A study on the prediction of aerofoil trailing‐edge noise for wind‐turbine applications

This paper presents a comparative study between the so‐called BPM and TNO models for the prediction of aerofoil trailing‐edge noise with particular emphasis on wind‐turbine applications (the BPM model is named after Brooks, Pope and Marcolini who first proposed the model, and the TNO model is named after the TNO institute of Applied Physics where it was first proposed). In this work, two enhanced versions of the BPM model are proposed, and their performances are compared against two recent anisotropic TNO models that require more detailed boundary‐layer information than the BPM‐based models. The two current enhanced models are denoted as BPMM‐PVII and BPMM‐BLkω, where the former uses a panel method with viscous‐inviscid interaction implemented (PVII) for boundary‐layer calculations, the latter estimates the boundary‐layer (BL) properties using a two‐dimensional k‐ω turbulence model (kω), and BPMM stands for BPM‐Modified. By comparing the predicted sound spectra with existing measurement data for seven different aerofoils tested in the current study, it is shown that the BPMM‐PVII model exhibits superior results to those by the other models for most cases despite the simplicity without considering anisotropy. The BPMM‐PVII model is then combined with Prandtl's nonlinear lifting‐line theory to calculate and investigate three‐dimensional rotor noise characteristics of an NREL UAE Phase‐VI wind turbine (NREL UAE stand for the National Renewable Energy Laboratory Unsteady Aerodynamic Experiment). It is demonstrated that the current approach may provide an efficient solution for the prediction of rotor aerodynamics and noise facilitating industrial design and development for low‐noise wind turbines. Copyright © 2016 John Wiley & Sons, Ltd.     

An improved prediction model of vortex shedding noise from blades of fans

The main source of the noise of an axial flow fan is the fluctuating pressure field on blade surfaces caused by the shedding of vortices at the trailing edge of blades. An analytical model to predict the vortex shedding noise generated at the trailing edge of blades of axial flow fans was proposed by Lee in 1993. In this model, for mathematical convenience, an idealized vortex street is considered. However, the agreement between the analytical results and the experimental data needs to be improved because of the simplification about the Karman vortex street in the wake of blade. In the present study, a modified model is proposed based on the prediction model by Lee. The boundary layer theory is used to analyze and calculate the boundary layer development on both the pressure and the suction sides of blades. Considering the effect of boundary layer separation on the location of noise source, the predicted overall sound pressure level compares favorably with the experimental data of an axial fan. In the calculation of A-weighted sound pressure level (L_A), considering the effect of static pressure on radiate energy, the predicted broadband noise with the modified model compares favorably with the experimental data of a multiblade centrifugal fan.     

基于时域积分的水平轴风力机风轮噪声预测理论及应用

给出了考虑水平轴风力机风轮厚度噪声与负荷噪声的延迟时形式的时域积分解及其噪声预测理论。基于Ffowcs Willians-Hawkings声学方程，减少了偏导数项的求解，提高了计算速度，避免了声学计算中的奇异性问题。对小型水平轴风力机FD2-300在3个方向的辐射噪声进行了预测，得到了声场各种源成分的噪声的分布与指向性规律。计算结果表明：在风轮的旋转平面，具有最大的总噪声级的指向性，负荷噪声在旋转平面以及风力机下游起着主导作用。对于600kW大型水平轴风力机进行了局部区域的噪声现场测量，并且与预测值进行了对比。结果表明：模型的预测结果与测试数据比较符合，且变化趋势一致，在整个测量区域，预测值比测量值低，这是由于计算模型只考虑到风力机叶片的负荷噪声与厚度噪声，对于实际运行的风力机来说，其辐射的总噪声除了与叶片的负荷、厚度有关，还与非定常来流、叶片本身的非定常性和气流粘性有关。若以该文建立的模型进一步考虑风力机的非定常性和粘性效应，将提高其预测准确性，在风力机整体优化设计以及噪声控制方面提供理论指导。     

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.     

基于ARMA模型的变压器噪声逆向还原实验研究

基于声辐射理论和激光测振原理，通过实验测量干式变压器模型的表面振速和辐射噪声声压，分别采用表面振速法和频响函数法求得变压器的声辐射指数。在此基础上，采用自回归滑动平均（ARMA）模型开展变压器噪声逆向还原研究，获取声压与声压级预测值，并与实验值进行对比。结果表明：采用频响函数法得到的声辐射指数比采用表面振速法得到的约大1.0 ～ 1.5 dB；采用基于ARMA模型的噪声预测算法得到的声压与实验得到的声压约相差0.015 Pa，声压级约相差1 dB；利用基于ARMA模型的预测算法和激光测振原理进行噪声逆向还原具有较好的可行性，且可推广应用于其他结构辐射噪声的预测。     

A full-scale prediction method for wind turbine rotor noise by using wind tunnel test data

The development of a low-noise wind turbine rotor and propeller is often cost-effective and is in fact a race against time to those who wish to build and test a small-scale rotor instead of an expensive full-scale rotor. The issue of this approach has to do with the interpretation of wind tunnel model test data in terms of both the frequency band and sound pressure level information for the noise scaling effect.This paper discusses a prediction method for the estimation of the noise generated from a full-scale wind turbine rotor using wind tunnel test data measured with both a small-scale rotor and a 2D section of the blade. The 2D airfoil self-noise and the scaled rotor noise were investigated with a series of wind tunnel experiments. Wind tunnel data post-processing considered four aspects: removal of the test condition effect, scaling to full scale, consideration of the wind turbine rotor operating conditions, and the most important terms of full-scale rotor noise as adjustments to address the differences between the wind tunnel test conditions and the full-scale operating conditions.A full-scale rotor noise prediction results comparison was performed by initially dividing the test conditions into the condition of a 2D section noise test and the condition of a small-scale rotor noise test. Based on an airfoil section, the rotor was selected from a blade section at r/R = 0.75. The small-scale rotor was scaled down by a factor of 5.71 for the wind tunnel test.Finally, the full-scale rotor noise data was compared with the wind tunnel test data using a scaling estimation method.     

Analysis of aerodynamic noise generated from inclined circular cylinder

IntroductionThe public attention to environment' has beenincreased in these days, and noise reduction of ventilationfan is extremely needed more than ever. We must reducethe generated noise and control the resources of thediscordant one. Recently, aerodynndc noise problems,e.g. wind-pass sound from high-speed mobiles, noisefrom cooling fan, are increased rapidly. Manyexperimental studies have been reported tO contfol thegenerated noise, and numerical prediction of aerodyntricsound (CAA; Comp…     

大型水平轴风力机噪声的测量

阐述了风力机噪声的传播、衰减和针对噪声的评估准则,以及风力机噪声的测量原理。针对风力机噪声测量测点布置进行了优化,给出了风力机噪声的测量实验方案和装置,并且采用自由声场法对风力机噪声进行了测量,得出了风力机噪声和周围环境噪声之间的合成声压级。     

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。     

基于塔筒添加螺旋线的风力机降噪性能优化研究

为降低风力机对周围居民的噪声污染,提出一种用于分布式风力机的塔架表面缠绕螺旋线的降噪方案。以S2030翼型风力机为计算模型,以螺旋线高度、螺距、螺头数、覆盖范围及旋向为因素,近尾迹辐射噪声总声压级为评价指标进行正交试验,在额定工况下利用ANSYS Fluent数值模拟平台LES/FWH方法进行数值计算。结果表明：螺旋线高度h为5.5 mm、螺距P/d为0.5、螺头数N为4、覆盖面积为全部、旋向为逆时针时为最优组合。各因素对总声压级影响的程度由大到小为螺距>高度>覆盖范围>螺头数>旋向。塔架缠绕螺旋线能有效降低200~2000 Hz中高频噪声声压级。降噪效果随轴向距离的增大而增大,最高可降低总声压级13.19 dB（A）。     

Noise simulations of flap devices for wind turbine rotors

The rotor of a large diameter wind turbine experiences more substantial and more dynamic loads due to the fluctuating and heterogeneous wind field. The project SmartBlades 2.0 investigated rotor blade design concepts that alleviate aerodynamic loading using active and passive mechanisms. The present work evaluates the acoustics of the two load alleviating concepts separately, an inboard slat and an outboard flap, using the Fast Random Particle Mesh/Fast Multipole Code for Acoustic Shielding (FRPM/FMCAS) numerical prediction toolchain developed at DLR with input from the averaged flow field from RANS. The numerical tools produce a comparable flap side-edge noise spectrum with that of the measurement conducted in the Acoustic Wind Tunnel Braunschweig (AWB). The validated FRPM/FMCAS was then used to analyze the self-noise from a slat at the inboard section of a rotor blade with a 44.45 m radius and compared with that from the outboard trailing edge. Furthermore, the rotational effect of the rotor was included in the post-processing to emulate the noise observed at ground level. The findings show an increase in the slat's overall sound pressure level and a maximum radiation upwind of the wind turbine for the case with the largest wind speed that represents the off-design condition. In operational conditions, the slat adds at most 2 dB to the overall sound pressure level. The toolchain evaluates wind turbine noise with conventional or unconventional blade design, and the problem can be scaled up for a full-scale analysis. As such, the tools presented can be used to design low-noise wind turbines efficiently.     

Can road traffic mask sound from wind turbines? Response to wind turbine sound at different levels of road traffic sound

Wind turbines are favoured in the switch-over to renewable energy. Suitable sites for further developments could be difficult to find as the sound emitted from the rotor blades calls for a sufficient distance to residents to avoid negative effects. The aim of this study was to explore if road traffic sound could mask wind turbine sound or, in contrast, increases annoyance due to wind turbine noise. Annoyance of road traffic and wind turbine noise was measured in the WINDFARMperception survey in the Netherlands in 2007 (n=725) and related to calculated levels of sound. The presence of road traffic sound did not in general decrease annoyance with wind turbine noise, except when levels of wind turbine sound were moderate (35–40 dB(A) Lden) and road traffic sound level exceeded that level with at least 20 dB(A). Annoyance with both noises was intercorrelated but this correlation was probably due to the influence of individual factors. Furthermore, visibility and attitude towards wind turbines were significantly related to noise annoyance of modern wind turbines. The results can be used for the selection of suitable sites, possibly favouring already noise exposed areas if wind turbine sound levels are sufficiently low.     

A Study of the Vortical Flow over a Delta Wing with a Leading Edge Extension

The present paper describes computational and experimental work on the vortex flow characteristics of a sharp-edged delta wing with a leading edge extension (LEX). Experiment was carried out using a low-speed wind tunnel that has a test section of 3.5 m(W)×2.45 m(H)×8.7 m(L). The angle of attack of the delta wing ranges from 10° to 30°. The free stream velocity is fixed at 20 m/s, which corresponds to Reynolds number of 0.88×106. Computations using the mass-averaged implicit 3D Navier-Stokes equations were applied to predict the complicated vortical flow over the delta wing. The governing equations were discretized in space using a fully implicit finite volume differencing formation. The standard k-e turbulent model was employed to close the governing equations. The present computations predicted the experimented flow field with a good accuracy.     

基于耦合方法的球阀偏心间隙结构数值分析

为了研究偏心间隙结构对阀门流场及管阀系统辐射声场的影响,采用流声固耦合的联合仿真方法,对含有偏心间隙结构和不含有此结构的两种流道模型展开对比分析。结果表明：两种模型的流量、阻力系数特性曲线均在球阀开启50°左右时出现转折点;偏心间隙处产生的高速射流会对阀内流场产生剧烈扰动,球阀腔体与下游管道连接处是阀内核心声源区;管阀系统的第1、第2阶模态振型为沿流道方向的振动,第3、第4阶振型为垂直于管道方向的振动;偏心半球阀的辐射噪声频谱呈宽频特性,高速射流对2 300～5 000 Hz范围内中高频段声压级幅值的提升有显著贡献;两种流道模型声压级频谱峰值点特征相似,与无偏心间隙模型的频谱规律相比,偏心间隙结构模型的频谱在相同的特征峰值点处对应更高的频率范围,且频谱响应曲线有整体右移的趋势;辐射噪声在偏心间隙结构存在的一侧具有显著的声学指向性。     

Wind turbine power and sound in relation to atmospheric stability

Atmospheric stability cannot, with respect to modern, tall wind turbines, be viewed as a ‘small perturbation to a basic neutral state’. This can be demonstrated by comparison of measured wind velocity at the height of the rotor with the wind velocity expected in a neutral or ‘standard’ atmosphere. Atmospheric stability has a significant effect on wind shear and increases the power production substantially relative to a neutral atmosphere. This conclusion from Dutch data is corroborated by other published wind shear data from the temperate climate zone. The increase in wind shear due to atmospheric stability also has a significant effect on the sound emission, causing it to be substantially higher than predicted from near‐ground wind velocity and a neutral atmosphere, resulting in a higher noise impact on neighbouring residences. Several measures are proposed to mitigate the noise impact. To reduce noise levels, the rotational speed can be controlled with the near‐ground wind speed or sound level as the control input. To reduce the fluctuation in the sound (‘blade thumping’), it is suggested to adjust the blade pitch angle of the rotating blades continuously. To prevent stronger fluctuations at night due to the coincidence of thumps from several turbines, it is suggested to add random variations in pitch angle, mimicking the effect of large‐scale turbulent fluctuations in daytime. Copyright © 2007 John Wiley & Sons, Ltd.     

基于Elman神经网络的风电场噪声预测模型

针对风电场噪声易受风速风向等多因素影响的特点,引入具有动态递归性能的Elman神经网络,综合考虑风速、风向和距离三个主要因素的影响,建立了基于Elman神经网络的风电场噪声预测模型,并以某风电场为例,选取基于无指向性经验拟合预测模型作为对比模型,分别预测风电场噪声,绘制风电场噪声等值线地图。结果表明,基于Elman神经网络的风电场噪声预测模型具有更高的拟合相关性系数,且噪声预测更符合实际情况。     

Broadband noise radiation analysis for an HAWT rotor

The paper demonstrates a computational methodology for the noise prediction of an horizontal axis wind turbine (HAWT) rotor in time domain. The aeroacoustic modeling is based on the Ffowcs Williams and Hawkings equation considering only the surface monopole and dipole noise sources. The accurate solution of the noise problem is strongly influenced by the unsteadiness of the rotor flowfield, the nonuniform inflow effects and the blade aerodynamic parameters which are included in the numerical model. The aerodynamic analysis uses a three-dimensional low-order panel method combined with a boundary layer correction model for the calculation of the blade pressure distribution, obtaining satisfactory agreement with experimental data. Acoustic pressure predictions for the NREL downwind rotor are presented for several cases proving that broadband noise propagation dominates at low- and mid-frequency ranges. Sound pressure level contours occur via Fourier transformations, while the directivity for a single frequency source is also examined.     

基于ATV技术的油底壳声辐射预测及板块贡献量分析

建立了油底壳的有限元模型和半消声室辐射声场边界元模型,将试验测得油底壳螺栓孔处振动加速度信号作为激励,对油底壳进行强迫响应计算,得到油底壳表面振速。运用声学传递向量（ATV）技术,计算得到了油底壳辐射声功率、外场域点声压（级）、结构面板声学贡献量,提出了油底壳优化设计方案,为整个动力总成的减振降噪奠定基础。     

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.     

基于SONAH的旋转风轮声源识别实验研究

在风洞开口实验段,针对不同风速及不同叶尖速比,应用Brükel&Kj?r公司60通道轮型声阵列及声信号采集系统对直径为1.4 m的S翼型风轮进行声场测试,并采用统计最优近场声全息(SONAH)技术进行旋转风轮低频噪声源识别及频域特征分析。实验结果表明:最大声强度是旋转叶片产生的基频噪声,其对应总声压级随风速增加呈函数f (x)=-0.0092x⁴+0.297x³-3.7403x²+23.186x+49.274增加,随叶尖速比增加呈函数f(x)=0.4467x⁴-10.273x³+87.728x²-328.75x+567.23增加;识别的噪声源最大能量中心集中于翼展位置约0.545 m,相对半径r/R=0.778处,且不随风速和尖速比的改变而改变。