Research On The Static And Dynamic Characteristics Of Three-leaf Foil Journal Bearing

Bump foil journal bearings have been widely used in various high-speed turbomachineries in foreign countries. Compared with traditional gas bearing, the structure offoil bearing is more complex. However, the elastic deformation characteristics of thefoil make berings have many kinds of outstanding advantages, such as: good runningstability, lower energy loss, a high speed, high temperature, and a strong adaptivecapacity, etc. The advantages already have been confirmed in practical applications.The three-leaf foil journal bearing which is studied in this thesis is a kind of bumpfoil journal bearing. There are three foils which are installed sequentially in thecircumferential direction of the bearing, and every structure of the foil is composed of atop foil and a bump foil. This thesis mainly studies the dynamic and staticcharacteristics of the three-leaf foil journal bearing, and provides some theoretical basisfor the design and application of the three-leaf foil journal bearing.The beam element is established by using the finite element method in this thesis,and air film thickness equation of the three-leaf foil journal bearing is established incoupled of the deformation of the foil. The air film thickness equation and Reynoldsequation are solved by using Matab, and the results are found by digital simulation,which include pressure distribution, air film thickness, load carry capacity, attitudeangle and the deformation of the foil in the three-leaf foil journal bearing. According tothe simulation results, the thesis analyses the influence of the eccentricity ratio, shaftspeed, top foil thickness, bump foil thickness, bump foil pitch on the staticcharacteristics of the three-leaf foil journal bearing.The small perturbation method is used to analyze the dynamic characteristics of thethree-leaf foil journal bearing. First of all, on the basis of gas bearing Reynolds equation,and defining a series of first order Taylor expansion of related variables, and in the sametime, linear perturbation method is used to formula the dynamic stiffness and dynamicdamping coefficient of the three-leaf foil journal bearing. The dynamic stiffness anddynamic damping coefficient of the three-leaf foil journal bearing are got by usingMatab. The center finite difference method and successive super relaxation iterationmethod is used to solve linear partial differential equations, and Simpson complexintegration method of numerical integration is used to solve dynamic characteristicscoefficient. The thesis analyses the influence of the eccentricity ratio, shaft speed,whirling ratio, top foil thickness, bump foil thickness on the dynamic characteristicscoefficient of the three-leaf foil journal bearing.