Thermohydrodynamic Analysis of Surface Roughness in the Flow Field

2005 ◽  
Vol 127 (2) ◽  
pp. 293-301
Author(s):  
Joon Hyun Kim ◽  
Joo-Hyun Kim
Keyword(s):  
Surface Roughness ◽  
Flow Field ◽  
Film Thickness ◽  
Shear Zone ◽  
Rough Surfaces ◽  
Hydrodynamic Pressure ◽  
Computational Procedure ◽  
Fluid Films ◽  
Lubricating Film ◽  
Fluid Film Thickness

The study deals with the development of a thermohydrodynamic (THD) computational procedure for evaluating the pressure, temperature, and velocity distributions in fluid films with a very rough geometry. A parametric investigation is performed to predict the bearing behaviors in the lubricating film with the absorbed layers and their interfaces as determined by rough surfaces with Gaussian distribution. The layers are expressed as functions of the standard deviations of each surface to characterize flow patterns between both rough surfaces. Velocity variations and heat generation are assumed to occur in the central (shear) zone with the same bearing length and width. The coupled effect of the surface roughness and shear zone dependency on the hydrodynamic pressure and temperature has been found in the noncontact mode. The procedure confirms the numerically determined relationship between the pressure and film gap, provided that its roughness magnitude is smaller than the fluid film thickness.

scholarly journals Hydrodynamic lubrication of rough surfaces

1982 ◽  
Vol 383 (1785) ◽  
pp. 439-446 ◽  
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Reynolds Equation ◽  
Hydrodynamic Lubrication ◽  
Rough Surfaces ◽  
Homogenization Method ◽  
Squeeze Film ◽  
Spatial Average

Using the two-space homogenization method we derive an averaged Reynolds equation that is correct to O (< H 6 > — < H 3 > 2 ), where H is the total film thickness and the angle brackets denote a spatial average. Applications of this mean Reynolds equation to a squeeze-film bearing with a sinusoidal or an isotropic surface roughness are discussed.

Comparison of tribological performance of roller follower and flat follower under mixed elastohydrodynamic lubrication regime

2016 ◽  
Vol 231 (8) ◽  
pp. 986-996 ◽  
Author(s):  
Amir Torabi ◽  
Saleh Akbarzadeh ◽  
Mohammadreza Salimpour
Keyword(s):  
Surface Roughness ◽  
Friction Coefficient ◽  
Numerical Model ◽  
Film Thickness ◽  
Thermal Effects ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Minimum Film Thickness ◽  
Cam Follower ◽  
Key Parameter

In this study, a numerical model is developed to show the performance improvement of a cam–follower mechanism when using a roller type follower compared to the flat-faced follower. Nonconformal geometry besides the thermal effects due to the shearing of the lubricant film results in formation of a thin film in which the asperities contribute in carrying the load. The numerical model is developed in which the geometry, load, speed, lubricant properties, and the surface roughness profile is taken as input and the film thickness and friction coefficient as a function of cam angle are predicted. The asperities are assumed to have elastic, elasto-plastic, and plastic deformation. Simulation results indicated that the thermal effects cannot be neglected. Surface roughness is also a key parameter that affects the pressure distribution, film thickness, and friction coefficient. Finally, asperity and hydrodynamic pressure is reported and the performance of the two mechanisms is compared. Roller follower has a considerable preference in terms of friction coefficient compared to flat-faced follower. The minimum film thickness, however, is slightly larger in the flat follower.

The Influence of the Roughness Parameters on the EHL Line Contact Using the Free Volume Model

2013 ◽  
Author(s):  
V. D’Agostino ◽  
V. Petrone ◽  
A. Senatore
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Free Volume ◽  
Rough Surfaces ◽  
Random Number Generator ◽  
Elastohydrodynamic Lubrication ◽  
Maximum Pressure ◽  
Line Contact ◽  
Volume Viscosity ◽  
Minimum Film Thickness

A numerical solution of elastohydrodynamic lubrication (EHL) contact between two rough surface cylinders is presented. In the theoretical approach the free-volume viscosity model is used to describe the piezo-viscous behavior of the lubricant in a Newtonian Elastohydrodynamic line contact [1,2]. Random rough surfaces with Gaussian and exponential statistics have been generated using a method outlined by Garcia and Stoll [3], where an uncorrelated distribution of surface points using a random number generator is convolved with a Gaussian filter to achieve correlation. This convolution is most efficiently performed using the discrete Fast Fourier Transform (FFT) algorithm, which in MATLAB is based on the FFTW library [4]. The maximum pressure and average film thickness are studied at different values of RMS, skewness, kurtosis, autocorrelation function and correlation length. Numerical examples show that skewness and kurtosis have a great effect on the parameters of EHD lubrication. Surface roughness, indeed, tends to reduce the minimum film thickness and it produces pressure fluctuations inside the conjunction which tend to increase the maximum stress. In this way the dynamic stress increases and tends to reduce the fatigue life of the components. It can be seen that the pressures developed in the fluid film in the case of rough surfaces fluctuate with the same frequency of the surface roughness. These pressure ripples correspond to the asperity peaks. This indicates that surface roughness causes very high local contact pressures which may lead to local thinning of the film. A significant reduction has been also observed in the minimum film thickness due to surface roughness.

scholarly journals On Fluid Inertia Effects in Infinitely Wide Foil Bearings

1970 ◽  
Vol 92 (3) ◽  
pp. 490-493 ◽  
Author(s):  
A. Eshel
Keyword(s):  
Film Thickness ◽  
Approximate Solutions ◽  
Fluid Film ◽  
Fluid Inertia ◽  
Inertia Effects ◽  
Foil Bearings ◽  
Lubricating Film ◽  
Fluid Film Thickness ◽  
Fluid Compressibility

Equations for a foil over a lubricating film in which the effects of fluid inertia are taken into account are derived. Approximate solutions showing the effect of inertia and fluid compressibility are obtained. The effect of inertia is to increase considerably the fluid-film thickness.

Surface Roughness Effects on Fluid Flow between Two Rotating Cylinders

2015 ◽  
Vol 642 ◽  
pp. 275-280
Author(s):  
Sutthinan Srirattayawong ◽  
Shian Gao
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Reynolds Equation ◽  
Surface Profile ◽  
Fluid Film ◽  
Real Surface ◽  
Contact Center ◽  
Roughness Effects ◽  
Fluid Film Thickness ◽  
Lubricant Viscosity

In general, the thin fluid film problems are explained by the classical Reynolds equation, but this approach has some limitations. To overcome them, the method of Computational Fluid Dynamics (CFD) is used in this study, as an alternative to solving the Reynolds equation. The characteristics of the two cylinders contact with real surface roughness are investigated. The CFD model has been used to simulate the behavior of the fluid flows at the conjunction between two different radius cylinders. The non-Newtonian fluid is employed to calculate the lubricant viscosity, and the thermal effect is also considered in the evaluation of the lubricant properties. The pressure distributions, the fluid film thickness and the temperature distributions are investigated. The obtained results show clearly the significance of the surface roughness on the lubricant flow at the contact center area. The fluctuated flow also affects the pressure distribution, the temperature and the lubricant viscosity in a similar pattern to the rough surface profile. The surface roughness effect will decrease when the film thickness is increased.

Linking Rigid and Flexible Multibody Systems via Thin Fluid Films Actively Controlled

2008 ◽  
Author(s):  
Edgar A. Estupinan ◽  
Ilmar F. Santos
Keyword(s):  
Film Thickness ◽  
Multibody Systems ◽  
Journal Bearing ◽  
Journal Bearings ◽  
Fluid Film ◽  
Fluid Films ◽  
Thin Fluid ◽  
Dynamically Loaded ◽  
Reaction Forces ◽  
Fluid Film Thickness

This work describes in details the steps involved within the mathematical modelling of multibody systems (rigid and flexible) interconnected via controllable thin fluid films. The dynamics of the mechanical components are described with help of multibody dynamics and finite element method. In this paper, the methodology is applied to reciprocating machines such as hermetic reciprocating compressors and internal combustion engines. In previous studies [1], it has been shown that for a light duty vehicle, the friction losses may reach until 48% of the total energy consumption of an engine and from that, almost 30% are coming from bearings and crankshaft. Therefore, considering that the dynamics of the fluid films in the journal bearings can be actively controlled by means of different types of actuators, allowing significant reduction of wear and vibrations, one of the aims of this paper is to study the feasibility of applying active lubrication to the main journal bearings of reciprocating machines. In this framework the paper gives a theoretical contribution to the combined fields of fluid-structure interaction and active vibration control. The hydrodynamic pressure distribution for an active lubricated finite journal bearing dynamically loaded can be calculated by numerically solving the modified Reynold’s equation [2], by means of finite-difference method and integrated over the pressure area in order to obtain the dynamic reaction forces among components. These forces are strongly nonlinear and dependent on the relative kinematics of the system. From the point of view of active lubrication and specifically considered the case of a dynamically loaded journal bearing, the injection pressure should be controlled in the time domain. However, taking into account that the pressures and reaction forces in a reciprocating machine have a cyclic behaviour, the fluid film thickness of the main bearings may be modified by controlling the oil pressure injection, depending on the crank angle and the load bearing condition. It can be mentioned that the pressure and flow may be controlled by mechanical cam systems, piezoelectric nozzles [3] [4] or servovalves [5] [6], therefore, an adequate control strategy has to be defined. The fluid film forces are coupled to the set of nonlinear equations that describes the dynamics of the mechanical system. Such a set of equations is numerically solved giving some insights into the following parameters: a) maximum fluid film pressure, b) minimum fluid film thickness, c) maximum vibration levels and d) viscous frictional forces. The behaviour of such parameters is investigated when the system operate with conventional hydro-dynamic lubrication, passive hybrid lubrication and controlled hybrid lubrication.

Dynamic lubrication analysis for a spherical pump

2018 ◽  
Vol 233 (1) ◽  
pp. 18-29 ◽  
Author(s):  
Dong Guan ◽  
Li Jing ◽  
Harry H Hilton ◽  
Junjie Gong
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Applied Load ◽  
Sine Wave ◽  
Fluid Film ◽  
Radial Clearance ◽  
Wave Loads ◽  
Lubrication Performance ◽  
Fluid Film Thickness ◽  
Lubricant Viscosity

Dynamic lubrication analyses for a spherical pump, consisting of a piston and cylinder, are presented. Contact forces between piston and cylinder are modeled first using an equivalent ball-on-plane model. Both the effects of external loads and operating conditions are considered in a dynamic elastohydrodynamic lubrication model, which is derived from Reynolds equation. Two assumed time-dependent sine-wave and square-wave loads are applied to the model. Fluid film thicknesses are estimated using the model and assumed loads, effects of different structural, and operational parameters, such as piston diameter, radial clearance, applied load, piston speed, lubricant viscosity, and surface roughness, on fluid film thickness are investigated. Fluid film thickness reactions of more realistic smooth and continuous sine wave loads are compared to discontinuous ones in order to verify whether or not assumed ideal loads are acceptable and reliable. Results indicate that piston diameter, speed, lubricant viscosity have positive relations on the dynamic lubrication performance, and increasing these values can improve the dynamic lubrication regime. While the parameters such as radial clearance, applied load, and surface roughness have the verse effects. Furthermore, the impacts of all the above parameters on fluid film are different either. These obtained results can be used to effectively optimize spherical pump lubrication performance.

Elastohydrodynamic Lubrication of Rough Surfaces Under Oscillatory Line Contact With Non-Newtonian Lubricant

2007 ◽  
Author(s):  
Mongkol Mongkolwongrojn ◽  
Khanittha Wongseedakaew ◽  
Francis E. Kennedy
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Power Law ◽  
Reynolds Equation ◽  
Initial Conditions ◽  
Rough Surfaces ◽  
Elastohydrodynamic Lubrication ◽  
Oscillatory Motion ◽  
Line Contact ◽  
Minimum Film Thickness

This paper presents the analysis of elastohydrodynamic lubrication (EHL) of two parallel cylinders in line contact with non-Newtonian fluids under oscillatory motion. The effects of transverse harmonic surface roughness are also investigated in the numerical simulation. The time-dependent Reynolds equation uses a power law model for viscosity. The simultaneous system of modified Reynolds equation and elasticity equation with initial conditions was solved using multi-grid multi-level method with full approximation technique. Film thickness and pressure profiles were determined for smooth and rough surfaces in the oscillatory EHL conjunctions, and the film thickness predictions were verified experimentally. For an increase in the applied load on the cylinders, the minimum film thickness calculated numerically becomes smaller. The predicted film thickness is slightly higher than the film thickness obtained experimentally, owing to cavitation that occurred in the experiments. For both hard and soft EHL contacts, the minimum film thickness under oscillatory motion is very thin near the trailing edge of the contact, especially for stiffer surfaces. The surface roughness and power law index of the non-Newtonian lubricant both have significant effects on the film thickness and pressure profile between the cylinders under oscillatory motion.

Thermohydrodynamic Lubrication Analysis Incorporating Thermal Expansion Across the Film

1994 ◽  
Vol 116 (4) ◽  
pp. 681-688 ◽  
Author(s):  
Nen-Zi Wang ◽  
Ali A. Seireg
Keyword(s):  
Thermal Expansion ◽  
Heat Generation ◽  
Central Zone ◽  
Computational Procedure ◽  
Computational Domain ◽  
Fluid Films ◽  
Pressure Profiles ◽  
Fluid Film Thickness ◽  
Experimental Findings ◽  
Peak Pressures

The study reported in this paper deals with the development of a thermohydrodynamic computational procedure for evaluating the pressure, temperature and velocity distributions in fluid films with fixed geometry between the stationary and moving bearing surfaces. The velocity variations and the heat generation are assumed to occur in a central zone with the same length and width as the bearing but with a significantly smaller thickness than the fluid film thickness. The thickness of the heat generation (shear) zone is developed empirically for the best fit with experimentally determined peak pressures for a journal bearing with a fixed film geometry operating in the laminar regime. A transient thermohydrodynamic computational model with a transformed rectangular computational domain is utilized. The analysis can be readily applied to any given film geometry. The computed distribution of the pressure in the film is in excellent agreement with the experimental findings for different oils and speeds. The developed procedure gives an analytical basis for explaining the “Fogy effect” where significant pressures can be generated in slider bearings with parallel surfaces as a result of the thermal expansion of the film in the direction of the thickness. The procedure confirms the experimentally determined square root relationship between the pressure and the sliding velocity reported in references [1–4]. The normalized pressure profiles computed for the different conditions of the journal bearings are identical to those obtained by isoviscous theory.

Elastohydrodynamic Line-Contact of Compressible Shear Thinning Fluids With Consideration of the Surface Roughness

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
J. Y. Jang ◽  
M. M. Khonsari
Keyword(s):  
Surface Roughness ◽  
Total Pressure ◽  
Reynolds Equation ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Shear Thinning ◽  
Line Contact ◽  
Lubricating Film ◽  
Shear Thinning Fluids ◽  
Modified Reynolds Equation

Applications involving highly loaded elastohydrodynamic lubrication (EHL), particularly when the lubricant experiences shear thinning, operating with small film thicknesses may necessitate consideration of surface asperities. A modified Reynolds equation with provision for surface roughness and shear thinning is treated to predict the pressure and surface asperity effect in an EHL line-contact. The unknown in the Reynolds equation is the hydrodynamic pressure instead of the total pressure to ensure that the pressure boundary condition at the outlet is properly posed. The Carreau viscosity model is used for characterizing the shear thinning behavior, Patir and Cheng flow factors for taking into the influence of roughness on the lubricating film, and Greenwood–Trip for determination of pressure at the asperity level. The modified Reynolds equation is solved for the hydrodynamic pressure instead of the total pressure with appropriately defined boundary conditions.

Sign in / Sign up

Export Citation Format

Share Document