Structurally nonlinear fluttering airfoil in turbulent flow

The dynamics and response of a structurally nonlinear two-dimensional airfo il in turbulent flow are investigated numerically. The solution is analyzed in terms of probability density function (PDF), response mean square, powe r spectral density, and Lyapunov exponent. Both the longitudinal and vertic al components of turbulence are considered. It is shown that turbulent flow , due to its longitudinal component, diminishes the stability of the aeroel astic system by advancing the flutter point and decreasing the damping, thu s confirming results from previous work where only the longitudinal compone nt was modeled. Furthermore, the shift in flutter airspeed is strongly depe ndent on the random stiffness terms. It is also observed that turbulence ma y advance the airspeed at which the pitch angle marginal PDF changes from u ni- to bimodal compared with the nonexcited deterministic case, whereas the heave transition appears to be postponed. This observation is attributed t o the nonlinearity considered, a cubic stiffness in torsion. Finally, in te rms of response mean square, the system appears to be more sensitive to the presence of the longitudinal excitation component at pre- rather than at p ostinstability airspeeds.