Hydrodynamic Pressure Generation Caused by Surface Roughness or Texture

It is well established that roughness or texture on bearing surfaces may generate hydrodynamic pressures exceeding those generated by smooth surfaces of the same nominal macro-geometry. The effect is often attributed to the local positive pressure excursions being larger than the negative ones. It is shown that this interpretation is erroneous, and that the effect of cavitation plays a very minor role. Similarly, solutions based on the Navier-Stokes equations indicate that asymmetric pressure profiles that may be generated at very steep edges of surface micro-profile excursions, usually have little effect. It is concluded that the increased pressure is essentially caused by the changes in flow impedance.