Efficient Aerodynamic Shape Optimization in MDO Context

The aerospace industry is increasingly relying on advanced numerical flow simulation tools in the early aircraft design phase. Today's flow solvers, which are based on the solution of the compressible Euler and Navier-Stokes equations, are able to predict aerodynamic behaviour of aircraft components under different flow conditions quite well 1]. Within the next few years numerical shape optimization will play a strategic role for future aircraft design. It offers the possibility of designing or improving aircraft components with respect to a pre-specified figure of merit, subject to geometrical and physical constraints. Here, aero-structural analysis is necessary to reach physically meaningful optimum wing designs. The use of single disciplinary optimizations applied in sequence is not only inefficient but in some cases is known to lead to wrong, non-optimal designs 2]. Although multidisciplinary optimizations (MDO) are possible with classical approaches for sensitivity evaluations by means of finite differences, these methods are extremely expensive in terms of calculation time, requiring the reiterated solution of the coupled problem for every design variable. However, adjoint approaches allow the evaluation of these sensitivities in an efficient way and lead to high accuracy. Firstly, we present the development and application of a continuous adjoint approach for single disciplinary aerodynamic shape design. This approach was previously developed at the German Aerospace Center (DLR) 3] and was the starting point for the extension to aero-structural wing designs. Secondly, we describe the adjoint approach and its implementation for the evaluation of the sensitivities for coupled aero-structure optimization problems 4] and its application to the drag reduction of the AMP wing by constant lift while taking into account the static deformation of this wing caused by the aerodynamic forces (see figures). Finally, we show the application of the coupled aero-structural adjoint approach for the Breguet formula of aircraft range, where in addition to the lift to drag ratio the weight of the AMP wing is taken into account (see figures). (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)