FLUTTER STUDY OF A TWO-DIMENSIONAL AIRFOIL WITH STRUCTUAL NONLINEARITIES

A two dimensional airfoil section with central freeplay and preload asymmetry freeplay is studied. A type of friction nonlinearity is adopted to weaken the effects of freeplay nonlinearities. The Roger rational function fitting method is adopted to deduce the approximate expressions of the time domain aerodynamic force, based on the coefficient matrices of unsteady aerodynamics in simple harmonic motion. The equations of motion are solved using the fourth-order Runge-Kutta numerical integration technique to provide the aeroelastic response. The result shows that the central freeplay and preload asymmetry freeplay produce similar effects on the system but with different sensitivities. The adopted friction nonlinearities can effectively stable the aeroelastic characteristics of the airfoil when the flow velocity is under the linear flutter speed. The present results also indicate that if the type of friction is confirmed, the value of initial torque, stiffness of the added friction and the added position of the friction can barely affect the rate of converge while its value is larger than a certain value.