Paroxysmal impulse vibration phenomena and mechanism of a dual–rotor system with an outer raceway defect of the inter-shaft bearing

•Impulse vibration behavior of a dual-rotor system with defective inter-shaft bearing.•Differences of paroxysmal impulse vibration and general impulse vibration.•Physical mechanism and occurrence condition of paroxysmal impulse vibration.•Experimental verification of two types of impulse vibration phenomena. This paper focuses on the dynamic phenomena, physical mechanism and occurrence condition of paroxysmal impulse vibrations in a dual-rotor system with inter-shaft bearing defect. The equations of motion of the dual-rotor system are established considering the force model for the inter-shaft bearing with an outer raceway defect. The fourth order Runge-Kutta method is adopted to investigate the vibration acceleration signals of the rotor system. The results show that there are paroxysmal impulse vibration phenomena when the dual-rotor system reaches some special rotation speed ratios. The time-domain waveforms, Hilbert envelope spectrums and inter-shaft bearing contact force curves of paroxysmal impulse vibrations are markedly distinguished from those of general impulse vibrations. The physical reason of paroxysmal impulse vibration phenomena is that the inter-shaft bearing loading position and defect position are intermittently anti-phase. It is found that the paroxysmal impulse vibration phenomena will occur if the rotation frequency of the high-pressure rotor (HP rotor) is equal to the fractional or multiple defect frequencies of the dual-rotor system. Based on this finding, an analytical formula related to the rotation speed ratio is derived, which can well predict the occurrence condition of paroxysmal impulse vibrations. At last, according to the guidance of the analytical formula, 6 experimental cases are executed, proving the dynamic phenomena and occurrence condition of the paroxysmal impulse vibrations.