Rotor Dynamic of Bearing-Rotor System Supported by Gas Foil Bearing Under Two Housing Excitations: Random Vibration and Transient Impulse

Abstract

Abstract. As the core component of the onboard refrigeration system, the turbo cooler is used to expand and cool the hot bleed of the engine, thus providing cold air. The extremely high rotating speed of the turbo cooler places significant demands on the reliability of the bearing. Gas foil bearing (GFB), as an oil-free bearing, is one of the best choices for turbo cooler due to the low friction loss and high stability. The turbo cooler experiences random vibration and transient impulse during operation, which can greatly affect the dynamic stability of the bearing-rotor system. It is crucial for the widespread onboard applications of gas foil bearing to adapt to the random vibration and the transient impulse, maintain the stability of the bearing-rotor system, and prevent rotor instability or resonance. This paper focuses on the assessment and validation of the prediction method for the nonlinear dynamic characteristics of the bearing-rotor system in the turbo cooler supported by gas foil bearing. In this paper, a dynamic model of the turbo cooler bearing-rotor system was developed based on the finite element method. The elastic shaft section was constructed using Timoshenko beam unit and the impeller and thrust disk were treated as rigid concentrated mass points. A mathematical characterization model was also established to describe the random vibration and transient impulse under the operating conditions of the turbo cooler. The nonlinear vibration characteristics of the bearing-rotor system of the turbo cooler under random vibration and transient impulse were studied. Additionally, the performance of the first-generation GFB and the third-generation GFB were compared and analyzed through the stability of the bearing-rotor system. Transient impulse and random vibration can significantly affect the dynamic stability of bearing-rotor system. Therefore, optimization studies on the stiffness distribution of gas foil bearings are essential to enhance the system's capability to withstand multiple excitation conditions. The prediction results indicate that the present method can approximately describe the random vibration and the transient impulse experienced by the turbocooler under actual operating conditions. Random vibration and transient impulse can significantly affect the dynamic stability of the bearing-rotor system. The rotor supported by the third-generation GFB can better overcome the adverse effects caused by random vibration and transient impulse. The rotor system using the third-generation GFB can maintain a small amplitude under excitation. At the same time, the orbit can quickly converge after the excitation, thereby maintaining the stable operation of the bearing-rotor system.