Vibration characteristics of hybrid gas foil bearing-rotor system in space microgravity

Space nuclear reactor power supplies are used in civil space missions such as Earth orbiting equipment, Mars and lunar exploration, and the space closed Brayton cycle thermoelectric converter is a core component of the nuclear power supply. The turbine rotor system in this conversion system necessitates bearing support, but oil-lubricated and magnetic levitation bearings must be capable of withstanding high temperatures, radiation exposure, and meeting life requirements. Gas bearings were selected as the optimal component due to their ability to utilize the gas within the closed Brayton cycle plant as a working medium. The dynamic gas bearing is unsuitable for high-power turbomachinery applications due to its low load capacity and stiffness. This study proposes the incorporation of a gas supply pipe into the dynamic foil bearing to create a hybrid gas foil bearing (HGFB). The introduction of an external gas supply through the gas supply pipe enhances the load capacity and stability of bearing, while varying the gas supply pressure opens up possibilities for controlling rotor vibration. This study employs the Newton iteration method to numerically solve a large hybrid gas foil bearing with a diameter of 80 mm. The impact of throttle hole count, diameter, and gas supply pressure on the bearing's static characteristics is analyzed, as is the effect of gas supply pressure on dynamic characteristics such as bearing stiffness and damping. Finally, the influence of bearing on the rotor vibration characteristics is examined. A microgravity ground-based simulation rotor system is established to investigate the effects of bearing unilateral clearances and gas supply pressure on the critical speed, vibration amplitude and other rotordynamic performance of the rotor system through experimental methods.