Interplay between wall slip and cavitation: A complementary variable approach

Abstract

In this work a stable and reliable numerical model based on complementary variables is developed to study lubricated contacts characterised by slip at one or both surfaces and in the presence of cavitation. This model can be used to predict surface behaviour when cavitation induced by e.g. the presence of surface texture, slip, or a combination of the two is encountered, with varying surface parameters. For this purpose, two different algorithms are coupled to predict the formation of cavitation, through a mass-conserving formulation, and the presence of slip at the wall. The possible slippage is described by a limiting shear criterion formulated using a Tresca model. To show the flexibility of our model, several bearing geometries have been analysed, such as a twin parabolic slider, a cosine profile used to mimic a bearing, and a pocketed slider bearing employed to study the effect of surface texture. We observe that the lubrication performance (i.e. low friction coefficient) can be improved by using materials that promote slippage at the moving wall. The location of the slippage region can be optimised to find the lowest value of friction coefficient. Our theoretical developments and numerical implementation are shown to produce useful guidelines to improve and optimise the design of textured superoleophobic surfaces in the presence of lubricated contacts.

Hydrodynamic Lubrication of Textured Journal Bearing Considering Slippage: Two-dimensional CFD Analysis Using Multiphase Cavitation Model

“…Their main finding was that the enhanced tribological performance of journal bearing could be achieved with well-designed slip/texture surface. In recent lubrication, using numerical model based on complementary variables, Biancofiore et al [21] reported that a very large increase in the pressure profile and significant decrease in friction coefficient are registered by introducing slippage.…”

Analysis of the Effect of the Slip-Pocket in Single and Double Parallel Bearing Considering Cavitation: A Theoretical Approach

“…Additionally, the effect of boundary slip and surface texturing was also studied, for example [8,16,19,20,[43][44][45][46][47][48], but ignoring the cavitation effect and mostly using a non-massconservation cavitation equation. In the present work, it will be shown that cavitation has a strong influence on performance and unrealistic conclusions may be drawn if the cavitation is ignored.…”

Lubricated textured plan parallel sliding contacts the effect of boundary slip and cavitation

“…This approach allowed sub atmospheric and even negative pressures, no matter how low they were [47]. In 1914, Gumbel [48] was the first to account for the film 'rupture'. According to his theory, for a steadily loaded bearing operating at constant angular velocity, the rupture originates in the immediate vicinity of the film's minimum clearance at a predetermined pressure pcav and remains constant at that value for the entire divergent region (Fig.…”

“…The more elusive problem in dealing with film rupture has been respecting the mass continuity within the confines of the Reynolds equation. Gumbel's condition [48] and the half Sommerfeld condition did not respect the continuity of mass; they just accounted for the fact that when and where the film ruptured, pressures became sub ambient (negative) and consequently automatically set to pcav in the final iteration (SS/ Gumbel) and every step in the full-film zone in the cavitated area iteration (HS). Today, the mass conservation cavitation has been used to analyse cavitation events.…”

“…Additionally, the effect of boundary slip and surface texturing was also studied, for example [8,16,19,20,[43][44][45][46][47][48], but ignoring the cavitation effect and mostly using a non-mass-conservation cavitation equation. In the present work, it will be shown that cavitation has a strong influence on performance and unrealistic conclusions may be drawn if the cavitation is ignored.…”