Herringbone-grooved Journal Bearings Research Articles

Comparative study on static and dynamic characteristics of pumping-out and pumping-in herringbone grooved journal bearings

The aim of this paper is to compare the static and dynamic performances of two types of herringbone grooved journal bearings (HGJBs), that is, pumping-out HGJB and pumping-in HGJB. Firstly, based on finite control volume method and the principle of flow balance, an equivalent Reynolds equation considering the turbulence effect is derived. Then, the journal motion considering angular displacement is analyzed with linear perturbation method. The equivalent Reynolds equation is linearized into static-form one and perturbed-form ones. These equations are solved by finite difference method and their solutions are integrated on the bearing surface to determinate the static characteristics and dynamic coefficients of HGJB. Additionally, the critical mass and critical whirl frequency are defined for evaluating the stability and rigidity of bearing by solving a motion equation with four degree of freedoms (DOFs). Finally, the static and dynamic characteristics of two types of HGJBS are analyzed and compared symmetrically in consideration of effects of eccentricity ratio, length to diameter ratio, groove angle, groove depth, the width of sealing damp, tilting degree of journal, and rotation speed. The results show that, within the interested range of investigated parameters, static performances of pumping-out HGJB are superior to that of pumping-in HGJB generally. Stability of pumping-in HGJB is better than pumping-out HGJB but bearing rigidity of pumping-in HGJB is inferior to pumping-out HGJB.

Design of a Herringbone-Grooved Bearing for Application in an Electrically Driven Air Compressor

A turbo compressor was investigated to ensure the operational reliability of the charging of fuel cell systems. This study investigated air-lubricated herringbone bearings to support the high-speed rotating shaft. For reliable operation of the rotor bearing system, stable operation in the whole speed range (up to 120 krpm), as well as low lift-off speed, is an important issue. Some publications containing guidelines for an optimized design in terms of stability and lift-off behavior date back to the 1970s, with some simplifying assumptions (such as narrow groove theory and small eccentricity analysis). Many publications have addressed the calculations, as well as the optimization of herringbone-grooved bearings; however, general design guidelines are still missing in the view of the authors. Although the investigations related to bearings for the support of a lightweight rotor for a special compressor of a fuel cell unit, this study could also indicate favorable bearing designs for other high-speed applications. Here, the compressible Reynolds equation was solved in the whole solution domain using a conservative finite difference scheme, and the corresponding bearing characteristics were determined. In a perturbation analysis, the linearized dynamic coefficients of the herringbone bearing are calculated. To compare the suitability and performance of the various herringbone-grooved bearing designs, especially at high speed, the simple model of a Jeffcott rotor airborne with two identical herringbone-grooved journal bearings (HGJBs) was used. The geometrical parameters of the HGJBs were varied, and their effects on bearing characteristics and stability were evaluated. Recommendations concerning favorable geometrical bearing parameters for a sufficiently high stability threshold speed and reasonable low lift-off speed were the result of the parameter study.

Performance Prediction of High-Speed Hydrogen Gas-Lubricated Herringbone Grooved Journal Bearing

The liquefaction of hydrogen is considered to be a crucial process in the large-scale utilization of hydrogen energy. In hydrogen liquefaction, hydrogen turbo-expander is a key refrigerating machine for high liquefaction efficiency. Performance of the turbo-expander is directly affected by the hydrogen gas bearings. To obtain a deep understanding of the performance characteristics of hydrogen gas bearings, the static and dynamic characteristics of herringbone grooved journal bearings under hydrogen and other lubricating gases were numerically calculated and compared. The bearing load capacity and critical mass of hydrogen gas bearings were slightly lower than those of helium-, air- and nitrogen-lubricated bearings. To improve the performance of the hydrogen gas bearings used in high-speed turbo-machinery, the influence of working conditions was analyzed. It is found that the load capacity of hydrogen gas bearings can be improved by increasing the ambient pressure, reducing the gas film clearance, and raising the bearing eccentricity ratio. Meanwhile, the critical mass increases, and the bearing dynamic stability is enhanced.

Experimental Investigation of Enhanced Grooves for Herringbone Grooved Journal Bearings

Abstract This paper presents the results of a theoretical and experimental investigation of the potential of enhanced groove geometries to increase the bearing clearance of a Herringbone Grooved Journal Bearing (HGJB) supported rotor. The theoretical study investigates various groove geometries of different complexities and their effect on the stability threshold of a particular rotor geometry. The theoretical results obtained from a rigid-body rotordynamic model suggest an increase of more than 300% in instability onset speed when enhanced groove geometries are used compared to a classical, helically grooved rotor featuring the same radial bearing clearance. As part of the experimental investigation, one rotor shaft with classical grooves, representing the baseline rotor, and four rotors of identical diameter and clearance, but featuring enhanced grooves of varying degrees of complexity, were manufactured and experimentally tested. Good agreement between the experimentally determined speed of instability onset and the prediction was found for the investigated enhanced groove patterns. Experimental results of the classical rotor suggest the onset of instability to occur at a rotational speed of 56 krpm, whereas a speed of 180 krpm was achieved when enhanced groove geometries were applied to the rotor, which agrees very well with the theoretically predicted results and confirms the potential of enhanced groove geometries to stabilize HGJBs. Furthermore, the rotor featuring only a varying groove angle along the rotor axis was found to perform similarly to fully enhanced grooves of varying groove width, depth, and angle, hence representing a good trade-off between performance increase and design cost.

Numerical study of hydrodynamic herringbone-grooved journal bearings combined with thrust bearings considering thermal effects

Abstract Hydrodynamic herringbone-grooved journal bearings (HGJBs) are analyzed by solving Navier–Stokes and energy equations. It is well known that the load capacity of hydrodynamic bearings may be affected by high temperatures and low oil viscosity. Therefore, the main objective of this study is to understand the pressure distribution of hydrodynamic HGJBs under different oil viscosity and eccentricity ratios. In this paper, 3 different configurations are studied, namely, a HGJB, a combined HGJB and thrust bearing, and a combined HGJB and grooved thrust bearing. The bearing characteristics, such as load capacity and attitude angle that vary with different eccentricity ratios, are also discussed. The results show that the load capacity of the bearing decreases with increasing temperature. The pressure difference also increases as the eccentricity ratio increases. The high-pressure region is concentrated at the tip of the groove for the HGJB. In addition, the combined HGJB and grooved thrust bearing can be used to stabilize the journal because of the low attitude angle. These findings may help and facilitate the design of hydrodynamic bearings suitable for working in warm and hot environments in the future.

Structural Design and Optimization of Herringbone Grooved Journal Bearings Considering Turbulent

In order to improve the performance of the traditional constant-width herringbone grooved journal bearing in a computed tomography tube under a high-temperature environment, the present study designed a convergent herringbone grooved journal bearing (HGJB) structure lubricated by liquid metal. The bearing oil film thickness and the Reynolds equation considering the influence of turbulence are established and solved by using the finite difference method in the oblique coordinate system. The performance of the two bearings was compared, and the static and dynamic performance change trends of the two bearing structures under different eccentricities were systematically studied. The results show that the convergent herringbone grooved journal bearings are superior to the constant-width herringbone grooved journal bearings in terms of bearing capacity and stiffness coefficient. At the same time, the influence of structural parameters, such as the number of grooves, helix angle, groove to ridge ratio, groove depth on the performance of the constant-width herringbone grooved journal bearings, and the convergent herringbone grooved journal bearings was studied. Finally, we conclude that the performance of the convergent herringbone grooved journal bearings is optimal when the number of grooves is 15–20, the helix angle is 30°–45°, the ratio of the groove to ridge is 1, and the groove depth is 0.02 mm –0.024 mm. This research has provided the thinking and reference basis for the design of liquid metal bearings for high-performance CT equipment.

Unstable tilting motion of flexibly supported gas bearing bushings

This paper presents measurements of the motion amplitudes from flexibly supported Herringbone Grooved Journal Bearing bushings. Measurements taken in four locations on the flexibly supported bearing bushing enable the distinction between the radial and the tilting motion, which allowed to identify an unstable bearing bushing tilting mode. The bushing tilting motion instability can be attributed to the cross-coupled tilting impedance of the gas bearing and its occurrence is characterized by the appearance of a sub-synchronous vibration at the speed of instability onset. The comparison between experimentally obtained data and the prediction of a two degrees of freedom dynamic model that includes the flexible support characteristics, the bushing transverse inertia as well as the gas bearing tilting impedance suggests an excellent agreement on both the Eigenfrequency and the rotor speed of instability onset. Furthermore, the effect of the flexible support tilting stiffness and bearing bushing transverse moment of inertia on the critical bushing tilting speed and onset of tilting instability has been investigated, which led to a design guideline to avoid the onset of an unstable bush tilting mode. In addition, experimental data gathered after the introduction of damping in the flexible support of the bearing bushing suggests a significant increase of the onset speed of the unstable bearing bushing tilting mode.

Study on static characteristics of water-lubricated textured herringbone grooved journal bearings based on laminar cavitating flow lubrication model

This paper aims to investigate static characteristics of water-lubricated textured herringbone groove journal bearing under laminar cavitating flow. A theoretical model for the bearing was established based on two-phase flow and population balance equation. Field distribution and static characteristics of the bearing are analysed. The result shows the friction torque of the bearing is reduced due to the texture effect; And the frictional torque is reduced with the increasing of texture area ratio and height. The load carrying capacity of the bearing is increased, while the friction torque are slightly affected by the cavitation effect. The existence of texture increases the bubble number density in the bearing-lubrication process.

Flexible Support for Gas-Lubricated Bearing Bushings

Herringbone-grooved journal bearings (HGJBs) for high-speed turbo-machinery are often supported on O-rings due to their favorable stiffness and damping characteristics for stability and alignment reasons. They yield limited lifetime at high temperatures, insufficient assembly repeatability, and dynamic characteristics that are difficult to measure and to tune, however. In order to overcome these shortcomings, a parametric model has been developed with the aim to design a flexible membrane bushing support that offers tunable tilting and radial stiffness and that can be coupled to various concepts to provide suitable damping levels to support a gas-lubricated bearing bushing. Three damping concepts have been investigated that offer independent tuning of the support damping coefficient in combination with the novel flexible bearing bushing support. The new flexible membrane support was manufactured and its stiffness in radial and tilting directions was measured before it was successfully implemented in a prototype. Test results obtained from the new prototype with membrane support show a significant improvement in bushing alignment quality compared to O-rings as well as stable operation up to the design rotor speed of 250 krpm.

Theoretical and Experimental Investigation of a Small-Scale, High-Speed, and Oil-Free Radial Anode Off-Gas Recirculation Fan for Solid Oxide Fuel Cell Systems

Abstract The Laboratory for Applied Mechanical Design (LAMD) designed, manufactured, and experimentally tested a novel recirculation fan for a 10 kWe solid oxide fuel cell (SOFC). The fan uses oil-free bearings, more specifically herringbone-grooved journal and spiral-grooved thrust gas bearings. The radial inducer-less fan with a tip diameter of 19.2 mm features backward-curved prismatic blades with constant height. Prior to coupling the recirculation fan with the SOFC, the fan was experimentally characterized with air at 200 °C. At the nominal point of 168 krpm, the measured inlet mass flow rate is 4.9 kgh–1, the total-to-total pressure rise 55 mbar, the isentropic total-to-total efficiency 55%, and the power 18.3 W. This paper compares the experimental data toward a computational fluid dynamic simulation of the full fan impeller and volute suggesting an excellent correlation at the nominal point which validates the numerical approach. However, the heat flows crossing the fan fluid domain have an increased effect at off-design conditions; thus, the experimental results need careful consideration. The fan backface leakage has negligible impact on the measurements.

Dynamic force coefficients identification on air-lubricated herringbone grooved journal bearing

Abstract The Narrow Groove Theory (NGT) is commonly used to simulate and design grooved gas bearing. However, measurements of dynamic force coefficients of Herringbone Grooved Journal Bearings (HGJBs) is missing, hence the validation historic NGT has never been performed, despite its importance. A test rig was built in order to identify stiffness and damping coefficients of HGJBs of a rotor perturbed by piezo-electric shakers. Results indicate that the NGT captures the qualitative behavior of HGJB well but tends to overestimate the stiffness and damping coefficients by 23 and 29% respectively. Gravity led to a eccentricity ratio in excess of 15% without significant effect. The direct damping coefficient was found to be mildly non-linear with the excitation amplitude.

A Simulation Study on the Behavior of Magnetorheological Fluid on Herringbone-Grooved Hybrid Slot-Entry Bearing

In recent years, extensive use of smart lubricants has been made in order to control the tribological performance of fluid film bearings. The grooved surfaces of the journal bearing greatly influence the performance of bearings. In the present work, various geometric shapes of herringbone grooves (rectangular, triangular, and parabolic) with groove angles (30° and 60°) have been considered to numerically simulate the performance of slot-entry bearings. The work reported in this article deals with the numerical simulation of magnetorheological (MR) fluid–lubricated slot-entry herringbone-grooved hybrid journal bearings. Dave equation, a constitutive relation of the Bingham model, was employed to simulate the flow behavior of MR fluid. Using the finite element method (FEM), the governing Reynolds equation for a hybrid slot-entry bearing model was solved. The result shows that the use of a herringbone-grooved surface and application of MR fluid in a slot-entry bearing offers better stability and higher fluid film stiffness and minimizes frictional torque.

Numerical study of a hydrodynamic journal bearing with herringbone grooves for oil leakage reduction

Hydrodynamic journal bearings and herringbone-grooved journal bearings were numerically analyzed using finite volume-based computational fluid dynamics software. Navier–Stokes equations were solved to describe pressure and velocity distributions in three dimensions. Values of the Sommerfeld number were calculated as a benchmark case for a hydrodynamic journal bearing. The predicted values of the Sommerfeld number are comparable to theoretical results from engineering tribology literature. For a hydrodynamic journal bearing, it is found that there is a positive correlation between the maximum pressure and the eccentricity ratio. For a hydrodynamic herringbone-grooved journal bearing, the peak pressures are found to occur at the tips of the grooves. It is further found that a herringbone-grooved design can reduce average axial velocity at the outlet by 84%, compared to a hydrodynamic journal bearing without eccentricity. This design could also address the oil leakage issue occurring often in hydrodynamic bearings. These findings may be useful for oil leakage reduction in a hydrodynamic herringbone-grooved journal bearing design.

Effects of humid air on aerodynamic journal bearings

Abstract The development of aerodynamic bearings applications where ambient conditions cannot be controlled (e.g., for automotive fuel cell compressor) raises the question of the effects of condensation in the humid air on performance. A modified Reynolds equation is obtained in relation to humid air thermodynamic equations, accounting for the variation of compressibility and viscosity in the gas mixture. The load capacity and stability of plain and herringbone-grooved journal bearings is computed on a wide range of operating and ambient conditions. In general, performance metrics show an independence on humid-air effects at moderated temperature, although the stability of the grooved journal bearing exhibits strong variations in particular conditions. In consequence, a safety margin of 25% is suggested for the critical mass.

Real-gas effects on aerodynamic bearings

Motivated by the use of aerodynamic bearings lubricated with high-pressure gases in energy conversion cycles, the Reynolds equation is adapted in order to include effects of real-gas and turbulence. Three geometries (Rayleigh-step slider, plain and herringbone-grooved journal bearing) serve to investigate real-gas effects on the static and dynamic properties with a wide variety of lubricants and nondimensional operating conditions. Computational results show a depreciation of the load capacity of journal bearings, with cases reaching a reduction of 50% with unequally affected force components. Stability can be affected both positively and negatively. Some stability losses reach nearly 100%, while improvements of several orders of magnitude with the grooved bearing are reported. Results are fluid-independent for similar reduced pressure and temperature.

Application of stabilized term in free boundary problems for optimizing bi-directional-rotation herringbone-grooved journal bearings

• Using an artificial term in Reynolds equation helps to solve free boundary problems. • Few studies have investigated reversible rotating journal bearings. • The load capacity and side leakage of miniature RHGJBs are optimized. • Geometrical appearance of a miniature RHGJB can be effectively optimized. • The number of full-factorial tests is greatly reduced from 5 9 to 450 runs. In order to deal with the free boundary problems occurred in cavitation region, this work incorporates an artificial term in Reynolds equation to stabilize the solution. The current result shows that adding the extra term gives accurate pressure distribution and benefits the selection of the groove shape and size. In addition, this study utilizes herringbone grooves on a reversible rotating journal bearing (RHGJB) and numerically analyzes the characteristics of miniature journal bearings with an inner diameter of 0.6 mm. Miniature journal bearings are limited in that the load capacity is significantly reduced with decreased bearing size, and therefore, the performances (load capacity and side leakage) of miniature RHGJBs are optimized. The optimum geometrical appearance of miniature RHGJBs is calculated by evaluating several groove parameters. Using the Taguchi parameter design methodology greatly reduces the number of full-factorial experimental design tests required to determine the optimal design parameters of the RHGJB from 5 9 (1,953,125) to 450 runs.

Design of Novel Hydrodynamic Grooved Journal Bearing with Dual-Layer Herringbone-Grooved Patterns

Due to that the load capacity of the conventional herringbone-grooved cylindrical journal bearing (HGJB) decreases significantly with a decreasing dimension, a requirement exists for miniature HGJB with high load capacity in miniaturized spindle motor applications. This paper investigates the design and characterization of a novel HGJB using dual-layer herringbone-grooved patterns for small spindle motors and cooling fans. In contrast to conventional HGJBs, the proposed HGJB contains another set of herringbone-grooved pattern on its outer surface. The performance of the proposed HGJB is characterized numerically using flow field analysis software. Results show that compared to the conventional HGJB presented by the current group in a previous study, the proposed HGJB can improve the load capacity by 53.7% of the previous value.

Geometry optimization for asymmetrical herringbone grooves of miniature hydrodynamic journal bearings by using Taguchi technique

Hydrodynamic bearings (HDBs) have been used for data storage applications because of low friction and shock resistance. However, load capacity of HDB is substantially reduced with a decreasing dimension. Few studies have investigated the behavior of the HDB with its inner diameter smaller than Ø = 2 mm. Therefore, the aim of this study was to efficiently analyze the performance of the miniature journal bearings Ø = 0.6 mm with asymmetrical herringbone grooves. To reduce the number of full-factorial experimental design tests, the Taguchi methodology is used to find out the optimal design parameters of the two-step Herringbone-grooved journal bearings.

Dynamic stability of herringbone-grooved journal gas bearing

Dynamic stability of herringbone-grooved journal gas bearing

Enhanced Groove Geometry for Herringbone Grooved Journal Bearings

Although gas-lubricated herringbone grooved journal bearings (HGJB) are known for high rotordynamic stability thresholds, small clearance to diameter ratios are required for stable rotor operation. Tight clearances not only increase bearing losses but also yield challenging manufacturing and assembly tolerances, which ultimately translate into cost. Traditionally, the grooves of HGJB are of helical nature with constant cross section and pitch. The current paper aims at increasing the clearance to diameter ratio and the stability threshold of grooved bearings by introducing enhanced groove geometries. The axial evolution of groove width, depth, and local pitch are described by individual third order polynomials with four interpolation points. The expression for the smooth pressure distribution resulting from the narrow groove theory is modified to enable the calculation of bearing properties with modified groove patterns. The reduced order bearing model is coupled to a linear rigid body rotordynamic model for predicting the whirl speed map and the corresponding stability. By introducing a critical mass parameter as a measure for stability, a criterion for the instability onset is proposed. The optimum groove geometry is found by coupling the gas bearing supported rotor model with a multiobjective optimizer. By maximizing both the clearance to diameter ratio and the rotordynamic stability it is shown that with optimal groove geometry, which deviates from helicoids with constant pitch and cross section, the critical mass parameter can be improved by more than one order of magnitude compared to traditional HGJB geometries. The clearance to diameter ratio can be increased by up to 80% while keeping the same stability margin, thus reducing both losses and manufacturing constraints. The optimum groove pattern distributions (width ratio, angle, and depth) are summarized for a variety of L/D ratios and for different compressibility numbers in a first attempt to set up general design guidelines for enhanced gas-lubricated HGJB.