Experimental investigation of an aeroelastic structure with continuous nonlinear stiffness

An experimental investigation is presented for the aeroelastic response of a two-degree-of-freedom airfoil positioned in an incompressible flow. In particular, the effects of cubic structural nonlinearities in the pitch degree-of-freedom are considered. These nonlinearities are introduced via a specially designed pitch cam, which permits different degrees of nonlinearity, as well as a linear system, to be obtained.Several linear and nonlinear system tests are presented, and the results compared and analyzed. The effects of linear plunge stiffness on the stability of the aeroelastic system are discussed, and the nonlinear system response is studied for different degrees of cubic nonlinearity in pitch.In several nonlinear system tests, limit cycle oscillations (LCO) are observed when the air speed is above the linear flutter speed. The effects of airfoil initial conditions and air speeds on the LCO amplitude, frequency, and convergence rate are studied.The effective linear flutter speed is predicted using the so-called "flutter-margin" method for both the linear and nonlinear cases. The prediction results for the nonlinear cases are compared with those for the linear cases and with the actual flutter speed