Airfoil motion in subsonic flow with strong cubic nonlinear restoring forces

Limit cycle oscillations of a two-degree-of-freedom airfoil motion with cubic nonlinearity in the restoring forces are investigated. The harmonic balance method is used to derive a frequency relation that depends only on airfoil parameters. The amplitudes of the pitch and plunge motions can be computed from analytical expressions once the frequency is known. The method is extended to higher harmonics. Illustrative examples are given and the results are compared with numerical computations.