A Circular Non-Newtonian Fluid Model: Part I—Used in Elastohydrodynamic Lubrication

1990 ◽  
Vol 112 (3) ◽  
pp. 486-495 ◽  
Author(s):  
Rong-Tsong Lee ◽  
B. J. Hamrock
Keyword(s):  
Shear Strength ◽  
Newtonian Fluid ◽  
Reynolds Equation ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Pressure Profile ◽  
Load Parameter ◽  
Viscosity Term ◽  
Pure Rolling ◽  
The Coefficient Of Friction

A circular non-Newtonian fluid model associated with the limiting shear strength was considered. Using this model a modified Reynolds equation was developed which is almost the same as the classical Reynolds equation except for the viscosity term. Results show that the calculation of the central and minimum film thicknesses from the classical Reynolds equation is still valid for pure rolling conditions. The effects on performance of dimensionless load parameter, dimensionless speed parameter, slide/roll ratio, different oils, the limiting shear strength proportionality constant were studied. Such parameters as the pressure profile, the film shape, the coefficient of friction, the dimensionless shear stress at surface a, and the velocitiy contour in the conjunction were considered.

scholarly journals Non-Newtonian Fluid Model Incorporated Into Elastohydrodynamic Lubrication of Rectangular Contacts

1984 ◽  
Vol 106 (2) ◽  
pp. 275-282 ◽  
Author(s):  
B. O. Jacobson ◽  
B. J. Hamrock
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Film Thickness ◽  
Numerical Solution ◽  
Newtonian Fluid ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Sliding Velocity ◽  
Minimum Film Thickness ◽  
Limiting Value

A procedure is outlined for the numerical solution of the complete elastohydrodynamic lubrication of rectangular contacts incorporating a non-Newtonian fluid model. The approach uses a Newtonian model as long as the shear stress is less than a limiting shear stress. If the shear stress exceeds the limiting value, the shear stress is set equal to the limiting value. The numerical solution requires the coupled solution of the pressure, film shape, and fluid rheology equations from the inlet to the outlet. Isothermal and no-side-leakage assumptions were imposed in the analysis. The influence of dimensionless speed U, load W, materials G, and sliding velocity U* and limiting-shear-strength proportionality constant γ on dimensionless minimum film thickness Hmin was investigated. Fourteen cases were investigated for an elastohydrodynamically lubricated rectangular contact incorporating a non-Newtonian fluid model. The influence of sliding velocity (U*) and limiting shear strength (γ) on minimum film thickness was observed to be small. Hence the film thickness equation obtained for a Newtonian fluid is sufficient for calculations considering non-Newtonian effects. Computer plots are also presented that indicate in detail pressure distribution, film shape, shear stress at the surfaces, and flow throughout the conjunction.

EHL of Coated Surfaces: Part II—Non-Newtonian Results

1994 ◽  
Vol 116 (4) ◽  
pp. 786-793 ◽  
Author(s):  
A. A. Elsharkawy ◽  
B. J. Hamrock
Keyword(s):  
Newtonian Fluid ◽  
Reynolds Equation ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Elastic Half Space ◽  
Hard Coatings ◽  
Surface Shear Stress ◽  
Coating Materials ◽  
Surface Shear ◽  
Pressure Profiles

A complete non-Newtonian elastohydrodynamic lubrication solution for multilayered elastic solids is introduced in this paper. A modified form for the Reynolds equation was derived by incorporating the circular non-Newtonian fluid model associated with a limiting shear strength directly into the momentum equations that govern the instantaneous equilibrium of a fluid element inside the lubricated conjunction. The modified Reynolds equation, the elasticity equations of multilayered elastic half-space, the lubricant pressure-viscosity equation, the lubricant pressure-density equation, and the load equilibrium equation were solved simultaneously by using the system approach. The effects of the surface coating on pressure profiles, film shapes, and surface shear stress profiles are shown. Furthermore, the effects of coating thickness on the minimum film thickness and on the coefficient of friction are presented for different coating materials. The results show that for hard coatings non-Newtonian fluid effects on the pressure profiles and film shapes are significant because of the increase in the contact pressure.

CFD Prediction of the Effects of Surface Roughness on Elastohydrodynamic Lubrication under Rolling/Sliding Conditions

2012 ◽  
Vol 184-185 ◽  
pp. 86-89 ◽  
Author(s):  
Shian Gao ◽  
Sutthinan Srirattayawong
Keyword(s):  
Surface Roughness ◽  
Shear Stress ◽  
Fluid Dynamic ◽  
Flow Behavior ◽  
Elastohydrodynamic Lubrication ◽  
Pressure Profile ◽  
Hertzian Contact ◽  
Pure Rolling ◽  
Large Fluctuations ◽  
Two Parameters

The surface roughness plays an important role in elastohydrodynamic lubrication (EHL). To improve the lubrication system the flow behavior and lubrication mechanism must be understood, especially in the thin film classification. The effects of surface roughness in the EHL problem are complicated and difficult to measure by experiment. Therefore numerical simulation using the computational fluid dynamic (CFD) approach is proposed in this research. The CFD model developed has taken the arbitrary surface roughness into consideration, and has been used to predict the characteristics of fluid flow, such as the pressure distribution, the minimal film thickness and the shear stress. The cylinder is considered to be under elastic deformation according to the theory of Hertzian contact and the surface of cylinder is defined to have an arbitrary roughness. The simulation results show that the surface roughness has significant effects on the pressure profile and shear stress, especially in the case of pure rolling, where the two parameters in the rough surface case show large fluctuations that are much higher than the corresponding smooth surface case.

Size Effect on the Behavior of Thermal Elastohydrodynamic Lubrication of Roller Pairs

2012 ◽  
Vol 134 (1) ◽  
Author(s):  
Xiaoling Liu ◽  
Jinlei Cui ◽  
Peiran Yang
Keyword(s):  
Size Effect ◽  
Newtonian Fluid ◽  
Effective Viscosity ◽  
Numerical Solutions ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Load Parameter ◽  
Performance Results ◽  
Thermal Ehl ◽  
Strong Size Effect

In order to investigate the size effect on elastohydrodynamic lubrication (EHL) of roller pairs, complete numerical solutions for both the Newtonian fluid and the Eyring fluid thermal EHL problems of roller pairs under steady state conditions have been achieved. It can be seen that there is no size effect on the isothermal EHL performance; however, there is a very strong size effect on the thermal EHL performance. Results show that the term of shearing heat is the most important factor for the film temperature when the size of a contact changes. Comparison between the Newtonian solution and the Eyring solution has been made under some operating conditions. It is interesting to see that the effective viscosity of the Eyring fluid is nearly the same as that of the Newtonian fluid when the size of a contact is large enough. The non-Newtonian effect, therefore, can be ignored when the size of a contact is very large. It is equally interesting to see that the thermal effect can be ignored when the size of a contact is very small. In addition, the influence of the velocity parameter, the load parameter, and the slide-roll ratio on the lubricating performance for various sizes of contacts has been investigated.

Modified Reynolds Equation for Non-Newtonian Fluid With Rheological Model in Frequency Domain

2005 ◽  
Vol 127 (4) ◽  
pp. 893-898 ◽  
Author(s):  
Chen Haosheng ◽  
Chen Darong
Keyword(s):  
Frequency Domain ◽  
Newtonian Fluid ◽  
Reynolds Equation ◽  
Load Capacity ◽  
Pressure Profile ◽  
Thickness Variation ◽  
Lubrication Equation ◽  
Shear Dependent Viscosity ◽  
Modified Reynolds Equation ◽  
Dependent Viscosity

The purpose of this paper is to provide a lubrication equation for non-Newtonian fluid. Three nonlinear functions instead of common power law model are used to describe non-Newtonian properties more completely. They are shear dependent viscosity, first normal stress difference and stress relaxation. After the coordinate conversion which is needed for the lubricant film thickness variation, the functions are involved in the modified Reynolds equation and show their effects on the lubrication results. As the principle factor in lubrication, viscosity is expressed by a first order transfer function in frequency domain. Its variation process is described by the function’s amplitude frequency response curve, which is validated by rheological experiment. Numerical results of the modified Reynolds equation show that non-Newtonian lubricant’s load capacity is not always higher or lower than Newtonian lubricant’s, and non-Newtonian lubricant has flatter pressure profile at high working speed.

Sign in / Sign up

Export Citation Format

Share Document