新型弹性箔片动压气体止推轴承启停性能的研究

在多功能气体轴承试验台上对西安交通大学制冷与低温工程研究所开发的新型弹性箔片动压气体止推轴承进行了启停性能的试验研究。分析了箔片材料的选择和表面的处理对新型弹性箔片动压气体轴承启停性能的影响。试验结果表明经过表面处理的新型弹性箔片动压气体止推轴承具有较好的启停性能和稳定性。     

箔片式动压径向气体轴承的发展

本文简要回顾了气体轴承和箔片式动压径向气体轴承的历史及国内、外目前的研究状况。详细介绍了箔片式动压径向气体轴承的起源、结构形式、应用范围和理论、实验及应用研究的发展,并提出了一种新型结构形式的弹性支承箔片动压径向气体轴承。     

箔片气体动压轴承研究进展综述

箔片气体动压轴承具有转速高、摩擦功耗低、无油润滑以及良好的减振性能等优势,已在飞机换气系统和曝气鼓风机等领域广泛应用。近年来随着全球“碳达峰碳中和”战略的提出和实施,氢燃料电池汽车等成为产业热点,箔片气体动压轴承在燃料电池空压机领域的应用呈现“井喷”态势,但箔片轴承在适应燃料电池汽车复杂工况所必须具备的长寿命、高抗振性及高可靠性等方面,还远远没有得到充分验证,目前仍处于路况验证和技术迭代阶段。因此有必要在新工况和新性能需求大背景下,对箔片气体动压轴承的现有研究成果进行系统梳理和深入分析。介绍了箔片气体动压轴承的结构及在燃料电池空压机中的应用;评述了箔片气体动压轴承的高速特性、比承载能力、动力学稳定性以及启停寿命等关键性能指标及当前发展水平;分别从箔片气体动压轴承理论建模、气固耦合特性仿真算法、气膜热特性及温升控制、轴承转子系统动力学稳定性、箔片轴承抗振性及疲劳寿命、箔片表面涂层技术及启停寿命、箔片轴承动态性能测试与试验技术等方面,对箔片轴承关键技术进行了系统分析和综述;最后结合燃料电池汽车工况对高速离心式空压机的性能需求,对箔片气体轴承关键技术的发展趋势进行了预测和展望。     

弹性箔片动压气体推力轴承承载性能研究

气弹耦合解是准确预测弹性箔片动压气体轴承承载性能的有效方法。通过引入箔片的弹性变形以及联立求解动压气体润滑Reynolds方程和弹性箔片的变形方程,给出了弹性箔片动压气体推力轴承的气弹耦合解。应用气弹耦合解理论,将顶层箔片的局部弹性变形纳入考虑范围,对弹性箔片动压气体推力轴承的承载性能进行了计算和分析。有限元数值仿真结果表明:顶层箔片在气膜压力作用下的局部弹性变形直接导致弹性箔片动压气体推力轴承承载能力的降低;根据轴承瓦块上气膜压力分布的特点合理设计支承拱箔的结构形式,可以减小顶层箔片的局部弹性变形,有效提高轴承的承载能力。得到了一种承载能力较高的弹性箔片动压气体推力轴承支承拱箔结构设计方案。     

箔片式动压止推气体轴承的发展

本文简要回顾了箔片式动压止推气体轴承的发展历史.详细介绍了箔片式动压止推气体轴承的主要类型及研究状况.     

高速透平箔片动压气体轴承固体润滑涂层研究进展

箔片动压气体轴承广泛应用于高速透平膨胀机、微小型燃气轮机、涡轮增压机等高速透平机械中。固体润滑涂层可为箔片动压气体轴承提供启停阶段的润滑保护,对保证箔片动压气体轴承稳定性与使用寿命至关重要。本文回顾了国内外箔片动压气体轴承固体润滑涂层的研究历史与现状;结合文献资料着重分析了PS系列、Korolon系列和DLC系列的固体润滑涂层特性,并对其应用场合和优缺点进行了探讨。     

微小型高速透平径向箔片动压气体轴承的研究

微小型高速透平膨胀机的发展对微小型动压气体轴承的开发提出迫切的要求,研制微小型动压气体轴承十分必要。在一台微小型高速透平膨胀机上对平箔型、弹性片支承型、鼓泡型3种不同的径向箔片气体轴承分别进行了研究。试验结果表明3种箔片轴承均能满足运行要求,通过比较发现,鼓泡型径向箔片气体轴承具有加工简单,运转稳定的特点。配合鼓泡型动压止推轴承,对全鼓泡型箔片轴承全动压透平膨胀机进行研究。初步试验最高转速可达22万r/min。     

基于流固耦合的波箔动压气体轴承承载性能优化

基于有限元软件Ansys Workbench,建立波箔动压气体轴承在可压缩流体介质中运动的有限元模型,采用6DOF动网格计算方法对轴承的运动状态进行流固耦合数值模拟,探讨不同转速和波箔片结构参数（波箔的长度比、高度以及厚度）对轴承承载性能的影响规律。结果表明：轴承气膜压力大小的分布与平箔片变形量的大小成对应关系,说明提出的流固耦合方法能很好地反映波箔动压气体轴承的润滑状态;随着转速的增大,轴承动压效应不断增强,承载力增大,且平箔片的结构变形不断增大,致使气膜压力的收敛区发生波动;随着波箔的长度比和波箔片厚度的增加,轴承承载力先快速增大后趋于稳定,而波箔片高度对承载力影响不大,表明适当增加波箔的长度比和波箔片厚度可以提高承载力。     

交错式波箔型气体动压轴承静态特性研究

为进一步提高箔片轴承性能,提出了交错式箔片轴承结构,并建立交错式波箔型气体动压轴承模型;应用有限元法和松弛迭代法对雷诺方程与气膜厚度方程进行差分迭代求解,通过控制气膜压力的收敛,得到交错式箔片轴承气膜厚度和压力分布,并计算相关的静态特性。结果表明:与传统波箔构型轴承相比,交错式波箔型气体动压轴承的承载力明显提升,而摩擦力矩有所增加,尤其在转速与长径比增大的情况下更为明显;随转速与长径比的增大,交错式波箔型气体动压轴承与传统轴承的偏位角大小与变化基本相同,气膜压力三维分布也相一致。     

弹性箔片轴承的研究进展*

近年来,弹性箔片轴承在高速透平机械的应用中展现出巨大的潜力。为获取轴承高承载力、减少轴承启停过程的摩擦与磨损、提高轴承的高速稳定性,研究人员开展了大量的理论、实验与应用研究。从弹性箔片轴承的结构特性、涂层特性和建模方法3个方面对气体弹性箔片轴承的研究进展进行综述。首先从轴承结构优化的角度,介绍箔片轴承结构改进的发展历程,以及具有新颖结构设计的多叶搭接式弹性动压箔片轴承及其优点;然后从减少轴承启、停阶段摩擦力,提高弹性箔片轴承使用寿命的角度出发,比较分析了应用广泛的多种涂层,总结国内外新型润滑剂的适用条件及减摩效果;最后从轴承建模角度,介绍经典的简单弹性模型、考虑箔间摩擦力与分离等影响因素的系列复杂模型,为后续模型构建与性能分析提供依据。展望弹性箔片轴承在高精尖等领域的前景,并对弹性箔片轴承的研究方向提出了建议。     

平箔式箔片止推气体轴承静特性的理论研究

根据平箔式箔片止推轴承的结构。导出了求解箔片止推气体轴承特性的方程。利用有限元法进行了数值求解。比较了箔片止推轴承与刚性轴承的不同之处，并讨论了影响箔片止推轴承特性的因素。     

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.     

Numerical and Compact Model of Metal Mesh Foil Bearings

Metal mesh foil bearings (MMFBs) are novel gas foil bearings with lower manufacturing costs and higher inherent material energy dissipation ability than traditional bump-type foil bearings. To improve the design guidelines of MMFBs and predict bearing performance, a compact theoretical model is presented by considering the metal mesh substructure as assembled springs and dry friction joints. The proposed analytical model considers the effects of several factors such as relative density, wire diameter, geometrical size, and radial interference of the metal mesh substructure. The predicted stiffness coefficients, which take the dry friction effect into account, show strong nonlinear characteristics with the increasing displacement and have a significant difference between the loading and unloading process. A series of static load tests are conducted to verify the theoretical model of MMFBs. The hysteresis loops of static load versus bearing deflection with respect to the different relative densities predicted by this model are demonstrated by experimental data. The minimum film thickness, journal eccentricity, and attitude angle with respect to different relative densities, rotational speeds, and applied loads are presented and analyzed. The predicted results of the dynamic force coefficients show that the equivalent viscous damping coefficient and relative density have significant effects on bearing dynamic performance. Furthermore, the influence of radial thickness, wire diameter, and radial interference on bearing static and dynamic performance is discussed.     

波箔式空气轴承箔片支承结构分析的研究进展

箔片结构作为箔片气体轴承的特殊组成部分,对轴承性能的影响很大.总结国内外学者对箔片结构刚度的研究情况以及库仑摩擦、刚度分布影响箔片结构性能的机制,指出箔片轴承结构发展趋势的理论依据.对一直被忽略的平箔变形问题进行阐述和相应的机制分析.     

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.     

Rotordynamics and Design Methods of an Oil-Free Turbocharger©

The feasibility of supporting a turbocharger rotor on air foil bearings is investigated based upon predicted rotordynamic stability load accommodations, and stress considerations. It is demonstrated that foil bearings offer a plausible replacement for oil-lubricated bearings in diesel truck turbochargers. Also, two different rotor configurations are analyzed and the design is chosen which best optimizes the desired performance characteristics. The method of designing machinery for foil bearing use and the assumptions made are discussed.     

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.     

Dynamic stability experiments of compliant foil thrust bearing with viscoelastic support

In order to reduce the complexity of machine construction and improve the mechanical efficiency, high speed rotation machineries usually implement self-acting gas bearings to substitute the traditional oil-lubricated bearings. This paper presents test results of a gas thrust bearing with viscoelastic support which is designed for high speed turbo-machinery. The gas bearing, which belongs to compliant foil bearings, consists of a top thin metal foil and a bottom thin rubber foil. Static and stability experiments are conducted on a high speed gas turbine test rig. The static results indicate that the structural stiffness of test bearing generally increases with the increase in axial load and the decrease in thickness of bottom foil. In the rotation tests, rotor runs stably with small vibration amplitude, which is dominant in waterfall plot during whole speed up procedure. It shows that test bearing has preferable stability characteristics for high speed gas turbines.     

影响箔片结构阻尼的因素及箔片径向轴承结构形式的进展

稳定性是影响箔片轴承应用的一个关键问题，它与轴承弹性支承结构的阻尼特性密不可分。影响箔片阻尼的因素很多，内部因素如材料本身结构和性能，外部因素有温度、承载力和滑流等。本文介绍了箔片支承结构形式的进展，分析了影响箔片结构阻尼的几个外部因素，并结合实践提出改善箔片支承结构阻尼的几个途径。     

应用于燃料电池的高速单级空气压缩机波箔轴承技术（英文）

The motivation to use air foil bearings in fuel cell compressors is driven by the demand for oil-free and high-power density system to reduce system volume and weight. The characteristics of air foil bearings that realize this demand are its independency on auxiliary system and no scheduled maintenance as well as their superb performance at high speeds. However, integration of the foil bearings to the compressor needs rigorous developmental tests for the bearing to withstand high g-load during vehicle maneuver and to remain stable in rotordynamics under external destabilizing forces. This paper presents multi-pads foil bearing technology applicable to single stage high speed fuel cell air compressors.Two different multi-pad air foil bearing designs(two-pad vs three-pad) were tested using a high-speed spin test rig to identify the differences in rotordynamics responses. The two-pad bearing is superior in rotordynamics without any sub-synchronous vibration while three-pad bearing provides more uniform load capacity in all directions with less rotordynamics stability. Frequency-domain modal analyses verify the experimental observations. Axial foil bearings with 38 mm outer diameter was designed and tested up to 140 krpm with load capacity of 90 N(1.4 bar specific load capacity).Finally, a platform design of single stage 15 k W fuel cell compressor with rated speed of 130 krpm is proposed using the multi-pad foil bearings and axial foil bearings developed through this paper.