High-Fidelity Aero-Structural Optimization of the Wing Twist using the NASA Common Research Model

Abstract

Gradient-based aero-structural optimization strategies using high-fidelity CFD methods and close-to-reality structural simulation models for the complete aircraft are a promising concept for multidisciplinary optimization (MDO) in view of new aircraft configurations. At DLR such an MDO process has been implemented for the NASA Common Research Model (CRM), a generic wide body aircraft configuration. The process capabilities have been demonstrated by optimizing the outer wing geometry including the engine. The structural optimization of the wingbox is done at each step of the aerodynamic optimization. A further development is provided in the present paper by computing and integrating design sensitivities of the structural discipline at system level. The performance of the CRM is evaluated at Ma=0.85 by solving the Reynolds-averaged-Navier-Stokes (RANS) equations, which are coupled iteratively with a structural model of the complete aircraft. The trimmed 1g cruise flight is achieved by adjusting the angle-of-attack and the elevator. The corresponding structural finite element model is generated and all involved simulation models are set up using a parametric approach. Aeroelastic loads are calculated by MSC Nastran for selected load cases that are assumed to be representative for the design loads. The load carrying structural components are then sized with the calculated loads. The structural process can be treated as a black box. High-fidelity, aerodynamic performance gradients with respect to a parameterized wing twist distribution are computed using the adjoint method. Structural gradients are determined by finite differences of the structural design process. Minimizing the product of the maximum root bending moment from the loads analysis and the drag coefficient shows to reduce the wing's structural mass by -12.22 % but also lowers the aerodynamic performance by -8.31 %. A Breguet based range optimization improves the aerodynamic performance by 0.7 % and increases the wing's structural mass by +2 %.