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Lubricants
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Accuracy and Reliability of Computational Modelling of Thermo-Elastohydrodynamic Lubrication
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Accuracy and Reliability of Computational Modelling of Thermo-Elastohydrodynamic Lubrication

A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: closed (31 March 2023) | Viewed by 6088

Special Issue Editor

Prof. Dr. Dieter Fauconnier

E-Mail Website
Guest Editor
Soete Laboratory, Department of Electromechanical, Systems and Metal Engineering, Ghent University, Technologiepark Zwijnaarde 46, 9052 Zwijnaarde, Belgium
Interests: thermo-elastohydrodynamic lubrication; computational fluid dynamics; computational solid mechanics; fluid–structure interactions; molecular modelling; gears; bearings

Special Issue Information

Dear Colleagues,

The rising demand for high power density, performance, and energy efficiency in modern electro-mechanical drivetrains often pushes gears, bearings, and cams to their limits in terms of power transfer, load capacity efficiency, durability, and reliability.

Adequate and efficient lubrication of these machine elements under various operating conditions is vital. A fundamental understanding of the physics of thermo-elastohydrodynamic lubrication (TEHL) in, e.g., bearings and gear contacts operating under stationary as well as transient and off-nominal operating conditions involving dynamic loading, accelerating/decelerating, and even oscillatory motion, is crucial to minimize premature failure and maximize efficiency.

Despite the advances in computational modelling and simulation of TEHL in the past few decades, it is no easy feat to achieve accurate, reliable predictions of thermo-elastohydrodynamic lubrication—often denoted as quantitative TEHL—relevant to real machine components operating under challenging, off-nominal conditions. Accurate and reliable TEHL modelling and simulation require a proper multiscale description of the complex, coupled multiphysics involved, which is often beyond the capabilities of the classic EHL approach. The final quality, i.e., accuracy and reliability, of predictions for film thickness, stresses, friction, etc., in TEHL depends on four intertwined aspects:

  1. The quality and completeness of the conservation laws to describe the (transient) lubricant flow and solid deformation of the solids (incl. surface roughness and heterogeneity), supplemented by proper boundary conditions.
  2. The quality and completeness of the thermodynamic conservation laws to describe transient heat transfer within the lubricant and the conjugate heat transfer into the solid phases, supplemented by proper boundary conditions.
  3. The quality and completeness of the constitutive models describing the thermal and mechanical material response of the lubricant as well as the solid material to the prevailing conditions of pressures, temperature, etc.
  4. The quality of the numerical techniques involving spatio-temporal discretization, algorithms, convergence, etc., for any of the above fields. 

This Special Issue aims to gather the latest research from leading international research groups working in the fields of advanced lubrication modelling, material modelling, and rheology with a focus on the achieved quality in one or more of the categories defined above. All contributions from scientists working on advanced, accurate, and reliable TEHL modelling and simulation are welcome.

Prof. Dr. Dieter Fauconnier
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Lubricants is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • thermo-elastohydrodynamic lubrication
  • advanced computational modelling
  • Reynolds equation
  • Navier–Stokes equations
  • fluid–structure interaction
  • viscous heating
  • conjugate heat transfer
  • constitutive modelling
  • molecular dynamics
  • non-Newtonian lubricants
  • high-pressure rheology
  • molecular dynamics
  • machine elements
  • gears and bearings

Published Papers (4 papers)

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Research

20 pages, 4736 KiB  
Article
Impact of Ad Hoc Post-Processing Parameters on the Lubricant Viscosity Calculated with Equilibrium Molecular Dynamics Simulations
by Gözdenur Toraman, Toon Verstraelen and Dieter Fauconnier
Lubricants 2023, 11(4), 183; https://doi.org/10.3390/lubricants11040183 - 19 Apr 2023
Cited by 1 | Viewed by 1399
Abstract
Viscosity is a crucial property of liquid lubricants, and it is theoretically a well-defined quantity in molecular dynamics (MD) simulations. However, no standardized protocol has been defined for calculating this property from equilibrium MD simulations. While best practices do exist, the actual calculation [...] Read more.
Viscosity is a crucial property of liquid lubricants, and it is theoretically a well-defined quantity in molecular dynamics (MD) simulations. However, no standardized protocol has been defined for calculating this property from equilibrium MD simulations. While best practices do exist, the actual calculation depends on several ad hoc decisions during the post-processing of the raw MD data. A common protocol for calculating the viscosity with equilibrium MD simulations is called the time decomposition method (TDM). Although the TDM attempts to standardize the viscosity calculation using the Green–Kubo method, it still relies on certain empirical rules and subjective user observations, e.g., the plateau region of the Green–Kubo integral or the integration cut-off time. It is known that the TDM works reasonably well for low-viscosity fluids, e.g., at high temperatures. However, modified heuristics have been proposed at high pressures, indicating that no single set of rules works well for all circumstances. This study examines the effect of heuristics and ad hoc decisions on the predicted viscosity of a short, branched lubricant molecule, 2,2,4-trimethylhexane. Equilibrium molecular dynamics simulations were performed at various operating conditions (high pressures and temperatures), followed by post-processing with three levels of uncertainty quantification. A new approach, “Enhanced Bootstrapping”, is introduced to assess the effects of individual ad hoc parameters on the viscosity. The results show a strong linear correlation (with a Pearson correlation coefficient of up to 36%) between the calculated viscosity and an ad hoc TDM parameter, which determines the integration cut-off time, under realistic lubrication conditions, particularly at high pressures. This study reveals that ad hoc decisions can lead to potentially misleading conclusions when the post-processing is performed ambiguously. Full article
(This article belongs to the Special Issue Accuracy and Reliability of Computational Modelling of Thermo-Elastohydrodynamic Lubrication)
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20 pages, 7077 KiB  
Article
Sensitivity of TEHL Simulations to the Use of Different Models for the Constitutive Behaviour of Lubricants
by Peyman Havaej, Joris Degroote and Dieter Fauconnier
Lubricants 2023, 11(3), 151; https://doi.org/10.3390/lubricants11030151 - 21 Mar 2023
Cited by 1 | Viewed by 1299
Abstract
This study compares the film thickness, lubricant temperature, and traction curves of two groups of commonly used constitutive models for lubricants in thermo-elastohydrodynamic lubrication (TEHL) modelling. The first group consists of the Tait equation of state, the Doolittle Newtonian viscosity model, and the [...] Read more.
This study compares the film thickness, lubricant temperature, and traction curves of two groups of commonly used constitutive models for lubricants in thermo-elastohydrodynamic lubrication (TEHL) modelling. The first group consists of the Tait equation of state, the Doolittle Newtonian viscosity model, and the Carreau shear thinning model. The second group includes the Dowson equation of state, the Roelands–Houpert Newtonian viscosity model, and the Eyring shear thinning model. The simulations were conducted using a Computational Fluid Dynamic and Fluid-Structure Interaction (CFD-FSI) approach, which employs a homogeneous equilibrium model for the flow simulation along with a linear elastic solver to describe the deformation of the solid materials. The simulations were conducted under a load range of 100 kN/m to 200 kN/m and a slide-to-roll-ratio (SRR) range between 0 and 2 using Squalane lubricant. The results show up to a 10% deviation in central film thickness, a 31% deviation in coefficient of friction (CoF), and a 38% deviation in maximum lubricant temperature when using the different constitutive models. This study highlights the sensitivity of TEHL simulation results to the choice of constitutive models for lubricants and the importance of carefully selecting the appropriate models for specific applications. Full article
(This article belongs to the Special Issue Accuracy and Reliability of Computational Modelling of Thermo-Elastohydrodynamic Lubrication)
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18 pages, 3798 KiB  
Article
Convergence of (Soft) Elastohydrodynamic Lubrication Simulations of Textured Slider Bearings
by Quentin Allen and Bart Raeymaekers
Lubricants 2023, 11(3), 92; https://doi.org/10.3390/lubricants11030092 - 21 Feb 2023
Viewed by 1500
Abstract
We study the convergence of elastohydrodynamic lubrication (EHL) simulations of textured slider bearings. EHL simulations are computationally expensive because the equations that describe the lubricant film pressure and the deformation of the bearing surfaces are coupled and, thus, must be solved simultaneously. Additional [...] Read more.
We study the convergence of elastohydrodynamic lubrication (EHL) simulations of textured slider bearings. EHL simulations are computationally expensive because the equations that describe the lubricant film pressure and the deformation of the bearing surfaces are coupled and, thus, must be solved simultaneously. Additional simulation requirements, such as maintaining a specific bearing load-carrying capacity or lubricant film thickness, further increase the computational cost because they impose additional constraints or add equations that must converge simultaneously with those that describe the lubricant film pressure and bearing surface deformation. We methodically quantify the convergence of EHL simulations of textured slider bearings as a function of simulation parameters, including different convergence metrics and criteria, but also cavitation models, texture design parameters, and bearing operating parameters. We conclude that the interplay between discretization, the convergence metric, and the convergence criterion must be carefully considered to implement numerical simulations that converge to the correct physical solution. Our analysis also illustrates that a well-designed convergence study can minimize the computational cost. Full article
(This article belongs to the Special Issue Accuracy and Reliability of Computational Modelling of Thermo-Elastohydrodynamic Lubrication)
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25 pages, 2322 KiB  
Article
Exact Model Order Reduction for the Full-System Finite Element Solution of Thermal Elastohydrodynamic Lubrication Problems
by Jad Mounayer and Wassim Habchi
Lubricants 2023, 11(2), 61; https://doi.org/10.3390/lubricants11020061 - 02 Feb 2023
Cited by 2 | Viewed by 1290
Abstract
The derivation of fast, reliable, and accurate modeling procedures for the solution of thermal elastohydrodynamic lubrication problems is a topic of significant interest in the Tribology community. In this paper, a novel model order reduction technique is introduced for the analysis of thermal [...] Read more.
The derivation of fast, reliable, and accurate modeling procedures for the solution of thermal elastohydrodynamic lubrication problems is a topic of significant interest in the Tribology community. In this paper, a novel model order reduction technique is introduced for the analysis of thermal elastohydrodynamic lubrication problems. The method uses static condensation to reduce the size of the linear elasticity part within the overall matrix system, followed by a splitting algorithm to avoid the burden of solving a semi-dense matrix system. The results reveal the exactness of the proposed methodology, which does not introduce any additional model-reduction approximations to the overall solution. They also reveal the reduction in computational times, which is in the order of 10–20% for line contacts, while it is in excess of 50% for circular contacts. The robustness of the proposed method is displayed by using it to model some relatively highly loaded contacts whose numerical solution is known to be rather challenging. Full article
(This article belongs to the Special Issue Accuracy and Reliability of Computational Modelling of Thermo-Elastohydrodynamic Lubrication)
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