Numerical prediction of drag force on spherical elements inside high-speed ball bearing with under-race lubrication

In high-speed ball bearings, the revolution of spherical elements is significantly influenced by drag force of lubricant fluid, impacting the bearing's dynamic and thermal performance. To investigate drag force in under-race lubrication ball bearings, a numerical study was conducted after the experimental verification. A multi-sphere flow model with a sandwich plate was tested, which indicates a strong agreement between numerical calculations and experimental data, with an error margin below 10 %. In the numerical simulation, pressure distribution and shear stress on the ball was studied, considering variables such as bearing rotational speed, oil flow rate, oil density, and oil viscosity. Results reveal low pressure at the upper hemisphere's center and high pressure on both sides. Shear stress is concentrated in contact areas between the element and components like the inner ring, outer ring, and cage. Oil injection from the inner ring significantly alters the pressure and shear stress distribution in the lower hemisphere. The direction of drag force is the same as the rolling element's revolution, acting as driving force for elements’ revolution. Increasing bearing rotating speed, oil flow rate, oil viscosity, and oil density all contribute to higher drag forces on the ball. Based on the numerical simulations, a predictive formula for the ball's drag force was developed.