Analysis of Tilting Effects and Geometric Non-Uniformities in Micro-Hydrostatic Gas Thrust Bearings

2005 ◽  
Author(s):  
C. J. Teo ◽  
Z. S. Spakovszky
Keyword(s):  
High Speed ◽  
Compressible Flows ◽  
Thrust Bearing ◽  
Coupled System ◽  
Orifice Diameter ◽  
Influence Coefficient ◽  
Analysis Tool ◽  
Thrust Bearings ◽  
Tilting Angle ◽  
Concomitant Reduction

The MIT microengine rotors are supported by hydrostatic gas journal and hydrostatic gas thrust bearings. Due to the low length-to-diameter ratio of the devices, the thrust bearings play an important role in providing sufficient tilting stiffness to resist any tilting motion about the spinning axis of the rotor. The performance of the thrust bearings can be influenced by geometric nonuniformities such as thrust bearing clearances and orifice diameters and profiles which arise in the process of microfabrication. To enable stable high speed operation of the micro-devices, it is important to quantify these effects. Furthermore, a thrust bearing analysis tool needs to be developed that is able to explore different thrust bearing arrangements and configurations. In this work, an analytical model is established for analyzing the effects of rotor tilt and geometric non-uniformities in micro-hydrostatic gas thrust bearings for application to microturbomachinery. A previously developed model (Teo and Spakovszky [1]) is generalized and extended for application to thrust bearings with orifices arranged in non-axisymmetric configurations. As a consequence of rotor tilt or geometric non-uniformities, the flow through individual orifices of the thrust bearing becomes non-uniform. The orifice flows are in turn coupled to the hydrostatic pressure field in the thrust bearing pad, and a Green’s function approach is adopted to solve the coupled system. The hydrodynamic thrust bearing forces induced by the pumping action of the rotor rotation are determined by solving the Reynolds equation. The model is able to predict thrust bearing tilting stiffness and variations in the thrust bearing mass flow rates as a function of rotor tilting angle for a variety of orifice arrangements. The model can be applied to analyze the effects of non-uniformities in orifice diameter and the presence of clogged orifices on tilting and the concomitant reduction in tilting stiffness. In addition, the effects of orifice taper are analyzed using an influence-coefficient technique for 1-D compressible flows. Results obtained for various taper ratios are presented and discussed. The model serves as a useful tool for specifying design tolerances during the fabrication of micro-hydrostatic gas thrust bearings and is used in the experiments to estimate the tilting angle of the rotor during operation.

Analysis of Tilting Effects and Geometric Nonuniformities in Micro-hydrostatic Gas Thrust Bearings

2005 ◽  
Vol 128 (4) ◽  
pp. 606-615 ◽  
Author(s):  
C. J. Teo ◽  
Z. S. Spakovszky
Keyword(s):  
High Speed ◽  
Thrust Bearing ◽  
Coupled System ◽  
Orifice Diameter ◽  
Influence Coefficient ◽  
Analysis Tool ◽  
Massachusetts Institute Of Technology ◽  
Thrust Bearings ◽  
Tilting Angle ◽  
Institute Of Technology

The Massachusetts Institute of Technology (MIT) microengine rotors are supported by hydrostatic gas journal and hydrostatic gas thrust bearings. Due to the low length-to-diameter ratio of the devices, the thrust bearings play an important role in providing sufficient tilting stiffness to resist any tilting motion about the spinning axis of the rotor. The performance of the thrust bearings can be influenced by geometric nonuniformities such as thrust-bearing clearances and orifice diameters, and profiles which arise in the process of micro-fabrication. To enable stable high speed operation of the micro-devices, it is important to quantify these effects. Furthermore, a thrust-bearing analysis tool needs to be developed that is able to explore different thrust-bearing arrangements and configurations. In this work, an analytical model is established for analyzing the effects of rotor tilt and geometric nonuniformities in micro-hydrostatic gas thrust bearings for application to micro-turbomachinery. A previously developed model (Teo and Spakovszky, 2006, “Modeling and Experimental Investigation of Micro-hydrostatic Gas Thrust Bearings for Micro-turbomachines,” ASME J. Turbomach., 128, pp. 597–605) is generalized and extended for application to thrust bearings with orifices arranged in nonaxisymmetric configurations. As a consequence of rotor tilt or geometric nonuniformities, the flow through individual orifices of the thrust bearing becomes nonuniform. The orifice flows are in turn coupled to the hydrostatic pressure field in the thrust-bearing pad, and a Green’s function approach is adopted to solve the coupled system. The hydrodynamic thrust-bearing forces induced by the pumping action of the rotor rotation are determined by solving the Reynolds equation. The model is able to predict thrust-bearing tilting stiffness and variations in the thrust-bearing mass flow rates as a function of rotor tilting angle for a variety of orifice arrangements. The model can be applied to analyze the effects of nonuniformities in orifice diameter and the presence of clogged orifices on tilting and the concomitant reduction in tilting stiffness. In addition, the effects of orifice taper are analyzed using an influence-coefficient method for one-dimensional compressible, viscous flows. Results obtained for various taper ratios are presented and discussed. The model serves as a useful tool for specifying design tolerances during the fabrication of micro-hydrostatic gas thrust bearings and is used in the experiments to estimate the tilting angle of the rotor during operation.

The Dynamic Optimization Analysis of High-Speed Hybrid Thrust Bearing

2010 ◽  
Vol 118-120 ◽  
pp. 507-511
Author(s):  
Kai Sun ◽  
Lan Wang ◽  
Xin Jun Zhao
Keyword(s):  
Dynamic Optimization ◽  
Dynamic Characteristics ◽  
High Speed ◽  
Thrust Bearing ◽  
Orifice Diameter ◽  
Optimization Analysis ◽  
Angular Misalignment ◽  
Thrust Bearings ◽  
Supply Pressure ◽  
Dynamic Moment

In this paper, the dynamic characteristics of high-speed hybrid thrust bearing with four-recesses are optimized for different orifice diameter and supply pressure at a given speed condition, the dynamic moment coefficients of hybrid thrust bearing are analyzed, considering the thrust collar angular misalignment case to determine the optimization of orifice diameter and supply pressure under a given speed. The results provide certain reference to the hybrid thrust bearings used in high speed precision spindle.

Dynamic Analysis of High-Speed Hybrid Thrust Bearings

2013 ◽  
Vol 365-366 ◽  
pp. 304-308
Author(s):  
Lei Wang
Keyword(s):  
Dynamic Analysis ◽  
High Speed ◽  
Reynolds Equation ◽  
Thrust Bearing ◽  
Dynamic Performance ◽  
Orifice Diameter ◽  
Thrust Bearings ◽  
Supply Pressure ◽  
Bearing Stiffness ◽  
Stiffness And Damping

An analysis is conducted and solutions are provided for the dynamic performance of high speed hybrid thrust bearing. By adopting bulk flow theory, the turbulent Reynolds equation is solved numerically with the different orifice diameter and supply pressure. The results show that increasing supply pressure can significantly improve the bearing stiffness and damping, while the orifice diameters make a different effect on the bearing stiffness and damping.

scholarly journals Measurements Versus Predictions for a Hybrid (Hydrostatic Plus Hydrodynamic) Thrust Bearing for a Range of Orifice Diameters

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Dara W. Childs ◽  
Paul Esser
Keyword(s):  
High Speed ◽  
Thrust Bearing ◽  
Fluid Film ◽  
Orifice Diameter ◽  
Axial Stiffness ◽  
Test Results ◽  
Flow Rates ◽  
Face To Face ◽  
Thrust Bearings ◽  
Inner Radius

A fixed-geometry hybrid thrust bearing is investigated with three different supply orifice diameters, (1.63, 1.80, and 1.93 mm). The test rig uses a face-to-face thrust-bearing design, with the test bearing acting as the rotor loading mechanism. A hydraulic shaker applies the static axial load, which is reacted by a second (slave) thrust bearing. The rotor is supported radially by two water-lubricated fluid-film journal bearings and is attached to a 30.6 krpm motor via a high-speed coupling with very low axial stiffness. Thrust bearings are tested for a range of supply pressures (5.17, 10.34, and 17.34 bars), fluid film thicknesses, and speeds (7.5, 12.5, and 17.5 krpm). The water-lubricated test bearings have eight pockets, with feed orifices located centrally in each pocket. Experimental results are compared to predictions from a bulk-flow model, showing generally good agreement. Thrust-bearing inlet supply and inner radius flow rates all decreased with decreasing orifice diameters and bearing axial clearances. In most cases, the bearings with larger orifice diameters exhibit higher recess pressure ratios, operating clearances, and flow rates. An optimum hybrid thrust-bearing orifice diameter will depend on the conditions of individual applications. Larger orifices generally provide larger operating clearances and higher stiffnesses, but also require higher flow rates. For most applications, a compromise of bearing performance parameters will be desired. The test results and comparisons presented will aid in sizing orifice diameters for future hybrid thrust-bearing designs and in validating and improving models and predictions.

On the performance of foil thrust bearing with misaligned bearing runner

2017 ◽  
Vol 69 (2) ◽  
pp. 105-115 ◽  
Author(s):  
Abdelrasoul M. Gad
Keyword(s):  
High Speed ◽  
Thrust Bearing ◽  
Approximation Technique ◽  
Hydrodynamic Effect ◽  
Stable Operation ◽  
Content Type ◽  
Thrust Bearings ◽  
Load Carrying ◽  
Foil Thrust Bearing ◽  
Stiffness And Damping

Purpose Compliant foil thrust bearings are promising bearings for high-speed oil-free turbomachinery. However, most previous experimental and numerical approaches to investigate the performance of these bearings have ignored the effect of bearing runner misalignment. Therefore, this paper aims to evaluate the effects of static and dynamic angular misalignments of the bearing runner on the performance of a gas-lubricated foil thrust bearing. Design/methodology/approach The bearing runner is allowed a maximum angular misalignment that produces a minimum gas film thickness as low as 20 per cent of the nominal clearance. Then, the variations of bearing load carrying capacity, viscous power loss and stiffness and damping coefficients of the gas film with runner misalignment are thoroughly analyzed. The flow in the gas film is modeled with compressible Reynolds equation along with the Couette approximation technique, and the deformation of the compliant bearing is calculated with a robust analytical model. Small perturbations method is used to calculate the force and moment dynamic coefficients of the gas film. Findings The results show that misaligned foil thrust bearings are capable of developing a restoring moment sufficient enough to withstand the imposed misalignments. Furthermore, the enhanced hydrodynamic effect ensures a stable operation of the misaligned bearing, and the results highlighted the role of the compliant bearing structure to maintain foil bearing prominent features even at misaligned conditions. Originality/value The value of this study is the evaluation of the effects of runner angular misalignments on the static and dynamic characteristics of Generation II bump-type foil thrust bearing.

Modeling and Experimental Investigation of Micro-Hydrostatic Gas Thrust Bearings for Micro-Turbomachines

2005 ◽  
Author(s):  
C. J. Teo ◽  
Z. S. Spakovszky
Keyword(s):  
Dynamic Stability ◽  
High Speed ◽  
Thrust Bearing ◽  
Dynamic Instability ◽  
Axial Stiffness ◽  
Stable Operation ◽  
Essential Information ◽  
Flow Choking ◽  
Thrust Bearings

One of the major challenges for the successful operation of high-power-density micro-devices lies in the stable operation of the bearings supporting the high-speed rotating turbomachinery. Previous modeling efforts by Piekos [1], Liu et al. [2] and Spakovszky and Liu [3] have mainly focused on the operation and stability of journal bearings. However, since thrust bearings play the vital role of providing axial support and stiffness, there is a need to gain a fuller understanding of their behavior. In this work, a rigorous theory is presented to analyze the effects of compressibility in micro-flows (characterized by low Reynolds numbers and high Mach numbers) through hydrostatic thrust bearings for application to microturbomachines. The analytical model, which combines a 1-D compressible flow model with Finite-Element Analysis, serves as a useful tool for establishing operating protocols and assessing the stability characteristics of hydrostatic thrust bearings. The model is capable of predicting key steady-state performance indicators, such as bearing mass flow, axial stiffness and natural frequency as a function of the hydrostatic supply pressure and thrust bearing geometry. The model has been applied to investigate the static stability of hydrostatic thrust bearings in micro-turbine-generators, where the electrostatic attraction between the stator and rotor gives rise to a negative axial stiffness contribution and may lead to device failure. Thrust bearing operating protocols have been established for a micro-turbopump, where the bearings also serve as an annular seal preventing the leakage of pressurized liquid from the pump to the gaseous flow in the turbine. The dual role of the annular pad poses challenges in the operation of both the device and the thrust bearing. The operating protocols provide essential information for the required thrust bearing supply pressures and axial gaps required to prevent the leakage of water into the thrust bearings for various pump outlet pressures. Good agreement is observed between the model predictions and experimental results. In addition, a dynamic stability analysis is also performed, which indicates the occurrence of unstable axial oscillations due to flow choking effects in both forward and aft thrust bearings. These a-priori dynamic stability predictions were subsequently verified experimentally on a micro-turbocharger. The frequencies of unstable axial oscillations predicted using the model compare favorably to those determined experimentally, thus vindicating the validity of the model. A simple and useful dynamic stability criterion is established, where the occurrence of flow choking in both thrust bearings give rise to dynamic instability.

Development of Foil Thrust Bearings with Simple Structure for Micro Turbines

2011 ◽  
Vol 368-373 ◽  
pp. 1392-1395 ◽  
Author(s):  
Quan Zhou ◽  
Yu Hou ◽  
Ru Gang Chen
Keyword(s):  
High Speed ◽  
Simple Structure ◽  
Thrust Bearing ◽  
Load Capacity ◽  
Complicated Structure ◽  
Thrust Bearings ◽  
Foil Bearings ◽  
Rotational Systems ◽  
Micro Turbine ◽  
Foil Thrust Bearing

Because of the low power loss and high stability, foil bearings are suitable lubrication components for high speed rotational systems. At present, the foil bearings used in actual applications almost have complicated structure and are hard to manufacture. In this paper, two kinds of foil thrust bearings with simple structure are presented. Configurations of these two foil thrust bearings are introduced; meanwhile, the load capacity and running stability are also tested in a high speed micro turbine. It is shown that viscoelastic supported foil thrust bearing has higher load capacity and hemisphere convex dots supported foil thrust bearing is more stable in high speed operational condition.

Modeling and Experimental Investigation of Micro-hydrostatic Gas Thrust Bearings for Micro-turbomachines

2005 ◽  
Vol 128 (4) ◽  
pp. 597-605 ◽  
Author(s):  
C. J. Teo ◽  
Z. S. Spakovszky
Keyword(s):  
High Speed ◽  
Scaling Laws ◽  
Thrust Bearing ◽  
Journal Bearings ◽  
Axial Stiffness ◽  
Stable Operation ◽  
Successful Operation ◽  
Element Analysis ◽  
Essential Information ◽  
Thrust Bearings

One major challenge for the successful operation of high-power-density micro-devices lies in the stable operation of the bearings supporting the high-speed rotating turbomachinery. Previous modeling efforts by Piekos (2000, “Numerical Simulation of Gas-Lubricated Journal Bearings for Microfabricated Machines,” Ph.D. thesis, Department of Aeronautics and Astronautics, MIT), Liu et al. (2005, “Hydrostatic Gas Journal Bearings for Micro-Turbo Machinery,” ASME J. Vib. Acoust., 127, pp. 157–164), and Spakovszky and Liu (2005, “Scaling Laws for Ultra-Short Hydrostatic Gas Journal Bearings,” ASME J. Vib. Acoust. 127, pp. 254–261) have focused on the operation and stability of journal bearings. Thrust bearings play a vital role in providing axial support and stiffness, and there is a need to improve the understanding of their dynamic behavior. In this work, a rigorous theory is presented to analyze the effects of compressibility in micro-flows (characterized by low Reynolds numbers and high Mach numbers) through hydrostatic thrust bearings for application to micro-turbomachines. The analytical model, which combines a one-dimensional compressible flow model with finite-element analysis, serves as a useful tool for establishing operating protocols and assessing the stability characteristics of hydrostatic thrust bearings. The model is capable of predicting key steady-state performance indicators, such as bearing mass flow, axial stiffness, and natural frequency as a function of the hydrostatic supply pressure and thrust-bearing geometry. The model has been applied to investigate the static stability of hydrostatic thrust bearings in micro-turbine generators, where the electrostatic attraction between the stator and rotor gives rise to a negative axial stiffness contribution and may lead to device failure. Thrust-bearing operating protocols have been established for a micro-turbopump, where the bearings also serve as an annular seal preventing the leakage of pressurized liquid from the pump to the gaseous flow in the turbine. The dual role of the annular pad poses challenges in the operation of both the device and the thrust bearing. The operating protocols provide essential information on the required thrust-bearing supply pressures and axial gaps required to prevent the leakage of water into the thrust bearings. Good agreement is observed between the model predictions and experimental results. A dynamic stability analysis has been conducted, which indicates the occurrence of instabilities due to flow choking effects in both forward and aft thrust bearings. A simple criterion for the onset of axial rotor oscillations has been established and subsequently verified in a micro-turbocharger experiment. The predicted frequencies of the unstable axial oscillations compare well with the experimental measurements.

Rotordynamic and Bearing Upgrade of a High-Speed Turbocharger

2002 ◽  
Vol 125 (1) ◽  
pp. 95-101 ◽  
Author(s):  
B. C. Pettinato ◽  
P. DeChoudhury
Keyword(s):  
High Speed ◽  
Thrust Bearing ◽  
Load Capacity ◽  
Journal Bearings ◽  
Experimental Results ◽  
Thrust Bearings ◽  
Vibration Data ◽  
Oil Leakage ◽  
Bearing Life ◽  
Thrust Load

The paper discusses the redesign of a high-speed turbocharger for improved bearing life and mechanical operation. The bearings were changed from a pair of combination journal/thrust bearings to a pair of redesigned journal bearings with double acting thrust bearing at the center of the unit. Internal oil passages, drain cavities, and seals were also revised. These modifications resulted in reduced oil leakage across end seals, reduced coke buildup at the turbine, increased thrust load capacity, and improved rotordynamics. Both the analytical and experimental results, which consisted of bearing performance and vibration data of original and modified systems are presented.

A semianalytical method for studying the performances of aerostatic thrust bearing

2018 ◽  
Vol 233 (4) ◽  
pp. 628-637
Author(s):  
Jianbo Zhang ◽  
Chunxiao Jiao ◽  
Donglin Zou ◽  
Na Ta ◽  
Zhushi Rao
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Film Thickness ◽  
Reynolds Equation ◽  
Thrust Bearing ◽  
Separation Of Variables ◽  
Orifice Diameter ◽  
Thrust Bearings ◽  
Supply Pressure ◽  
Semianalytical Method

The solution of Reynolds equation and computational fluid dynamics are widely employed for the lubrication performance analysis of aerostatic thrust bearing. However, the solution of Reynolds equation may be inaccurate and cannot present detailed performance near orifice, while computational fluid dynamics method has low computational efficiency with time consumption in mesh generation and solving Navier–Stokes equations. In order to overcome the drawbacks of Reynolds equation and computational fluid dynamics, based on the method of separation of variables, a semianalytical method is developed for describing the characteristics of aerostatic bearings available. The method of separation of variables considering the initial and viscous effect is more accurate than the Reynolds equation and can present detailed performance near orifice in the aerostatic thrust bearings, while method of separation of variables has great computational efficiency compared to computational fluid dynamics. Meanwhile, the pressure distribution calculated by method of separation of variables is compared to the published experimental data and the results obtained by computational fluid dynamics. The comparative results indicate validity of the method. Furthermore, the influences of flow and geometry parameters, such as supply pressure, orifice diameter, film thickness, and bearing radius, on the characteristics of aerostatic thrust bearings with single orifice are studied. The results show that there exists pressure depression phenomenon near orifice. The depression phenomenon is strengthened with increase of film thickness and supply pressure and decrease of orifice diameter and bearing radius, while the maximum speed increases with strengthening of pressure depression due to decrease of minimum local pressure near orifice. Moreover, the bearing capacity increases with increase of supply pressure, orifice diameter, and bearing radius and decreases with increase of film thickness, while mass flow rate increases with supply pressure, orifice diameter, and film thickness and it is not sensitive to bearing radius.

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