Nonlinear aeroelastic analysis of highly flexible wings using the modal rotation method

The paper presents a nonlinear, aeroelastic framework for the analysis of highly flexible wings accounting for large deformations, using a linear modal database. A nonlinear static analysis is conducted followed by a flutter analysis of the deformed shape. The Wing deformations are computed with the recently presented Modal Rotation Method (MRM) that computes large structural deformations using spatial derivatives of the mode shapes defined as curvature modes. The MRM is coupled with an aerodynamic model, based on the rigid configuration to compute static aeroelastic deformations. The method was extended to compute mode-shapes and frequencies of the deformed structure and to alter the unsteady aerodynamic matrices, in order to obtain a flutter solution of the deformed wing. Results were validated based on an experimental study from the literature. Static and dynamic flutter predictions were computed for a very flexible wing model that is currently being designed for wind-tunnel experiments. Flutter analyses were repeated for wings of different sweep angle. It was shown that flutter onset of the deformed wing occurs at lower dynamic pressure than for the undeformed wing. For a forward swept wing, the wing was shown to be stable beyond the linear divergence velocity.