Load Capacity for Adiabatic Infinitely Wide Plane Slider Bearings in the Turbulent Thermohydrodynamic Regime

A two-dimensional Navier-Stokes-based model developed using the Legendre collocation method is used to analyze turbulent plane slider bearings with wide ranges of bearing configuration, mean Reynolds number, and a parameter characterizing the viscosity variation. The load-capacity formulations are established for turbulent isothermal and turbulent thermohydrodynamic bearings. With the equations provided in this study, designers can quickly determine the load capacity without extensive computation.     

An Original Definition of the Profile of Compliant Foil Journal Gas Bearings: Static and Dynamic Analysis

This article deals with a numerical analysis of the static and dynamic performance of a compliant journal gas bearing. The common approach found in foil bearing literature consists in calculating the carrying capacity for a given shaft position. In this study the external load is fixed (magnitude and direction) and the related shaft position is investigated. Nevertheless, a rigid profile, able to support high imposed loads, is no longer valid if one considers that the bearing becomes compliant. An original calculation method of the initial profile considering rigid surfaces is proposed to overcome this problem. The prediction of nonlinear dynamic behavior, i.e., stability and response to external excitation, is investigated. Finally, a viscous damping model is introduced into the dynamic model in order to obtain the amount of structural damping necessary to increase the stability of the compliant journal gas bearing.     

Load Capacity for Adiabatic Finite-Width Plane Slider Bearings in the Turbulent Thermohydrodynamic Regime

A Navier-Stokes based model developed using the Legendre collocation method is used to analyze turbulent plane slider bearings with wide ranges of convergence ratio, slenderness ratio, mean Reynolds number, and a parameter characterizing the viscosity variation. The load-capacity formulations are established for turbulent isothermal and turbulent thermohydrodynamic bearings. With the equations provided in this study, designers can quickly determine the load capacity without extensive computation.     

Load Capacity Estimation of Foil Air Journal Bearings for Oil-Free Turbomachinery Applications

This paper introduces a simple “Rule of Thumb” (ROT) method to estimate the load capacity of foil air journal bearings, which are self-acting compliant-surface hydrodynamic bearings being considered for Oil-Free turbomachinery applications such as gas turbine engines. The ROT is based on first principles and data available in the literature and it relates bearing load capacity to the bearing size and speed through an empirically based load capacity coefficient, D. It is shown that load capacity is a linear function of bearing surface velocity and bearing projected area. Furthermore, it was found that the load capacity coefficient, D, is related to the design features of the bearing compliant members and operating conditions (speed and ambient temperature). Early bearing designs with basic or “first generation” compliant support elements have relatively low load capacity. More advanced bearings, in which the compliance of the support structure is tailored, have load capacities up to five times those of simpler designs. The ROT enables simplified load capacity estimation for foil air journal bearings and can guide development of new Oil-Free turbomachinery systems.     

On Performance Characteristics of Three-Lobe Porous Hydrodynamic Journal Bearings

This paper presents an analysis of a three-lobe porous hydrodynamic journal bearing for its static and dynamic performance characteristics. The performance characteristics of the bearing have been computed and presented in graphical form for a wide range of permeability parameter to investigate the effect of porosity on bearing performance. The stability margin of the three-lobe journal bearing system, in terms of crtical mass of journal, has been established using Routh's criteria. The nature of transient motion of the journal has been analyzed using the complex eigen values of characteristic equation and motion trajectories obtained by numerical integration of equations of motion.     

在短径向轴承中考虑压粘效应的润滑计算

在本文中应用线性化的压粘方程对短径向轴承的润滑进行了计算,得到了油膜中压强的解析解,并以此解析解为基础,推导了承载量系数,摩擦力,功耗等公式。计算结果与一些文献中关于润滑现象的家性叙述是一致的,在本文中考虑压粘效应的公式化描述可为设计计算提供依据。     

The Performance of Heavily Loaded Oscillating Roller Bearings from 300 F to 600 F

Over 1000 roller bearings have been evaluated at elevated temperatures as oscillating bearings and load-life characteristics determined through statistical analysis of failure data. Operating temperatures of 300 F, 450 F, and 600 F were investigated. Bearing materials investigated included AISI 52100 steel, M-2 tool steel and 440-C stainless steel. Grease lubrication was used. The bearing load range included 250,000 psi to 500,000 psi maximum Hertz stress. AISI 52100 steel proved satisfactory for temperatures to 450 F. Tool steel (M-2) and 440 C stainless steel proved satisfactory for temperatures to 600 F. Although failure modes were predominantly by plastic deformation, wear and oxidation, failure distribution frequencies fit the Weibull distribution commonly used in bearing fatigue studies. Data scatter was less than that expected for continuously rotating ball bearings.     

Performance and Durability of High Temperature Foil Air Bearings for Oil-Free Turbomachinery

The performance and durability of advanced, high temperature foil air bearings are evaluated under a wide range (10 to 50 kPa) of loads at temperatures from 25° to 650 °C. The bearings are made from uncoated nickel based superalloy foils. The foil surface experiences sliding contact with the shaft during initial start/stop operation. To reduce friction and wear, the solid lubricant coating, PS304, is applied to the shaft by plasma spraying. PS304 is a NiCr based Cr₂O₃ coating with silver and barium fluoride/calcium fluoride solid lubricant additions.

The results show that the bearings provide lives well in excess of 30,000 cycles under all of the conditions tested. Several bearings exhibited lives in excess of 100,000 cycles. Wear is a linear function of the bearing load. The excellent performance measured in this study suggests that these bearings and the PS304 coating are well suited for advanced high temperature, oil-free turbomachinery applications.     

Influence of Journal Speed and Load on the Static Operating Characteristics of a Tilting-Pad Journal Bearing with Ball-and-Socket Pivots

Results are described for experiments aimed at determining the effects of increased speed and load on ball-and-socket pivots in tilting-pad journal bearings. Experimental measurements of journal static operating position were made for a 70-mm (2.75-in.), five-pad tilting-pad journal bearing with ball-and-socket pivots. Testing consisted of journal rotational speeds from 1650 to 7840 rpm and bearing static loads as high as 4.45 kN (1000 lbs). These speeds and loads were sufficient to attain a range of heat generation and pivot thermal growths. Results showed that at low speeds substantial cross-coupling effects were present. However, with increased heat generation at elevated speeds and loads, these cross-coupling effects were significantly reduced.     

Properties and Performance of Gas-Expanded Lubricants in Tilting Pad Journal Bearings

Lubricants enable proper function and reduce friction in rotating machinery, but they can also contribute to power loss and heat buildup. Gas-expanded lubricants (GELs) have been proposed as tunable mixtures of lubricant and CO₂ under pressure with properties such as viscosity that can be controlled directly in response to changing environmental or rotordynamic conditions. In this work, experimental results of GEL viscosity, gas diffusivity, and thermal conductivity were combined with high-pressure phase equilibrium data to understand how these mixtures will behave in tilting pad journal bearings under a range of industry-relevant high-speed conditions. Simulations were carried out using the experimental data as inputs to a thermoelastohydrodynamic model of tilting pad journal bearing performance. Viscosity could be easily tuned by controlling the composition of the GEL and the effect on bearing efficiency was appreciable, with 14–46% improvements in power loss. This trend held for a range of lubricant chemistries with polyalkylene glycols, polyalpha olefins, and a polyol ester tested in this work. Diffusivity, which drives how readily CO₂ and lubricants form homogenous mixtures, was found to be a function of the viscosity of the synthetic lubricant, with more viscous lubricants having a lower diffusivity than less viscous formulations. Model results for a bearing in a pressurized housing suggested that cavitation would be minimal for a range of speed conditions. Other bearing parameters, such as eccentricity, temperature, and minimum film thickness were relatively unchanged between conventionally lubricated and GEL-lubricated bearings, suggesting that the efficiency improvements could be achieved with few performance tradeoffs.     

Performance Characteristics of Worn Journal Bearings in Both Laminar and Turbulent Regimes. Part II: Dynamic Characteristics

The effects of geometric change due to wear on the dynamic characteristics of journal bearings are determined theoretically in both laminar and turbulent regimes. The dynamic characteristics such as spring and damping coefficients and whirl onset speed of a rigid rotor supported by two identical symmetrically aligned bearings are analyzed by a semianalytical finite element method, and the numerical results for various wear depth parameters are indicated in graphical form.

The geometric change due to wear has significant effects on the principal spring coefficients and on the cross-coupled damping coefficients. The whirl onset speed for a worn journal bearing whose wear depth parameter is larger than 0.3 becomes higher than the speed for a nonworn bearing.     

气体静压径向轴承气膜流场及承载特性分析

研究偏心率及不同供气压强条件下,气体静压径向轴承节流孔附近的气膜流场特性及承载力变化情况,并通过优化节流孔张角,提高轴承承载力.建立气体静压径向轴承三维模型,划分网格并确立模型的边界条件,采用Fluent软件对轴承内部气膜流场进行仿真计算.计算结果表明,气体静压径向轴承偏心率的增加,会导致区域气膜的压力差增大,从而提高...     

Analysis of Journal Bearing with Double-Layer Porous Lubricant Film: Influence of Surface Porous Layer Configuration

This article presents an analysis of a long journal bearing with a double-layer porous lubricant film using couple stress and Newtonian fluids. The porous layer with infinite permeability analyzed in this study simulates the surface layer. The Brinkman model was utilized to model the flow in the porous region. The effects of couple stresses were analyzed based on Stokes microcontinuum theory. A double-layer porous lubricant film configuration, with a low-permeability porous layer on top of a high-permeability bearing adherent porous layer, improved the journal bearing performance characteristics. A surface porous layered lubricant film configuration increased the load-carrying capacity and reduced the coefficient of friction in a journal bearing.     

热膨胀对自密封滑动轴承润滑液泄漏的影响分析

本文以支承HDD主轴的自密封滑动轴承为对象,通过一个简化模型研究了因热膨胀导致的润滑液泄漏问题。分析表明,轴承的存油空间（包括间隙、油孔、油槽等）的容积膨胀率αT与润滑液的体膨胀系数αoil不匹配是造成温度变化时润滑液泄漏的重要原因。为减少泄漏,一方面应选用低膨胀液体作为润滑剂,另一方面应通过轴承设计以控制存油空间的膨胀率。控制αT的措施包括：（1）以线膨胀系数不同的材料制作滑动轴承摩擦副的不同零件（如轴套和外圈）;（2）根据轴承尺寸及材料、润滑液类型确定适当的轴承间隙比;（3）尽可能减少不油孔、油槽等除轴承间隙之外的存油空间。     

Effects of Excitation Frequency and Orbit Magnitude on the Dynamic Characteristics of a Highly Preloaded Three-Lobe Journal Bearing

The independent effects of excitation frequency and excitation magnitude on experimentally derived bearing coefficients for a highly preloaded three-lobe journal bearing were studied. The effect of excitation frequency was determined by applying external dynamic forces at half-synchronous, synchronous, and twice synchronous frequencies with respect to the operating speed. Effect of excitation magnitude was independently determined by applying either three or four different amplitudes of excitation force to the bearing resulting in orbit sizes ranging up to 30% of clearance. Applying static forces to the bearing housing controlled the Sommerfeld number, and thus, the static operating position. Data was reduced as linear dynamic coefficients, and presented relative to excitation frequency and excitation magnitude over a range of Sommerfeld numbers from 0.2 to 3.0 and operating eccentricities from 0.3 to 0.9. In general, neither excitation frequency nor excitation magnitude was shown to have a measurable effect over the ranges studied.     

The Effects of Lubricant Rheology on the Performance of Journal Bearings

Experiments have been carried out on a relatively simple journal bearing rig to test the theory that extra load-carrying capacity is generated the elasticity of viscoelastic lubricants. Model lubricants were used. The viscoelastic lubricants were solutions of high-molecular-weight polyisobutene in low-molecular-weight polyisobutene while the inelastic lubricant was low-molecular-weight polyisobutene.

The extra load-carrying capacity has been established. An analysis of the detailed results strongly indicates that the extra benefit of elasticity is much greater than that predicted by existing theory.     

Static Performance of Finite Hydrodynamic Journal Bearings Lubricated by Magnetic Fluids with Couple Stresses

Based upon the Stokes micro-continuum theory, the problem of lubrication of finite hydrodynamic journal bearing lubricated by magnetic fluids with couple stresses is investigated. By taking into account the couple stresses due to the microstructure additives and the magnetic effects due to the magnetization of the magnetic fluid, modified Reynolds equation is obtained. The effects of couple stresses are studied by defining the couple stress parameter L that can be considered as a measure of the chain length of the additive molecule. The magnetic effects of the magnetic fluid are investigated by the magnetic coefficient γ. Using the finite-difference technique and for different values of couple stress parameter and magnetic coefficient, the Reynolds equation is solved, and pressure distributions are obtained. The bearing static characteristics namely load carrying capacity, attitude angle, friction coefficient, and side leakage flow are determined. The results indicate that the influence of couple stresses and magnetic effects on the bearing characteristics are significantly apparent. It is concluded that fluids with couple stresses are better than Newtonian fluids. The improvement of the bearing characteristics is enhanced if the magnetic effects are present.     

Performance Characteristics of Worn Journal Bearings in Both Laminar and Turbulent Regimes. Part I: Steady-State Characteristics

The effects of geometric change due to wear on the hydrodynamic lubrication of journal bearings are determined theoretically and experimentally in both laminar and turbulent regimes. The steady-state characteristics of the bearings such as film pressure, attitude angle, and Sommerfeld number are analyzed by a semianalytical finite element method for various wear depth parameters, and the theoretical results are compared with the experimental results.

It is found that the geometric change due to wear has significant effects on the steady-state characteristics in both laminar and turbulent regimes. Good agreement is obtained between the theoretical and experimental results.