Experimental Response of Simple Gas Hybrid Bearings for Oil-Free Turbomachinery

2006 ◽  
Vol 128 (3) ◽  
pp. 626-633 ◽  
Author(s):  
Deborah A. Osborne ◽  
Luis San Andre´s
Keyword(s):  
High Speed ◽  
Damping Ratio ◽  
Dynamic Force ◽  
Test Results ◽  
Low Friction ◽  
Foil Bearings ◽  
Feed Pressure ◽  
Micropower Generators ◽  
Lift Off ◽  
Stiffness And Damping

Gas film bearings offer unique advantages enabling successful deployment of high-speed microturbomachinery (<0.4 MW). Current applications encompass micropower generators, air cycle machines and turbo expanders. Mechanically complex gas foil bearings are in use; however, their excessive cost and lack of calibrated predictive tools deters their application to mass-produced systems. The present investigation provides experimental results for the rotordynamic performance of a small rotor supported on simple and inexpensive hybrid gas bearings with static and dynamic force characteristics desirable in high-speed turbomachinery. These characteristics are adequate load support, stiffness and damping coefficients, low friction and wear during rotor startup and shutdown, and most importantly, enhanced rotordynamic stability. The test results evidence the paramount effect of feed pressure on early rotor lift-off and substantially higher threshold speeds of rotordynamic instability. Higher supply pressures also determine larger bearing direct stiffnesses, and thus bring an increase in the rotor-bearing system critical speed albeit with a reduction in damping ratio.

Experimental Response of Simple Gas Hybrid Bearings for Oil-Free Turbomachinery

2003 ◽  
Author(s):  
Deborah A. Wilde ◽  
Luis San Andre´s
Keyword(s):  
High Speed ◽  
Damping Ratio ◽  
Dynamic Force ◽  
Test Results ◽  
Power Generators ◽  
Foil Bearings ◽  
Feed Pressure ◽  
Micro Power ◽  
Lift Off ◽  
Stiffness And Damping

Gas film bearings offer unique advantages enabling successful deployment of high-speed micro-turbomachinery (&lt; 0.4 MW). Current applications encompass micro power generators, air cycle machines and turbo expanders. Mechanically complex gas foil bearings are in use; however, their excessive cost and lack of calibrated predictive tools deter their application to mass-produced systems. The present investigation provides experimental results for the rotordynamic performance of a small rotor supported on simple and inexpensive hybrid gas bearings with static and dynamic force characteristics desirable in high-speed turbomachinery. These characteristics are adequate load support, stiffness and damping coefficients, low friction and wear during rotor startup and shutdown, and most importantly, enhanced rotordynamic stability. The test results evidence the paramount effect of feed pressure on early rotor lift off and substantially higher threshold speeds of rotordynamic instability. Higher supply pressures also determine larger bearing direct stiffnesses, and thus bring an increase in the rotor-bearing system critical speed albeit with a reduction in damping ratio.

Rotordynamic Performance of Flexure Pivot Hydrostatic Gas Bearings for Oil-Free Turbomachinery

2007 ◽  
Vol 129 (4) ◽  
pp. 1020-1027 ◽  
Author(s):  
Xuehua Zhu ◽  
Luis San Andrés
Keyword(s):  
High Speed ◽  
Low Cost ◽  
Damping Ratio ◽  
Extreme Temperature ◽  
Gas Bearings ◽  
Speed Increase ◽  
Feed Pressure ◽  
Motor Test ◽  
Direct Stiffness ◽  
Commercial Applications

Micro-turbomachinery demands gas bearings to ensure compactness, light weight, and extreme temperature operation. Gas bearings with large stiffness and damping, and preferably of low cost, will enable successful commercial applications. Presently, tests conducted on a small rotor supported on flexure pivot hydrostatic pad gas bearings (FPTPBs) demonstrate stable rotordynamic responses up to 100,000rpm (limit of the drive motor). Test rotor responses show the feed pressure raises the system critical speed (increase in bearing direct stiffness) while the viscous damping ratio decreases. Predictions correlate favorably with experimentally identified (synchronous) direct stiffness bearing force coefficients. Identified experimental gas bearing synchronous damping coefficients are 50% or less of the predicted magnitudes, though remaining relatively constant as the rotor speed increases. Tests without feed pressure show the rotor becomes unstable at ∼81krpm with a whirl frequency ratio of 20%. FPTPBs are mechanically complex and more expensive than cylindrical plain bearings. However, their enhanced stability characteristics and predictable rotordynamic performance makes them desirable for the envisioned oil-free applications in high speed micro-turbomachinery.

Rotordynamic Performance of a Rotor Supported on Bump Type Foil Gas Bearings: Experiments and Predictions

2006 ◽  
Vol 129 (3) ◽  
pp. 850-857 ◽  
Author(s):  
Luis San Andrés ◽  
Dario Rubio ◽  
Tae Ho Kim
Keyword(s):  
High Speed ◽  
Critical Speed ◽  
Load Capacity ◽  
Test System ◽  
Foil Bearings ◽  
Rotor Imbalance ◽  
Synchronous Motion ◽  
Damping Characteristics ◽  
Rotor Surface ◽  
Stiffness And Damping

Gas foil bearings (GFBs) satisfy the requirements for oil-free turbomachinery, i.e., simple construction and ensuring low drag friction and reliable high speed operation. However, GFBs have a limited load capacity and minimal damping, as well as frequency and amplitude dependent stiffness and damping characteristics. This paper provides experimental results of the rotordynamic performance of a small rotor supported on two bump-type GFBs of length and diameter equal to 38.10mm. Coast down rotor responses from 25krpm to rest are recorded for various imbalance conditions and increasing air feed pressures. The peak amplitudes of rotor synchronous motion at the system critical speed are not proportional to the imbalance introduced. Furthermore, for the largest imbalance, the test system shows subsynchronous motions from 20.5krpm to 15krpm with a whirl frequency at ∼50% of shaft speed. Rotor imbalance exacerbates the severity of subsynchronous motions, thus denoting a forced nonlinearity in the GFBs. The rotor dynamic analysis with calculated GFB force coefficients predicts a critical speed at 8.5krpm, as in the experiments; and importantly enough, unstable operation in the same speed range as the test results for the largest imbalance. Predicted imbalance responses do not agree with the rotor measurements while crossing the critical speed, except for the lowest imbalance case. Gas pressurization through the bearings’ side ameliorates rotor subsynchronous motions and reduces the peak amplitudes at the critical speed. Posttest inspection reveal wear spots on the top foils and rotor surface.

Experimental and Theoretical Rotordynamic Characteristics of a Hybrid Journal Bearing

1997 ◽  
Vol 119 (1) ◽  
pp. 132-141 ◽  
Author(s):  
J. T. Sawicki ◽  
R. J. Capaldi ◽  
M. L. Adams
Keyword(s):  
Journal Bearing ◽  
Operating Conditions ◽  
Dynamic Force ◽  
Test Results ◽  
Force Measurements ◽  
Lubrication Equation ◽  
Load Cells ◽  
Theoretical Predictions ◽  
Stiffness And Damping

This paper describes an experimental and theoretical investigation of a four-pocket, oil-fed, orifice-compensated hydrostatic bearing including the hybrid effects of journal rotation. The test apparatus incorporates a double-spool-shaft spindle which permits independent control over the journal spin speed and the frequency of an adjustable-magnitude circular orbit, for both forward and backward whirling. This configuration yields data that enables determination of the full linear anisotropic rotordynamic model. The dynamic force measurements were made simultaneously with two independent systems, one with piezoelectric load cells and the other with strain gage load cells. Theoretical predictions are made for the same configuration and operating conditions as the test matrix using a finite-difference solver of Reynolds lubrication equation. The computational results agree well with test results, theoretical predictions of stiffness and damping coefficients are typically within thirty percent of the experimental results.

Rotordynamic Performance of a Shaft With Large Overhung Mass Supported by Foil Bearings

2016 ◽  
Vol 139 (4) ◽  
Author(s):  
Nguyen LaTray ◽  
Daejong Kim
Keyword(s):  
High Speed ◽  
Foil Bearings ◽  
Speed Test ◽  
Foil Bearing ◽  
Stable Conditions ◽  
Bending Mode ◽  
Mode Vibration ◽  
Lift Off ◽  
Compact Design ◽  
Bearing System

This work presents the theoretical and experimental rotordynamic evaluations of a rotor–air foil bearing (AFB) system supporting a large overhung mass for high-speed application. The proposed system highlights the compact design of a single shaft rotor configuration with turbomachine components arranged on one side of the bearing span. In this work, low-speed tests up to 45 krpm are performed to measure lift-off speed and to check bearing manufacturing quality. Rotordynamic performance at high speeds is evaluated both analytically and experimentally. In the analytical approach, simulated imbalance responses are studied using both rigid and flexible shaft models with bearing forces calculated from the transient Reynolds equation along with the rotor motion. The simulation predicts that the system experiences small synchronous rigid mode vibration at 20 krpm and bending mode at 200 krpm. A high-speed test rig is designed to experimentally evaluate the rotor–air foil bearing system. The high-speed tests are operated up to 160 krpm. The vibration spectrum indicates that the rotor–air foil bearing system operates under stable conditions. The experimental waterfall plots also show very small subsynchronous vibrations with frequency locked to the system natural frequency. Overall, this work demonstrates potential capability of the air foil bearings in supporting a shaft with a large overhung mass at high speed.

Influence of geometric parameters on the bump foil bearing performance

2019 ◽  
Vol 234 (7) ◽  
pp. 1017-1026
Author(s):  
Sadanand Kulkarni ◽  
Soumendu Jana
Keyword(s):  
Carrying Capacity ◽  
High Speed ◽  
System Development ◽  
Load Capacity ◽  
Radial Clearance ◽  
Load Carrying Capacity ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Load Carrying ◽  
Lift Off

High-speed rotating system development has drawn considerable attention of the researchers, in the recent past. Foil bearings are one of the major contenders for such applications, particularly for high speed and low load rotating systems. In foil bearings, process fluid or air is used as the working medium and no additional lubricant is required. It is known from the published literature that the load capacity of foil bearings depend on the operating speed, viscosity of the medium, clearance, and stiffness of the foil apart from the geometric dimensions of the bearing. In case of foil bearing with given dimensions, clearance governs the magnitude of pressure developed, whereas stiffness dictates the change in radial clearance under the generated pressure. This article deals with the effect of stiffness, clearance, and its interaction on the bump foil bearings load-carrying capacity. For this study, four sets of foil bearings of the same geometry with two levels of stiffness and clearance values are fabricated. Experiments are carried out following two factor-two level factorial design approach under constant load and in each case, the lift-off speed is measured. The experimental output is analyzed using statistical techniques to evaluate the influence of parameters under consideration. The results indicate that clearance has the maximum influence on the lift-off speed/ load-carrying capacity, followed by interaction effect and stiffness. A regression model is developed based on the experimental values and model is validated using error analysis technique.

Dynamic Force Coefficients of a Multiple-Blade, Multiple-Pocket Gas Damper Seal: Test Results and Predictions

1999 ◽  
Vol 122 (1) ◽  
pp. 317-322 ◽  
Author(s):  
Jiming Li ◽  
Ramon Aguilar ◽  
Luis San Andre´s ◽  
John M. Vance
Keyword(s):  
Control Volume ◽  
Pressure Ratio ◽  
Flexible Structure ◽  
Dynamic Force ◽  
Test Results ◽  
Force Coefficients ◽  
Exit Pressure ◽  
Identification Technique ◽  
Gas Damper ◽  
Stiffness And Damping

Experimental rotordynamic force coefficients and leakage for a four-blade, two-four pocket gas damper seal are presented and compared to predictions based on a one control volume bulk-flow model. The test rig comprises a vertical shaft and a test seal housing and flexible structure suspended from a rigid centering frame. The experiments were conducted at increasing rotor speeds to 6000 rpm and inlet/exit pressure ratios from 1.0 to 3.0. The seal force coefficients are obtained from impact response measurements of the seal and flexible structure using a frequency domain parameter identification technique. Both measurements and predictions show the seal direct stiffness and damping coefficients are proportional to the inlet/exit pressure ratio and insensitive to rotor speed. The agreement between experimental results and analytical predictions is acceptable. Predicted cross-coupled stiffness coefficients are of small amplitude. However, the test results evidence cross-coupled stiffnesses without journal rotation due to a structural asymmetry induced by the external pressurization into the seal. [S0742-4787(00)04201-6]

Rotordynamic Behavior of 225 kW (300 HP) Class PMS Motor–Generator System Supported by Gas Foil Bearings

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Bok Seong Choe ◽  
Tae Ho Kim ◽  
Chang Ho Kim ◽  
Yong Bok Lee
Keyword(s):  
Axial Length ◽  
High Speed ◽  
Load Capacity ◽  
Stability Margin ◽  
Generator System ◽  
Thrust Bearings ◽  
Foil Bearings ◽  
Speed Up ◽  
The Stability ◽  
Stiffness And Damping

This paper presents the dynamic behavior of a 225 kW class (300 HP), 60,000 rpm, permanent magnet synchronous (PMS) motor–generator system supported on gas foil bearings (GFBs). The rotor of a 225 kW PMS motor is supported by two identical gas foil journal bearings (GFJBs) and one pair of gas foil thrust bearings (GFTBs). The total weight and axial length of the coupled rotors are 272 N and 1042 mm, respectively. During the speed-up test to 60,000 rpm, unexpected large subsynchronous rotor motions appear at around 120–130 Hz above 35,040 rpm. After disassembling the motor, an inspection of the top foils of the GFJBs reveals significant rotor rubbing. Thus, the GFJBs are redesigned to have a smaller load capacity by reducing their axial length to 45 mm. In addition, three 50 μm thick shims are installed in the GFJBs at 120 deg intervals for reducing the swirl speed of air and producing bearing preloads. The modification delays the onset speed of subsynchronous motions to 43,200 rpm and decreases the amplitude of the subsynchronous motions from 20 to 15 μm. These results indicate that the modification improves the stability margin of the high-speed rotor system with increasing stiffness and damping. In addition, the logarithmic decrement trends are in good agreement with the test results.

Effect of Side Feed Pressurization on the Dynamic Performance of Gas Foil Bearings: A Model Anchored to Test Data

2008 ◽  
Author(s):  
Tae Ho Kim ◽  
Luis San Andre´s
Keyword(s):  
Test Data ◽  
High Speed ◽  
Gas Flow ◽  
Dynamic Performance ◽  
Rotor Speed ◽  
Mass Distributions ◽  
Foil Bearings ◽  
Feed Pressure ◽  
Run Up ◽  
Forced Cooling

Comprehensive modeling of gas foil bearings (GFBs) anchored to reliable test data will enable the widespread usage of these bearings into novel high speed turbomachinery applications. GFBs often need a forced cooling gas flow, axially fed through one end of the bearing, for adequate thermal management. The paper presents rotordynamic response measurements on a rigid rotor supported on GFBs during rotor speed run-up and coastdown tests with the GFBs supplied with increasing feed gas pressures to 2.8 bar. Rotor speed run-up tests to 35 krpm show that bearing end side feed gas pressurization delays the onset speed of rotor subsynchronous whirl motions. The test data validate closely predictions of the threshold speed of instability and whirl frequency ratio derived from a GFB model that implements the axial evolution of gas circumferential flow velocity as a function of the imposed side feed pressure. Rotor speed coastdown tests from 25 krpm with a low feed pressure of 0.35 bar evidences a nearly linear synchronous rotor response for small and moderately large imbalance mass distributions. A structural FE rotordynamics model integrates linearized synchronous speed GFB force coefficients and predicts synchronous responses, amplitude and phase angle, agreeing with the test data. The analysis and measurements demonstrate the profound effect of end side, feed gas pressurization on the rotordynamic performance of GFBs.

Rotordynamic Performance of a Shaft With Large Overhung Mass Supported by Foil Bearings

2016 ◽  
Author(s):  
Nguyen LaTray ◽  
Daejong Kim
Keyword(s):  
High Speed ◽  
Foil Bearings ◽  
Speed Test ◽  
Foil Bearing ◽  
Stable Conditions ◽  
Bending Mode ◽  
Mode Vibration ◽  
Lift Off ◽  
Compact Design ◽  
Bearing System

This work presents the theoretical and experimental rotordynamic evaluations of a rotor-air foil bearing system supporting a large overhung mass for high speed application. The proposed system highlights the compact design of a single shaft rotor configuration with turbomachine components arranged on one side of the bearing span. In this work, low speed tests up to 45krpm are performed to measure the lift off speed and to check the bearing manufacturing quality. Rotordynamic performance at high speeds is evaluated both analytically and experimentally. In the analytical approach, simulated imbalance responses are studied using both rigid and flexible shaft models with bearing forces calculated from transient Reynolds equation along with rotor motion. The simulation predicts that the system experiences small synchronous rigid mode vibration at 20krpm and bending mode at 200krpm. A high speed test rig is designed to experimentally evaluate the rotor-air foil bearings system. The high speed tests are operated up to 160krpm. The vibration spectrum indicates that the rotor-air foil bearing system operates under stable conditions. The experimental waterfall plots also show very small sub-synchronous vibrations with frequency locked to the system natural frequency. Overall, this work demonstrates the potential capability of air foil bearings in supporting a shaft with a large overhung mass at high speed.

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