Análise computacional da influência de trincas na resposta vibratória de eixos rotativos

• Ano de defesa: 2024
• Autor(a) principal: Vinícius Silvestre Cordeiro Lopes
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais
• Palavras-chave em Português: Engenharia mecânica; Fadiga; Aeronaves; Rotores; Motores; Método dos elementos finitos
• Link de acesso: https://hdl.handle.net/1843/77777

This work deals with an investigation of the dynamic behavior of an aeronautical engine rotor using the finite element method. The finite element model of the rotating system takes into account transverse cracks of different sizes, which intend to represent fatigue cracks caused by fatigue. The shaft model is based on the Timoshenko beam theory, including the gyroscopic moments and the shear effects. The natural frequencies and the whirling modes of the rotor used in the turbofan NSA-2HPT, accounting for the fatigue cracks, are computed under several operating conditions. A model for predicting the crack growth is employed to obtain the ratio between the crack dimensions and the rotating system finite element model. Four rotor models are used in this study – one represents a shaft without cracks and the other three represent cracked shafts with cracks of different lengths and depths. The values of the natural frequencies and the vibration modes for the rotor with and without cracks are estimated for the engine at rest and under operation. The influence of the crack size on the natural frequencies and on the backward and forward whirling modes of the rotor is described in this work. Besides, the Campbell diagrams are rendered for the four rotor models, leading to the estimates of the rotor critical speeds as a function of the shaft crack size. The crack propagation shows that for the forward orbital motion there is a decrease in the eigenvalues, whereas for the backward orbital motion the opposite behavior is observed, resulting in an increase in the eigenvalues. The results obtained in this work show that the introduction of cracks on the rotating shaft causes changes in the local shaft flexibility, which can affect the values of the rotating system natural frequencies. The data available in this work can provide technical insights into the dynamic behavior of turbofans with cracked shafts, giving a technical contribution to enlarge the knowledge about the crack propagation on rotors.