On an efficient implementation of non-linear structural optimization for the morphing leading edge of an active blown high lift system.

Abstract

The permanently increasing demands on performance and noise reduction in today's aircraft high lift systems enforces the study of adaptive technologies to overcome the restrictions of state of the art fully passive technologies. As an alternative to conventional slats and flaps, an active blown Coanda-flap based high lift system is investigated within the German national Collaborative Research Centre 880 to improve on the mentioned limitations. One key feature is provided by an adaptive gapless droop nose with an exceedingly high grade of leading edge morphing. The construction of this component is based on a structural optimization framework, developed at DLR. The framework consists of two hierarchical design steps, an optimization of the skin layout with discrete joints to the inner actuation mechanism and the topology optimization of the latter. In this paper, the methodology of the second step and its application to the droop nose is discussed. For efficiency reasons, the design of the inner mechanism is completely implemented in the matrix software environment MATLAB. A key component is given by a Finite Element based non-linear solver for the static calculation of the stiffness distribution on a regular grid. As part of the inner loop of this design process, this solver must be implemented as efficient as possible. Due to the lack of sensitivity information in commercial Finite Element programs, the direct implementation of the elasticity equations is further enforced. A main focus of this article concentrates on the underlying assembly approach for the needed system matrices. Finally the application of the tool chain to the droop nose compliant mechanism is presented.