1. Hydrodynamic lubrication

Hydrodynamic lubrication is a chapter of tribology that deals with contacts in which a viscous fluid is interposed between the surfaces involved. This fluid may be a liquid, practically incompressible, such as oil, water or even molten metal: this is the case with hydrodynamic bearings and thrust bearings. The fluid may also be a compressible gas, most often air: this is the case with gas bearings and thrust bearings (see article Aerodynamic thrust bearings and thrust bearings). in this treatise).

In hydrodynamic lubrication, the fluid film completely separates the two surfaces, which presupposes that the asperities and form defects of the surfaces are smaller than the film thickness. If this is not the case, there will be contact between the two surfaces at various points, and this is referred to as either mixed lubrication or boundary lubrication....