Numerical simulations of flutter and its suppression by active control

A method for predicting the unsteady, subsonic, aeroservoelastic response of a wing has been developed. The air, wing, control surface, and control system are considered to be elements of a single dynamical system. All equations are solved simultaneously in the time domain by an iterative scheme based on a predictor-corrector method. The scheme allows a wide range of nonlinear aerodynamic and structural models to be used and subcritical, critical, and supercritical aeroelastic behavior can be modeled without restrictions to small disturbances or periodic motions. In this paper, a general unsteady vortex-lattice method is used to model the aerodynamics. This method accounts for nonlinear effects associated with high angles of attack, unsteady behavior, large deformations of the wing, and the convection of vorticity. Two structural models have been employed: a linear model and a nonlinear model that accounts for finite curvature. Both models consider the flexural-torsional motion of an inextensional wing. A feedback-control system that governs the motion of control surfaces is implemented to suppress the motion of the wing. Results show that the suppression of flutter by means of active control is readily possible at velocities well beyond the flutter speed and that limit cycle solutions might exist near the flutter speed.