大展弦比夹芯翼大攻角颤振分析

首先导出大展弦比复合材料梁弯扭耦合模态的半解析解，对具有NACA0012翼型的大展弦比的夹芯翼，在模态空间内建立了运动方程。然后采用半经验的ONERA非线性气动力模型描述空气动力，形成了对大展弦比夹芯翼大攻角气动弹性问题的描述。通过结构求解器和空气动力求解器联合求解来完成非线性颧振边界的计算。为了验证非线性颤振边界的求解方法，还利用ONERA气动力模型中的线性部分建立了夹芯翼的线性颤振方程。结果表明：零翼根攻角时，线性颤振速度与用非线性颧振边界求解方法得到的颧振速度完全一致；颤振速度随翼根攻角的增加而迅速减小；复合层铺设方式对颤振速度有较大影响。     

Shape morphing of aircraft wing: Status and challenges

In this paper, the recent activity in conceptual design, prototype fabrication, and evaluation of shape morphing wing is concisely classified. Of special interest are concepts which include smart materials such as shape memory alloys (SMA), piezoelectric actuators (PZT), and shape memory polymers (SMP). We will also provide several concepts that have been developed and evaluated by the authors. Our work indicates that antagonistic SMA-actuated flexural structures form a possible enabling technology for wing morphing of small aircraft. The use of SMA-actuated structures in shape morphing wing designs reduces the weight penalty due to the actuation systems, because such SMA-actuated structures carry aerodynamic loads.     

Complete morphing wing design using flexible-rib system

This study is concerned with the complete design, analysis, functional prototyping and flight testing of a novel morphing wing system for use in a relatively small (<10 kg) unmanned aerial vehicles (UAVs). To achieve improved flight performance with limited weight penalty, camber-adjustable morphing wing was designed using flexible servomotor-actuated mechanisms. The current design, which was originally conceptualized by Monner et al. (Smart structures and materials: industrial and commercial applications of smart structures technologies. Proceedings of SPIE 3326, pp 60–70, 1998), ensures that the airfoil shape of the wing is able to continuously morph between the non-cambered and the cambered configurations. The morphing function of the wing is achieved using a flexible-rib system driven by onboard servomotor-rocker. This unique design of a flexible-rib assembly enables the airfoil of the wing to be accurately morphed to the target configuration. With the aid of aerodynamic and finite element analyses, the flexible rib assembly performance and structural integrity are evaluated and assessed. The design process was in compliance with aircraft design standards, including the Federal Aviation Regulations—Part 23. The functional prototype of the flexible rib morphing-wing enabled UAV was manufactured and assembled and a test plane was ground tested. The success of the entire project, including flight testing of the flexible rib assembly is summarized in this paper.     

基于多项式修正片条气动力的跨音速颤振分析方法及其试验验证

提出一种基于多项式修正片条气动力的跨音速颤振分析方法,以片条内升力和力矩随攻角变化斜率为修正目标,采用多项式方程模拟片条力矩分布,使整个翼面的气动力大小和分布都与目标相符,进而使用修正后的气动力进行跨音速区的颤振分析.计算结果经跨音速颤振风洞试验验证,该方法对翼吊发动机构型的机翼颤振型、带操纵面的尾翼颤振型都有较高的计...     

Gull-inspired joint-driven wing morphing allows adaptive longitudinal flight control

Birds dynamically adapt to disparate flight behaviours and unpredictable environments by actively manipulating their skeletal joints to change their wing shape. This in-flight adaptability has inspired many unmanned aerial vehicle (UAV) wings, which predominately morph within a single geometric plane. By contrast, avian joint-driven wing morphing produces a diverse set of non-planar wing shapes. Here, we investigated if joint-driven wing morphing is desirable for UAVs by quantifying the longitudinal aerodynamic characteristics of gull-inspired wing-body configurations. We used a numerical lifting-line algorithm (MachUpX) to determine the aerodynamic loads across the range of motion of the elbow and wrist, which was validated with wind tunnel tests using three-dimensional printed wing-body models. We found that joint-driven wing morphing effectively controls lift, pitching moment and static margin, but other mechanisms are required to trim. Within the range of wing extension capability, specific paths of joint motion (trajectories) permit distinct longitudinal flight control strategies. We identified two unique trajectories that decoupled stability from lift and pitching moment generation. Further, extension along the trajectory inherent to the musculoskeletal linkage system produced the largest changes to the investigated aerodynamic properties. Collectively, our results show that gull-inspired joint-driven wing morphing allows adaptive longitudinal flight control and could promote multifunctional UAV designs.     

飞机T型尾翼颤振计算的若干关键问题

摘要 由于飞机T型尾翼的结构与气动布局特点,T型尾翼颤振计算不能套用常规尾翼的分析方法,而需要考虑平尾面内运动以及静升力等因素的影响。从T型尾翼的工程颤振分析出发,讨论了T型尾翼颤振计算中的若干关键问题,阐述了T型尾翼颤振特性的特点和影响T型尾翼颤振特性的关键参数,分别介绍了现有的几种T型尾翼颤振计算中的气动力修正方法,提出了T型尾翼颤振工程计算中必须注意的问题。     

一种静、动气动弹性的一体化计算方法

用欧拉方程计算非定常气动力，在时域内求解结构运动方程。根据计算得到的广义坐标时间响应的特性来判断机翼在给定来流条件下是否发生了颤振或静发散。如广义坐标的时间响应是收敛的．则扰动消失后的机翼平衡位置即为最终的机翼静变形，同时也得到了考虑弹性影响的机翼气动特性。从而得出飞机的静、动弹性一体化计算结果,与传统计算方法结果的比较说明了本文方法的有效性。     

Framework for sensitivity and uncertainty quantification in the flutter assessment of bridges

The phenomenon of aerodynamic instability caused by wind is usually a major design criterion for long-span cable-supported bridges. If the wind speed exceeds the critical flutter speed of the bridge, this constitutes an Ultimate Limit State. The prediction of the flutter boundary therefore requires accurate and robust models. The state-of-the-art theory concerning determination of the flutter stability limit is presented. Usually bridge decks are bluff and therefore the aeroelastic forces under wind action have to be experimentally evaluated in wind tunnels or numerically computed through Computational Fluid Dynamics (CFD) simulations. The self-excited forces are modelled using aerodynamic derivatives obtained through CFD forced vibration simulations on a section model. The two-degree-of-freedom flutter limit is computed by solving the Eigenvalue problem.A probabilistic flutter analysis utilizing a meta-modelling technique is used to evaluate the effect of parameter uncertainty. A bridge section is numerically modelled in the CFD simulations. Here flutter derivatives are considered as random variables. A methodology for carrying out sensitivity analysis of the flutter phenomenon is developed. The sensitivity with respect to the uncertainty of flutter derivatives and structural parameters is considered by taking into account the probability distribution of the flutter limit. A significant influence on the flutter limit is found by including uncertainties of the flutter derivatives due to different interpretations of scatter in the CFD simulations. The results indicate that the proposed probabilistic flutter analysis provides extended information concerning the accuracy in the prediction of flutter limits.The final aim is to set up a method to estimate the flutter limit with probabilistic input parameters. Such a tool could be useful for bridge engineers at early design stages. This study shows the difficulties in this regard which have to be overcome but also highlights some interesting and promising results.     

采用等效刚度有限元模型的复合材料机翼颤振分析

采用等效刚度方法,研究了一种适用于机翼初步设计阶段的动力学和颤振分析的结构有限元模型。该方法首先计算不同布局形式的加筋壁板的刚度矩阵,然后将其赋予与加筋壁板平面形状相同的光板（等效板）上,使加筋壁板和等效板具相同的力学性能。该方法的优点是避免了加强筋的有限元建模,从而使有限元模型的复杂程度大大降低,但同时等效刚度结构有限元模型仍能反映机翼加筋壁板的结构特性。以某客机概念方案的机翼为例,建立了反映实际结构详细有限元及其等效刚度有限元模型。计算结果和对比分析表明,两种模型的固有频率、振动模态和颤振分析结果吻合得很好,从而验证了等效刚度方法在机翼结构动力学和颤振分析方面的准确性。由于该方法具有简单快速和准确的优点,可用于机翼初步设计阶段对颤振特性的评估。     

悬索桥跨径的空气动力极限

气动失稳是大跨度悬索桥设计中的关注重点之一。为了在悬索桥初步设计阶段,给主梁断面形式和跨径长度的确定提供参考,对主跨1000 m~5000 m悬索桥开展气动稳定性分析。基于跨径从888 m(虎门大桥)~1991 m(明石海峡大桥)的悬索桥动力特性,拟合在1000 m~5000 m跨径范围内主梁侧弯、竖弯与扭转基频随跨径增长的变化趋势。根据该趋势构建主跨介于1000 m~5000 m的双塔单跨悬索桥有限元模型,其中垂跨比为1/11。选取常用的流线形单箱、格构式桁架、窄开槽双箱与宽开槽双箱4种主梁断面,将主梁宽度统一为36 m以排除桥宽对气动稳定性的影响。结合风洞试验测得的静力三分力系数和颤振导数,采用考虑结构几何非线性和气动荷载非线性的三维非线性静风稳定分析方法及三维全模态频域颤振分析方法求解悬索桥在0°与±3°攻角的静风失稳临界风速和颤振临界风速。分析结果表明,跨径从1000 m增加到3000 m左右时静风失稳临界风速有下降趋势,在3000 m~5000 m时静风失稳风速随跨径增大而上升。颤振临界风速则随跨径不断降低,与主梁基频的衰减规律相似。对不同断面外形气动稳定性的比较显示,流线形单箱和格构式桁架悬索桥的最低静风失稳临界风速低于实测最大阵风风速的80 m/s;跨径超过2000 m时,四种断面悬索桥的颤振临界风速均小于70 m/s。研究结果表明,对于本文构建的悬索桥而言,跨径3500 m附近的流线形单箱和格构式桁架悬索桥有可能在现实中发生静风失稳,而颤振在大跨度悬索桥抗风设计中是控制因素,且颤振问题随跨径增大而越发严峻。

     

基于非定常气动力降阶的AGARD445.6硬机翼不同迎角颤振研究

以AGARD445.6硬机翼为研究对象,发展了基于计算流体力学与模态叠加的并行流固耦合方法,计算该机翼在不同初始迎角、不同来流速度的气动弹性时域响应,结果表明：初始迎角小于7°时,该机翼颤振速度随着初始迎角增加而降低;初始迎角7°～10°,颤振速度随着迎角增大而增加。在10°迎角条件建立了基于径向基神经网络的非定常气动降阶模型,准确预测不同速度、减缩频率的非定常气动力,并使用时域龙格库塔法和频域VG法预测10°迎角的颤振特性;建立考虑初始迎角输入的非定常气动降阶模型,预测机翼不同初始迎角的颤振特性。基于降阶模型的初始迎角对颤振边界影响的机理分析表明：小迎角时,随着迎角的增加广义力系数幅值比增加,导致颤振速度的下降;迎角大于7°后展向涡改变了机翼表面压强分布,导致一扭广义力系数幅值比降低,从而增加该机翼颤振速度。     

机翼跨音速风洞颤振试验模型的计算分析

以某民机机翼跨音速颤振模型为研究对象,采用N-S方程求解固定边界流场的气动力,简化的跨音速小扰动方程求解运动边界流场的气动力,结合结构动力学的模态分析结果进行颤振特性分析。模型风洞试验前完成所有计算工作,试验后通过比较表明,计算结果与试验结果吻合:(1)颤振频率一致;(2)颤振速度随马赫数的变化趋势一致;(3)跨音速凹坑的底部位置一致;(4)颤振速度的偏差最大不超过10%,且在马赫数0.60和0.70处,偏差1%。由此可见该计算方法的计算精度高,可用于风洞试验结果的预判,提升风洞试验结果的可信度和风洞试验的效率,也可作为民机适航符合性验证的一种手段。     

Structural optimization of an aeroelastically tailored composite flat plate made of woven fiberglass/epoxy

Summary Effects of aspect ratio, sweep angle, and stacking sequence of laminated composites were studied to find the optimized configuration of an aeroelastically tailored composite wing idealized as a flat plate in terms of flutter speed. The aeroelastic analysis has been carried out in the frequency domain. The modal approach in conjunction with doublet-lattice method (DLM) has been chosen for structural and unsteady aerodynamic analysis, respectively. The interpolation between aerodynamic boxes and structural nodes has been done using surface splines. To study the effect of stacking sequence the classical lamination theory (CLT) has been chosen. The parametric studies showed the effective ply orientation angle to be somewhere between 15 and 30 degrees, while the plates with lower aspect ratio seem to have higher flutter speeds. Forward-swept configurations show higher flutter speed, yet imposed by divergence constraints.     

飞机T型尾翼跨音速颤振特性研究

由于飞机T型尾翼的结构与气动布局特点,T型尾翼颤振计算不能套用常规尾翼的分析方法,而需要考虑平尾面内运动以及静升力等因素的影响。而跨音速空气压缩性效应和非定常气动力计算的不准确性,使得T型尾翼跨音速颤振计算更加困难,准确性较低。因此,需要采用试验为主计算为辅的方法来研究飞机T型尾翼跨音速颤振特性。针对某T型尾翼结构,用ZAERO软件等价片条势流跨音速颤振(ZTAIC)方法计算T型尾翼跨音速颤振特性,研究了马赫数、风洞气流密度和平尾迎角对T型尾翼颤振特性的影响。通过升力系数斜率空气压缩性修正计算方法和跨音速颤振模型风洞试验方法得到了飞机T型尾翼的跨音速颤振的凹坑曲线和空气压缩性特性,两种方法得到结果一致。     

含区间不确定性参数的机翼气动弹性优化

提出了一种具有区间不确定性的机翼颤振优化方法.采用拉丁超立方方法建立仿真试验表,基于MSC.Nastran平台进行颤振仿真分析.获得仿真数据之后,应用Kriging方法构造了包含区间不确定性参数的机翼颤振分析代理模型,并进行有效性检验.基于建立的代理模型并按照区间序数关系,将不确定性优化目标和约束条件转化为确定性表达形式,从面形成区间不确定性的结构优化设计方法.该方法将区间法优化和代理模型相结合,同时综合有限元仿真和遗传算法的优点,计算效率较高且应用范围较广.以某复杂机翼结构为例进行了含区间不确定性的颤振优化计算.分析结果表明了所提方法的正确性和可行性.     

T型尾翼颤振特性分析方法

由于T型尾翼特殊的结构和气动布局形式,其颤振特性的分析比较复杂,飞行状态和一些常规分析可以忽略的参数如上反角都会对颤振速度有很大影响。针对这些特殊问题,分析了T型尾翼的颤振特性受平尾上反角、平尾上的定常气动力和固有振动形式等因素的影响。重点研究了T型尾翼颤振计算中特殊的附加非定常气动力,建立了T型尾翼非定常气动力和颤振分析方法。在低速风洞中开展了T型尾翼缩比模型的颤振试验,验证了分析方法。结果表明T型尾翼特殊的气动效应主要影响垂尾的弯扭耦合颤振形式,颤振速度随平尾攻角增加而降低,在设计中采用一定的平尾下反角设计能够提高T型尾翼的颤振速度。通过对试验结果的理论分析,阐述了这种效应产生的机理,并对实际设计提出建议。     

Two‐dimensional transonic aeroservoelastic computations in the time domain

A computational method to perform transonic aeroelastic and aeroservoelastic calculations in the time domain is presented, and used to predict stability (flutter) boundaries of 2‐D wing sections. The aerodynamic model is a cell‐centred finite‐volume unsteady Euler solver, which uses an efficient implicit time‐stepping scheme and structured moving grids. The aerodynamic equations are coupled with the structural equations of motion, which are derived from a typical wing section model. A control law is implemented within the aeroelastic solver to investigate active means of flutter suppression via control surface motion. Comparisons of open‐ and closed‐loop calculations show that the control law can successfully suppress the flutter and results in an increase of up to 19 per cent in the allowable speed index. The effect of structural non‐linearity, in the form of hinge axis backlash is also investigated. The effect is found to be strongly destabilizing, but the control law is shown to still alleviate the destabilizing effect. Copyright © 2001 John Wiley & Sons, Ltd.     

基于3211多阶跃激励CFD模型的颤振导数识别研究

提出一种通过计算流体动力学(Computational Fluid Dynamics,CFD)建立离散时间气动模型并识别颤振导数的方法,该方法通过强迫模型按一种3211多阶跃方式运动,由CFD数值模拟得到作用在模型上的气动力.由于3211多阶跃包含了丰富的频率成份,能激励起气动力系统在这一连续频域范围内的广泛响应,因而可基于3211输入-气动力输出得到定义在某一频率范围的离散时间气动模型.该气动模型能对对应不同折算风速的简谐位移输入快速仿真得到气动力输出,通过这些输入-输出就可快速识别任意折算下的颤振导数,无需对不同折算风速重复进行CFD计算.应用本文方法识别了薄平板的颤振导数,并与薄平板风洞试验结果进行了比较,颤振导数的一致性证明了本文方法的有效性.     

大气紊流作用下超音速二元机翼的脉动响应

以二元机翼为研究对象,研究大气紊流作用下系统的脉动响应。将气动力分解为简谐振动气动力和脉动气动力两部分,采用随机场的三角级数合成法得到作用在机翼上的脉动压力,运用随机理论对机翼均方根响应值进行分析,着重考查了平均来流速度、湍流尺度、湍流强度等对系统均方根响应的影响。结果表明,系统的均方根响应随速度的增大而增大,在流体速度小于线性临界颤振速度时,其变化很平缓,当速度超过临界颤振速度时,其均方根响应迅速增大。而均方根响应几乎随紊流强度的变化呈线性增长,但其对紊流尺度的变化不很敏感。     

Design optimization framework for tiltrotor composite wings considering whirl flutter stability

This paper constructs the design optimization framework for the composite wing of a tiltrotor aircraft based on the Korea Aerospace Research Institute (KARI) Smart Unmanned Aerial Vehicle (SUAV) TRS4 model. The present optimal design attempts to find the cross-section layout that minimizes the structural weight of a composite wing, while satisfying a series of design constraints. The framework consists of various analysis and design tools that include a 2-D beam cross-section analysis, a whirl flutter analysis, and a 3-D strain/stress analysis under the worst wing-loading case. The variation of wing sectional properties of tiltrotor aircrafts in the course of design optimization greatly affects the whirl flutter stability and shows considerable influence on the structural integrity of the wing. In the design framework, the whirl flutter stability is analysed by the nonlinear flexible multibody analysis code DYMORE and the structural integrity is investigated using a MATLAB-based 3-D strain analysis module along with the previous load analysis result. The MATLAB is used to conduct the optimization with a gradient-based optimizer and integrate all of the design and analysis tools. The nonlinear constraints associated with the aeroelastic stability and the structural integrity are also considered. For optimal design examples using the developed framework, a simplified cross-section model based on the KARI SUAV TRS4 composite wing is considered as an initial model. Design optimization examples are investigated to show the validity of the proposed framework and to illustrate the reduction of the structural weight of the composite wing. It is observed that weight reductions of wing structures by 26% and 40% are achieved, while maintaining the whirl flutter stability margins.