Studies On Wing Nonlinear Aeroelasticity In Hypersonic Flow

In the current and future,wing nonlinear aeroelasticity in hypersonic flow is one of the most popular and difficult topics in the field of aerospace aircraft.To insure the flight stability and security of hypersonic aircraft and avoid the catastrophic failures,nonlinear flutter characteristics of hypersonic wing should be further studied.Moreover,the structural nonlinearities inevitably exist in the practical structures,and the severe aerodynamic heating and nonlinear aerodynamic force in the hypersonic flow are also considered.Thus,the nonlinear aeroelastic system can display complex noninear dynamic responses,including limit cycle oscollation(LCO),bifurcation and chaos.Researches on the aeroelastic characteristics of hypersonic wing system help undertand wing hypersonic flutter mechanisms.And it is of great academic and engineering importance to provide theoretical significance for the dynamic design of aircraft structures and the prevention of harmful nonlinear aeroelastic behaviorsIn the present study,a numerical integration approach with high efficiency and reliability is proposed for solving complex dynamic responses of nonlinear aeroelastic system.Moreover,an all-movable fin and a low-aspect-ratio fixed wing are typical components in the hypersonic aircraft,it is necessary to explore the effects of nonlinear parameter and system parameter on their nonlinear vibration behaviors,which can provide useful insight into ground vibration tests and structure dynamic design.On the other hand,considering the nonlinear aerodynamic force and thermal effect,the flutter stability and nonlinear aeroelastic responses of wing aeroelastic system are studied and discussed.The main contents are summarized as follows:(1)An improved precise integration method incorporated with Padé approximation(PadéPIM)is proposed for the nonlinear dynamic analysis of nonlinear aeroelastic system.For the aeroelastic system with this non-smooth nonlinearity,a predictorcorrection algorithm is adopted to avoid the numerical inaccuracy induced by the crossover of the switching points of freeplay nonlinearity.The results indicate that the PadéPIM method is unconditionally stable and has higher accuracy and efficiency than other methods,especially with high reliability for obtaining complex dynamic responses of nonlinear aeroelastic system.(2)The primary resonance and nonlinear dynamic responses of an all-movable fin are investigated.The averaged equations of the all-movable fin are first formulated and the approximate analytical solution of periodic motion can be obtained.That results show that the nonlinear stiffness of the freeplay nonlinearity in pitch exhibits a typical hardening-spring characteristic.The multi-value and jump phenomena exist in the primary resonance region.The system presents multi-period LCO and chaos under excitation frequency between 1/3 and 1/2 of the primary resonance frequency.The increase of preload can delay the occurrence of chaotic motions.It is also found that when the preload exists in the fin aeroelastic system with freeplay nonlinearity,the excitation amplitude will affect soft/hardening spring characteristics of the system.(3)Considering the effects of the thickness ratio,angle of attack(AOA)and sweep angle,the aerodynamic model is developed for obtaining hypersonic unsteady aerodynamic force of the all-movable fin.The equivalent temperature model is adopted to determine the effect of aerodynamic heating on the model.Furthermore,the effects of linear/nonlinear piston theory aerodynamics,single/multiple free-plays and aerodynamic heating on the bifurcation and chaotic motions of the system are investigated,respectively.It is found that the flutter boundary is improved by the increase of thickness ratio and AOA,and two flutter coupling modes are changed by the variation of sweep angle of leading edge.The LCO amplitude obtained by using the third-order piston theory is lower than that by using the first-order piston theory.There exist complex dynamic responses for the system with multiple freeplay nonlinearities.Due to the thermal effect,the amplitude of response is increased and the chaos region is also extended.Besides,the thickness ratio,AOA and sweep angle are important parameters that influence the nonlinear dynamic behaviors of the fin.(4)Based on von Karman large deformation theory,the Rayleigh-Ritz approach combined with the affine transformation is proposed to investigate the nonlinear vibration characteristics of a trapezoidal wing-like plate under transverse harmonic excitation.Using the present method,the ordinary beam mode functions can be used as the mode functions of the trapezoidal plate.The amplitude-frequency behaviors of the system with the primary and 1:3 internal resonances are analyzed by using multiple scales method.The effects of the system parameters on nonlinear vibration behaviors are also studied,especially with the 1:3 internal resonances case,where there exist the periodic,quasi-periodic and chaotic motions under different excitation amplitudes.(5)Nonlinear aeroelastic behavior of a trapezoidal wing in hypersonic flow is investigated.The von Karman plate theory and nonlinear third-order piston theory aerodynamics are used to establish the governing equations The Rayleigh-Ritz approach combined with the affine transformation is formulated and employed to transform the equations of a trapezoidal wing structure into modal coordinates.The effects of Rayleigh–Ritz mode truncation for various wing-plate geometrical characteristics are examined to determine the appropriate mode number for accurate modeling and fast calculation.Furthermore,we first explore the bifurcation and complex nonlinear dynamic responses for the trapezoidal wing-like plates with three typical geometries in hypersonic flow.In particular,the evolution processes of chaos exhibit remarkable difference for these three wing configurations...