Numerical simulation of waviness in a circular EHL contact under rolling/sliding in a point contact

Surface roughness and/or surface imperfections are well known to significantly affect the performance of concentrated contacts. Helped by improvements in computer hardware and software, related research in the field of Elasto Hydrodynamic Lubrication (EHL) with non-smooth surfaces is increasing. In general the configuration to be considered is a two dimensional transient one, since the (rough) surfaces move with respect to the contact. This time dependent point contact problem has been studied experimentally by Kaneta and numerically by, amongst others, the authors. For a single feature a good correlation between experiments was observed, both quantitatively and qualitatively [31]. In the present paper the influence (transient and steady state) of a global surface feature, i.e. waviness, on pressure and film thickness for such a two dimensional contact is investigated for operating conditions identical to those used previously in experimental research. The transient results apply to transverse waviness which is confined to one surface. Film thickness and pressure distributions have been calculated as a function of time for different slide to roll ratios. As was previously observed for the infinitely wide line contact, it is shown that film thickness modulations tend to be propagated through high viscosity regions at the average surface speed. For the case of waviness this implies that the film profile in such a region will be a combination of two oscillations, i.e. one component with the wavelength of the undeformed waviness and the second with a wavelength that is larger or smaller. With increasing load the latter oscillation will tend to dominate the film thickness.