Pocket Bearing Research Articles

Numerical Study of Comparison of Thrust Bearing Slip - No Slip Condition on Acoustic Performance

The acoustic power level (APL) produced by a thrust bearing during operation has a major effect on its performance. Therefore, this research aimed to investigate the impact of slip engineered on the noise generated by thrust bearings. A numerical approach was used to simulate open pocket bearings with varying film thickness depths. At the initial location of the slip area, three bearing models were analyzed: pocket slip, pocket no slip, and smooth slip. The results show that implementing slip can reduce noise levels, turbulence kinetic energy (TKE), and turbulence eddy dissipation (TED) rate. The average APL, TKE, and TED values were the lowest at the high film thickness

A comparative performance assessment of hydrostatic thrust bearings operating with electrorheological lubricant

PurposeAn electrorheological (ER) fluid comprises dielectric particles suspended in an insulating viscous medium. ER lubricants are considered smart lubricants. They have been applied in hydraulic valves, power transmission devices and damping systems. The purpose of this study is to investigate the performance of hydrostatic thrust bearing operating with ER lubricant.Design/methodology/approachReynold’s equation was used to model the flow of the ER lubricant in the bearing. The continuous Bingham model was used to express the viscosity of the ER lubricant as a function of yielding stress, applied electric field and shear strain rate. The Reynolds equation is solved using the finite element method (weighted residual approach) to compute the film pressure as a primary variable and the lubricant flow rate, load-carrying capacity, stiffness and damping parameters as associated performance indices.FindingsThe effects of the pocket shape, compensating elements and ER lubricant on the bearing performance were investigated. The application of ER lubricant significantly enhanced the load-carrying capacity (48.2%), stiffness (49.8%) and damping (4.95%) of the bearings. Circular and triangular pocket bearings with constant-flow valves have been reported to provide better steady-state and rotor-dynamic performances, respectively.Originality/valueThis study presents the effect of an ER lubricant on the rotor-dynamic performance of hydrostatic thrust bearings with different pocket shapes.

Design considerations for ferrofluid pressure bearing pads

The novel contribution of this research is insight into the influence of different parameters in the magnet configurations on the load and stiffness of a ferrofluid pressure bearing. It is shown that magnets with a small cross-section magnetized alternatively up and downwards combine a high load capacity and moderate stiffness while being low on material cost and complexity. The configuration where magnets are placed alternatively in left and right direction magnetized inter spaced with iron yields the highest load capacity and stiffness, albeit at the cost of weight and complexity. It is shown that an increase in the number of magnets is beneficial for the stiffness in both magnetization configurations, as is an increase in remanent flux density of the magnet. A metal bottom plate made of iron reduces the necessary height of the magnet in the up-down magnetization configuration. The model was validated using a bearing pad arranged in the up-down configuration. The force-displacement curve of this pad was measured in a load frame, using the APG 513 ​A ferrofluid from Ferrotec. A load capacity of 1.75 ​N/cm2 was achieved, this exceeds previous pressure bearing implementations and performs comparable or better than implementations of single seal ferrofluid pocket bearings. These results show that the ferrofluid pressure bearing is a passive alternative in motion systems where the designer otherwise would have needed to use an active bearing.

Numerical investigation on the static performance of aerostatic journal bearings with different pocket shapes by the finite-element method

In this work, to improve the static behavior of aerostatic journal bearings, we examine the effect of pockets with different shapes, including the square, rectangular 1, rectangular 2, and circular, manufactured on the surface of the aerostatic journal bearing. The effects of the pocket shapes, pocket area [Formula: see text], eccentricity ratio ɛ, orifice diameter df, average gas film thickness h0, and misalignment angles [Formula: see text] and [Formula: see text] on the static performance are investigated using simulations. The Reynolds equation is solved by the finite-element method in this work. Simulations reveal that the pocket area [Formula: see text], eccentricity ratio ɛ, gas film thickness h0, orifice diameter df, and misalignment angles [Formula: see text] and [Formula: see text] have a significant influence on the load force F and the stiffness K. In general, rectangular 2 pocket bearings are found to perform somewhat better than bearings with other pocket shapes, with the pocket depth set to one-half of h0, when the pocket area [Formula: see text] varies from one-twelfth to one. The pocket area [Formula: see text] should be set according to the average gas film thickness h0 and the orifice diameter df to achieve a better static performance for the bearings. For bearings operated with misalignment angles [Formula: see text] and [Formula: see text], different pocket areas [Formula: see text] should be set according to the pocket shapes for the optimal design.

Analysis of the Effect of the Slip-Pocket in Single and Double Parallel Bearing Considering Cavitation: A Theoretical Approach

In this paper, based on an analytical approach, the effect of pockets and boundary slip on the hydrodynamic performance of parallel sliding surfaces considering cavitation is investigated. A modified Reynolds theory is developed for solving two kinds of bearings: a single and a double pocket bearing. The performance is compared with respect to the variation of the pocket depth, pocket length, slip, and no-slip situation. The results show that the maximum pressure and load support increases with the reduction in pocket length. The main finding is that the pocket depth reduces the cavitation area. However, in the case of a single pocket, the role of pocket depth is more significant in reducing the cavitation effect than that in the case of a double pocket bearing.

Operational range of a ferrofluid pocket bearing

Ferrofluid pocket bearings are interesting for fast and precise positioning systems thank to the absence of stick-slip, the low viscous friction and their cost-effective nature. However, the characteristics of the bearing change due to over(de)compression since air escapes out of the enclosed pocket. This article presents an experimentally validated model that includes the air mass inside the pocket in the calculation of the equilibrium position of the ferrofluid bearing. Moreover, a simple and efficient way to obtain the operational range of the bearing is presented and a sensitivity analysis was performed. The sensitivity analysis showed that ferrofluid pocket bearings are always self-aligning and that the tilt stiffness increases when the fly height decreases or the tilt angle increases.

Increasing the load capacity of planar ferrofluid bearings by the addition of ferromagnetic material

Ferrofluid pocket bearings are a type of bearing that are able to carry a load using an air pocket encapsulated by a ferrofluid seal. Previously designed ferrofluid bearings show the great potential of the stick-slip-free and low viscous friction bearings, however until now the load capacity is limited. In this article a method is presented to increase the load capacity in a simple and cost effective way by the addition of ferromagnetic material around the magnet. First, a mathematical model of the bearing is presented and is validated by experiments using an axially magnetized ring magnet surrounded by two steel rings. The model is used to optimize the dimensions of the added ferromagnetic material for maximum load capacity. Depending on the fly height, the load capacity has been increased by a factor three to four by the addition of steel rings to the ferrofluid pocket bearing configuration.

In-plane friction behaviour of a ferrofluid bearing

Ferrofluid bearings have been demonstrated to be very interesting for precision positioning systems. The friction of these bearings is free of stick-slip which results in an increase of precision. More knowledge on the friction behaviour of these bearings is important for there application in precision positioning systems. This paper demonstrates that the friction of a ferrofluid bearing can be modelled by a viscous damper model and provides a basic model to predict the friction behaviour of a bearing design. The model consists of a summation of a Couette flow with a Poiseuille flow such that there is no net fluid transport under the bearing pads. The model is experimentally validated on a six degrees of freedom stage using ferrofluid bearings. A stiffness in the form of a closed-loop control gain is introduced in the system to create a resonance peak at the desired frequency. The damping coefficient can be identified from the peak height of the resonance, since the peak height is the ratio of total energy to dissipated energy in the system. The results show that the newly derived model can be used to make an estimate of the damping coefficient for small(∼1mm) stroke translations. Furthermore, the model shows that the load capacity of a ferrofluid pocket bearing is affected during sliding.

Design Optimization of an Automotive Turbocharger Thrust Bearing Using a CFD-Based THD Computational Approach

In a quest to reduce fuel consumption and emissions of automotive combustion engines, friction losses from many different sources need to be minimized. For modern designs of turbochargers commonly used in the automotive industry, reduction of friction losses results in better efficiency and also contributes to a faster transient response. The thrust bearing is one of the main contributors to the mechanical losses of a turbocharger. Therefore, it is crucial to optimize the design of the thrust bearing so that it has minimum friction losses while keeping sufficient thrust carrying capacity. One of the main challenges of turbocharger thrust bearing design, is that rotation speed is not fixed: the turbocharger may have a rotation speed which varies between 0 to as much as 250 kRPM. Moreover, the thrust bearing generates considerable heat, which changes the temperature of the oil film and its surroundings. In the present work, the design of the thrust bearing of an automotive turbocharger has been optimized. A CFD-based Thermohydrodynamic (THD) computational approach has been developed, taking into consideration heat dissipation, conjugate heat transfer throughout the bearing domain including the surrounding parts, as well as shear thinning and cavitation in the lubricant domain. An optimizer has been coupled to the CFD solver, with the aim of identifying bearing designs with reduced friction losses. Two bearing concepts have been evaluated: a taper-land design—which is a commonly applied thrust bearing concept—as well as a pocket bearing design. The resulting optimum pocket designs exhibit improved performance, in comparison to the optimum taper-land design. The present results indicate that (a) the pocket design concept can substantially contribute to further reducing the friction losses of a turbocharger, and (b) optimal design parameters of pocket bearings depend on the specific application (size, operating conditions), therefore detailed calculations should be performed to verify optimum performance.

Load and stiffness of a planar ferrofluid pocket bearing

A ferrofluid pocket bearings is a type of hydrostatic bearing that uses a ferrofluid seal to encapsulate a pocket of air to carry a load. Their properties, combining a high stiffness with low (viscous) friction and absence of stick-slip, make them interesting for applications that require fast and high precision positioning. Knowledge on the exact performance of these types of bearings is up to now not available. This article presents a method to model the load carrying capacity and normal stiffness characteristics of this type of bearings. Required for this is the geometry of the bearing, the shape of the magnetic field and the magnetization strength of the fluid. This method is experimentally validated and is shown to be correct for describing the load and stiffness characteristics of any fixed shape of ferrofluid pocket bearing.

3-D thermohydrodynamic analysis of textured, grooved, pocketed and hydrophobic pivoted-pad thrust bearings

In the present study, a computational investigation of thermohydrodynamic lubrication in pivoted-pad thrust bearings exhibiting different types of surface treatment is presented. Five different types of pivoted-pad thrust bearings are cross-evaluated for operation at different combinations of thrust load and rotational speed: (a) a pocket bearing, (b) a bearing with circumferential grooves, (c) a bearing with radial grooves, (d) a bearing with rectangular texturing, and (e) a hydrophobic bearing. A parametric analysis is conducted to identify the effect of the main design parameters (machining depth, radial/circumferential machining extents, slip length, radial/circumferential hydrophobic extents) on bearing performance. The performance gains obtained by each surface treatment type are evaluated against the performance of a conventional plain bearing of the same principal dimensions.

Performance comparison between textured, pocket, and tapered-land sector-pad thrust bearings using computational fluid dynamics thermohydrodynamic analysis

Different geometry patterns of the surface of thrust bearings have been proven very beneficial in terms of bearing load-carrying capacity and friction coefficient. In this study, four different types of sector-pad thrust bearings have been cross-evaluated for operation under realistic operating conditions: (a) an open pocket bearing, (b) a closed pocket bearing, (c) a tapered-land bearing, and (d) a bearing partially textured with rectangular dimples. Bearing performance has been computed by means of computational fluid dynamics simulations based on the numerical solution of the Navier–Stokes and energy equations for incompressible flow. Conjugate heat transfer at the bearing pad and rotor has been taken into account. Initially, for a reference design of each bearing, the effects of varying rotational speed and minimum film thickness have been investigated. Further, characterization of each bearing for a constant level of thrust load has been performed. Finally, the effects of varying the depth of each geometry pattern have been studied. The present results illustrate a superior performance of the open pocket bearing in comparison to the other bearing types.

Design and fast verification of pocket elliptical journal bearings

Purpose – The purpose of this paper was to conceive a fast method to verify design and performance of elliptical pocket journal bearings. Design/methodology/approach – The computer-aided verification of pocket journal bearings is performed by means of a suitable finite element analysis method. Findings – The results of sample analyses indicate that the machining tolerances are very influential on elliptical pocket bearing performances, and they must be included among the input data. Originality/value – Although elliptical pocket bearings are widely used in turbomachineries, the influence of their design on performance has not been specifically investigated. A lot of works about tribological models are available, but few of them focus on their application to bearing design at the industrial level.

Vibration Characteristics of Hydrodynamic Fluid Film Pocket Journal Bearings

Theoretical analyses of hydrodynamic fluid film bearings with different bearing profiles rely on solutions of the Reynolds equation. This paper presents an approach used for analysing the so‐called pocket bearings formed from a combination of offset circular bearing profiles. The results show that the variation of the dynamic bearing characteristics with different load inclinations for the pocket bearings is less than that for the elliptic bearing counterpart. It is shown that the natural frequencies as well as the critical speeds, and hence the vibrational behaviour, can also be significantly different for an industrial rotor supported by the different bearings.

Thermohydrodynamic Behavior of a Slider Pocket Bearing

Pocket-pads or steps are often used in journal bearing design, allowing improvement of the latter’s dynamic behavior. Similar “discontinuous” geometries are used in designing thrust bearing pads. A literature review shows that, to date, only isoviscous and adiabatic studies of such geometries have been performed. The present paper addresses this gap, proposing a complete thermohydrodynamic (THD) steady model, adapted to three-dimensional (3D) discontinuous geometries. The model is applied to the well-known geometry of a slider pocket bearing, operating with an incompressible viscous lubricant. A model based on the generalized Reynolds equation, with concentrated inertia effects, is used to determine the 2D pressure distribution. On this basis, a 3D field of velocities is constructed which, in turn, allows the resolution of the 3D energy equation. Using a variable-size grid improves the accuracy in the discontinuity region, allowing an evaluation of the magnitude of error induced by Reynolds assumptions. The equations are solved using the finite volume method. This ensures good convergence even when a significant reverse flow is present. Heat evacuation through the pad is taken into account by solving the Laplace equation with convective boundary conditions that are realistic. The runner’s temperature, assumed constant, is determined by imposing a zero value for the global heat flux balance. The constructed model gives the pressure distribution and velocity fields in the fluid, as well as the temperature distribution across the fluid and solid pad. Results show important transversal temperature gradients in the fluid, especially in the areas of minimal film thickness. This further justifies the use of a complete THD model such as the one employed.

Stability, Load Capacity, Stiffness, and Damping Advantages of the Double Pocket Journal Bearing

The double pocket bearing design is discussed and compared to the plain three axial groove bearing. Rigid rotor stability, load capacity, and stiffness and damping curves are shown for the two bearing designs illustrating the stability and load capacity advantages of the double pocket bearing. Results show that placing double opposing stepped pockets in the top pads of a three axial groove bearing is a simple, inexpensive, expedient modification that is effective in suppressing oil whirl instability. Furthermore, the bottom plain pad retains the load carrying capacity of the original three axial groove design. Frequency spectrums substantiating the stabilizing ability of the double pocket design are shown for a test stand instability problem.

Elastohydrostatic lubrication of capillary compensated circular pad thrust bearings

The effect of elastic deformation of the circular thrust pad was considered in determining the performance characteristics of a capillary compensated hydrostatic circular thrust bearing. The matched solution of the elastohydrostatic problem was obtained by using the finite element method and an iterative procedure. For the convenience of bearing designers a nondimensional deformation coefficient C ̄ d is defined in terms of p s , E, t h and h f . The performance characteristics of circular pocket thrust bearings are presented in terms of pocket pressure, load capacity, bearing flow, fluid film stiffness and damping coefficients for various values of the restrictor design parameter C ̄ s2 and the deformation coefficient C ̄ d . The values of the damping coefficients C ̄ are compared for circular and annular pocket bearings.

The application of finite element analysis to hydrodynamic and externally pressurised pocket bearings

The paper presents the finite element method for solving the Reynolds' equation. It utilises the variational calculus approach and shows how the appropriate matrix equations are derived. It deals also with the boundary condition, oil leakage and load capacity aspects of the problem. This leads to the setting up of a computer programme for handling the computation. A listing of this programme is included. The programme allows for the introduction of pockets connected to the oil supply by capillary tubes. By a double iteration process, incorporating the finite element analysis, the resulting externally pressurised bearing solution is obtained. Some results obtained for the straightforward hydrodynamic bearing are presented as a check on the method. A four pocket bearing is also analysed and the results obtained for various supply pressures, eccentricities, and relative pocket positions are given.

Paper 10: A Hydrodynamic Pocket Journal Bearing

The authors present theoretical and experimental results for a hydrodynamic pocket bearing. The bearing has a geometry similar to that of a conventional hydrostatic bearing, but no control device is incorporated in the supply line other than a non-return valve which prevents the leakage of fluid from those pockets where a pressure is generated. The load capacity of such bearings is greater than that of a circumferentially grooved hydrostatic bearing over the operating range of eccentricity tested by the authors, and is much greater than that of two short hydrodynamic bearings equal to the side sealing lands. Because of this the bearing offers a useful alternative mode of operation for a bearing (externally pressurized) which suffers a loss of its high-pressure oil supply.

A Note on the Hydrodynamic Pocket Bearing

Using relaxation methods, accurate solutions are presented for the hydrodynamic pocket bearing. These are compared with an approximate solution. It is found that the latter gives quite accurate results with a considerable decrease in time and effort.