Evaluating the Influence of CFRP Laminate Parametrization on a Shape and Sizing Optimization of High Aspect Ratio Wings

Abstract

A common multidisciplinary design optimization (MDO) task for aircraft is their aero-structural design. In this task, the shape and structure sizing of the aircraft are modified concurrently. A large parameter space necessitates gradient-based approaches where accurate gradients of all involved disciplines are needed to find the optimal design of the system. It was shown that CFRP laminate tailoring is already able to improve the structure design to increase the performance of commercial transport aircraft configurations. With growing interest in flexible, high aspect ratio wings, where the structure design is expected to have a larger impact on the aircraft performance, this technology shows a lot of potential. The MDO suite Lagrange, developed at Airbus Defence and Space, is coupled to DLR's computational fluid dynamics (CFD) code, TAU, within the high-performance computing (HPC) software integration framework FlowSimulator to accurately predict the aircraft performance. The usage of direct high-fidelity methods for structure sizing and aircraft hull shape sensitivity calculation are prohibitively expensive for the number of design variables occurring in industry relevant optimization problems. The adjoint method remains the only feasible method for cruise performance gradient calculation. To reflect aircraft industry requirements, the loads process engages a high number of load cases, that prevents the usage of high-fidelity CFD. Therefore, a linear aerodynamics model is coupled to the structure solver for the loads and sizing process. This enables the structural analysis in an optimization process without compromising the number of constraints and load cases. A set of optimizations for different structural parametrizations are compared to each other. It was seen that the optimizer altered the lift distribution significantly during the structural sizing by modification of the CFRP laminate layup, alleviating structural loads. While decreasing the weight of the primary wing structure, the aerodynamic performance deteriorated. A strong dependency of design freedom and structural weight was seen. The strong interaction of structural sizing and aerodynamic performance necessitates analyzing the aircraft performance in optimization. The Breguet range is chosen as an objective function, incorporating structural mass and aircraft performance parameters in the optimization problem. Here, the aerodynamic performance increased at the expense of structural weight for all considered design tasks. More design freedom in the structural design equated to a more efficient final design. The comparisons were done for large scale, industrially relevant optimization problems with strong performance and structure interaction. The optimization scenario chosen is a civil transport aircraft configuration, the DLR F25. This work is carried out collaboratively by DLR and Airbus Defence and Space as part of a research fellow sponsorship. This material is based upon work supported in part by the Clean Aviation Joint Undertaking and its members as part of the project Ultra Performance Wing (UP Wing, project number: 101101974). Co-funded by the European Union.