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A Metal Mesh Foil Bearing and a Bump-Type Foil Bearing:Comparison of Performance for Two Similar Size Gas Bearings

Work supported by the TAMU Turbomachinery Research Consortium

ASME Turbo Expo 2012 June 11-15, 2012, Copenhagen, Denmark

Accepted for journal publication

GT2012-68437

Southwest Research InstituteThomas Chirathadam

Turbomachinery Laboratory Texas A&M University

Luis San Andrés

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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.

Gas Bearings allow• weight reduction, energy and complexity savings• higher temperatures, without needs for cooling air • improved overall engine efficiency• reduced cost of operation / design / manufacturing

Oil-free bearing for turbomachinery

Indirect benefits : Energy security, reduced dependence on fossil fuels, widespread use of distributed power – Economic impact (jobs, wealth creation)

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Developed experimentally validated computational tools for predicting the performance of radial and thrust gas bearings (GFB, MMFB etc).

Gas bearing research program at TAMU

Since 2003, supported by NSF, NASA, Capstone Turbines, Borg-Warner and TRC

- Bearing structural analysis- Performance characteristics- Dynamic force coefficients- Rotordynamic performance- Thermal management- Non-linear structure models

Bump type gas foil bearing

Metal mesh foil bearingGas tilting pad bearing

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Metal Mesh Foil Bearing (MMFB)MMFB COMPONENTS: bearing cartridge, metal mesh ring and top foilHydrodynamic air film develops between rotating shaft and top foil.

Potential applications: ACMs, micro gas turbines, turbo expanders, turbo compressors, turbo blowers, automotive turbochargers, APUs

WHY METAL MESH ?

Bearing cartridge

Compressed metal mesh pads

Heat treated top foil (Inner surface coated with MoS2)

Bearing cartridge

Compressed metal mesh pads

Heat treated top foil (Inner surface coated with MoS2)

•Large hysteresis damping. •Wide temperature range•Damping not affected w/oil•Empirical model available

• Hybrid bearing with metal mesh + performance• More damping without compromising stiffness.• Static load does not affect damping• Shape memory alloys (expensive) gives +++ damping as excitation amplitude grows

(Vance et al., 2000-2005)

(Ertas et al., 2008-2010)

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San Andrés et al. (2010) J. Eng. Gas Turb. & Power, 132(3)Assembled the first prototype MMFB (L=D=28 mm). Load vs Deflection with hysteresis shows large structural damping 0.7). Frequency dependentstiffness agree with predictions.

San Andrés et al. (2009) ASME GT2009-59920Demonstrated operation to 45 krpm with early rotor lift off. Educated undergraduate students.

San Andrés et al. (2010) J. Eng. Gas Turb. & Power, 132Start and shut down to measure torque and lift-off speed. Low friction factor ~ 0.01 at high speed 60 krpm.

Past work Metal mesh foil bearings (2008-2011)

San Andrés and Chirathadam (2011) J. Eng. Gas Turb. & Power, 133Rotordynamic coefficients from unidirectional impact loads. Estimated stiffness and damping force coefficients at 50 krpm.

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San Andrés and Chirathadam (2011) J. Eng. Gas Turb. & Power, 133(12)Identification of rotordynamic coefficients using two e-shakers at 40-50 krpm, displacement amplitudes ( 20-30 m), static load ( 22-36 N). Estimated loss factor ~1

Past work Metal mesh foil bearings (2011-12)

San Andrés and Chirathadam (2012)GT 2012-68437Comparison of static and dynamic performance of similar size MMFB and generation I Bump Type Foil Bearing (BFB). MMFB shows 2-3 times BFB damping. Airborne drag friction factor ~ 0.03 for both bearings

today’s presentation

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Is a metal mesh foil bearing as good as a bump type foil bearing (generation I)?

Metal mesh pad

(a) Metal mesh foil bearing

Top foil fixed end Bump foil

Spinning shaft

Bearing cartridge

(b) Bump type foil bearing (generation I)

Gas film

Major question

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Top Foil

0.12 mm top foilChrome-Nickel alloyRockwell 40/45

Heat treated at ~ 450 ºC for 4 hours and allowed to cool. Foil retains arc shape after heat treatment

Sprayed with MoS2sacrificial coating

Bump foil

Made by compressing a flat steel strip in specially made die

Bearing cartridge (+top foil+ bump foil)

Bump foil and top foil inserted in steel bearing cartridge.

Bump foil bearing components – Gen I

Simple to manufacture but its engineered design demands time and $$

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MMFB components

Metal mesh pads

Compressed weave of copper wires

Compactness (density)=20%

Simple to manufacture and assemble

Top Foil

0.12 mm top foilChrome-Nickel alloyRockwell 40/45

Heat treated at ~ 450 ºC for 4 hours and allowed to cool. Foil retains arc shape after heat treatment

Sprayed with MoS2sacrificial coating

Bearing cartridge (+top foil+ metal mesh)

Metal mesh pads and top foil inserted inside bearing cartridge.

Top foil firmly affixed in a thin slot made with wire-EDM machining

Stiffness and damping of MMFB depend on metal mesh compactness

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Top Foil Metal mesh pad Bearing cartridge (+top foil+ metal mesh)

Compare bearings’ componentsMMFB

Top Foil Bump foil Bearing cartridge (+top foil+ bump foil)

BFB

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MMFB and BFB specifications

a) Metal mesh foil bearing

0.1100.0Bearing diametral clearance (mm)

36.6136.50Bearing inner diameter (mm)

0.120.12Steel top foil thickness (mm)

0.30Wire diameter (mm)

20 %Copper mesh density

36.74mesh inner diameter (mm)

42.07Copper mesh outer diameter (mm)

0.54Bump height (mm)

2.1Bump length (mm)

4.3Bump pitch (mm)

26No of bumps

38.1 38.0Bearing axial length, L (mm)

BFBMMFB

b) Bump type foil bearing

5 cm

5 cm36.5036.50Journal OD rotordynamic tests (mm)

36.6236.62Shaft OD static load-deflection tests (mm)

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Static load-deflection tests

Eddy current sensor

Lathe saddle

Test bearingShaft affixed in lathe chuck

Load cell

Lathe chuck

Lathe chuck holds shaft & bearing during loading/unloading cycles.

Lathe tool holder

Eddy Current sensor Load cell

Test bearing

Stationary shaft

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Structural stiffness

-60

-40

-20

0

20

40

60

-0.5 -0.3 -0.1 0.1 0.3 0.5

Displacement [mm]

Forc

e [N

]0

0.2

0.4

0.6

0.8

1

-0.25 -0.15 -0.05 0.05 0.15 0.25

Displacement [mm]

Stiff

ness

[MN

/m]

-60

-40

-20

0

20

40

60

-0.5 -0.3 -0.1 0.1 0.3 0.5Displacement [mm]

Forc

e [N

]

0

0.2

0.4

0.6

0.8

1

-0.25 -0.15 -0.05 0.05 0.15 0.25

Displacement [mm]

Stiff

ness

[MN

/m]

pullpush

90°

Top foil fixed end

Static load direction

3 cycles of push and pullLoad directed 90 degrees

to top foil fixed end

MMFB BFB

push

pull

Large hysteresis loop in MMFB: +

energy dissipation

Stiffness Stiffness

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Estimation of structure loss factor

-60

-40

-20

0

20

40

60

-0.5 -0.3 -0.1 0.1 0.3 0.5

Displacement [mm]

Forc

e [N

]

Ks=0.27 MN/m 45°

Top foil fixed end

Static load direction

2 21disp

s s

EFdx

K r K r

Loss factor

0.130.1870.2590º

0.120.1840.2645ºBFB

0.340.1480.2990º

0.270.1630.2745ºMMFB

Loss factor [-]Static displacement, r [mm]

Linear stiffness, Ks[MN/m]

Load direction

Bearing type

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MMFB rotordynamic test rig

Max. operating speed: 75 krpmTurbocharger driven rotorRegulated air supply: 9.30bar (120 psig)Test Journal: length 55 mm, 36.5 mm diameter

Journal press fitted on Shaft Stub

TC cross-sectional viewRef. Honeywell drawing # 448655

Twin ball bearing turbocharger, Model T25, donated by Honeywell Turbo Technologies

Bearing

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Torque & bearing lift-off measurements

Torque arm

Calibrated spring

GFB

Shaft (Φ 36.5 mm)

String

Eddy current sensor

Preloading using a rubber

band

5 cm

Force gauge

Variable applied static load

Top foil fixed end

Bearing housing

Ball bearing

Speed up to 75 krpm and deceleration to rest.MMFB

0

20

40

60

80

0 10 20 30

Time [s]

Rot

or s

peed

[krp

m]

0

100

200

300

400

0 10 20 30

Time [s]

Bea

ring

torq

ue [N

mm

]

Rotor starts

Rotor stops

Iift off speed

Lift off speed at lowest torque : airborne operation

36 N load

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Torque & bearing lift-off vs. shaft speed36 N load

0

20

40

60

80

0 10 20 30Time [s]

Rot

or s

peed

[krp

m]

0

100

200

300

400

0 10 20 30Time [s]

Bea

ring

torq

ue [N

mm

]

(a)

(b) MMFB torque

Rotor starts spinning

Rotor stops

MMFB

MMFB

Time [s]

Bea

ring

torq

ue [N

mm

] R

otor

spe

ed [k

rpm

]

Static load

Y

W

0

20

40

60

80

0 10 20 30

Time [s]

Rot

or s

peed

[krp

m]

0

100

200

300

400

0 10 20 30

Time [s]

Bea

ring

torq

ue [N

mm

](c)

(d) BFB torque

Rotor starts spinning

Rotor stops

BFB

BFB

Time [s]

Bea

ring

torq

ue [N

mm

] R

otor

spe

ed [k

rpm

] MMFB BFB

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Peak (max.) start-up torque – DRY sliding

Static load

0

100

200

300

400

0 10 20 30Net applied static load per unit area (W/LD ) [kN/m^2]

Peak

sta

rtup

torq

ue [N

mm

]

MMFBBFB

MMFB

BFB

~ Airborne drag torque airborne

MMFB

BFB

4.3 psi

MMFB has more drag torque when dry-sliding, but it lifts earlier (lower speed) than BFB

36 N load (max)

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Rotor acceleratesRotor accelerates

Friction factor vs. rotor speed

0.01

0.1

1

0 10 20 30 40 50 60 70Rotor speed [krpm]

Fric

tion

fact

or [-

]

35.6N

26.7N

17.8N

0.01

0.1

1

0 10 20 30 40 50 60 70

Rotor speed [krpm]

Fric

tion

fact

or [-

]

35.6N26.7N17.8N

f = (Torque/Radius)/(Static load)

f ~ 0.03 f ~ 0.03

Friction decreases with load and rotor speed (due to lift-off). MMFB lifts earlier (lower speed) than BFB

MMFB BFB

Static load36 N/LD=3.8 psi

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Rotordynamic test rig(X-Y 100 N shakers)

Test bearing

Positioning table

Load cell

Electromagnetic shaker

X Y

Dynamic load :25-100 N

Rotor speed: up to 75 krpm

Test identification range: Up to 400 Hz

Y

WX

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Identification model for force coefficients

KS,CS: soft SQ stiffness and damping

MS : effective mass

X

YKYY, CYY

KXY, CXY

Shaker force, FY

Bearing

Journal

KYX, CYX

KXX, CXX

Ω

X X X

Y Y Y

S X S X S XX XY XX XY X

YX YY YX YY YS Y S Y S

M a C v K X C C K K Fx xC C K K FM a C v K Y y y

EOM:

Shaker force, FX

KSX, CSX

KSY, CSY

SoftSupport structure

Kij ,Cij: test bearing stiffness and damping

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Stiffness vs. frequency

MMFB has lower dynamic stiffness. BFB hardens with frequency. Both bearings show little cross-coupled stiffnesses

Experimental

Shaft speed=50 krpm (833 Hz)

-3

-2

-1

0

1

2

3

200 250 300 350 400Frequency [Hz]

Stiff

ness

[MN

/m]

kxx kxykyx kyy

Kxx KxyKyx Kyy

(a) MMFB

KXY

KXX

KYX

KYY

0-3

-2

-1

0

1

2

3

200 250 300 350 400Frequency [Hz]

kxx kxykyx kyyKxx KxyKyx Kyy

(b) BFB

KXX

KYXKXY

KYY

MMFB BFB

15.5 N15.5 NFixed end

15.5 N15.5 NFixed endFixed end

22 N

22 N/LD=2.3 psi

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Damping vs. frequency

MMFB has lower viscous damping. Both bearings show little cross-coupled damping

Experimental

Shaft speed=50 krpm (833 Hz)

-1000

-500

0

500

1000

200 250 300 350 400Frequency [Hz]

Eq. v

isco

us d

ampi

ng [N

s/m

]

Cxx CxyCyx Cyy

(a) MMFB

-

CXX CYY

CYX CXY

MMFB

0

(b) BFB

-1000

-500

0

500

1000

200 250 300 350 400Frequency [Hz]

Cxx CxyCyx Cyy

CXX

CYY

CXY CYX

BFB

15.5 N15.5 NFixed end

15.5 N15.5 NFixed endFixed end

22 N

22 N/LD=2.3 psi

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0

0.5

1

1.5

2

200 250 300 350 400Frequency [Hz]

Loss

fact

or [-

]0 rpm MMFB50 krpm MMFB50 krpm BFB0 krpm BFBMMFB

BFB

Loss factor vs. frequency

MMFB has much more structural damping (ability to dissipate mechanical energy).

Estimation

Shaft speed=50 krpm (833 Hz)

MMFB

BFB

15.5 N15.5 NFixed end

15.5 N15.5 NFixed endFixed end

22 N

~ CK

Loss factor

22 N/LD=2.3 psi

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TEST bump foil bearing – gen. Istiffness K ~ 1,800-8,000 (LxD) lbf/in3 [487-2165 MN/m3]damping C ~ 0.5-1.85 (LxD) lbf-s/in3 [135-500 MN/m3]

TEST metal mesh foil bearing stiffness K ~ 1,000-1,600 (LxD) lbf/in3 [270-473 MN/m3] ,, damping C ~ 0.5-1.60 (LxD) lbf-s/in3 [135-433 MN/m3]

MMFB – structurally soft with large damping.BFB within ROT stiffness range.BFB and MMFB damping at the low end

Rule of thumb (ROT) Review of bump foil bearings (DellaCorte, 2010)stiffness K ~ 2,500-7,500 (LxD) lbf/in3

damping C ~ 0.1-10.0 (LxD) lbf-s/in3

Pap IJTC2010-41232

DellaCorte, C., 2010, “Stiffness and Damping Coefficient Estimation of Compliant Surface Gas Bearings for Oil- Free Turbomachinery,” STLE/ASME 2010 Int. J. Tribol. Conference, Paper No. IJTC2010-41232.

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Conclusions: MMFB vs BFB• Static load-deflection: BFB has larger mechanical hysteresis loop, loss factor is ~ 2- 3 times that of BFB.

• Drag torque increases with increasing static load

• When airborne, the friction factor (f ) ~ 0.03 for both test bearings. MMFB with larger dry-friction torque prior to lift-off.

• Dynamic load tests: MMFB has lesser dynamic stiffness and viscous damping than BFB.

• Both bearings show little cross-coupled K & C.

• MMFB structural damping > than BFB’s.

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Measurement of system thermal response coupled to rotordynamics

Rot

or T

empe

ratu

re [°

C]

Heater

T4

T1

T2

T3 Thermocouples on bearings OD

Heat flows from coil while rotor spins from 0 to 50 krpm

Current work: Thermal management

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Acknowledgments / thanks to

http://rotorlab.tamu.eduLearn more at:

Turbomachinery Research Consortium Honeywell Turbocharging Technologies

Korea Institute of Science and Technology (KIST)

Questions (?)

Copyright© 2012 Luis San Andres

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Performance at high temperatures, temperature and rotordynamic measurements. Effect of cooling rate of dynamic rotor response

2009-10

BFB rotordynamic force coefficient measurements. Measurement of drag torque, air-borne friction factor, and power loss. Estimation of Rule-of-thumb coefficients.

2010-11

Measurement of static load capacity, Identification of structural stiffness and damping coefficients. Ambient and high temperatures

2004-09

Model for ultimate load capacity, Isothermal model for prediction of GFB static and dynamic forced performance

2005-06

Rotordynamic measurements: instability vs. forced nonlinearity?

Effect of feed pressure and preload (shims) on stability of FBS.Measurements of rotordynamic response.

Integration of Finite Element structure model for prediction of GFB static and dynamic forced performance

2005-07

Thermoelastohydrodynamic model for prediction of GFB static and dynamic forced performance at high temperatures

2007-09

Topicyear

TAMU past work: BFBs

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year2011-12 Computational modeling- Prediction of force coefficients and performance

characteristics. High temperature experiments – measurement of rotor and bearing temperature with increasing rotor temperature and operating speed. Prediction and response of rotor response to speeds up to 50 krpm.

2011 Comparison of static and dynamic performance of similar size MMFB and Generation I Bump Type Foil Bearing (BFB). MMFB has 2-3 times BFB damping. Airborne friction factor ~ 0.03 for both bearings

2010-11 Identification of Rotordynamic coefficients using two orthogonally positioned electromagnetic shakers for varying rotor speeds (40-50 krpm), displacement amplitudes ( 20-30um), static load ( 22-36 N). Estimated loss factor ~1

2009-10 Demonstrated operation to 45 krpm with early rotor lift off. Educated undergraduate students.Further start and shut down operation, measurement of torque and lift-off speed. Low friction factor ~ 0.01 at high speed 60 krpm. Estimation of rotordynamic coefficients from unidirectional impact loads.

2008-09 Assembled the first prototype MMFB (L=D=28 mm). Load vs Deflection with hysteresis shows large structural damping (g~ 0.7). Frequency dependent stiffness agree with predictions.

TAMU past work: MMFBs