Performance degradation in scratched journal bearings

Abstract

In this work, performance degradation in scratched journal bearings is evaluated by means of numerical simulations. A hydrodynamic numerical model with global thermal effects is employed (lubricant temperature and viscosity are assumed to be uniform). A very fine mesh is used, which allows a deterministic representation of a large number of circumferential scratches of various sizes and rectangular cross-shape. The severity of the scratches is quantified using four parameters: their depth, the extent of the scratched region, the density of the scratches and the position of the scratched region with respect to the bearing mid-plane. The influence of each of these parameters is studied independently. In order to evaluate bearing performance degradation, several operating parameters are computed, including minimum film thickness, average oil temperature and maximum hydrodynamic pressure. Lastly, charts are presented showing the evolution of the different bearing operating parameters as a function of the scratch severity, allowing the identification of critical scratch configurations that can lead to bearing damage.