| The bump-type gas foil bearing has the advantages of strong carrying capacity and impact resistance,long working life,good working stability and high rotor working speed.It is widely used in turbomachinery,such as micro gas turbines,air compressors and air circulation devices,and it has a good development prospect in high-precision fields such as aerospace and precision machining.The theoretical research of foil bearings is a complex problem that crosses multiple disciplines.This paper studies the frictional problem inside the bump foil structure and analyzes the influence of loading history on the radial support stiffness of the bump foil and the static characteristics of the bearing.The finite element modeling of the bump foil is carried out by using beam elements,the frictional model of the bump foil structure is established,and an iterative calculation method for determining the frictional force of the contact nodes of the bump foil structure is proposed.By simulating the loading and unloading process of the horizontally spread bump foil,it is found that under the same load,the radial support stiffness in the unloading stage is always smaller than the stiffness in the loading stage.The thick plate element is used to carry out finite element modeling of the top foil,and the static characteristics of the bearing are studied by coupling the finite element method and the finite difference method to solve the aeroelastic coupling equation.Comparing the calculation results obtained by simulation with the experimental results in the literature verifies the correctness of the prediction model and proves that the bearing capacity can be improved by increasing the frictional coefficient between the contact surfaces.Based on the iterative judgment method of the frictional state of the contact nodes of the bump foil structure and the simulation method of the bearing static characteristics,the process of static loading and unloading process of the bearing is simulated.The hysteretic curve of the static equilibrium position of the bearing and the static load change with eccentricity is obtained,and the influence of frictional coefficient,rotor speed and eccentricity amplitude on the hysteretic effect of the friction is studied.The results show that increasing the amplitude of the eccentricity can aggravate the influence of the hysteretic effect of the friction on the carrying capacity of the bearing,while the rotor speed and frictional coefficient have little effect on it.A test rig for identifying the dynamic characteristics of bump-type gas foil radial bearings was designed and built,and the effect of rotor speed and excitation frequency on the dynamic stiffness and damping of the bearing was studied by solving the kinematic equation in the frequency domain.The results show that the main stiffness of the bearing increases with the increase of the excitation frequency,and the main stiffness in the vertical direction is greater than the main stiffness in the horizontal direction;the main damping of the bearing decreases with the increase in the excitation frequency;both the cross stiffness and the cross damping are significantly smaller than the main stiffness and the main damping respectively;increasing the rotor speed can increase the main stiffness but also reduce the main damping. |
