The Significance of the Effective Viscosity in Nonstationary Loaded Journal Bearings

Abstract

For pure hydrodynamic conditions in instationary loaded journal bearings, the viscosity characterizes the behavior of lubricants. Whereas the viscosity of Newtonian fluids changes with temperature and pressure, non-Newtonian lubricants are also affected by shear rate. These physical effects are not constant in circumferential and axial direction of a journal bearing. They form a definite viscosity distribution, which will be permanently changed by the varying conditions of dynamically loaded bearings. It is the object of this paper to define an effective value of viscosity concerning all these effects. Thus, determined effective viscosity is the basis of calculations which shall produce a better correlation to real conditions in journal bearings. This mathematical statement of evaluating an effective viscosity for Newtonian oils considers both the effective temperature as well as the viscosity-pressure-behavior by an exponential equation. Using non-Newtonian oils, a further logarithmic equation will estim...