Load Influence on Hydrostatic Oil Film Journal Bearing Stiffness Characteristics

Hydrostatic and hybrid oil film journal bearings have been widely used in various rotating machinery applications because of their unique features. The main advantages of hydrostatic bearings are negligible wear due to very low friction, high load carrying capacity, large fluid film stiffness and damping capacity, while a major actual disadvantage is a complexity of pressurized lubrication system. Hydrodynamic lubrication mechanism has been well studied analytically and experimentally and various types of bearings were developed to provide increasing operating speed, load capacity, stability and efficiency for modern rotating machines. Hydrostatically lubricated bearings has principal difference (in comparison with hydrodynamic bearings) and their characteristics have been an area of continued research.

Complete Navier-Stokes equations are used by many researchers to simulate the flow in a hydrostatic bearing pockets and obtain good agreement with the experimental results. This approach requires significant computational resources and pre-processor work and can be applied for the specific design only. Another approach is to use Reynold’s equations which derived from Navier-Stokes equations with some assumptions (neglecting the transversal velocity, constant pressure across the film thickness, etc) . Often, further simplifications for the Reynolds equations are used, for example by assuming zero eccentricity for the shaft, which sometimes lead to inaccuracy in hydrodynamical characteristics prediction.

The goal of this work is to develop robust algorithm, which allows to predict hydrodynamical characteristics and dynamic stiffness and damping coefficients of hybrid and hydrostatic bearings with the increased accuracy and which can be used in engineering/design purposes. The developed approach is based on Reynold’s equations, where the unknown parameters are the rotor position and fluid pressure in recess pockets. Solution for the generated system of equations is obtained using Newton’s method. Applying the developed approach, the effect of load influence on the hydrodynamical and the dynamic stiffness characteristics has been studied. Several hydrostatic bearing designs which are based on the published data were considered to compare the results calculated applying the approach with the experimental and theoretical data given in the literature. Comprehensive comparison shows that for the cases with comparatively low load/eccentricity the results are in a good agreement, while the difference is higher for the cases with high eccentricity.    

The developed approach can be utilized as a practical tool that allows to predict performance characteristics of hydrostatic bearing with increased accuracy. Performed analyses shows the load influence on hydrostatic oil film journal bearing stiffness characteristics. The study also allows to analyze how different design/geometrical parameters and initial conditions (supply pressure) influence bearing performance characteristics.