Papers Published

  1. Virgin, L. and Trickey, S. and Dowell, E., Stability transitions in a nonlinear airfoil, Proceedings of the 5th Experimental Chaos Conference (2001), pp. 335 - 44 .
    (last updated on 2007/04/10)

    Abstract:
    This paper describes some experiments conducted in a wind tunnel on a two-dimensional airfoil with a loose flap. The piecewise linear nature of the flap stiffness (incorporating a deadband) is a strong source of nonlinearity. It is also a good model of the inevitable and increasing looseness encountered in aircraft control surfaces, and in mechanical systems in general. In the absence of the freeplay nonlinearity the airfoil behaves in a classical manner (i.e., an eigenvalue problem) with aeroelastic flutter encountered at a critical flow speed, i.e., effective damping becomes negative at a Hopf bifurcation. When freeplay is added to the model a host of pre-flutter limit cycle behavior is observed together with sudden stability transitions. Quasi-periodicity and chaos is also encountered and many of the observed features are generic, in the sense that much of this behavior occurs in sequences familiar from the classical circle map. Numerical simulation is used to verify the results of the experiment using a standard aeroelastic analysis

    Keywords:
    aerodynamics;bifurcation;chaos;damping;eigenvalues and eigenfunctions;elasticity;external flows;flow instability;flow simulation;fluid oscillations;limit cycles;nonlinear dynamical systems;