Lubricant Selection for Minimum Traction in Elastohydrodynamic Lubrication Line Contacts During Accelerated Motion—A Numerical Approach

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Niraj Kumar ◽  
Punit Kumar
Keyword(s):  
Elastohydrodynamic Lubrication ◽  
Shear Thinning ◽  
Numerical Approach ◽  
Squeeze Film ◽  
Accelerated Motion ◽  
Line Contacts ◽  
Traction Coefficient ◽  
Minimum Variation ◽  
Starting Speed ◽  
Transient Thermal

Transient thermal elastohydrodynamic lubrication (EHL) line contact simulations are carried out to study the traction behavior during accelerated motion considering realistic shear-thinning behavior. Using three lubricants with different inlet viscosity and shear-thinning parameters, the application of present analysis for lubricant selection is demonstrated. Owing to squeeze film action, the film evolution is delayed, and EHL traction during acceleration is found to increase much above the designed value. This effect decreases with increasing starting speed. The most shear-thinning test oil considered here yields the lowest traction coefficient with minimum variation in its value desirable for smooth and vibration-free operation.

Traction in EHL Line Contacts Using Free-Volume Pressure-Viscosity Relationship With Thermal and Shear-Thinning Effects

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Punit Kumar ◽  
M. M. Khonsari
Keyword(s):  
Free Volume ◽  
Elastohydrodynamic Lubrication ◽  
Approximate Equation ◽  
Shear Thinning ◽  
Operating Conditions ◽  
Limiting Shear Stress ◽  
Line Contacts ◽  
Traction Coefficient ◽  
Simulation Results ◽  
Volume Equation

This paper investigates the traction behavior in heavily loaded thermo-elastohydrodynamic lubrication (EHL) line contacts using the Doolittle free-volume equation, which closely represents the experimental viscosity-pressure-temperature relationship and has recently gained attention in the field of EHL, along with Tait’s equation of state for compressibility. The well-established Carreau viscosity model has been used to describe the simple shear-thinning encountered in EHL. The simulation results have been used to develop an approximate equation for traction coefficient as a function of operating conditions and material properties. This equation successfully captures the decreasing trend with increasing slide to roll ratio caused by the thermal effect. The traction-slip characteristics are expected to be influenced by the limiting shear stress and pressure dependence of lubricant thermal conductivity, which need to be incorporated in the future.

Thermal Non-Newtonian Elastohydrodynamic Lubrication of Line Contacts Under Simple Sliding Conditions

1992 ◽  
Vol 114 (2) ◽  
pp. 317-327 ◽  
Author(s):  
Shao Wang ◽  
T. F. Conry ◽  
C. Cusano
Keyword(s):  
Film Thickness ◽  
Surface Temperature ◽  
Thermal Effects ◽  
Elastohydrodynamic Lubrication ◽  
Reduction Factor ◽  
Simple Formulation ◽  
Maximum Surface ◽  
Line Contacts ◽  
Traction Coefficient ◽  
Maximum Surface Temperature

A computationally simple formulation for the stationary surface temperature is developed to examine the thermal non-Newtonian EHD problem for line contacts under simple sliding conditions. Numerical results obtained are used to develop a formula for a thermal and non-Newtonian (Ree-Eyring) film thickness reduction factor. Results for the maximum surface temperature and traction coefficient are also presented. The thermal effects on film thickness and traction are found to be more pronounced for simple sliding than for combined sliding and rolling conditions.

Thermal and Non-Newtonian Numerical Analyses for Starved EHL Line Contacts

2005 ◽  
Vol 128 (2) ◽  
pp. 282-290 ◽  
Author(s):  
P. Yang ◽  
J. Wang ◽  
M. Kaneta
Keyword(s):  
Numerical Technique ◽  
Input Parameter ◽  
Elastohydrodynamic Lubrication ◽  
Continuity Condition ◽  
Thin Layers ◽  
Effective Thickness ◽  
Solid Surfaces ◽  
Line Contacts ◽  
Traction Coefficient ◽  
Multi Level

This paper focuses on the mechanism of starvation and the thermal and non-Newtonian behavior of starved elastohydrodynamic lubrication (EHL) in line contacts. It has been found that for a starved EHL line contact if the position of the oil-air meniscus is given as input parameter, the effective thickness of the available lubricant layers on the solid surfaces can be solved easily from the mass continuity condition, alternatively, if the later is given as input parameter, the former can also be determined easily. Numerical procedures were developed for both situations, and essentially the same solution can be obtained for the same parameters. In order to highlight the importance of the available oil layers, isothermal and Newtonian solutions were obtained first with multi-level techniques. The results show that as the inlet meniscus of the film moves far away from the contact the effective thickness of the oil layers upstream the meniscus gently reaches a certain value. This means very thin layers (around 1μm in thickness) of available lubricant films on the solid surfaces, provided the effective thickness is equal to or larger than this limitation, are enough to fill the gap downstream the meniscus and makes the contact work under a fully flooded condition. The relation between the inlet meniscus and the effective thickness of the available lubricant layers was further investigated by thermal and non-Newtonian solutions. For these solutions the lubricant was assumed to be a Ree-Eyring fluid. The pressures, film profiles and temperatures under fully flooded and starved conditions were obtained with the numerical technique developed previously. The traction coefficient of the starved contact is found to be larger than that of the fully flooded contact, the temperature in the starved EHL film, however, is found to be lower than the fully flooded contact. Some non-Newtonian results were compared with the corresponding Newtonian results.

A Quantitative Solution for the Full Shear-Thinning EHL Point Contact Problem Including Traction

2007 ◽  
Author(s):  
Yuchuan Liu ◽  
Q. Jane Wang ◽  
Scott Bair ◽  
Philippe Vergne
Keyword(s):  
Film Thickness ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Shear Thinning ◽  
High Viscosity ◽  
Viscosity Models ◽  
Pure Rolling ◽  
Volume Viscosity ◽  
Traction Coefficient ◽  
Simulation And Experiment

We present a realistic elastohydrodynamic lubrication (EHL) simulation in point contact using a Carreau-like model for the shear-thinning response and the Doolittle-Tait free-volume viscosity model for the piezoviscous response. The liquid is a high viscosity polyalphaolefin which possesses a relatively low threshold for shear-thinning. As a result, the measured EHL film thickness is about one-half of the Newtonian prediction. We derived and numerically solved the two-dimensional generalized Reynolds equation for the modified Carreau model based on Greenwood [1]. Departing from many previous solutions, the viscosity models used for the pressure and shear dependence were obtained entirely from viscometer measurements. Truly remarkable agreement is found in the comparisons of simulation and experiment for traction coefficient and for film thickness in both pure rolling and sliding cases. This agreement validates the use of a generalized Newtonian model in EHL.

The Application of Newton-Raphson Method to Thermal Elastohydrodynamic Lubrication of Line Contacts

1994 ◽  
Vol 116 (4) ◽  
pp. 733-740 ◽  
Author(s):  
R. Wolff ◽  
A. Kubo
Keyword(s):  
Film Thickness ◽  
Thermal Effects ◽  
Elastohydrodynamic Lubrication ◽  
Numerical Approach ◽  
Heavy Load ◽  
Rolling Velocity ◽  
Line Contacts ◽  
Pressure Spike ◽  
Newton Raphson ◽  
Raphson Method

The Newton-Raphson method was applied to solve the thermal EHD lubrication model of line contacts. By accounting for thermal effects in the Newton-Raphson scheme, a very stable numerical approach was obtained. Two models with viscosity constant and variable across the oil film were developed. The results under extremely heavy conditions of dimensionless load W = 52 * 10−5 (pH = 2 GPa) and dimensionless rolling velocity U = 20 * 10−11 are presented. They show that even for pure rolling, but under heavy load and high rolling velocity conditions, the thermal effects significantly reduce the minimum film thickness. The distributions of pressure, film thickness, and temperature for two rolling velocities and various loads are presented. They indicate that under high rolling velocity conditions the thermal effects have a strong influence on a pressure spike.

Elastohydrodynamic Lubrication Model With Limiting Shear Stress Behavior Considering Realistic Shear-Thinning and Piezo-Viscous Response

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Punit Kumar ◽  
Parinam Anuradha
Keyword(s):  
Shear Stress ◽  
Contact Zone ◽  
Present Model ◽  
Glassy State ◽  
Elastohydrodynamic Lubrication ◽  
Viscosity Coefficient ◽  
Shear Thinning ◽  
Limiting Shear Stress ◽  
Stress Behavior ◽  
Traction Coefficient

This paper addresses a largely ignored aspect pertaining to the elastohydrodynamic lubrication (EHL) traction behavior of fragile lubricants which undergo transition to glassy state at typical EHL contact zone pressures. For such lubricants, a conventional EHL model predicts extremely high and unrealistic values of traction coefficient, especially under near pure rolling conditions where thermal effect is negligible. Therefore, an EHL model incorporating the effect of limiting shear stress and the associated wall slip phenomenon is presented herein. Unlike the other such investigations involving limiting shear stress behavior, the present model employs Carreau-type power-law based models to describe the rheology of lubricants below the limiting shear stress along with realistic pressure-viscosity relationships (WLF and Doolittle-Tait). The use of Carreau-type shear-thinning model in this analysis allows the simultaneous prediction of minimum film thickness and traction coefficient for lubricants which shear-thin in the inlet zone and exhibit limiting shear stress behavior in the contact zone, a feature absent in the existing EHL models utilizing ideal visco-plastic or some other unrealistic rheological model. Using published experimental data pertaining to the shear-thinning and pressure-viscosity response of two fragile lubricants (L100 and LVI260), it has been demonstrated that the present model can explain the appearance of plateau in the experimental traction curve. Also, the influence of shear-thinning parameters and the pressure-viscosity coefficient on the predicted limiting shear stress zone has been studied.

Combined Effects of Shear Thinning and Viscous Heating on EHL Characteristics of Rolling/Sliding Line Contacts

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Punit Kumar ◽  
M. M. Khonsari
Keyword(s):  
Film Thickness ◽  
Thermal Effect ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Shear Thinning ◽  
Viscous Heating ◽  
Shear Thinning Fluids ◽  
Line Contacts ◽  
Power Law Index ◽  
Good Agreement

The combined influence of shear thinning and viscous heating on the behavior of film thickness and friction in elastohydrodynamic lubrication (EHL) rolling/sliding line contacts is investigated numerically. The constitutive equation put forward by Carreau is incorporated into the model to describe shear thinning. An extensive set of numerical simulations is presented. Comparison of the film thickness predictions with published experiments reveals good agreement, and it is shown that thermal effect plays an important role in the precise estimation of EHL film thickness and friction coefficient. Parametric simulations show that thermal effect in shear-thinning fluids is strongly affected by the power-law index used in the Carreau equation. Comparisons of prediction of the Newtonian fluid model are presented to quantify the degree to which it overestimates the film thickness.

Simulation of Plasto-Elastohydrodynamic Lubrication in Line Contacts of Infinite and Finite Length

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Tao He ◽  
Jiaxu Wang ◽  
Zhanjiang Wang ◽  
Dong Zhu
Keyword(s):  
Surface Roughness ◽  
Finite Length ◽  
3D Model ◽  
Three Dimensional ◽  
Elastohydrodynamic Lubrication ◽  
Axial Direction ◽  
Contact Length ◽  
Line Contact ◽  
Line Contacts ◽  
3D Surface Topography

Line contact is common in many machine components, such as various gears, roller and needle bearings, and cams and followers. Traditionally, line contact is modeled as a two-dimensional (2D) problem when the surfaces are assumed to be smooth or treated stochastically. In reality, however, surface roughness is usually three-dimensional (3D) in nature, so that a 3D model is needed when analyzing contact and lubrication deterministically. Moreover, contact length is often finite, and realistic geometry may possibly include a crowning in the axial direction and round corners or chamfers at two ends. In the present study, plasto-elastohydrodynamic lubrication (PEHL) simulations for line contacts of both infinite and finite length have been conducted, taking into account the effects of surface roughness and possible plastic deformation, with a 3D model that is needed when taking into account the realistic contact geometry and the 3D surface topography. With this newly developed PEHL model, numerical cases are analyzed in order to reveal the PEHL characteristics in different types of line contact.

Numerical and Experimental Investigations of the Transient Thermal Behavior of a Steam By-Pass Valve at Steam Temperatures Beyond 700 °C

2015 ◽  
Vol 7 (1) ◽  
Author(s):  
Anis Haj Ayed ◽  
Martin Kemper ◽  
Karsten Kusterer ◽  
Hailu Tadesse ◽  
Manfred Wirsum ◽  
...  
Keyword(s):  
Thermal Behavior ◽  
Power Plants ◽  
Numerical Approach ◽  
Life Assessment ◽  
Experimental Investigations ◽  
Steam Power ◽  
Steam Power Plants ◽  
Cyclic Operation ◽  
Measurement Results ◽  
Transient Thermal

Increasing the efficiency of steam power plants is important to reduce their CO2 emissions and can be achieved by increasing steam temperatures beyond 700 °C. Within the present study, the thermal behavior of a steam by-pass valve subject to cyclic operation with 700 °C steam is investigated experimentally and numerically. An innovative numerical approach was applied to predict the valve’s thermal behavior during cyclic operation, which is essential for fatigue life assessment of such a component. Validation of the applied numerical approach has shown good agreement with measurement results, indicating the potential of its application for the valve design process.

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