Nonlinear energy sink for passive mitigation of propeller whirl flutter

The electrification of aviation propulsion has resulted in new aircraft configurations that typically feature lightweight wings with high aspect ratios, along with multiple propellers distributed along the wingspan. Since the propellers are flexibly attached to the wing, an aeroelastic instability known as whirl flutter can occur. The rotating blades generate additional forces and moments, and due to gyroscopic effects, the propeller hub exhibits a whirling motion. Therefore, it is essential to explore various techniques to mitigate this aeroelastic instability. This paper examines the impact of a nonlinear energy sink (NES) on reducing the whirl flutter of a basic propeller-nacelle model. The proposed approach considers a propeller with pitch and yaw degrees of freedom, while modeling the dynamical contributions of the wing structure with equivalent nonlinear stiffness and viscous damping. The structural model of the propeller is coupled with a cubic nonlinear energy sink to passively mitigate oscillations. An initial characterization of the uncontrolled system is performed through frequency domain analysis, resulting in the creation of a velocity-damping-frequency diagram. The paper discusses a nonlinear adaptation of the propeller-nacelle model and conducts a bifurcation analysis using numerical continuation to characterize the dynamic behavior of the propeller-nacelle-NES system. The effects of attaching the NES are analyzed through bifurcation, parametric investigations, and energy transfer analysis of the device design parameters.