Analysis of Viscosity Interaction and Heat Transfer on the Dual Conical-Cylindrical Bearing©

Viscosity is an essential property in hydrodynamic lubrication. In general, the lubricant is not considered to have uniform viscosity within a given bearing. The viscosity of the lubricant is affected by both pressure and temperature. The viscosity of the lubricant increases with pressure and, for most lubricants, this effect is much larger than that of temperature or shear when the pressure is significantly above atmospheric pressure. This study analyzes the thermal effect of dual conical-cylindrical bearing performance parameters via the viscosity-pressure-temperature relationships of lubricants. The results reveal that pressure increases both the film viscosity and temperature.     

Thermohydrodynamic Modeling of Leading-Edge Groove Bearings under Starvation Condition

A recent trend in industry is to use directly lubricated bearings with reduced oil flow to achieve minimum power consumption. However, too much oil flow reduction would cause bearing failure. This work presents a comprehensive thermohydrodynamic algorithm that predicts the performance of the leading-edge groove bearing under low oil flow and starvation conditions. Because of starvation, more analyses are added and extra uncertainties are inevitably introduced in the theoretical models. The influence of starvation on pad temperature, power loss, journal eccentricity, attitude angle, and dynamic coefficients are investigated and discussed. The numerical results are compared with published experimental data with generally satisfactory agreement.     

导轴承性能热流体动力分析

建立了导轴承性能热流体动力分析的数学模型,应用有限元法对表示油膜压力的Reynolds方程及表示油膜温度的Energy方程和表示温度和粘度关系的粘温方程进行了联立求解,获得了多瓦导轴承的瓦块压力分布,温度分布及其它轴承静态和动态参数.并根据这些参数对多瓦导轴承的性能作了分析,其结果对该轴承设计具有一定的指导作用,并对运行过程具有预测作用.     

Surface Roughness Effects in Journal Bearings with Non-Newtonian Lubricants

The static performance of finite journal bearings lubricated with non-Newtonian power law fluids is analyzed by using a control volume method with an Elrod algorithm to solve the average Reynolds equation and determine the cavitation region accurately. The results show that the flow behavior index of power law fluids has an insignificant affect on the load ratios, side flow ratios and cavitation regions, while it significantly affects load capacities and side flow rates. Furthermore, the effects of film thickness ratios, pressure flow factors, shear flow factors, slenderness ratios, eccentricities and inlet pressures on the variations of cavitation regions are also discussed.     

固体润滑剂在轴承上的应用研究

以水轮发电机轴承为应用研究实例，介绍了轴承镶嵌固体润滑剂的摩擦磨损机理，镶嵌轴承套的结构，固体润滑剂材料；并用摩擦学性能试验及台架模拟试验验证；在水轮发电机轴承上使用固体润滑剂可以提高润滑性能、降低摩擦系数，使摩擦副间能不断形成自补偿固体润滑转移膜，说明在重载，低速，摆动，间歇运动和泥水环境苛刻条件下工作的水轮发电机轴承使用固体润滑剂，比液体润滑具有更优越的性能。     

Dynamic and Static Irradiation of Nuclear Power Plant Lubricants

Proper choice of lubricating greases for use in machinery exposed to high energy radiation requires not only a sound estimate of the service the radiation dose, but also careful consideration of the normal lubrication variables. Interaction of all the variables may be complex. Static and dynamic test results are given which illustrate this point, and which reveal utility of some commercial mineral oil greases and a new high temperature radiation resistant grease.

Irradiation tests of turbine oils show that maximum expected radiation dose in current and projected power plants over a twenty year period does not change the physical properties of the oil. Oxidation stability and other properties are therefore still of most importance in turbine oil selection. Some experimental radiation-resistant fluids are discussed which have potential for fluid lubricant use where radiation resistance may be required.     

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.     

Non-Newtonian Effects of Powder-Lubricant Slurries in Hydrostatic and Squeeze-Film Bearings

This paper presents the result of pressure measurements made in hydrostatic and squeeze-film bearings lubricated with a powder-lubricant slurry. The powder lubricant was powdered graphite and the carrier fluid was ethylene glycol. Pressure measurements compared favorably with analytical predictions based on a power law rheological model.

The behavior of ethylene glycol acting alone as a lubricant was also analyzed to provide a baseline for comparing the effects of the graphite powder additive on pressure and flow rate.

The hydrostatic bearing test showed that the addition of graphite powder into ethylene glycol can raise the load-carrying capacity of a lubrication system however pumping requirements are also raised. Squeeze-film bearing tests showed that the damping factor is increased with the addition of powdered graphite into the carrier fluid.     

Calculated Performance of Non-Newtonian Lubricants in Finite Width Journal Bearings

A numerical procedure has been developed for the calculation of the performance of non-Newtonian, polymer-thickened lubricants in finite width journal bearings. Such oils were found to act as if they had averaged “anisotropic viscosities,” i.e., different viscosities in the circumferential and side leakage directions, even though the viscosity was taken to have one definite value, a function of the resultant shear stress, at each point in the oil film. Overall, polymer oils carried less load at a given eccentricity, gave less friction and a flatter pressure distribution than mineral oils of the same low shear viscosities. By analogy with the previously calculated infinite width case, which gave similar results, it is expected that the flatter viscosity temperature slope of the polymer oils will compensate for their apparent viscosity decrease. The program has also been adapted to “natural” boundary conditions, which improve upon the delineation of the cavitation region on the inlet side of the bearing.     

螺旋面扇形瓦推力轴承热动力润滑性能分析

提出了一种适用于推力轴承的新型瓦——螺旋面扇形瓦,并对其热动力润滑性能进行了分析。螺旋面瓦与平面瓦比较,因其本身具有一定的斜度而具有许多特点,如油膜厚度大,承载能力大,剪切速率低,粘性耗散小,温升较小,功耗少而且制造加工容易等,因此可以很好地取代平面扇形瓦。     

支点位置分布对径向可倾瓦滑动轴承热动力润滑性能的影响

径向可倾瓦滑动轴承瓦块支点的分布情况对轴承性能影响很大.本文详细分析了瓦块支点位置分布对滑动轴承热动力润滑性能的影响.结果表明采用非均布支点布置有利于提高在大型低速重载条件下径向可倾瓦滑动轴承的热动力润滑性能.     

Thermohydrodynamic Behavior of Misaligned Plain Journal Bearings: Theoretical and Experimental Approaches

Hydrodynamic journal bearings are essential components for supporting and guiding the rotating shafts of high-speed machinery. Manufacturing defects in assembly or thermal distortions may introduce problems during running, such as misalignment. The destructive effects of this kind of running problem have justified the development of a numerical model to predict the bearing operating characteristics under steady-state conditions. The present work presents in detail the three-dimensional thermohydrodynamic approach adopted in this study in order to consider the thermal field variations. This model also includes lubricant film rupture and reformation phenomena by conserving the mass flow rate. In addition, an experimental validation is made by comparison with measurements carried out on our test device for various operating conditions and misalignment torques. The influence of misalignment direction is also investigated by considering numerical and experimental approaches used in the study of bearing behavior variations.     

温度的非牛顿效应及其润滑失效机理分析

本文通过分析温度对粘度的影响建立了润滑剂因温度而产生的非牛顿流体模型。通过对简化问题分析表明：由于温度效应的普遍存在，一般润滑条件下也会表现出十分明显的流体非牛顿化现象。并根据给出的剪应力极值曲线指出了温度引起的非牛顿性可以导致重载条件下的润滑失效发生。     

水润滑轴承材料设计

本文列举了水润滑轴承的特点，介绍了水润滑轴承用的金属材料、塑料、陶瓷及其他材料的特点，以及水中滑动性能和在各种速度及负荷匹配中的应用情况。     

Thermohydrodynamic Analysis and Thermal Management of Spherical Spiral Groove Gas Bearings

A thermohydrodynamic model of spherical spiral groove bearings is presented by considering the effect of bearing temperature change on the material property of lubricant, gas flow characteristics in the grooves, and thermal energy transported in the entire bearing system. A gas mixing model in the grooves is introduced as the boundary condition to solve the bearing temperature distribution simultaneously with the heat conduction at the shaft and the housing. The bearing and rotor expansion caused by temperature increases, which is considerable compared to bearing clearance, is also examined. Prediction results show that the thermal expansion determined by actual bearing clearance has a crucial influence on the bearing load capacity. Manufacturing bearings with proper materials has significant effects on controlling thermal expansion effects on the bearing performance. The load capacity, which corresponds to the lubricant gas pressure, and gas suck flow rate have the same variation tendencies as the variation in groove depth and spiral angle. These similar tendencies have an opposite influence on the temperature and result in the temperature increase not being affected by the variation in grooves. However, varying the groove characteristics has a similar effect in carrying away the thermal energy as the variation in heat transfer coefficient, which could significantly control the temperature increase at the same time.     

TEHD Analysis for Tilting-Pad Journal Bearings Using Upwind Finite Element Method

A general approach for incorporating heat transfer and elastic deformation effects into a tilting-pad journal bearing simulation model is presented. A global analysis method is used, which includes variable viscosity and heat transfer effects in the fluid film, elastic deformation and heat conduction effects in the pads, and elastic deformation effect in the pivots. The two-dimensional variable viscosity. Reynolds equation produces pressure distributions in the axial and circumferential directions. The energy equation is two-dimensional, assuming that the temperature variation in the axial direction is negligible. The elasticity and heat conduction models are also two-dimensional, being in the midline cross-section of the bearing, including the circumferential and cross-film directions. An upwind technique is used in the finite element formulation of the energy equation to remove numerical instability due to the convective term. Simulation results are compared with the test and predicted values of previous researchers.     

A Study of Dynamically Loaded Finite Journal Bearings in Mixed Lubrication Using a Transient Thermohydrodynamic Analysis

A transient analysis of dynamically loaded finite journal bearings in mixed lubrication is made by solving the modified generalized Reynolds equation, 2-D energy equation in the oil, and heat conduction equation in the journal simultaneously including mass conserving cavitation. ISOADI (isothermal shaft and adiabatic bushing inner surface) thermal boundary condition is used. Journal temperature is treated as quasi-steady over one loading cycle. Two kinds of contact model are used. Numerical solutions using the finite difference method are presented. Results shows that the bearing behavior is closely tied to the roughness texture and topography, asperity contact load, bearing geometry, and operating conditions.     

指数率非牛顿流体的等温线接触弹流润滑分析

应用多重网格解法，求得了指数率非牛顿流体在稳态等温线接触条件下的弹流润滑数值解，分析了油膜压力和油膜厚度随指数及滑滚比的变化关系，并与相同工况下牛顿流体弹流润滑的结果进行了比较。     

小型低风速风力发电机永磁轴承的设计与分析

风能是重要的可再生能源,低风速风能的利用对风力发电的发展有重要意义。磁力轴承能有效地减小风力发电机的启动阻力矩、降低启动风速。永磁轴承具有体积小、无功耗、结构简单、零响应时间等优点而被广泛应用。对永磁轴承的结构设计进行了分析,并采用轴向磁化轴向叠加多环径向永磁轴承作为低风速风力发电机主轴支承,用有限元法分析计算了的永磁径向轴承的径向力,完成了实验样机,对比实验表明,该样机的启动阻力矩比传统的风力发电机降低了40%。     

Non-Newtonian Temperature and Pressure Effects of a Lubricant Slurry in a Rotating Hydrostatic Step Bearing

The purpose of this research was to investigate the pressure and temperature effects of graphite powder lubricant when added to a Newtonian carrier fluid and applied in a rotating hydrostatic step bearing. Temperature and pressure profiles were determined both analytically and experimentally. The rheological behavior of the non-Newtonian lubricant was modeled using a power law model previously shown to approximate experimental data for this fluid. Ethylene glycol was used as the Newtonian lubricant, providing a check on the test apparatus and a base line for comparison with the non-Newtonian graphite slurry.

Data revealed a temperature increase with bearing rotational speed for both fluids and compared favorably with the mathematical predictions. A significantly higher temperature rise was seen in the non-Newtonian lubricant due to the higher shear rates. The pressure profile was not directly dependent on bearing rotational speed in the mathematical model, but experimental data demonstrated a reduction in pressure at higher rotation speeds. This loss was greater for the non-Newtonian lubricant and attributed to temperature dependence of power law constants. It was concluded that the effects of operating speed and temperature on a non-Newtonian lubricant should be considered as well as their greater load-carrying capacity.