EHL Film Thickness Computations at Low Speeds: Risk of Artificial Trends as a Result of Poor Accuracy and Implications for Mixed Lubrication Modelling

Abstract

When numerical and experimental results are compared to validate elasto-hydrodynamic lubrication (EHL) models, it is of utmost importance that grid-converged results are used. In particular at low speeds and high loads, solutions obtained using grids that are not sufficiently dense will exhibit an artificial trend that does not represent the behaviour of the continuous modelling equations. As it coincides with a trend observed in experiments this may lead to the erroneous conclusion that the theoretical model on which the numerical simulations are based is accurate. This risk is illustrated in detail. It is further shown that EHL models based on the Reynolds equation in a steady state circular contact predicts a positive film thickness as long as the grid used in the calculations is sufficiently dense. This has significant implications for the validity of results obtained using mixed lubrication models based on a Reynolds model and a film thickness threshold.

An Experimental and Theoretical Investigation of Micropiiting in Wind Turbine Gears and Bearings

“…To improve the convergence rate and reduce the computational time, Li and Kahraman [26] introduced the asymmetric integrated control volume discretization scheme, which also reduces the dependence of the solution accuracy on grid density. This dependence was shown to be a potential shortcoming of the models of [29,30] especially when the rolling speed is low [31]. With the superior robustness and numerical efficiency, the point contact mixed EHL model of [26] is employed here for the surface traction determination.…”

From Continuous to Molecular Scale in Modelling Elastohydrodynamic Lubrication: Nanoscale Surface Slip Effects on Film Thickness and Friction

“…However, recent studies focused on low viscosity fluids as lubricants [4] or on severe EHL operating conditions [5] show film thicknesses of the order of some nanometres.…”

A steady-state elastohydrodynamic lubrication model aimed at natural hip joints with physiological loading and anatomical position

“…It is well known that the accuracy of numerical simulations of EHL problems is affected by the number of discretization points, especially when considering low viscosities and/or entraining speeds that lead to thin lubricant films [44,45]. In the current analysis, numerical accuracy problems are also accentuated by the 'soft' nature of the bounding surfaces.…”