Film Collapse in EHL and Micro-EHL

1991 ◽  
Vol 113 (2) ◽  
pp. 372-377 ◽  
Author(s):  
Jinn-an Shieh ◽  
Bernard J. Hamrock
Keyword(s):  
Film Thickness ◽  
Stagnation Point ◽  
Newtonian Fluid ◽  
Fluid Model ◽  
Surface Irregularity ◽  
Operating Parameters ◽  
Stationary Surface ◽  
Surface Irregularities ◽  
Film Collapse

The pressure, film thickness, and streamline patterns within the lubrication conjunction in elastohydrodynamic and microelastohydrodynamic lubrication are presented for various operating parameters. The circular non-Newtonian fluid model was used and periodic stationary surface irregularities were considered. Results obtained from different operating parameters are compared to illustrate the reason why film collapses occur in EHL and micro-EHL problems. Effects of speed, slide-roll ratio, and surface irregularity were studied in establishing when film collapse is more likely to occur. The occurrence of vortices and the location of the stagnation point within the conjunction are shown for the operating parameters considered.

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.

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.

Numerical simulation of blood nanofluid flow over three different geometries by means of gyrotactic microorganisms: Applications to the flow in a circulatory system

2020 ◽  
pp. 095440622094745 ◽  
Author(s):  
H Thameem Basha ◽  
R Sivaraj
Keyword(s):  
Blood Flow ◽  
Stagnation Point ◽  
Newtonian Fluid ◽  
Fluid Transport ◽  
Fluid Model ◽  
Circulatory System ◽  
Blood Flow Rate ◽  
Fluid Models ◽  
Gyrotactic Microorganisms ◽  
Tangent Hyperbolic Fluid

Biomedical engineers, medical scientists, and clinicians are expressing a notable interest in the measurement of blood flow rate because it is used to detect cardiovascular diseases such as atherosclerosis and arrhythmia. Several researchers have adopted various non-Newtonian fluid models to investigate blood flow in the circulatory system. Because many non-Newtonian fluid models like Herschel Buckley, Powell-Eyring fluid, tangent hyperbolic fluid, and Williamson fluid exhibit the characteristics of blood. The tangent hyperbolic fluid model expresses the rheological characteristics of blood more accurately due to its shear-thinner properties. This work is performed to express the significance of the induced magnetic field and gyrotactic microorganisms on the flow of tangent hyperbolic nanofluid over a plate, wedge and stagnation point of the plate. Suitable self-similarity variables are employed to convert the fluid transport equations into ordinary differential equations which have been solved with the use of the Runge-Kutta-Fehlberg (RKF) approach. The impacts of active parameters on transport properties of the fluid are illustrated with graphs and tables. The growing magnetic parameter lessens the blood nanofluid velocity over three geometries. Blood nanofluid has a higher heat transfer rate over a stagnation point compared with other two geometries. Blood nanofluid temperature augments for uplifting the thermophoresis parameter. Peclet number shows a high impact on microorganisms density in a blood nanofluid. This exploration can provide a clear view regarding the heat and mass transfer behavior of blood flow in a circulatory system and various hyperthermia treatments like treatment of cancer.

SURFACE IRREGULARITIES AS A COMPLEX SIGNAL OF TOOL REPRESENTATION TOGETHER WITH UNEVEN DISPLACEMENT IN RESPECT TO THE WORKPIECE

2014 ◽  
Vol 21 (1) ◽  
pp. 133-144 ◽  
Author(s):  
Adam Boryczko ◽  
Wojciech Rytlewski
Keyword(s):  
Machining Process ◽  
Surface Irregularity ◽  
Complex Signal ◽  
Complex Phenomenon ◽  
Tool Profile ◽  
Surface Irregularities ◽  
The Individual ◽  
Frequency Functions

Abstract In a dynamic machining process, distortion in surface irregularity is a very complex phenomenon. Surface irregularities form a periodic representation of the tool profile with various kinds of disturbance in a broad range of changes in the height and length of the profile. To discern these irregularity disturbances, interactions of the tool in the form of changes perpendicular and parallel relative to the workpiece were analyzed and simulated. The individual kinds of displacement of the tool relative to the workpiece introduce distortions in the changes of height and length. These changes are weakly represented in standard height and length irregularity parameters and their discernment has been found through amplitude-frequency functions.

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.

Simple Formulas for Performance Parameters Used in Elastohydrodynamically Lubricated Line Contacts

1989 ◽  
Vol 111 (2) ◽  
pp. 246-251 ◽  
Author(s):  
Ping Pan ◽  
B. J. Hamrock
Keyword(s):  
Film Thickness ◽  
Curve Fitting ◽  
Center Of Pressure ◽  
Operating Parameters ◽  
Performance Parameters ◽  
Practical Applications ◽  
Line Contacts ◽  
Pressure Spike

The film thickness and pressure in elastohydrodynamically lubricated conjunctions have been evaluated numerically for a rather complete range of operating parameters (dimensionless load, speed, and materials parameters) normally experienced in practical applications. From the film thickness and pressure throughout the conjunction a number of performance parameters were evaluated. By curve fitting the data, formulas were obtained that allow easy evaluation of the amplitude and location of the pressure spike, the minimum and central film thicknesses, the value of ρeHe, and the center of pressure.

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