Couette Dominance Used for Non-Newtonian Elastohydrodynamic Lubrication

1994 ◽  
Vol 116 (1) ◽  
pp. 47-55 ◽  
Author(s):  
C. M. Myllerup ◽  
A. A. Elsharkawy ◽  
B. J. Hamrock
Keyword(s):  
Newtonian Fluid ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Shear Strain Rate ◽  
High Shear Stress ◽  
Line Contacts ◽  
Stress Boundary Conditions ◽  
Stress Boundary ◽  
Good Agreement ◽  
Low Shear

The perturbational approach that assumes Couette dominance in non-Newtonian elastohydrodynamic lubrication analysis is discussed. The assumption is found valid for non-Newtonian fluid models exhibiting Newtonian properties at low shear strain rate. A general non-Newtonian fluid model which meets that requirement is incorporated into elastohydrodynamic lubrication analysis of line contacts by using the perturbational approach. In the case of a circular fluid model the results obtained from the perturbational approach are in good agreement with those obtained from the direct approach. However, a better convergence and the possibility of avoiding using stress boundary conditions at high shear stress can be achieved by using the perturbational approach. Results are presented for various values of the shape exponent in the general model, and it transpires that this also is an important parameter of the fluid model.

A Complete Solution for Thermal-Elastohydrodynamic Lubrication of Line Contacts Using Circular Non-Newtonian Fluid Model

1992 ◽  
Vol 114 (3) ◽  
pp. 540-551 ◽  
Author(s):  
Hsing-Sen S. Hsiao ◽  
Bernard J. Hamrock
Keyword(s):  
Boundary Conditions ◽  
Newtonian Fluid ◽  
Energy Equation ◽  
Control Volume ◽  
Fluid Model ◽  
Complete Solution ◽  
Circular Model ◽  
Line Contacts ◽  
Stress Boundary Conditions ◽  
Stress Boundary

A complete solution is obtained for elastohydrodynamically lubricated conjunctions in line contacts considering the effects of temperature and the non-Newtonian characteristics of lubricants with limiting shear strength. The complete fast approach is used to solve the thermal Reynolds equation by using the complete circular non-Newtonian fluid model and considering both velocity and stress boundary conditions. The reason and the occasion to incorporate stress boundary conditions for the circular model are discussed. A conservative form of the energy equation is developed by using the finite control volume approach. Analytical solutions for solid surface temperatures that consider two-dimensional heat flow within the solids are used. A straightforward finite difference method, successive over-relaxation by lines, is employed to solve the energy equation. Results of thermal effects on film shape, pressure profile, streamlines, and friction coefficient are presented.

A Circular Non-Newtonian Fluid Model: Part II—Used in Microelastohydrodynamic Lubrication

1990 ◽  
Vol 112 (3) ◽  
pp. 497-505 ◽  
Author(s):  
Rong-Tsong Lee ◽  
B. J. Hamrock
Keyword(s):  
Newtonian Fluid ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Hertzian Contact ◽  
Surface Irregularity ◽  
Good Prediction ◽  
Moving Surface ◽  
Stationary Surface ◽  
Lubrication Performance ◽  
Line Contacts

A circular non-Newtonian fluid model and system approach is used in this paper to study the effect of a stationary surface irregularity where the film shape has been modified in the conjunctions of line contacts. A modified transient Reynolds equation is developed in this paper and is used to study the effect of a moving surface irregularity in the problem of microelastohydrodynamic lubrication. Lubrication performance factors such as pressure and film profiles were studied for both a stationary and a moving surface irregularity in a lubricated conjunction. The shear stress and traction coefficient for various height of the surface irregularity were also studied for a stationary surface irregularity. Results show that the film shape obtained from full-film elastohydrodynamic lubrication theory still gave a good prediction except when the surface irregularity occurred at inlet (Xp = − 1.0), but it failed to explain the high pressure and film fluctuations around the surface irregularity which was in the Hertzian contact zone. A bump or a groove occurring in the outlet around (Xp = 1.0) significantly affected the location of the outlet boundary, and the depth of the nip film thickness in the outlet caused by the surface irregularity profoundly affected the pressure spike for both a stationary and a moving surface irregularity.

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.

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.

Sign in / Sign up

Export Citation Format

Share Document