Comprehensive Nonlinear Flutter Instability Analysis via Time-Domain Modal Decomposition in Rotorcraft

Aeroelastic instabilities are emerging as a significant challenge in both fixed-wing aircraft and propeller design. Although the general conditions that lead to their onset are understood, accurately characterizing the underlying mechanisms remains complex. This paper presents a time-domain modal analysis technique aimed at tracking the development of such instabilities, with particular focus on their onset behavior. Coupled computational fluid dynamics/computational structural dynamics simulations are performed on a flat-plate rotor configuration, and evidence points to a mode-coalescence-type flutter instability that, over a specific range of rotational speeds [Formula: see text], evolves into a limit-cycle oscillation driven by stall flutter. The results show satisfactory agreement with available experimental data, although areas for improvement in the simulation setup are identified, including material modeling choices and the absence of hysteresis effects associated with blade loading. The proposed analysis method has been validated only for the flat-plate geometry that, despite offering simplifications in simulation setup, introduces complex aerodynamic nonlinearities. As such, future work will focus on extending the validation to classical airfoil sections.