叶顶端板对H型风力机气动特性与三维绕流场的影响

本文采用笛卡尔动网格方法数值模拟研究了叶顶端板对H型垂直轴风力机非定常气动特性与三维黏性绕流场的影响。选用SST湍流模型,假设全流场为湍流流动。叶尖速比为1.86~2.57,以实验模型为研究对象,对未加装叶顶端板的H型风力机进行了三维数值模拟研究。在实验模型的基础上给每个叶片的顶部分别加装了端板,采用同样的数值模拟方法,选择低、中、高三个叶尖速比研究了带有叶顶端板的H型风力机的三维非定常气动特性。利用不带端板和带有端板的风力机模型计算得到的功率系数与实验数据进行了比较,讨论了单个叶片和风轮载荷沿周向的变化,分析了一个旋转周期叶顶附近相对速度的变化规律,揭示了加装端板后风力机气动载荷提高的原因。     

海上风电叶片智能控制实验系统研制及控制效果分析

随着风力机大型化发展,叶片尾缘襟翼控制技术,作为叶片流场主动控制的一种有效手段,能够有效、快速、灵活地降低叶片载荷,提高风力机,特别是大型风力机的可靠性、经济性,该技术受到国内外的广泛关注。为深入了解叶片襟翼实际作用效果及降载机制,在大量数值仿真计算工作基础上,需进一步开展带有襟翼控制的模型风力机风洞实验工作。本文在相似准则基础上,引入叶片展向环量、Polar线相似条件,对NREL 5 MW风力机叶片按1:105进行缩比设计,采用伺服电机驱动襟翼的结构方案对叶片参数进行修正,并根据BEM理论优化带有襟翼叶片的气动性能,最终确定带有襟翼控制的风力机叶片设计方案。最后利用气弹耦合仿真计算平台对带有襟翼控制的模型风力机进行性能计算,确定理想实验工况点及对应的降载效果。本文所开展的工作不仅能够为叶片缩比设计提供新思路,更有意义的是为襟翼控制系统在叶片中的实现提供有效借鉴。     

低速轴流风扇格尼襟翼气动作用实验与数值研究

本文通过实验的方法研究了低雷诺数轴流风扇中格尼襟翼的气动作用。风扇叶片压力面尾缘加装高度分别为1.25%、2.5%和5%弦长的Gurney襟翼,与原始风扇性能进行对比。结果表明,风扇加装格尼襟翼之后,风扇工作失速点基本保持不变,但是襟翼风扇工作范围有所扩大,风扇的额定工况点朝着大流量方向移动。相同流量下,风扇加装格尼襟翼能提高风扇压升,且格尼襟翼的高度越高,压升提高的幅度越大。     

极端风剪切风况下的风电叶片载荷智能控制流动机理研究

本文以UpWind/NREL 5 MW为参考风力机,外部风况为IEC标准的极端风剪切(EWS),在自主开发的基于柔性尾缘襟翼(DTEF)的"智能叶片"整机气动伺服弹性仿真平台的基础上,研究了基于DTEF智能叶片系统在EWS情况下叶根所受极限载荷的变化情况,并同时分析了其对塔架,传动机构及变桨机构的影响。结果表明:采用该基于柔性尾缘襟翼的智能叶片系统不仅有效地减少了叶根所受极限载荷,同时对塔架,传动机构及变桨机构等受到的极限载荷都发挥了非常积极的作用。最后,详细分析了该控制系统背后的流动控制机理。结果表明:尾缘襟翼的主动作用有效地减弱了由于极端风剪切引起的叶片与流动之间较强的流固耦合作用。     

极端风剪切风况下的风电叶片载荷智能控制流动机理研究EI北大核心CSCD

本文以UpWind/NREL 5 MW为参考风力机,外部风况为IEC标准的极端风剪切(EWS),在自主开发的基于柔性尾缘襟翼(DTEF)的"智能叶片"整机气动伺服弹性仿真平台的基础上,研究了基于DTEF智能叶片系统在EWS情况下叶根所受极限载荷的变化情况,并同时分析了其对塔架,传动机构及变桨机构的影响。结果表明:采用该基于柔性尾缘襟翼的智能叶片系统不仅有效地减少了叶根所受极限载荷,同时对塔架,传动机构及变桨机构等受到的极限载荷都发挥了非常积极的作用。最后,详细分析了该控制系统背后的流动控制机理。结果表明:尾缘襟翼的主动作用有效地减弱了由于极端风剪切引起的叶片与流动之间较强的流固耦合作用。     

风力机翼型尾缘襟翼动态特性分析

采用计算流体力学方法研究了带有运动尾缘襟翼的风力机翼型,考察了襟翼偏转角频率对翼型气动参数及非定常特性的影响。结果表明:多数情况下,翼型升力系数滞后于偏转角变化,且相位差随着角频率的增加先增大后减小;尾缘襟翼改变升力系数的能力随着角频率的增加而减小;以尾缘襟翼长度为特征尺度定义的襟翼折合频率可作为尾缘襟翼问题非定常特性的判断准则,当该折合频率大于或接近0.01时,流场具有明显的非定常特性。     

带端板的垂直轴风机性能的数值研究

本文采用课题组开发的一套通用计算流体力学软件UCFD,对叶片两端添加端板的H型Darrieus垂直轴风力机的流场进行了三维数值模拟,考察了所加端板形状和尺寸大小对风力机风能利用率的影响。结果表明:叶片两端添加适当尺寸的端板可有效抑制叶片端部的绕流涡强度,改善了风力机叶片叶梢附近表面的压力分布状况,从而提高了风力机叶片单位展向长度的风能利用率,且也有助于提高此类风机的运行稳定性。     

轴流风扇叶片端导叶作用的研究

本文采用数值方法研究了叶片端导叶对轴流风扇性能的影响。通过与普通开式轴流风扇比较,分析了叶片端导叶对内部流动作用的机理.数值计算结果表明:叶片端导叶的安装位置将影响轴流风扇气动效率,安装叶片端导叶不能提高风扇静压升,但是在压力面安装时能有效地减小风扇叶顶泄漏流与主流的掺混损失;在设计流量下,压力面安装叶片端导叶使泄漏涡的作用范围较小,涡核更靠近吸力面;吸力面安装叶片端导叶弱化了泄漏涡的强度但没有减小泄漏涡的作用范围。     

叶尖小翼对扩压叶栅气动特性影响的数值研究

通过在叶片顶端加装小翼来降低叶顶二次流的叶尖小翼技术在叶轮机械领域受到关注。本文对具有不同叶尖小翼方案的压气机叶栅进行了全三维数值模拟,并详细分析了叶尖小翼对叶顶间隙流场的影响.结果表明,合理选择叶尖小翼的安装位置及自身宽度可以在一定程度上降低叶顶泄漏损失,在叶顶吸力面侧加装宽度为5 mm的小翼可以较好的削弱泄漏流动的强度,减少泄漏涡卷吸起更多的吸力面/端壁角区的低能流体及较早地阻止上通道涡的形成和发展。     

涡流发生器对风力机叶片流动控制的数值研究

基于γ-Reθt转捩模型,对旋转工况下加装涡流发生器NREL Phase Ⅵ风力机进行CFD数值模拟.本研究在叶片吸力面加装30对涡流发生器,分析来流风速7、10、13、15、20、25 m/s六个工况下,叶片表面绕流、风轮转矩和叶片表面压力系数及表面流线的气动仿真结果,并与NREL试验数据、光滑叶片模拟结果比较分析.研究结果表明,涡流发生器明显改善叶片表面的流动分离,提高叶片输出转矩,其中10、15、20 m/s风速下分别提升3.7％、10.8％、14.6％;从剖面流场看,涡流发生器可以使涡强度减小、涡高度降低、分离涡后移,对提升风力机气动性能等意义重大.计算结果与Phase Ⅵ风力机试验结果吻合良好,湍流模型的输出转矩最大误差仅9.3％.     

锯齿尾缘降噪翼型优化设计研究

大量研究工作表明旋转风电叶片的主要气动噪声来自叶尖尾缘区域,一直以来都是严重影响居民生活和叶片气动性能发挥的重要因素之一.为此,针对决定叶片重要气动特性单元——二维翼型,采用有别于传统的仿猫头鹰翅膀锯齿尾缘流动控制方法,将锯齿关键尺寸参数融入到风力机翼型设计之中,从而开发仿生锯齿翼型的优化设计方法,获得低噪声与高气动性...     

Optical-velocimetry, wake measurements of lift and induced drag on a wing

Particle Tracking Velocimetry was used, in a low-speed wind-tunnel study, to obtain simultaneous cross-flow velocity measurements in three planar regions downstream of an airfoil having a NACA 0015 profile. In order to measure both the total lift and induced drag, and their distributions on the airfoil, a wake integration technique based on the control volume approach was used. The airfoil model was tested in clean wing configuration and with a 3.33% Gurney flap attached to the trailing edge. The Gurney flap was found to increase the complexity of the wake and cause a systematic increase in lift and induced drag values. The changes in total lift and induced drag resulting from the fitting of a Gurney flap compared very favourably to investigations using traditional aerodynamic techniques demonstrating the validity of the method.     

任意空间曲面三元叶轮叶片厚度对气动性能的影响

以任意空间曲面三元闭式叶轮为对象,研究了不同展向和流向叶片厚度分布方案对离心压缩机气动性能的影响。数值结果表明:对等厚叶片沿展向和流向进行合理地削薄,均能在基本不改变小流量工况性能的情况下,显著提升大流量工况的性能。展向削薄叶片和流向削薄叶片带来的性能提升幅度可以叠加,通过组合叶片厚度分布改型,本文压缩机设计工况点等熵效率提升了约2.08%。相比于沿流向削薄前缘和尾缘厚度,沿展向削薄叶尖厚度具有更大的性能提升能力。研究工作为三元闭式离心压缩机叶轮的优化设计提供了有益的参考。     

Vortex shedding noise of low tip speed,axial flow fans

Noise and performance tests were conducted on three low tip speed, half-stage, axial flow fans to determine the nature of the vortex shedding noise mechanism. Each fan was 356 mm in diameter and had eight equally spaced, variable pitch blades. The noise measurements were made in a free field environment and the fan back pressure and speed were varied during the tests. An acenaphthene coating on the blades was used to determine the regions of laminar and turbulent flow.Vortex shedding can be a significant source of noise when the fan is operated in a lightly loaded condition. Essentially it is due to instabilities in the laminar boundary layer on the suction side of the blade where these instabilities are in the form of Tollmien-Schlichting (T-S) waves. These instabilities interact with the trailing edge of the blade and generate acoustic waves which radiate from the trailing edge and form a feedback loop with the source of the instabilities. Vortex shedding noise can contribute as much as 5 dB in overall noise level and up to 22 dB at higher frequencies (8–14 kHz).Serrations located at the leading edge, at the mid-chord, or near the trailing edge on the suction side were found to reduce the vortex shedding noise significantly. The mid-chord location was found to be the most satisfactory because, as well as eliminating the noise, the serrations provided a 3% improvement in peak efficiency. This improvement occurred because separation of the laminar boundary layer was prevented on the suction side. On the other hand, serrations placed at the other two locations tended to degrade fan performance.     

Visualization of aerodynamic noise source around a rotating fan blade

The purpose of this study is to understand the aerodynamic noise source distribution around a rotating fan blade by measuring the noise signal and velocity field around the blade. The local noise-level distribution over the fan blade is measured by microphone arrays, and the flow field is visualized by smoke and phase-averaged PIV measurement. The noise source distribution is examined by cross-correlation analysis between noise signal and velocity fluctuation. It is found that the noise source is located near the rotating fan blade, especially around leading and trailing edges. The separation and reattachment of flow are observed near the leading edge, and the tip vortices and vortex shedding are found near the trailing edge. The cross-correlation distribution of the noise signal and the radial velocity fluctuation shows large magnitude in the correlated regions, which indicates the noise generation by the formation of vortex structure around the blade.     

On vortex–airfoil interaction noise including span-end effects,with application to open-rotor aeroacoustics

A linear analytical model is developed for the chopping of a cylindrical vortex by a flat-plate airfoil, with or without a span-end effect. The major interest is the contribution of the tip–vortex produced by an upstream rotating blade in the rotor–rotor interaction noise mechanism of counter-rotating open rotors. Therefore the interaction is primarily addressed in an annular strip of limited spanwise extent bounding the impinged blade segment, and the unwrapped strip is described in Cartesian coordinates. The study also addresses the interaction of a propeller wake with a downstream wing or empennage. Cylindrical vortices are considered, for which the velocity field is expanded in two-dimensional gusts in the reference frame of the airfoil. For each gust the response of the airfoil is derived, first ignoring the effect of the span end, assimilating the airfoil to a rigid flat plate, with or without sweep. The corresponding unsteady lift acts as a distribution of acoustic dipoles, and the radiated sound is obtained from a radiation integral over the actual extent of the airfoil. In the case of tip–vortex interaction noise in CRORs the acoustic signature is determined for vortex trajectories passing beyond, exactly at and below the tip radius of the impinged blade segment, in a reference frame attached to the segment. In a second step the same problem is readdressed accounting for the effect of span end on the aerodynamic response of a blade tip. This is achieved through a composite two-directional Schwarzschild's technique. The modifications of the distributed unsteady lift and of the radiated sound are discussed. The chained source and radiation models provide physical insight into the mechanism of vortex chopping by a blade tip in free field. They allow assessing the acoustic benefit of clipping the rear rotor in a counter-rotating open-rotor architecture.     

空调风机叶道内旋涡流动分析及进气口偏心的影响

本文采用CFD方法,详细分析了空调用多翼离心风机叶道中的气流分布以及进气口偏心的影响。研究表明,风机叶道内存在大范围的气流分离现象。在后盘附近,存在分离现象的叶道约占2/3,主要分布在蜗壳内侧;而在“前盘”附近,几乎所有叶道都存在分离现象。在“前盘”附近,蜗舌下方的叶道中气流几乎停滞,蜗舌下游叶道为回流和尾缘旋涡所充满,至临近蜗壳出口侧,前缘旋涡逐步形成、发展并融合尾缘旋涡,最后衰减、消失。风机进气口向蜗壳内侧偏置适当距离, “前盘”附近叶道旋涡分布范围明显减小。     

前缘弯掠斜流转子叶顶间隙流动特性数值分析

本文对前缘弯掠斜流转子叶顶间隙内的流动特性进行了数值分析。结果表明:叶顶间隙气流与主流发生卷吸而生成泄漏涡。泄漏涡作用的区域具有较低的压力分布。在叶片通道内,泄漏涡沿着与转子旋向相反的方向朝相邻叶片的压力面移动。大间隙时的泄漏涡比小间隙时强烈。低流量时泄漏涡的作用区域比高流量时大。在各种流量特性下,叶顶尾缘近吸力面区域都存在着二次间隙流。