Dynamic Flow Field Simulation And Instability Analysis Of High Speed Hybrid Gas Bearings

Gas bearing is a type of sliding bearing with viscous gas as the main lubricating medium,which has obvious advantages in the fields of high speed,high precision,low friction and extreme working conditions.When the bearing rotates at high speed,the transient flow field of the gas is very complicated.The phenomenon of whirl instability and gas film oscillation occurs when gas bearing is running,which lead to the failure of bearings and restrict the wide application of gas bearings.The axis trajectory of gas bearing reflects the working state of the bearing,which can reflect the stability of the bearing rotor system and the rationality of the design parameters of the bearing;the complex change of the dynamic characteristics of the gas bearing gas film directly affects the motion state of the bearing rotor.Therefore,the calculation and analysis of the axis trajectory and stiffness and damping coefficients of gas bearings are of great engineering significance for the study of the stability of gas bearings.In this thesis,the spherical hybrid gas bearings is taken as the research object,and the three-dimensional finite element model of the gas film is established according to the structural parameters of the hybrid gas bearings.Based on FLUENT,the pressure distribution on the gas film grid point of the hybrid gas bearings was calculated by using the 6 DOF dynamic mesh calculation method,which can analyze the lubrication characteristics of the gas film transient flow field accurately.The pressure distribution of gas film transient flow field is calculated numerically,and the axis trajectory is simulated.The bearing axis trajectory is simulated and analyzed by using 6DOF dynamic mesh calculation method.And the bearing stiffness and damping coefficient can be obtained by using dynamic characteristic coefficient calculation method.The influence of speed and gas supply pressure on the stability of gas bearing is analyzed by combining the axis trajectory and dynamic characteristic coefficients.The stability characteristics of gas bearings under step load,rectangular load and sinusoidal load are studied from three aspects: axis trajectory,bearing gas film force and stiffness and damping coefficient.When bearing is subjected to unidirectional impact load in normal operation,it exhibits a certain resistance,and the recovery ability is also different after the load disappears.At the same time,the influence of bi-directional load on the stability characteristics of gas bearings is analyzed.As a whole,the stability characteristics of gas bearings under uni-directional load are better than that under bi-directional load.The ultimate load-carrying capacity of gas bearings from stable operation to instability is also simulated and analyzed.The hybrid gas bearings are tested and analyzed on the gas bearing test machine.Formulates the experiment plan,and the data of the rotor speed increase was collected.The axis trajectory and spectrogram of the rotor at different speeds were obtained by data processing.And compared with the results of simulation data,the validity and correctness of the simulation calculation method are verified.