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 estimate the effect of shear rate.

Regarding these relations, theoretical investigations of journal displacements in a one-cylinder 4-stroke diesel-engine main bearing are presented. The results compare journal displacements computed by considering a continuously changing effective viscosity with data, calculated with a constant viscosity. Furthermore, these computations enable the comparison of Newtonian and non-Newtonian fluids with respect to their behavior in instationary loaded journal bearings…

Presented as an American Society of Lubrication Engineers paper at the ASLEIASME Lubrication Conference in New Orleans, Loulslana, October 5–7, 1981

Notes

Presented as an American Society of Lubrication Engineers paper at the ASLEIASME Lubrication Conference in New Orleans, Loulslana, October 5–7, 1981