Research On Hydrodynamic Characteristics Of Rotor Multileaf Foil Journal Bearings Systems

During the late 1960s and early 1970s, in support of U.S. Air Force and NASA, the Multileaf Foil Bearings has been successfully developed by ASAC (Allied Signal Aerospace Co.) to meet the requirements of turbine machine, especially in the aerospace field. The elastic lubrication surface of Multileaf Foil Bearings which make it has many unique performances, such as strong self-adaptive ability, high speed, wide working temperature range, good reliability, etc; therefore the traditional ball bearings were gradually replaced by Multileaf Foil Bearings in the low temperature refrigeration, aerospace and other fields. But the application of Multileaf Foil Bearings was limited for its low bearing capacity and strict requirements of processing, so according to the actual situation the research about oil-lubricated Multileaf Foil Bearings has practical significance. The static and dynamic characteristics of Multileaf Foil Bearings was calculated and analyzed, and also the influence on the dynamic characteristics of rotor systems.First, the static and dynamic characteristics of oil-lubricated cylindrical bearings were calculated and analyzed. The oil film pressure distribution were obtained by considering Reynolds boundary condition and using Successive Over Relaxation Method (SOR) to solve Reynolds equation, then the bearing capacity and equilibrium position of shaft can get. The eight dynamic coefficients were obtained by using small disturbance method on balance position to solve Reynolds equation. The accuracy and reliability of compute method and mentality about bearings static and dynamic characteristic were verified by comparing to the literature.Second, Multileaf Foil Bearings with five symmetrical arrangements leaves foil, for example, the formula of its oil film thickness were obtained by analyzing its geometric features. The foil will be regarded as cantilevered curve beam, and mutually point contact, then the foil deformation equation and formula of counterforce between each other were obtained. Based on the compute method and mentality of oil-lubricated cylindrical bearings, the oil film pressure were got by coupled solving deformation equation with Reynolds equation, and then the bearing capacity,take-off speed, axis equilibrium position etc were determined. The dynamic characteristic coefficients were obtained by coupled solving the derived dynamic deformation equation with dynamic Reynolds equation. The influence on the bearings static and dynamic characteristic were discussed by analyzing the oil film pressure and thickness distribution, rotating speed and whirl frequency.Last, the dynamic stiffness and damping obtained by calculating were introduced into the movement equation of rotor system, the critical speed and unbalance response were computed by using finite element method (FEM). The influence on dynamic characteristics of rotor system was discussed by analyzing the dynamic stiffness and damping of Multileaf Foil Bearings.