Experimental and numerical study on cavitation under elastohydrodynamic lubrication point contact

2021 ◽  
pp. 135065012110527
Author(s):  
Mingfei Ma ◽  
Wen Wang ◽  
Wenxun Jiang
Keyword(s):  
Contact Area ◽  
Numerical Study ◽  
Ambient Pressure ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Hertzian Contact ◽  
Pressure Area ◽  
Cavitation Pressure ◽  
Experimental Researches ◽  
State 1

As a common phenomenon in elastohydrodynamic lubrication, cavitation has an effect on the completeness of the oil film in the contact area. Many studies have therefore been conducted on cavitation. Experimental researches on cavitation usually rely on optical interference observation, which offers a limited resolution and observation range. In this paper, an infrared thermal camera is used to observe the cavity bubbles on a ball-on-disc setup under sliding/rolling conditions. The results show that the cavity length increases with an increases of the entrainment speed and the viscosity of the lubricants. These observations are explained by a numerical model based on Elrod's algorithm. Effects of entrainment speed and lubricant viscosity on the breakup of cavitation bubbles and the cavitation states are investigated. Both the simulation and experimental results show that a negative pressure area is present behind the Hertzian contact area. The ambient pressure plays a role in maintaining cavitation state 1. The cavitation pressure is close to the vacuum pressure when the entrainment speed is low and to the ambient pressure instead when the entrainment speed is high.

Analysis of EHL Circular Contact Shut Down

2002 ◽  
Vol 125 (1) ◽  
pp. 76-90 ◽  
Author(s):  
Jiaxin Zhao ◽  
Farshid Sadeghi
Keyword(s):  
Steady State ◽  
Film Thickness ◽  
Contact Area ◽  
Elastohydrodynamic Lubrication ◽  
Hertzian Contact ◽  
Analytical Prediction ◽  
Transient Pressure ◽  
Mean Velocity ◽  
Thickness Change ◽  
Contact Width

In this paper, an isothermal study of the shut down process of elastohydrodynamic lubrication under a constant load is performed. The surface mean velocity is decreased linearly from the initial steady state value to zero. The details of the pressure and film thickness distributions in the contact area are discussed for the two stages of shut down process, namely the deceleration stage and the subsequent pure squeeze motion stage with zero entraining velocity. The nature of the balance between the pressure, the wedge and the squeeze terms in Reynolds equation enables an analytical prediction of the film thickness change on the symmetry line of the contact in the deceleration period, provided that the steady state central film thickness relationship with velocity is known. The results indicate that for a fixed deceleration rate, if the initial steady state surface mean velocity is large enough, the transient pressure and film thickness distributions in the deceleration period solely depend on the transient velocity. The pressure and film thickness at the end of the deceleration period are then the same and do not depend on the initial steady state velocity. From the same initial steady state velocity, larger deceleration rates provide higher central pressure increase, but also preserve a higher film thickness in the contact area at the end of the deceleration period. Later in the second stage when the axisymmetric pressure and film thickness patterns typical of pure squeeze motion form, the pressure distribution in the contact area resembles a Hertzian contact pressure profile with a higher maximum Hertzian pressure and a smaller Hertzian half contact width. As a result, the film thickness is close to a parabolic distribution in the contact area. The volume of the lubricant trapped in the contact area is then estimated using this parabolic film thickness profile.

Analysis of Microelastohydrodynamic and Mixed Lubrication Effects in Gear Tooth Contacts

2003 ◽  
Author(s):  
M. J. A. Holmes ◽  
H. P. Evans ◽  
R. W. Snidle
Keyword(s):  
Contact Area ◽  
Transient Analysis ◽  
Gear Tooth ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Contact Analysis ◽  
Line Contact ◽  
Hydrodynamic Equations ◽  
Analysis Technique ◽  
Film Thinning

The paper presents results obtained using a transient analysis technique for point contact elastohydrodynamic lubrication (EHL) problems based on a formulation that couples the elastic and hydrodynamic equations. Results are presented for transverse ground surfaces in elliptical point contact that show severe film thinning at the transverse limits of the contact area. This thinning is caused by transverse leakage of the lubricant from the contact in the remaining deep valley features. A comparison is also made between the point contact results on the entrainment centre line and the equivalent line contact analysis.

The Shear-Thinning Elastohydrodynamic Film Thickness of a Two-Component Mixture

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Yuchuan Liu ◽  
Q. Jane Wang ◽  
Ivan Krupka ◽  
Martin Hartl ◽  
Scott Bair
Keyword(s):  
Film Thickness ◽  
Ambient Pressure ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Shear Thinning ◽  
Component Mixture ◽  
Base Oil ◽  
Viscosity Models ◽  
Viscosity Behavior ◽  
Pure Rolling

Lubricant base oils are often blends of different molecular weight cuts to arrive at a specified ambient pressure viscosity and, to improve the temperature-viscosity behavior or to simply increase the viscosity, viscosity-modifying polymer additives are often added to the base oil. This paper investigates the effect of mixture rheology on elastohydrodynamic lubrication (EHL) film thickness using EHL contact measurements and a full numerical analysis for three synthetic lubricants including two single-component lubricants PAO650 and PAO100 and a mixture of these. The pressure and shear dependences of the viscosity of these lubricants were measured with high-pressure viscometers; viscosities were not adjusted to fit experiment. The point contact film thicknesses for these lubricants in pure rolling were measured using a thin-film colorimetric interferometry apparatus. Numerical simulations based on the measured rheology show very good agreement with the measurements of film thickness while the Newtonian prediction is up to twice the measurement. These results validate the use of realistic shear-thinning and pressure-viscosity models, which originate from viscosity measurements. It is conceivable that simulation may provide a means to “engineer” lubricants with the optimum balance of film thickness and friction through intelligent mixing of components.

Numerical study on the interaction of transversely oriented ridges in thermal elastohydrodynamic lubrication point contacts using the Eyring shear-thinning model

2016 ◽  
Vol 231 (1) ◽  
pp. 93-106 ◽  
Author(s):  
Jinlei Cui ◽  
Peiran Yang ◽  
Motohiro Kaneta ◽  
Ivan Krupka
Keyword(s):  
Friction Coefficient ◽  
Numerical Study ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Shear Thinning ◽  
Solid Surfaces ◽  
Point Contacts ◽  
Transient Behaviour ◽  
Contact Surfaces ◽  
Thinning Effect

Transient behaviour of tribo-characteristics caused by transversely oriented ridges on point contact surfaces was investigated based on a thermal elastohydrodynamic lubrication analysis. The ridges were assumed to exist on both the contact surfaces with different velocities. Results show that the interaction of ridges gives a large influence on the local film thickness, pressure, friction coefficient, temperatures on both the solid surfaces and temperature in the oil film. It is also pointed out that the size of the contact bodies brings strong effect on the temperature distribution and shear rate as well as on the friction coefficient. Furthermore, it is revealed that under rolling-sliding conditions, the shear-thinning property of the lubricant is negligible when the size of the contact body is large enough. However, shear-thinning effect plays an important role when the size is extremely small.

Three-Dimensional Temperature Distribution in EHD Lubrication: Part II—Point Contact and Numerical Formulation

1993 ◽  
Vol 115 (1) ◽  
pp. 36-45 ◽  
Author(s):  
Kyung-Hoon Kim ◽  
Farshid Sadeghi
Keyword(s):  
Temperature Distribution ◽  
Film Thickness ◽  
Numerical Study ◽  
Control Volume ◽  
Three Dimensional ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Lubricant Film ◽  
Numerical Formulation ◽  
Energy Equations

A numerical study of Newtonian thermal elastohydrodynamic lubrication (EHD) of rolling/sliding point contacts has been conducted. The two-dimensional Reynolds, elasticity and the three-dimensional energy equations were solved simultaneously to obtain the pressure, film thickness and temperature distribution within the lubricant film. The control volume approach was employed to discretize the differential equations and the multi-level multi-grid technique was used to simultaneously solve them. The discretized equations, as well as the nonorthogonal coordinate transformation used for the solution of the energy equation, are described. The pressure, film thickness and the temperature distributions, within the lubricant film at different loads, slip conditions and ellipticity parameters are presented.

scholarly journals Analysis of Mixed Lubrication Effects in Simulated Gear Tooth Contacts

2004 ◽  
Author(s):  
M. J. A. Holmes ◽  
H. P. Evans ◽  
R. W. Snidle
Keyword(s):  
Transient Analysis ◽  
Gear Tooth ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Hertzian Contact ◽  
Asperity Contact ◽  
Hydrodynamic Equations ◽  
Contact Rates ◽  
Analysis Technique ◽  
Film Thinning

The paper presents results obtained using a transient analysis technique for point contact elastohydrodynamic lubrication (EHL) problems based on a formulation that couples the elastic and hydrodynamic equations. Results are presented for transverse ground surfaces in elliptical point contact that show severe film thinning and asperity contact at the transverse limits of the contact area. This thinning is caused by transverse leakage of the lubricant from the contact in the remaining deep valley features between the surfaces. A comparison is also made between the point contact results on the entrainment centre line and the equivalent line contact analysis. The extent of asperity contact is shown to be dependent on the Hertzian contact aspect ratio. It is also shown that transverse waviness (superimposed on the roughness) of even relatively small amplitude can lead to large increases in asperity contact rates over all waviness peaks in the contact.

Influence of Two-Sided Surface Waviness on the EHL Behavior of Rolling/Sliding Point Contacts Under Thermal and Non-Newtonian Conditions

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Peiran Yang ◽  
Jinlei Cui ◽  
Z. M. Jin ◽  
D. Dowson
Keyword(s):  
Ambient Pressure ◽  
Elastohydrodynamic Lubrication ◽  
Hertzian Contact ◽  
Point Contacts ◽  
Surface Waviness ◽  
Time Step ◽  
Entrainment Velocity ◽  
Eyring Model ◽  
Cyclic Time ◽  
Elliptic Contact

The influence of the transversely and/or longitudinally oriented surface waviness on the lubricating behavior in the rolling/sliding elliptic contact composed of two steel bodies and lubricated with a non-Newtonian lubricant was investigated theoretically with full numerical solution of the thermal elastohydrodynamic lubrication. The entrainment velocity was assumed to be along the minor axis of the Hertzian contact ellipse. The waviness of each surface was given by a sinusoidal function. The non-Newtonian flow of the lubricant was described by the Eyring model with a constant Eyring shear stress at the ambient pressure and temperature. The velocity of the faster surface was assumed to be four times as that of the slower surface in order not only to highlight the thermal and non-Newtonian effects, but also to ensure a cyclic solution when both surfaces were with transversely oriented waviness. Starting from a quasisteady solution, the cyclic time-dependent solution was achieved numerically time step by time step. The results show that the thermal and non-Newtonian effects can be enlarged significantly by the surface waviness, and the worst configuration of the surface topography is that both surfaces are with longitudinal waviness.

scholarly journals Analysis of Mixed Lubrication Effects in Simulated Gear Tooth Contacts

2005 ◽  
Vol 127 (1) ◽  
pp. 61-69 ◽  
Author(s):  
M. J. A. Holmes ◽  
H. P. Evans ◽  
R. W. Snidle
Keyword(s):  
Transient Analysis ◽  
Gear Tooth ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Hertzian Contact ◽  
Asperity Contact ◽  
Hydrodynamic Equations ◽  
Contact Rates ◽  
Analysis Technique ◽  
Film Thinning

The paper presents results obtained using a transient analysis technique for point contact elastohydrodynamic lubrication (EHL) problems based on a formulation that couples the elastic and hydrodynamic equations. Results are presented for transverse ground surfaces in elliptical point contact that show severe film thinning and asperity contact at the transverse limits of the contact area. This thinning is caused by transverse leakage of the lubricant from the contact in the remaining deep valley features between the surfaces. A comparison is also made between the point contact results on the entrainment center line and the equivalent line contact analysis. The extent of asperity contact is shown to be dependent on the Hertzian contact aspect ratio. It is also shown that transverse waviness (superimposed on the roughness) of even relatively small amplitude can lead to large increases in asperity contact rates over all waviness peaks in the contact.

Effects of transversely oriented defects and thickener lumps on grease elastohydrodynamic lubrication films

2001 ◽  
Vol 215 (3) ◽  
pp. 279-288 ◽  
Author(s):  
M Kaneta ◽  
H Nishikawa ◽  
M Naka
Keyword(s):  
Film Thickness ◽  
Contact Area ◽  
Surface Defects ◽  
Film Formation ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Optical Interferometry ◽  
Transient Behaviour ◽  
Different Types

Using the optical interferometry technique, transient behaviour of grease films at an elastrohydrodynamic lubrication (EHL) point contact caused by a transversely oriented groove and long bump passing through the contact area is directly observed with three different types of diurea grease without additives. The effects of the thickener content on the grease film formation are also examined. It has been found that the behaviour of EHL films depends strongly on the thickener structure, and the effects of surface defects on EHL films become pronounced as the film thickness decreases. It has also been found that the thickener lumps move through the EHL conjunction while repeating attachment to the surfaces and detachment from them, and the thickener lumps deposited on the surfaces affect the film behaviour as a kind of solid bump.

Abnormal Phenomena Appearing in EHL Contacts

1996 ◽  
Vol 118 (4) ◽  
pp. 886-892 ◽  
Author(s):  
M. Kaneta ◽  
H. Nishikawa ◽  
T. Kanada ◽  
K. Matsuda
Keyword(s):  
Elastic Modulus ◽  
Contact Area ◽  
Contact Surface ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Transient Behavior ◽  
Surface Velocity ◽  
Lubricating Oil ◽  
Radius Of Curvature ◽  
Direct Observations

In a previous paper the authors showed that when the surface velocity of a body having lower elastic modulus is faster than that of a body having higher elastic modulus, and when the radius of curvature of the former is larger than that of the latter, a deep conical depression (dimple) is produced in the contact surface. This dimple occurs in place of the flat plateau predicted by the point contact elastohydrodynamic lubrication (EHL) theory. In this paper, the effects of surface kinematic conditions on the formation of such abnormal phenomena, which cannot be predicted by the present EHL theory, are investigated under rolling/sliding conditions using the optical interferometry technique. Transient behavior of the dimple caused by a groove passing through the EHL conjunction is also discussed based on direct observations. It has been found that the dimple occurs when the lubricating oil in the contact area is composed of solidified and unsolidified parts, and the dimple itself corresponds to the solidified part. On the basis of this finding, it has been asserted that the establishment of a new EHL theory is needed.

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