Research On The Nonlinear Flutter For Wings Of Hypersonic Vehicle

Hypersonic aeroelastic is one of the important technologies of hypersonic vehicles. For the new generation of hypersonic vehicles, the lightweight materials will be widely used, and the thin-willed structure will be designed. In the aerodynamic design of the hypersonic vehicles, the slender body, lifting body and complete or partial wave-riders layout is used. Special structural design, material selection, aerodynamic and flight environment makes hypersonic aircraft aeroelastic problem is particularly prominent. In variety of aeroelastic problems, the flutter of wings is one of the most important issues in science and engineering. And in the engineering, there is a wide variety of nonlinearity resulting limit cycle oscillator or chaotic phenomena before the linear flutter velocity, reduce the aircraft’s flight stability and security.In this paper, the nonlinear flutter problem of hypersonic wings is studied systemically, and the structures, thermal / structural nonlinear factors existing in actual engineering are considered. The hypersonic flutter model of wings with structural nonlinear or thermal nonlinear is established, the efficient, accurate and practical method for nonlinear flutter analysis is studied, and the stability law of nonlinear hypersonic wing flutter is explored.First, the flutter model of 2-D hypersonic wing is established based on Lagrange equation, where the expressions of the unsteady aerodynamic lift and moment are given in terms of the third-order piston theory. Also considered is the loss of torsional stiffness that may be incurred by lifting surface subject to axial stresses induced by aerodynamic heating. And the flutter response of hypersonic wing is analyzed by Runge-Kutta method, the flutter velocity is determined.Second, the flutter of hypersonic wings with freeplay nonlinearity is studied. The nonlinear flutter model of hypersonic wings with freeplay nonlinear is established, considering the freeplay between the full rudder and the steering gear or structural, and the impact of aerodynamic heating of structure is comsidered. An improved homotopy perturbation method is presented by coupling the homotopy perturbation and the modified Lindstedt-Poincare method, and the accuracy is greatly improved. The improved method is applied to flutter problem of wing with freeplay nonlinearity, and we found that the convergence of the method is not good. To this end, a new modified homotopy analysis method is proposed based on the idea of the minimum of the squared residual of governing equations, and the convergence control parameters is easy to be selected. And the new homotopy analysis method is applied to study the nonlinear flutter problem. The effect of parameters, such as the freeplay size, asymmetric freeplay and structural parameters, on nonlinear flutter is studied by the modified homotopy analysis method.Third, the flutter problem of hypersonic wings with cubic nonlinearity is studied. In order to reduce aerodynamic drag, the wing of hypersonic vehicle generally use a thin wing, that making the wing structural deformation in the event of its stiffness will vary with the amount of deformation, showing cubic nonlinear stiffness, thus affecting the aircraft aeroelastic flutter characteristics of the system. The nonlinear flutter model of hypersonic wing with stiffness cubic nonlinear is established based on Lagrange equation. The elliptic harmonic balance method is introduced to analysis the nonlinear flutter problem, the accuracy of harmonic balance method is improved. But the elliptic harmonic balance method is complexity for the high order solution, for which an improved harmonic balance method is proposed. In this method, the nonlinear problem is fist translated to a minimization problem, the Particle Swarm Optimization which has high calculate efficiency is suggested to solve the minimization problem. The nonlinear flutter of hypersonic wing with cubic nonlinear is studied, and the effect of nonlinear factors, the centroid position, mass ratio and the location of the elastic axis on nonlinear flutter is also studied.Fourth, the thermal / structural nonlinear flutter problem of hypersonic wings is studied. Thermal environment is one of the main features for hypersonic vehicle. Aero-thermal environment will lead to the existence of a thermal nonlinear deformation aircraft structure, thermal stresses within the structure stiffness changes, changing the wing flutter speed, affect vehicle stability margin. The thermal nonlinear flutter of hypersonic wings is presented according to Von-Karman theory of large deformation under load temperature thermal, which can take account of the unequal temperature. The differential quadrature method is introduced to deal with hypersonic thermal nonlinear flutter problem. The validity of the differential quadrature method is confirmed by comparing the FEM solutions for the natural frequencies and the prevenient results for nonlinear flutter characteristics. A detailed parametric study is carried out to examine the influence of temperature load, temperature distribution and other structural parameters on their hypersonic flutter behavior.Finally, the thermal / structural nonlinear flutter problem of hypersonic wing composite skins is studied. The thermal nonlinear flutter model of hypersonic composite skins is presented by the elastic theory under temperature load, and the flutter behavior is analyzed by differential quadrature method. A detailed parametric study is carried out to examine the influence of ply angle, skin area and skin thickness on their hypersonic flutter behavior. And the dynamic response of nonlinear flutter of hypersonic composite skin is presented. The effects of temperature loads and structural parameters on hypersonic composite skins nonlinear heat flutter are studied.In this paper, the flutter of hypersonic wings with nonlinearity is systematically studied. The accurately of the analysis method for flutter critical speed of hypersonic aircraft wing is effectively improved, and the hypersonic aeroelastic technology is further developed.