Design,Fabrication, and Performance of Open Source Generation I and II Compliant Hydrodynamic Gas Foil Bearings

Foil gas bearings are self-acting hydrodynamic bearings made from sheet metal foils comprised of at least two layers. The innermost “top foil” layer traps a gas pressure film that supports a load while a layer or layers underneath provide an elastic foundation. Foil bearings are used in many lightly loaded, high-speed turbomachines such as compressors used for aircraft pressurization and small microturbines. Foil gas bearings provide a means to eliminate the oil system leading to reduced weight and enhanced temperature capability. The general lack of familiarity of the foil bearing design and manufacturing process has hindered their widespread dissemination. This paper reviews the publicly available literature to demonstrate the design, fabrication, and performance testing of both first- and second-generation bump-style foil bearings. It is anticipated that this paper may serve as an effective starting point for new development activities employing foil bearing technology.     

Axial load capacity of water-lubricated hydrostatic conical bearings with spiral grooves for high speed spindles: Comparison between rigid and complaint surface bearings

In this paper, two types of water-lubricated hydrostatic conical bearings with spiral grooves for high-speed spindles are investigated. One has a rigid bearing surface and the other has a compliant one. In these bearings, pressurized water is first fed to the inside of the rotating shaft and then introduced into spiral grooves through feeding holes. Therefore, water pressure is increased due to the effect of the centrifugal force at the outlets of the feeding holes by shaft rotation and, furthermore, water pressure is also increased by the viscous pump effect of spiral grooves. The static characteristics of these bearings are theoretically predicted and calculated results are compared with experimental results. It was found that the compliant surface bearing had a larger load capacity in a relatively large bearing clearance than the rigid surface bearing, and lower bearing power consumption in a small bearing clearance although the load capacity is reduced.     

Wave Journal Bearing with Compressible Lubricant—Part I: The Wave Bearing Concept and a Comparison to the Plain Circular Bearing

To improve hydrodynamic journal bearing steady-stale and dynamic performance, a new bearing concept, the wave journal bearing, was developed at the author's lab. This concept features a waved inner bearing diameter. Compared to other alternative bearing geometries used to improve bearing performance such as spiral or herringbone grooves, steps, etc., the wave bearing's design is relatively simple and allows the shaft to rotate in either direction. A three-wave bearing operating with a compressible lubricant; i.e., gas, is analyzed using a numerical code. Its performance is compared to a plain (truly) circular bearing over a broad range of bearing working parameters, e.g., bearing numbers from 0.01 to 100. The geometry of the wave bearing gives the bearing its high load; i.e., stiffness, and stability characteristics. The wave bearing's performance is dependent upon the amplitude of the wave and the position of the waves relative to the applied load. To maximize wave bearing performance, the waves' position relative to the applied load should be carefully selected. The wave journal bearing offers better stability than the plain circular bearing' under all operating conditions and all wave-load orientations. Specifically, an unloaded journal bearing can be made to run stably in any operating regime by incorporating the wave geometry.     

均压槽与静压气体轴颈轴承承载特性的关系研究

主要研究通过开设不同结构形式的均压槽来提高静压气体轴颈轴承的承载能力和刚度,利用加权余量法和有限元离散化方法求解雷诺方程进行数值计算和仿真,针对单排孔和双排孔轴颈轴承,分析不同长度的周向均压槽,以及不同数量、不同位置和不同长度的轴向均压槽对轴承承载能力和刚度的影响规律。结果发现:开设周向均压槽和轴向均压槽都可以提高轴承的承载能力,相比开设周向均压槽,开设轴向均压槽对提高轴承的承载能力更为有效,而且只开设一条或两条轴向均压槽就能显著提高轴承的承载能力,通常将轴向均压槽置于气膜间隙较小的位置时能使轴承的承载能力和刚度最大。数值仿真结果通过试验进行验证,研究结果可用以指导高承载和高刚性静压气体轴颈轴承的设计。     

往复泵自生增压系统动态特性仿真

往复泵自生增压系统是一种新型的轨姿控发动机增压系统,根据系统的工作原理,建立了考虑传热过程的自由活塞往复泵模型以及增压系统仿真模型。针对该系统进行了动态特性仿真,获得了增压系统启动特性以及往复泵的热特性。结果表明,所建立的模型能够较好地反映增压输送过程,为系统和组件设计提供重要依据。     

CHARACTERISTCS OF FLUID FILM IN OPTIMIZED SPIRAL GROOVE MECHANICAL SEAL

In order to investigate the sealing performance variation resulted from the thermal deformation of the end faces, the equations to calculate the fluid film pressure distribution, the bearing force and the leakage rate are derived, for the fluid film both in parallel gap and in wedgy gap. The geometrical parameters of the sealing members are optimized by means of heat transfer analysis and complex method. The analysis results indicate that the shallow spiral grooves can generate hydrodynamic pressure while the rotating ring rotates and the bearing force of the fluid film in spiral groove end faces is much larger than that in the flat end faces. The deformation increases the bearing force of the fluid film in flat end faces, but it decreases the hydrodynamic pressure of the fluid film in spiral groove end faces. The gap dimensions which determine the characteristics of the fluid film is obtained by coupling analysis of the frictional heat and the thermal deformation in consideration of the equilibrium condition of the bearing force and the closing force. For different gap dimensions, the relationship between the closing force and the leakage rate is also investigated, based on which the leakage rate can be controlled by adjusting the closing force.     

Experimental Investigation Regarding the Effects of Grooves on Conical Bearing Performance

An experimental investigation is made regarding conical bearing characteristics related to the introduction of grooves. Load capacities of three bearing types are compared, i.e., smooth bearings, bearings with radial grooves, and bearings with inclined grooves rotated in both directions. The obtained results indicate that the presence of grooves significantly affects conical bearing performance. It is concluded that for the maximum load capacity, a bearing with inclined grooves should be used with forward rotation, i.e., when the entry part of the groove advances ahead of the exit of the groove.     

A Noise Analysis of Cylindrical Roller Bearings Operating Under Zero External Load

The purpose of this article is to numerically investigate one source of acoustic noise in roller bearings, that which results from the motion of the rollers in the bearing under zero external load. For the sake of simplification, it was assumed that the cylindrical roller bearings are infinitely long. Furthermore, the effects of the following on the noise of the bearing were also examined: the radial clearance of the bearing, the viscosity of the lubricant, and the number of rollers. The results of the study show that the fundamental frequency of the noise components of the cylindrical roller bearing corresponds to the multiplication of the number of rollers and the whirling frequency of the roller center. The acoustical frequency spectra of the cylindrical roller bearing are pure tone spectra, containing the fundamental frequency of the roller bearing and its superharmonics. The factors that decrease the sound pressure level of a cylindrical roller bearing include low lubricant viscosity, high radial clearance, and a reduced number of rollers. The results and discussions of the present article could aid in the design of low-noise cylindrical roller bearings.     

螺旋槽-波锥坝组合型非接触式机械密封性能分析

针对液体润滑非接触式机械密封在低黏环境下承载性能不足的问题,提出一种新型螺旋槽-波锥坝动静压组合型机械密封结构,采用MATLAB软件利用有限差分法求解考虑质量守恒空化边界的雷诺方程,并将组合槽与螺旋槽、波锥坝的密封性能进行比较,进一步分析不同结构参数与工况参数对组合槽性能参数的影响规律。结果表明:新槽型波数与螺旋槽数重合时组合密封在径向出现2个压力峰值,相较于单一槽型结构拥有更好的承载能力与较小的摩擦扭矩;液膜力与泄漏量随波锥比或径向宽度比的增加而增大,外径压力和转速越大,组合槽的承载性能提升越显著,但外径压力的升高会造成较大的径向泄漏。组合槽结合了波锥槽的静压承载与螺旋槽的动压承载综合优势,将有效提升液体润滑非接触式机械密封在低黏环境下的润滑性能。     

Steady-State Performance of Oil Lubricated Helical Groove Journal Bearing

The provision of helical grooves on the surface of a plain journal bearing should, in principle, improve the overall performance of the bearing. This improvement, however, depends on a number of parameters such as the arrangement of the grooves along the axial length of the bearing. In order to verify this supposition, two types of helical groove bearing with different groove arrangements and a reference plain journal bearing were studied to assess their steady-state performance when lubricated with an oil. It was found that the steady-state performance of both types of helical groove bearing is not as good as that of the plain bearing. Of the two helical groove bearings tested, the asymmetrical bearing proved to be a more energy efficient than the symmetrical bearing.     

The Performance of Externally Pressurized Bearings Using Simple Orifice Restrictors

The load capacity and vibration characteristics of externally pressurized thrust and journal bearings have been investigated. The bearings used orifices sufficiently recessed back from the bearing surface to ensure that the area of the orifice is the minimum presented to the gas flow. The journal bearings consist of plain cylinders with one or two rows of eight orifices, and the thrust plates of plain discs with six orifices drilled in equispaced circumferential grooves.

The load capacity of the thrust plates agrees with that calculated but the vibrations are greater than predicted. The load capacity of journal bearings is about half that calculated assuming axial flow conditions in the bearing, but circumferential flow can account for the difference. Synchronous and half-speed vibrations of a shaft rotating within these bearings have been measured and found to agree with those calculated on the assumption that the gas films behave as linear springs.     

Research on Effects of Groove Shape Optimization on Cavitation and Lubricating Characteristics for Microgroove Rotary Seal

This article studies the effects of groove shape optimization on cavitation and lubricating characteristics of microgroove rotary seals (MGRS). A lubrication model considering cavitation effects for MGRS is established to obtain the variation in cavitation and lubricating characteristics with operating conditions. Furthermore, an optimization model of groove shape based on the lubrication cavitation model is developed and an optimal groove is obtained by co-designing the parameters of both groove shape structures and molded lines. The effects of optimal grooves and ordinary spiral grooves on cavitation and lubricating characteristics are compared and validation tests are carried out. Theoretical and experimental results indicate that the lubrication cavitation model based on the mass conservation boundary condition for MGRS could accurately predict the cavitation region of ordinary spiral grooves. Optimal grooves improve the pressure distribution of the groove area and restrain the generation of a cavitation region; therefore, the fluid bearing capacity and dynamic stiffness of optimal grooves are much larger than those of ordinary spiral grooves.     

Correlating Computerized Rolling Bearing Analysis Techniques to the ISO Standards on Load Rating and Life

Computer-aided design of bearing systems is finding its way into many industrial sectors requiring high reliability and trouble-free performance from rotor/bearing systems. This trend will accelerate as more bearing analysis codes are ported to the personal computer and incorporate user-friendly interfaces. This paper describes and explains the theoretical basis for bearing load rating and life estimating as reflected in such programs. The calculation of individual bearing and system B-10 Fatigue Life and their correlation to the ISO International Standard 281 for dynamic load ratings and rating life is presented. Showing the continuity from the standard methods to the more fundamental computer analysis of bearing systems will allow for a smooth transition from one to the other.     

Theoretical Analyses and Design Guidelines of Oil-Film-Lubricated Mechanical Face Seals with Spiral Grooves

The oil-film-lubricated mechanical face seal is a kind of pure hydrodynamic lubricated noncontacting mechanical face seal with zero leakage. On the basis of systematic theoretical analyses, the design calculation formulas under zero-leakage condition for mechanical face seals with different spiral groove patterns, including double-row spiral grooves such as splay pattern and single-row spiral grooves, are derived. The effects of groove geometry including number of grooves, balance ratio, spring force, rotating speed, and differential pressure on the seal performance are discussed in detail. Finally, the design guidelines of this kind of seal with zero leakage and no wear are put forward. The seals designed according to the guidelines can withstand the pressure disturbance and speed change by means of a slight change of oil-film thickness. Seals developed according to the design guidelines have been tested on a test rig in detail and applied successfully in high-speed turbocompressors of the oil refinery and petrochemical industries.     

Numerical simulation and experimental research on passive hydrodynamic bearing in a blood pump

The current research of hydrodynamic bearing in blood pump mainly focuses on the bearing structure design.Compared with the typical plane slider bearing and Rayleigh step bearing,spiral groove bearing has excellent performance in load-carrying capacity.However,the load-carrying capacity would decrease significantly with increasing flow rate in conventional designs.In this paper,the special treatment is made to the upper spiral groove bearing to make sure that both the circulatory flowing and load-carrying capacity are high.Three-dimensional computational fluid dynamics(CFD) models in the space between rotor and shaft are developed by using FLUENT software.Effects of groove number,film height and groove depth on load-carrying capacity of the spiral groove bearings are investigated by orthogonal experiment design.The experimental results show that film height is the most remarkable factor to the load-carrying capacity.The variation tendency of load-carrying capacity reveals that the best combination of geometry is the one with groove number of 8,film height 0.03 mm and groove depth 0.08 mm.The velocity and pressure distributions in spiral groove bearings are also analyzed,and the analysis result shows that the distributions are in conformity with the design of the blood pump based on the principle of hydrodynamic bearing.The displacement of the rotor with the best combination parameters is tested by using laser displacement sensors,the testing result shows that the suspending performance is satisfactory both in axial and radial directions.This research proposes a bearing design method which has sufficient load-carrying capacity to support rotor as an effective passive hydrodynamic bearing.     

A study on the sound of roller bearings operating under radial load

The purpose of the paper is to numerically investigate the sound characteristics of roller bearings operating under radial load. For the sake of simplifying the analysis, it was assumed that the roller bearings are infinitely long, a noise source due to pressure fluctuation of oil film is taken as a line noise source, and acoustic energy losses in the bearing are neglected. To obtain sound characteristics of the bearing, the rolling contact load and the sound pressure level distributions were calculated for various operating conditions, and the results were compared with each other. How much the bearing noise can be affected by the design parameters, such as radial clearance of the bearing, viscosity of lubricant, and the number of rollers was also investigated. The results and discussions of the present paper could aid in the design of low-noise roller bearings and to solve the noise problems related to such bearings.     

Analysis of Foil Journal Bearings with Backing Springs

Gas-lubricated foil journal bearings are simple, in construction, lightweight and well suited for high-temperature applications in turbomachinery. Hearing stiffness is governed primarily by the foil flexural stiffness. The bearing consists essentially of thin overlapping circular metal foils, one end of which is cantilevered to the bearing housing and. the other end rests on an adjacent foil.

An analysis of gas-lubricated foil bearings is presented with a specific type of backing spring used under the foils to control bearing preload, and stiffness. The backing spring acts like, an elastic foundation tinder the foil and radically changes the hydrodynamic pressure distribution generated in the gas film. The pressure distribution is obtained by simultaneously solving the compressible Reynolds equation and. the elasticity equations governing the compliant bearing surface, consisting of foils and backing springs. An iterative scheme is used, to obtain pressure distributions for heavily loaded cases, involving extensive computation, because of the sensitivity of pressure solution to small changes in film thickness distributions attributable to the compliant bearing surface. Pressure distribution, film thickness, bearing load capacity, iterative solution convergence characteristics and bearing power dissipation are presented as a function of journal eccentricity.     

Thermohydrodynamic Analysis and Thermal Management of Spherical Spiral Groove Gas Bearings

A thermohydrodynamic model of spherical spiral groove bearings is presented by considering the effect of bearing temperature change on the material property of lubricant, gas flow characteristics in the grooves, and thermal energy transported in the entire bearing system. A gas mixing model in the grooves is introduced as the boundary condition to solve the bearing temperature distribution simultaneously with the heat conduction at the shaft and the housing. The bearing and rotor expansion caused by temperature increases, which is considerable compared to bearing clearance, is also examined. Prediction results show that the thermal expansion determined by actual bearing clearance has a crucial influence on the bearing load capacity. Manufacturing bearings with proper materials has significant effects on controlling thermal expansion effects on the bearing performance. The load capacity, which corresponds to the lubricant gas pressure, and gas suck flow rate have the same variation tendencies as the variation in groove depth and spiral angle. These similar tendencies have an opposite influence on the temperature and result in the temperature increase not being affected by the variation in grooves. However, varying the groove characteristics has a similar effect in carrying away the thermal energy as the variation in heat transfer coefficient, which could significantly control the temperature increase at the same time.     

Application of Spiral Grooves in Fuel Pump for Medium-Speed Diesel Engines

The lubrication characteristics of fuel pumps with spiral grooves are investigated by numerical analysis. The two-dimensional Reynolds equation is used to evaluate lubrication characteristics with variations in grooves and viscosity. Moreover, the equilibrium equation of moment and forces in the horizontal and vertical directions is used to determine the motion of the plunger. The lubrication characteristics of the fuel pump with spiral grooves are compared to those without spiral grooves. The lubrication characteristics of the pump are investigated by comparing the film parameters. The fuel pump with spiral grooves is effective for relieving any uneven pressure distribution surrounding the plunger and can improve the lubrication characteristics. The application of spiral grooves is shown to be more effective in a low-viscosity condition compared to in a high-viscosity condition.     

Thermal characteristics of misaligned finite journal bearings

Adiabatic analysis of a journal bearing is presented for maximum allowable misalignment with a length: diameter ratio of one. The direction of journal misalignment is allowed to vary up to the axial plane containing the load vector. Reynolds and energy equations are solved simultaneously using finite differences, considering both axial and spiral oil inlet conditions. The results show that bearing behaviour is significantly affected by journal misalignment. It is also noted that thermal effects are more pronounced for bearings with axial rather than spiral oil inlet grooves.