Vibration response of coupled rotor systems with crack and misalignment

Earlier research on the vibration signatures of a crack or misalignment fault have typically been attempted considering one fault at a time. The condition of simultaneous existence of crack and misalignment (in addition to unbalance) was ignored. However, prolonged existence of misalignment preload could develop a fatigue crack in the rotor shaft. The present study aims to investigate the steady-sate vibration response of misaligned coupled rotors with a crack on one of the rotor shafts. This is perhaps the first study where unbalance, crack, and misalignment faults are considered simultaneously. Along with the axial and torsional vibration features, a detailed full spectrum analysis is carried out to reveal the fault-specific whirl signatures. Two new whirl parameters δ₁ and δ₂ were introduced based on differences in forward and backward whirling 1X and 2X spectral components. The influence of misalignment level and type, crack size, and crack location on these parameters is investigated for examining the effect of growth of one fault on the whirl nature of the vibration motion of the rotors with coexisting faults (i.e. unbalance, crack, and misalignment). The effects of a fault growth on the whirl parameters are found to be typical of a fault for crack and parallel misalignment faults. However, for the angularly misaligned rotors, the increase in misalignment level results in decrease/no change in the parameter δ₂ in the presence/absence of a crack. This non-linear trend of the δ₂ parameter cannot be related to any single fault, but it is typical of the coexisting faults.