Dynamic characteristics of a dual-rotor system with parallel non-concentricity caused by inter-shaft bearing positioning deviation

Abstract

The machining deviation of the positioning hole of the inter-shaft bearing can cause the fault of the non-concentricity of the dual-rotor system. Aiming at the above problem, a type of parallel non-concentricity is defined, the phase angle and the offset of which are utilized to modify the contact force model of the inter-shaft bearing. The results obtained by the Newmark-β method show that the non-concentricity phase angle and the non-concentricity offset will change the amplitude when the dual-rotor system passes the first critical speed. It is observed that there are 2X and 3X frequencies of the rotational speeds of high- and low-pressure rotors and several combination frequencies of the two rotational speeds, in which the subtraction frequency of high- and low-pressure rotors is dominant. With the non-concentricity phase angle changes, the shape of the orbit and the envelope curve of the orbit of high- and low-pressure rotors will shift. The quantitative correspondence between the polar angle difference and the non-concentricity phase angles is discovered, which can be used to diagnose the fault of the non-concentricity of the dual-rotor system.