Analysis of Oil-Air Two-Phase Flow Characteristics inside a Ball Bearing with Under-Race Lubrication

Abstract

Under-race lubrication can increase the amount of lubricating oil entering a bearing and greatly improve lubrication and cooling effects. The oil-air two-phase flow characteristics inside a ball bearing with under-race lubrication play a key role in lubrication and cooling performance. The motions of ball bearing subassemblies are complicated. Ball spin affects the oil volume fraction. In this paper, the coupled level set volume of fluid (CLSVOF) method is used to track the oil-air two-phase flow inside the ball bearing with under-race lubrication. The influence of various factors on the oil volume fraction inside the ball bearing with under-race lubrication is investigated, particularly rotating speeds, inlet velocity and the size of oil supply apertures under the inner ring. The influence of the ball spinning is analyzed separately. The result demonstrates that, on account of the centrifugal force, lubricating oil is located more on the outer ring raceway at rotational speeds of 5000 r/min, 10,000 r/min, 15,000 r/min and 20,000 r/min. The oil volume fraction inside the bearing gradually increases at an oil inlet velocity of 5 m/s, 10 m/s and 15 m/s. The circumferential distribution of oil is also similar. As the diameter of the oil supply aperture increases from 1.5 mm to 2 mm, the oil volume fraction increases inside the ball bearing. However, the oil volume fraction slightly decreases from 2 mm to 2.5 mm of oil supply aperture diameter. Ball spin does not affect the circumferential distribution trend of the lubricating oil, but slightly reduces the oil volume fraction. Furthermore, ball spin causes the surface fluid to rotate around its rotation axis and increases the speed.

Analysis of temperature field and convection heat transfer of oil-air two-phase flow for ball bearing with under-race lubrication

“…The boundary conditions are set based on the author’s previous study (Bao et al , 2020). Furthermore, the multiple reference frames method is used to reflect the rotation speed of the fluid domain, and all bodies are combined into one part to complete the data transmission at the interfaces.…”

Numerical investigation of the oil–air distribution inside ball bearings with under-race lubrication

“…The previously established computational domain for studying the oil-air flow behavior inside bearing with under-race lubrication starts from the position of the inner race feed holes of the bearing. 1,6,23…”

“…This assumption is the standard practice for studying the characteristics of the oil-air two-phase flow inside the bearing. 1,6,[14][15][16][17][18][19][20][21][22][23] With these assumptions, the rheology of the lubricant oil and the surface elastic deformation of the elements can be neglected. The EHL film is commonly calculated by special tools, which is not the focus of this study.…”

“…4,5 For the high-speed ball bearing with under-race lubrication, the oil volume fraction and distribution inside the bearing directly affect the lubrication characteristics. 6 A smaller amount of oil flow cannot take away all the heat generated by the bearing assemblies in time, while a larger amount of oil flow may cause higher power consumption and excessive parasitic losses. 7 The load-independent churning loss of the bearing is mainly related to the oil-air distribution inside the bearing.…”

“…The form and speed of the oil shedding from the bearing are found to be strongly dependent on the shaft speed, and the shedding speed is slightly higher than the cage linear speed. Bao et al 6 used the coupled level set volume of fluid (VOF) method to track the oilair two-phase flow inside the ball bearing with under-race lubrication and analyzed the influence of different factors (rotating speed, oil inlet velocity, aperture diameter, and ball spin) on the oil volume fraction and distribution. Considering the ball spin, the lubricant oil volume fraction inside the bearing is slightly higher.…”