基于涡尾迹方法的风力机非定常气动特性计算

给出了一种水平轴风力机三维非定常气动特性计算方法.风力机的绕流用预定涡尾迹模型确定,并引入涡核模型和考虑粘性引起的耗散效应对模型进行修正,解决了涡尾迹方法在大叶尖速比时普遍存在的计算发散问题.通过对Leishman-Beddoes动态失速模型中动态失速判据和模拟的修正,更准确计算侧偏风时风轮叶片的非定常气动响应.将三维旋转失速延迟模型与预定涡尾迹模型和动态失速模型适当耦合,从而计算包括三维旋转效应对叶片气动载荷非定常响应的影响,提高了风力机风轮和叶片非定常气动特性计算的准确度.     

风力机近尾迹区域涡量变化规律及噪声的数值预测

采用大涡模拟(LES)和标准κ-ε模型求解风力机近尾迹区域的非定常流动,获得涡量场信息和声源项信息,采用快速傅里叶变换将源项的时域信息转换为频域信息,利用K-FWH声学模型预测其噪声特性。结果表明,风轮在旋转过程中,风力机风轮下游同一截面在不同尖速比下涡量分布规律是从计算截面中心沿半径增大的方向分别经过3个压力脉动变化强烈的区域,它们是计算圆心区域、中心涡区域、叶尖涡区域,计算点在上述3个区域都会出现涡量的峰值;在同一尖速比不同截面下,风轮近尾迹区域涡量的变化规律是沿着X轴正方向远离风轮旋转平面计算截面上的中心涡区域和叶尖涡区域的半径增大,不断向外迁移;计算截面的最大声压级的数值计算值和试验值吻合较好,证明了噪声计算模型的正确性。     

风力机次声波的空间辐射及其沿叶片翼展和弦长方向的声压分布规律研究

以FW-H气动声学方程为基础,分析水平轴风力机次声波的产生机理,提出水平轴风力机的远场次声波辐射计算公式。以翼型为NACA 23015的三叶片10 k W水平轴风力机为例,在额定风速8 m/s、叶片半径10 m、转速107 r/min,升力角14°、升力系数1.2的情况下,研究次声波在空间辐射、次声波声压翼展方向和弦向的分布等规律。计算结果表明:省略近声场噪声可显著提高声压计算速度、精度;风力机次声波噪声由厚度噪声和载荷噪声组成,载荷噪声和厚度噪声声压绝对值基本相等;风力机次声波在空间分布上具有一定的指向性;其中风力机次声波产生区域主要集中在沿叶展方向r′/R=0.6~0.9处,同时沿翼型弦向产生的次声波集中在前端1/3弦长处。     

风力机风轮非定常气动载荷计算

运行中的风力机风轮经常受到自然风变化带来的非定常气动力的作用。数值模拟这一非定常气动力对于风力机的安全优化运行和性能改进具有重要意义。文章介绍了所开发的基于粘性修正的三维速度势面元方法,以速度势方程作为流动控制方程,使用Prandtl-Schlichting方法考虑空气在叶片表面的粘性作用。通过与风力机的试验数据对比显示,计算值均与试验值吻合良好,显示了用该计算方法估算风力机三维非定常气动力和扭矩的应用价值。     

风轮风载荷等效系数计算方法研究

在风力发电机支撑结构设计初期,风轮的载荷多根据建筑风载荷规范确定,但建筑风载荷计算中常采用的体型系数却无法准确计算旋转机构荷载。文章首先分析了水平轴风力机叶片推力系数与体型系数的关系,然后根据功率系数计算叶片推力系数,从而获得整个风轮的风载荷,据此提出了考虑实际叶片工作效率的风轮风载荷等效系数计算方法。应用该方法对某1.5 MW水平轴风力机进行计算,并与商用软件Bladed的计算结果进行比较,结果表明,该方法能够满足风力机风载荷计算的要求,是一种精度较高、适于工程应用的方法。     

偏航和风切变下风力机气动特性的研究

采用基于滑移网格技术的三维非定常CFD方法,以TJ?REBORG和NREL Phase VI风力机为例,数值模拟轴向均匀来流条件下风力机气动性能的变化规律并与实验值进行比较,确定该方法的可靠性。在此基础上探讨风切变以及偏航条件下水平轴风力机风轮的气动特性,分析其影响规律、叶片旋转平面附近流场中的流动细节及尾迹的变化。     

基于流固耦合的风力机气动噪声影响研究

考虑风力机叶片与空气的流固耦合作用,基于ANSYS workbench工作平台,采用双向流固耦合的方法,模拟预测风力机的气动噪声,并与额定工况下的实验数据对比。结果发现:耦合作用下风力机气动噪声增大,且耦合模拟得到的气动噪声声压级与实验值更为接近,证明计算模型的准确性;风轮后的辐射声最大声压级在叶片径向0.57R~0.71R位置,风力机叶片与空气的流固耦合作用,增大了辐射声的声压级,而对于辐射声的传播规律影响很小;耦合作用下随尖速比的增加,相同位置气动噪声的声压级呈现缓慢增大的趋势,不同尖速比下气动噪声的声压级随轴向距离的增加变化规律大致相同,均呈不断减小的趋势。     

风力机旋转风轮振动模态分析

对水平轴风力机旋转风轮振动模态计算分析方法和影响固有频率计算结果的因素进行了研究。应用多体动力学的方法，探讨了旋转叶片动力刚化效应产生的原因；考察了叶片动力刚化效应以及玻璃钢／复合材料的各向异性性质对叶片振动模态的影响；通过自行开发的前处理软件建立叶片实体模型，运用ANSYS结构分析软件对所设计的600kW风力机旋转风轮的振动模态作了仿真分析，得到了风力机复合材料叶片动力刚化效应振动模态数值分析结果，并对结果进行了分析比较。     

基于风剪切的多风轮风力发电系统叶片载荷研究

搭建由10个50 W水平轴风力机组成的多风轮发电系统,并对该系统所在位置风剪切系数进行测试。基于叶素理论建立水平轴风力发电机叶片载荷简化计算公式。在同样的风剪切条件下,计算总功率为500 W单风轮风力机和多风轮风力发电机的叶片载荷,考察叶片方位角、风轮半径、风力机安装高度、风剪切系数和风速对叶片载荷的影响。结果表明,风轮半径越长、风力机安装高度越低、风剪切系数越大,叶片旋转过程中载荷变化越大;用多个小型风力机取代单个大型风力机可有效减小风剪切的影响。     

偏航工况下水平轴风力机叶片气动变形数值模拟研究

以非定常叶素动量方法和水平轴风力机结构动力学为基础,建立风力机气弹计算的仿真程序,将偏航模型耦合进气弹程序中,针对某5 MW水平轴风力机进行仿真计算,分析比较了该风力机在不同偏航角工况下叶片变形沿径向和周向的分布情况,总结了不同偏航工况对风力机叶片变形的影响规律。研究结果对风力机叶片设计和疲劳寿命的预测有一定的指导意义。     

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.     

带失速延迟模型的改进型升力线法预测风力机性能

采用带Du-Selig静态失速延迟模型的改进升力线法对风力机不同来流风速下的性能进行预测,静态失速延迟模型可以弥补对输出功率的低估;还分析了来流风速在7.0~10.0m/s时沿径向的攻角分布以及有无失速延迟模型时的升阻力系数分布。通过比较发现在中间叶高处出现最大攻角,相应地在该叶高位置最先发生流动分离。     

非对称锯齿结构对叶片气动声学性能的影响

为降低水平轴风力机叶片的气动噪声,受鸮类静音飞行能力的启发,提取鸮类翅膀羽毛的非对称锯齿结构,并重构于风力机叶片尾缘处。采用大涡模拟（LES）和FW-H方程对改型叶片和原型叶片的流场及声场特性分别进行研究。同时通过改变非对称锯齿尾缘的结构参数,以探究不同锯齿夹角、锯齿宽度和锯齿间距对非对称锯齿尾缘的降噪效果的影响。结果显示：非对称锯齿尾缘具有较好的降噪效果,尤其是在低频和中频区域,总声压级最多可降低10 dB。当锯齿夹角分别为30°、40°和50°时,随着锯齿夹角的增加,噪声声压级在多数方位角下呈增加的趋势;锯齿宽度分别为10、12.5和15 mm时,随着锯齿宽度的增加,噪声声压级在多数方位角下明显降低;锯齿间距的改变,对0°方位角下的噪声声压级影响显著。而从涡分布图中可发现,非对称锯齿尾缘未改变叶片表面涡脱落的位置,但会减小涡结构和涡强度,增大涡间距,从而抑制噪声的产生。     

CFD study of some factors affecting performance of HAWT with swept blades

Most modern high-power wind turbines are horizontal axis type with straight twisted blades. Upgrading power and performance of these turbines is considered a challenge. A recent trend towards improving the horizontal axis wind turbine (HAWT) performance is to use swept blades or sweep twist adaptive blades. In the present work, the effect of blade curvature, sweep starting point and sweep direction on the wind turbine performance was investigated. The CFD simulation method was validated against available experimental data of a 0.9?m diameter HAWT. The wind turbine power and thrust coefficients at different tip speed ratios were calculated. Flow field, pressure distribution and local tangential and streamwise forces were also analysed. The results show that the downstream swept blade has the highest C_p value at design point as compared with the straight blade profile. However, the improvement in power coefficient is accompanied by a thrust increase. Results also show that the best performance is obtained when the starting blade sweeps at 25% of blade radius for different directions of sweep.     

水平轴风力机风轮结构特性综合剪裁

基于静态与动态测试技术,对水平轴风力机风轮的结构特性进行了综合剪裁。在静态结构特性方面,用单点加集中荷载所得数据来综合评定受分布荷载作用的风轮叶片的强度及变形特性。为风轮叶片强度设计提供有效的判据。在动态测试方面,应用ＤＡＳ动态信号分析与故障诊断系统,对水平轴风力机的风轮叶片进行了试验模态分析,通过测量风轮叶片的振动信号,得到了风轮叶片的各阶模态分布,为风力机总机的总体优化设计提供了可靠的依据。     

水平轴风力风轮静态结构特性试验研究

提出了一种研究水平轴风力机风轮静态结构特性的测试方法，用单点加集中荷载所得数据来综合评定受分布荷载作用的风轮叶片的强度及变形特性，用于检验风轮叶片结构设计的合理性，获得在定常荷载作用下，叶片受力的危险截面，以小型水平轴风力机FD2-300的风轮叶片为例进行了试验研究。获得了该叶片的危险截面，试验证明：通过以抗弯截面系数和定常荷载作用下的截面弯矩曲线的颁上为判据进行叶片结构形状合理性分析是一种快速、实用的测试方法，可为研究风力机气动弹性稳定性和改进风轮叶片设计提供判据。     

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.     

基于压力表示法的水平轴风力机风轮气动弹性稳定性模型及应用

该文对影响水平轴风力机气动弹性稳定性的物理机理进行了分析，对国内外的研究方法进行了阐述。建立了基于压力表示法的水平轴风力机风轮气动弹性稳定性敏感性分析方法的物理与数学模型，综合考虑了风力机风轮的气动与结构参数对气动弹性稳定的影响。以600kw水平轴风力机风轮为例，对其气动弹性稳定性进行了分析与研究，获得了该风力机的气动弹性稳定性裕度和工作范围。考虑到风力机三维流动、风轮与塔架的藕合以及来流湍流和阵风等来流工况的复杂性，该分析模型目前还没有将上述因素考虑在内。若均考虑在内，则其能够提供较高的气动弹性稳定性预测精度。     

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.     

A study on stall-delay for horizontal axis wind turbine

The study on the stall-delay phenomenon for horizontal axis wind turbine (HAWT) was carried out by employing the boundary layer analysis, the numerical simulation and the experimental measurement. The effects of rotation on blade boundary layers are investigated by solving the 3D integral boundary layer equations with assumed velocity profiles. It is shown that rotation has a generally beneficial effect in delaying separation compared with that under 2D stationary condition. Next, the detailed flow fields are simulated on the conditions of 2D stationary and 3D rotation by CFD code. The computation results show that rotation affects the pressure distribution on the surface of the foil, which can give rise to 3D stall-delay in stalled condition HAWT. Finally, the flow fields behind a model HAWT are measured with a hot-wire probe in the wind tunnel. The results show good agreement with those from 3D computation calculations, suggesting that the stall-delay should be taken into consideration, in order to accurately predict the loading and performance of a HAWT operating in stall.