Fluid-Solid Coupled Heat Transfer Characteristics of High-Speed Ball Bearings with Under-Race Lubrication

High temperature rise is one of the critical factors influencing the service performance of high-speed rolling bearings used in the main shaft of high thrust-to-weight ratio aviation engines. The prerequisite for addressing this issue is to predict temperature. The magnitude of temperature in the bearing depends on both the heat generation and heat transfer. Heat is generated mainly due to the frictional heat inside the bearing, while it is dissipated primarily through the convection of lubricant which is related to the lubricant flow inside the bearing cavity. Aviation engine bearings typically employ the under-race lubrication method in which oil is supplied through under-race oil holes, then enters into the bearing cavity, mixes with the ambient air, and finally forms a two-phase lubrication environment. The degrees of mixing and flow characteristics of the two-phase flow have an impact on the heat dissipation of the bearing, which makes it challenging to predict bearing temperature. To address this issue, a fluid-solid coupled heat transfer model for aero-engine three-point contact ball bearings with under-race lubrication was established through combining with the bearing dynamics model, frictional heat generation model, two-phase flow model and multiple reference frame method. After numerical simulations of this model, the effects of rolling element self-rotation, bearing rotational speed, oil supply velocity and cage structural parameters on the thermal characteristics of the bearing were analyzed. The results indicated that at lower bearing speeds, the self-rotation of rolling elements reduced the oil phase volume within the bearing cavity, whereas at higher speeds, the opposite effect was observed. Additionally, the self-rotation of rolling elements decreased their own temperature significantly. As the bearing speed increasing, the average oil phase area ratios in the raceway wall surfaces decreased, while the average temperatures of both the inner and outer rings increased obviously and the magnitude of temperature rise was larger for the inner ring. The temperatures of the inner and outer rings reached minimum in the circumferential azimuth angle in front of the oil supply hole, gradually increased along the direction of bearing rotation, and reached the highest in the circumferential azimuth angle behind the oil supply hole. With an increase in oil supply velocity, the average oil phase area ratios in the raceway wall surfaces increased, while the average temperatures of the inner and outer rings first decreased and then increased. Furthermore, as the width of the bearing cage increased, the oil phase in the inner ring decreased, while that in the outer ring increased. As a result, the average temperature of the inner ring rised, while that of the outer ring decreased slightly. An increase in the pocket diameter of the cage resulted in a slight rise in the average temperatures of both the inner and outer rings, because the average oil phase area ratios in the raceway wall surfaces of both the inner and outer rings decreased. Lastly, with an increase in cage thickness, the oil phase volume area ratios in the raceway wall surfaces first increased and then decreased, the average temperature of the inner ring initially decreased and then significantly increased, while that of the outer ring showed minimal change. These findings provided a basis for reducing the temperature rise in high-speed ball bearings with under-race lubrication from the perspectives of oil supply parameter selection and cage structure parameter design.