Research On Aerodynamic/Dynamic Multidisciplinary Design Optimization For Tilt-rotor Aircraft

The design of tilt-rotor aircraft must satisfy different flight modes at the same time, it is a typical multi-objective design optimization problem. The design is concerned to aerodynamics, structural dynamics, flight dynamics disciplines and so on, these disciplines are influenced and coupled each other, so it is also a typical multidisciplinary design optimization problem, whereas, the optimization technology is an effective method to solve the problem.The dissertation firstly analyzed the research situation of tilt-rotor aircraft at home and abroad, in allusion to the key design problems of tilt-rotor aircraft which include aerodynamic and dynamic design, the aerodynamic analysis model and dynamic analysis model are established separately, then the application of multiobjective design optimization technology and multidisciplinary design optimization technology in tilt-rotor aircraft design are investigated.Considering the characteristics of tilt-rotor's large nonlinear distribution of blade twist and nonlinear distributions of blade chord and thickness, aerodynamic performance analysis model of tilt-rotor has been established based on the free-wake method. The free-wake method, which considers wake and wake constriction as well as the effect of blade-vortex interactions on induced velocity, can describe the aerodynamic environment of rotor accurately. Furthermore, the aerodynamic performance and rotor/wing aerodynamic interaction experiments for tilt-rotor are performed, it is verified that the aerodynamic analysis model is effective by the comparisons between calculations and experimental data. The design of a variable-diameter tilt-rotor structure and aerodynamic performance experiment are also performed, and some significant conclusions are obtained simultaneously. Tilt-rotor aerodynamic design optimization task is proceeded based on the above analysis models, the hover figure of merit and cruise propulsive efficiency are selected as optimization objective functions, the blade aerodynamic planform parameters are selected as design variables, the tilt-rotor aerodynamic design optimization problem is deduced, multi-island genetic algorithm, non-dominated sorting genetic algorithm and multi-objective collaborative optimization strategies are used in tilt-rotor aerodynamic single-objective and multi-objective design optimization process.The tilt–rotor/nacelle/wing coupled system aeroelastic stability analysis model is established on the assumption that the rotor blade and nacelle are rigid body, and the wing is an elastic beam. In this model, the blade pitch/flap/lag structural coupling, and the pitch/gimbal coupling are adhibitted, the bending-torsion coupling of wing is also considered. The aeroelastic stability analysis model is used to analyse the dynamic characteristics of tilt-rotor/nacelle/wing system as well as the aeroelastic response in hover and cruise, influences of rotor and wing dynamic parameters on dynamic characteristics of tilt-rotor aircraft are also discussed, and some significant conclusions are obtained from the study. It is verified that the dynamic analysis model is correct by the examples.Based on the design oriented analysis models of aerodynamic and dynamic, the coupling relation between tilt-rotor aerodynamic and dynamic disciplines are analyzed, rotor/wing aerodynamic and dynamic parameters effects on the aerodynamic performance as well as dynamic characteristics of tilt-rotor aircraft are studied based on experimental design method. For the tilt-rotor aerodynamic and dynamic multidisciplinary design optimization problem, the hover figure of merit, cruise propulsive efficiency and minimal mode damping in cruise flight are selected as optimization objective functions, rotor and wing aerodynamic and dynamic parameters are selected as design variables, then the tilt-rotor aircraft aerodynamic and dynamic multidisciplinary design optimization model is set up. The Multidisciplinary Design Optimization (MDO) methods such as Multi-Disciplinary Feasible method (MDF) and Collaborative Optimization (CO) are adopted in the optimization problem. The multidisciplinary design optimization frameworks based on aerodynamic/dynamic disciplines decomposition and hover/cruise flight modes decomposition are presented. In order to improve the efficiency and accelerate the optimization procedure while keeping adequate computational accuracy, surrogate model technology and hybrid search strategy are presented to solve the above problems. Then tilt-rotor aerodynamic and dynamic multidisciplinary design optimization is performed based on the above optimization methods and optimization strategies, global optimization design parameters are got, aerodynamic performance and dynamic characteristics of tilt-rotor aircraft are improved while satisfy the constraints, and the maximum cruise velocity is also increased simultaneously. The overall performance of tilt- rotor aircraft is improved after optimization. It has formed a set of appropriate aerodynamic and dynamic multidisciplinary design optimization system for tilt-rotor aircraft.