动压箔片轴承气膜厚度分布特点

建立了考虑平箔片下垂效应的动压箔片轴承气弹耦合模型,以Reynolds方程描述气膜压力,以Euler梁单元描述平箔,以简单弹簧单元描述波箔。采用有限差分法和Newton-Raphson迭代法求解气膜压力方程,采用有限元法计算箔片变形,利用气膜压力与气膜厚度相互迭代逼近气弹耦合的收敛解。结果表明,在气膜压力较大区域相邻两支承箔拱之间的平箔段会发生微小的下陷弯曲,并伴随有压力场的局部变化。     

箔片轴承气弹耦合求解方法

气弹耦合求解是计算箔片动压气体轴承承载性能的有效方法。提出一种简单的箔片动压气体轴承气弹耦合求解方法。该方法以简单弹性基础模型为基础,将气膜厚度控制方程代入Reynolds是方程,获得箔片动压气体轴承气弹耦合控制方程,运用有限差分法结合Newton-Raphson迭代法对气弹耦合控制方程进行求解。计算方法获得的轴承内部压力分布与文献结果吻合很好。该方法的优势在于,省略了除最底层的牛顿迭代之外的其他所有迭代过程,使迭代次数大大减少,从而使计算效率获得提高。     

波箔型径向气体轴承静态特性分析

建立考虑气体可压缩性和箔片变形的波箔型轴承气膜厚度模型,采用有限差分和松驰迭代法耦合求解Reyn olds方程和气膜厚度方程,得到波箔型轴承气膜厚度和气膜压力分布,并分析波箔型动压径向气体轴承结构参数和运行参数对其静态性能的影响.结果表明:波箔型轴承数值分析结果与相关文献试验数据相符度较好,证明该模型的科学性与精确性;对比箔片轴承和传统刚性表面轴承气膜压力和气膜厚度的分布特点,表明箔片轴承具有更高的承载能力;随着偏心率、转速的增大,箔片轴承承载能力增大,偏位角减小;随着转速增大,气膜压力提高,箔片变形增大,最小气膜厚度增大.     

多叶式波箔气体动压轴承静特性研究

随着旋转机械的不断发展,箔片动压轴承已经发展到了第四代.其中,多叶式波箔气体动压轴承以其大预紧力和耐高温涂层技术的应用而拥有广阔的发展前景.以多箔叠加弹性结构作为切入点,应用悬臂弯曲梁模型和线性弹簧模型来等效箔片结构中的顶层平箔和支承波箔,从而获得不同于前三代箔片动压轴承的气膜厚度方程.基于有限差分法耦合气膜厚度方程和...     

基于弹性壳体模型的波箔型气体动压径向轴承静特性分析

采用有限单元法,对波箔型气体动压径向轴承的箔片建立了弹性壳体单元模型。该模型综合考虑了箔片膜效应与弯曲效应之间的耦合,更能真实地反映出波箔和平箔的变形。运用有限差分法及Newton-Raphson迭代法耦合求解Reynolds方程和气膜厚度方程,分析了轴承气膜厚度分布、压力分布、箔片变形量分布以及承载能力,并与实验结果进行了比较,证明了该方法的可行性和精确性。分析了转速、箔片厚度对轴承特性的影响,结果表明:转速上升,承载能力增大;箔片厚度小于0.2mm时,厚度的改变对轴承的影响较大。     

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。     

表面粗糙度对气体箔片推力轴承润滑性能的影响

以波箔型气体箔片推力轴承为研究对象,运用弹性力学理论构建了箔片结构的受力变形模型,在考虑黏温效应的条件下,耦合求解了可压缩气体雷诺方程及能量方程。将数值模拟得到的顶箔和推力盘的微观粗糙表面引入计算模型,提出了一种考虑表面粗糙度的气体箔片推力轴承润滑性能数值计算方法。通过对具体算例的研究,绘制了轴承气膜压力、气膜厚度、气膜温度及箔片结构变形量的分布图,并通过粗糙度与气膜厚度和箔片变形之间的定量对比说明了考虑表面粗糙度的必要性。研究结果表明：推力盘表面粗糙度越大,最大气膜压力、最小气膜厚度、黏性摩擦力矩和端泄流量的波动越明显,而顶箔粗糙度的影响相对较小;两粗糙表面的高度组合越大,最大气膜压力和黏性摩擦力矩的平均值越大,最小气膜厚度和端泄流量的平均值越小;提高转速可减小最大气膜压力的平均值,并增大最小气膜厚度、黏性摩擦力矩和端泄流量的平均值。     

分离式波箔动压气体推力轴承压力场特性研究

分离式波箔气体轴承是新一代柔性气体轴承,其承载能力的准确预测是该类轴承性能预测和设计准则确定的基础,箔片的变形和气膜压力的求解是承载能力预测的关键。分别采用线性刚度模型和薄板弯曲模型对分离波箔片和平箔片变形进行建模。应用非线性数值求解方法对可压缩气体Reynolds方程和变形方程进行气弹耦合数值求解,获得了轴承的压力分布。结果表明分离式波箔片可以提高轴承的承载能力,而平箔片的变形会导致承载能力的降低。通过比较发现计算结果和实验数据具有较好的一致性。     

弹性支承箔片动压气体径向轴承理论模型的研究

提出了一种新型结构弹性支承箔片动压气体径向轴承,针对此种结构,提出了求解弹性流体动力润滑问题(EHDL)的弹性基础支承箔片轴承流.固耦合物理模型,分析了弹性基础支承材料的特性,建立了弹性基础受力三维六自由度变形和考虑了包括非线性项动态气膜力和轴承不对中(角偏差)效应的非定常可压缩雷诺方程的数学模型;然后从控制方程出发,给出了求解弹性支承箔片动压气体径向轴承静态特性参数(压力分布、承载力、偏位角、摩擦力矩)的分析方法;并以静特性分析为基础,采用Lund的线性化假设,分析了弹性支承箔片动压气体径向轴承的动态性能(4个刚度系数及4个阻尼系数);最后在动特性分析的基础上,采用刚性对称转子模型,分析了轴承的稳定性.     

止推轴承中多层鼓泡箔片支承结构弹性变形的数值研究

针对单层鼓泡箔片动压止推气体轴承在实验中出现的易磨损、承载能力低等缺陷,设计双层和三层鼓泡箔片支承结构。采用ANSYS Workbench有限元软件建立单层、双层和三层3种鼓泡箔片支承结构的数值模型,利用有限差分法和Newton-Raphson迭代法通过MATLAB编程求解得到同等轴承尺寸下的气膜压力分布;将气膜压力施加在3种支承结构的平箔片表面进行数值求解,得到不同支承结构的弹性变形情况。结果表明:平箔片的变形量相对鼓泡箔片要大,因此在对该类轴承分析时不应忽略平箔片的变形作用;在多层鼓泡箔片支承结构中,越靠近轴承间隙的鼓泡箔片的变形量越大,其支承作用也越明显;对于多层鼓泡箔片支承结构,可通过加大平箔片厚度来更好地发挥鼓泡箔片的支承作用;三层鼓泡箔片支承结构具有较好的弹性分布,在鼓泡箔片动压止推轴承的设计中应优先采用。     

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.     

Elasto‐aerodynamic lubrication analysis of a self‐acting air foil journal bearing

Nowadays, air foil bearings find widespread use in very high speed, lightly loaded oil‐free rotating turbomachineries such as compressors and microgas turbines because they have theoretically no speed limitations and they are environmentally benign. In the design of such bearings, it is of cardinal importance to enhance their steady‐state and dynamic performance characteristics for the safety operation, especially against the external dynamic excitations. Most of elasto‐aerodynamic approaches under dynamic conditions proposed in the technical literature include only the static pressure induced deformation of foils. This paper presents a theoretical investigation on the effects of both static and dynamic deformations of the foils on the dynamic performance characteristics and stability of a self‐acting air foil journal bearing operating under small harmonic vibrations. For the dynamic deformations of foils to be taken into account, the perturbation method is used for determining the gas‐film stiffness and damping coefficients for given values of excitation frequency, compressibility number and compliance factor of the bump foil. The rotor‐dynamic coefficients serve as input data for the linear stability analysis of rotor‐bearing system. The nonlinear stationary Reynolds' equation is solved by means of the Galerkin's finite element formulation, whereas the finite differences method are used to solve the first‐order complex dynamic equations resulting from the perturbation of the transient compressible Reynolds' equation. As a first approximation, the corrugated subfoil is modelled as a simple elastic foundation, i.e. the stiffness of a bump is uniformly distributed throughout the bearing surface. It was found that the dynamic properties and stability of the compliant finite length journal bearing are significantly affected by the compliance of foils especially when the dynamic deformation of foils is considered in addition to the static one by applying the principle of superposition. Copyright © 2012 John Wiley & Sons, Ltd.     

Three-Dimensional Thermohydrodynamic Analyses of Rayleigh Step Air Foil Thrust Bearing with Radially Arranged Bump Foils

A three-dimensional (3D) thermohydrodynamic (THD) model for air foil thrust bearings (AFTBs) is presented. The nonisothermal Reynolds equation is solved using pressure boundary conditions at the cooling air plenum considering local temperature-dependent viscosity and density. Air film temperature is calculated using the 3D energy equation with thermal boundary conditions at the top foil, thrust runner, and top foil’s leading edge. The cooling air plenum distributes the cooling air to multiple radially arranged cooling channels. The plenum temperature and pressure are found from mass and energy balance equations applied to the plenum. Temperature fields of the top foil, bump foils, thrust disc runner, bearing plate, and cooling air channels are also solved through appropriate energy balance equations with their surroundings. A robust computational algorithm with multiple iteration loops was developed to find all the temperature fields. THD analyses were performed for AFTB with outer radius of 50 mm up to 100,000 rpm. As the cooling air source pressure is increased, the plenum pressure also increases and its temperature decreases due to more cooling capacity. However, cooling effectiveness is not necessarily proportional to the pressure because the flow residence time inside the cooling channels is inversely proportional to the pressure. The analyses show that the thrust disc temperature is a parabolic function with speed, and thermal expansions of the thrust disc and thrust plates contribute to the most significant driving force of thermal instability. Optimum cooling air pressure was found around 12,500 Pa for the proposed AFTB design at the reference simulation condition.     

Theoretical considerations of static and dynamic characteristics of air foil thrust bearing with tilt and slip flow

The thrust pad of the rotor is used to sustain the axial force generated due to the pressure difference between the compressor and turbine sides of turbomachinery such as gas turbines, compressors, and turbochargers. Furthermore, this thrust pad has a role to maintain and determines the attitude of the rotor. In a real system, it also helps reinforce the stiffness and damping of the journal bearing. This study was performed for the purpose of analyzing the characteristics of the air foil thrust bearing. The model for the air foil thrust bearing used in this study is composed of two parts: one is an inclined plane, which plays a role in increasing the load carrying capacity using the physical wedge effect, and the other is a flat plane. This study mainly consists of three parts. First, the static characteristics were obtained over the region of the thin air film using the finite-difference method (FDM) and the bump foil characteristics using the finite-element method (FEM). Second, the analysis of the dynamic characteristics was conducted by perturbation method. For more exact calculation, the rarefaction gas coefficients perturbed about the pressure and film thickness were taken into consideration. At last, the static and dynamic characteristics of the tilting condition of the thrust pad were obtained. Furthermore, the load carrying capacity and torque were calculated for both tilting and nontilting conditions. From this study, several results were presented: (1) the stiffness and damping of the bump foil under the condition of the various bump parameters, (2) the load carrying capacity and bearing torque at the tilting state, (3) the bearing performance for various bearing parameters, and (4) the effects considering the rarefaction gas coefficients.     

以高压CO2为介质的推力箔片轴承静特性分析

针对超临界二氧化碳布雷顿循环用压缩机中的推力箔片轴承开展了数值研究,通过MATLAB编程数值计算求解变密度、变黏度湍流雷诺方程和耦合弹性箔片变形方程,得到楔形间隙内气膜压力分布及推力箔片轴承承载力和摩擦功耗,并与空气润滑介质对比;进一步分析推力箔片轴承节距比、瓦张角、楔形高度及最小气膜厚度对轴承承载力和摩擦功耗的影响。计算结果表明:高压CO₂下弹性箔片变形比常压空气时更大,轴承承载力远高于常压空气轴承;瓦张角为45°和节距比为0.5的推力箔片轴承具有较高的承载力和较低的摩擦功耗;楔形高度设计过大会降低承载力,增大摩擦功耗,使载荷集中在水平区域;增大最小气膜厚度设计值虽能减小摩擦功耗,但却引起承载力的显著降低。     

基于牛顿迭代法的波箔型止推轴承不对中特性分析

为研究波箔型气体轴承运行过程中偏角不对中对轴承性能的影响,选择波箔气体止推轴承作为研究对象,从Reynolds控制方程出发,研究偏角不对中情况下,轴承各个部分的气膜厚度分布情况;结合边界条件,运用牛顿迭代算法计算得到气膜压力分布,进一步分析不对中对波箔止推轴承的承载能力和摩擦力矩的影响。研究结果表明:偏角不对中对于波箔止推轴承的性能有较大影响;随着偏角的增大,最大气膜压力增加,轴承的压力分布越来越不均匀,轴承摩擦力矩增大,系统稳定性大幅降低,但承载能力有一定增强;当偏角过大时,不能得到收敛的结果,轴承几乎失效,对比正常运行的波箔型止推轴承,性能大幅下降;扇形箔数量的增加会导致轴承的承载能力与稳定性均减小。     

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.     

基于箔片非线性刚度模型的气体箔片轴承静特性研究*

基于箔片轴承结构刚度试验结果推导单个波纹箔片非线性刚度模型,通过有限差分法耦合求解气体Reynolds方程、气膜厚度方程和单个波纹箔片非线性刚度方程得到了轴承静态特性,研究波纹箔片非线性刚度对轴承静态特性的影响。通过对波纹箔片非线性模型和文献中的波纹箔片等刚度模型仿真结果进行对比分析,结果表明：单个波纹箔片刚度具有很强的非线性,轴承气膜压力分布不均使得轴承承载区波纹箔片的刚度要远远大于非承载区的刚度,并且轴承轻载时非线性刚度模型刚度值较小导致仿真得到的轴颈偏心率和非承载区的气膜厚度都明显大于文献恒定刚度模型的结果。此外,通过分析得出了一种先进行刚度试验得到单个箔片非线性刚度模型后利用数值方法进行求解的箔片轴承静特性分析方法。