Nonlinearity of a Two-Dimensional Aeroelastic System in Transonic Flow

Nonlinear aeroelastic phenomena of a two-dimensional system in the transonic regime were examined numerically. Investigation was made of the unsteady aerodynamics excited by pitching and heaving oscillations, based on the first harmonic component of the aerodynamics computed by Navier-Stokes code. The results indicate that nonlinearity exists not only in oscillations accompanying massive flow separation but also in pitching oscillations with small amplitudes of less than 0.5°. Stability analysis of the first harmonic component of the unsteady aerodynamics resulted in a bifurcation diagram from which an estimate of the Limit Cycle Oscillation (LCO) amplitude could be obtained. The estimated LCO amplitude was confirmed by numerical simulation. Nonlinearity of the low-amplitude unsteady aerodynamics, which affects the stability boundary, was found to be highly correlated with boundary layer transition.