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Analytical and experimental investigations of hybrid air foil bearingsKumar, Manish 15 May 2009 (has links)
Air foil bearings offer several advantages over oil-lubricated bearings in high
speed micro-turbomachinery. With no contact between the rotor and bearings, the air foil
bearings have higher service life and consequently lesser standstills between operations.
However, the foil bearings have reliability issues that come from dry rubbing during
start-up/shutdown and limited heat dissipation capability. Regardless of lubricating
media, the hydrodynamic pressure generated provides only load support but no
dissipation of parasitic energy generated by viscous drag and the heat conducted from
other parts of the machine through the rotor.
The present study is a continuation of the work on hybrid air foil bearings
(HAFB) developed by Kim and Park, where they present a new concept of air foil
bearing combining hydrodynamic air foil bearing with hydrostatic lift. Their
experimental studies show that HAFB has superior performance compared to its
hydrodynamic counterpart in load capacity and cooling performance.
In this article, the bearing stiffness and damping coefficients of HAFB are calculated
using a linear perturbation method developed for HAFB. The study focuses on circular
HAFB with a single continuous top foil supported by bump foil. The research also includes a parametric study which outlines the dependence of the stiffness and damping
coefficients on various design parameters like supply pressure ( P s ), feed parameter ( Г s ),
excitation frequency (v), and bearing number (Λ).
Furthermore the present research also includes experimental investigation of
HAFB with bump foil as compliant structure. In the first phase of the experimental
research a high speed test facility was designed and fabricated. The facility has the
capability of running up to 90,000 RPM and has an electric motor drive. This article
gives detailed description of this test rig and also includes data acquired during the
commissioning phase of the test rig. The test rig was then used to measure the load
capacity of HAFB.
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MANUFACTURING OF A GAS FOIL BEARINGS FOR PALMED-SIZED TURBOMACHINERYCreary, Andron 2009 May 1900 (has links)
Compliant Air Foil Bearings are used in a wide variety of applications. The
versatility, ease of manufacture, and low cost of foil bearings are a few of the reasons
foil bearing have been so thoroughly researched.
Miniaturization of gas foil bearings has been explored using silicon parts with
marginal success. An approach utilizing a well known micro-fabrication technique called
LIGA (German acronym meaning Lithography, Electroplating, and Molding) is
suggested as an alternative method. X-ray LIGA and UV-LIGA were explored and
elastic foundations 200?m and 1mm in depth were made for an impulse turbine test
setup. The main difference in between the two methods is resolution and depth that each
is capable of producing. In addition, precision machine forming was used to create a top
foil for the foil bearing.
The predicted performance of the bearing was investigated through the orbit
simulation method. A parametric study based on preload, as well as loss factor, was
conducted in which the rotor speed was varied and the responses were used to create
cascade plots. Both the response and cascade plots are useful to determine the onset of instability and the maximum operating speed of the foil bearing manufactured through
LIGA. The unique features of the gas foil bearing introduced provide great promise in
terms of its application considering the high stable operating speed is just above 1000
krpm.
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Effect of Cooling Flow on the Operation of a Hot Rotor-Gas Foil Bearing SystemRyu, Keun 2011 December 1900 (has links)
Gas foil bearings (GFBs) operating at high temperature rely on thermal management procedures that supply needed cooling flow streams to keep the bearing and rotor from overheating. Poor thermal management not only makes systems inefficient and costly to operate but could also cause bearing seizure and premature system destruction. To date, most of thermal management strategies rely on empirically based "make-and-break" techniques which are often inefficient.
This dissertation presents comprehensive measurements of bearing temperatures and shaft dynamics conducted on a hollow rotor supported on two first generation GFBs. The hollow rotor (1.36 kg, 36.51 mm OD and 17.9 mm ID) is heated from inside to reach an outer surface temperature of 120 degrees C. Experiments are conducted with rotor speeds to 30 krpm and with forced streams of air cooling the bearings and rotor. Air pressurization in an enclosure at the rotor mid span forces cooling air through the test GFBs. The cooling effect of the forced external flows is most distinct when the rotor is hottest and operating at the highest speed. The temperature drop per unit cooling flow rate significantly decreases as the cooling flow rate increases. Further measurements at thermal steady state conditions and at constant rotor speeds show that the cooling flows do not affect the amplitude and frequency contents of the rotor motions. Other tests while the rotor decelerates from 30 krpm to rest show that the test system (rigid-mode) critical speeds and modal damping ratio remain nearly invariant for operation with increasing rotor temperatures and with increasing cooling flow rates. Computational model predictions reproduce with accuracy the test data. The work adds to the body of knowledge on GFB performance and operation and provides empirically derived guidance for successful integration of rotor-GFB systems.
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Rotordynamic performance of a rotor supported on bump-type foil bearings: experiments and predictionsRubio Tabares, Dario 16 August 2006 (has links)
Gas foil bearings (GFB) appear to satisfy most requirements for oil-free
turbomachinery, i.e. relatively simple in construction, ensuring low drag friction and
reliable high speed operation. However, GFBs have a limited load capacity and minimal
amounts of damping. A test rig for the rotordynamic evaluation of gas foil bearings was
constructed. A DC router motor, 25 krpm max speed, drives a 1.02 kg hollow rotor
supported on two bump-type foil gas bearings (L = D = 38.10 mm). Measurements of
the test rotor dynamic response were conducted for increasing mass imbalance
conditions. Typical waterfalls of rotor coast down response from 25 krpm to rest
evidence the onset and disappearance of severe subsynchronous motions with whirl
frequencies at ~ 50% of rotor speed, roughly coinciding with the (rigid mode) natural
frequencies of the rotor-bearing system. The amplitudes of motion, synchronous and
subsynchronous, increase (non) linearly with respect to the imbalance displacements.
The rotor motions are rather large; yet, the foil bearings, by virtue of their inherent
flexibility, prevented the catastrophic failure of the test rotor. Tests at the top shaft speed,
25 krpm, did not excite subsynchronous motions. In the experiments, the
subsynchronous motion speed range is well confined to shaft speeds ranging from 22
krpm to 12 krpm. The experimental results show the severity of subsynchronous motions
is related to the amount of imbalance in the rotor. Surprisingly enough, external air
pressurization on one side of the foil bearings acted to reduce the amplitudes of motion
while the rotor crossed its critical speeds. An air-film hovering effect may have
enhanced the sliding of the bumps thus increasing the bearings damping action. The
tests also demonstrate that increasing the gas feed pressure ameliorates the amplitudes of subsynchronous motions due to the axial flow retarding the circumferential flow velocity
development. A finite element rotordynamic analysis models the test rotor and uses
predicted bearing force coefficients from the static equilibrium GFB load analysis. The
rotordynamic analysis predicts critical speeds at ~8 krpm and ~9 krpm, which correlate
well with test critical speeds. Predictions of rotordynamic stability are calculated for the
test speed range (0 to 25 krpm), showing unstable operation for the rotor/bearing system
starting at 12 krpm and higher. Predictions and experimental results show good
agreement in terms of critical speed correlation, and moderate displacement amplitude
discrepancies for some imbalance conditions. Post-test inspection of the rotor evidenced
sustained wear at the locations in contact with the bearings' axial edges. However, the
foil bearings are almost in pristine condition; except for top foil coating wear at the
bearing edges and along the direction of applied static load.
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FACTORS INFLUENCING THE PERFORMANCE OF FOIL GAS THRUST BEARINGS FOR OIL-FREE TURBOMACHINERY APPLICATIONSDykas, Brian David 07 April 2006 (has links)
No description available.
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Analyse non-linéaire des paliers aérodynamiques à feuilles et applications à la dynamique des rotors / Non-linear analysis of aerodynamic foil bearing and application for rotor dynamicsBenchekroun, Omar 10 December 2018 (has links)
Les paliers à feuilles sont des organes de guidage en rotation adaptés pour des rotors légers fonctionnant à des grandes vitesses de rotation. Leur fonctionnement ne nécessite aucun apport d’huile ni de graisse. Ces paliers sont réalisés avec une structure compliante. La présence de frottements dans la structure apporte l’amortissement nécessaire au système rotor-palier.Après une présentation de la technologie, un tour d’horizon des modèles existants et des limitations de chacun d’eux est exposé. Par la suite, un modèle non-linéaire du coussinet compliant est introduit. Dans ce modèle les feuilles sont considérées comme des solides élastiques. Les forces de frottement et les jeux entre les feuilles sont pris en compte par l’utilisation de la condition de non-interférence de Moreau-Signorini. Les efforts normaux et les forces de frottement sont calculés respectivement par la méthode des multiplicateurs de Lagrange augmentés et la méthode des pénalités. Ensuite, cette structure compliante est couplée au film fluide, traité par la résolution de l’équation de Reynolds en conditions de lubrification mixte.L’intérêt est ensuite accordé au palier dans sa globalité : structure déformable, film fluide, rotor. En régime statique, cette étude passe par l’analyse des démarrages du rotor puis de son fonctionnement à des hautes vitesses de rotation et sous de très fortes charges statiques. L’effet des erreurs d’usinage est mis en évidence. En régime dynamique, l’étude se fait par l’analyse non-linéaire d’un rotor de Jeffcott supporté par des paliers à feuilles. Les résultats montrent les limites de stabilité du système rotor-paliers et l’influence du balourd. / The foil bearings are used for guiding and supporting small rotors with high rotational speeds. Their operating functioning does not require any oil or grease. These bearings have a compliant structure. The presence of friction in the compliant structure brings damping, which is necessary for the rotor-bearing system operating at high speeds.After a presentation of the technology, an overview of the existing models and the limitations of each of them is exposed. Subsequently, a nonlinear model of the compliant structure is introduced. In this model, foils are considered as elastic solids. The friction forces and the gaps between the foils are taken into account by using the Moreau-Signorini non-interference condition. Normal forces and friction forces are calculated by using the augmented Lagrange multiplier method and the penalty method. Then, the compliant structure is coupled to the fluid film, dealt with the Reynolds equation for mixed lubrication conditions.The study is then focused on the bearing as a whole : compliant structure, fluid film, rotor. The start-up torque, the lift-off speed as well as operating conditions at high speeds and important static loads are part of the steady regime analyses. The effect of machining errors is highlighted. For the dynamic regime, the study consists of the non-linear analysis of a Jeffcott rotor supported by foil bearings. The results show the stability limits of the rotor-bearing system and the influence of unbalance.
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Refrigerant-lubricated gas foil bearings : A thermo-hydrodynamic study (application to rigid bearings) / Lubrification par gaz réfrigérant des paliers à feuilles : Une étude thermo-hydrodynamique (application aux paliers à feuilles rigides)Garcia, Mathieu 11 December 2012 (has links)
Des études internes à Liebherr-Aerospace France, concernant la conception de nouveaux compresseurs lubrifiés par gaz réfrigérant, ont montré que dans des conditions de fonctionnement spécifiques, un mélange de vapeur et de liquide apparaît au sein du compresseur, au lieu d'une phase vapeur seule. De ce fait, le comportement des paliers à feuilles lubrifiés au gaz réfrigérant est étudié, y compris la possibilité d'un écoulement diphasique du lubrifiant. L'étude porte sur le comportement du lubrifiant uniquement, dans des conditions de fonctionnement qui sont celles des paliers à feuilles. L'approche Thermo-Hydrodynamique décrit les caractéristiques du lubrifiant telles que la pression, la densité, la viscosité et la température. Dans ce modèle, une équation de Reynolds généralisée pour écoulement turbulent, une équation d'état non-linéaire pour écoulement diphasique et une équation de l'énergie tridimensionnelle pour film-mince et écoulement turbulent sont utilisées. Les paramètres globaux du palier sont calculés en régime permanent. / Internal experiments at Liebherr-Aerospace FRANCE on new refrigerant-lubricated compressor designs have shown that under specific operating conditions, a mixture of vapor and liquid appears in the compressor, instead of a single-phase vapor flow. Therefore, refrigerant-lubricated foil bearings behavior is studied, including the likelihood of two-phase flow in the lubricant. We focus on the lubricant behavior only, in the operating conditions of foil bearings. The Thermo-Hydrodynamic approach describes lubricant characteristics such as pressure, density, viscosity, and temperature. It involves the use of a generalized Reynolds equation for turbulent flow, a nonlinear cubic equation of state for two-phase flow and a 3D turbulent thin-film energy equation. Journal bearing global parameters are calculated for steady-state conditions.
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