Numerical Methods for Simple Nonlinear Aeroelastic Problems

One of the main issues concerning numerical flutter analyses is the possibility to model the structural nonlinearities. The flutter investigations are typically conducted by neglecting the nonlinear behaviour of the structure. In this manner, it is possible to take advantage of the frequency domain approach, which is helpful for both structural and aerodynamic calculations. Thus, nonlinearity could be considered one of the primary barriers to increasing the models’ reliability. In this field, one of the most common nonlinearities deals with gaps and clearances of command lines resulting in the free play of control surfaces. Another one is the whirl flutter phenomenon, whose critical speed is strongly affected by stiffness and damping nonlinearities. In this work, a time-domain approach has been implemented to integrate two, three and four degrees of freedom models of an airfoil and the whirl flutter equations, taking into account the stiffness nonlinearities for the first case and also the damping nonlinearities for the second one. The results have been experimentally validated with experiments found in the literature in the airfoil case and employing an in-house developed small-scale demonstrator for the whirl flutter case.