Journal Motion Simulation of Hybrid Journal Bearing Considering Viscosity Variation Due to Temperature Change

A journal bearing system, if journal is disturbed from its equilibrium position, experiences change in the hydrodynamic forces acting on it. This disturbs the equilibrium of the journal and makes its center to whirl around the static equilibrium position. The dynamic response of a journal bearing system under these conditions can be obtained using either linear or non-linear equation of journal motion. The present work is aimed to determine realistic dynamic response of hole-entry hybrid journal bearing system compensated with constant flow valve restrictor. In this paper, the nonlinearized dynamic response of the journal bearing system is studied by considering two cases of journal mass (M_J) with respect to critical mass (M^l_c obtained from linear analysis. i.e M_J = M^l_c and M_J > M^l_c. The deviation in stability margins is established by comparing the results obtained from the linearized and nonlinearized stability analysis for each case namely, isothermal, elastohyrdostatic, thermohydroststic and thermoelastohydrostatic. The coupled solution of Reynold’s, energy, conduction and elasticity equations is obtained using finite element method and the equation of motion is computed using fourth order Runga-Kutta method. The results obtained in the present work for nonlinear dynamic analysis of a constant flow valve compensated hole-entry hybrid journal bearing shows a increase in stability margin as compared to linear analysis for a case when isothermal conditions are assumed and bearing is considered rigid. When variation of viscosity with temperature is considered i.e. THS case, the stability margin is found to be about 20% higher than that estimated by linear analysis.