The Influence Mechanism of the Gas Fraction in Lubricant on Hydrostatic Bearing Characteristics at Different Shear Rates

Abstract The purpose of this article is to explore the mechanism and law of the gas fraction in lubricants affecting hydrostatic bearings at different shear rates. Based on the coupling between the Reynolds and Rayleigh–Pleset equations, the two-phase flow shear viscosity model, and the finite volume method, a mathematical model of gas–liquid two-phase lubrication of hydrostatic bearings was established. We systematically analyze the influence of gas fraction (1–10 vol%) on oil film characteristics and static/dynamic bearing performance under different eccentricities and shaft speeds. The key findings are summarized as follows: With increasing gas fraction (1–10 vol%), two distinct behavioral patterns emerge. At low shaft speed, the viscosity of the oil sealing surface increases, while the load-carrying capacity and oil film mass flow decrease. Conversely, at high shaft speed, the viscosity of the oil sealing surface decreases, but the load-carrying capacity and the mass flow of oil film gradually increase. Notably, when the cavitation effect is not severe, an increased gas fraction in the lubricant reduces static pressure but amplifies dynamic pressure in hydrostatic bearings. Consequently, the main stiffness coefficient exhibits a slight reduction, whereas the cross stiffness, main damping, and cross damping coefficients all increase—with these variations intensifying proportional to eccentricity and shaft speed.