Experimental static thermal performance analysis of nanolubricants based elliptical journal bearings

This paper presents the development of a finite element procedure for the dynamic analysis of flexible rotors supported on fluid-film elliptical journal bearings operating under several operating conditions. The rotating shaft is modeled by using Timoshenko beam theory and the coupled rotating components, such as disks and impellers, are modeled by using lumped masses. The modeling of the elliptical journal bearings is performed by solving the lubrication equations generated from the application of a linearized perturbation method on the classical Reynolds equation. The bearing carrying-load capacity and the linearized dynamic force coefficients can be predicted for elliptical bearings with different preloads and journal eccentricities. The rotor transient whirling unbalance response is estimated by performing the time integration of the finite element equations using Newmark method. Experimental whirling unbalance response of a rotating shaft supported at two identical journal bearings is used to validate the finite element procedure. A comparative analysis of the dynamic response of flexible rotors supported on both cylindrical and elliptical journal bearings is performed to show that some elliptical bearings are capable of attenuating the rotor unbalance response more efficiently than cylindrical bearings are.

Computational fluid dynamics study to investigate the performance of fluid film journal bearings with different geometries

Purpose The non-circular journal bearings may be used over circular journal bearings because of their superior thermal stability. The paper aims at experimental study of thermal performance of two different true elliptical and orthogonally displaced non-circular journal bearing profiles. Design/methodology/approach The experiments have been conducted on a specially designed test rig which simultaneously evaluates oil film pressure and temperature along the circumference of non-circular journal bearing. The tests are conducted for the designed true elliptical and orthogonally displaced journal bearing at three different rotational speeds of 2,000, 3,000 and 4,000 rpm under the influence of steadily applied load varied from 0.5 to 2.0 kN. The data collected during experimentation have been used to evaluate thermal performance parameters such as maximum pressure, flow rate and effective temperature of the bearings under study. Findings It has been observed experimentally that two lobes of pressure and temperature have been obtained for both the elliptical and orthogonally displaced journal bearing. The negative pressure zone (cavitation area) has been observed to be reduced along the circumference for both the journal bearings which results in less thermal degradation of an oil as compared to circular journal bearing. The oil film pressure and temperature increases with the increase in radial load of both the bearings. The maximum temperature rise of oil film is more in case of elliptical bearing as compared to the orthogonally displaced bearing. Originality/value The experimental data presented in this paper will help the designers to select such kind of non-circular journal bearing for various applications. The designed bearings have resulted in reduced cavitation zone and two positive pressure lobes have been observed which may result in application of such bearings as an alternate for circular journal bearing.

The high rotational speeds and loads of gears operating in acceleration gearboxes causes problems related to the correct choice and design of journal or rolling bearings. In the case of journal bearings, these problems are connected with thermoelastohydrodynamic lubrication theory and the dynamics of the bearing system. However, of major importance is the problem of thermal effects in journal bearings. This has been considered for bearings used in a double‐helical gearbox with the pinion and output shaft operating in cylindrical journal bearings. The oil film pressure, temperature, viscosity distributions, and maximum and mean oil film temperatures have been determined. In calculations, laminar adiabatic and turbulent adiabatic models of oil films have been applied. The results of the calculations can be used in the design of cylindrical or other types of journal bearing in rotating machinery, including acceleration or reduction gearboxes.

This paper presents an analysis of the pressure distribution of hydrodynamic journal bearing for different surface texture, velocity variation and load variation. The performance of journal bearing depends on speed, load carrying capacity, viscosity of oil and temperature condition. Therefore, the effects of these parameters on the performance of journal bearing, on the pressure distribution and on the load carrying capacity have been analyzed on the basis of number of revolution per minute of the shaft. The lubricating oil used for the experimental work is SAE 40. Eight pressure distribution profiles were generated by making eight combinations of speed of the shaft and load on journal bearing. It was observed from the profiles that texture bearing can sustain at more pressure as compared to the smooth bearing. Reason behind this result is the presence of holes in texture bearing. These holes behaves like a reservoir and lubricating oil was filled in it, due to which metal to metal contact reduced and friction was minimized. Hence the performance of the bearing was improved.

The enhanced shear properties of non-Newtonian fluids have garnered considerable interest, resulting in their growing utilization as lubricants. This work explores the lubrication mechanism of journal bearings with surface roughness by analyzing the influence of cavitation in lubricated textured contacts. Commercial computational fluid dynamics (CFD) software is utilized to employ numerical techniques for evaluating the tribological characteristics, namely the distribution of hydrodynamic pressure, in lubricated textured contacts. The analytical results indicate that incorporating surface roughness can significantly enhance the hydrodynamic pressure, leading to an augmentation in load-carrying capacity, a drop in the friction coefficient, and a drop in acoustic levels. Furthermore, the quantitative results indicate that incorporating cavitation modeling significantly affects the performance. Disregarding cavitation results in less precise outcomes.

Investigations on the thermal effects in non-circular journal bearings

Multi-objective optimization of surface textured journal bearing by Taguchi based Grey relational analysis

High-speed rotating machinery has extremely high requirements for the performance and reliability of aerostatic bearings, and the design of pressure-equalizing groove structure is a key factor determining the performance of aerostatic bearings under high-speed conditions. At present, research on the influence of pressure-equalizing groove structure on the performance of high-speed aerostatic bearings is still relatively limited. In this study, aerostatic thrust gas bearings with three pressure-equalizing groove structures (rectangular, fan-shaped and drop-shaped) were designed, and their performance characteristics were comprehensively analyzed by numerical simulation method. A CFD model of the bearing was established based on the Navier-Stokes equations and the model accuracy was verified. The performance of bearings with each structure under different working conditions of air film thickness, supply pressure and rotational speed was explored. The study found that the shape of pressure-equalizing groove has a significant impact on the load-carrying capacity, pressure distribution, stiffness and stability of the bearing. Under high-speed conditions, vortices in the groove critically affect the pressure distribution in the high-pressure zone of the bearing, which in turn determines the load-carrying capacity. Fan-shaped and drop-shaped grooves can effectively suppress vortices due to their divergent structures, and their load-carrying capacity and stiffness during high-speed operation are superior to those of rectangular grooves, while rectangular and fan-shaped grooves have smaller pressure fluctuations and exhibit better stability. There is a clear correlation mechanism between the divergent characteristics of different pressure-equalizing grooves and vortex suppression. Fan-shaped and drop-shaped grooves can promote the expansion of the high-pressure area of the air film and enhance the hydrodynamic effect, while the complete vortex in the rectangular groove limits the development of the high-pressure area. The research results provide theoretical support for the design and optimization of aerostatic bearings, and contribute to the research and development of high-performance bearings adapted to high-speed rotating machinery.

Multirecess hydrostatic/hybrid journal bearings are being used in many applications owing to their excellent characteristics. The Noncircular journal bearing configurations too are quite frequently used in high speed machinery as they are efficient, less costly and provide better shaft stability. The Two lobe bearing (elliptical bearing) are among the commonly used noncircular journal bearing configuration. The multilobe multirecess hybrid journal bearings have been developed to combine the features of noncircular and circular hybrid journal bearing configurations. In the present work a theoretical investigation of a two lobe multirecess hydrostatic/hybrid journal bearing system have been carried out. The multilobe journal bearing configuration is designed as an arc of the circle with the centre points placed on the symmetry line of the single lobe. The journal offset has been accounted by defining an offset factor ‘δ’. The finite element method has been used to solve the Reynolds equation governing the flow of lubricant in the clearance space of the journal bearing system. The bearing static and dynamic performance characteristics have been presented for the various values of the offset factors (0.75, 1, 1.25 and 1.50) for hybrid mode of operation of the bearing. The simulated results of the studies reveals that, a two lobe recessed hybrid journal bearing provides an improved performance in respect of fluid film stiffness and damping coefficients as compared to that of circular recessed journal bearing. It has been observed that for a multilobe bearing having offset factor more than one has a favourable effect on the dynamic performance characteristics of the two lobe bearing.

Viscosity is the most important lubricant parameter as lubricant requires suitable values to ensure its performance in industrial applications under a high pressure and temperature. In this study, the effects of viscosity on temperature for engine oil (SAE 20W40) and palm oil were studied in journal bearing application using the ANSYS FLUENT CFD (computational fluid dynamic) method. In addition, this study also compared the effects of constant viscosity and viscosities that dependent on temperature for engine oil (SAE 20W40) for an application of journal bearing at a different rotational speed of journal bearing start from 200 rpm, 400 rpm, 600 rpm, 800 rpm, and 1000 rpm. The results show that the pressure distribution in journal bearing is in agreement with the experiment by using the correct method in ANSYS FLUENT. Finally, under the hydrodynamic lubrication regime, the lubricant viscosity has a significant impact on the improvement of a journal bearing’s most essential aspects (maximum pressure and load carrying capacity). Hence decision to consider constant viscosity conditions or viscosities that dependent on temperature cases will give a different result that will affect the overall performance of journal bearing. The numerical validation study was done to validate data from simulation and experimental studies.KeywordsJournal bearingPalm oilCFDANSYS FLUENTViscosityTribology

Hydrodynamic journal bearings are widely used to support high-speed rotating equipment due to their excellent strength and load-bearing capacity. Therefore, bearings are essential mechanical elements to improve the quality of rotating equipment. Bearing performance depends on various factors but pressure and frictional torque plays a vital role in load carrying capacity of bearing. In this present work, both experimental and analytical approach of a typical journal bearing has been carried out to determine the optimal performance of the bearing. Taguchi-based optimisation method has been proposed for journal bearing. Taguchi L27 orthogonal array has been planned to study peak pressure and frictional torque with three input parameters speed, load and viscosity index. The result shows that loading criterion influences much on performance of bearing. The experimental data is obtained from a journal bearing test rig and the analytical data are generated by MINITAB 18. From the experiment, it can be confirmed that speed – 2000 rpm, load – 600 N and viscosity index – 150 are the ideal process parameters for lower peak pressure and less frictional torque.

In high speed compressors and turbine drive trains, the tilting 5-pad journal bearings are applied. Tilting-pad journal bearings are good option because they have very good hydrodynamic stability at high speed and are less sensitive to load direction and shaft misalignment. The paper introduces thermo-elastic deformations of tilting 3-pad journal bearing with asymmetric support of pads and operating at the conditions of adiabatic oil film. The deformations of pads were obtained based on the oil film pressure and temperature distributions. Reynolds, energy, geometry and viscosity equations have been solved numerically on the assumption of aligned orientation of bearing and journal axis and at static equilibrium position of journal.

Performance of worn non-recessed hole-entry hybrid journal bearings

Varnish is a kind of fouling adhered on bearing inner face near the load zone. The model to analyze its influence on bearing performance and rotor vibration was set up. Pressure and temperature distribution were solved on the basis of the Reynolds equation by the iteration method simultaneously. It is found that bearing performance is changed by the step flow effect at the leading edge of the varnish. Its influence is more obvious when the rotating speed is low. Bearing varnish results in a large decrease of minimum clearance and an increase in the oil film temperature and pressure. Loading capacity of bearing is also decreased. It is harmful to the bearing. With the varnish, the minimum oil film thickness decreases. This leads to an increase of bearing stiffness and damping coefficients. Its influence is larger in the horizontal direction than that in the vertical direction. The trend of unbalance response to rotating speed is similar. There is little influence of the varnish on the modal frequency. However, system stability is improved due to the increased bearing damping coefficients.