Synchronous impact phenomenon of a high-dimension complex nonlinear dual-rotor system subjected to multi-frequency excitations

The “synchronous impact” is a phenomenon that increases the dynamic load of the inter-shaft bearing, when the frequency of the aerodynamic excitation is close to the contact frequency of the inter-shaft bearing. This work addresses the “synchronous impact” phenomenon of an aero-engine. The 104 degree-of-freedom dynamical model of an aero-engine is established by the finite element method, in which the complex nonlinearity of the Hertzian contact force of the inter-shaft bearing with clearance is included, and the multi-frequency excitations such as the unbalanced excitations of the high- and low-pressure rotors and the aerodynamic excitation are considered. A harmonic balance method combined with the alternating frequency time-domain method (HB-AFT) is introduced to obtain periodic responses of the high-dimension complex nonlinear dual-rotor system. The results show that there emerges a peak value of the amplitude-frequency response for the contact frequency harmonic component of the outer ring of the inter-shaft bearing, when the aerodynamic excitation frequency is close to the contact frequency. In addition, the dynamic load of the inter-shaft bearing increases significantly. Moreover, the parametric analysis shows that the “synchronous impact” phenomenon is sensitive to the change of the speed ratio of the high- and low-pressure rotors. The dynamic load of inter-shaft bearing can be significantly reduced by changing the speed ratio by 1%. The results obtained in this paper not only provide more insight into the mechanism of the “synchronous impact” phenomenon but also demonstrate the HB-AFT method as a potential semi-analytical tool to explore the high-dimension complex nonlinear system.