Applying Central Manifold Theory in the Definition of Active Gas Foil Bearing Configurations for High-Speed Stability of Rotors

This work explores the extension of threshold speed of instability in higher speeds, in rotors mounted in Active Gas Foil Bearings (AGFBs). An alternative configuration of an AGFB is presented including actuator elements which act independently under an optimization scheme, in order to establish such a shape of the top foil, that the effective damping property is achieved at a specific value. In this way, the bump foil structure existing in the conventional Gas Foil Bearings is not included. Operating speed higher than 100 kRPM is achieved in stable regimes for a D100 shaft. A simple rigid rotor mounted on two identical AGFBs is examined in the quality of instability, this described by the type of Hopf bifurcation (supercritical or subcritical) through the central manifold theory. The active foil shapes are elastic, and they are produced by eight piezoelectric actuators located at the bearing’s circumference, establishing lobe-type configuration. The elastoaerodynamic lubrication problem is modeled by the coupled state equations of the rotating journal displacement, the gas pressure distribution, and the elastic foil deformation, evaluated by finite difference method and finite element method respectively. The optimization pattern targets to set the damping ratio of the system in specific values. Several design scenarios for the AGFB are studied through dimensionless design parameters. The threshold speed of instability is located at ultra-high speeds and the type of Hopf bifurcation can be controlled with respective configurations.