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.     

Non-newtonian thermal analysis of an EHD contact lubricated with MIL-L-23699 oil

A thermal and non-Newtonian fluid model under elastohydrodynamic lubrication conditions is proposed, integrating some particularities, such as the separation between hydrodynamic and dissipative phenomena inside the contact. The concept of apparent viscosity is used to introduce the non-Newtonian behaviour of the lubricant and the thermal behaviour of the contact into the Reynolds equation, acting as a link element between the hydrodynamic and dissipative components of the EHD film, independently of the rheological and thermal models considered. The apparent viscosity enables the application of the rheological model better adapted to each lubricant, without appealing to special formulations of the EHD problem.The Newton–Raphson technique is used to obtain the lubricant film geometry and the pressure distribution inside the EHD contact. The shear stresses developed in the fluid film are evaluated assuming the non-linear Maxwell rheological model. The surfaces and lubricant temperature distributions are determined using the simplified Houpert's method, applied to the inlet contact zone, and the thermal method proposed by Tevaarwerk is applied in the high pressure contact zone.The non-Newtonian thermal EHD model is applied to the analysis of a contact lubricated with MIL-L-23699 oil. Significant results are obtained for the centre and minimum film thickness, for the inlet shear heating and film thickness reduction factor (φ_T), for the temperature rise of the lubricant and of the surfaces and for the friction coefficient inside the contact, considering wide ranges of the operating conditions (maximum Hertzian pressure, inlet oil temperature, rolling speed and slide-to-roll ratio).Finally, the numerical traction curves determined are compared with the corresponding experimental results, showing very good correlation.     

Variable-viscosity effects in externally pressurized spherical oil bearings

Externally pressurized spherical bearings were analysed considering the rotational inertia of the lubricant and the variation of the lubricant viscosity along the flow. The equations of motion expressed in spherical coordinates were suitably reduced to describe the lubricant flow through the bearing clearance. A numerical solution of the resulting equations, in which the variation of viscosity with temperature was considered, was obtained using the finite-difference technique. The effects of bearing geometry, bearing speed, inlet oil temperature, bearing load, lubricant flow rate and frictional torque on pressure and temperature distributions under adiabatic flow conditions were investigated. Satisfactory agreement between experiment and the adiabatic solution was found for a high speed factor. The theory is applicable to both fitted and clearance-type spherical bearings.     

球磨机滑履轴承油温升高的处理

根据球磨机滑履轴承的结构,从滑动轴承动压润滑的润滑机制,分析了球磨机正常工作时,滑履轴承油温居高不下的原因。根据分析结果,找到油温升高的主要原因是由于带油不畅和供油量不足引起,提出刮瓦和改造低压供油装置的措施。改造后效果良好,解决了球磨机滑履轴承油温升高的问题。     

Experimental study on the characteristics of pad fluttering in a tilting pad journal bearing

The fluttering characteristics of the upper unloaded pads in a tilting pad journal bearing were studied experimentally. In order to investigate the fluttering phenomena of the pad, the absolute vibration of the pad, the relative vibration between the bearing and the shaft, and the circumferential film thickness/film pressure were measured with the variation of the supply oil flow rate, the shaft speed, and bearing load. By analyzing the circumferential distributions of the film thickness, it was identified that the film shape of the upper pad continuously alternates between the wedge shape and the diverged shape in the rotational direction while the shaft is rotating. And it was discovered that the pads tend to a representative sub-synchronous self-excited vibration exactly like classical rotor-bearing instability, defined as the oil whirl and oil whip phenomena, with the increase of rotating speed from the cascade plot of the pad. The major finding was that the incipient fluttering velocity of the pad increased with the increase of the supply oil flow rate but decreased with the increase of the bearing load. The experimental results also showed that the fluttering amplitudes of the pad can be effectively suppressed by controlling the supply oil flow rate.     

高档数控机床静压转台双环形油腔流场特性仿真

为了提高高档数控机床的加工精度和稳定性,设计了一种新型的双环形油腔结构。基于流体动力学理论,并采用计算流体动力学(Computational Fluid Dynamics,CFD)数值模拟方法,研究了入口雷诺数对油腔内部流场结构和油腔承载力的影响。结果表明:入口雷诺数对于油腔内部流场结构和油腔承载力均具有重要影响;随着入口雷诺数的增大,油腔中心凹槽内部由单胞对流发展成多胞对流;同时,油腔承载力也相应增加。通过与传统圆形油腔对比发现,在相同入口雷诺数条件下,双环形油腔具有更高的承载力。该研究对设计高档数控机床新型油腔结构、优化油腔几何结构、提高承载力和加工精度有指导意义。     

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.     

Static and dynamic analysis of elastohydrodynamic elliptical journal bearing with micropolar lubricant

In this paper the effect of deformation of the bearing liner on the static and dynamic performance characteristics of an elliptical (two-lobe) journal bearing operating with micropolar lubricant is presented. Lubricating oil containing additives and contaminants is modeled as micropolar fluid. A generalized form of Reynold's equation is derived from the fluid flow and diffusion equations. Finite element technique is used to solve the modified Reynold's equation governing the flow of micropolar lubricant in the clearance space of the journal bearing and the three-dimensional elasticity equations governing the displacement field in the bearing shell. The static and dynamic characteristics of the bearing are computed for a wide range of deformation coefficient which takes into accountant the flexibility of bearing liner by treating operating lubricant as (i) Newtonian and (ii) micropolar. The computed results show that the increasing volume concentration of additives and mass transfer of additives produce significant changes on the performance characteristics.     

Aeration effects on the performance of a turbocharger journal bearing

Turbocharger bearings have to work under high temperature, and are moreover rotated at high speed. They have to be designed by overcoming the high temperature. The type of oil inlet port, the inlet oil temperature and the sort of engine oil should be designed, controlled and selected carefully in order to reduce the bearing's inner temperature. In this study, the influence of aerated oil on a high-speed journal bearing is also examined by using the classical thermohydrodynamic lubrication theory coupled with analytical models for viscosity and density of an air–oil mixture in a fluid-film bearing. Convection to the walls and mixing with supply oil and re-circulating oil are considered. The considered parameters for the study of bubbly lubrication are the oil inlet port's type, oil aeration level and shaft speed. It is found that the type of oil inlet ports and shaft speed play important roles in determining the temperature and pressure distribution, and the friction in a journal bearing at high-speed operation. Also, the results show that, under extremely high shaft speed, the high shear effects on aerated oil and the high-temperature effects cancel out each other. So, the bearing load and friction show almost no difference between aerated oil and pure oil.     

The Prediction of Contact Pressure–Induced Film Thickness Decay in Starved Lubricated Rolling Bearings

Under starved conditions the thickness and distribution of the lubricant film in an elastohydrodynamically lubricated (EHL) contact is directly related to the distribution of lubricant on the track in the inlet to the contact. In starved lubricated rolling bearings this lubricant distribution is determined by many effects. The authors have developed a model to predict the oil lost from the track induced by EHL pressure with no replenishment. A complete bearing is modeled with multiple rolling element EHL contacts and with the applied load to the rolling elements varying along the circumference of the bearing. Results of the oil layer thickness on the track are presented for a ball bearing and a spherical roller bearing for different bearing loads and rotational speeds. The predicted layer thickness decay rate for a ball bearing is significantly larger than for a spherical roller bearing and the predicted effect of the bearing load on the decay rate is small compared to the effect of the rotational speed. The predicted decay periods due to the contact pressure effect are small compared to the observed (grease) life of bearings. The results show that a bearing cannot sustain an adequate layer of oil on the running track unless significant replenishment takes place.     

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.     

扇形推力轴瓦润滑性能的数值分析

采用数值分析方法研究了重型机械装备中扇形推力轴瓦的润滑性能问题,计算了单个扇形推力轴瓦瓦面的油膜形状性能、油膜压力和油膜温度的分布规律,以及功率损失和流量等参数。对不同工况下扇形推力轴瓦润滑参数进行计算,可以实现扇形推力轴瓦润滑性能的预报,计算结果可供扇形推力轴瓦设计和润滑性能研究作参考。     

Isoviscous flow past a rigid sphere partially immersed in a thin oil film

Numerical solutions to steady state circular contact elastohydrodynamic lubrication problems normally employ Reynolds equation, forcing the assumption that the flow through the conjunction is two‐dimensional and single‐phase. In this paper, the full Navier–Stokes equations are used on a simpler rigid isoviscous sliding point contact. The aim of the study was to compute the lubricant flow patterns through and around the conjunction of a point contact when the oil inlet is a free surface that has a similar wavy shape to the wake. This model is like some seen experimentally in a ball and plate machine or industrially in a radial ball bearing with insufficient lubricant supply. There is first a discussion on the alteration with time of the oil wake geometry after it has left the conjunction. Then, the computed results mapped the areas of varying concentration between oil and air. They showed an accumulation of oil and vapour forming a reservoir at the inlet to the conjunction. Within it was a vortex attached to the stationary surface, just downstream of which, the main pressure distribution commences. The computed flow patterns were compared with experimental pictures wherever possible. Copyright © 2007 John Wiley & Sons, Ltd.     

Degradation of High Temperature Lubricants and Metals by Fluoroelastomers

This paper compares and analyzes the influence of lubricant supply temperature on the performance of a tilting-pad, equalizing thrust bearing. The paper presents experimental data for a 267-mm (10 ½-in OD) bearing, operating at shaft speeds up to 13 000 rpm with loads ranging up to 3.45 MPa (500 psi). The data presented demonstrate the relative effect that changes in lubricant supply temperature have on bearing power loss and babbitt temperature. Some conclusions are drawn based upon the trend in relative performance for each lubricant supply temperature tested.     

滚滑轴承滑块的油-气两相流润滑分析

为改善滚滑轴承的润滑,运用两相流理论对其滑块进行油气润滑设计,建立滑块的油-气两相流CFD模型,分析不同入口角度、进气速度、进油速度和润滑油黏度对流场油相分布的影响。结果表明:油-气混合润滑方式能在内外滚道接触区形成有效的润滑油膜;油气管道夹角影响油滴分布,角度过大时大量油滴会在滑块侧面上附着,角度过小时油滴会在外滚道入口处堆积,造成供油连续性不好,油膜稳定性下降;进气速度过大会降低油滴附着率,无法形成有效油膜,而进油速度过大会造成润滑油累积,出现搅油现象,因此选择合适的进气和进油速度,才能控制油滴的大小和保持润滑过程的连续性;润滑油黏度会影响油滴在滑块上的附着效果,合理地选择润滑油黏度,才能保证流场油相分布均匀。     

基于有限元的盾构机主轴承腔内润滑特性研究

盾构机主轴承具有尺寸大、承受载荷高且转速慢的特点,研究其主轴承腔内润滑状况,对于保证盾构机主轴承的可靠性至关重要。运用三维建模软件及流体仿真软件对盾构机主轴承进行建模及腔内流体域仿真,研究主要润滑参数包括进油口位置分布、进油口的选择、润滑油黏度对腔内润滑状态的影响,以及腔内润滑状态与温度的关系。结果表明：进油口位置分布对润滑状态有着较大影响,非对称进油口分布对这种极低速旋转及重载的盾构机主轴承更有利;为改善润滑状态,进油口应分主进油口和副进油口,保持主进油口常开,副进油口的打开视工况而定;润滑油黏度对润滑状态及温度都有较大影响,存在最佳黏度区间使得温度保持较低水平且润滑状态良好;对应位置润滑油体积分数与温度成反比关系。     

基于CFD的可倾瓦轴承静动特性研究

目前对于可倾瓦轴承的静动特性研究方法,主要是先研究单块瓦片的特性,再通过瓦片子系统的叠加得到轴承整体特性,在计算中忽略了瓦间间隙及瓦块相互之间的流场影响。用瓦块独立计算模型模拟理论计算中只考虑轴瓦与轴颈间隙流场的情况,整体计算模型考虑轴承瓦间间隙的影响,在Fluent软件中计算两种模型的静动特性参数,并进行对比和分析。计算结果表明,瓦间间隙对轴承流场的影响不能忽略,尤其是在涉及温度场计算时,瓦块独立计算模型计算的结果与整体模型计算结果相差很大。     

FLUID FLOW SEPARATION CHARACTER ON NOVEL HYBRID JOURNAL BEARING

The influence of the structure and running parameters of a novel spiral oil wedge hybrid journal bearing on the fluid flow trace is investigated. The governing equation of the flow trace of lubricant is set up, and the simulation is carried out by using finite difference method. The results show that the lubricant flow status and end leakage quantity are greatly influenced by spiral angle, and that the rotating speed has little influence on the flow status. With advisable geometry design, the separation of lubricant between different oil wedges can be obtained, which can decrease the temperature rise effectively.     

3D thermohydrodynamic analysis of a textured slider

Analysis of a 3D inlet textured slider bearing with a temperature dependent fluid is performed. Numerical simulations are carried out for a laminar and steady flow. Hot and cold lubricant mixing in the groove is modelled and examined for different operating conditions. Thermohydrodynamic performance of the bearing is analyzed for different texture lengths.Results show that texture has a stronger and positive influence on load carrying capacity when thermal effects are considered. This beneficial effect is at a maximum for the longest dimples with a length shorter than the pad length. Texture is also beneficial for the load carrying capacity when the sliding speed and inlet flow rate are varied. The load carrying capacity of the slider can be increased by up to 16% in severe operating conditions (high sliding speed).     

Effects of operating conditions and supply hole diameter on the performance of a rectangular aerostatic bearing

The present study is an experimental investigation of the performance characteristics of an externally pressurized rectangular recessed gas bearing operating under different working conditions. It includes the measurements of pressure, load carrying capacity, and mass flow rate. The experiments covered a wide range of film thicknesses and supply pressures. In addition, pads of different supply hole diameters were used. The results obtained from the present investigation show that the effect of varying the supply hole diameter on bearing performance is significant. Increasing the supply hole diameter to bearing length ratio has the effect of increasing the recess pressure and load carrying capacity. Further, as the supply pressure and/or film thickness increases the dimensionless load carrying capacity decreases and the lubricant mass flow rate increases.