Calculation And Analysis On Dynamics Of Aerodynamic Gas-lubricated Bearings

Rotating machinery is mainly composed by three parts,which includes shaft,disks and bearings.As one of traditional machines,rotating machinery plays an irreplaceable role in various industry fields.With increase of demand for productivity and change of operating environment,requirements on rotating speed,operation precision and extreme environment adaptability are increased for rotating machinery.However,the traditional bearing supports cannot satisfy these requirements as some cases.Gas bearings are widely used in gas turbines compressor,expander,circulator,centrifuge and other rotating machines due to their advantages,such as high speed,small frictional resistance,wide operating temperature range and low noise.For the aerodynamic bearings,the working mechanism is that the hydrodynamic pressure generates in the bearing wedge-shaped to support the load and there is not additional gas supply device,so it can be used more conveniently in all kinds of environments.But the Aerodynamic bearings have some disadvantages,such as low bearing capacity and poor stability.Aerodynamic bearings need further improvement of stability and bearing capacity if they want to be widely applications.Therefore,the study of aerodynamic bearing has very important theoretical and engineering value.In this paper,the dynamic characteristics of aerodynamic bearing with different structures are theoretically analyzed,numerical simulation and experimental verification.The concrete contents are as follows:(1)Dynamic analysis of plain gas journal bearings(PGJB).Based on the fluid-structure interaction method,the displacement and pressure data are exchanged through the coupling surface of the finite element method and the finite volume method respectively.The dynamic response of the dynamic gas bearing rotor system in the fully self-suspended state is studied.At the same time,through the theoretical method Yang Jinfu model which describes the gas flow is brought into the rotor dynamics equation for calculation and analysis.The theoretical results are compared with the numerical simulation results.The results show that under different parameters the trends of the two methods results are basically the same.With the increase of speed and rotor quality,unstable T-periodic motion phenomenon will occur.This part can lay a foundation for further optimization of aerodynamic bearing.(2)Study on optimization about dynamic parameters of herringbone groove gas journal bearing(HGGJB).Under the condition of keeping the entertain boundary,the stability of the HGGJB and the PGJB is compared and the parameters of the HGGJB are optimized.The influences of bearing structural parameters on stability are analyzed.The results show that the selection of spiral angles,nominal gas film thickness,number of herringbone grooves and groove depth can't be too large or too small for HGGJB.The ratio of length to diameter selection is the greater the better for the load capacity.At the same time,the finite difference method is used to compare and analyze the Reynolds equation model of HGGJB and PJGB.The results show that the calculation results of two kinds of bearings through the two methods are basically the same trend.(3)The dynamic coefficients and stability of PGJB and HGGJB.Based on the simple harmonic excitation method and the influence coefficient method,the basic eight dynamic parameters of the PGJB and the HGGJB are calculated by the computational fluid dynamics theory.The influence of the dynamic coefficients under different operating conditions on the stability of the rotor gas bearing system is studied.The variation of stiffness damping and stability of two different bearings with rotating speed,bearing capacity and temperature were obtained.The stability of the two kinds of bearings are compared.The research shows that the two kinds of bearings stability have the same variation regular that the stability decreased with the increase of rotating speed and temperature,while the stability increases with the increase of bearing capacity.The HGGJB relative to the PGJB has higher stability.(4)Study on dynamic response of foil gas bearing rotor system.The finite element models of the bearing sleeve,the foil support structure and the rotor are established respectively under the entrainment boundary condition and completely autosuspension condition.The rotor-foil structure coupling gas film model was analyzed by two-way fluid-structure method.The dynamic response of the foil gas bearing is analyzed under this method.In order to improve the stability of foil structure,the herringbone groove is made in the foil structure to optimize the structure of the foil bearing.At the same time,the dynamic characteristics of the foil structure are analyzed theoretically by finite difference coupling rotor dynamics equation.(5)The experimental verification analysis of rotor PGJB and HGGJB.The gas bearing test rig was constructed and the experimental study on the PGJB and the HGGJB was carried out at different whirl speeds.And the experimental calculation results of the gas bearing rotor system were compared with the results by the fluid-solid coupling method.The results show that the results of the experiment and simulation are consistent.With the increase of rotational speed,the motion range of the two kinds of gas bearing rotors increases,and the shaft moves upward near the bearing center.The HGGJB has higher stability at the same rotational speed.