1

Parametric Study of Bump Foil Gas Bearings for

Industrial Applications

2011 ASME Turbo Expo Congress & Exhibition

GT2011-46767

http://rotorlab.tamu.edu

Oscar De SantiagoCIATEQ A.C.

Queretaro, Qro, Mexico

Luis San AndresTexas A&M University

College Station, TX, USA

http://www.ciateq.mx/

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Oil-Free Bearings for Turbomachinery

JustificationCurrent advancements in vehicle turbochargers and midsize gas turbines need of proven gas bearing technology to procure compact units with improved efficiency in an oil-free environment. Also, Oil-free turbomachinery and subsea compression are among major focuses in modern energy industry.DOE, DARPA, NASA interests range from applications as portable fuel cells (< 60 kW) in microengines to midsize gas turbines (< 250 kW) for distributed power and hybrid vehicles.

Gas Bearings allow• weight reduction, energy and complexity savings• higher temperatures, without needs for cooling air • improved overall engine efficiency

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Magnetic bearings

Available Bearing TechnologiesAvailable Bearing Technologies

• Low to medium temperatures• Moderate loads• Need control systems• Need back-up bearings• Long history of operation in some specific industrial applications

•Current Magnetic Bearing solution is expensive and even more expensive (and difficult) to make it reliable

Schweitzer/Maslen 2009

www.skf.com, 2011

www.synchrony.com, 2011

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• Oil-Free • NO DN limit• Low friction and power loss• Thermal management

GAS BEARINGS

AIAA-2004-5720-984

Gas Foil Bearing

GT 2004-53621

Flexure Pivot Bearing

AIAA 2004-4189

Rolling element bearings

PowerMEMS 2003

• Low temperatures• Low DN limit (< 2 M)• Need lubrication system

NICH Center, Tohoku University

Herringbone grooved bearing

• Precision fabrication process• Low load capacity and stiffness and little damping

Available Bearing TechnologiesAvailable Bearing Technologies

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Microturbomachinery as per IGTIMicroturbomachinery as per IGTI

ASME Paper No. GT2002-30404

Honeywell, Hydrogen and Fuel Cells Merit

Review

Automotive turbochargers, turbo expanders, compressors,

Distributed power (Hybrid Gas turbine & Fuel Cell), Hybrid vehicles

Drivers:deregulation in distributed power, environmental needs, increased reliability & efficiency

International Gas Turbine Institute

Max. Power ~ 250 kWatt

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Micro Gas TurbinesMicro Gas Turbines

MANUFACTURER OUTPUT POWER (kW)Bowman 25, 80

Capstone 30, 60, 200Elliott Energy

Systems35, 60, 80, 150

General Electric

175

Ingersoll Rand

70, 250

Turbec, ABB & Volvo

100

Microturbine Power Conversion Technology Review, ORNL/TM-2003/74.

Cogeneration systems with high efficiency

• Multiple fuels (best if free)• 99.99X% Reliability• Low emissions• Reduced maintenance• Lower lifecycle cost

60kW MGT

www.microturbine.com

Hybrid System : MGT with Fuel Cell can reach efficiency > 60%

Ideal to replace reciprocating engines. Low footprint desirable

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Examples of commercial applicationsExamples of commercial applications

Micro Turbines•Capstone of California

Turbo chargers•Honeywell “on the race”

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Industrial Air Compressors

•Samsung’s successful Micro Turbo Master line of compressors feature gas foil bearings

•Pressures up to 130 psig

•Powers up to 0.13 MW

•Samsung has another line (Turbo Master) of air compressors with pressures up to 300 psig and power up to 2.4 MW (~20x larger). Run on TPJB.

What’s next ??

Examples of commercial applicationsExamples of commercial applications

www.samsungtechwin.com, 2011

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Largest power to weight ratio, Compact & low # of parts High energy density

Reliability and efficiency,Low maintenance

Extreme temperature and pressure

Environmentally safe (low emissions)

Lower lifecycle cost ($ kW)

High speed

Materials

Manufacturing

Processes & Cycles

Fuels

Rotordynamics & (Oil-free) Bearings & Sealing

Coatings: surface conditioning for low friction and wearCeramic rotors and components

Automated agile processesCost & number

Low-NOx combustors for liquid & gas fuelsTH scaling (low Reynolds #)

Best if free (bio-fuels)

MTM – Needs, Hurdles & Issues

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Gas Bearings for Oil-Free MTM

Advantages of gas bearings over oil-lubricated bearings

– Process gas is cleaner and eliminates contamination by buffer lubricants

– Gases are more stable at extreme temperatures and speeds (no lubricant vaporization, cavitation, solidification, or decomposition)

– Gas bearing systems are lower in cost: less power usage and small friction, enabling savings in weight and piping

Gas Bearings Must Be Simple!Gas Bearings Must Be Simple!

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 Ideal gas bearings for MTM

Simple – low cost, small geometry, low part count, constructed from common materials, manufactured with elementary methods.  

Load Tolerant – capable of handling both normal and extreme bearing loads without compromising the integrity of the rotor system.

High Rotor Speeds – no specific speed limit (such as DN) restricting shaft sizes. Small Power losses.

Good Dynamic Properties – predictable and repeatable stiffness and damping over a wide temperature range.

Reliable – capable of operation without significant wear or required maintenance, able to tolerate extended storage and handling without performance degradation.

+++ Modeling/Analysis (anchored to test data) available

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Gas Bearings for MTM

What are the needs?

Make READY technology for industrial application by PUSHING development to

• make out of the shelf item with proven results for a wide range of applications;

• engineered product with well known manufacturing process;

• known (verifiable) performance with solid laboratory and field experiences

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Gas Bearings Research at TAMU

Thrust: Investigate conventional bearings of low cost, easy to manufacture (common materials) and easy to install & align.

Combine hybrid (hydrostatic/hydrodynamic) bearings with low cost coating to allow for rub-free operation at start up and shut down

Major issues: Little damping, Wear at start & stop, Nonlinear behavior (subsync. whirl)

See References at end

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Gas Bearing Research at TAMU

2001/2 - Three Lobe Bearings

2003/4 - Rayleigh Step Bearings

2002-09 - Flexure Pivot Tilting Pad Bearings

2004-11: Bump-type Foil Bearings

2008-12: Metal Mesh Foil Bearings

Stability depends on feed pressure. Stable to 80 krpm with 5 bar pressure

Worst performance to date with grooved bearings

Stable to 93 krpm w/o feed pressure. Operation to 100 krpm w/o problems. Easy to install and align.

Industry standard. Reliable but costly.Models anchored to test data.

Cheap technology. Still infant. Users needed

See References at end

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Gas Foil Bearings

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Gas Foil Bearings

Advertised advantages: high load capacity (>20 psig), rotordynamically stable, tolerance of misalignment and shocks

: Bump spot weld X

Rotor spinning

Housing

Bump strip layer

Top foil

Gas film

Y

Top foil spot weld

Ω

Ө

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Gas Foil Bearings – Bump type

• Series of corrugated foil structures (bumps) assembled within a bearing sleeve.

• Integrate a hydrodynamic gas film in series with one or more structural layers.

Applications: APUs, ACMs, micro gas turbines, turbo expanders

• Reliable • Tolerant to misalignment and

debris, also high temperature• Need coatings to reduce friction at

start-up & shutdown• Damping from dry-friction and

operation with limit cycles

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Foil Bearings (+/-)• Increased reliability: load capacity (< 20 psi)• No lubricant supply system, i.e. reduce weight • High and low temperature capability (> 1,000 C) • No scheduled maintenance • Tolerate high vibration and shock load. Quiet

operation

• Endurance: performance at start up & shut down (lift off speed)

• Little test data for rotordynamic force coefficients & operation with limit cycles (sub harmonic motions)

• Thermal management for high temperature applications (gas turbines, turbochargers)

• Predictive models lack validation for GFB operation at HIGH TEMPERATURE

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Computational analysis

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Theoretical basis

• Solve Reynolds equation for compressible flow (isothermal case).

• Coupled to bump metal sheet deformation (non-linear stiffness and damping).

• Iterative solution to find bearing equilibrium position.

• Perturbation analysis to find dynamic performance (frequency-dependent stiffness and damping coefficients).Refs: San Andrés (2009), Arghir (2004), Iordanoff (1999), Heshmat (1992)

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The computational program

Code: XL_GFBTHD

• Windows OS and MS Excel 2003 (minimum requirements)

• Fortran 99 Executables for FE underspring structure and gas film analyses. Prediction of forced – static & dynamic- performance.

• Excel® Graphical User Interface (US and SI physical units). Input & output (graphical)

• Compatible with XLTRC2 and XLROTOR codes

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Graphical User Interface

Worksheet: Shaft & Bearing models (I)

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Graphical User Interface

Worksheet: Shaft & Bearing models (II)

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Graphical User Interface

Worksheet: Top Foil and Bump Models

Box 8

Box 9

Box 10

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Graphical User Interface

Worksheet: Foil Bearing (Operation and Results)

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Parametric Study

: Bump spot weld X

Rotor spinning

Housing

Bump strip layer

Top foil

Gas film

Y

Top foil spot weld

Ω

Ө

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Results

Bearing diameter: 0.0349 metersBearing axial length: 0.0445 metersL/D= 1.28

Original bump geometryBump foil thickness, tb 7.62E-05 metersBump pitch, s0 3.18E-03 metersBump half length, l0 1.27E-03 metersBump height, hb 5.10E-04 metersFoil Elastic modulus, E 214.00 GPaFoil Poisson's ratio, ν 0.29Friction Coefficient, μf 0

Original bump stiffness/area 1.65E+10 N/m3

• Bump unit area stiffness lowers as bump pitch increases

• Bump unit area stiffness increases with foil thickness

• Example bearing (Ref [3]):

0.00E+00

5.00E+09

1.00E+10

1.50E+10

2.00E+10

2.50E+10

0.002 0.003 0.004 0.005 0.006Bump pitch (m)

Un

it s

tiff

ne

ss

(N

/m3

)

1.0E+08

1.0E+09

1.0E+10

1.0E+11

1.0E+12

1.0E+13

0.0E+0 1.0E-4 2.0E-4 3.0E-4 4.0E-4 5.0E-4

Bump foil thickness (m)

Un

it s

tiff

ne

ss

(N

/m3

)

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Results

• Benchmarking with independent experiments – Generation 1 bearing (Ref [3]).

• Used to find practical limit of film thickness

Measured load capacity (Ref [3])

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

0 20 40 60 80 100 120 140

Bear

ing

Loa

d Ca

paci

ty (

Bar)

Rotor Speed (k rpm)

No Cu

With Cu31 psi

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 20,000 40,000 60,000 80,000 100,000 120,000 140,000

Film

Th

ickn

ess

(mic

ron

s)

Rotor Speed (RPM)

Minimum Film Thickness

Minimum film

Calibration point 2

Calibration point 1

Current predictions, constant load of 31 psi

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Results

0.00

30.00

60.00

90.00

120.00

150.00

1.0E+08 1.0E+09 1.0E+10 1.0E+11 1.0E+12

Dis

pla

cem

ent

(mic

ron

s)

Bump unit stiffness (N/m3)

Operating eccentricity

Eccentricity Min film thickness

0.00

10.00

20.00

30.00

40.00

50.00

0 0.5 1 1.5 2 2.5

Dis

pla

cem

ent

(mic

ron

s)

L/D (-)

Operating eccentricity

Eccentricity Min film thickness

0.00

10.00

20.00

30.00

40.00

50.00

60.00

0 100 200 300 400

Dis

pla

cem

ent

(mic

ron

s)

Unit Load (kPa)

Operating eccentricity

Eccentricity Min film thickness

Bearing diameter: 0.0349 metersBearing axial length: 0.0445 metersL/D= 1.28

Original bump geometryBump foil thickness, tb 7.62E-05 metersBump pitch, s0 3.18E-03 metersBump half length, l0 1.27E-03 metersBump height, hb 5.10E-04 metersFoil Elastic modulus, E 214.00 GPaFoil Poisson's ratio, ν 0.29Friction Coefficient, μf 0

Original bump stiffness/area 1.65E+10 N/m3

• Base bearing (Ref [3]):

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Rule of thumb for design

• Bearing scaling: use Della Corte´s rule:W ~ N L D^2

• Bump scaling:Knew = Korig / f ; f is de diameter scale factor

From observations of bump stiffness and bearing performance predictions:

1.0E+08

1.0E+09

1.0E+10

1.0E+11

1.0E+12

1.0E+13

0.0E+0 1.0E-4 2.0E-4 3.0E-4 4.0E-4 5.0E-4

Bump foil thickness (m)

Un

it s

tiff

ne

ss

(N

/m3

)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 20,000 40,000 60,000 80,000 100,000 120,000 140,000

Film

Th

ickn

ess

(mic

ron

s)

Rotor Speed (RPM)

Minimum Film Thickness

Minimum film

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Application example

Rotor Diameter, D 132 mm (5.21 in)Length, L 169 mm (6.64 in)Radial clearance, c

*96 µm (3.8 mil)

Load, W 1,421 N (319 lb)W/LD 0.636 bar (9.21 psi)

• Industrial compressor for injection service

• 8 impellers, 640 lb rotor

• Re-configured rotor – move bearings INBOARD of gas seals

• Use larger diameter at bearing location

Expected speed range:3 to 20 krpm

13-15 krpm MCOS most typical

Bearing characteristics

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Application - rotordynamics

Damped Eigenvalue Mode Shape Plot

Example compressor on Foil Bearings

f=7556.7 cpmd=17.0342 qfacN=7557 rpm

forwardbackward

5th

Mode Frequency (cpm)

Log dec AF Comments

1st 2600 1.306 2.5 Forward, horizontal, cylindrical

2nd 2906 1.494 2.2 Forward, horizontal, conical

3rd 5333 0.837 3.8 Forward, vertical, flexible(DE overhung)

4th 5556 0.677 4.7 Forward, vertical, flexible(DE overhung)

5th 7557 0.185 17 For/backward,

horizontal, 1st

rotor flexible

6th 8503 0.676 4.7 Forward,

vertical, 1st

rotor flexible

7th 17,554 0.054 58 Backward, vertical/horizon

tal, 2nd flexible

8th 18,580 0.045 70 Forward, vertical/horizon

tal, 2nd flexible

Linear stability analysis

Undamped Critical Speed Map

100

1000

10000

100000

1000000

10000000

100000000

1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07

Bearing Stiffness, lbf/in

Crit

ica

l Sp

ee

d, c

pm

Example rotor on Foil Bearings

Predicted stiffness range

Compressor can´t cross

these speeds

(requires more

damping)

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Observations– Conceptually, scaled gas foil bearings can support an

industrial, flexible rotor.

– Re-location of bearings is necessary to decrease unit load, but it is feasible in the compressor working environment.

– Rotor-bearing system requires additional damping to control shaft vibration at critical speeds.

Rotordynamic Response Plot

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 5000 10000 15000 20000Rotor Speed, rpm

Res

po

nse

, mils

pk-

pk

Major Amp

Horz Amp

Vert Amp

Example Compressor on Foil Bearings

Sta. No. 10: M idspan

Excitation = 1x

Shaft11815105

Shaft11

-30

-20

-10

0

10

20

30

0 20 40 60 80 100

Axial Location, inches

Sh

aft

Ra

diu

s,

in

ch

es

Example Compressor on Foil Bearings

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ClosureDominant challenges for gas bearing technology:

– Low gas viscosity requires minute clearances to generate load capacity.

– Damping & rotor stability are crucial

– Inexpensive coatings to reduce drag and wear

– Bearing design & manufacturing process well known

– Adequate thermal management to extend operating envelope into high temperatures

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ClosureOther pressing challenges for gas bearing

technology: intermittent contact and damaging wear at startup

& shut down, and temporary rubs during normal operating

conditions

Current research focuses on coatings (materials), rotordynamics (stability) & high temperature (thermal management)

Need Low Cost & Long Life Solution!

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References

Oil-Free Bearings for Turbomachinery

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References Foil Bearings

ASME GT2011-46767 De Santiago, O., and San Andrés, L., 2011, “Parametric Study of Bump Foil Gas Bearings for Industrial Applications”

ASME GT2011-45763 San Andrés, L.., and Ryu, K., 2011, “On the Nonlinear Dynamics of Rotor-Foil Bearing Systems: Effects of Shaft Acceleration, Mass Imbalance and Bearing Mechanical Energy Dissipation.”

ASME GT2010-22508NASA/TM 2010-216354

Howard, S., and San Andrés, L., 2011, “A New Analysis Tool Assessment for Rotordynamic Modeling of Gas Foil Bearings,” ASME J. Eng. Gas Turbines and Power, v133

ASME GT2010-22981 San Andrés, L., Ryu, K., and Kim, T-H, 2011, “Thermal Management and Rotordynamic Performance of a Hot Rotor-Gas Foil Bearings System. Part 2: Predictions versus Test Data,” ASME J. Eng. Gas Turbines and Power, v133

ASME GT2010-22981 San Andrés, L., Ryu, K., and Kim, T-H, 2011, “Thermal Management and Rotordynamic Performance of a Hot Rotor-Gas Foil Bearings System. Part 1: Measurements,” ASME J. Eng. Gas Turbines and Power, v133

8th IFToMM Int. Conf. on Rotordynamics

San Andrés, L., Camero, J., Muller, S., Chirathadam, T., and Ryu, K., 2010, “Measurements of Drag Torque, Lift Off Speed, and Structural Parameters in a 1st Generation Floating Gas Foil Bearing,” Seoul, S. Korea (Sept.)

ASME GT2009-59920 San Andrés, L., Kim, T.H., Ryu, K., Chirathadam, T. A., Hagen, K., Martinez, A., Rice, B., Niedbalski, N., Hung, W., and Johnson, M., 2009, “Gas Bearing Technology for Oil-Free Microturbomachinery – Research Experience for Undergraduate (REU) Program at Texas A&M University

AHS 2009 paper Kim, T. H., and San Andrés, L., 2010, “Thermohydrodynamic Model Predictions and Performance Measurements of Bump-Type Foil Bearing for Oil-Free Turboshaft Engines in Rotorcraft Propulsion Systems,” ASME J. of Tribology, v132

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References Foil BearingsASME GT2009-59919 San Andrés, L., and Kim, T.H., 2010, “Thermohydrodynamic Analysis of Bump Type gas

Foil Bearings: A Model Anchored to Test Data,” ASME J. Eng. Gas Turbines and Power, v132

IJTC2008-71195 Kim, T.H., and San Andrés, L., 2009, "Effects of a Mechanical Preload on the Dynamic Force Response of Gas Foil Bearings - Measurements and Model Predictions," Tribology Transactions, v52

ASME GT2008-50571IJTC2007-44047

Kim, T. H., and San Andrés, L., 2009, “Effect of Side End Pressurization on the Dynamic Performance of Gas Foil Bearings – A Model Anchored to Test Data,” ASME J.

Eng. Gas Turbines and Power, v131. 2008 Best PAPER Rotordynamics IGTI

ASME GT2007-27249 San Andrés, L., and Kim, T.H., 2009, “Analysis of Gas Foil Bearings Integrating FE Top Foil Models,” Tribology International, v42

AIAA-2007-5094 San Andrés, L., and T.H. Kim, 2007, “Issues on Instability and Force Nonlinearity in Gas Foil Bearing Supported Rotors,” 43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Cincinnati, OH, July 9-11

ASME GT2005-68486 Kim, T.H., and L. San Andrés, 2008, “Heavily Loaded Gas Foil Bearings: a Model Anchored to Test Data,” ASME J. Eng. Gas Turbines and Power, v130

ASME GT2006-91238 San Andrés, L., D. Rubio, and T.H. Kim, 2007, “Rotordynamic Performance of a Rotor Supported on Bump Type Foil Gas Bearings: Experiments and Predictions,” ASME J. Eng. Gas Turbines and Power, v129

ASME GT2004-53611 San Andrés, L., and D. Rubio, 2006, “Bump-Type Foil bearing Structural Stiffness: Experiments and Predictions,” ASME J. Eng. Gas Turbines and Power, v128

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ReferencesASME GT2011-45274 San Andrés, L., and Chirathadam, T., 2011, “Metal Mesh Foil Bearings: Effect of

Excitation Frequency on Rotordynamic Force Coefficients

ASME GT2010-22440 San Andrés, L., and Chirathadam T.A., 2010, “Identification of Rotordynamic Force Coefficients of a Metal Mesh Foil Bearing Using Impact Load Excitations.”

ASME GT2009-59315 San Andrés, L., Chirathadam, T. A., and Kim, T.H., 2009, “Measurements of Structural Stiffness and Damping Coefficients in a Metal Mesh Foil Bearing.”

AHS Paper San Andrés, L., Kim, T.H., Chirathadam, T.A., and Ryu, K., 2009, “Measurements of Drag Torque, Lift-Off Journal Speed and Temperature in a Metal Mesh Foil Bearing,” American Helicopter Society 65th Annual Forum, Grapevine, Texas, May 27-29

Other

ASME DETC2007-34136

Gjika, K., C. Groves, L. San Andrés, and G. LaRue, 2007, “Nonlinear Dynamic Behavior of Turbocharger Rotor-Bearing Systems with Hydrodynamic Oil Film and Squeeze Film Damper in Series: Prediction and Experiment.”

Metal mesh foil bearings

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CIATEQ´s full-size rotordynamic rigCIATEQ´s full-size rotordynamic rig

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Acknowledgments

Thanks to

NSF (Grant # 0322925) NASA GRC (Program NNH06ZEA001N-SSRW2), Capstone Turbines, Inc., Honeywell Turbocharging Systems, Korea Institute of Science and Technology (Dr. Tae-

Ho Kim) Foster-Miller, MiTI, TAMU Turbomachinery Research Consortium (TRC) CIATEQ A.C.

Learn more:http://rotorlab.tamu.edu