Investigation On Fatigue Problem Caused By Vibration Of Aero-engine Drum Rotor

Aero-engine, as the heart of the aircraft, has a close relationship with the performance of it. And the rotor which has complex structure and poor working environment is also the key part of gas turbine. It can suffer low cycle fatigue, high cycle fatigue, thermal fatigue, creep, corrosion, friction and other kinds of loss, which seriously affects the safety of aero-engine. Since the rotor often works under cyclic loading, the fatigue failure is the most common form of failure.In order to adapt to the variability of the actual fighting, military aircraft often needs to start-up and shut down frequently or switch between various working conditions. When the rotor working condition changes, on the one hand with the increase of the temperature difference between gas and rotor, the rotor will suffer alternating thermal stress at the stress concentration during its start and stop cycle. On the other hand, when rotor’s rotation speed crosses the critical speed, the vibration amplitude rises and drops suddenly, which would lead to large alternating mechanical stress. These all lead rotor to fatigue failure. The existing researches mainly focus on rotor fatigue problem caused by thermal stress, while researches on rotor vibration impact on its fatigue life are less. So it is very meaningful to study on the fatigue problem caused by aero-engine rotor vibration.Transient rotor dynamics model is presented in this paper, and unbalance responses of rotor transient start-up and shut down processes are obtained using numerical integral method. The rotor transient dynamics characteristics under both symmetrical and asymmetrical supports with different amount of unbalance and different starting speeds are obtained..The mechanism of rotor alternating mechanical stress is analyzed. And the low cycle fatigue life of rotor under symmetrical and asymmetrical supports is calculated using critical plane method and rain-flow counting method. The influence of unbalance and support symmetry on rotor low cycle fatigue life.Rotor axisymmetric finite element model is established, and the temperature distribution and the distribution of static stress caused by thermal stress and centrifugal force of rotor at steady state are simulated. The high fatigue life of rotor is calculated with alternating stress caused by asymmetrical supported rotor.Through the study of this paper, the vibration of aero-engine rotor is analyzed, and the influence of start-up time, unbalance and supporting symmetry on rotor transient dynamic characteristics is discussed. The low cycle fatigue life and high cycle fatigue life of rotor at different conditions are obtained. It found that the asymmetrical support of rotor will lead to sharply reduced of low cycle fatigue life and cause aero-engine rotor with high cycle fatigue problem.