Bearing Power Loss Research Articles

Evaluation of Operational Characteristics in a Large Thrust Bearing

In this paper the non dimensional load parameter, volumetric flow rate, energy flux, oil film temperature and power loss of a large thrust pad bearing are formulated. The objective of the paper is to determine the novel non dimensional thermal, volumetric and power loss parameters in addition to the known load and energy flux parameters of the bearing. The computation is done by formulating and numerically solving the oil film thickness, two dimensional Reynolds', Vogel-Cameron and energy equations at the different nodes of the pad oil film using a finite difference procedure. The lower the degree of the objective shape polynomial more is the accuracy of the slider bearing shape and pressure distribution. The developed derives the value of ‘a' for which the load is maximum. The variation of the dominant bearing centre of pressure with respect to the corresponding values of ‘a' is studied. From the equation of fluid film temperature the minimum rise in bearing temperature corresponding to the values of ‘a' are determined. The oil film temperature distribution results are found satisfactory in terms of computer time and convergence criteria. The accuracy of the results is thoroughly validated by the variation of the load and thermal contours. This data and analysis serves as an input for rotor dynamic studies and includes the scope to develop safe operation of the bearing at high speeds in vertical hydro-electric rotors.

Design and Materials Selection for Environmentally Friendly Ship Propulsion System

The selection of the material regarding specific design of the stern tube journal bearings in vessels is critical taking into account the lubrication system, whether oil or water based, and the consequent lubricant leakage. Therefore, the present study examines the feasibility and the advantages of implementing water lubricated polymer shaft bearings instead of conventional white metal bearings lubricated by oil. The investigation method is related to the numerical model and the software application based on finite difference method and isoviscous model. Results, based upon data collected from three different types of actual vessels in service, have shown that power loss in polymer bearings is at least 6 times less than in conventional white metal ones indicating that polymer journal bearings are significantly more energy efficient and environmentally friendly.

On the Possibilities of Decreasing Power Loss in Large Tilting Pad Thrust Bearings

Different systems of direct oil supply have been developed in order to facilitate efficient introduction of fresh lubricant to the oil gap and reduction of churning power loss in tilting pad thrust bearings. Up to now there is no documented application of the supply groove in large thrust bearings used in water power plants. The results of modeling lubricant flow in the lubricating groove of a thrust bearing pad will be presented in the paper. CFD software was used to carry out fluid film calculations. Such analysis makes it possible to modify groove geometry and other parameters and to study their influence on bearing performance. According to the results a remarkable decrease in total power loss due to avoiding churning losses can be observed in the bearing.

The Influence of the Raceway Curvature Ratio on Power Loss and Temperature of a High-Speed Jet Engine Ball Bearing

High-speed jet engine ball bearings operate under challenging operating conditions, such as high speeds, loads, and temperatures. In addition, they have to meet the highest reliability standards. Thus, they require advanced materials, designs, and cooling systems. Though new materials, heat treatments, and component designs have been developed to meet these challenging requirements, the design of the raceway curvature ratio mainly follows the classical rolling bearing life theory, which is based on subsurface fatigue. But the frictional heating in the contact zone due to the phenomenon of microsliding is not considered in the design of high-speed ball bearings. This article presents the results obtained from rig testing with a state-of-the-art high-speed jet engine ball bearing with various curvature ratios on the inner and outer races. The influence of the curvature ratio on the bearing ring temperatures and the bearing power loss is demonstrated.

Empirically derived optimization model: Theoretical formulation and validation

A set of empirically derived equations that accurately predict leakage flow and power loss in journal bearings are proposed. The proposed equations take into account the effect of groove geometry, groove location, as well as the supply pressure and the bearing geometry. Simulation results show maximum deviation of 15% on leakage flow and 10% on power loss as compared to 25% and 13%, respectively, for models in the literature. Utilizing the proposed equations, a hybrid optimization technique that minimizes power loss and side leakage in journal bearings operating in laminar flow is developed. The results also indicated that the groove location has a significant effect on the optimization model and significant power loss savings may be realized with appropriate location of oil groove.

Refined simulation of friction power loss in crank shaft slider bearings considering wear in the mixed lubrication regime

Friction reduction is a fundamental factor in decreasing fuel consumption of internal combustion engines. During the design stage of the engine the simulation of friction in the crank mechanism plays a vital role to develop optimum solutions. Due to the interaction of oil and elastic structures with rough surfaces in slider bearings, complex simulation models have to be used for representing the relevant physical behavior. The following article is focused on crank shaft slider bearings of large engines. The article describes a procedure evaluated by measurements showing how to model wear profiles of slider bearings to reach a high quality friction forecast. A fundamental influencing factor of bearing friction is given by the mixed lubrication regime and it is considered in the simulation model as part of asperity contact friction and hydrodynamic friction. Further effects result from the compliance in radial and width directions of the bearing structure and the wear of the bearing surface. Furthermore, the specific operating conditions of the slider bearing such as load, temperature, shaft speed and oil characteristics are essential and have to be taken into account. The objective of this investigation is to propose the wear profile of the bearing surface for the simulation model to be treated iteratively, where simulation results for the amount of mixed lubrication are successively assessed. For this purpose an iterative procedure is introduced and validated by measurements on a slider bearing test rig. The applied simulation method is based on elastic multi-body systems; the lubrication film contact is calculated based on Reynolds differential equation via the pressure balance calculated iteratively in the time domain. The model accounting for the mixed lubrication regime is based on the theory of Greenwood and Tripp.

Wall slip effects in (elasto) hydrodynamic journal bearings

In recent years it has been shown experimentally by a number of workers that, for certain engineered surfaces, the no-slip boundary condition is not a valid one. Moreover, researchers demonstrate that like surface texturing, well-chosen slip/no-slip surface patterning can considerably improve the performance of fluid bearings. Firstly, a finite element analysis is proposed in order to study the influence of wall slip over the load carrying capacity and power loss in hydrodynamic fluid bearings. A systematic comparison is made with textured bearing conditions. A significant number of numerical simulations show that, comparing with the textured bearings, wall slip conditions lead to better power loss improvements. Concerning the load capacity, the two solutions can lead to similar improvements, but only for specific surface patterns. Also, particular care must be taken in choosing the texture/slip zone geometry because an inappropriate choice can lead to a drastic deterioration of the bearing performance, especially in relation to load-carrying capacity. Secondly, the study is extended to the influence of wall slip in highly loaded compliant bearings, for steady-state and dynamical load conditions. The predictions show that well-chosen slip/no-slip surface pattern can considerably improve the bearing behaviour and largely justify future numerical and experimental works.

Parametric Testing and Heat Generation Modeling of 133-mm Bore Ball Bearings: Part I—Results with Metal Rolling Elements

133 mm bore ball bearings with metal rolling elements were tested at the following conditions: speeds from 1.5 × 106 to 2.6 × 106 DN; thrust loads from 13,350 to 53,400 N; oil delivery temperatures from 66 to 121°C; and oil flow rates from 7.3 to 11.4 L/min. The resulting bearing outer race temperature, oil exit temperature, and power loss determined from the shaft torque and power loss determined from the oil temperature rise are reported. Experimental power loss values are compared to the analytical results obtained with the computer code SHABERTH.The experimental data are also fitted to an empirical equation to predict the total bearing power loss. The results indicate that bearing operating temperature is a challenge for next-generation engines, primarily driven by limits of polyolester lubricants used in gas turbine engines. The results also indicate that the computer code SHABERTH underpredicts the bearing lower loss at high load conditions. A new empirical model was able to reasonably predict the bearing power loss over the conditions studied.

A Novel 3-DOF Axial Hybrid Magnetic Bearing

In this paper, we propose a novel structure of permanent-magnet-biased axial hybrid magnetic bearing. It has four segments of poles to control three degrees of freedom (3-DOF). Based on the inner and outer air gaps in conventional axial magnetic bearings, a novel air gap, called the subsidiary air gap, is constructed between the permanent magnet and the stator poles. This air gap separates the bias flux paths from the control flux paths. As a result, lower power loss of the axial magnetic bearing can be achieved due to lower magnetic reluctance of the control flux paths. Furthermore, by means of the equivalent magnetic circuit method and the 3-D finite-element method (FEM), we analyze and model the 3-DOF axial hybrid magnetic bearing. Experimental results show that the presented axial magnetic bearing has good control performance and little coupling among X, Y, and Z directions. However, the rotational power loss will be large at high speed because of the alternating flux density in the thrust plate produced by four segments of stator poles. Therefore, we propose a novel stator, named the parallel-slot stator, and novel thrust plate to reduce the rotational power loss effectively, which is assembled by DT4 and nanocrystalline materials. Meanwhile, we have designed and assembled an axial hybrid magnetic bearing prototype with the novel stator and thrust plate, which is applied in the five-degrees-of-freedom reaction flywheel system with angular momentum of 15 Nms at 5000 r/min. It is validated by the experimental results.

Constrained Design Optimization of Rotor-Tilting Pad Bearing Systems

Design of a rotor-bearing system is a challenging task due to various conflicting design requirements, which should be fulfilled. This study considers an automatic optimization approach for the design of a rotor supported on tilting-pad bearings. A numerical example of a rotor-bearing system is employed to demonstrate the merits of the proposed design approach. The finite element method is used to model the rotor-bearing system, and the dynamic speed-dependent coefficients of the bearing are calculated using a bulk flow code. A number of geometrical characteristics of the rotor simultaneously with the parameters defining the configuration of tilting pad bearings are considered as design variables into the automatic optimization process. The power loss in bearings, stability criteria, and unbalance responses are defined as a set of objective functions and constraints. The complex design optimization problem is solved using heuristic optimization algorithms, such as genetic, and particle-swarm optimization. Whereas both algorithms found better design solutions than the initial design, the genetic algorithms exhibited the fastest convergence. A statistical approach was used to identify the influence of the design variables on the objective function and constraint measures. The bearing clearances, preloads and lengths showed to have the highest influence on the power loss in the chosen design space. The high performance of the best solution obtained in the optimization design suggests that the proposed approach has good potential for improving design of rotor-bearing systems encountered in industrial applications.

A Three-Dimensional Foil Bearing Performance Map Applied to Oil-Free Turbomachinery

To effectively apply compliant foil gas bearings to increasingly larger and more challenging turbomachinery, a comprehensive method that compares a foil bearing's capabilities with the application's operating requirements is needed. Extensive laboratory and field experience suggests that foil bearing failure is generally due to thermal stress brought on by excessive viscous power loss; therefore, a map that graphically relates component- and system-level parameters (bearing size, applied loads, and shaft rotational speeds) directly to bearing power loss is more elucidating than a map based on a lumped speed/load parameter like the Sommerfeld number. In this article we describe a performance map featuring a three-dimensional contour plot that illustrates the expected power loss in a foil bearing as a function of applied load and shaft speed. Using this performance map, bearing capabilities can be examined at the anticipated system operating conditions and safety margins between an operating point and incipient bearing failure can be ascertained. To demonstrate the concept's features and usefulness, we present a performance map generated from foil bearing power loss test data. We expect that these maps, combined with other predictive tools, will help evaluate a foil bearing's general suitability for a candidate rotor system and will lead to more robust and successful oil-free turbomachinery designs.

A New Structure for Permanent-Magnet-Biased Axial Hybrid Magnetic Bearings

We propose a new structure for a permanent-magnet-biased axial hybrid magnetic bearing. Starting with the inner air gap and the outer air gap of conventional axial magnetic bearings, we first construct a novel air gap between the permanent magnet and the outer housing, which we call the second air gap, separating the bias flux paths from the control flux paths. As a result, the control flux paths will have lower reluctance, and the power loss of the axial magnetic bearing will be lower. Next, we modeled this axial hybrid magnetic bearing and analyzed it using the equivalent magnetic circuit method, 2-D finite element method (FEM), and 3-D FEM. We have designed and assembled an axial hybrid magnetic bearing prototype for a reaction flywheel system with angular momentum of 15 Nmiddotmmiddots at a speed of 5000 r/min. The theoretical analysis and the prototype experiments show such advantages as simple structure, good force current and force displacement, and high operating reliability.

Unsteady Flow and Dynamic Behavior of Ultrashort Lomakin Gas Bearings

Ultrashort microscale high-speed gas bearings exhibit a whirl instability limit and dynamic behavior much different from conventional hydrostatic gas bearings. In particular, the design space for a stable high-speed operation is confined to a narrow region and involves a singular behavior. The previously developed ultrashort gas bearing theory (Liu et al. (2005, “Hydrostatic Gas Journal Bearings for Micro-Turbomachinery,” ASME J. Vibr. Acoust., 127(2), pp. 157–164)) assumed fully developed flow in the journal bearing gap. There is experimental evidence that this assumption might not be fully applicable for the relatively short flow-through times in such bearings. This has an impact on the estimation of whirl instability onset, bearing operability and power requirements. In this paper, unsteady flow effects in the bearing gap are investigated with the goal to quantify their impact on the bearing dynamic behavior. It is shown that although three-dimensional flow calculations in the ultrashort journal bearing are necessary to quantify the onset of whirl instability, the underlying mechanisms can be qualitatively described by the impulsive starting of a Couette flow. Using this description, two time scales are identified that govern the journal bearing dynamic behavior: the viscous diffusion time and the axial flow-through time. Based on this, a reduced frequency parameter is introduced that determines the development of the flow field in the journal bearing and, together with bearing force models, yields a criterion for whirl instability onset. Detailed three-dimensional computational fluid dynamics calculations of the journal bearing flow have been conducted to assess the criterion. A singular behavior in whirl ratio as a function of the reduced frequency parameter is observed, verifying the refined stability criterion. Using high-fidelity flow calculations, the effects of unsteady journal bearing flow on whirl instability limit and bearing power loss are quantified, and design guidelines and implications on gas bearing modeling are discussed. The stability criterion is experimentally validated demonstrating repeatable, stable high-speed operation of a novel microbearing test device at whirl ratios of 35.

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. Presented at the STLE Annual Meeting in Toronto, Ontario, Canada May 17-20, 2004 Review led by Luis San Andres

Reducing Power Loss in Magnetic Bearings by Optimizing Current Allocation

Conventional magnetic bearings control current or flux by operating symmetrically about a bias current or bias flux. This approach is known to be much easier to control than operating without a bias but has the disadvantage of introducing additional power loss. Although one obvious way to minimize the power loss is to alternate activation of the two opposing electromagnetic actuators, this single actuator allocation strategy has not been successful in practical applications because it results in severe performance degradation. In this paper, we investigate the fundamental reasons behind the performance degradation under the single actuator allocation strategy. One major reason is voltage saturation in the circuit systems. On the basis of this result, we formulate the problem of minimizing the energy consumption by allocating the currents under the constraint of bounded voltages. We establish necessary conditions and properties for the optimal solution, which we use to determine the optimal allocation strategy for some common force signals. Since the optimal solution is very sensitive to the variation of the force signal, we propose a simple static allocation strategy to approximate the optimal solution.

Multiobjective optimization of a journal bearing using the Pareto optimality concept

This paper deals with multiobjective optimization (minimization of temperature rise, minimization of oil feed flow, minimization of power loss) and discrete design variables (lubricant viscosity, radial clearance, length-diameter ratio) related to the design of a journal bearing. The aim of this paper is to show the sensitivity of radial clearance, oil viscosity and length-diameter ratio on bearing power loss and oil flow. The paper attempts to remove the difficulty of selecting the weighting factor in multiobjective journal bearing optimization problems. The optimization model is based on a hybrid solution scheme for journal bearings. The objective of bearing optimization is to minimize a linear combination (weighted sum) of power loss and oil flow. Constraints are imposed on the maximum fluid film pressure, minimum film thickness, maximum temperature rise and critical speed. A generic algorithm is used as the optimization tool with a penalty to those solutions that violate constraints. The three-level Taguchi method is used to measure the effect of design variables on the optimum solution. The Pareto-optimal set approach is adapted to segregate the superior design vectors. The results of power loss, oil flow, temperature rise, maximum pressure and minimum film thickness are presented in tabular and graphical form for comparative study. Three journal bearing design examples are included, demonstrating the effectiveness of the proposed method.

Tapered roller bearings for automotive driveline and transmission applications

This paper focuses on the performance enhancement of tapered roller bearings in automotive axle and transmission applications. It also provides an objective comparison, based on test results, with alternative ball bearing arrangements. The influence of different design parameters is quantified in the analytical and experimental investigation. The bearing power loss is calculated and measured for operating conditions that are relevant in a vehicle fuel economy cycle.

Ultra-High-Speed Performance of Ball Bearings and Annular Seals in Liquid Hydrogen at Up to 3 Million DN (120,000 rpm)©

The ultra-high-speed performance of a hybrid ceramic 25-mm-bore ball bearing, as well as that of floating-ring seals with a sealing diameter of 30 mm, was determined in liquid hydrogen at speeds to 120,000 rpm, 3 million DN, under thrust loads to 3,140 N and sealed pressures to 1.7 MPaG. The bearings had Si3N4 balls and a single outer land-guided retainer. The hybrid ceramic bearing exhibited excellent performance at high load, contrasting with the seized all-steel bearing; however, the ceramic balls developed superficial micro-cracks due to frictional heating. Effective cooling of the bearing was achieved by increasing the jet speed through the nozzles. The bearing power loss drastically increased with increasing speed and cooling flow rate. The critical load capacity without bearing damage was also evaluated. Furthermore, the sealing performance of the one-ring seal was superior to that of the two-ring seal in preventing the sealing ring seizure against the runner.

Performance of synthetic oils in the hydrodynamic regime ‐ II. Generalisation

AbstractIn Parti I the results of an extensive experimental investigation of the performance of environmentally adapted oils in the hydrodynamic regime were reported. Four oils were tested in a tilting‐pad thrust bearing for different combinations of load, shaft speed, and supply oil temperature. In this second part, details of a generalisation procedure are described. A number of parameters representing the physical properties of an oil, such as viscosity and viscosity‐temperature coefficient, are adopted. The influence of each of these parameters on minimum oil film thickness, maximum temperature rise, and bearing power loss is then analysed. It is shown that viscosity measured at the supply oil temperature is the most important parameter. The effects of the viscosity‐temperature coefficient and oil thermal conductivity are less pronounced and yet significant. It is also shown that it is not possible to select an optimum oil that yields maximised oil film thickness, minimised temperature rise, and minimised power loss at the same time.

Performance of synthetic oils in the hydrodynamic regime — 1. experimental

AbstractAn investigation of the performance of environmentally adapted synthetic oils in the hydrodynamic lubrication regime has been carried out. Four oils have been tested: polyalphaolefin and ester based ISO VG46 oils as well as mineral ISO VG68 and VG46 oils. Tests were conducted in a facility containing two identical tilting‐pad thrust bearings typical of the design in general use. The differences between the mineral and synthetic oils in terms of maximum operating temperature, minimum oil film thickness, and bearing power loss have been examined. Substitution of the mineral ISO VG68 oil with an ISO VG46 oil slightly reduces the bearing operating temperature. This is due to a decrease in the basic viscosity. It is concluded that the ester base ISO VG46 oil can be used as an environmentally adapted replacement for the mineral ISO VG68 oil without sacrificing bearing safety. Such a change also offers noticeable energy savings. If the ester based oil is used instead of a mineral oil of the same viscosity grade, bearing reliability is improved by the increased oil film thickness.