Exploring elastohydrodynamic lubrication using finite-volume computational modelling techniques
File(s)
Author(s)
Lee, Damon
Type
Thesis
Abstract
Elastohydrodynamic lubrication is a regime of lubrication that occurs in lubricated rolling-sliding
non-conformal contacts, such as those in rolling bearings and gears. Under EHL, the solid surfaces
are completely separated by a lubricant film that is built up through a hydrodynamic action and
the fluid pressures are sufficiency high to cause significant elastic deformation of the solids.
EHL is typically modelled using numerical solutions to some form of Reynolds equation. These
methods can be used to simulate EHL to predict variables such as friction, film thickness and
temperature rise.
The Reynolds equation is derived from the general fluid flow equations by assuming certain
gradients are negligible. In contrast, Computational Fluid Dynamics (CFD) methods can solve
the general fluid flow and heat transfer equations fully. Advantages include modelling the full
convective heat transfer effects at the contact entrance, extension of the simulation domain further
than Reynolds models and truer simulated multiphase flow.
Comparisons between the simulation methods are very limited, with only a few papers that
compare CFD solutions to a Reynolds models under conditions that show solution differences.
This project is aimed at investigating CFD simulation of EHL, chiefly in situations where the
assumptions of Reynolds derived models of EHL are tentative or incorrect by comparing Reynolds
derived EHL models to a CFD model parametrically.
In developing and using the CFD model to gain new insight into EHL the CFD model solutions
were compared with experimental results for film thickness profile at varying entrainment speeds
and slide-roll ratios (SRRs). The CFD model was also used to study the thermal effects in EHL
in relation to Archards temperature rise equation inside the contact, as well as the thermal effects
outside of the contact. Thermal solution comparisons between a thermal modified Reynolds model
and the CFD model at varying SRR (0–1.8) and dimensionless entrainment (U = 1 × 10−10–5 ×
10−10) were carried out and finally parametric comparisons between CFD predicted and literature
film thickness reduction factors were made.
Results show that at moderate conditions the solutions obtained using these two modelling
strategies are nearly identical in terms of film thickness (Thermal loading parameter below 1);
however, at high viscosity, high entrainment and high SRR, CFD solutions differ in predicted film
thickness and/or friction from Reynolds-based models due to terms neglected in the Reynolds equation derivation. In general CFD results predict higher temperature rise due to thermal convective
effects at the contact inlet.
non-conformal contacts, such as those in rolling bearings and gears. Under EHL, the solid surfaces
are completely separated by a lubricant film that is built up through a hydrodynamic action and
the fluid pressures are sufficiency high to cause significant elastic deformation of the solids.
EHL is typically modelled using numerical solutions to some form of Reynolds equation. These
methods can be used to simulate EHL to predict variables such as friction, film thickness and
temperature rise.
The Reynolds equation is derived from the general fluid flow equations by assuming certain
gradients are negligible. In contrast, Computational Fluid Dynamics (CFD) methods can solve
the general fluid flow and heat transfer equations fully. Advantages include modelling the full
convective heat transfer effects at the contact entrance, extension of the simulation domain further
than Reynolds models and truer simulated multiphase flow.
Comparisons between the simulation methods are very limited, with only a few papers that
compare CFD solutions to a Reynolds models under conditions that show solution differences.
This project is aimed at investigating CFD simulation of EHL, chiefly in situations where the
assumptions of Reynolds derived models of EHL are tentative or incorrect by comparing Reynolds
derived EHL models to a CFD model parametrically.
In developing and using the CFD model to gain new insight into EHL the CFD model solutions
were compared with experimental results for film thickness profile at varying entrainment speeds
and slide-roll ratios (SRRs). The CFD model was also used to study the thermal effects in EHL
in relation to Archards temperature rise equation inside the contact, as well as the thermal effects
outside of the contact. Thermal solution comparisons between a thermal modified Reynolds model
and the CFD model at varying SRR (0–1.8) and dimensionless entrainment (U = 1 × 10−10–5 ×
10−10) were carried out and finally parametric comparisons between CFD predicted and literature
film thickness reduction factors were made.
Results show that at moderate conditions the solutions obtained using these two modelling
strategies are nearly identical in terms of film thickness (Thermal loading parameter below 1);
however, at high viscosity, high entrainment and high SRR, CFD solutions differ in predicted film
thickness and/or friction from Reynolds-based models due to terms neglected in the Reynolds equation derivation. In general CFD results predict higher temperature rise due to thermal convective
effects at the contact inlet.
Version
Open Access
Date Issued
2018-09
Date Awarded
2019-02
Copyright Statement
Creative Commons Attribution NonCommercial Licence
Advisor
Kadiric, Amir
Dini, Daniele
Sponsor
SKF (Company)
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)