Hydrodynamic Lubrication of Face Seal in a Turbulent Flow Regime

1996 ◽  
Vol 118 (3) ◽  
pp. 589-600 ◽  
Author(s):  
Jen Fin Lin ◽  
Chih Chung Yao
Keyword(s):  
Porous Material ◽  
Film Thickness ◽  
Hydrodynamic Lubrication ◽  
Normal Load ◽  
Mixed Lubrication ◽  
Turbulent Regime ◽  
Face Seal ◽  
Hydrodynamic Load ◽  
Asperity Height ◽  
The Mean

Models for thermohydrodynamic lubrication in the turbulent regime are developed for a mechanical end face seal with various combinations of asperity height and roughness pattern. A surface wear model, based on deformation, is established for mixed lubrication such that the displacement is at most equal to the mean asperity height. Only normal load is involved in the solution of asperity deformation, and the mean film thickness is determined based on a total volume conservation hypothesis, in conjunction with an elastic-exponential hardening model. The singularity problem, present in the expected form of the Reynolds equation for a seal surface with circumferentially-oriented roughness grain sphere grooves, is avoided by viewing the seal roughness as porous material, thereby introducing roughness permeability. Flow permeability is thus obtained by combining Darcy’s law for porous material with the average flow model developed by Patir and Cheng for mixed lubrication. The hydrodynamic pressure and thereby the hydrodynamic load support are relatively higher from a seal with radially-oriented roughness. Both the mean film thickness and the hydrodynamic load support are substantially elevated by increasing the composite rms roughness, raising the inlet-flow pressure, and decreasing the rotational speed. Good agreement has been obtained from the comparison between the results herein and Lebeck’s experimental results.

Hydrodynamic Lubrication and Wear in Wavy Contacting Face Seals

1978 ◽  
Vol 100 (1) ◽  
pp. 81-90 ◽  
Author(s):  
A. O. Lebeck ◽  
J. L. Teale ◽  
R. E. Pierce
Keyword(s):  
Surface Roughness ◽  
Hydrodynamic Lubrication ◽  
Surface Profile ◽  
Operating Conditions ◽  
Face Seal ◽  
Hydrodynamic Load ◽  
Surface Waviness ◽  
Wear Rates ◽  
Elastic Deflection ◽  
Face Seals

A model of face seal lubrication is proposed and developed. Hydrodynamic lubrication for rough surfaces, surface waviness, asperity load support, elastic deflection, and wear are considered in the model. Predictions of the ratio of hydrodynamic load support to asperity load support are made for a face seal sealing a low viscosity liquid where some contact does occur and surface roughness is important. The hydrodynamic lubrication is caused by circumferential surface waviness on the seal faces. Waviness is caused by initial out of flatness or any of the various distortions that occur on seal ring faces in operation. The equilibrium solution to the problem yields one dimensional hydrodynamic and asperity pressure distributions, mean film thickness, elastic deflection, and friction for a given load on the seal faces. The solution is found numerically. It is shown that the fraction of hydrodynamic load support depends on many parameters including the waviness amplitude, number of waves around the seal, face width, ring stiffness, and most importantly, surface roughness. For the particular seal examined the fraction of load support would be small for the amount of waviness expected in this seal. However, if the surface roughness were lower, almost complete lift-off is possible. The results of the analysis show why the initial friction and wear rates in mechanical face seals may vary widely; the fraction of hydrodynamic load support depends on the roughness and waviness which are not necessarily controlled. Finally, it is shown how such initial waviness effects disappear as the surface profile is altered by wear. This may take a long or short time, depending on the initial amount of hydrodynamic load support, but unless complete liftoff is achieved under all operating conditions, the effects of initial waviness will vanish in time for steady state conditions. Practical implications are drawn for selecting some seal parameters to enhance initial hydrodynamic load support without causing significant leakage.

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

2005 ◽  
Vol 219 (4) ◽  
pp. 285-290 ◽  
Author(s):  
C. H. Venner
Keyword(s):  
Steady State ◽  
Film Thickness ◽  
Reynolds Equation ◽  
Hydrodynamic Lubrication ◽  
Mixed Lubrication ◽  
Validity Of Results ◽  
Erroneous Conclusion ◽  
Low Speeds ◽  
Lubrication Models ◽  
Circular Contact

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.

A Method for Determining the Non-Gaussian Probability Density Functions of Asperity Heights for Two Contact Surface Conditions

2007 ◽  
Author(s):  
Jeng Luen Liou ◽  
Jen Fin Lin
Keyword(s):  
Probability Density ◽  
Contact Surface ◽  
Elastic Recovery ◽  
Normal Load ◽  
Plasticity Index ◽  
Asperity Height ◽  
Engineered Surfaces ◽  
Change In The Mean ◽  
The Mean ◽  
Non Gaussian

Most statistical contact analyses assume that asperity height distributions (g(z*)) follow a Gaussian distribution. However, engineered surfaces are frequently the non-Gaussian with a character dependent upon the material and surface state being evaluated. When two rough surfaces experience contact deformations, the original topography of the surfaces varies with different loads. Two kinds of topographies are considered in the present study. The first kind of topography is obtained during the contact of two surfaces under a normal load. The second kind of topography is obtained from a rough contact surface after the end of the elastic recovery. The g(z*) profile is quite sharp and has a large value at its peak if it is obtained from the surface contacts under a normal load. The g(z*) profile defined for a contact surface after the elastic recovery is quite close to the g(z*) profile before contact deformations occur if the plasticity index is a small value. However, the g(z*) profile for the contact surface after the end of elastic recovery is closer to the g(z*) profile shown in the contacts under a normal load if a large plasticity index is assumed. Skewness (Sk) and kurtosis (Kt), which are the parameters in the probability density function, are affected by the change in the mean separation of two contact surfaces, or the initial skewness (the initial kurtosis is fixed in this study), or the plasticity index of the rough surface are also discussed on the basis of the topography models mentioned above.

A Performance Prediction of Microgrooved Bearings Under Mixed Lubrication

2008 ◽  
Author(s):  
Katsuhiro Ashihara ◽  
Hiromu Hashimoto
Keyword(s):  
Film Thickness ◽  
Contact Pressure ◽  
Hydrodynamic Lubrication ◽  
Calculation Model ◽  
Mixed Lubrication ◽  
Severe Condition ◽  
Oil Film ◽  
Precise Prediction ◽  
Lubrication Condition ◽  
Bearing Alloy

In the designs and analysis of engine bearings for automobiles, the precise prediction of the lubrication condition in severe condition is important. In the mixed-elasto-hydrodynamic lubrication analysis, the contact between the projections of surface roughness distributed stochastically is usually considered. This paper describes a theoretical model under the mixed lubrication in the microgrooved bearing. In this modeling, it is assumed that the section shape of microgrooved bearing alloy takes the circular arc form. In the part where contact is caused, the contact pressure is calculated by the Hertzian equation. The elastic deformation of the bearing by the mixed pressure with which oil film pressure and contact pressure are mixed by each allotment ratio is considered. Moreover, the balance requirement between the sum total of mixed pressure on bearing surface and the journal load is met. Under such an assumption, the numerical calculation model is newly obtained to predict the bearing performance in the mixed lubrication of microgrooved bearing. The numeric solutions of EHL based on the mixed lubrication are compared with EHL based on the fluid lubrication. The predicted oil film thickness at the center of bearing by the mixed lubrication model is remarkably thin compared with that by the fluid lubrication model. This shows that the load ability of the oil film thickness decreases by generating contact.

Calculations of the Meniscus Force and the Contact Force Formed in the Microcontacts of a Rough Surface and a Smooth, Rigid Surface with a Thin Water Film

2008 ◽  
Vol 24 (1) ◽  
pp. 1-11 ◽  
Author(s):  
J. F. Lin ◽  
S. C. Chen
Keyword(s):  
Relative Humidity ◽  
Film Thickness ◽  
Rough Surface ◽  
Present Model ◽  
Normal Load ◽  
Water Film ◽  
Meniscus Force ◽  
The Mean ◽  
Thin Water Film ◽  
Meniscus Profile

ABSTRACTA present model is developed to calculate the adhesion meniscus force due to a rough surface with surface asperity in contact with a smooth, rigid flat covered by a thin water film. The original thickness of this film before surface contacts is dependent upon the relative humidity in the air. Microcontact deformations of surface asperities in the elastic, elastoplastic, and fully plastic regimes are included in the present model under a normal load. The new water film thickness under the condition of microcontact deformations is considered changing with the normal load, and it is obtained from the equation developed on the basis of the volume conservation principle for the new film thickness and the water film volume displaced by the asperities heights dipping in the film. The meniscus profile is also calculated from the balance of the surface tension force and the pressure difference force across the meniscus profile if the new film thickness is available. Water film thickness and the meniscus force are increased by decreasing the mean separation of two contact surfaces, or increasing the relative humidity, or increasing the plastic index. A significant difference in the meniscus force is found between the present model and the model of the literature, which is enhanced by either decreasing the mean separation, or raising the plasticity index, or increasing the relative humidity. The effects of the meniscus force on the load capacity are also evaluated at different mean separations, relative humidity and plasticity indices.

Measurements of Friction in Cold Metal Rolling

1996 ◽  
Vol 118 (3) ◽  
pp. 629-636 ◽  
Author(s):  
P. E. Tabary ◽  
M. P. F. Sutcliffe ◽  
F. Porral ◽  
P. Deneuville
Keyword(s):  
Film Thickness ◽  
Hydrodynamic Lubrication ◽  
Strip Thickness ◽  
Secondary Importance ◽  
Smooth Film ◽  
The Mean ◽  
Cold Metal ◽  
Aluminium Strip ◽  
Additive Molecule

Measurements of friction in rolling of aluminium strip on an experimental mill are described. Friction depended most strongly on the ratio Λ of the smooth film thickness to the combined roughness of the roll and strip, and on the reduction in strip thickness. Whether the greater roughness was on the roll or on the strip was found to be unimportant. Varying the oil temperature from 40 to 60°C was also found to be of secondary importance. Profilometry results suggested that friction was determined by the mean film thickness between the surfaces. At the slowest speeds and smallest films, friction was close to the value of 0.09 found in separate measurements in a disk machine of the boundary additive properties. At the highest speed the friction values, which were less than 0.01, could be explained by hydrodynamic lubrication. The transition between these two extremes occurred when the film thickness was of the order of the additive molecule length of 3 nm.

Profile Design for Misaligned Journal Bearings Subjected to Transient Mixed Lubrication

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Thomas Gu ◽  
Q. Jane Wang ◽  
Shangwu Xiong ◽  
Zhong Liu ◽  
Arup Gangopadhyay ◽  
...  
Keyword(s):  
Film Thickness ◽  
Performance Metrics ◽  
Journal Bearing ◽  
Hydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Industrial Applications ◽  
Mixed Lubrication ◽  
Asperity Contact ◽  
Minimum Film Thickness ◽  
Profile Design

Misalignment between the shaft and the bearing of a journal bearing set may be inevitable and can negatively impact journal bearing performance metrics in many industrial applications. This work proposes a convex profile design of the journal surface to help counteract the negative effects caused by such a misalignment. A transient mass-conserving hydrodynamic Reynolds equation model with the Patir–Cheng flow factors and the Greenwood–Tripp pressure–gap relationship is developed to conduct the design and analysis. The results reveal that under transient impulse loading, a properly designed journal profile can help enhance the minimum film thickness, reduce mean and peak bearing frictions, and increase bearing durability by reducing the asperity-related wear load. The mechanism for the minimum film thickness improvement due to the profile design is traced to the more even distribution of the hydrodynamic pressure toward the axial center of the bearing. The reason for the reductions of the friction and wear load is identified to be the decreased asperity contact by changing the lubrication regime from mixed lubrication to nearly hydrodynamic lubrication. Parametric studies and a case study are reported to highlight the key points of the profile design and recommendations for profile height selection are made according to misalignment parameters.

scholarly journals Homogenization in Hydrodynamic Lubrication: Microscopic Regimes and Re-Entrant Textures

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
İ. N. Yıldıran ◽  
İ. Temizer ◽  
B. Çetin
Keyword(s):  
Film Thickness ◽  
Theoretical Study ◽  
Hydrodynamic Lubrication ◽  
Type Equation ◽  
Homogenization Theory ◽  
Review Of The Literature ◽  
Comprehensive Review ◽  
New Models ◽  
The Mean

The form of the Reynolds-type equation which governs the macroscopic mechanics of hydrodynamic lubrication interfaces with a microscopic texture is well-accepted. The central role of the ratio of the mean film thickness to the texture period in determining the flow factor tensors that appear in this equation had been highlighted in a pioneering theoretical study through a rigorous two-scale derivation (Bayada and Chambat, 1988, “New Models in the Theory of the Hydrodynamic Lubrication of Rough Surfaces,” ASME J. Tribol., 110, pp. 402–407). However, the resulting homogenization theory still remains to be numerically investigated. For this purpose, after a comprehensive review of the literature, three microscopic regimes of lubrication will be outlined, and the transition between these three regimes for different texture types will be extensively demonstrated. In addition to conventional textures, representative re-entrant textures will also be addressed.

Boundary Lubrication of Materials

MRS Bulletin ◽  
1991 ◽  
Vol 16 (10) ◽  
pp. 54-58 ◽  
Author(s):  
Stephen M. Hsu
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Boundary Lubrication ◽  
Hydrodynamic Lubrication ◽  
Close Contact ◽  
Normal Load ◽  
Fluid Film ◽  
Dominant Factor ◽  
Surface Contact ◽  
Fluid Film Thickness

Lubrication may be defined as any method used to achieve control of friction and wear of interacting surfaces in relative motion under load. Gases, liquids, and solids have been used successfully as lubricants. To prevent surface contact, liquids and gases provide a film under hydrodynamic pressure to support the load.When the load is high and/or the speed is low, the hydrodynamic or hydrostatic pressure may not be sufficient and the surfaces come into close contact. The amount and the extent of the surface contact depends on many factors: surface roughness, fluid film pressure, normal load, hardness of the materials, etc. When the surfaces come into close contact, many of the asperities undergo elastic deformation. The condition is generally referred to as elasto-hydrodynamic lubrication (EHL). EHL theories are well-developed. They describe and predict the surface temperatures, fluid film thickness, and hydrodynamic pressures. Contact pressure increases beyond the EHL conditions causes asperities to deform plastically and thinning of the fluid film. When the average fluid film thickness falls below the average surface roughness, the interaction between the contacting surfaces becomes the dominant factor in supporting the load.This condition is referred to as the boundary lubrication (BL) regime. Theories for BL are not well-developed and the detailed processes are not understood. The classical view of boundary lubrication postulates the formation of a surface chemical film which is easily sheared and protects the surface.

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