Aero-structural Wing Design Optimization Using High-fidelity Sensitivity Analysis

This paper develops and implements a framework for the computation of coupled aero-structural sensitivities which are required for the design of aircraft where aeroelastic interactions are significant. All aero-structural sensitivities are computed using high-fidelity models of both the aerodynamics and the structure of the wing with a coupled-adjoint approach that uses single discipline sensitivity information to calculate the sensitivities of the coupled system. The sensitivities of drag with respect to a set of shape design variables are computed using the aero-structural adjoint method and compared with sensitivities given by the complex-step derivative approximation and finite-differences. The aero-structural adjoint is shown to be both accurate and efficient, and to have a significant cost advantage when the gradient of a small number of functions with respect to a large number of design variables is needed. To demonstrate the usefulness of computing aero-structural sensitivities with the proposed method, results of two drag minimization problems with 190 shape design variables are presented. These results emphasize the importance of aero-structural coupling even in a conventional swept-wing design. Introduction A considerable amount of research has been conducted on MultiDisciplinary Optimization (MDO) and its application to aircraft design. The survey paper by Sobieski [16] provides a comprehensive discussion of much of the work in this area. The efforts described therein range from the development of techniques for inter-disciplinary coupling to applications in real-world design problems. In most cases, sound coupling and optimization methods were shown to be extremely important since some techniques, such as sequential discipline optimization, were unable to converge to the true optimum of a coupled system. Wakayama [17], for example, showed that in order to obtain realistic wing planform shapes with aircraft design optimization, it is necessary to include multiple disciplines in conjunction with a complete set of real-world constraints. Aero-structural analysis has traditionally been carried out in a cut-and-try basis. Aircraft designers have a pre-conceived idea of the shape of an “optimal” load distribution Copyright c ©2001 by the authors. Published by the Confederation of European Aerospace Societies with permission.