Nonlinear Dynamic Analysis of a Rotor System With Aerodynamic Journal Bearings

Abstract

This paper investigates nonlinear dynamic characteristics of a rotor system with aerodynamic journal bearings. The Finite Difference Method (FDM) is employed to solve the Reynolds equation, which is used to determine the nonlinear compressible gas force of the aerodynamic bearing. By applying the gas bearing force to system equations of motion, the system response can be determined by the numerical integration method. Results show that the aerodynamic bearing will provide higher loading capacity to support the rotor when the eccentricity ratio is increased. The aerodynamic bearing force increases when the rotor is speeding up or the squeeze frequency is raised. The rotor trajectory presents aperiodic behavior, and it becomes significant as the rotor mass increases. When the squeeze frequency decreases or the rotor mass increases, the radius of the rotor trajectory will increase. Recursive Least Square Method and Kalman Filter Method are used to identify the aerodynamic bearing parameters from the system response. The parameters include the damping and stiffness coefficients of the aerodynamic bearing. According to the results of identification, both identified parameters by these two methods are in good accordance. The results show that the aerodynamic bearing force can be precisely identified and the system response can be quickly solved by the identified system with less computer time. But the identified system lost its accuracy as the rotor speed or the squeeze frequency increase because these will enhance the nonlinearity of the aerodynamic bearing force.