Turbulent Lubrication—Its Genesis and Role in Modern Design

Turbulence, a phenomenon well known in fluid flow, was first reported in journal bearings and thrust bearings in 1949. The observations were of higher torques and greater temperature rises than were expected from lower speed data. The transition from laminar behavior occurred at a Reynolds’ number corresponding to the predicted occurrence of Taylor vortices. This was the starting point for efforts to understand the phenomenon and to establish rules of behavior useful for predicting turbulent bearing performance. From an engineering point-of-view, good results in design have been achieved by treating turbulence as an increase in lubricant viscosity, the percent of increase being a function of the ratio of inertia forces to viscous forces, the Reynolds’ number. The effective result is greater film thickness and larger power losses in turbulent lubrication than would be anticipated from laminar theory. Where will the designer of the future encounter turbulence, and how will he treat its effects? Large turbogenerators have already reached a size where turbulent operation is experienced. The gradually increasing use of process-fluid-lubricated machinery, often involving low viscosity fluids such as water, liquid metal, and liquified gases, offers the designer fresh opportunities to understand and take advantage of turbulence in both hydrodynamic and hydrostatic designs.