主动式气动滑片对翼型气动及噪声特性影响研究

动态失速现象严重影响风力机气动性能,在翼型前缘布置主动式气动滑片可有效改善失速现象。为此基于NACA0012翼型,通过数值模拟研究气动滑片对翼型气动性能及噪声特性的影响。结果表明：前缘气动滑片可有效提高翼型上仰过程中的气动性能,较原始翼型气动滑片翼型的平均升力系数提高24.2%、阻力系数降低11.7%;翼型上仰过程中,气动滑片可抑制前缘分离涡向尾缘发展,延缓前缘与尾缘分离涡的融合,阻止分离涡从翼型表面脱落;气动滑片并未增加翼型噪声水平,但降低了翼型尾缘压力功率谱主频;当改变翼型折合频率时,气动滑片翼型的总声压级与原始翼型保持一致。     

尾缘襟翼动态气动特性与控制策略研究

为改善风力机动态气动特性及延长其运行寿命,基于NACA0012翼型,设计应用于垂直轴风力机的襟翼翼型,通过CFD计算得到运行时流场、力矩系数及升阻力特性。以此为基础给出两种襟翼控制策略,通过改变不同方位角下襟翼摆角,达到抑制尾涡分离、延迟动态失速和降低气动力剧烈波动变化幅度的目的。计算结果显示翼型上仰过程中脱落的涡主要呈条状,而下俯过程中脱落的涡则呈圆形,且条状尾涡的升阻力特性明显优于圆形尾涡。由此提出一种减幅控制策略,极大地减少了尾涡分离现象,减小最大转矩达50%。同时为防止风力机转速过快,提出一种襟翼控制策略调节翼型失速从而达到气动刹车效果,增大襟翼摆角可促使翼型尾缘失速涡快速脱落,迅速增大翼型的阻力系数,且随襟翼摆角的增大,力矩系数也随之减小,减速效果越明显。     

纵荡运动对风力机翼型动态失速特性影响研究

采用带转捩SST k-ω湍流模型，以S809翼型为研究对象，探讨纵荡运动方向、频率、幅度对复合运动（俯仰+纵荡）下动态失速的影响规律。结果表明：纵荡频率增加，迎风下的翼型湍动能增强，边界层流体的能量提高、扰动程度加深，使得翼型升力提高的同时提前失速；高纵荡频率工况下，迎风下的前缘涡强度高且覆盖范围广，加速了涡的脱落。顺风条件下，纵荡削弱了前缘涡的诱导效应，有效缩小尾缘涡的拓扑结构。随着纵荡幅度增大，翼型升阻力系数的响应幅值显著增加，尤其是在翼型迎风状态下的上仰阶段。研究揭示了纵荡运动对翼型动态失速的影响规律，对准确认识和评估漂浮式风力机气动性能具有重要意义。     

基于非结构动网格的风力机翼型失速特性研究

根据翼型俯仰运动规律,采用非结构动网格技术和不同的湍流模型对风力机的动态失速特性进行计算,其结果表明,动网格技术能有效计算振荡翼型的气动特性,较好地捕捉出风力机翼型在动态失速过程中涡的产生、脱落及湮灭过程;并得出SST k-ω湍流模型在运动翼型气动性能的计算方面有较高精度。     

尾缘气动弹片对翼型动态失速特性影响研究

通过研究尾缘气动弹片对翼型动态失速特性影响,提出一种基于气动弹片的主动控制策略,使其于大攻角时抬起,小攻角时闭合。并采用计算流体动力学方法对比分析主动式气动弹片对不同厚度翼型抑制流动分离作用的效果。结果表明：对于薄翼型,发生动态失速时,气动弹片可延缓翼型尾缘涡旋与前缘主流涡的相互作用,减小翼型升力系数骤降幅度;随翼型厚度增加,流动分离点从翼型前缘转向后缘,气动弹片可有效分割较大分离涡,减轻流动分离程度,限制分离涡发展,同时抑制尾缘伴随小涡产生,提高翼型升阻比。     

翼型前缘对翼型动态气动性能影响的数值分析

为研究前缘对翼型气动性能影响,以NACA0012翼型为基础,通过曲线参数化方法改变翼型前缘吸力面及压力面型线,设计了8种不同前缘的翼型,并采用SST k-ω湍流模型研究了翼型在俯仰运动过程中的动态失速特性。结果表明:翼型动态失速特性受翼型压力面外形的影响较小;翼型吸力面加厚,将有效改善俯仰运动过程中的动态气动性能;翼型前缘弯度上弯将加剧翼型失速现象;翼型前缘弯度下弯可在一定程度上有效抑制动态失速现象,且变形量越大,抑制效果越好。     

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。     

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。     

覆冰对风力机专用翼型气动性能影响的数值研究

利用商用CFD软件和S-A湍流模型,对风力机常用的NREL S809翼型在不同覆冰形态、覆冰厚度下的静态流场和动态流场进行了数值计算,得到了Re=1×106时各种覆冰情况下该翼型的气动性能,并研究了不同的覆冰形态对风力机翼型静态、动态失速特性的影响.结果表明：向吸力面生长的覆冰形态会造成覆冰层后的分离涡,随着攻角的增加分离涡向后缘生长,造成升力系数的较大下降,阻力系数增加;沿弦向生长的覆冰对尾缘分离涡的生成影响较小;在动态失速情况下,翼型周围流场比较复杂,覆冰形态对翼型升力系统的影响规律也较复杂;从静态流场特性分析,覆冰破坏了翼型的流线从而直接影响了翼型的气动性能;从动态流场特性分析,覆冰改变了翼型动态升力系数曲线的斜率从而影响到风力机的气动弹性稳定性.     

齿形襟翼对风力机翼型气动噪声影响的数值研究

为分析齿形襟翼（SGF）尾缘对风力机翼型气动性能及噪声特性的影响,利用SST k-ω湍流模型对装设Gurney襟翼（GF）和SGF的NACA0018翼型进行数值模拟,研究齿高和齿宽对气动性能和静压分布的影响,并采用大涡模拟（LES）对气动性能最优的SGF进行噪声预估和涡结构分析。结果表明：SGF可有效提高翼型升力系数并延迟失速;SGF-0.8-6.7模型可使最大升阻比提高8.61%,失速攻角延迟3°,其在拓宽高升力区间、延迟失速等方面具有最优性能;SGF翼型上下翼面噪声无明显差异,平均声压级随攻角增大而提高;SGF-0.8-6.7模型的尾迹噪声随攻角增大呈现先增后减的变化趋势,随距离增加而降低;翼型辐射噪声呈典型偶极子状,GF噪声小攻角下降低,而大攻角下则增大,SGF在不同攻角下均降噪显著,最大降噪量达10.2 dB;SGF尾涡稳定有序,能耗及损失降低,由此使气动性能和噪声得以明显改善。     

On the S809 airfoil's unsteady aerodynamic characteristics

The S809 airfoil dynamic characteristics, which are based on the airfoil dynamic tests at the University of Glasgow, are presented in this paper. The airfoil tests include static, ramp‐type (ramp‐up and ramp‐down) and oscillatory motions at Reynolds numbers of 1.0 × 10⁶ and 1.5 × 10⁶ with and without the sand‐tripped leading edge. This study aimed to explore the unsteady aerodynamic features of the S809 airfoil, such as the progression of separation from leading edge to trailing edge, the large trailing edge separation before stalling, the stall onset inception and the re‐attachment convection, and to provide some useful data for tuning/refining the semi‐empirical dynamic stall (DS) models, such as the Leishman–Beddoes DS model or its variations. Experimental results show that the S809 airfoil has a complicated DS process that renders this airfoil a challenge for any modeller of the unsteady airloads. The leading‐edge roughness has small effect on the static features, but significantly invokes earlier stall onset inception under dynamic conditions, while has small influence on the convective phase of the re‐establishment of fully attached flow. Copyright © 2009 John Wiley & Sons, Ltd.     

翼型前缘对风力机翼型气动性能的影响

基于翼型参数化方法对翼型S809进行两类不同的前缘修改，采用翼型设计分析软件Xfoil对修改前、后的翼型进行气动性能计算分析，并采用计算流体力学（CFD）数值模拟方法进行流场特性分析。结果表明：翼型前缘下弯使得翼型在失速区升力系数增大，阻力系数减小，俯仰力矩系数减小，转捩现象延迟，翼型前缘上弯对气动性能的影响与之相反；翼型前缘上弯和下弯使得翼型表面压力系数分布均匀，吸力面及压力面压力系数增大；翼型前缘下弯能够抑制流动分离，抑制涡的形成，延迟翼型失速，翼型前缘上弯对翼型流场特性的影响则与之相反。     

前缘改形对风力机翼型气动性能影响的数值研究

基于翼型参数化方法对翼型S809进行4类不同的前缘修改,分别为前缘压力面加厚、前缘吸力面加厚、前缘上弯和前缘下弯,采用翼型设计分析软件Xfoil和商用CFD(Computational Fluid Dynamics)软件FLUENT分别对翼型气动参数和翼型周围流场进行计算。结果表明:翼型气动特性与流场特性受翼型压力面外形变化影响较小;在研究范围内,翼型吸力面加厚使得翼型在失速区升力系数增加,阻力系数减小;翼型前缘上弯使得翼型在大攻角工况下升力系数减小,阻力系数增大,且使翼型提前失速;在一定范围内翼型前缘下弯,使得翼型升力系数增大,阻力系数减小,且延迟失速。     

吸力面弹片改善翼型失速特性的数值研究

为改善流动分离造成叶片气动效率降低,基于鸟鹰类翅膀羽毛在大范围流动分离时自适应弹起的特点,在翼型吸力面设置功能类似羽毛的弹片。弹片在未发生大范围流动分离时贴附翼型表面,使原始翼型轮廓发挥作用,并于攻角增大时弹起以改善翼型失速特性。以NREL S809为原始翼型,对不同攻角下多个弹片角度进行了数值计算,并对所得气动参数进行分析。研究表明:在大范围流动分离时,弹片可有效提高升阻比,最高达50%～60%;气流贴附弹片流动至其末端,从而抑制和拖延了涡的发展,进而提高了流场稳定性,使波动更规律且幅度更小;所研究攻角范围内,改善翼型气动性能的最佳弹片角度随攻角呈近似线性变化。     

凹槽-襟翼对翼型动态失速特性影响研究

风力机复杂运行环境使叶片常处于失速环境,导致翼型升力骤降,严重影响风力机气动性能。为改善翼型流动分离,延缓失速,对凹槽-襟翼对翼型动态失速特性作用效果开展研究,并利用计算流体力学方法分析不同折合频率与翼型厚度时凹槽-襟翼对翼型气动性能的影响。结果表明：俯仰振荡过程中,凹槽-襟翼可有效提升翼型吸力面流速,降低失速攻角下逆压梯度,减缓流动分离;可提升尾缘吸力面流体下洗能力,抑制尾缘涡的形成,有效增加翼型失速攻角;同时避免翼型二次失速,翼型气动性能明显提高;较原始翼型,凹槽-襟翼翼型俯仰振荡平均升阻比增量随折合频率增加而增大,而平均升阻比提高百分率随翼型厚度增大呈整体减小趋势。     

Dynamic stall modelling of the S809 aerofoil and comparison with experiments

An analysis of dynamic stall for the S809 aerofoil has been performed in conjunction with the Leishman–Beddoes dynamic stall model that was modified for wind turbine applications. Numerical predictions of the lift, drag and pitching moment coefficients were compared with measurements obtained for an oscillating S809 aerofoil at various reduced frequencies, mean angles of attack and angle of attack amplitudes. It was found that the results using the modified model were in good agreement with the experimental data. Hysteresis in the aerodynamic coefficients was captured well, although the drag coefficient was slightly underpredicted in the deep stall flow regime. Validation against the experimental data showed overall good agreement. The mathematical structure of the model is such that it can be readily incorporated into a comprehensive analysis code for a wind turbine. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of acceleration on dynamic stall of airfoil in unsteady operating conditions

In this paper the effect of accelerated flow over a moving airfoil is considered and based on the flow field around the airfoil the dynamic stall is evaluated. In contrast to ordinary pitching motion, the dynamic stall evaluation in this study is performed with a different motion pattern, in which the airfoil has a heaving motion in one direction. This motion pattern is also similar to rotation of an element of blade in horizontal axis wind turbines (HAWTs). In present investigation, the Reynolds number is changed during simulation time and variations of this parameter from initial to final values are shown by acceleration parameter. The operating Reynolds number is more than 10⁶, and a S809 airfoil is selected to move with accelerations of 1, 4 and 6 m/s² in normal direction to free stream. To resolve accelerated flow filed in the two‐dimensional computational domain and to achieve results within a reasonable computation time, the unsteady Reynolds‐Averaged Navier–Stokes (URANS) equations are employed. The governing equations are discretized based on the finite volume approach and semi‐implicit method for pressure linked equations algorithm is used for pressure–velocity coupling. Furthermore, turbulence effect on flow field is accounted using shear stress transport (SST) k‐ω model. It is shown that the accelerated flow can significantly influence on the aerodynamic loads and dynamic stall trend. This study may introduce a new concept regarding dynamic stall and aerodynamic loads when the rotational acceleration is involved in HAWTs. Copyright © 2014 John Wiley & Sons, Ltd.     

尾缘非定常射流襟翼对垂直轴风力机气动特性影响研究

为提升垂直轴风力机气动性能并改善其动态失速特性,将射流襟翼布置于翼型尾缘压力面,并提出5种射流控制策略,采用计算流体力学方法研究不同策略对垂直轴风力机气动性能影响,从而确定最佳控制策略。结果表明：在180°~360°相位角范围内施加射流控制可使风力机风能利用系数在最佳尖速比下提升31.31%,并有效抑制吸力面尾缘涡形成与发展,增大翼面两侧压差;射流越靠近尾缘,垂直轴风力机气动性能提升效果越好。