Geometrically Nonlinear Coupled Adjoint Aerostructural Optimization of Natural-Laminar-Flow Strut-Braced Wing

Novel aircraft concepts employing ultrahigh-aspect-ratio wings, such as the strut-braced wing (SBW) configuration, are promising ways to achieve the next-generation sustainable and fuel-efficient aviation goals. However, as the wing aspect ratio increases, the wing increasingly exhibits more flexibility, higher deformation, and geometrically nonlinear behavior that cannot be accurately simulated by conventional sizing methods and typical linear structural analysis models. This paper establishes a framework for SBW aircraft conceptual design, conceptual optimization, and aerostructural optimization. The presented aerostructural optimization method has medium-fidelity and physics-based features. A geometrically nonlinear structural analysis solver and a quasi-three-dimensional aerodynamic solver are coupled for the aerostructural optimization of composite natural-laminar-flow SBW aircraft. A medium-range (MR)-SBW aircraft is initially designed and optimized in the conceptual design stage. A gradient-based aerostructural optimization is performed using the proposed tool for minimizing the fuel mass of the initially sized and optimized MR-SBW aircraft. The optimization results in a more than 10% reduction in fuel mass, a more than 8% reduction in aircraft maximum takeoff mass, and a more than 30% reduction in wing and strut structural weight by optimizing the wing box structure, the wing planform, and the airfoil shape while satisfying the constraints on structural failure, wing loading, and aileron effectiveness.