Combined Aerostructural Wing and High-Lift System Optimization

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Current wing design processes are strongly governed by cruise design requirements. This approach to wing design leaves little room for high-lift device design optimization where trade-offs may be required between cruise wing and high-lift wing design. Moreover, the optimization of high-lift devices typically focuses on optimizing flap/slat setting, gap and overlap, without taking into account aeroelastic effects on high-lift performance and the effect of flap design on wing weight. Ideally, the aerostructural optimization of the high-lift system and cruise wing should therefore be combined throughout the complete optimization process. In this study, an existing aerostructural analysis and optimization tool used for cruise wing design is extended to include the analysis and optimization of high-lift systems. The analysis tool makes use of a quasi-three-dimensional (Q3D) aerodynamic analysis in which a three-dimensional inviscid analysis is coupled with two-dimensional viscous analyses performed at several spanwise sections. The Q3D aerodynamic analysis is extended with high-lift capabilities, where the Pressure Difference Rule is used to predict maximum lift coefficient. Coupling of the extended aerodynamic analysis to the structural solver FEMWET enables high-lift aerodynamic analysis while taking into account aerelastic deformation. As a test case, the aerostructural optimization of a Fokker 100 class wing has been considered for minimizing fuel weight. Design variables included wing geometry, airfoil shape, structural thickness and flap settings and span. The proposed optimization formulation resulted in a fuel weight reduction of 9.65%, while satisfying airfield performance requirements of the initial design. This proves that combined aerostructural optimization of wing and high-lift system design is effective and deserves continued research.