POSTINSTABILITY BEHAVIOR OF A 2-DIMENSIONAL AIRFOIL WITH A STRUCTURALNONLINEARITY

A two-dimensional airfoil with a free-play nonlinearity in pitch subje ct to incompressible flow has been analyzed. The aerodynamic forces on the airfoil were evaluated using Wagner's function and the resulting equations integrated numerically to give time histories of the airfoil motion. Regions of limit cycle oscillation are detected for velocitie s well below the linear flutter boundary, and the existence of these r egions is strongly dependent on the initial conditions and properties of the airfoil. Furthermore, for small structural preloads, narrow reg ions of chaotic motion are obtained, as suggested by power spectral de nsities, phase-plane plots, and Poincare sections of the airfoil time histories. The existence of this chaotic motion is strongly dependent on a number of airfoil parameters, including, mass, frequency ratio, s tructural damping, and preload.