeds. The localized vortices shedding from the leading‐edge tubercles, which can generate a much greater peak of the leading‐edge suction pressure than that from the straight leading‐edge case, are the physical essentials to enhance the wavy blade's aerodynamic performances as the blade goes into stall. In particular, the outboard segment from the 60%R station to the blade tip is the key region for wavy leading‐edge blades to improve the aerodynamic characteristics at high‐speed inflows. In this key region, a wavy blade can obtain a greater power output as the wavelength l and the waveheight δ increase. The present numerical results also show that the wavy leading‐edge shape is unfavorable for a wind turbine blade under the design conditions (e.g., at the rated wind speed). At these conditions, an early boundary‐layer separation as a result of the geometric disturbances of the leading‐edge tubercles will inevitably result in a visible shaft‐torque reduction in the wavy‐blade cases. Anyway, the wavy blades still tend to generate a more robust power output as a whole from 10 to 20 m s ^?1 than the original NREL phase‐VI blade. Copyright © 2011 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.     

偏航工况下叶片翼型动态特性研究

首先通过理论分析,研究风力机偏航运行时叶片各翼型的攻角变化规律,建立翼型俯仰运动模型;然后基于大涡模拟（LES）方法,研究偏航工况下叶片翼型的动态气动特性。结果表明：风轮在偏航工况下运行时,叶片各截面翼型攻角变化呈近似的正余弦规律;叶片不同展向位置翼型均发生不同程度的流动分离,出现动态失速现象,越靠近叶根,由偏航引起的动态迟滞效应越明显;翼型俯仰过程中,吸力面前缘分离泡的动态变化过程,导致吸力面前缘压力出现小范围的剧烈振荡,增大流动的不稳定性。     

Integrated free‐form method for aerostructural optimization of wind turbine blades

A typical approach to optimize wind turbine blades separates the airfoil shape design from the blade planform design. This approach is sequential, where the airfoils along the blade span are preselected or optimized and then held constant during the blade planform optimization. In contrast, integrated blade design optimizes the airfoils and the blade planform concurrently and thereby has the potential to reduce cost of energy (COE) more than sequential design. Nevertheless, sequential design is commonly performed because of the ease of precomputation, or the ability to compute the airfoil analyses prior to the blade optimization. This research compares 2 integrated blade design approaches. The precomputational method combines precomputation with the ability to change the airfoil shapes in limited ways during the optimization. The free‐form method allows for a complete range of airfoil shapes, but without precomputation. The airfoils are analyzed with a panel method (XFOIL) and a Reynolds‐averaged Navier‐Stokes computational fluid dynamics method (RANS CFD). Optimizing the NREL 5‐MW reference turbine showed COE reductions of 2.0%, 4.2%, and 4.7% when using XFOIL and 2.7%, 6.0%, and 6.7% when using RANS CFD for the sequential, precomputational, and free‐form methods, respectively. The precomputational method captures most of the benefits of integrated design for minimal additional computational cost and complexity, but the free‐form method provides modest additional benefits if the extra effort is made in computational cost and development time.     

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.     

风力机叶片外形设计及三维实体建模研究

基于贝茨理论,结合具体工程实际,对某中型风力机叶片进行外形设计.并在此基础上提出了风力机叶片的三维建模方法,即利用点的坐标变换理论来计算叶片各断面翼型的空间实际坐标,然后运用UG强大的三维曲面建模功能来建立叶片复杂曲面.该文提出的方法减少了风力机叶片等复杂曲面的建模工作量;叶片实体模型的建立也为叶片的气动性能计算和结构设计与分析奠定了基础.     

Localization of wind turbine noise using a microphone array in wind tunnel measurements

An experimental investigation on scaled wind turbine models in a wind tunnel with a microphone array is presented. Our study focuses on the localization and quantification of aerodynamic noise sources on rotating wind turbine blades with the aim of identifying the contributing factors that have an impact on the source spectra. Therefore, wind tunnel measurements were conducted for three different blade geometries (NACA 4412 shape, Clark-Y shape, and sickle shape), five pitch angles between ?2° and +8° and five wind velocities between 5 and 13 ms^??1. For the localization of rotating sound sources with a microphone array, a rotating beamforming method based on the acoustic ray method is used. The Clean-SC deconvolution method was used to improve the resolution of the acoustic sources, and integrated spectra were calculated for the individual blades. The sound sources were localized at the wind turbine blades and assigned to the leading edge and trailing edge subregions. The results show a high dependency on the sound source distribution and the source strength with regard to the observed one-third octave bands, wind velocity, and blade geometry. Hence, the localization of rotating sound sources with a microphone array is a suitable method for the development of wind turbine blades that emit less noise.     

风电叶片低粗糙敏感性厚翼型优化方法研究

基于叶片设计需求,将厚翼型设计点性能随前缘粗糙的敏感性参数化并引入到厚翼型设计中,改进其优化模型;结合翼型几何设计、性能分析以及最优化算法建立厚翼型低粗糙敏感性优化设计方法。通过35%相对厚度翼型案例设计,验证了该方法在实现光滑表面下高气动性能的同时,可有效降低粗糙表面下的性能损失。     

基于CFD的微水头双向水轮机叶片比选及整机性能分析

针对微水头双向灯泡贯流式水轮机叶片翼型和形状对其性能的影响,在相同设计水头下,对3种叶片的微水头双向贯流式水轮机进行了CFD数值模拟,对比分析了正反向工况下3种叶片的水轮机的外特性(流量、效率、出力)、叶片表面静压分布和相对流速矢量分布,最终确定了叶片C为较优叶片,进而分析了较优水轮机模型下的各部分水头损失以及内部流场规律。结果表明,正向工况下由于灯泡体后置,使得出水流道内出现回流、漩涡等不良流态,增加了撞击损失,故正向工况的效率低于反向工况。     

A wind turbine blade profile analysis code based on the singularities method

The aerodynamic characteristics of wind turbines are closely related to the geometry of their blade profiles. The innovation and the technological development of wind turbine blade profiles can be centred on two tendencies. The first is to improve the shape of the existing airfoils and the second is to design new shapes of airfoils in order to get some more ambitious aerodynamic characteristics and enhanced performance.The aim of this paper is to develop an accurate airfoil analysis lower order code, based on the singularities method, for wind turbine applications. The 2D incompressible potential flow model has been used. In the implementation of the singularities method, source–vortex distributions over the airfoil contour are used to compute the flow characteristics. The accuracy and the validity of the results have been tested using experimental data obtained from Wind Turbine Airfoil Catalogue “Risø National Laboratory, Roskilde, Denmark, August 2001” and have shown considerable agreement.     

The inverse design of the wind turbine blade sections by the singularities method

The aerodynamic characteristics of wind turbines are closely related to the geometry of their blades. The innovation and the technological development of wind turbine blades can be centred on two tendencies. The first is to improve the shape of existing blades; the second is to design new shapes of blades. The aspiration in the two cases is to achieve an optimal circulation and hence enhancing some more ambitious aerodynamic characteristics. This paper presents an inverse design procedure, which can be adapted to both thin and thick wind turbine blade sections aiming to optimise the geometry for a prescribed distribution of bound vortices. A method for simulating the initial contour of the blade section is exposed, which simultaneously satisfy the aerodynamic and geometrical constraints under nominal conditions. A detailed definition of the function characterising the bound vortex distribution is presented. The inviscid velocity field and potential function distributions are obtained by the singularities method. In the design method implemented, these distributions and the circulation of bound vortices on the camber line of the blade profile, are used to rectify its camber in an iterative calculation leading to the final and optimal form of the blade section once convergence is attained. The scheme proposed has been used to design the entire blade of the wind turbine for a given span-wise distribution of bound circulation around the blade contour.     

Active load alleviation potential of adaptive wind turbine blades using shape memory alloy actuators

Upscaling of wind turbine blades calls for implementation of innovative active load control concepts that will facilitate the flawless operation of the machine and reduce the fatigue and ultimate loads that hinder its service life. Based on aeroelastic simulations that prove the enhanced capabilities of combined individual pitch and individual flap control at global wind turbine scale level, a shape adaptive concept that encompasses an articulated mechanism consisting of two subparts is presented. Shape memory alloy (SMA) actuators are investigated and assessed as means to control the shape adaptive mechanism at airfoil section level in order to alleviate the developed structural loads. The concept is embedded in the trailing edge region of the blade of a 10‐MW horizontal axis wind turbine and acts as a flap mechanism. Numerical simulations are performed considering various wind velocities and morphing target shapes and trajectories for both normal and extreme turbulence conditions. The results prove the potential of the concept, since the SMA controlled actuators can accurately follow the target trajectories. Power requirements are estimated at 0.22% of the AEP of the machine, while fatigue and ultimate load reduction of the flap‐wise bending moment at the blade root is 27.6% and 7.4%, respectively.     

An experimental investigation of the heat transfer in a ribbed triangular cooling channel

One of the most challenging aspects of gas turbine cooling is the cooling of the first stages of turbine blades. Here the highest external heat load is seen at the leading edge of the blade. The present study investigates the internal cooling in a triangular channel with a rounded edge as a model of a leading edge cooling channel for a gas turbine blade. A transient liquid crystal method is used to measure the heat transfer. Experimental results are reported for a number of new 3D rib configurations for Reynolds numbers between 50 000 and 200 000. From the experimental results it has been found that 60 deg. ribs provide in general higher heat transfer enhancements than 45 deg. ribs. However, this results in extremely high friction factors for the 60 deg. ribs. Taking the local and mean distributions of the heat transfer coefficients (as well as the increase in friction factors) into consideration, it was found that the most promising rib arrangement for leading edge cooling is a 3D rib with 45 deg. angle and double-sided fully overlapped ribs in the arc area. These ribs provide uniform heat transfer in the arc area as well as a high level of the heat transfer coefficients in the channel. The resulting friction factors are in an acceptable range for these ribs.     

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,然而随着尾缘厚度的适量增加,翼型最大升阻比及设计升力系数即气动性能的下降率呈减小趋势,表明适当增加尾缘厚度可有效降低风力机叶片粗糙敏感性。     

前缘改形对翼型气动噪声特性影响

为得到高气动性能、低噪声的风力机专用翼型,基于参数化建模翼型,研究前缘外形对风力机翼型气动性能及气动噪声的影响规律。通过分离涡模拟方法和声学类比方程建立噪声预测方法。针对非对称翼型S809通过样条函数参数化处理前缘改形进行气动噪声计算。结果表明:翼型压力面前缘加厚,对翼型升阻力系数无明显影响,但大攻角时翼型周围压力分布均匀,流动相对稳定,且气动噪声声压级低于原始翼型,随压力面厚度增加气动噪声越大;吸力面加厚使得翼型升力系数增大,阻力系数减小,能抑制翼型失速时尾缘涡与前缘涡的生成,变形量越大气动噪声越小;翼型前缘上弯,翼型在失速区升力系数减小,阻力系数增大,流动越加不稳定,声压级随着攻角的增加呈递增趋势;翼型前缘下弯,翼型处于失速区升力系数增大,阻力系数减小,能抑制流动分离,未生成前缘涡和尾缘涡,当前缘下弯不变时,随加厚厚度增加翼型声压级呈减小趋势,且前缘下弯翼型声压级小于前缘上弯。     

Predictions of ice formations on wind turbine blades and power production losses due to icing

Prediction of ice shapes on a wind turbine blade makes it possible to estimate the power production losses due to icing. Ice accretion on wind turbine blades is responsible for a significant increase in aerodynamic drag and decrease in aerodynamic lift and may even cause premature flow separation. All these events create power losses and the amount of power loss depends on the severity of icing and the turbine blade profile. The role of critical parameters such as wind speed, temperature, liquid water content on the ice shape, and size is analyzed using an ice accretion prediction methodology coupled with a blade element momentum tool. The predicted ice shapes on various airfoil profiles are validated against the available experimental and numerical data in the literature. The error in predicted rime and glime ice volumes and the maximum ice thicknesses varies between 3% and 25% in comparison with the experimental data depending on the ice type. The current study presents an efficient and accurate numerical methodology to perform an investigation for ice‐induced power losses under various icing conditions on horizontal axis wind turbines. The novelty of the present work resides in a unified and coupled approach that deals with the ice accretion prediction and performance analysis of iced wind turbines. Sectional ice profiles are first predicted along the blade span, where the concurrence of both rime and glaze ice formations may be observed. The power loss is then evaluated under the varying ice profiles along the blade. It is shown that the tool developed may effectively be used in the prediction of power production losses of wind turbines at representative atmospheric icing conditions.     

Non-destructive and contactless defect detection inside leading edge coatings for wind turbine blades using mid-infrared optical coherence tomography

Leading edge erosion of wind turbine blades is one of the most critical issues in wind energy production, resulting in lower efficiency, as well as increased maintenance costs and downtime. Erosion is initiated by impacts from rain droplets and other atmospheric particles, so to protect the blades, special protective coatings are applied to increase their lifetime without adding significantly to the weight or friction of the blade. These coatings should ideally absorb and distribute the force away from the point of impact; however, microscopic defects, such as bubbles, reduce the mechanical performance of the coating, leading to cracks and eventually erosion. In this work, mid-infrared (MIR) Optical Coherence Tomography (OCT) is investigated for non-destructive, contactless inspection of coated glass-fiber composite samples to identify subsurface coating defects. The samples were tested using rubber projectiles to simulate rain droplet and particle impacts. The samples were subsequently imaged using OCT, optical microscopy, and X-ray tomography. OCT scanning revealed both bubbles and cracks below the surface, which would not have been detected using ultrasonic or similar non-destructive methods. In this way, OCT can complement the existing quality control in turbine blade manufacturing, help improve the blade lifetime, and reduce the environmental impact from erosion.     

基于Theodorsen理论的新型动态失速预测模型及其应用

风力机叶片动态失速时的非定常气动特性及严重的迟滞现象使得风力机功率实测值严重偏离其静态预测值。鉴于此,基于Theodorsen理论、基尔霍夫势流理论,在忽略低阶附加质量引起的下洗气流加速度项及状态变量转换后,提出一种包括翼型附着流和后缘动态分离流的新型动态失速模型。利用该模型分析NREL 5 MW海上风力机叶片6种翼型的非定常动态失速特性得出：通过翼型的气流在完全附着流与完全分离流之间不断转换,受附着流脱落尾诱导的动态下洗气流影响及边界层动态分离产生的压力滞后的双重作用,动态升力系数变化曲线和静态升力现象曲线偏差较大,6种翼型动态升力系数变化曲线均呈非常明显的迟滞环现象。DU40、DU35、DU30、DU25、DU21和NACA64这6种翼型动态升力系数增幅明显,分别达17.6%、60.9%、60.7%、55.1%、63.7%和40.8%。动态失速攻角极大地超过静态失速攻角,分别增大到36.53°、21.40°、20.20°、17.68°、16.97°和21.42°。6种翼型动态失速预测结果与公开实验数据结论一致,证实所提出的动态失速气动模型计算结果准确可信,具有较强通用性。