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。     

实度对低风速风电机组风轮气动性能影响研究

为提高低风速地区的风能利用率,研究风轮实度对低风速风电机组气动性能的影响。考虑影响风轮实度因素（叶片数量、弦长及安装角）,设计2组不同弦长叶片与可调安装角轮毂。安装角改变时不仅会引起实度变化,还会使叶尖速比发生改变。通过车载试验验证安装角不同时对风轮气动性能的影响主要与叶尖速比相关。根据不同风轮表面压力分布数值模拟结果得出：相同风速下,弦长由叶根到叶尖逐渐增大的叶片更易启动。相同条件下,试验机组输出功率与数值模拟机组输出功率最大相差5.37%,说明数值模拟结果可信。随着风轮实度的增加,风速5 m/s时,其风能利用系数呈增大趋势,风速8 m/s时,其风能利用系数呈减小趋势,两趋势相交时实度为25.38%,得出该实度下风轮气动性能较优,即可得到适合低风速地区的风轮实度。     

气动力和离心力对风力机叶片应力影响研究

针对自行研制的NACA4415翼型水平轴风力机,通过流固耦合的数值模拟计算方法,考虑气动力和离心力以及两者耦合作用,选取叶片最大弦长、中部弦长、气动中心线展向以及最大应力点位置,分析风力机叶片在不同工况下的应力特性分布规律。结果表明:在气动力作用下,叶片相同弦长位置处迎风面应力小于背风面应力,且随尖速比和入流风速增大而增大,最大应力点位置随着尖速比增大沿翼展向外且靠近叶片前缘方向延伸;在离心力作用下,叶片相同弦长位置处迎风面应力大于背风面应力,且随尖速比增大而增大,而最大应力点均在叶根最大弦长位置(9.93 mm,10.80 mm,-126.33 mm);在耦合作用下,叶片相同弦长位置处迎风面应力大于背风面应力,随尖速比和入流风速增大而增大,且依次大于气动力和离心力产生的应力,而最大应力点均在叶根最大弦长位置。仿真结果对于风力机翼型的选择及优化设计具有重要的理论意义及参考价值。     

风轮声源及其动态应变相关性实验研究

在直流低速风洞中,应用BK公司的60通道圆形声阵列、丹麦BK公司PULSE结构振动测试分析系统及应力应变动态旋转遥测技术,针对直径1.4 m的某S翼型水平轴风力机风轮模型开展实验得出不同工况下,噪声总声压级分布特征以及噪声源位置分布规律及沿翼展方向上应变幅值的变化规律。实验结果表明:风轮旋转时,噪声源能量最大区域主要集中在叶片中部(r/R=0.54),且不会随风速和尖速比的改变而改变最大噪声源位置;噪声源能量最大区域主要发生在叶片振幅最大区域处;应变最大幅值区域主要集中在叶片中部(r/R=0.51处),最大幅值区域不随风速和尖速比的改变而改变。利用SPSS统计分析软件,对噪声声压级和应变幅值做沿叶片展向方向上的互相关分析得到,在0.17R~0.74R区域内,相关系数大于0.8呈高度相关,0.85R区域附近的相关系数为0.782,呈中度相关。     

H型风轮流动控制的实验研究

为了提高H型风轮的气动性能,将上游来流引入叶片尾缘并在尾缘缝隙形成射流的被动流动控制方法应用到H型风轮并在低速风洞进行风洞实验,得到了原型风轮与流动控制下风轮的基本气动性能。实验结果表明:原型风轮的气动性能系数(扭矩系数Cm、风能利用系数Cp)均随着尖速比λ的增大先增大,在尖速比λ>1时取得最大值,然后再减小,随着来流风速的增大,气动性能系数增大,且气动性能系数最大值对应的尖速比λ增大;相对于原型风轮,流动控制下风轮的气动系数均有提高,尤其是尖速比λ>1.2,气动性能系数显著增加,随着来流风速的增大,流动控制效果减弱,在尖速比λ<1.2时,流动控制效果减弱明显。     

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。     

水平轴风力机尾迹叶尖涡运动轨迹的实验研究

利用高频PIV系统采集水平轴风力机下游远至4.5倍风轮直径范围内的尾流数据。首先通过对涡量场云图分析发现叶尖涡"交互跳跃"现象;然后对比不同翼型、风速、尖速比下,1、2、3、4倍风轮直径处的平均涡量值发现:随着尖速比的增加,叶尖涡"交互跳跃"现象提前发生;随着风速的增加,叶尖涡"交互跳跃"现象推后发生;得出叶尖涡"交互跳跃"现象的出现是尾流速度开始恢复的标志。而NACA4415翼型叶片发生叶尖涡"交互跳跃"现象的时间比S翼型叶片推迟,所以NACA4415翼型叶片的尾流速度恢复比S翼型叶片推迟。     

水平轴风力机风轮子午面流场结构的实验研究

利用线式互相关PIV系统,采用轴编码器定位周期采样技术,在不同尖速比下对旋转水平轴风力机风轮不同子午面下游流场结构进行测量.分析得到不同条件下的瞬时图、时均图,重点对叶尖涡诱导效应区进行研究.实验结果表明:在风轮下游尾迹中可清晰看到叶轮近尾迹流场中的外部主流区、叶尖涡诱导效应区和中心尾迹区.其中风轮下游尾迹流管廓线是锥形螺旋体;叶尖涡核直径随轴向距离的增加而增大,随着测试方位角的增加,尾迹中各叶片产生的叶尖涡沿螺旋锥形廓线有序地向下游扩散流动;随着尖速比的增加,内部中心尾迹区轴向速度亏损值逐渐增加,并且中心尾迹区的范围逐渐扩大.     

叶片数及弦长对升力型垂直轴风力机的影响

文章基于非对称翼型NACA4415,以功率系数为依据,以CFD仿真为手段,研究了在不同尖速比下叶片数与叶片弦长对升力型垂直轴风力机气动性能的影响,以及不同尖速比和叶轮实度不同时,垂直轴风力机功率系数的变化。研究结果显示,该类升力型垂直轴风力机叶轮实度取0.25~0.45,尖速比λ取2.5~3.4时,具有较高的功率系数。流场分析表明,当叶片弦长与叶片数的变化对流场的扰动能力小于垂直轴风力机从流场中获取风能的能力时,叶片弦长与叶片数的变化会增加垂直轴风力机的功率系数;反之,垂直轴风力机的功率系数降低。该研究为此类20 k W垂直轴风力机的设计与选型提供依据。     

风力机叶片叶根应力集中区应力状态实验研究

为分析风力机叶片旋转时叶根应力集中区的平面应力状态,采用旋转机械应力应变无线遥测技术,通过叶根最大弦长处压力面应变花测点的布置,在直流式低速风洞开口段进行实验研究,结果表明:在额定风速8 m/s,尖速比由4.5增至6.5的过程中,直角应变花3个方位线应变的绝对值逐渐增大,且沿叶片展向0°方位和45°方位的线应变为正值,以拉弯应变为主,90°方位的应变为负值,受叶片压力面载荷的挤压作用所致;翼型截面弦向测点的最大主应力值大于相应测点的最大剪切应力值,且随着尖速比的增加均增大,其较大值均出现在靠近截面形心的翼型表面,是叶片易受损的危险位置;最大主应力方位角受翼型截面的几何形状和载荷作用效果的影响,自前缘向后缘发展并不呈现一致的规律性。该研究为分析和判断叶片裂纹、预测损坏部位提供直接的实验依据。     

塔架对风轮旋转过程中声场及流场的影响探究

基于压力脉动与声压之间的关系,利用Fluent数值模拟平台对风力机旋转过程中整机和单转子的声场和流场进行分析。对比2种模型的最大声压级位置,发现由于塔架的介入,整个模型的声场落后于流场约30°。分析塔旁y轴负向测点处压力脉动与声压级第1个峰值对应的方位角,结果发现在y/R=0.14、y/R=0.42、y/R=0.71与y/R=1时声压级（SPL）分别落后于压力脉动22°、5°、9°与18°。分析风力机旋转过程中两种模型塔附近监测点的声压级与压力脉动的变化趋势,结果表明：声压级振幅沿展向先增大后减小,在y/R=0.71处达到最大值;同样,在y/R=0.71时压力波动幅度最大。     

不同材质风力机叶片绕流流场特征变化PIV实验研究

考虑风力机叶片变形对绕流流场的影响,通过粒子图像测速（PIV）方法,采集两副翼型相同、材质分别玻璃聚酯（叶片Ⅰ）和玻璃聚醋内部填充泡沫（叶片Ⅱ）的水平轴风力机叶片绕流流场信息,对不同测试截面处流场数据进行分析。研究结果表明：相比于叶片Ⅰ,相同工况下,叶片Ⅱ的总体涡量、回流区的面积和时均速度更大,轴向雷诺应力更小;随着相对轴向距离的增加,时均速度在相对高度方向波动减小,材质对轴向雷诺应力影响逐渐减弱。实验工况下,叶片材质对绕流流场特征的影响大于叶尖速比对其的影响,并沿径向方向有增大的趋势。     

Effects of pulsation on separated flow and heat transfer in enlarged channel

Numerical results of three-dimensional separated flow and heat transfer in an enlarged rectangular channel are presented in this paper.The expansion ratio and aspect ratio of the channel are 2.0 and 16.0,respectively.Reynolds number of the flow is 200 and it is over the critical Reynolds number.Over the critical Reynolds number,the flow in the symmetric channel becomes asymmetric and deflects to one side of the walls.Effects of the pulsating fluctuation at the inlet upon the flow in the channel are investigated.It is clarified that the inlet flow with a pulsating fluctuation of Strouhal number 0.05 and 0.10 strongly affects on the flow in the channel,and heat transfer on the walls is enhanced,especially on the wall surface covered with long separation bubble.On the other hand,the pulsation of St=0.0125 oscillates the shear layer more weakly than that of St=0.05,0.10 and the enhancement of heat transfer is smaller,though some vortices are shed from the vicinity of the side wall near the reattachment region.The oscillation of the main flow calms down gradually as the Strouhal number of the pulsation increases over 0.10.The influence of pulsation of St=0.20 on the flow is restricted in the near downstream of the step,and heat transfer on the walls is almost similar to that of the steady flow in the channel.     

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...     

PIV measurements and CFD simulation of the performance and flow physics and of a small‐scale vertical axis wind turbine

The aerodynamics generated by a small small‐scale vertical axis wind turbine are illustrated in detail as a NACA0022 rotor blade carries out a complete rotation at three tip speed ratios. These aerodynamic details are then linked to the wind turbine performance. This is achieved by using detailed experimental measurements of performance and near‐blade particle image velocimetry (PIV) and also by using a two‐dimensional Reynolds‐averaged Navier–Stokes‐based computational fluid dynamics (CFD) model. Uniquely, therefore, the CFD model is validated against both PIV visualizations and performance measurements. At low tip speed ratios ( λ = 2), the flow field is dominated by large‐scale stalling behaviour as shown in both the experimental results and simulations. The onset of stall appears to be different between the experiment and simulation, with the simulation showing a gradual separation progressing forward from the trailing edge, while the experiment shows a more sudden leading‐edge roll‐up. Overall, similar scales of vortices are shed at a similar rate in both the experimental results and simulations. The most significant CFD–PIV differences are observed in predicting flow re‐attachment. At a higher tip speed ratio ( λ = 3), the flow separates slightly later than in the previous condition, and as occurs in the lower tip speed ratio, the main differences between the experiment and the simulation are in the flow re‐attachment process, specifically that the simulations predicts a delay in the process. At a tip speed ratio of 4, smaller predicted flow separation in the latter stages of the upwind part of the rotation is the main difference in comparison to the experiment. Copyright © 2013 John Wiley & Sons, Ltd.     

On the extension of k−ω−SST corrections to predict flow separation on thick airfoils with leading-edge roughness

Modern wind turbines employ thick airfoils in the outer region of the blade with strong adverse pressure gradients and high sensitivity to flow separation, which can be anticipated by leading-edge roughness. However, Reynolds average Navier-Stokes simulations currently overpredict the Reynolds shear stresses near the surface, and the flow separation is not correctly predicted. Hence, these methods are not representative enough to optimize the blade design to avoid flow separation, which becomes relevant for rough blades. While several eddy-viscosity corrections in the $k-\omega -SST$ turbulence model have been previously studied to predict flow separation over smooth airfoils, the present study aims to extend their applicability to airfoils with leading-edge roughness. Two corrections, whose effect on flow physics has not been empirically quantified, are addressed. Particle image velocimetry measurements have been performed on a 30% thick airfoil to quantify the impact of these corrections. The reduction of the eddy viscosity introduced by the corrections leads to a shift of the peak location of the Reynolds shear stresses away from the surface, which, in turn, promotes flow separation and improves the prediction of the mean velocity and the pressure-coefficient distribution. Besides, the ratio between the main turbulent shear stress and turbulent kinetic energy is demonstrated to be lower than the standard value used in the $k-\omega -SST$ turbulence model at the boundary-layer outer edge. Adjusting this ratio for an angle of attack of 0° decreases the error on the predicted lift and drag coefficients from 75% to 3% and from 58% to 39%, respectively.     

振动膜片的流动控制机理研究

采用计算流体力学方法,研究了主流风速为10 m/s,翼型弦长雷诺数为1.2×10~5条件下振动膜片对NACA0012翼型在18°攻角深失速下流动分离的影响。研究表明:振动膜片能明显提高翼型升力系数、降低阻力系数、改善流场状况;当无量纲频率处在1~1.5范围内时,翼型升阻比可大幅提升,最大可提高75.7%;无量纲振幅对翼型升阻比的影响也很显著,相对于原型存在一个最佳的振幅使得翼型升阻比能获得最大提升;不同振幅下,最佳升阻比对应的无量纲频率随振幅增大而减小。     

Geometrical characterization of stall cells on rectangular wings

The onset of stall cells (SCs) is experimentally investigated on a flattop loaded 18% thick airfoil optimized for use on wind turbine blades, exhibiting trailing edge separation. SCs are dynamic coherent vortical structures that appear on wings under separated flow conditions. Although SCs have been known for long, neither are their characteristics completely documented nor their generating mechanisms fully understood. The present investigation aims at providing additional information on the geometric characteristics in terms of width, length and occupied area. The relevant data are presented as functions of Reynolds (Re) number, angle of attack and aspect ratio (AR) of the model. In the tests reported, the dynamic character of SCs is suppressed by imposing a localized flow disturbance. For the specific airfoil and for the Re and AR range tested, it is found that: the angle of attack at which SCs are initially formed decreases linearly with Re number and independently of the AR; unlike two‐dimensional separation, their chordwise length increases with Re; the SC area relative to the wing planform area (defined as the relative SC area) grows asymptotically with angle of attack and Re number reaching an upper bound, which is independent of the AR; at intermediate angles of attack, the SC relative area is higher for the lower AR wing; for a fixed increment in Re number, the growth of the SC relative area is independent of the initial Re number; at lower angles of attack, the actual SC area is independent of the wing span. Copyright © 2013 John Wiley & Sons, Ltd.     

Aerofoil trailing‐edge noise prediction models for wind turbine applications

This paper proposes a modified TNO model for the prediction of aerofoil trailing‐edge noise for wind turbine applications. The capabilities of the current modified model and four variants of the TNO model are analysed through a comprehensive study which includes 10 aerofoils and involves two different wind tunnels. The Reynolds numbers considered are between 1.13 and 3.41 million, and the effective angles of attack are between ?2.20° and 13.58°. The merit of a model is assessed by comparing two aspects of the numerically predicted and the experimentally measured sound pressure level spectra: the sound pressure level difference between two different aerofoils at similar lift coefficients within a certain frequency range (referred to as the delta noise); and the closeness in terms of spectral magnitude and shape of the predicted and measured sound pressure level spectra. The current modified model is developed by deriving new formulations for the computation of the wall pressure fluctuation spectrum. This is achieved by using the approximate ratio of the normal Reynolds stress components for an anisotropic flow over a flat plate to estimate the vertical Reynolds stress component, and by introducing new stretching factors to take the effects of turbulent flow anisotropy into account. Compared with the four TNO model variants tested, the current modified model has strong delta noise prediction ability, and is able to predict sound pressure level spectra that are more consistent and closer to measurements for the vast majority of aerofoils and flow conditions tested in the two wind tunnels. Copyright © 2017 John Wiley & Sons, Ltd.