Theoretical and experimental studies on nonlinear dynamic performances of gas journal bearing with three pads-rotor system

Gas journal bearings (GJBs)-rotor system develops toward the goals of high speed, light weight, high energy efficiency and automation, resulting in its dynamic behaviors become increasingly complex. An accurate prediction to the dynamics and stability of GJBs-rotor system is urgently needed to overcome the abnormal vibration. A flexible gas journal bearing with three pads (GJBTPs)-rotor system is proposed and its fractional order nonlinear dynamic model is developed to predict the dynamic characteristics. The effects of the rotational speed ratio Ω_ω and fractional order α_d on the dynamic performances of GJBTPs-rotor system are studied by means of the time history diagram, rotor orbits, phase diagrams, Poincaré maps and spectrum diagrams. A test platform for studying the nonlinear dynamic characteristics of GJBTPs-rotor system is built up, and its vibration responses test under different rotational speed ratios Ω_ω is carried out to verify the rationality of the theoretical model. Results show that the GJBTPs-rotor system presents complex dynamic behaviors, including subsynchronous vibrations and whirling instability. The vibration amplitude of GJBTPs-rotor system increases when the rotational speed ratio Ω_ω increases or the fractional order α_d decreases. When the rotational speed ratio Ω_ω increases from 2.0 to 3.0, the fractional order α_d of GJBTPs-rotor system increases by 3.896%, while the synchronous vibration amplitude diminishes by 23.916%.