Dynamics of rub-impact of dual-rotor systems and the experimental verification based on vibration accelerations measurement

Based on the rub-impact characteristics of aero-engine, the dynamic model of a dual-rotor system under rub-impact was established. The elastic deformation, contact penetration and elastic damping support during rub-impact between the casing and wheel disk were fully considered. The finite element model and its boundary conditions of a quayside gantry crane were established. The collision force and friction were calculated by utilizing the Hertz contact theory and Coulomb model, then the kinetic differential equation of rub-impact under dry rubbing status was derived. The first ten natural frequencies, the corresponding mode shapes and time-history of displacement responses were given based on the analysis of the modes and dynamic responses of the gantry crane system. The calculation and analysis above are helpful for preventing the gantry crane from working in resonant area and for keeping the oversize dynamic deformation under restraint, which can be applied in designing quayside gantry crane systems. Applying the variable step size fourth order Runge-Kutta method, the rub responses of the dual-rotor system were obtained. As for aero-engine, it may not be accessible to directly detect the displacement signals of the rotor system, and only the acceleration signals on the pedestal are easy to be acquiced. In order to analyse the bearing pedestal acceleration characteristics under rub-impact status, a dual-rotor system test rig was designed. Rub-impact experiments were carried out and the vibration acceleration signals collected from the bearing pedestal were analyzed by means of frequency spectrum and envelop analysis in order to extract the rubbing faults' characteristics. The results indicate that the doubling frequency and combination frequencies from two different exciting sources can be considered as the typical characteristics of rub-impact in aero-engines. The beat vibration usually becomes noticeable when the speed difference between the two dual-rotor speeds is less than 20% of the operating speeds. The results of the dynamic simulation are in accordance with the experiments, which verifies the effectiveness of the proposed rub-impact model of dual-rotor systems.