Design of tilted hydrostatic thrust bearings

Hydrostatic bearings are usually designed to operate under parallel conditions, but structural and thermal deformations cause tilting of the pad. A semianalytical solution of the pressure equation is used. It is shown that tilting of hydrostatic thrust bearings gives rise to negative pressures and that cavitation may occur depending on the tilt parameter. The characteristic values of the bearing are found to be strong functions of the tilt parameter and of the bearing number.     

An isoviscous,isothermal model investigating the influence of hydrostatic recesses on a spring-supported tilting pad thrust bearing

Tilting-pad hydrodynamic thrust bearings are used in hydroelectric power stations around the world, reliably supporting turbines weighing hundreds of tonnes, over decades of service. Newer designs incorporate hydrostatic recesses machined into the sector-shaped pads.With the aid of external oil pressurisation at low rotational speeds, oil film thickness is increased, thereby reducing friction and wear to the benefit of service life and reliability. It follows that older generating plants, lacking such assistance, stand to benefit from being retrofitted with hydrostatic lubrication systems. The design process is not trivial however – the need to increase the groove area to permit spontaneous lifting of the turbine under hydrostatic operation conflicts with the need to preserve performance of the original plane pad design. A haphazardly designed recess can change the pressure distribution of the oil film in such a way as to tilt the pad away from its optimum position. This may lead to reduced oil film thickness and increased temperature, which is concomitant with reduced mechanical efficiency and increased risk of damage to the bearing surfaces. It is therefore, inadvisable to ignore the presence of grooves in simulations. In this work, a numerical study of a sector-shaped pad is undertaken to understand how recess size and shape can affect the performance of a typical bearing. An isoviscous, isothermal model has been used in this instance because the operating conditions of the turbine in question were shown not to be severe enough to warrant the computational expense of a fully coupled thermoelastic hydrodynamic model.     

The behaviour of hydrostatic pads with grooved lands

A hydrostatic pad is usually made up of a recess surrounded by a land. Viscous fluid is supplied under pressure to the recess. The land, being separated from the bearing surface by a relatively small clearance, will act as the hydraulic impedance needed to separate the required bearing pressure inside the recess from the pressure of the surrounding environment. If the pad is moved relative to the bearing surface, the film of fluid in the clearance, being viscous, will be sheared. This shearing action will initiate viscous shear stresses between the fluid layers and hence viscous drag between the moving pad and the bearing surface. The lands of the pad, having a much smaller clearance from the bearing surface, will be subjected to a much higher drag force than the recess. The power required to overcome such a drag force, and cause the required motion of the pad relative to the bearing surface, will be transformed mainly into heat. Sometimes, especially under high relative speeds and with small clearances, the generated heat can be detrimental to the bearing action, and if excessive, may lead to bearing failure.     

Tilting effects on the performance of hydrostatic and hybrid gas thrust bearings

A hydrostatic gas thrust bearing is analysed to determine the effect of tilting on its performance characteristics. The governing Reynolds Equation is solved simultaneously with the mass flow rate equation by numerical methods to determine the inlet pressure and the pressure distribution throughout the pad. It is shown that the load, friction, and lubricant mass flow rate are strong functions of the bearing number λ, restrictor coefficient λ_o, supply pressure and tilt parameter     

液压马达滑靴副倾侧状态下的静压支承特性分析

建立了描述滑靴副倾侧状态下的静压支承特性的数学模型，综合考虑了油液粘温效庆及流体动压效应对流场的影响，在此基础上通过数值方法求解流场控制方程，得到了滑块倾侧角度、曲轴转速以及温升对静压支承性能的影响关系，分析表明，滑靴倾侧对静压支承特性的影响随曲轴转速增大而增大，油液粘温关系对承载力影响较大，对抗倾能力影响不大。     

Influence of pad–pivot friction on tilting pad journal bearing

Some experimental studies reported that the performance of tilting pad journal bearing is related with the pad–pivot friction. Only a few researches, however, consider the friction as a factor even though many ones have theoretically analyzed the performance of bearing. Also, there is no mathematical model for the friction to explain the effect of friction on the performance of bearing. Therefore, this study proposes a mathematical model for the pad–pivot friction and analyzes the effect of friction on the tilting pad journal bearing.The results of this analysis show that the friction has a large influence on the attitude angle of the journal. It is found that the eccentricity direction of the journal does not coincide with the load direction when the friction is not zero. According to working conditions, the attitude angle can be up to 25° when friction coefficient is equal to 0.5. It is also found that the tilt angle of the pad is not determined as a fixed value in case of the bearing with non-zero friction, even though working conditions is given for the static analysis. This study represents four different tilt angles under same working conditions.     

Experimental assessment of hydrostatic thrust bearing performance

This work presents an experimental study to assess the performance characteristics of hydrostatic thrust bearings. A test rig is designed for testing two configurations of hydrostatic bearings compensated by a capillary tube, one with a mid-circular recess and the other with multi-sectors (four recesses of different recess radii ratios). The performance characteristics have been measured, namely, oil film thickness, recess pressure, pressure distribution and oil flow rate. A specially devised computer program using an iterative technique has been adopted to compute numerically the pressure distribution and predict other performance characteristics. Good agreement has been obtained between predicted theoretical performance and that experimentally measured. The results demonstrate that the bearing recess size and location have a great influence on the performance of the hydrostatic thrust bearing.     

刚性和弹性支撑可倾瓦推力轴承稳态特性分析

建立刚性球头支撑和弹性橡胶垫支撑可倾瓦推力轴承热弹流耦合模型；在弹性橡胶垫支撑可倾瓦推力轴承橡胶垫的弹性变形分析中采用了变形协调矩阵方法，以协调匹配橡胶垫变形和水膜厚度分布，同时在搜索稳态解的过程中引入模拟退火算法；基于变分原理求解Reynolds方程，得到了轴承水膜压力分布，并比较2种推力轴承在转子存在角不对中时的静特性。结果表明：理想工况下，刚、弹支可倾瓦推力轴承稳态特性没有明显区别；当转子存在不对中时，刚性球头支撑可倾瓦轴承在不同瓦块之间受力偏载严重，进而导致瓦面最小水膜厚度过小，瓦块容易出现磨损，而弹性支撑瓦不同瓦块之间水膜力分布更均匀，利于轴承的长期可靠运行。     

Investigation into the effects of orifice size, offset and overclamp ratio on the lubrication of slipper bearings

This paper represents the results of an experimental investigation of the performance of hydrostatic slipper bearings in axial piston pumps and motors. The effect of clamping ratio, offset loading and orifice size on the behaviour of overclamped and underclamped slippers is outlined. It is shown that the slippers run satisfactorily with no orifice and have their greatest resistance to tilting couples and to minimum film thickness. The underclamped slippers and slippers with larger orifice diameter run with relatively larger clearance and tilt than those of overclamped slippers with no orifice. Cavitation tends to affect the slippers, especially at the rear of the slipper. Ineffective flood lubrication may be the cause and oil jet pressure must be maintained to prevent oil starvation.     

Determination of Optimum Proportions for Hydrostatic Bearings

The effect of recess size on the pressure, flow and power requirements of several hydrostatic bearing configurations is described in terms of dimensionless coefficients called performance factors. Performance factors are determined analytically for a circular hydrostatic thrust bearing with a circular recess (for which there is a known solution), compared graphically with the electric analog solutions for this bearing and found to be in excellent agreement. The electric analog approach is also used to determine the performance factors of several other bearing configurations for which there are no known solutions. These data are presented in the form of dimensionless curves. It was found that for a given bearing configuration, there is a particular recess size which will give minimum supply pump power. Where limiting factors, such as, pump output pressure and/or flow do not dominate, it is suggested that bearings be designed to operate at the minimum pump power point.     

Theoretical investigations on the performance of an externally adjustable fluid-film bearing including misalignment and turbulence effects

An externally adjustable fluid-film bearing has been devised whereby the hydrodynamic conditions can be changed as required in a continuously controlled manner. Principal feature of the externally adjustable pad bearing is the facility to control the bearing clearance and film thickness gradient in circumferential direction, irrespective of the operating conditions. Unlike a tilting pad bearing, this bearing can have both radial and tilt adjustments. A single pad externally adjustable pad bearing will perform as a conventional partial arc bearing when the adjustments are set to zero.The paper deals with the effect of turbulence and misalignment on steady state characteristics of a centrally loaded 120° single pad externally adjustable bearing. The bearing has an aspect ratio of one and operates over a wide range of eccentricity ratios with adjustments and degrees of misalignment. Reynolds equation incorporated with linearized turbulent lubrication model of Ng and Pan is solved using a finite difference method. Static performance characteristics calculated are presented in terms of attitude angle, Sommerfeld number, friction variable, misalignment moment and oil flow. A study with various adjustments predicts that negative radial and negative tilt adjustment configuration results in superior static characteristics as compared to a conventional fluid-film bearing.     

Design of annular recess hydrostatic thrust bearing under dynamic loading

Design charts are presented of a dynamically loaded thrust bearing with as annular recess. The effect of non-parallelism between the bearing and the runner surfaces is also considered, since this is a common problem in hydrostatic thrust bearings. Based on pre-assigned dynamic excitations the pressure equation is solved numerically by finite difference methods to render the bearing performance characteristics namely: load capacity; bearing stiffness; damping coefficient; and lubricant flow rate. Results concluded that the bearing performance chareacteristics are dependent on the bearing radii ratios, the squeeze number, the bearing number and the tilt parameter.     

大型动静力径向可倾瓦轴承热弹流体润滑研究

用有限元素法建立瓦块3维弹性变形计算模型。针对小包角瓦块支点非均匀布置方式及下方瓦块设有高压油顶起油囊的大型低速重载动静力润滑径向可倾瓦轴承,研究了由于瓦块3维弹性变形对轴承热动力润滑性能的影响。结果表明,在低速重载条件下需要考虑瓦块的弹性变形对动静力可倾瓦轴承热动力润滑性能的影响。     

静压孔位置对油膜支承可倾瓦轴承承载性能的影响分析

为了提高汽轮机转子系统中支承轴承的油膜刚度,以三瓦油膜支承可倾瓦轴承为研究对象,研究静压孔相对位置对轴承承载性能的影响规律。建立了油膜支承可倾瓦轴承油膜润滑模型,并运用计算流体动力学方法数值求解三维N-S方程,揭示了不同静压孔相对位置下轴承压力分布、最小膜厚、偏心率、刚度等性能参数的变化规律。分析结果表明：在载荷为890 N的情况下,改变孔的位置可以提高轴承油膜刚度;当静压孔相对位置γ=5°左右时,孔位置接近油膜最大压力分布区,与γ=0°时相比,最小膜厚和偏心率分别减小9.8%和48%,主刚度kyy、kxx接近原结构的1.4倍和1.1倍,此时静压孔位置为相对最优位置区域。依据分析结果开发了新型油膜支承可倾瓦轴承（γ=5°）,通过试验对比分析了普通滑动轴承与新型油膜支承可倾瓦轴承的综合性能,结果表明,高转速时所开发的新型油膜支承可倾瓦轴承具有更好的承载性能与减振性能。研究结果对油膜支承可倾瓦轴承的性能分析具有一定的参考价值,设计轴承静压孔时可根据油膜压力分布规律对其优化以提高轴承性能。     

Influence of recess shape on the performance of a capillary compensated circular thrust pad hydrostatic bearing

This work describes a theoretical study concerning the static and dynamic performance of a circular thrust pad hydrostatic bearing having recesses of different geometric shapes. The Finite Element Method has been used to compute the performance characteristics of a circular thrust pad hydrostatic bearing with circular, rectangular, elliptical and annular recesses. The performance has been compared on the basis of the same bearing operating and the same geometric parameters, i.e. the same ratio of bearing to pocket area ( ) and the same value of restrictor design parameter . Further, a comparative study of the various bearing configurations has been carried out vis-à-vis different compensating devices such as capillary, orifice, and constant flow valve restrictors so as to study the combined influence of the geometric shape of recesses and the compensating device on bearing performance. The computed results indicate that to get an improved performance from a hydrostatic circular thrust pad bearing, a proper selection of the geometric shape of the recess in conjunction with the type of restrictor and the value of the restrictor design parameter is essential.     

Theoretical analysis of the dynamic stiffness of conical hydrostatic thrust bearings under tilt,eccentricity and rotation

A theoretical study of the dynamic stiffness characteristics of capillary compensated annular recess conical hydrostatic thrust bearings under conditions of tilt, eccentricity and rotation is reported. The influences of aspect ratios, cone angles and resistance ratios on the dynamic stiffness are discussed.     

柔性支承结构对可倾瓦轴承稳定性的影响

为了进一步提高可倾瓦轴承支承转子系统的稳定性，提出由弹簧支承的柔性可倾瓦轴承结构。设计制造单层弹簧和双层弹簧支承的2种柔性可倾瓦轴承试样，在转子-轴承实验台上开展稳定性实验研究。实验结果表明：由弹簧支承的柔性可倾瓦轴承综合支承刚度小于普通可倾瓦轴承的支承刚度，新型柔性可倾瓦轴承具有降低转子临界转速的作用；相比于普通可倾瓦轴承，柔性支承可倾瓦轴承明显降低轴频振幅，能够有效提高转子-轴承系统的运行稳定性，且双层弹簧支承的可倾瓦轴承稳定性提高更为显著。     

涡旋式制冷压缩机止推轴承润滑性能研究的最新进展

在涡旋式制冷压缩机运行过程中,止推轴承动止推盘两端的压力差对轴承的润滑性能有显著的影响;止推轴承本身的结构特点,如键槽的存在,也会影响止推间隙的压力分布以及倾斜角,从而影响止推轴承的润滑性能.对止推轴承动止推盘两端的压力差、止推轴承本身结构等影响因素从理论或试验等方面进行探讨,并对将来涡旋式制冷压缩机止推轴承润滑性能的研究进行展望.     

An experimental investigation into the performance of externally pressurized rectangular air bearings

An experimental programme which was designed to investigate the performance characteristics of externally pressurized rectangular air bearings considering the effects of pad geometry and inlet gas conditions is presented. Three forms of rectangular bearings were considered: one arrangement consisted of continuous plane surfaces, the second had a recessed pad and a plane bed and the third had a plane bed and a recessed pad with a step in the bearing area following the recess.

The results revealed that the recess length has a dominant effect on the pressure distribution in the air film. The effect of pressure depression is obvious at extremely small clearances and supply pressures. Such an effect is exaggerated when a step is introduced in the pad surface. The introduction of the step improves the load-carrying capacity of the bearing as long as the bearing is free from shock-wave formation.     

圆形可倾瓦推力轴承润滑的计算机仿真

针对大型设备中所应用的圆形可倾瓦推力轴承的润滑问题,采用计算机对圆形可倾瓦推力轴承的润滑性能进行了仿真,通过软件程序计算了单个圆形可倾瓦推力轴承瓦面的油膜形状分布情况、油膜压力分布规律及油膜温度分布规律、功率损耗大小、流量多少等参数。结果表明,通过该仿真程序可模拟出不同工况下圆形可倾瓦推力轴承润滑参数,进而提前实现对圆形可倾瓦推力轴承润滑特性的预测,为大型设备中所使用的圆形可倾瓦推力轴承的设计、润滑和实验提供基础数据。