Prevention of fluttering fatigue damage in a tilting pad journal bearing

Tilting pad journal bearings have been widely used to support high-pressure/fast rotating turbine rotors owing to their inherent dynamic stability characteristics. However, fatigue damage in the upper unloaded pads and the break of locking pins by pad fluttering continuously take place in actual steam turbines. The purpose of this paper is to develop a bearing model that can prevent bearing problems effectively using pad fluttering in a tilting pad journal bearing. A developed bearing model with a wedged groove is suggested from studies of a fluttering mechanism performed in previous research. The fluttering characteristics of the upper unloaded pad are studied experimentally in order to verify the reliability of the bearing model. It was found that very little pad fluttering nearly occurs in the bearing model under various experimental conditions. In addition, no type of bearing failures by pad fluttering was detected in applications involving actual steam turbines.     

Analysis of heavy duty tilting-pad journal bearing taking into account pad distortion and possible adoption of rubber pad segments

In this work a comparative study has been made between the thermo-hydrodynamic performance of a three shoe tilting-pad journal bearing with rigid and elastic pads subjected to unbalance load. A case study of a bearing adopting three rubber pad segments has also been studied. The distortion of the elastic pad is introduced into the distribution of the film thickness through an iterative scheme to assess its effect on the load carrying capacity of the bearing. A finite element mesh is used to calculate the distortion of the elastic pad while a finite difference mesh is used to calculate the pressure field in the lubricant film. Results have shown a number of interesting conclusions regarding the adoption of rubber pad segments instead of tilting-pads. There is an increase in minimum oil film thickness when using elastic pad or even rubber pad segments compared with rigid pads. Also the maximum pressure and load carrying capacity are not significantly affected.     

Analysis of a tilting pad journal bearing to avoid pad fluttering

This paper describes the investigation into the static and dynamic performance of a tilting pad lightly loaded journal bearing. Some of the bearings were operating with some of the pads fluttering. The analysis of the bearings confirmed the likelihood of pad fluttering and so three possible means to overcome this phenomenon were investigated. Introducing a pad preload would require the installation of a number of shims into the bearing. Similarly, installing pad stops and/or springs introduced more working parts to each bearing. The third option of machining a leading edge taper or relief on each pad was deemed to be the better solution. The geometry of this relief (depth and length around the arc) was found to be an important design parameter. The larger the angular extent of the relief and the deeper it is were found to increase the oil flow rate, thereby reducing the operating temperature of the bearings. The direct stiffness of the bearing is improved by introducing a relief to the leading edge of each pad. Design changes were made to the actual bearings with a significant reduction in bearing operating temperature and wear.     

可倾瓦推力轴承瞬态热效应的实验研究

:通过实验 ,研究了可倾瓦推力轴承在空载快速启动及慢速启动过程中油膜温度的瞬态变化规律 ,探讨了加载时载荷变化、转速变化及转速变化率等因素对推力轴承油膜温度的影响。实验时 ,在瓦块进油、出油边及油膜与瓦块接触面上布置了若干根铜 -康铜热电偶 ,并选用了英国施伦伯杰公司的 IMP分布式数据转换器与一台主频为16 6 MHz的计算机组成了动态温度、油膜厚度数据采集系统。实验表明 :油膜温度变化速度并不如现有的关于数值计算的文献报导的迅速。转速或载荷增大时 ,油膜温度上升 ,油膜厚度减小 ,但是转速变化对油膜瞬态温度的影响要比载荷的影响大。值得注意的是 ,在一定载荷下 ,转速增加时 ,油膜温度首先上升 ,到达峰值后逐渐下降。     

可倾瓦推力轴承惰转过程的最小膜厚预测方法

为建立可倾瓦推力轴承惰转过程中最小油膜厚度的预测方法,依据核主泵推力轴承的实际工作情况,基于雷诺方程的自编程序,分别进行热态和冷态下主、副轴瓦润滑性能参数的计算与数值模拟分析,提出可倾瓦推力轴承的最小油膜厚度的理论拟合公式,并对最小膜厚的计算值和拟合值进行对比和分析。结果表明：随着转速降低,主轴瓦的最小膜厚单调减小,副轴瓦的最小膜厚先增加后减小;主、副轴瓦最小膜厚的计算值可以和拟合值较好地对应,验证了理论拟合公式的可靠性。提出的理论拟合公式可以通过额定转速下的最小膜厚计算结果预测多种工作条件下的最小油膜厚度,为主泵惰转的安全性提供重要参考。     

滑动轴承动压特性的影响因素研究

以某发动机惰齿轮轴承为研究对象,采用一维动力学方法进行多工况计算,针对油孔布置、载荷方向、载荷大小、轴承转速4种因素,分析滑动轴承润滑油流量、最小油膜厚度、偏位角、最大油膜压力4个动压特性参数的变化规律。结果表明：油孔布置和载荷方向主要对润滑油流量有明显影响,而对其他3个动压特性参数影响较小;油孔数量越多,油孔在圆周方向上越靠近油膜厚度最大处,则润滑油流量越大;油孔分布越均匀,因载荷方向改变引起的流量波动越小;载荷大小和轴承转速对4个动压特性参数都有明显影响;随载荷增加,最大油膜压力大致呈线性增加,而其他3种动压特性的变化速率降低;随转速增大,最大油膜压力减小的速率逐渐降低,而其他3种动压特性大致呈线性增加。     

Hydrodynamic Performance of a Thrust Bearing with Micropatterned Pads

The primary objective of this study was to investigate the influence of surface texturing on hydrodynamic lubrication of tilting-pad thrust bearings in terms of bearing power loss, operating temperature, and oil-film thickness. For this purpose, the working faces of six thrust pads from a 228.6-mm-outer-diameter bearing were textured. The textured surface consisted of a system of crossing channels of less than 10 μm in depth. Tests were conducted with a VG68 mineral turbine oil supplied to the bearings at a constant temperature of 50°C and flow rate of 15 L/min. The following parameters were measured: frictional torque, pad and collar temperatures, oil-film thickness, and pressure profiles along two circumferential lines. No significant change in collar and pad temperature could be observed when the patterned bearing was used. However, the textured bearing showed a tendency to exhibit lower power loss especially when an optimum oil flow supply rate was used. At the same time, inlet and outlet film thicknesses for the patterned bearing showed larger values than those obtained during tests on the plain babbitt pads.     

Measurement of fluid film thickness on the valve plate in oil hydraulic axial piston pumps (I)-bearing pad effects-

The tribological mechanism between the valve plate and the cylinder block in oil hydraulic axial piston pumps plays an important role on high power density. In this study, the fluid film thickness between the valve plate and the cylinder block was measured with discharge pressure and rotational speed by use of a gap sensor, and a slip ring system in the operating period. To investigate the effect of the valve plate shapes, we designed two valve plates with different shapes : the first valve plate was without a bearing pad, while the second valve plate had a bearing pad. It was found that both valve plates behaved differently with respect to the fluid film thickness characteristics. The leakage flow rates and the shaft torque were also experimented in order to clarify the performance difference between the valve plate without a bearing pad and the valve plate with a bearing pad. From the results of this study, we found out that in the oil hydraulic axial piston pumps, the valve plate with a bearing pad showed better film thickness contours than the valve plate without a bearing pad.     

Performance of synthetic oils in the hydrodynamic regime ‐ II. Generalisation

In Parti I the results of an extensive experimental investigation of the performance of environmentally adapted oils in the hydrodynamic regime were reported. Four oils were tested in a tilting‐pad thrust bearing for different combinations of load, shaft speed, and supply oil temperature. In this second part, details of a generalisation procedure are described. A number of parameters representing the physical properties of an oil, such as viscosity and viscosity‐temperature coefficient, are adopted. The influence of each of these parameters on minimum oil film thickness, maximum temperature rise, and bearing power loss is then analysed. It is shown that viscosity measured at the supply oil temperature is the most important parameter. The effects of the viscosity‐temperature coefficient and oil thermal conductivity are less pronounced and yet significant. It is also shown that it is not possible to select an optimum oil that yields maximised oil film thickness, minimised temperature rise, and minimised power loss at the same time.     

Comparison of an optimum‐profile hydrodynamic thrust bearing with a typical tilting‐pad thrust bearing

The oil gap profile in a hydrodynamic thrust bearing exerts a great influence on the bearing properties, and hence the optimisation of the oil gap profile is one method for improving the bearing properties. In the present work, the properties of two hydrodynamic thrust bearings have been experimentally compared under realistic load/ speed conditions. One was a typical tilting‐pad bearing and the other was an unconventional bearing with an elastic thrust plate. The latter was designed using oil gap profile optimisation and design parameter selection. Owing to the design method used, the oil gap profile was close to optimum for the assumed load/speed conditions. The results show a substantial increase in the minimum oil film thickness and lower temperature in the bearing with the elastic thrust plate. This improvement of properties is thought to be because of the optimised oil gap profile in the bearing.     

Design of an offset hydrostatic thrust bearing under dynamic loading conditions

An offset hydrostatic thrust bearing is analysed to determine the effect of vibration of the rotating plate on the performance characteristics. The flow developed is asymmetric because the surface rotation axis is offset from the bearing axis. The governing Reynolds equation is solved using semianalytical methods. The average load capacity, frictional force and lubricant flow rate are strong functions of the bearing offset L, bearing number λ, film thickness profile H, film thickness variation ? and the ratio between the frequency of vibration of the rotating plate and the angular speed of rotation.     

运行过程中转速变化时可倾瓦推力轴承油膜温度瞬态变化规律的实验研究

本文实验研究了可倾瓦推力轴承在运行过程中的不同载荷下、不同升速时间下从起始转速８００ｒ／ｍｉｎ升到截止转速５０００ｒ／ｍｉｎ时油腊温度和油膜厚度变化值的瞬态变化规律。实验时,在瓦块进油、出油边及油腊与瓦块接触面上布置了若干根铜－康铜热电偶和电涡流传感器。实验表明大运行过程中。转速升高时,不同的升速时间对油膜温度、进油边温度、出油边温度以及油腊厚度变化的影响基本相同;不同载荷对油膜温度、进油边温度以     

A FEM approach to simulation of tilting-pad thrust bearing assemblies

Finite-element method (FEM) modelling is applied to analysis of the performance of hydrodynamic tilting-pad thrust bearing assemblies. A 3D model of the bearing assembly that includes the bearing pad and shaft is used to assess the influence of operating conditions on bearing parameters such as temperature and oil film distributions across the pads. The model is first applied to the investigation of a spherically pivoted-pad. Through comparison with results from experiments carried out on just such a bearing, good correlation between the model and experimental results is found for maximum oil film temperature, pressure distribution and thickness. The model is then applied to the examination of a bearing having spring-supported babbitt pads. The effect of different oil types on a spring-supported thrust bearing is analysed. Further application of the model to investigate the same spring-supported pad, this time with a resilient surface coating, is discussed.     

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。     

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.     

轴承腔中均匀流体/壁面油膜分层流动分析

航空发动机轴承腔精确的润滑与换热设计依赖于对其内油气两相润滑介质流动与换热本质的认识。针对轴承腔内复杂的油气两相润滑介质流动状态,建立轴承腔均匀流体/壁面油膜分层流动分析模型,开展腔内油气两相润滑介质流动特性研究,探讨转子转速和润滑油供油量对均匀流体和壁面油膜两相介质压力、速度以及温度分布的影响。分析模型中,气相介质(含油滴)的等效物理特征参数通过离散油滴和气相介质的组分比例关系确定,各固体壁面与流体介质的对流换热系数根据其各自的传热特性确定。研究结果表明,均匀流体与壁面油膜两相介质的压力随着润滑油供油量的增加而增大,受转子转速的影响较为复杂;均匀流体与壁面油膜两相介质的速度随着转子转速的增高而增大,受润滑油供油量影响较小;均匀流体的温度随着润滑油供油量的增加而减小,受转子转速的影响较小;与均匀流体温度不同,壁面油膜的温度随着转子转速的增加而增大,随着润滑油供油量的增加而减小。建立了轴承腔试验台系统,开展了轴承腔油气两相流动状态下的压力和温度测试,压力和温度试验结果与理论计算结果均具有较好的吻合性,验证了提出的理论分析方法的可靠性。     

多叶动压气体滑动轴承静态特性的有限差分算法

多叶动压气体滑动轴承因其结构简单、摩擦阻力低、旋转精度高和无环境污染等优点,在高速离心分离机、空气压缩机和透平膨胀机等旋转机械中应用广泛。为探究多叶动压气体滑动轴承的静态性能,通过数学变换将三叶动压轴承的气体润滑Reynolds方程转化为标准偏微分方程形式,利用有限差分法和超松弛迭代法进行数值求解,研究气膜厚度和气膜压力分布、承载力、摩擦因数和质量流量等静态性能,随偏心率、预负荷系数、轴承数、长径比及瓦块分布位置的变化规律。结果表明：三叶轴承的承载力和轴颈表面摩擦因数随偏心率和长径比的增加而增加,而偏位角和质量流量随偏心率和预负荷系数的增加则呈现出相反的变化趋势;随着轴承数和预负荷系数的增大,承载力和摩擦因数显著提高,偏位角和质量流量则逐渐减小;瓦块分布位置对三叶动压气体滑动轴承的静态性能影响显著,其中瓦上承载方式的承载力、偏位角和质量流量明显高于瓦间承载方式。     

柴油机曲轴润滑与弯曲振动耦合影响研究

为研究柴油机强化过程中曲轴的弯曲振动和润滑性能的耦合关系,基于曲轴动力学和润滑理论,考虑曲轴和轴承座的弹性变形,建立某型12缸柴油机曲轴计算模型,分析主轴颈弯曲振动和最小油膜厚度间的耦合关系,并研究轴承宽度、半径间隙和润滑油黏度对两者的影响。结果表明:最小油膜厚度与弯曲振动变化趋势相反,两者存在耦合关系,同时油膜能够对振动起到一定的缓冲作用;在研究范围内,最小油膜厚度随主轴承宽度和润滑油黏度的增加而增加,弯曲振动随之减小;半径间隙对润滑和振动的影响较大,适当增大间隙值,最小油膜厚度增加,过大的间隙值加大轴颈的振动冲击,降低最小油膜厚度。该结果对柴油机强化设计过程中曲轴的润滑与振动预测和控制提供了参考。     

Theoretical and Experimental Study on the Axial Oil Film Stiffness of Tilting Pad Thrust Bearings

Tilting pad thrust bearings are a key component of marine propulsion shaft systems. The dynamic performance of thrust bearings has a significant influence on the propeller vibration. To investigate the axial oil film stiffness of tilting pad thrust bearings, a two-dimensional thermohydrodynamic model incorporating the vibration frequency is developed. The test apparatus and experimental identification model are also constructed. The axial oil film stiffness is experimentally identified at different speeds, loads, and temperature employing the hammer impulse excitation. The axial oil film stiffness between theoretical and experimental results is compared. The discrepancies are not more than 7% for 30 kN operation cases but increase with axial static load. This is partially because the influence of the pivot stiffness becomes obvious with the axial static load increase and cannot be ignored. The results indicate that axial oil film stiffness is at a magnitude of 10⁹ N·m^?1. Compared to foundation stiffness of the thrust bearing system, the influence of axial oil film stiffness needs to be considered for bearing–rotor system design of marine propulsion systems in engineering practice.     

不同轴向载荷下氮化硅全陶瓷轴承润滑特性

全陶瓷球轴承广泛应用在航天航空领域、燃气发动机和极端工况下,然而针对全陶瓷轴承油润滑特性的研究比较少见。以氮化硅6206全陶瓷深沟球轴承作为研究对象,在轴承测振仪上开展陶瓷轴承润滑特性实验研究,采用拟静力学和最小油膜厚度理论通过MatLab的牛顿迭代法得到比较精确的数值解,分析陶瓷轴承的接触载荷、轴向载荷、离心力、最小油膜厚度之间的关系,并通过改变供油量和轴向载荷得到陶瓷轴承在不同工况下的振动规律。实验结果表明：在轴向载荷相同条件下球与外圈之间的接触载荷比球与内圈之间的接触载荷大,轴向位移随着轴向载荷增加呈递增趋势;在轴向载荷一定时,存在一个最佳供油量使轴承振动最小,在干摩擦条件下轴承振动随着轴向载荷增加呈先减少后增大的趋势。