Geometrically Nonlinear Coupled-Adjoint Aerostructural Optimization of Ultra-High Aspect Ratio Wings with Flutter Constraints

Abstract

To reach the next generation of sustainable and fuel-efficient aviation goals, novel aircraft concepts with Ultra-High Aspect Ratio Wings (UHARW), such as the Strut-Braced Wing (SBW) configuration, are promising. However, UHARW are more flexible and therefore more prone to flutter compared to moderate aspect ratio wings. In this work, a flutter constraint is integrated with the geometrically nonlinear structural model for aircraft conceptual design, which is developed for the rapid transonic flutter analysis based on transonic indicial functions. The code is fully differentiated for the coupled adjoint aerostructural optimization. Aerostructural optimization studies are performed for an SBW aircraft with UHARW. The design variables include wing box structure, wing airfoil shapes, wing planform, and strut thickness-to-chord ratios. The optimization is to reduce the aircraft fuel mass while meeting the constraints on the wing and strut structural failure, aileron efficiency, wing loading, and flutter. The aerostructural optimization reduces the aircraft fuel mass by more than 6% and reduces the wing and strut structural mass by 7.4%. The optimizer increases the stiffness of the wing, and reduces the distance between the wing sectional center of gravity and the elastic axis, producing an optimized wing free from flutter within the flight envelope.