Analysis Of Lubrication Characteristics Of Micro Self-Acting Bearings Under Non-isothermal Conditions

Micro high-speed gas bearings are the key support components of micro-turbine engine,micro high-speed motors and other new generation of power MEMS.It is important to investigate the lubrication characteristics of micro high-speed gas bearings for design of micro rotating machinery.However,due to the extremely small gas film thickness and high rotational speed of the micro gas bearing,the continuity and gas film isothermal assumptions under the normal scale conditions are n o longer applicable,so the influence of the gas rarefaction effect and thermal effect must be considered.This dissertation focuses on the above two aspects,the main works are as follows(1)For micro high-speed gas bearings,the modified Reynolds equations under the first order,the second order and the MGL(Molecular Gas Film Lubrication)slip model are given.Based on the Galerkin weighted residual approach,the Reynolds equation for micro gas bearing lubrication is numerically solved by the finite element method.The static characteristics of micro gas bearings considering the rarefaction effect are studied.(2)Dynamic eccentric ratio and dynamic attitude angle are expressed as plural forms with periodic perturbation,and the expressions of dynamic film pressure and dynamic film thickness in the complex plane are obtained.The dynamic stiffness and damping coefficients of micro gas bearing are calculated by the partial derivative method.At the same time,the effect of rarefaction on dynamic stiffness and damping coefficients is studied,and then the unbalance responses of micro gas bearing-rotor system are analyzed.(3)By considering the effects of temperature and pressure on viscosity,density,specific heat capacity and thermal conductivity of gas film and airflow velocity,a thermal lubrication model of micro gas bearing is constructed based on the energy equation of gas film,the equation of temperature field of the bearing sleeve,the thermal flow continuity equation and the modified Reynolds equation.The temperature field and pressure field of the first order slip model are solved by the finite element method.The influence of the ambient temperature,rotating speed of bearing,eccentric ratio and bearing clearance on three-dimensional temperature distribution and static characteristics of lubrication film of micro gas bearings are analyzed.(4)For the operation temperature environment of the micro turbine engine,the first-order slip boundary condition considering the thermal creep is given.The modified Reynolds equation with the thermal creep is deduced.The effect of the thermal creep of the micro gas bearing under the extreme temperature difference is analyzed.The above works have certain reference significance for the study of the lubrication characteristics of micro gas bearings.