旋翼非定常动态失速的三维效应分析

采用建立的高精度计算流体动力学(CFD)方法,针对旋翼非定常动态失速的三维（3D）效应特性进行研究。以Helishape 7AD旋翼为基准,开展三维效应对旋翼非定常气动特性的影响分析。研究了来流马赫数对旋翼翼型动态失速特性影响。在此基础上,针对三维情形旋翼动态失速非定常涡流动特性及诱导分离特征开展了数值分析,通过与二维情形对比表明:受旋翼旋转、轴向诱导速度等三维效应影响,旋翼桨叶剖面动态失速涡的产生、对流和脱落明显滞后于二维翼型情形,并且涡强度也更弱。越靠近桨叶内段,桨叶剖面非定常动态失速特性与二维旋翼翼型情形的差距越为明显。      

基于后缘小翼的旋翼翼型动态失速控制分析

针对后缘小翼(TEF)的典型运动参数对旋翼翼型动态失速特性的控制进行了研究。发展了一套适用于带有后缘小翼控制的旋翼翼型非定常流动特性模拟的高效、高精度CFD方法。通过求解Poisson方程生成围绕旋翼翼型的黏性贴体和正交网格,为保证后缘小翼附近的网格生成质量,建立了基于翼型点重构的方法来描述后缘小翼的偏转运动;为克服变形网格方法可能导致网格畸变的不足,发展了一套适用于带有后缘小翼控制的旋翼翼型运动嵌套网格方法。基于非定常雷诺平均Navier-Stokes(URANS)方程、双时间法、Spalart-Allmaras(S-A)湍流模型和Roe-Monotone Upwind-centered Scheme for Conservation Laws(Roe-MUSCL)插值格式,发展了旋翼翼型非定常气动特性分析的高精度数值方法,并采用Lower-Upper Symmetric Gauss-Seidel(LU-SGS)隐式时间推进方法及并行技术提高计算效率。以有试验结果验证的HH-02翼型和SC1095翼型为算例,精确捕捉了动态失速状态下的气动力迟滞效应,验证了本文方法的有效性。着重针对SC1095旋翼翼型的动态失速状态开展后缘小翼的控制分析,提出了可以体现翼型升力、阻力及力矩综合特性的关系式Po和Pc,揭示了后缘小翼振荡频率、相位差和偏转幅值对动态失速特性影响的规律。研究结果表明:当后缘小翼偏转的相对运动频率为1.0,且小翼运动规律与翼型振荡规律之间的相位差为0°时,后缘小翼能够更好地抑制翼型动态失速现象;在此状态下,当偏转幅值为10°时,SC1095翼型最大阻力系数和最大力矩系数可以分别降低19%和27%。     

Aerodynamic shape optimization for alleviating dynamic stall characteristics of helicopter rotor airfoil

In order to alleviate the dynamic stall effects in helicopter rotor, the sequential quadratic programming(SQP) method is employed to optimize the characteristics of airfoil under dynamic stall conditions based on the SC1095 airfoil. The geometry of airfoil is parameterized by the class-shape-transformation(CST) method, and the C-topology body-fitted mesh is then automatically generated around the airfoil by solving the Poisson equations. Based on the grid generation technology, the unsteady Reynolds-averaged Navier-Stokes(RANS) equations are chosen as the governing equations for predicting airfoil flow field and the highly-efficient implicit scheme of lower–upper symmetric Gauss–Seidel(LU-SGS) is adopted for temporal discretization. To capture the dynamic stall phenomenon of the rotor more accurately, the Spalart–Allmaras turbulence model is employed to close the RANS equations. The optimized airfoil with a larger leading edge radius and camber is obtained. The leading edge vortex and trailing edge separation of the optimized airfoil under unsteady conditions are obviously weakened, and the dynamic stall characteristics of optimized airfoil at different Mach numbers, reduced frequencies and angles of attack are also obviously improved compared with the baseline SC1095 airfoil. It is demonstrated that the optimized method is effective and the optimized airfoil is suitable as the helicopter rotor airfoil.     

旋翼翼型非定常动态失速响应的计算

基于旋翼非定常翼型气动模型,给出了计算分离流和深度失速状态下的翼型非定常升力、俯仰力矩的数值计算方法。该方法采用半经验指数响应公式,利用数值离散方法来求解翼型的非定常法向力和俯仰力矩。分别计算了NACA0012和SC-1095翼型上的非定常气动载荷,并与可得到的试验结果进行了对比,验证了方法的有效性。文中还讨论了缩减频率和马赫数对动态失速响应的影响;然后,这个模型被改进以适用于后掠流下的翼型动态失速响应计算,分析了后掠角对翼型动态失速响应的影响。最后,得出了一些结论。     

翼型动态失速影响因素及流动控制研究进展

深入认识翼型动态失速，结合有效流动控制手段，对解决直升机、风力机桨叶等动态失速引起的高阻力、大低头力矩等气动问题具有重要意义。本文首先介绍了翼型动态失速的流场特点和危害，进而分析了缩减频率、雷诺数、马赫数以及翼型型面等参数对动态失速的影响，并在此基础上总结了常见的动态失速流动控制方法及其研究进展。等离子体气动激励易于产生快速、可控的宽频带气动激励，在动态失速控制领域具有潜力，本文着重介绍了等离子体气动激励动态失速控制的概念和流动控制原理，总结了近来年等离子体激励在翼型动态失速控制上的进展。     

基于状态空间法的低马赫数翼型气动载荷计算

Leishman-Beddoes(L-B)非定常动态失速模型适用于中等马赫数(Ma>0.3),而在低马赫条件(Ma<0.3)下存在与翼型气动试验数据不符合的问题,为此首先研究了低马赫数条件下翼型的非定常动态失速气动特性,其次采用状态空间法从翼型表面气流变化的角度修正了L-B模型,最后通过与翼型气动载荷试验数据的对比表明在低马赫数条件下对L-B模型的修正是正确的,能够准确预测及分析翼型的气动载荷,且该修正模型易于耦合进直升机综合分析代码中.      

Dynamic stall on a supercritical airfoil

For the present investigations of dynamic stall a supercritical airfoil was chosen. This new airfoil designed by DLR will be used in dynamic stall control research activities (project ADASYS) planned for the near future: the leading edge portion of the airfoil will be drooped down dynamically to improve dynamic stall characteristics on the retreating side during blade motion. The optimised transonic properties of the airfoil, i.e., reduction of shock strength over a Mach number range will improve in addition the performance of the advancing rotor blade. Dynamic stall experiments on the rigid supercritical airfoil have first been carried out in the DNW-TWG transonic wind tunnel with a 1 m × 1 m cross section of the test section and adaptive top and bottom – walls. This tunnel has the advantage to cover the speed range of both retreating and advancing blade. Emphasis has been placed on unsteady pressure measurements along the adaptive walls simultaneously with the unsteady pressure measurements on the pitching model. In addition to the experiments corresponding numerical simulations with a RANS-code have been carried out and their results are compared with the experimental data. Of main concern are the influence of laminar-turbulent boundary-layer transition as well as wind-tunnel-wall interference effects on the unsteady results.     

涡流发生器对轴流压气机叶顶流动不稳定性影响的实验研究

为了探究涡流发生器对轴流压气机叶顶流动不稳定性的影响,在一台低速轴流压气机转子上开展了实验研究。将梯形和半球形两种涡流发生器分别安装在转子叶顶上游机匣上,基于不同的安装角度共制定了五种控制方案。分析了气动性能的变化,并采用频谱分析和统计分析方法考察了壁面脉动压力特性的变化。实验结果表明：采用梯形涡流发生器后,除安装角为90°的方案外,其它方案在各工况下扩压能力均略有下降,失速时的流量也明显减小。在流场存在旋转不稳定性或失速的工况,-45°方案时涡流发生器增加了来流的正预旋,增加了气流动量,同时产生的诱导涡会径向迁移,进而抑制了叶顶区域的旋转不稳定性或旋转失速的强度。     

Numerical investigation of dynamic stall suppression of rotor airfoil via improved co-flow jet

The decrease in aerodynamic performance caused by the shock-induced dynamic stall of an advancing blade and the dynamic stall of a retreating blade at low speed and high angles of attack limits the flight speed of a helicopter. However, little research has been carried on the flow control methods employed to suppress both the dynamic stall induced by a shock wave and the dynamic stall occurring at high angles of attack. The dynamic stall suppression of a rotor airfoil by Co-Flow Jet(CFJ) is nume...     

翼型动态失速等离子体流动控制试验

针对动态失速引起的翼型气动性能恶化的问题,利用小型化的激励电源和介质阻挡放电等离子体激励器,借助动态压力测量和外触发式粒子图像测速（PIV）等手段开展了翼型动态失速等离子体流动控制试验研究。结果表明,等离子体气动激励能够有效控制翼型动态失速,改善平均气动力,提高翼型气动效率,减小气动力随迎角变化的迟滞区域。等离子体诱导出前缘附近的贴体翼面涡,促进分离流再附;增加了上翼面0.2~0.4弦长区域的吸力,减小了升力系数功率谱密度（PSD）分布的二、三、四阶能量幅值,在研究工况下实现了平均升力系数增加7.1%、失速迎角推迟1.3°和迟滞区域减小4.5%的明显控制效果;4°~9°迎角段,等离子体使得翼型平均阻力系数减小40%。此外,振荡频率增加使翼型绕流的非定常性增强,较高雷诺数下的翼型动态分离涡更加难以被抑制,均需要增加等离子体激励强度才能达到较好的控制效果。     

仿生正弦前缘对翼面动态失速的影响

动态失速导致叶片气动载荷急剧变化，造成振动载荷激增，桨叶寿命大幅衰减。针对动态失速问题，从座头鲸胸鳍在动态倾转下取得良好的流动特性获得启示，据此模化出仿生正弦前缘翼面（包含3种波峰和2种波长），旨在实现动态失速控制。借助三维非定常数值模拟方法，采用运动网格技术，基于SC1095旋翼翼型，研究了仿生前缘动态失速流动控制机理及运动参数和来流速度的影响。结果表明：正弦前缘大幅度降低俯仰力矩系数峰值和阻力系数峰值；前缘波峰越大、波长越小，阻力系数峰值与俯仰力矩系数峰值的抑制效果越明显，虽然升力系数峰值减小，但其减小量远小于前两者，例如其中一种仿生翼使俯仰力矩系数峰值减小了47.7%，阻力系数峰值减小了36.4%，升力系数峰值减小14.1%；在最大迎角附近，正弦前缘能够缓和失速特性，使载荷变化更为平缓；在高平均迎角、低俯仰频率、低马赫数下，仿生翼动态失速控制效果更强，相比较而言迎角振幅的影响较小。     

带有气动及结构非线性的二元机翼颤振分析

研究了翼型在低马赫数条件下的非定常气动特性,从翼型表面气流运动的角度对Leishman-Beddoes(L-B)模型进行了修正,并在此基础上建立了适合低马赫数颤振研究且带有气动及结构非线性的二元机翼气弹系统分析模型.对比低马赫数翼型气动载荷试验结果表明对L-B模型的修正是有效的,且机翼颤振试验结果亦验证了二元机翼气弹分析模型.研究结果表明:二元机翼气弹系统的失速颤振与初始变距角和来流速度密切相关,且耦合的三次非线性变距和浮沉刚度是造成系统呈现准周期运动的主要原因.      

Parametric analyses on dynamic stall control of rotor airfoil via synthetic jet

The effects of synthetic jet control on unsteady dynamic stall over rotor airfoil are investigated numerically. A moving-embedded grid method and an Unsteady Reynolds Averaged Navier-Stokes(URANS) solver coupled with k-x Shear Stress Transport(SST) turbulence model are established for predicting the complex flowfields of oscillatory airfoil under jet control. Additionally, a velocity boundary condition modeled by sinusoidal function has been developed to fulfill the perturbation effect of periodic jet. The validity of present CFD method is evaluated by comparisons of the calculated results of baseline dynamic stall case for rotor airfoil and jet control case for VR-7 B airfoil with experimental data. Then, parametric analyses are conducted emphatically for an OA212 rotor airfoil to investigate the effects of jet control parameters(jet location, dimensionless frequency, momentum coefficient, jet angle, jet type and dual-jet) on dynamic stall characteristics of rotor airfoil. It is demonstrated by the calculated results that efficiency of jet control could be improved with specific momentum coefficient and jet angle when the jet is located near separation point of rotor airfoil. Furthermore, the dual-jet could improve control efficiency more obviously on dynamic stall of rotor airfoil with respect to the unique jet, and the influence laws of dual-jet's angles and momentum coefficients on control effects are similar to those of the unique jet. Finally,unsteady aerodynamic characteristics of rotor via synthetic jet which is located on the upper surface of rotor blade in forward flight are calculated, and as a result, the aerodynamic characteristics of rotor are improved compared with the baseline. The results indicate that synthetic jet has the capability in improving aerodynamic characteristics of rotor.     

直升机动态失速研究

本文简要介绍了旋翼和翼型的动态失速特性、动态失速主动和被动控制、旋翼综合法预测使用的一些动态失速模拟方法.UH-60A直升机飞行试验11029飞行是一个典型的旋翼动态失速实例,表演出旋翼后行桨叶上出现高攻角引起的动态失速,而前行桨叶上则出现因为激波诱导前缘分离引起的动态失速.翼型的动态失速特性方面介绍了典型的动态失速迟滞回线(攻角正弦变化和锯齿变化)、缩减频率和雷诺数对翼型动态失速特性的影响等.动态失速主动控制介绍可动前缘翼型的情况,被动控制则是使用前缘涡发生器的情况.     

翼型动态失速的变下垂前缘控制数值模拟

用CFD方法对VR-12翼型可压缩动态失速的变下垂前缘控制概念进行了数值模拟研究.模拟结果显示,变下垂前缘控制能在最大升力下降不大的情况下,非常显著地降低最大阻力,减小俯仰力矩负峰值,明显改善动态失速的负面效应.在流动机理上,变下垂前缘控制完全消除了动态失速涡.对参数影响的模拟研究表明,变下垂前缘控制的优势对马赫数、简缩频率或下垂控制方式的变化不敏感,是一种健壮的翼型可压缩动态失速控制手段.      

应用协同射流原理的旋翼翼型增升减阻试验研究

协同射流技术作为一种新型主动流动控制技术,是突破旋翼翼型高增升减阻设计的最有潜力的发展方向之一。以 OA312 旋翼翼型作为基准翼型,研制微型涵道风扇组为驱动的旋翼翼型 CFJ 风洞测力模型,开展基于前缘高负压零质量内循环协同射流原理的旋翼翼型高增升减阻低速风洞试验,研究吹气口大小、吸气口大小和上翼面下沉量等基础参数对增升减阻的影响规律,探讨 CFJ 旋翼翼型关键参数最佳取值。结果表明：与OA312 基准翼型相比,小攻角状态时,CFJ 旋翼翼型可显著降低阻力系数,甚至出现“负阻力”现象,实现了零升俯仰力矩基本不变;大攻角状态时,CFJ 旋翼翼型可显著提升最大升力系数和失速迎角,其中,最大升力系数可提升约 67.5%,失速迎角推迟了近 14.8°。     

翼型近尾迹流动的PIV研究—动力学机制

利用在线式互相关PIV(ParticleImageVelocimetry)系统,在低速风洞中对NACA0012翼型在雷诺数2.39×105,0°和4°攻角下的近尾迹流动进行了详细测量。实验结果表明,翼型近尾迹存在有序的涡街结构,涡街在尾缘处形成后,在向下游的迁移中,会经历一个发展壮大、失稳破碎的演化过程,流动从有序走向无序。翼型的近尾迹是一种以旋涡的运动学特性和动力学机制为主导的流动现象。本文着重探讨了翼型尾缘处的涡街形成机理,尾迹内的流动机制,以及近尾迹的流动稳定性。      

Parametric analyses for synthetic jet control on separation and stall over rotor airfoil

Numerical simulations are performed to investigate the effects of synthetic jet control on separation and stall over rotor airfoils. The preconditioned and unsteady Reynolds-averaged Navier–Stokes equations coupled with a k x shear stream transport turbulence model are employed to accomplish the flowfield simulation of rotor airfoils under jet control. Additionally,a velocity boundary condition modeled by a sinusoidal function is developed to fulfill the perturbation effect of periodic jets. The validity of the present CFD procedure is evaluated by the simulated results of an isolated synthetic jet and the jet control case for airfoil NACA0015. Then, parametric analyses are conducted specifically for an OA213 rotor airfoil to investigate the effects of jet parameters(forcing frequency, jet location and momentum coefficient, jet direction, and distribution of jet arrays) on the control effect of the aerodynamic characteristics of a rotor airfoil. Preliminary results indicate that the efficiency of jet control can be improved with specific frequencies(the best lift-drag ratio at F+= 2.0) and jet angles(40 or 75) when the jets are located near the separation point of the rotor airfoil. Furthermore, as a result of a suitable combination of jet arrays, the lift coefficient of the airfoil can be improved by nearly 100%, and the corresponding drag coefficient decreased by26.5% in comparison with the single point control case.     

翼型近尾迹流动的PIV研究—运动学特性

利用在线式PIV系统(ParticleImageVelocimetry),在低速风洞中对NACA0012翼型在雷诺数2.39×105,0°和4°攻角下的近尾迹流动进行了实验研究。实验结果表明,在较高的雷诺数下翼型近尾迹流动是一种以旋涡的运动学和动力学特性为主导的湍流剪切流。在测量范围内,翼型的尾缘处是近尾迹涡街的形成区;尾缘后0.5倍弦长的区域存在类似于卡门涡街的有序结构,是旋涡发展区域,旋涡具有较好的稳定性;距翼型尾缘0.5倍弦长至1倍弦长的区域,是翼型近尾迹流动由有序走向无序区域,旋涡开始破裂。翼型表面边界层对翼型近尾迹湍流剪切流的演化有重要影响。实验结果还给出了近尾迹流动的平均速度、湍流强度和剪切应变变化率,以及速度脉动量的二阶关联量u'u',u'v'和v'v' 的分布。      

大湍流度对超低雷诺数下翼型受力及绕流的影响

实验测量了超低雷诺数(Re=5 300)下 NACA 0012翼型在自由来流下的升力系数和阻力系数,重点研究来流的湍流度对升力系数和阻力系数的影响,并进一步通过对翼犁流场的研究揭示湍流度对翼型受力产生影响的机理.结果显示,低湍流度下升力系数和阻力系数均无失速特征;当湍流度提高,升力系数和阻力系数在12°～15°迎角下表...