Spiral Groove Bearing Research Articles

Thermohydrodynamic Model of Cavitating Flow and Dynamic Characteristic Calculation for High-Speed Water-Lubricated Pump-Out Spiral Groove Bearing

A complete thermohydrodynamic lubrication model for pump-out spiral groove thrust bearings (SGTB) with cavitating flow is established based on two-phase flow and transport theory. Various effects (cavitating flow interface effect, convective heat transfer effect, heat conduction effect, inertia effect, breakage and coalescence of bubbles) of water lubricant at high speed are included when modeling. The bubble size distributions, bubble number density of the cavitating flow, and the dynamic coefficients of the SGTB are predicted using this model. The probability distribution of the bubble size, bubble number density, and axial film stiffness coefficient agree with the experimental values. The results show that the number of small-sized bubbles is much larger than the number of large-sized bubbles in cavitating flow. When the SGTB has a specified spiral angle, the direct stiffness coefficients increase and the cross-stiffness coefficients decrease due to the cavitation effect, but the influence of the cavitation effect on the damping coefficient is not obvious.

Lubrication performance of conical spiral-groove bearings with rough surfaces

A mixed lubrication model of conical spiral-groove bearings is established by integrating partial fluid lubrication theory and G-W statistical theory. Considering the effect of bearing surface roughness, the equivalent average Reynolds equation is derived based on average flow model, which is solved by boundary fitted coordinate system and finite difference method. The G-W contact model is used to calculate the axial force and friction force produced by the contact of multi asperities. The coefficients of friction are calculated and measured under different rotational speed and the theoretical results are in accordance with the test results. The results show that comparing with bearings with deep groove, ones with shallower groove have lower transition speed and lower friction coefficient at low speeds.

The Impact of Pulsatile Flow on Suspension Force for Hydrodynamically Levitated Blood Pump.

Hydrodynamically levitated rotary blood pumps (RBPs) with noncontact bearing are effective to enhance the blood compatibility. The spiral groove bearing (SGB) is one of the key components which offer the suspension force to the RBP. Current studies focus on the suspension performance of the SGB under continuous flow condition. However, the RBP shows pulsatile characteristics in the actual clinical application, which may affect the suspension performance of the SGB. In this paper, the impact of pulsatile flow upon the suspension force from the SGB is studied. A model of the SGB with a groove formed of wedge-shaped spirals is built. Then, the CFD calculation of the hydrodynamic force offered by designed SGB under simulated pulsatile flow is introduced to obtain the pulsatile performance of the suspension force. The proposed method was validated by experiments measuring the hydrodynamic force with different bearing gaps. The results show that the suspension force of the SGB under pulsate flow is the same as under steady flow with equivalent effective pressure. This paper provides a method for suspension performance test of the SGB.

Reducing friction power losses of flywheel energy storage systems using PTFE composites: A technical note

This technical note aims to reduce friction power loss of flywheel energy storage system (FESS) supported by hydrodynamic spiral groove bearing and permanent magnetic bearing (PMB). An approach is proposed to fabricate the spiral groove bearing using polytetrafluoroethylene (PTFE) composite. A test rig is developed to test tribological properties of the spiral groove PTFE bearings. Also, two PTFE composites (C-PTFE: 80 vol.% PTFE filled with 20 vol.% graphite; C-Cu-PTFE 50 vol.% PTFE filled with 20 vol.% graphite and 30 vol.% copper powder) are tested. Results show that the friction power losses of the C-PTFE and C-Cu-PTFE bearings are lower than that of the traditional albronze (CuAl) bearing in the whole speed range. In addition, the spiral groove PTFE bearings show an excellent friction-reducing property under boundary or mixed lubrication condition. Finally, a case study is given to show the spiral groove PTFE bearing is capable of reducing the friction power loss of the FESS.

A transient hydrodynamic lubrication comparative analysis for misaligned micro-grooved bearing considering axial reciprocating movement of shaft

Abstract A transient hydrodynamic lubrication model is proposed to investigate the lubrication performance of micro-grooved journal bearings, considering the axial flow caused by the axial reciprocating movement of the shaft. The lubrication performance of the bearing engineered with three different microgroove distributions, i.e. straight groove, spiral groove, and herringbone groove are compared systematically, including the load capacity and friction coefficient. The results suggest that the herringbone-grooved bearing exhibits the maximum load capacity in the positive axial movement, followed by straight-grooved bearing, and finally spiral-grooved bearing. The spiral-grooved bearing produces the minimum fluctuation amplitude of load capacity and attitude angle in one reciprocating period. The increased frequency of the axial movement can increase the value of load capacity for three micro-grooved bearings during the positive movement of the shaft; however, it does not affect the distribution trends of load capacity among the three micro-grooved bearings. Moreover, the effects of groove angle (β), degree of misalignment (Dm), and misalignment direction angle (α) on the lubrication performance of the micro-grooved bearing are investigated. The results indicate that the herringbone-grooved bearing exhibits better lubrication performance than the spiral-grooved bearing in the positive axial movement at any β. The present study also indicates that the load capacity of considering axial movement is more sensitive to Dm than that of not considering axial movement. The misalignment direction angle will result in the decreased load capacity of the micro-grooved bearing.

Suppression of low-frequency vibration for rotor-bearing system of flywheel energy storage system

Abstract A nonsynchronous low-frequency whirling occurs frequently for flywheel energy storage system (FESS) with permanent magnetic bearing (PMB) and spiral groove bearing. To suppress low-frequency vibration of a large-mass FESS, a radial magnetic pendulum tuned mass damper (TMD) and an axial magnetic pendulum TMD have been developed; and identification method of dynamic parameter for the magnetic pendulum TMD has been proposed. Dynamic model for the FESS has been established using the Lagrange’s equation; and effectiveness of the two magnetic pendulum TMD’s has been evaluated by analyzing mode damping ratios of the FESS. The results show that the two TMD’s can be effective for the low-frequency vibration of the high-capacity FESS with PMB and spiral groove bearing; and radial magnetic pendulum TMD is superior to the axial magnetic pendulum TMD due to its lower resonant frequency and larger mode damping ratio for the FESS.

Study of Spiral Groove Bearing Effect on a Mechanical Heart Assist Device by using Computational Fluid Dynamic

Background: Mechanical heart assist device is a viable alternative to the escalating problems of worldwide heart failure. For a long-term support, this device must have an excellent compatibility with blood. However, due to complex flow pattern within the hydrodynamic bearing clearance affect severely on both hemolysis and thrombosis. To tackle this problem, spiral groove bearing was imprinted at the rotor of the blood pump. This hydrodynamically bearing suspends the moving impeller within the blood field thus reduces the mechanical contact (shear stress) as it generated localized pressure.

Nonlinear Analysis of Stability and Unbalanced Response on Spherical Spiral-Grooved Gas Bearings

ABSTRACTThis study conducts a nonlinear numerical analysis of the stability and the unbalance response of spherical spiral-grooved bearings (SSGBs) using a nonlinear orbit simulation method. This method is more accurate than the linear method, especially at high bearing loads. Parametric analyses are also performed with respect to nominal clearance and groove depth to optimize groove parameters. Shaft trajectories reflect the nonlinear characters of SSGBs when mass unbalance increases. Fast Fourier transform analyses of rotor orbit responses facilitate identification of the subsynchronous whirling and unbalance response in rotor vibration behavior. Results show that optimum dimensionless groove depths vary for different nominal clearances or rotational speeds. The static performance and stability characteristics of spherical bearings can be significantly influenced by the spiral grooves on the journal surface.

Dynamics of Flywheel Energy Storage System With Permanent Magnetic Bearing and Spiral Groove Bearing

Developing a flywheel energy storage system (FESS) with permanent magnetic bearing (PMB) and spiral groove bearing (SGB) brings a great challenge to dynamic control for the rotor system. In this paper, a pendulum-tuned mass damper is developed for 100 kg-class FESS to suppress low-frequency vibration of the system; the dynamic model with four degrees-of-freedom is built for the FESS using Lagrange's theorem; mode characteristics, critical speeds, and unbalance responses of the system are analyzed via theory and experiment. A comparison between the theoretical results and the experiment ones shows that the pendulum-tuned mass damper is effective, the dynamic model is appropriate, and the FESS can run smoothly within the working speed range.

Maintenance free gas bearing helium blower for nuclear plant

This paper describes the design, testing and operation of novel helium blowers used to recirculate the helium blanketing gas in the nuclear reactor used as a neutron source at the Institut Laue Langevan, Grenoble, France. The laser sintered shrouded centrifugal wheel operates at speeds up to 45000 rpm supported on helium lubricated hydrodynamic spiral groove bearings, and is driven by a sensorless permanent magnet motor. The entire machine is designed to keep the helium gas (polluted by a small amount of D2O) out of contact with any iron or copper materials which would contribute to the corrosion of parts of the circuit. It is designed to have zero maintenance during a lifetime of 40,000 hours of continuous operation. This paper will describe the spiral groove journal and thrust bearings. Design and manufacture of the 1 kW motor and centrifugal wheel will be explained including their CFD and FEA analyses. Measurements of rotor displacement will be presented showing the behaviour under factory testing as well as details of the measured centrifugal wheel and motor performances. Two machines are incorporated into the circuit to provide redundancy and the first blower has been in continuous operation since Jan 2015. The blower was designed, manufactured, assembled and tested in the UK using predominantly UK suppliers.

Chaotic Behaviour Investigation of a Front Opposed-Hemispherical Spiral-Grooved Air Bearing System

In recent years, spiral-grooved air bearing systems have attracted much attention and are especially useful in precision instruments and machines with spindles that rotate at high speed. Load support can be multidirectional and this type of bearing can also be very rigid. Studies show that some of the design problems encountered are dynamic and include critical speed, nonlinearity, gas film pressure, unbalanced rotors, and even poor design, all of which can result in the generation of chaotic aperiodic motion and instability under certain conditions. Such irregular motion on a large scale can cause severe damage to a machine or instrument. Therefore, understanding the conditions under which aperiodic behaviour and vibration arise is crucial for prevention. In this study, numerical analysis, including the Finite Difference and Differential Transformation Methods, is used to study these effects in detail in a front opposed-hemispherical spiral-grooved air bearing system. It was found that different rotor masses and bearing number could cause undesirable behaviour including periodic, subperiodic, quasi-periodic, and chaotic motion. The results obtained in this study can be used as a basis for future bearing system design and the prevention of instability.

Dynamic Characteristics of Spiral-Grooved Opposed-Hemisphere Gas Bearings

The traditional eight-coefficient bearing model only considers the translational motion of the bearings and neglects the tilting motion and coupling effects between them. In this paper, the dynamic characteristics of the spiral-grooved opposed-hemisphere gas bearing considering five degrees-of-freedom are studied, and 50 dynamic coefficients including the translational, tilting, and coupling components are completely calculated. The Reynolds equations and their perturbed equations are solved by the finite element method to obtain the dynamic stiffness and damping coefficients. The effects of the tilting motion on the dynamic coefficients and response are analyzed, respectively. The results show that the coupling coefficients between the translational and tilting motions, which have been neglected in most previous studies, are significant at large eccentricity ratio. But these coupling coefficients have little effect on the dynamic response. On the other hand, the influences of the tilting motion on the synchronous response and natural frequency are remarkable and will decrease the stability of the rotor bearing system.

Thermohydrodynamic Analysis and Thermal Management of Spherical Spiral Groove Gas Bearings

ABSTRACTA thermohydrodynamic model of spherical spiral groove bearings is presented by considering the effect of bearing temperature change on the material property of lubricant, gas flow characteristics in the grooves, and thermal energy transported in the entire bearing system. A gas mixing model in the grooves is introduced as the boundary condition to solve the bearing temperature distribution simultaneously with the heat conduction at the shaft and the housing. The bearing and rotor expansion caused by temperature increases, which is considerable compared to bearing clearance, is also examined. Prediction results show that the thermal expansion determined by actual bearing clearance has a crucial influence on the bearing load capacity. Manufacturing bearings with proper materials has significant effects on controlling thermal expansion effects on the bearing performance. The load capacity, which corresponds to the lubricant gas pressure, and gas suck flow rate have the same variation tendencies as the variation in groove depth and spiral angle. These similar tendencies have an opposite influence on the temperature and result in the temperature increase not being affected by the variation in grooves. However, varying the groove characteristics has a similar effect in carrying away the thermal energy as the variation in heat transfer coefficient, which could significantly control the temperature increase at the same time.

Plasma Skimming in a Spiral Groove Bearing of a Centrifugal Blood Pump.

Plasma skimming is a phenomenon in which discharge hematocrit is lower than feed hematocrit in microvessels. Plasma skimming has been investigated at a bearing gap in a spiral groove bearing (SGB), as this has the potential to prevent hemolysis in the SGB of a blood pump. However, it is not clear whether plasma skimming occurs in a blood pump with the SGB, because the hematocrit has not been obtained. The purpose of this study is to verify plasma skimming in an SGB of a centrifugal blood pump by developing a hematocrit measurement method in an SGB. Erythrocyte observation using a high-speed microscope and a bearing gap measurement using a laser confocal displacement meter was performed five times. In these tests, bovine blood as a working fluid was diluted with autologous plasma to adjust the hematocrit to 1.0%. A resistor was adjusted to achieve a pressure head of 100 mm Hg and a flow rate of 5.0 L/min at a rotational speed of 2800 rpm. Hematocrit on the ridge region in the SGB was measured using an image analysis based on motion image of erythrocytes, mean corpuscular volume, the measured bearing gap, and a cross-sectional area of erythrocyte. Mean hematocrit on the ridge region in the SGB was linearly reduced from 0.97 to 0.07% with the decreasing mean bearing gap from 38 to 21 μm when the rotational speed was changed from 2250 to 3000 rpm. A maximum plasma skimming efficiency of 93% was obtained with a gap of 21 μm. In conclusion, we succeeded in measuring the hematocrit on the ridge region in the SGB of the blood pump. Hematocrit decreased on the ridge region in the SGB and plasma skimming occurred with a bearing gap of less than 30 μm in the hydrodynamically levitated centrifugal blood pump.

Nonlinear Dynamic Analysis of a Rigid Rotor Supported By a Spiral-Grooved Opposed-Hemisphere Gas Bearing

ABSTRACTThe nonlinear dynamic behavior of a rigid rotor supported by a spiral-grooved opposed-hemisphere gas bearing is investigated in this article, focusing particular attention on its whirl motion. The finite element method combined with the finite difference method is employed to solve the time-dependent Reynolds equation that is coupled with the rotor motion considering five degrees of freedom. The rotor responses to the initial disturbance and synchronous and nonsynchronous excitations are investigated. To analyze the complicated dynamic behavior of the rotor–bearing system, the trajectories of the rotor centerline, time responses, phase portraits, power spectra, Poincare maps, and bifurcation diagrams are obtained from the numerical procedure. The results show that the conical whirl instability appears earlier than the cylindrical whirl instability with increasing rotational speed for the rotor–bearing system with no unbalance mass. Moreover, it reveals that the complex dynamic behavior of the system excited by unbalance mass varies with rotational speed and rotor mass. In addition, bifurcation diagrams employing the rotating speed and rotor mass as bifurcation parameters are obtained. Finally, the nonsynchronous excitation responses are presented, which behave in a different way than the synchronous excitation responses. The results of this study offer a further understanding of the nonlinear characteristics of spiral-grooved opposed-hemisphere gas bearings.

Thermohydrodynamic analysis of micro spherical spiral groove gas bearings under slip flow and surface roughness coupling effect

The effects of gas rarefaction and surface roughness are temperature-related and always neglected in macroscale. These effects were considered in the analysis of the thermohydrodynamic performance of micro spherical spiral groove bearings. The Reynolds equation and the energy equation incorporated with Wu's slip model and the Weierstrass---Mandelbrot function to analysis the coupling effect of slip flow and surface roughness. The effects of spherical grooves on computational accuracy were reduced through parameter transformation and oblique coordinates. To describe the temperature boundary condition at the grooved region, a simple gas-mixing model was presented for the grooves. Prediction results showed that temperature reduced bearing forces and friction torque through the slip flow effect. Surface roughness increased not only temperature significantly but also bearing forces and friction torque through a high eccentricity ratio and a low bearing clearance.

Numerical analysis of spiral grooved opposed-hemisphere gas bearings: A parametric study

Although the spiral grooved opposed-hemisphere gas bearings have been widely applied in supporting the spin axis of inertial grade gyroscopes, the accurate prediction of the performance characteristics of the bearings is still very difficult because of their structural complexity. In this paper, the static characteristics of the bearings considering the coupling effects between the journal and two hemisphere bearings are obtained theoretically. The Reynolds equations modeling the journal and hemisphere bearings are solved simultaneously by the finite element method satisfying the continuous boundary conditions between these three bearings. The fluctuations of the bearing load and reaction torque caused by rotating grooves are shown and can be neglected at large number of grooves. The results show that neglecting the coupling effects between the journal and two hemisphere bearings will result in large discrepancies at high rotational speeds and large eccentricity ratios. And the hydrodynamic effect can be divided into two regions for spiral grooved gas bearings: the groove effect domain region and the converged wedge effect domain region. A parametric study provides efficient guidance for the optimal design of the opposed-hemisphere gas bearing.

Optimization of the double sided spiral groove thrust bearing: A comparison to approximate analytical solutions

AbstractReliable high performance bearings are essential in rotordynamics. As speeds and loads are continuously increased the demands on bearing technology grow simultaneously. Optimization of bearing characteristics becomes more important under these circumstances. For hydrodynamic thrust bearings, recently a special design has been presented, which is supposed to enhance the load carrying capacity by 60% compared to the best known thrust bearing type. The bearing consists of two spiral grooved surfaces and is therefore called a double sided spiral groove bearing. Early calculations of the bearing performance base on approximate analytical methods.In order to verify those results, a detailed numerical model of the bearing is presented by the authors. With the help of a particle swarm optimization method, optimal bearing parameters are determined and a comparison is drawn to other thrust bearing designs. It is shown that previously published results overestimate the performance of the double sided spiral groove bearing severly. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Design of Spherical Spiral Groove Bearings for a High-Speed Air-Lubricated Gyroscope

A spherical spiral groove gas bearing has the ability to not only support radial and axial loads simultaneously but also tolerate extensive misalignment. Thus, this bearing type is considered suitable as a supporting and lubrication component of inertial components such as gyroscopes in the fields of aerospace and navigation. In this study, we propose a numerical method for predicting static and dynamic characteristics and conduct a parametric analysis of an aerodynamic spherical bearing with rotating spiral grooves. The finite difference method and the perturbation method are used to calculate the Reynolds equation to obtain the force coefficients. Given the complicated groove distribution, as well as film discontinuity and compressibility, solving the equations numerically in the spherical coordinates system is difficult. Parameter transformation and oblique coordinate transformation are thus applied in this study to modify the Reynolds equation into the planar oblique coordinate system. An eight-point method is also utilized to deal with film thickness discontinuity. The predictions of this proposed method show good agreement with the available experimental data. Parametric studies on nominal clearance, eccentricity ratio, rotating speed, groove depth, groove angle, and perturbation frequency are then conducted to determine optimum design parameters. The results show that these factors significantly affect bearing characteristics in both the radial and axial directions.

Evaluation of erythrocyte flow at a bearing gap in a hydrodynamically levitated centrifugal blood pump.

We have developed a hydrodynamically levitated centrifugal blood pump for extracorporeal circulatory support. In the blood pump, a spiral groove bearing was adopted for a thrust bearing. In the spiral groove bearing, separation of erythrocytes and plasma by plasma skimming has been postulated to occur. However, it is not clarified that plasma skimming occurs in a spiral groove bearing. The purpose of this study is to verify whether plasma skimming occurs in the spiral groove bearing of a hydrodynamically levitated centrifugal blood pump. For evaluation of plasma skimming in the spiral groove bearing, an impeller levitation performance test using a laser focus displacement meter and a microscopic visualization test of erythrocyte flow using a high-speed microscope were conducted. Bovine blood diluted with autologous plasma to adjust hematocrit to 1.0% was used as a working fluid. Hematocrit on the ridge region in the spiral groove bearing was estimated using image analysis. As a result, hematocrits on the ridge region with gaps of 45 μm, 31 μm, and 25 μm were calculated as 1.0%, 0.6%, and 0.3%, respectively. Maximum skimming efficiency in this study was calculated as 70% with a gap of 25 μm. We confirmed that separation of erythrocyte and plasma occurred in the spiral groove bearing with decrease in bearing gap in a hydrodynamically levitated centrifugal blood pump.