Modelling the hydrodynamic support of cylinder bore and piston rings with laser textured surfaces

This paper investigates the effects of differential scheme and mesh density on elastohydrodynamic lubrication (EHL) film thickness based on a full numerical solution with a semi-system approach. The solution variation with different schemes and mesh sizes is revealed based on a set of numerical cases in a wide range of central film thickness from several hundred nanometers down to a few nanometers. It is observed that when the film is thick, the effects of differential schemes and mesh density are not significant. However, if the film becomes ultra-thin, e.g., below 10‐20 nanometers, the influence of mesh density and differential schemes becomes more significant, and a proper dense mesh and differential scheme may be highly desirable. The present study also indicates that the solutions from the 1st-order backward scheme give the largest film thickness among all the solutions from different schemes at the same mesh size. DOI: 10.1115/1.2194916

Effects of Differential Scheme and Mesh Density on EHL Film Thickness in Point Contacts

It is now 60 years since Ertel produced the first solution to the elastohydrodynamic lubrication (EHL) problem. There has been enormous progress since then, both in numerical modelling and in experimental research on EHL. The moving, rough surface EHL problem can now be solved on laptop-level computers, while maps of film thickness, pressure and temperature can be obtained experimentally from within rolling/sliding contacts. However, there remain some important questions that have not been fully resolved. One of the most contentious is how to describe the rheological properties of lubricants under the very severe conditions present in thin film EHL contacts. A second is how to model mixed lubricated contact, where the fluid film can break down at asperity conjunctions. But perhaps the greatest challenge to researchers in EHL is to produce useful design equations for predicting the performance of machine components operating in EHL and thereby ensure that EHL theory becomes an integral part of the design process. Copyright © 2006 John Wiley & Sons, Ltd.

Sixty years of EHL

The lubrication mechanism of concentrated polymer brushes (CPBs) exhibiting ultralow frictional property was investigated. The frictional force and hence the frictional coefficient μ between CPBs of polystyrene (PS) were measured as a function of shear velocity υ and degree of swelling. The degree of swelling was precisely controlled by varying the composition of solvent , which consisted of a mixture of toluene (good solvent for PS) and 2-propanol (nonsolvent for PS), from the brush highly stretched state (toluene rich) to glassy state (2-propanol rich). The μ data of the mixtures revealed two lubrication mechanisms, i.e., boundary and hydrodynamic lubrication. Boundary lubrication with μ values less dependent on shear velocity was observed both in ultralow (μ on the order of 10–4) and high frictional (μ on the order of 0.1) regimes. On the other hand, hydrodynamic lubrication was well described by the relation μ = β·υα with α having an almost constant value of ca. 0.7. It was found that parameter β depe...

Lubrication Mechanism of Concentrated Polymer Brushes in Solvents: Effect of Solvent Quality and Thereby Swelling State

Effect of surface roughness parameters on mixed lubrication characteristics

This paper presents a transient thermal model for mixed lubrication problems in point contacts. The model deterministically calculates pressure and surface temperature by simultaneously solving a system of equations that govern the lubrication, contact and thermal behaviors of a point contact interface. The pressure distribution on the entire computation domain is obtained through solving a unified Reynolds equation system without identifying hydrodynamic or asperity contact regions. The point heat source integration method is applied to determine the temperature distributions on contact surfaces. The interactions between pressure and temperature are considered through incorporating viscosity-temperature and density-temperature relations in the Reynolds equation, then solving the equation system iteratively. With the successful implementation of an FFT-based algorithm (DC-FFT) for calculation of surface deformation and temperature rise, the numerical analysis of lubricated contact problems, which used to involve a great deal of computation, can be performed in acceptable time. The model enables us to simulate various lubrication conditions, from full film elastohydrodynamic lubrication (EHL) to boundary lubrication, for a better understanding of the effect of surface roughness. Numerical examples are analyzed and the results show that the present model can be used to predict pressure and surface temperature over a wide range of lubrication conditions, and that the solution methods are computationally efficient and robust.

A Computer Thermal Model of Mixed Lubrication in Point Contacts

Deterministic solutions and thermal analysis for mixed lubrication in point contacts

A numerical analysis of stiffness and damping coefficients for gas film face seals in three degrees of freedom is presented in this paper. By applying small perturbation approximation, the steady and perturbed Reynolds equations, taking account of both hydrodynamic and hydrostatic effects, are obtained and solved by finite element method. Several numerical samples, including externally pressurized annular thrust gas bearings and spiral groove thrust gas bearings, validate the model and numerical algorithm. The results show that the interactions between axial and angular perturbation are negligible. Hence, in the dynamic analysis of gas film face seals, the perturbation in three degrees of freedom can be simplified as two independent ones, an axial movement and an angular wobble around two orthogonal axes perpendicular to axial direction.

Numerical Analysis of Dynamic Coefficients for Gas Film Face Seals

Several spiral groove gas film face seals (SGFS) with different layouts are compared quantitatively to analyze their merits and faults and application behaviors. In addition, a parametric study on downstream mode SGFS is conducted to determine its optimal parameters under certain working conditions. In the computation of gas film pressure on the face, finite element method (FEM) is applied to adapt to complicated geometrical boundary.

Yuchuan Liu

Papers

A Computer Thermal Model of Mixed Lubrication in Point Contacts

Deterministic solutions and thermal analysis for mixed lubrication in point contacts

Numerical Analysis of Dynamic Coefficients for Gas Film Face Seals

Performance comparison and parametric study on spiral groove gas film face seals