Investigation Of Structural Nonlinear Aeroservoelasticity Based On Unsteady Vortex Method

Modern aircraft equipped with advanced flight control systems has replaced the role of the manpower operational vehicles at the initial stage of the power flight history. Servo control system is also included, coupled with aerodynamics, elasticity and inertial force, and a new subject aeroservoelasticity evolves from aeroelasticity. The aircraft also progresses in the direction of integrating design of aerodynamics, structure and control system as a whole.Most of the effort in aeroservoelasticity is restricted in linear systems, but nonlinearity inevitably exists in the real aircraft structures, especially in all-moving aerodynamic surface of aircraft such as all-moving horizontal tail plane, and it has a remarkable effect on its aeroelastic response and flutter characteristics. The most direct way to study the nonlinear aeroservoelasticity is time domain simulation, and a universal approach is to develop aerodynamics formulations, coupled with structural dynamics equations and control blocks.This paper reviews aeroelasticity and aeroservoelasticity's development history first, and points out active aspects in this research field. Airfoil in subsonic, incompressible flow is presented in this paper. Aerodynamics is formulated by an unsteady vortex method, and the aeroelastic equation is established in state space form. Linear flutter speed is calculated out and coincides well with classical V-g method.A nonlinear model called hysteresis is put forward, which combines dry friction with freeplay model. Nonlinear aeroelastic equation is constructed in piecewise linear form. The flutter result is worked out, and comparison of LCO's amplitudes has been made with that of Roger's method and Describing functions. The flutter result of freeplay model is also compared with the hysteresis model.For aeroservoelasticity of an airfoil section, this paper mainly considers with time delayed feedback control. Utilizing the plunging and pitching signals as the feedback, the principle of active aeroelasticity is studied in detail. Transfer function of linear aeroservoelastic system is achieved, stability analysis is made, and the result is compared with time domain simulation results from MATLAB/SIMULINK environment.Finally, an introduction is made for how to build aeroelastic model and nonlinear structural model in MATLAB/SIMULINK environment. The unsteady vortex formulation is generalized to airfoil with control surface. Linear flutter result is carried out for the airfoil model and coincides well with classical V-g method. Feedback control for active flutter suppression is carried out for a hysteresis nonlinearity at the pitching degree of freedom.