Computational Terms to Be Considered in the Investigation of Whirl-Flutter Phenomenon in Installed Propeller Aeroengine Systems

Abstract Whirl-flutter is a critical aeroelastic instability phenomenon which occurs in rotating machinery with un-ducted open blades/propellers such as helicopter rotors, turboprop engines, and wind turbines. The phenomenon is characterized by an interaction between the rotational motion of the propeller blades (whirling), the aerodynamics forces and moments applied to the blades that form cross-coupling stiffness and damping effects, and the elastic motion of the structures (i.e., mounts, nacelle, and wing) supporting them. Whirling is stimulated by any elastic rotating shaft, which generates a circling motion around the rotating system’s axis of rotation. Meanwhile, flutter is categorized as a vibrational instability attributed to fluid-structure interaction. Under certain circumstances related to specific vibration modes, the system’s damping tends to reach values that lead to dynamic instability. Consequently, this leads to an exponential surge in the amplitude of motion over time, which can potentially culminate in structural failure if not appropriately managed. Whirl-flutter couples the whirling in rotating parts and the flutter of the supporting structures, they interact with each other in a complex manner and can lead to serious stability problems if the stiffness and damping effects of the engine supports are not correctly set. As the aerospace industry progresses towards the development of novel un-ducted fan engines for civil aviation, addressing the whirl-flutter phenomenon has become an imperative aspect of modern engine design. Consequently, there is an escalating demand for innovative numerical tools and methodologies to conduct detailed investigations of this phenomenon. These advanced tools enable the study of the dynamic responses of the engines when the fan experiences excitation through aerodynamic forces. This paper provides a detailed examination of incorporating gyroscopic effects of propeller, aerodynamic forces and moments on the propeller and aerodynamic forces on the wing using finite element software MSC Nastran. Sensitivity analysis is performed on several parameters to help practitioners understand how these various parameters affect the stability of the system. Through these simulation models, engineers can gain invaluable insights into how best to design and optimize the engine and its supporting structures.