Comparative Evaluation Of Unsteady Aerodynamic Mathematic Models Of Aircraft

Unsteady aerodynamic modeling at high angle of attack is one of the most important and the most difficult problems in the region of modern fighters. But there have not been a feasible method which can model all of unsteady experiments, because each method has its localization. The researches of this thesis are focused on the several kinds of modeling methods with application of system modeling and identification theory, which based on the basis of SDM large amplitude oscillation tests:1. The preface of this thesis introduces the background and actuality of modeling unsteady aerodynamics, and expounds briefly the equipments, the methods and the results of the unsteady oscillation tests in 4m×3m wind tunnel of CARDC.2. Non-linear algebraic models are proposed to study the characteristics of unsteady aerodynamics at high angle of attack, and the method of parameter identification is also presented. The order influence of the Non-linear algebraic models is discussed, and the examples show that it is not a better model with higher order.3. A nonlinear unsteady indicial response model of aerodynamic coefficient could be approximated by the use of Fourier analysis function at high angle of attack. The every item of model has clear physical meaning, and it is helpful to understand the characteristic of nonlinear unsteady aerodynamics.4. The differential equation modeling methods of nonlinear unsteady aerodynamics have been studied at high angle of attack. Both state space model and difference equation model are proposed according to the different differential variables. The physical meaning and identification of the most important parameters are given. The applications in the SDM test show that differential equation models can be a good expression to the unsteady aerodynamic characteristics.5. The fuzzy logic modeling method of nonlinear unsteady aerodynamic at high angle of attack is proposed, and a new fuzzy logic model has been developed in combination with the difference model. The applicability and accuracy of the model are studied. The effects of different membership functions and internal functions in the results calculating are also given. The feasibility of fuzzy logical model has been proved by the applications.6. The end of this thesis compares and analyzes above models, and then presents the shortage of the work and the direction about the future research.