Aeroelastic Analysis by Coupled Non-Linear Time Domain Simulation

Kurzfassung

For an accurate prediction of the steady and unsteady behaviour of an aircraft it is necessary to take into account the deformations of the structure due to the aerodynamic loads and thus the changing of the aerodynamic surface. This is of special importance for transonic and viscous flows, which are very sensitive to small contour changes. The appearance of strong shocks, shock boundary-layer interaction and shock induced flow separation may significantly affect the flutter boundary of an aircraft and cause limit cycle flutter oscillations of the structure. These effects can not be predicted by classical flutter stability computations and without adopting Computational Fluid Dynamics (CFD) codes. Non-linear aerodynamics and high fidelity structure models have to be taken into account within a high-precision fluid structure interaction simulation. In this paper some of the activities at the Institute of Aeroelasticity in the area of steady and unsteady fluid structure interaction will be presented. A process chain for both steady and unsteady aeroelastic applications has been developed in the last years, allowing the coupling between DLR’s in-house CFD code TAU and the commercial FEM-based structural mechanics solver MSC.NASTRAN. Steady and unsteady applications are presented to demonstrate the suitability of the approach, including whole aircraft configurations and various windtunnel experiments. At first we are going to give an overview of the methods used inside the coupling procedure. For several experimental 2- and 3-dimensional test cases results will be presented. The predicted static aeroelastic behaviour of test configurations is in good agreement with windtunnel results. Obtained results for flutter simulations in the time domain demonstrate the superiority of coupled fluid-structure simulations compared to classical flutter calculations for viscous and transonic flows. The characteristic drop of the flutter boundary in transonic flow, the well-known “transonic dip” is well captured and limit cycle flutter is predicted. Finally, the paper discusses future developments necessary to further enhance the simulation capabilities for multidisciplinary simulation and optimization in the field of aeroelasticity