RESEARCH ON THE NONLINEAR BEHAVIOR OF THE TURBINE ROTOR ASSEMBLED BY RABBET JOINTS

Double-stage turbine rotor assembled by rabbet joints is widely used in aero-engine, the mechanical properties of which depends highly on the compression state of the joints' contact interfaces. The accumulated damages during operation lead to the deterioration of the contact state, which could cause the sliding or partial separation on the interface, and will affect the dynamic characteristics of the rotor system. In this paper, the static mechanical properties, mainly angular stiffness, were studied using the static contact Finite Element Analysis (FEA) method to reveal the nonlinear variation in different conditions. One dynamic model of the rotor with rabbet joints was built based on the Lagrange equations, which was numerically solved by the Runge-Kutta method for the dynamic response of the rotor with nonlinear stiffness. The results show that the rabbet joints stiffness nonlinearity will decrease the critical speed of the flexural mode and cause amplitude sudden jump phenomena during acceleration or deceleration. Moreover, the chaotic motion and impact dynamic response may appear in the vicinity of the flexural mode critical speed. The axial preload is an essential influencing factor affecting the nonlinear response characteristics of the flexural mode, and an adequate preload will minimize or prevent the effects of stiffness nonlinearity during operation.