Post-flutter analysis of flexible high-aspect-ratio wings

The nonlinear aeroelastic modeling and post-flutter behavior of HALE wings are discussed. By employing a geometrically exact 3-dimensional structural beam model coupled with the modified Beddoes-Leishman incompressible unsteady aerodynamic model, the study of a reduced-order model obtained by the Galerkin method is carried out. Continuation tools are employed to path follow both the nonlinear static equilibria as well as the limit cycles past the flutter velocity where the Hopf bifurcation occurs. Aeroelastic simulations are concurrently performed by reducing the governing equations to a form amenable to numerical integration in a finite element solution platform. Initial investigations are carried out on the nonlinear HALE wing model coupled with a quasi-steady aerodynamic model. It is highlighted that the number of mode shapes in the reduced-order models for the equilibrium response in the pre-flutter range becomes important for increasing air speeds. The stable post-flutter branches terminate at fold bifurcations, a somewhat expected result which, however, represents an important assessment of the conducted investigations. Further investigations present the effects of the unsteady aerodynamics for moderately large angles of attack described by the modified Beddoes-Leishman incompressible unsteady aerodynamic model that accounts for flow separation and dynamic stall. The ongoing investigations aim to study the aeroelastic behavior of these highly nonlinear wings, for an improved understanding of the nonlinear behavior in the neighborhood of the flutter boundary and in the post-critical regime, and in high angle-of-attack regimes where the unsteady aerodynamic effects due to flow separation and stall are more significant. ©2012 AIAA.