Master thesis and internship[BR]- Master's thesis : Computational method for whirl-flutter analysis of urban air mobility vehicles[BR]- Internship

Abstract

This thesis examines the whirl-flutter phenomenon in urban air mobility vehicles, crucial for the safety and efficiency of next-generation aircraft. The rise of Electric Vertical Take-Off and Landing (E-VTOL) vehicles, driven by the demand for fast urban transport, emphasizes the need to understand and mitigate aeroelastic instabilities like whirl-flutter, particularly in designs with distributed electric propulsion systems. Historically, whirl-flutter has caused catastrophic failures, highlighting the need for comprehensive analysis in modern aircraft designs.

The objective of this work is to develop a comprehensive computational model using the Finite Element Method to fully capture the dynamics between rotating, expressed in a floating frame of reference, and stationary parts of a structure, enabling a more accurate study of the whirl-flutter phenomenon. This analysis is conducted using the Floquet theory to study the stability of the system, particularly in a fixed-rotating frame of reference. The model includes an innovative time dependent mechanical coupling strategy for the mass, gyroscopic, and centrifugal stiffness structural matrices therefore fully preserving the dynamics of the structure, a first in the literature.

The research methodology involves the validation of various finite element matrices and components derived from Euler-Bernoulli 3D beam elements, followed by the implementation of time-dependent coupling between rotating and stationary components. This coupling is validated through case studies, including a ground resonance model and a rotating shaft with blades. Finally, the developed model is applied to a wing-propeller structure, illustrating its capability to work on complex geometry structures.

The results show that the partial coupling, specifically the coupling between translational degrees of freedom of rotating structures and those of stationary structure at the hub, is successfully validated. However, it is demonstrated that the Newmark integration scheme does not provide consistent results, highlighting the need for alternative approaches such as Runge-Kutta scheme for accurate time integration. Although the full coupling is not entirely validated, the initial results suggest that the implementation is correctly performed and shows promise for future validation efforts. This partial success demonstrates the potential of the developed model as a tool for accurately capturing critical dynamics in whirl-flutter analysis, contributing to the design and certification of future urban air mobility vehicles.