不同微结构静压轴承油膜流动特性研究

在剪切力和压缩力共同作用下,液体静压轴承黏性油膜的液阻和流速会发生变化,导致油膜的散热能力不稳定,而增加油膜流动阻力,减小流动速度可以有效提高油膜的散热能力。为增加流体的扰动进而增强换热,在静压轴承工作面上加工不同的微结构(矩形、三角形、椭圆形),通过数值仿真方法研究微结构在不同跨度、不同深度、不同间距下对轴承工作面油膜流动速度的影响,得到黏性油膜增阻减速的有效范围。结果表明：综合微结构深度、跨度、间距变化对油膜液阻的影响,矩形微结构增阻效果最明显,椭圆形微结构次之,三角形微结构最差;当微结构间距单一变化时,只有矩形微结构可起到降低流场平均速度的作用。因此,矩形微结构可起到增阻减速的作用,且增阻减速的最佳间距范围为0.01～0.04 mm。     

Effect of recess geometry on shock wave formation in circular gas bearings

An analytical method, based on the concept of shock wave formation in the bearing clearance, is used to develop a mathematical model by which the pressure distribution along the fluid film can be predicted. Based on this model, the limiting conditions for shock free operation are determined. The effects of recess geometry and inlet gas conditions are analysed. Experimental pressure distributions along the fluid film at different values of film thickness, supply pressure and rotating speed compare well with the theory. The analysis reveals that a bearing with a tapered recess has a higher resistance to shock wave formation than a conventional bearing having the same recess volume. Moreover, the tapered recess bearing has superior stability to the conventional bearing for the same recess depth.     

A numerical method for the calculation of lubricant pressures in bearings with mixed lubrication

A model for mixed lubrication, assuming that the total normal load applied to the plane of the lubricated surfaces is carried partly by the hydrodynamic action of the lubrication film and partly by asperity contacts and that the total friction force between the lubricated surfaces is partly due to viscous friction and partly to asperity contacts, was used to develop a numerical solution for pressure distribution in a bearing experiencing mixed lubrication. The geometry treated and the pressure distribution obtained were for a simple slider bearing, but the method could easily be extended to other shapes. The model is based on measured roughness of a real surface. Real load carrying capacity and drag can therefore be determined since they are related directly to bearing pressure distribution     

The Behavior of the Centrally Pivoted Thrust Bearing Pad with Hydrostatic Recesses Pressurized by a Constant-Rate Flow

The tilting behavior of the centrally pivoted, externally pressurized tilting thrust pad is investigated. The pressure distribution in the oil film is obtained by solving the Reynolds' equation which takes into account the external pressurization induced by a constant-rate flow. The relation between the size of the hydrostatic recess and the tilt angle of the pad is described. Calculations show that a pad with pressure recesses may have a negative tilt angle, depending on the size of the recess. The pressure variation around the hydrostatic pressure recess causes the moment to force the pad to tilt backward. At high shaft rotational speeds, the pad tilts backward too much and eventually fails to support the load. The hydrostatic pressure recess that is utilized to avoid the metal contact may cause this. The result was confirmed by experiments.     

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.     

推力轴承支承方式及间隙影响研究

研究了推力轴承支承方式及油膜间隙对推力轴承性能的影响,利用Newton-Raphson法编制差分计算程序,求得了推力轴承Reynolds方程和二维能量方程的数值解,得到了不同支撑方式下瓦块的油膜厚度、压力分布和温度分布。计算结果表明,点支承扇形瓦推力轴承的热力学性能要好于线支承扇形瓦推力轴承,同时支承处的油膜厚度对瓦块的承载能力影响很大。可以通过控制每个瓦块支承处的油膜厚度,避免推力轴承内部偏载的发生,降低推力瓦块的最大温升。     

非牛顿介质中图形化表面对减阻效果的影响

为研究图形化表面在非牛顿介质中对减阻效果的影响,在微摩擦试验机(UMT)上进行了销盘润滑实验。实验中在硅片的表面刻蚀了纵向和横向2种沟槽以形成不同的表面图形。实验表明,与光滑表面相比,当剪切速率处于牛顿流动区时,沟槽具有一定的减阻效果;而当剪切速率处于剪切稀化区时,沟槽表面的阻力上升;并且横向沟槽表面的阻力总是大于纵向沟槽表面的阻力。流体数值计算的结果表明,横向沟槽侧壁的压差阻力和纵向沟槽侧壁的粘性阻力无法完全补偿沟槽底面上的阻力损失,因而产生了减阻效果。     

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。     

Axial load capacity of water-lubricated hydrostatic conical bearings with spiral grooves for high speed spindles: Comparison between rigid and complaint surface bearings

In this paper, two types of water-lubricated hydrostatic conical bearings with spiral grooves for high-speed spindles are investigated. One has a rigid bearing surface and the other has a compliant one. In these bearings, pressurized water is first fed to the inside of the rotating shaft and then introduced into spiral grooves through feeding holes. Therefore, water pressure is increased due to the effect of the centrifugal force at the outlets of the feeding holes by shaft rotation and, furthermore, water pressure is also increased by the viscous pump effect of spiral grooves. The static characteristics of these bearings are theoretically predicted and calculated results are compared with experimental results. It was found that the compliant surface bearing had a larger load capacity in a relatively large bearing clearance than the rigid surface bearing, and lower bearing power consumption in a small bearing clearance although the load capacity is reduced.     

A revised design of circular hydrostatic bearings for optimal pumping power

A modification of the circular flat externally pressurized thrust bearing is presented in this paper. This involves the addition of a central step in the bottom of the rotating pad for the purpose of restricting the lubricant flow and minimizing the pumping power required for continuous operation. The performance of such a bearing configuration under static loads is analysed and the key design parameters are discussed, grouped and presented in a design chart. In addition to the minimization of pumping power, the proposed configuration provides higher thrust loads and enables the bearing to withstand radial loads, an advantage which could not be achieved in other hydrostatic thrust bearing configurations. The bearing is also able to restore concentricity due to the lateral damping provided by the squeezed lubricant film in the clearance between the step and the recess.     

压缩机可倾瓦轴承先进模型预测与测试数据的对比

The paper details fundamental progress on the analysis of tilting pad journal bearings that includes both pivot flexibility and pad surface deformation due to pressure and pad crowning due to thermal effects.The work introduces a novel model for the mixing of flow and thermal energy at a lubricant feed port that sets the temperature of the lubricant entering a pad leading edge. Precise estimation of this temperature, the inlet oil viscosity, and the flow rate entering a pad largely determines the temperature rise along the pad lubricated surface as well as the drag power loss, and ultimately the bearing load capacity. The model predictions are validated against bearing test data applicable to a compressor. The paper delivers recommendations for a novel feed port efficiency parameter that represents various types of oil supply configurations. Importantly enough, and as is done in actual practice, the model allows the specification of the delivery flow date into the bearing rather than a supply pressure.     

CHARACTERISTCS OF FLUID FILM IN OPTIMIZED SPIRAL GROOVE MECHANICAL SEAL

In order to investigate the sealing performance variation resulted from the thermal deformation of the end faces, the equations to calculate the fluid film pressure distribution, the bearing force and the leakage rate are derived, for the fluid film both in parallel gap and in wedgy gap. The geometrical parameters of the sealing members are optimized by means of heat transfer analysis and complex method. The analysis results indicate that the shallow spiral grooves can generate hydrodynamic pressure while the rotating ring rotates and the bearing force of the fluid film in spiral groove end faces is much larger than that in the flat end faces. The deformation increases the bearing force of the fluid film in flat end faces, but it decreases the hydrodynamic pressure of the fluid film in spiral groove end faces. The gap dimensions which determine the characteristics of the fluid film is obtained by coupling analysis of the frictional heat and the thermal deformation in consideration of the equilibrium condition of the bearing force and the closing force. For different gap dimensions, the relationship between the closing force and the leakage rate is also investigated, based on which the leakage rate can be controlled by adjusting the closing force.     

Analysis of Multi-Land High Pressure Oil Seals

An analysis for the laminar/turbulent flow in high pressure oil ring seals is presented. A fully-developed bulk-flow model for low axial Reynolds numbers is introduced to predict the static and dynamic force response of multi-land oil seals. The model includes the effects of bearing surface roughness, variable seal clearances, fluid inertia and viscous loss effects at the inlet of the first land in a multi-land oil seal. Internal groove pressures in the seals are determined via a mass conservation algorithm with Reynolds condition at the cavitation inception zone. Predictions show that the viscosity effect at the seal inlet is minimal for turbulent flow across the seal. However, for laminar oil seals, the entrance loss viscous effect can substantially increase the direct stiffness. Load capacity and rotordynamic force coefficients for one-land, two-land and three-land seal examples are discussed in detail.     

基于格子Boltzmann方法的动压气体轴承黏性热耗散研究

箔片气体轴承微间隙内的流场常处于滑移区,甚至过渡区,会出现一些微观效应,其热特性的研究采用宏观方法已不再合适。为研究不同工况下动压气体轴承间隙热特性变化规律,基于格子Boltzmann方法建立包含黏性热耗散项的径向轴承间隙传热数值模型;采用总能形式的双分布函数热模型,通过有限差分离散将其应用到贴体网格中,同时引入速度滑移和温度阶跃边界条件,通过数值计算得到不同参数下的轴承间隙气膜温度分布,并分析了不同埃克特数（Ec）、偏心率和转速条件以及温度阶跃对黏性热耗散的影响。结果表明,当Ec数、偏心率和转速增大时,气膜最高温度增加,两侧的温度阶跃增加;温度阶跃效应的忽略均会导致黏性热耗散量不同程度的低估。     

Characteristics of a hybrid journal bearing with one recess: Part 1: Dynamic considerations

A fluid film hybrid journal bearing with one recess, as used in tandem cold rolling mills, is studied theoretically in two ways. The dynamic response of the hybrid bearing, under isothermal conditions due to the decrease in hydrostatic pressure, is considered and presented in Part 1 of the study, while the thermal effects on the load capacity, temperature distribution, etc of the bearing will be dealt with and described in Part 2.In this paper, the dynamic behaviour of the journal due to the decrease in hydrostatic pressure is presented in the form of transient orbits and squeezed-film speeds, which are shown to be dependent on the initial equilibrium conditions. In the analysis, when the recess pressure is dropped below the hydrodynamic pressure generated by the fluid film, it is found to be difficult to obtain a convergent solution. The dynamic response of the bearing, due to the shut-off of external pressure is, therefore, simulated by the dynamic behaviour of the journal due to a series of pressure drops in arbitrary time intervals. The results show that the journal is quite stable in such conditions.     

Wall slip and hydrodynamics of two-dimensional journal bearing

In the present paper, based on the limiting shear stress model, a multi-linearity finite element algorithm and quadratic programming technique are used to study the influence of wall slip on the hydrodynamic lubrication performance of a two-dimensional journal bearing (finite length journal bearing). It is found that if the lubricated surfaces are designed as homogeneous slip surfaces, the hydrodynamic force will be decreased. If the shaft surface (rotation) is a slippery surface with very low limiting shear stress, almost no fluid load support can be generated. If the sleeve surface is designed as the homogeneous slip surface, a low fluid load support together with a small friction drag can be obtained. However, if the sleeve surface is designed as an optimized slip surface with a slip zone in the inlet region, a high load support and low friction coefficient can be obtained. Optimization of the shape and the size of the slip zone can give the journal bearing many advanced properties.     

RZS盘式制动器制动倍率的研究

介绍了RZS盘式制动器的常用工作制动、停放制动和手动释放3种工况下的工作原理。分析和计算了该制动器的自由度,并根据两侧闸瓦间隙值的不同初始状态,确定了各运动铰点在制动前后的位置。对各零部件进行了静力学分析,得到了作用在推盘活塞上的压缩空气力和制动力之间的关系式。研究和比较了闸瓦间隙补偿前后的制动倍率变化规律。计算结果表明：闸瓦间隙值的微小变化会导致制动力产生较大波动。     

推力圆柱滚子轴承预紧力的测量和计算

数控立车工作台底部推力圆柱滚子轴承的预紧力是通过压缩碟簧获得的,但结构空间狭小,无法直接测量。通过测量齿轮匀速转动时圆周某点处的切向拉力来间接测量轴承预紧力,并通过调整垫调整碟簧压力获得要求的预紧力。     

大轴径离心压缩机磁流体密封传热特性研究

高温会降低磁流体饱和磁化强度,造成永磁铁退磁,影响磁流体密封装置的可靠性及稳定性。为探讨磁流体密封装置传热特性,以大轴径离心压缩机磁流体密封为研究对象,同时考虑磁流体摩擦热和轴承摩擦热对磁流体密封装置传热特性的影响,利用有限元数值计算与磁流体、轴承摩擦功耗理论分析相结合的方法,研究磁流体密封装置温度分布规律,分析齿宽、密封间隙和转速对永磁铁和磁流体最高稳态温度的影响,并确定相关工况所需冷却液质量流率。结果表明：由于轴径尺寸较大,表面线速度高,磁流体黏性摩擦热及轴承摩擦热对密封装置传热特性有显著影响,在无冷却工况下,密封装置最高温度超过磁流体和永磁铁的极限使用温度,需通过强制对流换热的方式进行降温处理;永磁铁及磁流体最高稳态温度随着齿宽增加而升高,随着密封间隙增加而减小;随着转速的增加,永磁铁及磁流体最高稳态温度升高,且转速越大,相同转速梯度差之间的温度差越大。     

Properties and Performance of Gas-Expanded Lubricants in Tilting Pad Journal Bearings

Lubricants enable proper function and reduce friction in rotating machinery, but they can also contribute to power loss and heat buildup. Gas-expanded lubricants (GELs) have been proposed as tunable mixtures of lubricant and CO₂ under pressure with properties such as viscosity that can be controlled directly in response to changing environmental or rotordynamic conditions. In this work, experimental results of GEL viscosity, gas diffusivity, and thermal conductivity were combined with high-pressure phase equilibrium data to understand how these mixtures will behave in tilting pad journal bearings under a range of industry-relevant high-speed conditions. Simulations were carried out using the experimental data as inputs to a thermoelastohydrodynamic model of tilting pad journal bearing performance. Viscosity could be easily tuned by controlling the composition of the GEL and the effect on bearing efficiency was appreciable, with 14–46% improvements in power loss. This trend held for a range of lubricant chemistries with polyalkylene glycols, polyalpha olefins, and a polyol ester tested in this work. Diffusivity, which drives how readily CO₂ and lubricants form homogenous mixtures, was found to be a function of the viscosity of the synthetic lubricant, with more viscous lubricants having a lower diffusivity than less viscous formulations. Model results for a bearing in a pressurized housing suggested that cavitation would be minimal for a range of speed conditions. Other bearing parameters, such as eccentricity, temperature, and minimum film thickness were relatively unchanged between conventionally lubricated and GEL-lubricated bearings, suggesting that the efficiency improvements could be achieved with few performance tradeoffs.