Nonlinear response analysis for a dual-rotor system supported by ball bearing

Abstract

Rolling element bearings are used as main supports and are key sources of vibrations for aero-engine rotor systems. Mainly including the inner and outer rings, cages, and balls or rollers, the complicated mechanical structures of rolling element bearings exhibit nonlinear behaviors due to the bearing clearance, nonlinear Hertzian contact forces, and defects. Due to imbalanced rotations, which are unavoidable, a wide variety of nonlinear behaviors can be expected in dual-rotor systems. Thus, in this study, we focus on the nonlinear behaviors of a dual-rotor system supported by a rolling element bearing. The nonlinear characteristics, such as the time-varying stiffness and primary resonance behaviors affected by the ball bearing parameters, are discussed. A dual-rotor system supported by a ball bearing was built while considering the nonlinear factors from the 4# ball bearing (at left end of the high-pressure rotor system). The nonlinear governing equations were established using the finite element method. Using the numerical methods, the effects of the bearing clearance on the time-varying stiffness and primary resonance behaviors are analyzed in detail. The results indicate that the mean values of the equivalent stiffness of the system and the rotation speed for forced resonance decrease as the clearance of the ball bearing increases. Periods of “zero-stiffness” occur when Ω1 (the rotation speed of the high-pressure rotor system) is less than 800 rad/s, and the periods of “zero-stiffness” over one period grow as the bearing clearance is increased. Meanwhile, in the case of a small or even zero clearance of a ball bearing, the amplitude–frequency curves still exhibit “hard characteristics” in the forced resonance domain, and hysteresis and jump resonance occur. All of the results can be used to establish base-line behaviors for system status determination, prediction, and control and to eliminate vibrations.