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.     

弹性支承箔片动压气体径向轴承的实验研究

对新型结构弹性支承箔片动压气体径向轴承进行试验研究,在高速透平膨胀机(主轴轴径D=25.0mm、转子总长l=250.5mm、转子质量Gm=891g、额定工作转速10.64×104r/min)上达到了转子转速14.8×104r/min、超速40%的良好试验效果。对这种弹性支承箔片动压气体径向轴承的振动特性和稳定性进行试验研究。结果表明,该轴承具有优良的动态特性与稳定性,能有效抑制高速自激涡动的发展,在正确选择结构参数和表面处理方法后,有望替代目前在高速透平机械中广泛应用的静压气体轴承。     

波箔型动压气体径向轴承的应用与研究进展

简要综述了波箔型动压气体径向轴承的发展过程、具体结构形式和应用.详细介绍了国内、外关于波箔型动压气体径向轴承试验和理论方面研究的最新进展情况.     

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。     

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.     

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。     

挠性气体动压径向轴承的理论分析

本文对挠性气体动压径向轴承提出了一种新的理论分析方法。用等参有限元法分析二维动压润滑，借助于约束矩阵和简化递推算法求解弹性体变形，得到了一定转速和偏心距下的气膜厚度和压力分布，计算了轴承的承载能力，刚度和起动力矩等性能参数。     

波箔动压空气径向轴承实验台设计

现有的波箔动压空气径向轴承实验台存在最大工作转速达不到轴承实际工作转速,无法在不影响轴承正常工作的情况下对轴承施加径向载荷,无法测量轴承的阻力距等缺点.为了全面满足波箔动压空气径向轴承的实验需要,设计一种最高转速为60 000 r/min的波箔动压空气径向轴承实验台,可以在不影响轴承正常工作的情况下对轴承施加径向载荷,可以同时测量转轴转速、轴承阻力距、转轴水平和竖直方向的位移、轴承工作温度、冷却空气的压力.     

高速动压气体轴承箔片材料表面处理的探讨

针对高速透平机械动压气体轴承——箔片式气体轴承金属箔片材料的表面处理问题进行了一定的探讨。对箔片式气体轴承箔片材料的选择、材料的表面处理方法以及该轴承的启停性能和稳定性进行了实验研究。分析表明：通过对箔片材料及表面处理方法的合理选择，可以显著改善箔片式动压气体轴承的启停性能。     

Misalignment In A Complete Shell Gas Foil Journal Bearing

The effect of misalignment on the performance of a complete shell gas foil bearing is discussed. An iterative theoretical model based on the finite element method is used. The model includes membrane and elastic foundation effects in the structural model. An isothermal perfect gas is used as the lubricant fluid. Results are presented demonstrating the effect of misalignment on load capacity, minimum clearance, and moments acting normal to the journal.     

The Experimental Study of Aerodynamic Plate-Foil Journal Bearings for High Speed Cryogenic Turboexpander

Experiments have been conducted on the application of a new type of gas lubricated self-acting journal bearing—plate-foil bearing to a high speed cryogenic turboexpander. The 25.0 mm diameter bearing consists of a rigid housing and a flexible foil element; different structure parameters of the bearing are selected in the experiments. Experimental results indicate the foil bearing presented here offers better system stability performance and high durability, and it confirmed that the application of this type of plate-foil bearing to the cryogenic turboexpander is feasible. The experiment results, including the effect of the plate-foil bearing structure parameters on the rotor-bearing system stability, are described in this paper.     

An Experimental Investigation into the Temperature Profile of a Compliant Foil Air Bearing

A series of tests was performed to determine the internal temperature profile in a compliant bump-type foil journal air bearing operating at room temperature under various speed and load conditions. The temperature profile was collected by instrumenting a foil bearing with nine type-K thermocouples arranged in the center and along the bearing's edges in order to measure local temperatures and estimate thermal gradients in the axial and circumferential directions. To facilitate the measurement of maximum temperatures from viscous shearing in the air film, the thermocouples were tack-welded to the backside of the bumps that were in direct contact with the top foil. The mating journal was coated with a high-temperature solid lubricant that, together with the bearing, underwent high-temperature start-stop cycles to produce a smooth, steady-state run-in surface. Tests were conducted at speeds from 20 to 50 krpm and loads ranged from 9 to 222 N.

The results indicate that, over the conditions tested, both journal rotational speed and radial load are responsible for heat generation with speed playing a more significant role in the magnitude of the temperatures. The temperature distribution was nearly symmetric about the bearing center at 20 and 30 krpm but became slightly skewed toward one side at 40 and 50 krpm. Surprisingly, the maximum temperatures did not occur at the bearing edge, where the minimum film thickness is expected, but rather in the middle of the bearing, where analytical investigations have predicted the air film to be much thicker. Thermal gradients were common during testing and were strongest in the axial direction from the middle of the bearing to its edges, reaching 3.78° C/mm. The temperature profile indicated the circumferential thermal gradients were negligible.     

The Role of Radial Clearance on the Performance of Foil Air Bearings

Load capacity tests were conducted to determine how radial clearance variations affect the load capacity coefficient of foil air bearings. Two Generation III foil air bearings with the same design but possessing different initial radial clearances were tested at room temperature against an as-ground PS304 coated journal operating at 30000 rpm. Increases in radial clearance were accomplished by reducing the journal's outside diameter via an in-place grinding system. From each load capacity test the bearing load capacity coefficient was calculated from the rule-of-thumb (ROT) model developed for foil air bearings.

The test results indicate that, in terms of the load capacity coefficient, radial clearance has a direct impact on the performance of the foil air bearing. Each test bearing exhibited an optimum radial clearance that resulted in a maximum load capacity coefficient. Relative to this optimum value are two separate operating regimes that are governed by different modes of failure. Bearings operating with radial clearances less than the optimum exhibit load capacity coefficients that are a strong function of radial clearance and are prone to a thermal runaway failure mechanism and bearing seizure. Conversely, a bearing operating with a radial clearance twice the optimum suffered only a 20% decline in its maximum load capacity coefficient and did not experience any thermal management problems. However, it is unknown to what degree these changes in radial clearance had on other performance parameters, such as the stiffness and damping properties of the bearings.     

平箔动压止推气体轴承的试验研究

本文提出了一种新型结构的箔片止推动压气体轴承，搭建了多功能止推轴承试验台，并主要针对其承载力性能进行了初步的试验研究，试验轴承的外径为φ38mm，内径为φ16mm，在11000r/min的转速下获得的最大轴向承载力为44.1N。     

Minimum Film Thickness in a Gas Foil Journal Bearing with an Unbalanced Rotor

A gas-lubricated foil journal bearing consists of a compliant metal shell structure that supports a rigid journal or rotor by means of a gas film. The response of this system to the periodic forces of an unbalanced rotor supported by a single bearing is predicted using perturbation analysis. The foil structure and the gas film are modeled with an analytically perturbed finite element approach to predict the rotor dynamic coefficients. A dynamic model of the rotor is used to predict periodic journal motion. The perturbation analysis is then used with the periodic response of the rotor to calculate periodic changes in the gas film thickness. Other quantities such as the gas film pressure and the foil deflection can also be calculated. The model includes bending and membrane effects in the top foil, coupled radial and circumferential deflections in the corrugated sub-foil, and the equivalent viscous dissipation of Coulomb friction effects in the foil structure. The approach is used to investigate the effects of top-foil thickness on minimum film thickness in a bearing.     

Dynamic Stiffness and Damping Characteristics of a High-Temperature Air Foil Journal Bearing

Using a high-temperature optically based displacement measurement system, a foil air bearing s stiffness and damping characteristics were experimentally determined. Results were obtained over a range of modified Sommerfeld Number from 1.5E6 to 1.5E7, and at temperatures from 25° to 538°C.

An Experimental procedure was developed comparing the error in two curve fitting functions to reveal different modes of physical behavior throughout the operating domain. The maximum change in dimensionless stiffness was 3.0E-2 to 6.5E-2 over the Sommerfeld Number range tested. Stiffness decreased with temperature by as much as a factor of two from 25° to 538°C. Dimensionless damping was a stronger function of Sommerfeld Number ranging from 20 to 300. As the temperature is increased, the damping shifts from a viscous type to a frictional type.     

Journal Design Considerations for Turbomachine Shafts Supported on Foil Air Bearings

Foil air bearings can offer substantial improvements over traditional rolling element bearings in many applications and are attractive as a replacement to enable the development of advanced oil-free turbomachinery. In the course of rigorous testing of foil journal bearings at NASA Glenn Research Center, shaft failure was repeatedly encountered at high ambient temperature and rotational speed, with moderate radial load. The cause of failure is determined to be excessive non-uniform shaft growth, which increases localized viscous heating in the gas film and eventually leads to a high-speed rub and destruction of the bearing and journal. Centrifugal loading of imbalance correction weights and axial temperature gradients within the journal due to the hydrodynamic nature of the foil bearings, determined by experiment and finite element analysis, are shown to be responsible for the non-uniform growth. Qualitative journal design guidance is given to aid in failure prevention.