A STUDY ON TRANSIENT ANALYSIS OF CAPILLARY COMPENSATED 4-POCKET MULTIRECESS JOURNAL BEARING

Abstract

Most published work relating to dynamically loaded journal bearings are directed to determining the minimum film thickness from the predicted journal trajectories. These do not give any information about the sub synchronous whirl stability of journal bearing system. (Since they do not consider the equations of motion. It is, however, necessary to know whether the bearing system operation is stable or not under such an operating condition. The purpose of the study is to analyse the stability characteristics of the system. A linearized perturbation theory about the equilibrium point can predict the threshold of stability; however it does not indicate post whirl orbit detail. The linearized method may indicate that a bearing is unstable for a given operating condition whereas the nonlinear analysis may indicate that it forms a stable limit cycle. For this reason, a nonlinear transient analysis of a rigid rotor supported on oil journal bearings under different loads can be performed. The hydro dynamic forces can be calculated after solving the time-dependent Reynolds equation by a finite difference method. Using these forces, equations of motion can be solved by the fourth- order Runge-Kutta method to predict the transient behaviour of the rotor. With the aid of a high-speed digital computer and graphs the journal trajectories can be obtained for several different operating conditions. The main objective of the present work is to evaluate the stability of circular and two lobe journal bearings with consideration of two approaches linear and nonlinear. The Reynolds equation is solved by using FEM in order to calculate the fluid film pressure in bearing clearance space and other performance parameters. The numerically simulated results are presented in the form of static performance characteristics such as bearing flow, maximum fluid film pressure and minimum fluid film thickness as well as the dynamic performance characteristics such as fluid film stiffness/damping coefficients.the performance characteristics of circular bearing are compared with two lobed bearing.