Numerical Unsteady Analysis of Thin Film Lubricated Journal Bearing

Abstract

The performance characteristics of a thin film lubricated journal bearing are investigated by means of three-dimensional computational fluid dynamics analysis. The 3D Navier Stokes compressible equations were integrated to simulate the flow. Turbulence effects were included in the computation of unsteady transient analysis of journal bearing, taking into account gravity. The Journal bearing is designed in Gambit software, the journal is modeled as a ''moving wall'' with an absolute rotational speed of 3000rpm. The flow is simulated using Ansys Fluent software. Design parameters like relative eccentricity, dimensionless load carrying capacity, dimensionless wall shear stress, friction coefficient, Reynolds number, Sommerfeld number, strain rate, pressure distribution, temperature distribution and lubricant flow properties like turbulent viscosity, and velocity magnitude are considered for the analysis. It is assumed that the flow of lubricant is laminar and isothermal. Unsteady transient analysis is carried out for the journal bearing with different L/D ratios of 0.25, 0.5, 1, 1.5, and 2 and the corresponding results: relative eccentricity vs. Sommerfeld number, Dimensionless load carrying capacity vs. relative eccentricity, and dimensionless friction coefficient vs. relative eccentricity are presented in the analysis. Index Terms—Eccentricity, journal bearing, load carrying capacity, turbulent dissipation rate, unsteady, wall shear stress. I. INTRODUCTI ON A bearing is a system of machine elements whose function is to support an applied load by reducing friction between the relatively moving surfaces. As modern science and technology is developing, one discovered that the lubricant is affected by the gap of bearing. The interaction degree between the lubricant and solid surface influences the lubrication property of the bearing clearly. A thin film lubricated journal bearing is to develop positive pressure by virtue of relative motion of two surfaces separated by a fluid film. Thin film bearings are those in which although lubricant is present, the working surfaces partially contact each other at least part of the time. These bearings are also called Boundary Lubricated Bearings. Recently, following the progress in computer technology, many researchers began to use commercial computational fluid dynamics (CFD) programs in their investigations. The main advantage of CFD code is that it uses the full Navier-Stokes equations and provides a solution to the flow problem, whereas finite difference codes are based on the Reynolds equation. The results obtained by the two approaches are therefore likely to differ. Moreover, the CFD packages are applicable in very complex geometries.