Calculation of Surface Roughness Effects on Air-Riding Seals

2002 ◽  
Author(s):  
C. Guardino ◽  
J. W. Chew ◽  
N. J. Hills
Keyword(s):  
Surface Roughness ◽  
Compressible Flows ◽  
Reynolds Equation ◽  
Incompressible Flows ◽  
Numerical Solutions ◽  
Cfd Analysis ◽  
Roughness Effects ◽  
Stationary Wall ◽  
Comparative Results ◽  
Effect Of Surface

The effects of surface roughness on air-riding seals are investigated here using the Rayleigh-pad as an example. Both incompressible and compressible flows are considered using both CFD analysis and analytical/numerical solutions of the Reynolds equation for various 2D or 3D roughness patterns on the stationary wall. A ‘unit-based’ approach for incompressible flows has also been employed and is shown to be computationally much less expensive than the full-geometry solution. Results are presented showing the effect of surface roughness on the net lift force. The effects of varying the Reynolds number are demonstrated, as well as comparative results for static stiffness.

Calculation of Surface Roughness Effects on Air-Riding Seals

2004 ◽  
Vol 126 (1) ◽  
pp. 75-82 ◽  
Author(s):  
C. Guardino ◽  
J. W. Chew ◽  
N. J. Hills
Keyword(s):  
Surface Roughness ◽  
Compressible Flows ◽  
Reynolds Equation ◽  
Incompressible Flows ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Roughness Effects ◽  
Stationary Wall ◽  
Comparative Results ◽  
Effect Of Surface

The effects of surface roughness on air-riding seals are investigated here using the Rayleigh pad as an example. Both incompressible and compressible flows are considered using both CFD analysis and analytical/numerical solutions of the Reynolds equation for various two-dimensional or three-dimensional roughness patterns on the stationary wall. A “unit-based” approach for incompressible flows has also been employed and is shown to be computationally much less expensive than the full-geometry solution. Results are presented showing the effect of surface roughness on the net lift force. The effects of varying the Reynolds number are demonstrated, as well as comparative results for static stiffness.

Surface Roughness Effects on Circular Cylinders at High Reynolds Numbers

2002 ◽  
Author(s):  
M. Eaddy ◽  
W. H. Melbourne ◽  
J. Sheridan
Keyword(s):  
Surface Roughness ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Flow Induced Vibration ◽  
Roughness Effects ◽  
Vortex Induced Vibration ◽  
Smooth Cylinder ◽  
Lift Forces ◽  
High Reynolds ◽  
Effect Of Surface

The problem of flow-induced vibration has been studied extensively. However, much of this research has focused on the smooth cylinder to gain an understanding of the mechanisms that cause vortex-induced vibration. In this paper results of an investigation of the effect of surface roughness on the cross-wind forces are presented. Measurements of the sectional RMS fluctuating lift forces and the axial correlation of the pressures for Reynolds numbers from 1 × 105 to 1.4 × 106 are given. It was found that surface roughness significantly increased the axial correlation of the pressures to similar values found at high subcritical Reynolds numbers. There was little effect of the surface roughness on the sectional lift forces. The improved correlation of the vortex shedding means rough cylinders will be subject to larger cross-wind forces and an increased possibility of vortex-induced vibration compared to smooth cylinders.

On the effects of two-dimensional Reynolds roughness in hydrodynamic lubrication

1978 ◽  
Vol 364 (1716) ◽  
pp. 89-106 ◽  
Keyword(s):  
Surface Roughness ◽  
Numerical Computation ◽  
Autocorrelation Function ◽  
Reynolds Equation ◽  
Hydrodynamic Lubrication ◽  
The Other ◽  
Roughness Height ◽  
Two Dimensional ◽  
Roughness Effects ◽  
Dimensional Surface

The hydrodynamic lubrication of rough surfaces is analysed with the Reynolds equation, whose application requires the roughness spacing to be large, and the roughness height to be small, compared with the thick­ness of the fluid film. The general two-dimensional surface roughness is considered, and results applicable to any roughness structure are obtained. It is revealed analytically that two types of term contribute to roughness effects: one depends on the shape of the autocorrelation function and the other does not. The former contribution was neglected by previous workers. The numerical computation of an example shows that these two contributions are comparable in magnitude.

Some Remarks on the Validity of Reynolds Equation in the Modeling of Lubricant Film Flows on the Surface Roughness Scale

2004 ◽  
Vol 126 (4) ◽  
pp. 703-710 ◽  
Author(s):  
T. Almqvist ◽  
R. Larsson
Keyword(s):  
Surface Roughness ◽  
Reynolds Equation ◽  
Numerical Solutions ◽  
Fluid Dynamic ◽  
Lubricant Film ◽  
Continuity Equations ◽  
Newtonian Case ◽  
Eyring Model ◽  
Wavelength Scale ◽  
Film Flows

The objective of this paper is to investigate the flow in a lubricant film on the surface roughness scale and to compare the numerical solutions obtained by two different solution approaches. This is accomplished firstly by the CFD-approach (computational fluid dynamic approach) where the momentum and continuity equations are solved separately, and secondly the Reynolds equation approach, which is a combination and a simplification of the above equations. The rheology is assumed to be both Newtonian and non-Newtonian. An Eyring model is used in the non-Newtonian case. The result shows that discrepancies between the two approaches may occur, primarily due to a singularity which appears in the momentum equations when the stresses in the lubricant attain magnitudes that are common in EHL. This singularity is not represented by the Reynolds equation. If, however, the rheology is shifted to a non-Newtonian Eyring model the deviations between the two solution approaches is removed or reduced. The second source of discrepancies between the two approaches is the film thickness to wavelength scale ω. It will be shown that the Reynolds equation is valid until this ratio is approximately O10−2.

Thermohydrodynamic Analysis of Submerged Oil Journal Bearings Considering Surface Roughness Effects

1997 ◽  
Vol 119 (1) ◽  
pp. 100-106 ◽  
Author(s):  
J. Ramesh ◽  
B. C. Majumdar ◽  
N. S. Rao
Keyword(s):  
Surface Roughness ◽  
Thermal Effects ◽  
Hydrodynamic Pressure ◽  
Height Distribution ◽  
Asperity Contact ◽  
Roughness Effects ◽  
State Behavior ◽  
Total Load ◽  
Contact Loads ◽  
Effect Of Surface

A theoretical study of a submerged oil journal bearing is made considering surface roughness and thermal effects. The total load-supporting ability under such condition is due to the thermohydrodynamic as well as the asperity contact pressure. The effect of surface roughness and viscosity-temperature dependency on hydrodynamic pressure has been found by solving the average Reynolds equation, energy equation and heat conduction equations simultaneously. The cavitation model of Jacobsson-Floberg has been modified to take the surface roughness effects into consideration. A parametric study of steady-state behavior has been carried out. Finally, the isothermal, thermohydrodynamic, and contact loads for a model bearing have been calculated, assuming the surface height distribution as Gaussian.

Surface Roughness Effects in High-Speed Hydrodynamic Journal Bearings

1997 ◽  
Vol 119 (4) ◽  
pp. 776-780 ◽  
Author(s):  
H. Hashimoto
Keyword(s):  
Surface Roughness ◽  
High Speed ◽  
Reynolds Equation ◽  
Computation Time ◽  
Experimental Results ◽  
Roughness Effects ◽  
Modified Reynolds Equation ◽  
Nonlinear Simultaneous Equations ◽  
Theoretical Results ◽  
Good Agreement

This paper describes an applicability of modified Reynolds equation considering the combined effects of turbulence and surface roughness, which was derived by Hashimoto and Wada (1989), to high-speed journal bearing analysis by comparing the theoretical results with experimental ones. In the numerical analysis of modified Reynolds equation, the nonlinear simultaneous equations for the turbulent correction coefficients are greatly simplified to save computation time with a satisfactory accuracy under the assumption that the shear flow is superior to the pressure flow in the lubricant films. The numerical results of Sommerfeld number and attitude angle are compared with the experimental results to confirm the applicability of the modified Reynolds equation in the case of two types of bearings with different relative roughness heights. Good agreement was obtained between theoretical and experimental results.

A Numerical Study of Surface Roughness Effects on Ultra-Thin Gas Films

1986 ◽  
Vol 108 (2) ◽  
pp. 171-177 ◽  
Author(s):  
J. W. White ◽  
P. E. Raad ◽  
A. H. Tabrizi ◽  
S. P. Ketkar ◽  
P. P. Prabhu
Keyword(s):  
Surface Roughness ◽  
Rough Surface ◽  
Reynolds Equation ◽  
Numerical Study ◽  
Surface Film ◽  
Maximum Load ◽  
Roughness Effects ◽  
Number Range ◽  
Pressure Diffusion ◽  
Bearing Number

A wedge bearing with transverse sinusoidal roughness pattern is studied numerically in order to predict the effect of surface roughness on compressible fluid films. A variable grid implicit finite difference scheme is used to provide steady-state solutions of the Reynolds equation over a bearing number range of five orders of magnitude. At a fixed bearing geometry and orientation, the bearing load is found to increase to a maximum as the bearing number increases, then to decrease and asymptotically approach a limiting value as the bearing number increases further. This is quite unlike the behavior of an incompressible fluid bearing. Analysis indicates that the maximum load occurs at a condition where pressure diffusion and Couette effects of the fluid film are of an equal order of magnitude. The increased emphasis of the pressure diffusion physics is due to the short length scales of the rough surfaces which “trigger” the higher derivative diffusion terms in the Reynolds equation. The criterion required for validity of an infinite bearing number solution with a rough surface is found to be much more restrictive than that of a smooth surface bearing. Last, the type of rough surface film clearance averages used in incompressible lubrication are shown to be incorrect for analysis of very thin gas films. It would appear that one application of this information would be the design of an artificially roughened surface for the take-off and landing of magnetic head sliders so as to minimize contact and wear of the magnetic media.

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.

A Study of Vibration in Caliper-Disc Brake Systems With Surface Roughness Effects: Part B — Inclusion of Surface Roughness Effects in the Equations of Motion and Results

2000 ◽  
Author(s):  
Glenn Meinhardt ◽  
Kambiz Farhang ◽  
Jamil Abdo
Keyword(s):  
Surface Roughness ◽  
Equations Of Motion ◽  
Companion Paper ◽  
Brake System ◽  
Disc Brake ◽  
Roughness Effects ◽  
Vibration Model ◽  
Nonlinear Contact ◽  
Effect Of Surface ◽  
Elastic Characteristics

Abstract Vibration of mechanical systems with friction depends on the physical characteristics of the frictional contact. The elastic characteristics are developed in a companion paper, wherein the results show the surface roughness manifested through nonlinear contact stiffnesses. This paper, the second of two companion papers, incorporates the elastic characteristics of contact between the pad surfaces and the rotor in a vibration model of an automotive caliper-disc brake system. The elastic representation of contact, in the form of polynomial functions of the relative pad/rotor displacements, are used to account for the effect of surface roughness on the vibration response of a caliper-disc brake system. The results indicate a range of frequencies due to the roughness induced stiffness nonlinearities.

Scaling Criteria for Slider Miniaturization Using the Generalized Reynolds Equation

1993 ◽  
Vol 115 (4) ◽  
pp. 566-572 ◽  
Author(s):  
R. M. Crone ◽  
P. R. Peck ◽  
M. S. Jhon ◽  
T. E. Karis
Keyword(s):  
Surface Roughness ◽  
Reynolds Equation ◽  
Normal Load ◽  
Flying Height ◽  
Magnetic Storage ◽  
Roughness Effects ◽  
Scaling Equation ◽  
Wide Range ◽  
Slider Design ◽  
Generalized Reynolds Equation

The current trend in the magnetic storage industry is the reduction of the slider size and the height at which the slider flies over a rigid disk. Lower flying heights are achieved by miniaturizing sliders and reducing the normal load. In this paper, force scaling criteria are determined for 3370 and 3370K sliders that are dynamically loaded or operated in contact start/stop mode. Two forms of the generalized Reynolds equation (the first-order and continued fraction formulations) are incorporated into the analysis. The new scaling equation relates the steady-state flying height to design and operating parameters such as the disk velocity, normal load, ambient pressure, and the shape and dimension of the slider rail. The resulting quadratic equation contains two slider design dependent parameters which are calculated from two full scale numerical solutions to the generalized Reynolds equation for the slider design of interest. The new scaling equation accurately fits numerical and experimental results over an extremely wide range of ambient pressures, normal loads, disk velocities, and slider size reduction. The utility of the scaling equation is that it can rapidly and accurately predict the load required to obtain a desired flying height at a given disk velocity for any slider geometry. The scaling analysis also has the ability to qualitatively account for surface roughness effects. The equation could be applied to the design of contact recording devices, if surface roughness effects could be quantitatively incorporated into the analysis.

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