Showing papers on "Fluid bearing published in 2018"

Comparison of Perturbed Reynolds Equation and CFD Models for the Prediction of Dynamic Coefficients of Sliding Bearings

Abstract: The accuracy and utility of rotordynamic models for machinery systems are greatly affected by the accuracy of the constituent dynamic bearing models. Primarily, the dynamic behavior of bearings is modeled as linear combination of mass, damping, and stiffness coefficients that are predicted from a perturbed Reynolds equation. In the present paper, an alternative method using Computational Fluid Dynamics (CFD) with a moving boundary is used to predict the dynamic coefficients of slider bearings and the results are compared with the more commonly employed perturbed Reynolds equation model. A linear slider bearing geometry is investigated and the results serve as precursors to similar investigations involving the more complex journal bearing geometries. Time and frequency domain methods for the estimation of dynamic coefficients are shown to give comparable results. For CFD with a moving boundary, temporal inertia is found to have a significant effect for a reduced, squeeze Reynolds number less than one. The temporal inertia effect is captured through an added mass coefficient within the dynamic model of the bearing.

Dynamics response of an on-board rotor supported on modified oil-film force considering base motion:

Abstract: In an on-board rotor journal bearing system, hydrodynamic bearing forces are affected by the coupling motion between rotor and base. To study the system dynamic response, a model of the on-board ro...

Hydrodynamic Friction of Viscosity-Modified Oils in a Journal Bearing Machine

Abstract: The friction properties of a range of viscosity modifier-containing oils in an engine bearing have been studied in the hydrodynamic regime using a combined experimental and modelling approach. The viscometric properties of these oils were previously measured and single equations derived to describe how their viscosities vary with temperature and shear rate (Marx et al. Tribol Lett 66:92, 2018). A journal bearing machine has been used to measure the friction properties of the test oils at various oil supply temperatures, while simultaneously measuring bearing temperature using an embedded thermocouple. This shows the importance of taking account of thermal response in journal bearings since the operating oil film temperature is often considerably higher than the oil supply temperature. For Newtonian oils, friction coefficient measurements made over a wide range of speeds, loads and oil supply temperatures collapse onto a single Stribeck curve when the viscosity used in determining the Stribeck number is based on an effective oil film temperature. Journal bearing machine measurements on VM-containing oils show that these give lower friction than a Newtonian reference oil. A thermo-hydrodynamic model incorporating shear thinning has been used to explore further the frictional properties of the VM-containing oils. These confirm the findings of the journal bearing experiments and show that two key factors determine the friction of the engine bearing; (i) the low shear rate viscosity of the oil at the effective bearing temperature and (ii) the extent to which the blend shear thins at the high shear rate present in the bearing.

Thermo-hydrodynamic analysis of large-eccentricity hydrodynamic bearings with texture on journal surface:

Abstract: To improve the performance of a heavy-loaded and high-speed hydrodynamic bearing, partial texture is designed on the journal surface. A three-dimensional thermo-hydrodynamic analysis model is devel...

Numerical optimization of surface texture for improved tribological performance of journal bearing at varying operating conditions

Abstract: Journal bearings are used in numerous rotary machines The load carrying capacity and friction of a bearing have been major concerns in design Recent developments in surface texturing have showed potential outcomes to improve the tribological characteristics of mating surfaces This study aims to investigate surface textures, which are transverse to the sliding direction, for frictional response of the journal bearing,A hydrodynamic lubrication model is considered to evaluate the effect of surface texturing on the performance of a journal bearing at varying operating conditions The two-dimensional generalized Reynolds equation, coupled with mass-conserving Elrod cavitation algorithm, is solved to evaluate texture-induced variations in tribological performance parameters,Results have showed remarkable improvements in frictional response Moreover, micro-textures on the journal surface alter the cavitation response and film-reformation in the hydrodynamic conjunction of the plain bearing,Operating condition-based comprehensive exhaustive optimization of texture geometry is performed to generate widespread conclusion

Measured and Predicted Operating Characteristics of a Tilting-Pad Journal Bearing with Jacking-Oil Device at Hydrostatic, Hybrid, and Hydrodynamic Operation

Abstract: Jacking-oil pockets are applied in many journals and thrust bearing applications in order to provide a hydrostatic oil film force that ensures a wear free run-up following a successful lift-off procedure. However, all components of the jacking-oil system have to be carefully designed in order to limit costs and prevent significant disturbance of hydrodynamic operation after deactivation of lift-oil. Experimental data and predictions for a four-pad tilting-pad journal bearing in load between pivot configuration are presented. Dynamic processes of the lift-off procedure as well as characteristic parameters of stationary conditions are studied. Moreover, hydrodynamic operation and hybrid lubrication providing a combined hydrodynamic and hydrostatic pressure distribution are investigated for sliding speeds up to 20 m/s. Analyzes of lift-off procedure prove that characteristic parameters such as lift-off pressures and vertical lift displacements are considerably influenced by manufacturing tolerances and misalignments. The comparison of hydrodynamic and hybrid lubrication provides a significant increase of load carrying capacity by additional jacking-oil supply at the maximum journal speed. In summary, results of measurements and predictions correlate well for all three investigated lubrication conditions.

Theoretical and Experimental Investigations on Transient Run-Up Procedures of Journal Bearings Including Mixed Friction Conditions

Abstract: This paper focuses on the operating behavior of journal bearings for industrial machinery application during run-ups. For this purpose, a numerical simulation code that is based on a two-dimensional extended and generalized Reynolds equation and a full three-dimensional energy equation, was advanced by a theoretical model considering the effects of mixed friction and warming of journal components during start-up. The mixed friction routine contained the elastic half-spaces model proposed by Boussinesq, which considers the influence of rough surfaces by implementing flow factors and calculates additional stiffness and dissipation in areas with solid interactions. Furthermore, a transient term was added in the energy equation to consider the thermal inertia of journal, and bearing to ensure a realistic heating during run-ups. Results of the prediction were compared to experimental data taken from a special test rig built up for validation procedures. Besides the conventional sensors for temperature, oil flow, and relative motion between shaft and stator, a contact voltage measurement was installed to determine the intensity of mixed friction. The evaluation of experimental data by Stribeck curves, based on a shaft torsion measurement, indicated a significant influence of run-up time on frictional moment. The friction coefficient of the rotor bearing system was strongly influenced by the run-up time. A short run-up time reduced the frictional coefficient in the mixed lubrication regime while the opposite behavior was observed in the hydrodynamic lubrication regime. The numerical code predicted these tendencies in good agreement with experimental data, however, only if the transient energy model was applied.

Influence of Centrifugal Forces on Oil Flow in Journal Bearing of Planetary Gear

Abstract: Introduction Planetary gears have a wide application in different areas of industry. At present moment, they find application in geared turbofan aircraft engine. For high speed or heavy-loaded gears fluid film bearings used in supports. Main characteristics of fluid film bearing such as stiffness and damping based upon hydrodynamic fluid pressure caused by relative motion of sliding surfaces. In most of applications, fluid inertia forces are negligible in comparison with hydrodynamic forces, but if some applications their influence on bearing characteristics could be sufficient and should be taken into account. Planet wheel journal bearing are an example where influence of fluid inertia forces have an influence on bearing characteristics. For taking into account inertia forces acting on oil film in journal bearing of planet wheel the conventional mathematical model for oil flow in journal bearing based on Reynolds equation requires modification. 1. Inertia forces For any type of planetary gear each planet wheel (2) taking a part in compound motion: rotation with carrier (H) with angular speed ωH and rotation about self axis with angular speed ω2 (Figure 1). One sliding surface of bearing is a part of carrier and another is a part of planet wheel and this causes fluid velocity distribution in bearing gap. Therefore centrifugal and Coriolis forces acting on fluid in bearing gap. These forces can be determined using carrier and planet wheel angular speeds that receiving for selected type of planetary gear and transmission ratio. Centrifugal and Coriolis forces in fluid should be taken into account in fluid flow in bearing mathematical model.

Investigation on inner flow field characteristics of groove textures in fully lubricated thrust bearings

Abstract: Purpose The purpose of this study is to investigate the inner flow field characteristics of groove textures in thrust bearings. Cavitation and vortex are studied simultaneously to enrich the theories of surface texture. Design/methodology/approach Navier–Stokes equations are solved using computational fluid dynamics. The MIXTURE model is adopted to study the gas–liquid mixture flow under the cavitation condition. Findings Re number, the depth ratio as well as the area ratio of the groove texture and the bottom shape are all influencing factors of the inner flow field characteristics. When cavitation region and vortex region occupy the bottom of the groove texture, these do not overlap because of the pressure gradient. The positive pressure gradient in the non-cavitation region introduces nonlinearity into the velocity profiles, which affects the load-carrying capacity and friction. Originality/value Cavitation and vortex are studied simultaneously only in this study. The characteristics of the textured thrust bearing can be analyzed and explained with the combined effect of cavitation and vortex.

Numerical analysis and experimental research on load carrying capacity of water-lubricated tilting-pad thrust bearings

Abstract: Water-lubricated bearings are expected to be widely used because of convenience, green, safe and energy saving. The purpose of this study is to investigate the load carrying property of water-lubricated tilting-pad thrust bearings. A large amount of numerical analyses are undertaken based on computational fluid dynamics and the optimization method of pivot location and the calculation method of minimum film thickness are summarized. A thrust bearing is designed according to the numerical results and is tested by experiments. The experimental results validate the numerical method and the minimum film thickness to surface roughness ratio corresponding to the change of bearing lubrication regime from mixed lubrication to hydrodynamic lubrication is obtained.

Efficient Thermohydrodynamic Radial and Thrust Bearing Modeling for Transient Rotor Simulations

Abstract: Hydrodynamic bearings are usually employed to support rotating machines, both in the axial as well as in the radial direction. Both bearing types influence the vibration behavior of rotors. Moreover, the oil-temperature influences the hydrodynamic bearing forces. In this work, efficient thermohydrodynamic bearing models for thrust and radial bearings are developed. Run-up simulations are performed for the identification of the influence of the bearings on the nonlinear rotor vibrations. The Reynolds equation, which describes the hydrodynamic pressure distribution in the bearings, is solved using a highly efficient approach. The Global Galerkin approach, using appropriate trial and test functions, is used for the approximation of the solution of the Reynolds equation, leading to heavily reduced simulation times when compared with Finite Difference or Finite Element approaches. For radial bearings, a novel semi-analytical method is developed using also the Global Galerkin approach. The oil-temperature in the thrust bearings is captured through the energy equation, which is decoupled from the Reynolds equation under appropriate assumptions. For the oil-temperature in radial bearings with full- as well as semi-floating rings a global thermal energy balance is used between the two oil-films and the bearing ring. The transient temperature terms in this energy balance are taken into consideration and their significance for the numerical stability of the solver is demonstrated. A turbocharger rotor is modeled in a multibody simulation software. The complete system consists of a flexible shaft, a turbine and a compressor wheel, as well as a thrust bearing and two full-floating ring bearings. The equations of motion of the turbocharger rotor are coupled with the equations of the thermohydrodynamic bearing models and they are solved simultaneously at each time-integration step during a run-up simulation. The simulation results show that the oil-temperature and the gas forces in the axial direction exert a large influence on the rotor vibrations. The geometry of the pads in thrust bearings will be optimized using a novel approach. In this work, statistical and neural network methods are used, avoiding the drawbacks of optimization algorithms. Usually, thrust bearings are optimized for higher load capacity and lower friction losses. Using the proposed optimization approach, thrust bearings can be optimized not only for load capacity and friction losses but also towards a better vibration behavior of the complete rotordynamic system. The validation of the thrust and the radial bearing modeling is performed through comparisons with experimental results. For radial bearings, a standard shaft motion test is used and for the thrust bearing a new testing approach is implemented. The simulation results are in a good agreement with the experimental data.

Combined effects of fluid–solid interfacial slip and fluid inertia on the hydrodynamic performance of square shape textured parallel sliding contacts

Abstract: Lubrication performances of square shape textured parallel sliding contacts are examined under the combined influence of both fluid inertia and fluid slippage at the fluid–solid interface. A two-component slip length model and first-order perturbation method are adopted to formulate pressure governing equation consisting of fluid-slip and fluid inertia terms. The effect of texture size (aspect ratio), texture height ratio, reduced Reynolds number, slip length coefficient and critical threshold shear stress on the performance parameters like load support, end flow and friction parameter of parallel sliding contacts is studied. The results indicate that effect of fluid-slip is more influential than fluid inertia; therefore, the result shows similar and closer trend to the fluid-slip results. However, the magnitude of performance parameters depends on the effect of fluid inertia. Moreover, aspect ratio of 0.3–0.5 and lower value of texture height ratios can be used to achieve better hydrodynamic lubrication performance in parallel sliding contacts.

Characteristics of Modified Spiral Thrust Bearing through Geometries and Dimension Modifications

Abstract: This research focuses on the optimum design of fluid dynamic bearing (FDB) named modified spiral design. The objective is to improve the pressure and velocity distribution inside the FDB. In this paper, the current spiral design has 12 number of grooves while the modified spiral design has 24 number of grooves. Both design can be classified into two, bearing with seal and without seal. Air was chosen to replace the oil as the lubricant. Results show that the modified spiral bearing design has comparable characteristics compared to conventional spiral design in terms of pressure and velocity distribution. Modified spiral geometries also shows a tendency to replace the function of seals in FDB. This makes it possible to simplify bearing design without using any seal just by modifying its geometries based on novel modified spiral geometries. Experimental verifications also proved that the modified spiral bearing design has better air leakage control compared to the conventional ones. This phenomenon occurs in both design parameters, where when the designs are compared with respect to increase of rotational speed and air film thickness.

Multiple-relaxation-time lattice Boltzmann method of hydrodynamic lubrication in lemon-bore bearing

Abstract: The lattice Boltzmann method has superiority over conventional computational fluid dynamics methods, particularly for the flow simulations in complex geometries. In the present work, the performanc...

Thermal-hydrodynamic behaviour of coated pivoted pad thrust bearings: Comparison between Babbitt, PTFE and DLC

Abstract: The hydrodynamic lubrication and thermal analysis of tilting pad thrust bearings has been a major subject for many studies in the field of tribology. There is only a limited number of studies regarding thrust bearings with coated surfaces. The purpose of this study is to build a parametric, iterative algorithm in order to perform a complete thermal and hydrodynamic lubrication analysis for pivoted pad thrust bearings with coatings. The analytical model is mainly based on the energy, continuity and Navier–Stokes equations, which are solved numerically with the Semi-Implicit Method for Pressure Linked Equations Consistent (SIMPLEC) method. The analysis focuses on a single pivoted pad of the thrust bearing. The thermal properties of the coating material are taken into account and the resulting thermal and flow fields are solved. The basic hydrodynamic and tribological characteristics are calculated for an uncoated, a Babbitt coated, a PTFE coated and a diamond like carbon (DLC) coated pivoted pad thrust bearing. The pressure and the film thickness distribution, as well as the load capacity and the frictional forces, are determined for several pad positions and velocities of the rotor. A mineral oil lubricant is used to estimate the shear thinning or thickening effects on the pad tribological performance. The results indicate that pads coated with PTFE and DLC show lower friction forces compared to the common steel and Babbitt applications. At the same time, the DLC coating seems to affect the bearing’s flow and thermal fields less than the PTFE, making it more suitable for thrust bearings applications.

Lubricant Rheological Behavior Effect Analysis on the Performance of Finite Porous Self- Lubricating Journal Bearings

Abstract: In this paper, the hydrodynamic lubrication of finite porous self-lubricating journal bearings is investigated taking into account the rheological lubricant behavior effect. The modified Reynolds equation is derived by considering both the fluid flow in the porous matrix and the lubricant rheological behavior where Darcy’s law and powerlaw model were used. Governing differential equations were solved numerically using the finite difference method. Static characteristics are obtained by considering three types of lubricants: pseudo-plastic, dilatant and Newtonian fluids. Obtained results showed that the power law index, n, has important effects on the performance of porous and non-porous bearings. An improvement in the fluid bearing characteristics (load capacity, pressure) is observed for dilatant fluids (n>1) while these characteristics decreased for pseudoplastic fluids (n<1). The permeability of the porous structure has significant effects on the performance of porous journal bearings of finite length, particularly at higher eccentricity ratios. Good agreement is observed between the results obtained in this study and those of literature revue.

Motor-started air flotation type turbocharger

Abstract: The invention relates to a turbocharger, in particular to a motor-started air flotation type turbocharger. The motor-started air flotation type turbocharger mainly comprises a centrifugal impeller, acheck valve, an air filter, an air storage tank, a reducing valve, a pair of radial bearings, a pair of thrust bearings, a centripetal turbine, a volute, a motor, air entraining pipelines, accessoriesand the like. The turbocharger uses air bearings to support the centripetal turbine, the motor and the centrifugal impeller, and a working medium of the air bearings is provided by high-pressure airat an outlet of an air compressor housing. The motor-started air flotation type turbocharger has the characteristics of being simple in structure, stable in operation during high-speed rotation, fastin acceleration of starting, high in reliability and long in life.

Investigation of Cooled Pads for Tilting-Pad Bearings

Abstract: Several rotating machines are nowadays equipped with both thrust and journal tilting-pad bearings. The maximum temperature in the pads is critical for applications running at high speeds and loads, where significant temperatures can originate, due to shear stresses in the oil-film or by the surroundings. In these cases, the minimum oil-film thickness and the pad thermal crowning must be considered. Leading edge groove bearings can partially solve the problem by controlling the oil inlet temperature in the shoes. Other attempts to reduce the bearing temperature can be found in several industrial bearings and are mainly focused on the nozzles of the oil inlet. Another approach for the reduction of the heat generated in the lubricant fluid, is based on the use of suitable cooling circuits inside the pads, where the pads are cooled by an external cooling fluid. This method can be applied both to the pads of tilting-pad thrust bearings (axial load) and tilting-pad journal bearings (radial load). The cooling circuit among consecutive pads of the bearing can be also optimized considering for the temperature distribution in the bearing. Furthermore, the same oil used for the lubrication process can be used as cooling fluid. Because rotating machines are already equipped with an external cooling system for the lubricant fluid, negligible modifications in the machine layout can be required for the installation of this kind of pads, if the same lubricating oil is used as cooling fluid. Conversely, a more suitable and efficient cooling fluid can be adopted. The manufacturing issues of the cooling channels inside the pad, can be solved with the additive manufacturing technology. In the paper, the results of numerical simulations for a cooled pad bearing will be described. Several paths and cross sections of the cooling circuit will be investigated by means of computational fluid dynamics (CFD) simulation allowing the maximum temperature reduction to be obtained.

Combined Roller and Plain Bearings for Forming Machines: Design Methodology and Validation

Abstract: By merging bearing specific advantages, combined roller and plain bearings can be used to meet the increasing requirements for high performance machine tools. Due to their sensitive functionality, a robust bearing design is indispensable for its industrial applicability. Different bearing types lead to different and sometimes contradictory requirements. This article presents a design methodology including basic design rules for industrially applicable bearing combinations. The methodology respects the conflict of objectives in the distribution of the force flow to the different bearing components. The bearing stiffness is used as an indicator for the bearing’s functional capability. A semi-analytical model based on the theory of hydrodynamic lubrication was extended by a roller bearing model to simulate the bearing behaviour. In addition, both full-rotation and pivoting tests were carried out to validate the model and investigate the influence of rotational speed and radial displacement on the bearing’s stiffness.