超声速气流中受热壁板的二次失稳型颤振

研究了超声速气流中受热壁板的非线性气动弹性响应,发现了一种新的动态失稳现象——二次失稳型颤振。基于von Karman非线性应变-位移关系、Reissner-Mindlin板理论和一阶活塞理论建立超声速气流中三维壁板的有限元模型。通过数值算例,研究了超声速气流中受热壁板发生二次失稳型颤振的条件,并运用非线性振动理论分析了二次失稳型颤振的机理。研究表明,超声速气流中受热壁板在平衡态的稳定性未发生变化时,也会因系统参数的变化引起气动弹性响应性质的突变,导致壁板的二次失稳型颤振。二次失稳型颤振能否发生不仅受到气流速压和壁板温升的影响,而且还与初始扰动有关。当扰动引起壁板的初始变形较小时,不能激发出二次失稳型颤振,壁板的气动弹性响应最终收敛到屈曲平衡态。应用二次失稳型颤振理论和分析方法,确定了前人给出的一个金属壁板模型的热颤振边界的风洞试验结果,而且计算结果与试验结果符合良好,从而对这一壁板热颤振现象的风洞试验结果作出了较合理的理论解释。     

高速流场中变刚度复合材料层合板颤振分析

变刚度复合材料层合板在高速流场中的颤振行为是设计中需要考虑的问题。本文研究了高速流场中的曲线纤维变刚度层合复合材料壁板非线性颤振响应,分析了边界条件和纤维方向对颤振特性的影响。利用von-Karman大变形应变-位移关系,采用气动力活塞理论,根据虚功原理和有限元法建立变刚度复合材料壁板颤振的气动弹性力学模型,采用Newmark法对壁板的颤振方程求解。给出了不同边界条件和纤维方向条件下层合复合材料壁板的颤振特性。计算结果表明：随着纤维在板中心处或在边界±a/2处与x方向夹角（T₀或T₁）的增大,颤振临界动压减小;相同动压下,随着T₀或T₁的增大,极限环振幅增大。研究表明采用曲线纤维进一步提高了复合材料层合板的可设计性,通过调整曲线纤维路径可以改变复合材料壁板的颤振特性。     

Suppressing nonlinear aeroelastic response of laminated composite panels in supersonic airflows using a nonlinear energy sink

This paper proposes using a Nonlinear Energy Sink (NES) to suppress the nonlinear aeroelastic response of laminated composite panels in supersonic airflows. Relevant aeroelastic equations are established using Hamilton’s principle and a finite element approach, drawing upon Von Karman’s large deflection theory and first order piston theory. The idea of the NES suppression region is proposed and the effects of NES parameters on the NES suppression region are studied in detail. The results show that the nonlinear aeroelastic responses of the panel can be completely suppressed by the Transient Resonance Capture (TRC); the appropriate NES parameter values can increase the critical dynamic pressure for flutter and suppress the nonlinear aeroelastic response effectively. Increasing the mass ratio of the NES can improve the NES suppression region; the nonlinear stiffness coefficient and damping of the NES within a specific range can suppress the nonlinear aeroelastic response. The most effective installation position for a NES is in a specific region behind the center-line of the panel in the direction of the airflow.     

高超声速飞行器受热壁板的气动弹性声振分析

高超声速飞行器壁板在非定常气动力、热载荷和噪声载荷构成的多物理场联合作用下,将表现出复杂的非线性气动弹性声振响应,特别是在颤振临界动压附近,受热载荷以及声载荷作用,壁板表现出复杂的跳变运动。基于von Karman大变形板理论,建立了热-声载荷和气动力共同作用下的壁板运动方程,分析了超声速气流中受热壁板的屈曲变形及热屈曲稳定性,借助势阱概念初步分析了壁板跳变运动产生的机理。通过定义“穿零频次”给出了跳变运动定量的分类方法,并计算得到不同温升和动压情况下,壁板发生跳变运动所对应的临界声压级。结果表明：在颤振临界动压之前,随着动压的增加,受热壁板势阱的深度先增大后减小,且受热壁板的势阱深度随着温升的增加而增大。     

考虑间隙非线性的控制舵非线性气动弹性分析

间隙结构的气动弹性系统非线性颤振问题是飞行器气动弹性力学工程领域的研究热点和难点,研究 考虑间隙非线性的控制舵系统的气动弹性特性具有重要意义。基于最小状态拟合方法获得时域降阶气动力模 型,并通过Lagrange方程获得系统非线性气动弹性方程;对比分析三种不同非线性控制舵系统的极限环颤振 及非线性动力学响应特性,并与等效线化法和时域仿真的结果进行一致性对比。结果表明:俯仰和扑动弹簧刚 度的变化对系统颤振边界有显著影响,当俯仰和扑动两个方向同时含有间隙非线性时,系统在线性颤振速度内 存在倍周期、混沌等复杂非线性动力学现象。     

Hypersonic flutter and flutter suppression system of a wind tunnel model

The aeroelastic behavior of a thin flat rudder model was numerically simulated and experimentally investigated in a hypersonic wind tunnel. In particular, a flutter suppression system taking advantage of collision within small gaps was proposed and a novel system for the flutter simulation of the whole nonlinear aeroelastic system including the flutter suppression system was developed. First, the critical flutter dynamic pressure of the rudder without the flutter suppression system was calculated with different methods. Then, the whole nonlinear aeroelastic system, including theflutter suppression system, was simulated to design the gap size. Finally, the flutter suppression system was experimentally validated in a hypersonic wind tunnel operating at Mach number 5. The typical phenomenon of Limit Cycle Oscillation(LCO) was observed, avoiding the structural failure of the model and the consistency between numerical and experimental results was demonstrated.The proposed suppression system can improve the design and reusability of test models of hypersonic flutter experiments.     

Nonlinear aeroelastic analysis of the folding fin with freeplay under thermal environment

The nonlinear aeroelastic behavior of a folding fin in supersonic flow is investigated in this paper. The finite element model of the fin is established and the deployable hinges are represented by three torsion springs with the freeplay nonlinearity. The aerodynamic grid point is assumed to be at the center of each aerodynamic box for simplicity. The aerodynamic governing equation is given by using the infinite plate spline method and the modified linear piston theory. An improved fixed-interface modal synthesis method, which can reduce the rigid connections at the interface, is developed to save the problem size and computation time. The uniform temperature field is applied to create the thermal environment. For the linear flutter analyses, the flutter speed increases first and then decreases with the rise of the hinge stiffness due to the change of the flutter coupling mechanism. For the nonlinear analyses, a larger freeplay angle results in a higher vibration divergent speed. Two different types of limit cycle oscillations and a multiperiodic motion are observed in the wide range of airspeed under the linear flutter boundary. The linear flutter speed shows a slight descend in the thermal environment, but the effect of the temperature on the vibration divergent speed is different under different hinge stiffnesses when there exists freeplay.     

Review of unsteady transonic aerodynamics: Theory and applications

Unsteady transonic flow theory is reviewed and classical results from the nonlinear asymptotic theory are combined with new results from computational fluid dynamics. The emphasis is on applications to the field of aeroelasticity and on clarifying the limitations of linearized theories in problems involving mixed subsonic-supersonic flows. The inherent differences between nonlinear transonic aerodynamics and linear subsonic and supersonic aerodynamics are considered from a theoretical and computational standpoint, and the practical implications of these differences in formulating suitable aerodynamic models for aeroelastic stability calculations are discussed. Transonic similarity principles are reviewed and their relevance in understanding flutter, divergence, and control reversal phenomena of transonic aircraft is illustrated through practical examples.     

含不确定参数的复合材料壁板热颤振分析

研究了含有不确定结构参数的壁板颤振问题,利用vonKarman大变形应变-位移关系、气动力活塞理论和准定常热应力理论建立了复合材料壁板颤振的气动弹性力学模型,考虑在壁板颤振分析模型中存在的不确定参数,将其用区间向量定量化,基于区间扩张理论和Taylor级数展开,并结合有限元计算方法,提出了区间分析的方法来估计含有不确定参数的壁板结构颤振临界风速的区间,以及发生极限环振动时振幅的变化区间。通过数值算例,将本文提出的壁板颤振的区间有限元模型与随机有限元模型进行了比较,显示了本文方法的有效性和可行性。这种方法的优点是只需要知道不确定参数的所在范围界限,为解决含有不确定参数的壁板颤振这类复杂的气动弹性动力学问题提供了一个途径。     

Robust fault-tolerant control for wing flutter under actuator failure

Many control laws, such as optimal controller and classical controller, have seen their applications to suppressing the aeroelastic vibrations of the aeroelastic system. However, those control laws may not work effectively if the aeroelastic system involves actuator faults. In the current study for wing flutter of reentry vehicle, the effect of actuator faults on wing flutter system is rarely considered and few of the fault-tolerant control problems are taken into account. In this paper, we use the radial basis function neural network and the finite-time H_∞ adaptive fault-tolerant control technique to deal with the flutter problem of wings, which is affected by actuator faults, actuator saturation, parameter uncertainties and external disturbances. The theory of this article includes the modeling of wing flutter and fault-tolerant controller design. The stability of the finite-time adaptive fault-tolerant controller is theoretically proved. Simulation results indicate that the designed fault-tolerant flutter controller can effectively deal with the faults in the flutter system and can promptly suppress the wing flutter as well.     

均匀流场拉条模型颤振导数识别试验研究

拉条模型作为介于全桥气弹模型和节段模型之间的一种气弹模型,在以往的研究中,常用来比较分析节段模型和全桥气弹模型试验结果的差异而使用,而没有利用该模型进行主梁断面颤振导数识别的研究报道。本文则引入模态参数识别方法进行拉条模型颤振导数识别,并设计了一个平板断面的拉条模型,在均匀流场下进行了颤振导数识别试验研究,与理想平板颤振导数理论解进行了比较,试验结果与理论解的吻合说明了拉条模型颤振导数识别方法的可靠性。     

叶轮机超音速非失速颤振边界研究

把叶片简化为具有对称截面、长、直、带预扭的非均匀弹性梁 ,并结合超音速状态下计算由振动引起的非定常气动载荷的气动模型 ,用哈密尔顿原理建立一组旋转状态下失调叶栅气弹稳定性方程 ;这组方程对弯曲—弯曲—扭转之间耦合严重的失调叶栅尤有意义。对一个风扇级进行的气弹稳定性分析结果表明 :失调及其幅度、阶次 ,扭心位置 ,耦合效应及其程度对叶栅气弹稳定性有明显的影响     

Limit cycle oscillation control of wing with static output feedback control method

This paper presents a static output feedback controller (SOFC) for aeroelastic control of a cantilevered rectangular wing in low subsonic flow. For this purpose, an optimal formulation of this control method is developed, and a solution method is proposed for the related matrix equation. This optimal solution is obtained by solving combined Lyapunov and Riccati equations. At first these equations are transformed into a set of nonlinear algebraic equations and then are solved with iterative Newton–Raphson?s method. This solution method is applicable to the full state feedback case. The controller is designed to extend flutter boundary and suppress limit cycle oscillation (LCO) of a low aspect ratio rectangular nonlinear structural wing. This structural nonlinearity is given by Von Karman plate theory. Both full and reduced order aerodynamic models are examined based on the modified vortex lattice theory. Results show combination of SOFC with reduced order aerodynamic model would be an effective choice for aeroelastic stabilization, and this controller has a very comparable result with linear quadratic regulator (LQR).     

Numerical studies of a non-linear aeroelastic system with plunging and pitching freeplays in supersonic/hypersonic regimes

The flutter and post flutter of a two-dimensional double-wedge lifting surface with combined freeplay and cubic stiffness nonlinearities in both plunging and pitching degrees-of-freedom operating in supersonic/hypersonic flight speed regimes have been analyzed. In addition to the structural nonlinearities, the third-order piston theory aerodynamics is used to evaluate the unsteady non-linear aerodynamic force and moment. Such model accounts for stiffness and damping contributions produced by the aerodynamic loads. Responses involving limit cycle oscillation and chaotic motion are observed over a large number of parameters that characterizes the aeroelastic system. Results of the present study show that the freeplay in the pitching degree-of-freedom and soft/hard cubic stiffness in the pitching and plunging degrees-of-freedom have significant effects on the LCOs exhibited by the aeroelastic system in the supersonic/hypersonic flight speed regimes. The simulations also show that the aeroelastic system behavior is greatly affected by physical structural parameters, such as the radius of gyration and the frequency ratio, especially in post-flutter regimes, when accounting for all system nonlinearities. It has been shown that at high Mach numbers the non-linear aerodynamic stiffness yields detrimental effects from the aeroelastic point of view, while the damping one do not.     

不同气流偏角下的壁板热颤振分析及多目标优化设计

 研究了考虑热效应的不同气流偏角下的壁板颤振问题及其多目标优化设计。采用考虑气流偏角影响的一阶活塞气动力、Von-Karmon大变形理论和准定常热应力理论建立了复合材料壁板热颤振方程。利用模拟退火算法,对不同温度场下的偏航壁板颤振速度进行计算。以偏航壁板热颤振速度和壁板重量为多目标函数,在不发生热屈曲的条件下进行优化设计。结果显示：温升使偏航壁板颤振发生“跳跃”现象,对应的气流偏角发生变化;当壁板热颤振模态不变时,偏航壁板颤振速度随温升呈下降趋势,两者呈线性关系;而当热颤振模态发生变化,即偏航壁板颤振发生“跳跃”现象时,偏航壁板颤振速度随温升先升高而后降低,两者呈非线性关系;Pareto解对应的多目标函数之间呈线性关系。     

低速流场中柔性悬臂板的后颤振响应

建立了一个新的非线性气动弹性模型,对低速流场中柔性悬臂板的后颤振响应特性进行了分析。建模中考虑了结构几何非线性、气动力非线性以及两者之间的强耦合效应。通过实验数据对所建立的气动弹性模型进行了验证。发现在低速流场中柔性悬臂板可能会以周期加倍的方式进入混沌运动。结构几何非线性效应和翼尖涡引起的非定常气动力效应对柔性悬臂板的结构响应有显著影响,而尾涡变形引起的非定常气动力对结构运动的影响较小。还研究了不同耦合算法的差异,给出了小展弦比大柔性结构非线性气动弹性数值仿真时耦合策略的选择依据。     

Aeroelastic stability of cascades in turbomachinery

State-of-the-art prediction of the aeroelastic stability of cascades in axial-flow turbomachines is reviewed. The first main chapter of the article presents a comprehensive formulation of the two- and three-dimensional classical (unstalled) flutter problem of tuned and mistuned rotor blade rows and bladed disc assemblies. Within the framework of linearized analysis, a complete and generalized theory in modal form is outlined, comprising the various formulations of the cascade flutter problem distributed in fragments throughout the literature. Brief outlines are also made of recent advances in unsteady aero-dynamic methods for turbomachinery aeroelastic applications. The second main chapter contains a parametric study of the classical flutter stability characteristics of compressor and turbine cascades in subsonic and supersonic flow. Stability boundaries and dominant trends in flutter behaviour are outlined, and the significant effects of blade mistuning on the aeroelastic stability of turbomachine bladings are highlighted.     

地面颤振模拟试验中的非定常气动力模拟

地面颤振模拟试验作为一种颤振研究的新方法,可以有效地弥补传统气动弹性试验的不足。对地面颤振模拟试验的主要难点,即非定常分布式气动力集成减缩加载的方法开展研究:基于亚声速偶极子格网法和活塞理论建立了亚声速以及超声速翼面的非定常气动力模型,通过曲面样条插值以及有理函数拟合获得了试验时域减缩气动力;提出以颤振关键模态的振型为优化目标,使用遗传算法搜寻气动力最优减缩位置的优化方法;建立了闭环系统的时域状态空间模型,使用颤振时域仿真结果与频域理论结果进行对比,对比发现二者误差可控制在3%以内。研究结果表明,该文提出的非定常气动力模拟方法可以很好地表征翼面非定常气动力分布特性,可以作为地面颤振模拟试验研究可靠的理论基础。     

Adaptive aeroelastic vibration suppression of a supersonic airfoil with flap

This paper concerns the flutter, post-flutter and adaptive control of a non-linear 2-D wing-flap system operating in supersonic/hypersonic flight speed regimes. An output feedback control law is implemented and its performance toward suppressing flutter and limit cycle oscillations (LCOs) as well as reducing the vibrational level in the subcritical flight speed range is demonstrated. This control law is applicable to minimum phase systems and we provide conditions for stability of the zero dynamics. The control objective is to design a control strategy to stabilize the pitch angle while adaptively compensating for uncertainties in all the aeroelastic model parameters. It is shown that all the states of the closed-loop system are asymptotically stable.     

Time-domain nonlinear aeroelastic analysis and wind tunnel test of a flexible wing using strain-based beam formulation

A theoretical formulation for time-domain nonlinear aeroelastic analysis of a flexible wing model is presented and validated by wind tunnel tests. A strain-based beam model for nonlinear structural analysis is combined with the Unsteady Vortex Lattice Method (UVLM) to form the complete framework for aeroelastic analysis. The nonlinear second-order differential equations are solved by an implicit time integration scheme that incorporates a Newton-Raphson sub-iteration technique. An advanced fiber optic sensing technique is firstly used in a wind tunnel for measuring large structural deformations. In the theoretical study, the nonlinear flutter boundary is determined by analyzing the transient response about the nonlinear static equilibrium with a series of flow velocities. The gust responses of the wing model at various gust frequencies are also studied. Comparisons of the theoretical and experimental results show that the proposed method is suitable for determining the nonlinear flutter boundary and simulating the gust response of flexible wings in the time domain.