Investigation of structural modelling methods for aeroelastic calculations

Flutter clearance and aeroelastic analysis of aircraft is of vital importance, as avoidance of the non-linear phenomena involved is critical to the safe operation of an aircraft. However, the complexity of the behaviour involved makes detailed analysis extremely difficult and, hence, in practise simplified linear methods have been used for all previous and current designs. However, the non-linear nature of the actual responses means that such methods have inherent inaccuracies, which requires the use of large safety margins, in turn imposing significant weight penalties. Increasing computational power has allowed more complicated forms of analysis and, hence, fully coupled CFD and CSD solution methods are currently under development, allowing more accurate results to be generated. This paper considers a coupled full non-linear CFD solver and structural dynamic solver, and compares different approaches to modelling the structural behaviour in this method. Specifically mode extraction and mass and stiffness matrix analysis are considered. The former is more commonly used, the latter more complex and computationally intensive. However, it is demonstrated here that for small to moderate structural grid sizes, the latter has significant advantages in generality of approach and response accuracy and consistency, at negligible computational expense.