Acoustic Structural Interactions in Rotor Cavities of an Aeronautical Engine

This Master’s Thesis work is developed in collaboration with GE Avio Aero and its goal is to analyze possible solutions to assess the vibroacoustic phenomena within the aeronautical engine cavities. These cavities, mainly contoured by turbine disks, are complex environments where coupling between acoustic waves and structural vibrations can significantly threaten the integrity of the mechanical components. The acoustic waves are basically dynamic pressure fluctuations that can grow in time if excited at the acoustic natural frequency of the cavity and that can couple with the structural vibration modes, potentially leading to excessive vibrations and, consequently, High Cycle Fatigue (HCF) phenomena. In these domains, where some portion of air is taken from the compressor to contribute to the cooling purpose of the mechanical components, different sources of pressure excitation can coexist, usually not clearly distinguishable and predictable. Therefore, this work explores the capabilities of Finite Element Method (using Ansys APDL) and the Campbell diagram to analyze and identify the structural and acoustic mode shapes that can interact, in order to avoid a priori the destructive phenomenon of "triple crossing", an intersection in frequency of structural and acoustic modes that, united with the excitation line, indicates a resonance phenomena. Moreover, the method has been applied to a test case. Finally, a detailed analysis of the acoustic domain is conducted, where some comparisons and sensitivity analyses have been developed to improve the modeling of the acoustic domain and simplify the preparation of the FE models, for the future approach to the problem. The numerical analyses have been performed exploiting the properties of axial symmetry of the structures and of the acoustic domains.