scholarly journals Starved Lubrication of Elliptical EHD Contacts

2004 ◽  
Vol 126 (1) ◽  
pp. 105-111 ◽  
Author(s):  
B. Damiens ◽  
C. H. Venner ◽  
P. M. E. Cann ◽  
A. A. Lubrecht
Keyword(s):  
Numerical Model ◽  
Film Thickness ◽  
Numerical Simulations ◽  
Excellent Agreement ◽  
Experimental Approach ◽  
Operating Conditions ◽  
Inlet Region ◽  
Inlet Length ◽  
Thickness Measurements ◽  
Circular Contact

This paper focuses on the lubrication behavior of starved elliptical Elasto-HydroDynamic (EHD) contacts. Starvation is governed by the amount of lubricant available in the inlet region and can result in much thinner films than occurring under fully flooded conditions. Therefore, it would be desirable to be able to predict the onset and severity of starvation and to be able to relate film reduction directly to the operating conditions and lubricant properties. The aim of this work is to explore the influence of these parameters on starvation. A combined modeling and experimental approach has been employed. The numerical model has been developed from an earlier circular contact study [1]. In this model, the amount and distribution of the lubricant in the inlet region determines the onset of starvation and predicts the film decay in the contact. Numerical simulations for a uniform layer on the surface show that a single parameter, characteristic of the inlet length of the contact in the fully flooded regime, determines the starved behavior. Film thickness measurements under starved conditions were performed to validate this theory. For a circular contact excellent agreement was found. In theory the same mechanism applies to elliptic contacts, however, the behavior is more complicated.

scholarly journals A Quantitative Determination of Minimum Film Thickness in Elastohydrodynamic Circular Contacts

2021 ◽  
Author(s):  
Wassim Habchi ◽  
Philippe Vergne
Keyword(s):  
Experimental Data ◽  
Finite Element ◽  
Numerical Model ◽  
Film Thickness ◽  
Quantitative Determination ◽  
Excellent Agreement ◽  
Operating Conditions ◽  
Pure Rolling ◽  
Minimum Film Thickness

Abstract The current work presents a quantitative approach for the prediction of minimum film thickness in elastohydrodynamic lubricated (EHL) circular contacts. In contrast to central film thickness, minimum film thickness can be hard to accurately measure, and it is usually poorly estimated by classical analytical film thickness formulae. For this, an advanced finite-element-based numerical model is used to quantify variations of the central-to-minimum film thickness ratio with operating conditions, under isothermal Newtonian pure-rolling conditions. An ensuing analytical expression is then derived and compared to classical film thickness formulae and to more recent similar expressions. The comparisons confirmed the inability of the former to predict the minimum film thickness, and the limitations of the latter, which tend to overestimate the ratio of central-to-minimum film thickness. The proposed approach is validated against numerical results as well as experimental data from the literature, revealing an excellent agreement with both. This framework can be used to predict minimum film thickness in circular elastohydrodynamic contacts from knowledge of central film thickness, which can be either accurately measured or rather well estimated using classical film thickness formulae.

Paper 3: Lubrication of Rollers with Oils Containing Polymers

1966 ◽  
Vol 181 (15) ◽  
pp. 192-199
Author(s):  
G. M. Hamilton ◽  
W. G. Robertson
Keyword(s):  
Film Thickness ◽  
Polymer Solutions ◽  
Shear Stresses ◽  
Oil Viscosity ◽  
Base Oil ◽  
Oil Film ◽  
Mineral Oils ◽  
Inlet Region ◽  
Thickness Measurements

The shear stresses in an elastohydrodynamic oil film have been calculated. In the inlet region they are of the order of 107 and in the outlet 109 dyn/cm2. While such stresses do not affect mineral oils they are liable to cause breakdown of polymers in multigrade oils. To test this film thickness measurements were carried out in a four-disc machine with a range of polymer solutions. It was found that the degree of viscosity loss varied greatly; some polymer solutions showed no loss whilst others merely exhibited their base oil viscosity. By measuring the viscosity of samples scraped from the disc surfaces it was possible to divide the observed viscosity loss into permanent and temporary components.

A strategy for wear analysis using numerical and experimental tools, applied to orbital type hydraulic motors

2015 ◽  
Vol 230 (12) ◽  
pp. 2086-2097 ◽  
Author(s):  
J Furustig ◽  
A Almqvist ◽  
L Pelcastre ◽  
CA Bates ◽  
P Ennemark ◽  
...  
Keyword(s):  
Numerical Model ◽  
Numerical Simulations ◽  
Lubricant Film ◽  
Operating Conditions ◽  
Wear Depth ◽  
Hydraulic Motor ◽  
K Value ◽  
Wear Analysis ◽  
Depth Analysis ◽  
Hydraulic Motors

An accurate and reliable wear analysis requires detailed knowledge of the tribological conditions of the studied system. In this work, a numerical model which can quantify wear and is applicable to hydraulic motors is developed. Detailed tribological knowledge can be acquired through strategic experimental testing and numerical simulations. The model is constructed to include the effect on wear from varying lubricant film thickness. The development of the wear model includes consideration of wear observed in the Scanning Electron Microscopy (SEM) analysis of tested motors. The model is of the Archard type, in which the k-value is estimated from experiments, after considering the effect of lubrication. The contact pressure is the solution to a lubrication model that governs both the hydrodynamics of the lubricant film and the direct contact between the rough surfaces. To validate the model, a hydraulic motor is run at different operating conditions and the apparent wear depth is analysed after the tests. Numerical simulations mimicking the same configuration are performed and the predicted wear depths are compared to the experimental results. Similarities and differences are discussed and it is evident that a clear correlation exists between the wear predicted with the model and the measurement data of the apparent wear in the hydraulic motor. There are also discrepancies because of the model simplicity and the uncertainty in the specifications of the tested system. The results imply that wear analysis using numerical simulations aid the understanding of wear in machinery. The combined knowledge of physical conditions on different important scales enables in-depth analysis with numerical tools which cannot be achieved through experimental investigations alone. Furthermore, the numerical model can be refined leading to better wear predictions.

Capacitive Film Thickness Measurements in a Ventless Aero-Engine Bearing Chamber—Influence of Operating Conditions and Offtake Design

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Wolfram Kurz ◽  
Klaus Dullenkopf ◽  
Hans-Jörg Bauer
Keyword(s):  
Film Thickness ◽  
Thickness Distribution ◽  
Operating Conditions ◽  
Chamber Pressure ◽  
Shaft Speed ◽  
Suitable Parameter ◽  
Accuracy And Repeatability ◽  
Thickness Measurements ◽  
Engine Bearing

The paper presents results from film thickness measurements in a bearing chamber test rig. The measurements were performed at different operating conditions and with two offtake designs. A discussion of the measurement technique using in situ calibrated capacitive sensors shows good accuracy and repeatability. The film thickness results are first compared to measurements with the same chamber in a vented configuration. The analysis of the measurements at various operating conditions shows a strong influence of the shaft speed, the chamber pressure, and the offtake design. In contrast to that, flow rate and scavenge ratio have only minor influence. Furthermore, the momentum flux of the core air flow is proposed as a suitable parameter with which the influence of shaft speed and pressure can be correlated to the film thickness distribution.

Capacitive Film Thickness Measurements in a Ventless Aero-Engine Bearing Chamber: Influence of Operating Conditions and Offtake Design

2013 ◽  
Author(s):  
Wolfram Kurz ◽  
Klaus Dullenkopf ◽  
Hans-Jörg Bauer
Keyword(s):  
Film Thickness ◽  
Thickness Distribution ◽  
Operating Conditions ◽  
Chamber Pressure ◽  
Shaft Speed ◽  
Suitable Parameter ◽  
Accuracy And Repeatability ◽  
Thickness Measurements ◽  
Engine Bearing

The paper presents results from film thickness measurements in a bearing chamber test rig. The measurements were performed at different operating conditions and with two offtake designs. A discussion of the measurement technique using in-situ calibrated capacitive sensors shows good accuracy and repeatability. The film thickness results are first compared to measurements with the same chamber in a vented configuration. The analysis of the measurements at various operating conditions shows a strong influence of the shaft speed, the chamber pressure, and the offtake design. In contrast to that, flow rate and scavenge ratio have only minor influence. Furthermore, the momentum flux of the core air flow is proposed as a suitable parameter with which the influence of shaft speed and pressure can be correlated to the film thickness distribution.

A Numerical Solution of the Elastohydrodynamic Film Thickness in an Elliptical Contact

1970 ◽  
Vol 92 (1) ◽  
pp. 155-161 ◽  
Author(s):  
H. S. Cheng
Keyword(s):  
Film Thickness ◽  
Numerical Solution ◽  
Reynolds Equation ◽  
Contact Theory ◽  
Line Contact ◽  
Hertz Theory ◽  
Inlet Region ◽  
Elliptical Contact ◽  
Elastohydrodynamic Film Thickness ◽  
Circular Contact

A numerical solution of the elastohydrodynamic film thickness in an elliptical contact is developed. The two-dimensional Reynolds’ equation in the inlet region is solved by a finite-difference method. The deformation contour in the inlet region is calculated according to the classical Hertz theory for elliptical contacts. Results are presented as side leakage film reduction factors, which are defined as the ratios of the film thickness of the finite contact to that calculated by a line contact theory based on the same maximum Hertz stress. The results obtained for a b/a → ∞, which corresponds to a line contact, and for b/a = 1, which corresponds to a circular contact, agree with those obtained in [2]. Comparison with experimental data [1] indicates that this theory predicts a film thickness slightly higher than those measured by the experiment.

A New Tire Model to Predict Vibration Emission of Counterbalance Trucks

2000 ◽  
Vol 28 (2) ◽  
pp. 119-137 ◽  
Author(s):  
P. Lemerle ◽  
P. Mistrot
Keyword(s):  
Numerical Model ◽  
Numerical Simulations ◽  
Close Agreement ◽  
Industrial Sector ◽  
Tire Model ◽  
Suspension Systems ◽  
Truck Tires ◽  
Pneumatic Tires

Abstract Counterbalance trucks are machines in widespread use in every industrial sector. Unlike cars, they are not designed with suspension systems. Consequently, they are considered to be high vibrating vehicles. Nevertheless, like suspension seats, tires can be selected as suspension parts. This paper presents a new numerical model for the analysis of the vibratory behavior of counterbalance truck tires. This model was intended to be a part of a fork lift truck model, including axles, chassis, and cabin. All the results reported here show a close agreement between measurements and numerical simulations. Thus, it can predict the vibration emission values at the driving position and is used to compare the efficiency of solid tires with pneumatic tires in terms of transmitted vibration levels.

scholarly journals Experimental performance comparison between circular and elliptical tubes in evaporative condensers

2021 ◽  
Author(s):  
Giuseppe Starace ◽  
Lorenzo Falcicchia ◽  
Pierpaolo Panico ◽  
Maria Fiorentino ◽  
Gianpiero Colangelo
Keyword(s):  
Heat Transfer ◽  
Experimental Approach ◽  
Fluid Dynamic ◽  
Major Axis ◽  
Performance Comparison ◽  
Operating Conditions ◽  
Condensation Temperature ◽  
Air Cooled Condensers ◽  
Reduced Scale ◽  
Dynamic Phenomena

AbstractIn refrigeration systems, evaporative condensers have two main advantages compared to other condensation heat exchangers: They operate at lower condensation temperature than traditional air-cooled condensers and require a lower quantity of water and pumping power compared to evaporative towers. The heat and mass transfer that occur on tube batteries are difficult to study. The aim of this work is to apply an experimental approach to investigate the performance of an evaporative condenser on a reduced scale by means of a test bench, consisting of a transparent duct with a rectangular test section in which electric heaters, inside elliptical pipes (major axis 32 mm, minor axis 23 mm), simulate the presence of the refrigerant during condensation. By keeping the water conditions fixed and constant, the operating conditions of the air and the inclination of the heat transfer geometry were varied, and this allowed to carry out a sensitivity analysis, depending on some of the main parameters that influence the thermo-fluid dynamic phenomena, as well as a performance comparison. The results showed that the heat transfer increases with the tube surface exposed directly to the air as a result of the increase in their inclination, that has been varied in the range 0–20°. For the investigated conditions, the average increase, resulting by the inclination, is 28%.

The behaviour of heavily loaded line contacts with transverse roughness

1999 ◽  
Vol 213 (4) ◽  
pp. 309-320 ◽  
Author(s):  
C. J. Hooke
Keyword(s):  
Surface Roughness ◽  
Full Range ◽  
Numerical Results ◽  
Operating Conditions ◽  
Entrainment Velocity ◽  
Original Surface ◽  
Line Contacts ◽  
Transverse Roughness ◽  
Inlet Length

In heavily loaded, piezoviscous contacts the surface roughness tends to be flattened inside the conjunction by any relative sliding of the surfaces. However, before it is flattened, the roughness affects the inlet to the contact, producing clearance variations there. These variations are then convected through the contact, at the entrainment velocity, producing a clearance distribution that differs from the original surface. The present paper explores this behaviour and establishes how the amplitude of the convected clearance varies with wavelength and operating conditions. It is shown that the primary influence is the ratio of the wavelength to the inlet length of the conjunction. Where this ratio is large, the roughness is smoothed and there is little variation in clearance under the conjunction. Where the ratio is small, significant variations in clearance may occur but the precise amplitude and phasing depend on the ratio of slide to roll velocities and on the value of a piezoviscous parameter, c. The numerical results agree closely with existing solutions but extend these to cover the full range of operating conditions.

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