Suppression of Aeroelastic Instabilities due to Freeplay Nonlinearity

Abstract

We explore the triggering mechanism of aeroelastic instability due to freeplay in a 2-dimensional rigid airfoil with a control surface. This 3-DOF aeroelastic model is mounted on a cubic nonlinear stiffness in heave and pitch, with the freeplay being piecewise linear (i.e., nonsmooth); and the quasisteady aerodynamic theory is considered. Similar to the 2-DOF aeroelastic model, the LCO triggering consists of a series of resonance captures and escapes from resonances. Furthermore, the nonlinear modal interactions become more complicated for full LCO development due to nonsmooth dynamics introduced when the angular displacement of the control surface reaches the clearance limit. Understanding such LCO triggering, we apply a nonlinear energy sink (NES) such that the NES can interact primarily with the heave mode to prevent its initial triggering from being developed further, and also that it can engage in attenuating the pitch mode response. Three distinct suppression mechanisms by means of targeted energy transfers can be identified: recurrent burstouts and suppressions, partial suppression and complete elimination of aeroelastic instability. We explore the respective mechanisms extensively by numerical methods such as a numerical continuation method and wavelet transform spectra.