Comprehensive analysis of fluid-film instability in journal bearings with mechanically indented textures

Abstract

This paper theoretically and experimentally investigates the effects of textures produced by a mechanical indentation on the stability of journal bearings. The research primarily aims at lightly loaded journal bearings used, e.g. in vertical rotors and microturbines. The results show that textures located close to the minimum oil film thickness can noticeably improve the stability at low specific loads but have only a negligible effect at a specific load of 0.15 MPa. The texturing also impacts the bearing temperature, which is closely related to the bearing friction. Since the textured journal bearings are prone to the formation of cavities in the oil film, the paper also deals with computational methods. It is demonstrated that an accurate estimate of stability threshold requires very dense computational meshes, which are impractical for mass-conserving treatment of cavitation due to CPU requirements. Interestingly, errors due to non-conservation of mass are up to the same magnitude as uncertainties due to employed numerical algorithms. The results demonstrate that numerical results describing lightly-loaded textured journal bearings are very sensitive to the density of the computational mesh. Hence, the simplified cavitation treatment can be legitimate in applications where the CPU time is a concern, such as the optimisation, iterative algorithms and time-integration of equations of motion.