Eventos Anais de eventos
COBEM 2023
27th International Congress of Mechanical Engineering
COMPARATIVE ANALYSIS OF THE STATIC CHARACTERISTICS OF SIMPLIFIED AND FINITE HYDRODYNAMIC JOURNAL BEARING MODELS
Submission Author:
Aline de Almeida Soares , SP
Co-Authors:
Aline de Almeida Soares, Gabriel Alves Marques, Flávio Yukio Watanabe
Presenter: Aline de Almeida Soares
doi://10.26678/ABCM.COBEM2023.COB2023-0308
Abstract
Hydrodynamic lubrication is a subject of great importance in engineering and it is essential to the operation of bearings in large hydraulic turbines, reciprocating hermetic compressors and magnetic read heads. The effects of hydrodynamic lubrication were discovered experimentally by Beauchamp Tower in 1883 and mathematically formulated by Osborne Reynolds in 1886, resulting in the theory of hydrodynamic lubrication applied to cylindrical journal bearings, synthesized in a partial differential equation: the Reynolds equation. This equation, derived from the Navier-Stokes and continuity equations applied to the bearing fluid film, describes the behavior of lubricant pressure along the axial and radial/circumferential directions of the bearing, based on dimensional characteristics, operating conditions and properties of the lubricating fluid, usually characterized by the Sommerfeld number, a dimensionless parameter used in hydrodynamic lubrication analysis. The analytical solution of the Reynolds equation is only possible if some simplifications of the differential equation are adopted and resulting in the infinitely long bearing and short bearing models. The whole Reynolds equation can be solved by applying numerical approaches such as Finite Difference Method (FDM), Finite Volume Method (FVM) and Finite Element Method (FEM), generating finite bearing models. Although limited, the simplified models results are close to the complete solution for some geometric configurations and specific operation conditions. Additionally, in the radial clearance divergence field, mathematical or numerical solutions result in negative hydrodynamic pressures in the fluid film, which does not actually occur, since there is a rupture of the fluid film often characterized as a kind of cavitation phenomenon. In this way, different boundary conditions make it possible to obtain feasible results such as Gümbel, Swift-Stieber/Reynolds and Jakobsson-Floberg-Olsson (JFO) boundary conditions. Although the literature on the subject presented is wide, there is a gap in the direct comparison between simplified and finite models of hydrodynamic journal bearings. Therefore, the main objective of this study is to present this comparative analysis, considering characteristic results such as pressure profile in the fluid film, rotor static equilibrium position (eccentricity x attitude angle), load capacity, frictional torque and axial flow, as a function of the Sommerfeld number. The differences and similarities between different models are evidenced providing an understanding of the limits of use of the results obtained from the simplified models of hydrodynamic journal bearings.
Keywords
Hydrodynamic lubrication, Reynolds equation, boundary conditions, Analytical Solution, Finite Difference Method
