Design-Driven Modeling of Surface-Textured Full-Film Lubricated Sliding: Validation and Rationale of Nonstandard Thrust Observations

Our recent experimental work showed that asymmetry is needed for surface textures to decrease friction in full-film lubricated sliding (e.g., thrust bearings) with Newtonian fluids; textures reduce the shear load and produce a separating normal force (Schuh and Ewoldt in Tribol Int 97:490–498, 2016). However, standard slider bearing theory cannot explain the sign of the observed normal thrust, and any effort to optimize surface textures would be premature if modeling and simulations are not validated with experiments. Here we model the flow with the Reynolds equation in cylindrical coordinates, numerically implemented with a pseudo-spectral method. The model predictions match experiments, rationalize the sign of the normal force, and allow for design of surface texture geometry. To minimize sliding friction with angled cylindrical textures, an optimal angle of asymmetry β exists. The optimal angle depends on the film thickness but not the sliding velocity within the applicable range of the model. Outside the scope of this paper, the model is being used to optimize generalized surface texture topography (Lee et al. in J Mech Design, to appear).