scholarly journals Effects of Gas Rarefaction on Dynamic Characteristics of Micro Spiral-Grooved Thrust Bearing

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Ren Liu ◽  
Xiao-Li Wang ◽  
Xiao-Qing Zhang
Keyword(s):  
Dynamic Characteristics ◽  
Reynolds Equation ◽  
Flow Model ◽  
Thrust Bearing ◽  
Slip Flow ◽  
Continuum Flow ◽  
Slip Flow Regime ◽  
Small Perturbation Method ◽  
Volume Method ◽  
The Continuum

The effects of gas-rarefaction on dynamic characteristics of micro spiral-grooved-thrust-bearing are studied. The Reynolds equation is modified by the first order slip model, and the corresponding perturbation equations are then obtained on the basis of the linear small perturbation method. In the converted spiral-curve-coordinates system, the finite-volume-method (FVM) is employed to discrete the surface domain of micro bearing. The results show, compared with the continuum-flow model, that under the slip-flow regime, the decrease in the pressure and stiffness become obvious with the increasing of the compressibility number. Moreover, with the decrease of the relative gas-film-thickness, the deviations of dynamic coefficients between slip-flow-model and continuum-flow-model are increasing.

Second Order Slip Flow Effects on Heat Transfer Performance of Microchannels

2009 ◽  
Author(s):  
Cem Dolu ◽  
Lu¨tfullah Kuddusi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Flow Model ◽  
Slip Flow ◽  
Second Order ◽  
Flow Models ◽  
Uniform Wall Temperature ◽  
Uniform Wall ◽  
Slip Flow Regime ◽  
Flow Effects

First and second order slip flow models in rectangular microchannels heated at constant and uniform wall temperature are studied. The velocity and temperature profiles for hydrodynamically and thermally developed incompressible slip flow regime available in literature are used. The average nondimensional slip velocity and temperature jump are found by using first and second order slip flow models. The average Nusselt number is also derived by using both first and second order slip flow models. The effects of Knudsen number, aspect ratio and second order slip flow model on the heat transfer characteristics of microchannel are explored.

scholarly journals Effect of groove texture on the dynamic characteristics of water-lubricated thrust bearing

2018 ◽  
Vol 213 ◽  
pp. 01003
Author(s):  
Huihui Feng ◽  
Liping Peng
Keyword(s):  
Dynamic Characteristics ◽  
Reynolds Equation ◽  
Thrust Bearing ◽  
Water Film ◽  
Geometrical Parameters ◽  
Damping Coefficients ◽  
Rotary Speed ◽  
Stiffness And Damping ◽  
Groove Texture ◽  
Film Lubrication

In this study, the effects of groove texture on the dynamic characteristics of water-lubricated thrust bearing are theoretically investigated. The turbulent Reynolds equation and its perturbation equations for water-film lubrication are derived and solved by using finite difference method. Dynamic characteristics including the stiffness and damping coefficients of the bearing are calculated. The effects of rotary speed, film clearance and geometrical parameters including groove texture depth and circumferential angle on the dynamic characteristics of the bearing have been investigated.

High Knudsen Number Molecular Rarefaction Effects in Gas-Lubricated Slider Bearings for Computer Flying Heads

1987 ◽  
Vol 109 (2) ◽  
pp. 276-282 ◽  
Author(s):  
Y. Mitsuya ◽  
T. Ohkubo
Keyword(s):  
Film Thickness ◽  
Reynolds Equation ◽  
Flow Model ◽  
Slip Flow ◽  
Ambient Air ◽  
Mean Free Path ◽  
Lubricating Film ◽  
Modified Reynolds Equation ◽  
Air Film ◽  
Rarefaction Effects

This paper presents a study into the gas lubrication capability of an ultra-thin 0.025 μm film (converted value for ambient air film). The experimental results obtained using subambient helium as the lubricating film are compared with the calculated results using the modified Reynolds equation considering flow slippage due to the molecular mean free path effects. This comparison confirms that the slip flow model holds true within the range of the present experiments, and that the modified Reynolds equation is applicable for designing the computer flying heads operating at such thin spacing. The reason for the excellent agreement is discussed considering the locality of rarefaction effects on the lubricating surfaces and the anisotropy of these effects between the film thickness and the slider width.

scholarly journals A Multicoefficient Slip-Corrected Reynolds Equation for Micro-Thin Film Gas Lubrication

2005 ◽  
Vol 2005 (2) ◽  
pp. 105-111 ◽  
Author(s):  
Eddie Yin-Kwee Ng ◽  
Ningyu Liu
Keyword(s):  
Slip Velocity ◽  
Reynolds Equation ◽  
Flow Model ◽  
Slip Flow ◽  
Velocity Model ◽  
Slip Model ◽  
Direct Simulation ◽  
Control Techniques ◽  
Linearized Boltzmann Equation ◽  
Quality Control Techniques

This work investigates and analyzes the performance of conventional slip models among various regimes of Knudsen number and developes a new multicoefficient slip-velocity model, by using Taguchi quality control techniques and numerical analysis. A modified Reynolds equation is also derived based on the new slip-flow model. The multicoefficient slip model and its slip-corrected Reynolds equation are suitable to a wide Knudsen range from slip to transition regime. In comparison with other conventional slip models, it is found that the current results have a better agreement with the solution obtained from the linearized Boltzmann equation and direct simulation of Monte Carlo method (DSMC).

Modified Reynolds Equation for Ultra-Thin Film Gas Lubrication Using 1.5-Order Slip-Flow Model and Considering Surface Accommodation Coefficient

1993 ◽  
Vol 115 (2) ◽  
pp. 289-294 ◽  
Author(s):  
Y. Mitsuya
Keyword(s):  
Thin Film ◽  
Reynolds Equation ◽  
Flow Model ◽  
Slip Flow ◽  
Accommodation Coefficient ◽  
Second Order ◽  
Flow Models ◽  
Gas Lubrication ◽  
Modified Reynolds Equation ◽  
Ultra Thin Film

A 1.5-order modified Reynolds equation for solving the ultra-thin film gas lubrication problem is derived by using an accurate higher-order slip-flow model. This model features two key differences from the current second-order slip-flow model. One is the involvement of an accommodation coefficient for momentum. The other is that the coefficient of the second-order slip-flow term is 4/9 times smaller than that for the current model. From the physical consideration of momentum transfer, the accommodation coefficient is found to have no affect on the second-order slip-flow term. Numerical calculations using the 1.5-order modified Reynolds equation are performed. The results are compared with those obtained using three kinds of currently employed modified Reynolds equations: those employing the first- and second-order slip-flow models and those utilizing the Boltzmann equation. These comparisons confirm that the present modified Reynolds equation provides intermediate characteristics between those derived from the first- and second-order slip-flow models, and produces an approximation closer to the exact solution resulting from the Boltzmann-Reynolds equation.

Averaged Reynolds Equation Extended to Gas Lubrication Possessing Surface Roughness in the Slip Flow Regime: Approximate Method and Confirmation Experiments

1989 ◽  
Vol 111 (3) ◽  
pp. 495-503 ◽  
Author(s):  
Y. Mitsuya ◽  
T. Ohkubo ◽  
H. Ota
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Approximate Method ◽  
Flow Regime ◽  
Reynolds Equation ◽  
Slip Flow ◽  
Roughness Effects ◽  
Gas Lubrication ◽  
Slip Flow Regime ◽  
Average Film Thickness

The average film thickness theory is extended to gas lubrication possessing surface roughness in the slip flow regime. A simplified averaged Reynolds equation is derived and its applicability is confirmed through comparing with experiments. This averaging equation makes use of the mixed average film thickness defined as Havem = αHm + (1 − α)Hmˆ, where m = 1, 2 and 3; α indicates the mixing ratio; and H¯ and Hˆ denote the arithmetically and harmonically averaged film thicknesses. The experiments were performed using computer flying heads having precisely photolithography-fabricated longitudinal, transverse or checkered pattern roughnesses under submicron spacing conditions. From the excellent agreement obtained between the calculated and experimental results, it can be concluded that the assumption that velocity slippage occurs along the surface even if roughnes is present is justified, and that the approximate method is applicable for determining the surface roughness effects in the slip flow regime.

A compressible flow model for the air-rotor–stator dynamics of a high-speed, squeeze-film thrust bearing

2010 ◽  
Vol 655 ◽  
pp. 446-471 ◽  
Author(s):  
J. E. GARRATT ◽  
K. A. CLIFFE ◽  
S. HIBBERD ◽  
H. POWER
Keyword(s):  
Compressible Flow ◽  
High Speed ◽  
Reynolds Equation ◽  
Flow Model ◽  
Thrust Bearing ◽  
Finite Amplitude ◽  
Squeeze Film ◽  
Axial Position ◽  
Rotor Support ◽  
Rotor Stiffness

A compressible air-flow model is introduced for the thin film dynamics of a highly rotating squeeze-film thrust bearing. The lubrication approximation to the Navier–Stokes equations for compressible flow leads to a modified Reynolds equation incorporating additional rotation effects. To investigate the dynamics of the system, the axial position of the bearing stator is prescribed by a finite-amplitude periodic forcing. The dynamics of the squeeze-film are modelled in the uncoupled configuration where the axial position of the rotor is fixed. The coupled squeeze-film bearing dynamics are investigated when the axial position of the rotor is modelled as a spring-mass-damper system that responds to the film dynamics. Initially the uncoupled squeeze-film dynamics are considered at low operating speeds with the classical Reynolds equation for compressible flow. The limited value of the linearized small-amplitude results is identified. Analytical results indicate that finite-amplitude forcing needs to be considered to gain a complete understanding of the dynamics. Using a Fourier spectral collocation numerical scheme, the periodic bearing force is investigated as a nonlinear function of the frequency and amplitude of the stator forcing. High-speed bearing operation is modelled using the modified Reynolds equation. A steady-state analysis is used to identify the effect of rotation and the rotor support properties in the coupled air-flow–structure model. The unsteady coupled dynamics are computed numerically to determine how the rotor support structures and the periodic stator forcing influence the system dynamics. The potential for resonant rotor behaviour is identified through asymptotic and Fourier analysis of the rotor motion for small-amplitude, low-frequency oscillations in the stator position for key values of the rotor stiffness. Through the use of arclength continuation, the existence of resonant behaviour is identified numerically for a range of operating speeds and forcing frequencies. Changes in the minimum rotor–stator clearance are presented as a function of the rotor stiffness to demonstrate the appearance of resonance.

Sign in / Sign up

Export Citation Format

Share Document