Unsteady Aerodynamic Modeling At High Angle Of Attack And Nonlinear Dynamic Characteristics Analysis

With the development of aerospace technology and the requirement in real battle, the motion characteristics of aircraft gradually extended to the nonlinear region. When the aircraft maneuvers at a high angle of attack, airflow separating and vortex breaking appears obviously. Meanwhile, the aerodynamic force will show a strong nonlinear, hysteretic characteristics and the whole aircraft movement will has a highly bifurcation phenomenon. As a result, the conventional small disturbance linearization method can't meet with the needs any more. In this dissertation, we discussed the unsteady aerodynamic modeling at a high angle of attack and the nonlinear dynamic analysis in detail. All the works are as follow:(1) Established an unsteady aerodynamic model for pitch, yaw, pitch and yaw coupling movement separately using multivariate orthogonal polynomial fitting method. Compared with the traditional polynomial fitting method, the modeling technique developed in this thesis is compact and efficient. There is no need to determine the structure of the model in advance. It is global validity which has a widely application foundation and more convenient for the future aircraft design or analysis.(2) Introduced the Bifurcation Analysis and Catastrophe Theory Methodology(BATCM) method. The nonlinear dynamic characteristics of the wing rock phenomenon has been analyzed as well as the stability properties and the the Hopf bifurcation point by using the MATCONT software. Meanwhile, the longitudinal of one vehicle is discussed through the bifurcation analysis method. At the same time, we can know the impact of the fixed control parameter to the bifurcation curves by varying the value of the fixed control parameter which is meaningful for vehicle parameter design.(3) The longitudinal characteristics of the hypersonic vehicle with a typical ride wave structure are discussed. Through the aerodynamic theories, the data of the aerodynamic and thrust are calculated respectively. Then the mode shapes and generalized force can be worked out. Based on the Extended Bifurcation method, the bifurcation curves are got. As the gravity center is in front of the pressure center, all the trim points are unstable. At the same time, the maximum change of Angle of Attack caused by the structural flexibility of the fuselage is very small in cruising flight.