Study of rotor dynamics considering a fluid film bearing

Abstract

Abstract Fluid film bearings are widely used in supports of gas turbines, pumps and compressors. They also present in test benches designed for overspeed tests of aircraft engine’s discs. Stiffness and damping of these supporting elements are nonlinear. Moreover fluid film bearing reactions include circulation forces that can bring to well-known types of self-excited vibrations – whirl and whip. Magnitudes of those oscillations are almost not influenced by unbalances and are determined by the system’s properties, in particular – properties of damping and circulation forces. If this type of vibrations does not arise and only forced oscillations present, the corresponding resonance frequencies will depend on unbalances because of fluid film bearing nonlinear stiffness and damping. The listed considerations bring to the necessity of account of nonlinear non-conservative support’s properties in modeling of rotor dynamics. The paper describes the appropriate approach that includes joint use of finite element model of rotor and nonlinear models of supports. The vibrations of rotor with rolling and fluid film bearings in supports are considered as example. Rolling bearings were modeled by nonlinear exponential dependencies of forces on displacements. Those dependencies were computed from the Hertz contact theory. Fluid film bearing was modeled with analytical solution of the Reynolds equation. The problem was solved in nonlinear nonstationary formulation considering mutual influence of rotor displacements and bearing reactions. Results of multiple simulations performed for different values of rotor speed are presented as a frequency response function and a waterfall plot. The results were verified with experimental data.