Lubricant levitation in high-speed bearings

What is it about?

This study examines how lubricants behave inside high-speed bearings, which are widely used in many machines. As the rotational speed increases, the lubricant tends to lift off the bearing surfaces rather than adhering to them. This behavior is driven by the Aerodynamic Leidenfrost Effect, where a thin layer of air entrains between the surface and the lubricant, preventing proper contact and causing it to levitate. We used a high-speed test rig and camera setup to observe how lubricant droplets interact with different bearing components, the ball, inner race, and outer race under varying speeds. We also tested different oils and surface coatings to evaluate their effect on lubricant adhesion. The results showed that higher speeds and certain oil properties, such as extensional viscosity increase lubricant levitation.

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Photo by Glen Carrie on Unsplash

Photo by Glen Carrie on Unsplash

Why is it important?

Poor lubrication is one of the main reasons why rolling element bearings fail early in industrial applications. In high-speed bearings, most energy losses come from two sources: fluid drag caused by the motion of the lubricant, and solid friction when surfaces make direct contact. The way lubricant moves inside the bearing is critical to minimizing these losses. At high speeds, the thin oil film that normally prevents metal-to-metal contact can break down, leading to increased friction, heat, vibration, and wear. This not only shortens the life of the bearing but also reduces the efficiency of machines. In systems like electric vehicles, jet engines, and turbines, these friction losses can account for a significant portion of total energy consumption. That’s why understanding how lubrication behaves at high speeds is essential for designing more reliable and efficient machinery.

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