基于变弯度技术和协同射流的混合流动控制技术研究

现代飞机强调高速巡航特性且兼顾隐身特性,因此翼型往往采用厚度较小,前缘半径不大,弯度不大的薄翼型。这类翼型的低速气动性能较差,容易失速,限制了这类飞机的短距起降特性和载重能力,因此需要借助流动控制技术来改善低速特性。该文讨论新型的协同射流主动流动控制技术,同变弯度技术包括后缘变弯和前缘下垂技术等被动流动控制技术相结合,探索混合流动控制技术的流动控制机理和控制效果。基于数值模拟的结果发现:仅采用单一的流动控制技术在薄翼型上得到的控制效果有限,而将协同射流同变弯度技术结合的混合流动控制技术可同时发挥不同流动控制技术的优点(例如协同射流引起的后缘失速的推迟,下垂前缘带来的前缘失速推迟,后缘襟翼带来的零升迎角减小)。该文提供的混合流动控制方案可以将薄翼型的最大升力系数提升至C_Lmax=3.3127,相对原始构型提升了96%,具有广阔的工程应用前景。     

Control of the aerodynamic characteristics of wing airfoils by nonstationary energy supply in transonic flow

The possibility of controlling the aerodynamic characteristics of wing airfoils in transonic regimes of flight using one-sided pulse-periodic energy supply has been studied. The flow structure near the symmetric airfoil at different angles of attack and its aerodynamic characteristics as functions of the value of energy in its nonsymmetric (about the airfoil) supply have been determined by numerical solution of two-dimensional nonstationary gasdynamic equations. A comparison of the obtained results and the data of calculation of flow past the airfoil at different angles of attack without energy supply has been made. It has been established that a prescribed lift can be obtained, using energy supply, with a much higher fineness ratio of the airfoil than that in the case of flow past it at an angle of attack. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 1, pp. 18–22, January–February, 2009.     

基于数论网格法与Morris法的翼型气动特性敏感性分析

针对在风力机翼型气动特性敏感性分析中计算效率较低的问题，提出了一种基于数论网格（number theoretic net，NT-net）法与Morris法的翼型气动特性敏感性分析方法。首先，构建了拟合精度较高的翼型参数化模型；其次，阐述了NT-net法的计算原理，采用NT-net法对翼型参数化模型的多项式系数进行抽样；然后，以风力机翼型S832为研究对象，采用Morris法进行翼型气动特性的全局敏感性分析；最后，进一步分析在特定工况下风力机翼型参数化模型的多项式系数对翼型外形及气动特性的影响。结果表明：影响翼型气动特性的主要因素依次为翼型的最大相对厚度和最大相对弯度、前缘半径和后缘厚度；当来流攻角较小时，最大相对厚度和最大相对弯度取适当的较小值、前缘半径取适当的较大值可有效增强该工况下风力机翼型的气动特性，同时也验证了NT-net法的计算效率更高。研究结果为风力机翼型气动设计提供了理论参考。     

弹性特征对跨声速抖振边界的影响研究

跨声速抖振直接影响飞机结构强度和疲劳寿命,易引发飞行事故。对于刚性静止翼型,其跨声速抖振特性仅与来流状态参数（马赫数、迎角和雷诺数）有关。该文通过释放翼型的俯仰自由度,采用非定常雷诺平均N-S方程建立了流场和结构的耦合求解方法,研究翼型结构弹性特征对跨声速抖振始发边界的影响。研究发现,结构固有频率对弹性支撑翼型的抖振边界影响较大,系统会在更小的来流迎角下失稳;而质量比对抖振边界影响较小。弹性支撑翼型的抖振始发迎角较刚性静止翼型的抖振起始迎角降低了近1°,因此翼型的弹性特征是跨声速抖振研究的重要因素。     

高层建筑顶部横梁的风效应

结合CFD数值方法和风洞试验分析了高层建筑顶部横梁的气动力和风荷载特性。CFD数值结果显示建筑顶部绕流会显著增大横梁处的气流风攻角;横梁气动力的数值计算结果和风洞试验结果均证实横梁为驰振稳定截面;风振分析显示横梁的峰值升力大于峰值阻力,通过进一步分析广义力功率谱密度函数和频率比对峰值升力的影响,证实横梁在50年重现期强风作用下处于涡激共振状态。     

Design and Optimization of airfoils in non-stalling incompressible flow with a prescribed range of the angle of attack

A simple and reliable method of aerodynamic design of airfoils is proposed for a given range of the angle of attack. The method is based on the solution of a new inverse boundary-value problem of aerohydrodynamics. In the problem the initial velocity distributions are given along the contour of the required airfoil as a function of the are co-ordinate for extreme values of the angle of attack from a fixed range. We justify a method of choice of these distributions which guarantees a non-stalling flow around the airfoil. The problem of airfoil optimization is also considered. Results of numerical calculations are presented.     

Microtab对翼型跨音速抖振始发特性的影响

研究了microtab对翼型跨音速抖振始发特性的影响。采用SST湍流模型对RANS方程进行封闭,以NACA0012翼型为对象,用CFD方法计算了在其后缘附近安装microtab后,翼型的跨音速流场。对比分析了在翼型后缘附近的上表面、下表面单独安装和上下表面对称安装microtab后,对翼型跨音速抖振始发特性的影响,并研究了microtab的高度和弦向安装位置对跨音速抖振边界的控制作用。结果表明：在翼型后缘附近的上表面加装microtab能够提高抖振始发攻角,并且随着microtab高度的增加,抖振始发攻角有增大的趋势。在翼型后缘附近的下表面加装microtab能够提高抖振始发时的升力系数,且抖振始发时的升力系数随着microtab高度的增加而增大。microtab的弦向安装位置的变化对于抖振始发攻角影响较小,但是对抖振始发时的升力系数有明显的影响。         

Controlling aerodynamic characteristics of airfoils by means of periodic pulsed energy supply

The possibility of controlling the aerodynamic characteristics of lifting airfoils by means of local periodic pulsed energy supply in transonic flight regimes has been studied. Using a numerical solution of two-dimensional nonstationary equations of gasdynamics, a change in the flow structure near a symmetric airfoil is determined as dependent on the amount of energy supplied to the lower side of the airfoil in a range of attack angles.     

不同迎流攻角下正三角柱流致振动数值模拟研究

采用嵌入式迭代浸入边界法对不同迎流攻角下正三角柱的流致振动(VIV)进行了二维数值模拟研究,其中迎流攻角为α=0°～60°(当α=60°时三角柱顶点迎流),雷诺数为Re=100,质量比为m~*=5和折合流速为U_r=2～20。详细分析了不同迎流攻角下横流向振幅、振动频率、水动力系数、升力与位移的相位差以及尾涡模式随折合流速变化的情况。结果发现,三角柱振动随迎流攻角表现为3种不同的振动模式:涡振-驰振联合模式(α=0°～15°)、涡振-驰振分离模式(α=20.0°～22.5°)和涡振模式(α=25°～60°)。选取α=0°、α=20°、α=60°3个迎流攻角详细论述了不同模式下三角柱的振动特性。此外,还发现虽然三角柱在迎流攻角α=0°时关于来流方向对称,三角柱的平衡位置在某些折合流速下出现了偏移,该现象与升力中偶次谐波分量的出现有关。最后,应用准稳态分析得到了驰振出现的攻角范围,结果与数值模拟的情况吻合较好,说明准稳态分析可以准确预测三角柱驰振的攻角范围。     

翼型动态风洞试验洞壁效应研究

翼型动态失速导致气动非线性特征突出,与洞壁效应耦合给风洞试验数据带来极大的不确定性,该文通过试验和数值手段揭示了翼型动态试验洞壁效应产生机理和影响规律,结果表明:相比于静态试验,由于洞壁的存在,动态试验翼型的尾流区的总压和静压分布更不均匀,动态试验翼型在相同迎角下的洞壁干扰更严重,表现为翼型在大迎角段,洞壁干扰导致模型中间截面附近和端部截面附近的速度分布和压力分布差异更明显,且相比于压力面,吸力面流动的二维性变得较差。侧壁干扰抑制了翼型中间截面附近的流向分离,诱导了端部附近的展向分离流。上洞壁和下洞壁的非定常压力系数随翼型实时迎角变化也呈迟滞环曲线,迟滞环方向相反,且脉动一阶主频率与翼型俯仰振荡频率一致。风洞洞壁干扰下,翼型动态失速三维涡结构呈“Ω”型。风洞上下壁干扰使得翼型线性段的升力系数和升力线斜率均增加,诱导翼型提前失速;在负行程,则使得翼型升力系数降低。侧壁干扰在负行程诱导了翼型表面的展向流动、减小了翼型弦向流动速度,引起翼型升力系数减小,正行程范围则影响较小,且翼型失速延迟。FL-11风洞翼型动态试验的上下壁干扰效应为主导因素;但是侧壁干扰不可忽略,特别是在翼型振荡周期的大迎角和负行程范围。     

NACA0012翼型抖振现象实验研究

通过在风洞侧壁安装动态压力传感器测量侧壁脉动压力的方法针对NACA0012翼型开展了零攻角状态下跨声速抖振特性的实验研究,并测量了翼型沿弦向与展向的压力分布。从时域和频域两个方面分析了脉动压力结果,得到了NACA0012翼型的跨声速抖振起始马赫数和抖振频率等抖振特性。研究结果表明:风洞二维性较好,侧壁区域的压力情况能够反映核心流压力变化情况;抖振发生在实验马赫数Ma_exp = 0.88~0.89范围内;随着马赫数的增大,抖振频率有所增加。     

翼型绕流分离的微楔控制

基于大涡模拟(LES, Large Eddy Simulation),结合3阶WENO(Weighted Essentially Non-Oscillatory)格式与沉浸边界法(IBM, Immersed Boundary Method),对NACA0012翼型在来流马赫数为Ma=0.5以及10°攻角下,有无微型三角楔涡流发生器作用的三维绕流进行了数值模拟,对比了两者的流场结构变化。数值结果表明,微楔能显著改变翼型绕流的尾涡结构,并能缩小其表面边界层的分离,提高升力,并对微型三角楔涡流发生器的流体分离抑制机理进行了讨论。     

Two-dimensional leaflet valves with maximum reverse-flow moment

Summary Camber and thickness distributions and a hinge point, are chosen for thin airfoils, to maximise the de-stabilising moment about that hinge point, in steady reversed flow. This optimisation is carried out subject to the constraints that the airfoil be in equilibrium for steady forward flow, and that the mean square camber be held fixed.Note: Unsteady effects have now been included in a further study, University of Adelaide, Applied Mathematics Report T8106, July 1981.     

超空泡航行体尾部流体动力特性试验研究

在水洞中采用前支撑方式模型进行了通气超空泡试验,对不同的超空泡形态下超空泡航行体尾部阻力系数、升力系数及俯仰力矩系数的变化规律进行了研究,并对航行体有无攻角情况下的尾部流体特性进行了比较,获得了攻角对尾部流体动力特性的影响。研究表明,在空泡开始包裹到尾部天平时,随着空泡形态的增长,尾部阻力系数迅速下降,而升力系数和俯仰力矩系数则迅速上升。当空泡将航行体上表面包裹,而下表面沾湿时,阻力系数减小趋势变平缓,而升力系数和俯仰力矩系数则均到达峰值。当空泡完全包裹航行体时,升力系数和俯仰力矩系数迅速回落至零值附近,此时阻力系数在零值附近变化不大。攻角1度情况下的航行体尾部阻力系数减小幅度与无攻角时相比明显降低,最大升力系数和俯仰力矩系数均远大于无攻角情况。     

基于品质因数的翼型绕流多孔抽吸控制

基于品质因数,对雷诺数Re=104,攻角α=6°,抽吸起始位置位于分离点的NACA0012翼型绕流分离控制进行了数值模拟,讨论了抽吸区域与抽吸系数变化对控制收益与升阻比等参数的影响。结果表明:翼型升力与升阻比系数随控制区域增加而升高,但只有一个控制区域使阻力系数最小。相同控制区域,翼型最大升阻比对应一个最佳抽吸系数。若固定抽吸控制区域,则抽吸系数应尽量小,才能获得最多控制收益。另外,存在一个最佳控制区域尺度,使控制收益最高。     

风力机翼型动态失速气动特性仿真

基于Beddoes-Leishman(B-L)半经验动态失速模型,从附着流、分离流和动态涡三个方面阐述了风力机翼型在动态失速情况下非定常气动力系数的计算方法。在此基础上根据风力机翼型工作时的实际特点对原B-L模型中分离流和动态涡气动力系数的计算进行了改进,并将模型扩充到适用于全范围攻角的动态失速计算。利用所编制的程序仿真了风力机翼型S809和NACA4415动态失速下的升力、阻力和力矩系数。计算结果与实验数据吻合良好。改进模型与原B-L模型计算结果的对比表明,改进后的模型提高了对非定常气动力系数计算的精确性和适用区间,能更好地预测动态失速气动力的变化。     

Controlling the Flow past a Semicircular Airfoil at Zero Angle of Attack Using Slot Suction in One or Two Vortex Cells for Attaining Extremal Lift

Calculations using multiblock computational technologies and a model of shear-stress transport modified with allowance for the curvature of streamlines in turbulent airflow were performed at a zero angle of attack for a semicircular airfoil containing one or two surface vortex cells with slot suction. The results showed evidence of stabilization of a nearly undetached flow and attainment of an extremal lift of C _y = 5.2 and a lift-to-drag ratio of K = 24 with allowance for energy losses for suction in the vortex cells.     

Optimization design of axial fan blade

A series airfoil was obtained through optimization design which aimed to promote lift–drag ratio, and the new airfoil series was used to construct a blade. The chord length and installation angle of the blade along the blade height were optimized by using orthogonal optimization. Three design options (straight blades, C-type blades and forward swept blades) are examined in this paper. Taking an axial fan as the research object, the whole 3D numerical simulation was conducted by using Ansys-CFX. Axial fans with three kinds of blades are discussed and compared under design and off-design conditions. The present results show that: under design conditions, the total pressure efficiency of the axial flow fan with the forward swept blade is the highest, and the C-type blade has slightly lower efficiency while the straight blade has the lowest efficiency. Under off-design conditions, the aerodynamic performance of the forward-swept blade and C-type blade fans are better than that of the straight-blade fans.     

仿生翼型对半主动扑翼捕能性能的影响

为了分析仿生翼型对半主动扑翼捕能性能的影响,该文在Fluent流体求解器的基础上,通过二次开发,编制了一套可有效求解流体流动、扑翼主动转动和被动往复扑动的计算程序。在此基础上,研究仿蜻蜓翼型、仿海鸥翼型、NACA0012和NACA0015四种翼型的捕能性能,结果表明采用仿生翼型的扑翼具有更好的捕能性能。进一步通过对不同外形扑翼的流场分析发现,采用仿生翼型可使扑翼在被动往复扑动过程中产生更强的涡流,并且在俯仰运动过程中可延缓涡流从扑翼表面脱落,从而使扑翼具有较好的捕能性能。     

基于当地流活塞理论的气动弹性稳定性分析方法研究

基于改进的当地流活塞理论,推导了用模态坐标表示的弹性振动翼面的非定常广义气动力表达式。通过与非定常Euler方程的比较,证明该气动力模型具有较高的数值精度,放宽了原始活塞理论对翼型厚度、迎角、马赫数的限制。再耦合两自由度结构运动方程,在时域和频域内实现了超音速、高超音速气动弹性的稳定性分析。应用算例计算了一系列二元机翼和三维舵面的气动弹性特性。通过与耦合非定常Euler方法或实验结果的比较,证明该方法在保证精度的同时大大提高了超音速气动弹性的计算效率,在颤振分析中有较高的工程实用价值。