Vibration stability study on the aero-engine rotor with spline joint structure

When the clearance fit is applied for the positioning of the cylindrical surfaces spline structure of the engine, the misalignment between the two connected rotors is large, and the inner and outer splines are prone to produce internal friction during the rotor working, and the risk of rotor instability is high. By analyzing the relative motion of inner and outer spline, the expression of work by internal friction is derived, as well as instability threshold speed of rotor with spline structures is further analyzed when the internal damping is considered. The Newmark-β method have been used to simulate dynamic characteristics of established single-disc cantilever rotor model and the effects of critical parameters such as rotor damping, friction coefficient, and misalignment about stability of the rotor with coupling sleeve structure are discussed. The results show that the increase in friction coefficient and misalignment will aggravate the instability of the rotor system. When the modal damping ratio of the rotor is less than 1%, the sub-harmonic frequency appears in rotor vibration and the instability frequency is the first-order natural frequency of the rotor. When the modal damping ratio of the rotor increase to 4.5%, the sub-harmonic components disappear in vibration. Therefore, increasing the damping of rotor can restrain instability of rotor system.