Thermohydrodynamic Analysis of Bump Type Gas Foil Bearings: A … · 2020-03-16 · San Andrés, L., and Chirathadam, T., 2011,“Metal Mesh Foil Bearings: Effect of Excitation Frequency

This material is based upon work supported by NASA NNH06ZEA001N-SSRW2, Fundamental Aeronautics: Subsonic Rotary Wing Project and the Texas A&M Turbomachinery Research Consortium

Thermohydrodynamic Analysis of Bump Type Gas Foil Bearings:A Model Anchored to Test Data

Luis San AndrésMast-Childs Professor

June 2011 - Update

Tae Ho Kim Post-Doc Research Associate

Keun RyuPhD Research Assistant

2

Outline• Statement of Work & Sources for Presentation• Objectives and accomplished work in 2007-08

Computational model. Validation with published data. Rotordynamic measurements at TAMU

• Objectives and accomplished work in 2008-09Description of test rig and foil bearings at TAMUEffect of temperature on bearing temperatures,

coastdown speed and rotor motionsEffect of cooling flow on shaft and bearing

temperatures. Validation of computational model* The computational code

Graphical User Interface. Further predictions• GFB thermal management tests and preds. • Added Value and Closure

3

Topic• Statement of Work & Sources for Presentation

• Objectives and accomplished work in 2007-08Computational model. Validation with published data. Rotordynamic measurements at TAMU


coastdown speed and rotor motionsEffect of cooling flow on bearing and shafttemperatures. Validation of computational model

* The computational codeGraphical User Interface. Further predictions

• GFB thermal management tests and preds.• Closure & added value

4

Gas Foil Bearings (+/-)Increased reliability: large load capacity (< 100 psi)No lubricant supply system, i.e. reduce weightHigh and low temperature capability (up to 2,500 K) No scheduled maintenance Ability to sustain high vibration and shock load. Quiet operation

Less load capacity than rolling or oil bearingsWear during start up & shut downNo test data for rotordynamic force coefficientsThermal management issuesPredictive models lack validation. Difficulties in modeling + dry-friction damping + effects of temperature on material properties and components’ expansion.

Applications: ACMs, micro gas turbines, turbo expanders

5

To develop a detailed, physics-based computational model of

gas-lubricated foil journal bearings including thermal effects to predict bearing

performance.

The result of this work shall include a fully tested and experimentally verified design tool for

predicting gas foil journal bearing torque, load, gas film thickness, pressure, flow field,

temperature distribution, thermal deformation, foil deflections, stiffness, damping, and any

other important parameters.

SOW – Main Objective

Ω

Agreement NASA NNH06ZEA001N-SSRW2

6

References Foil Bearings

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, v 132

ASME GT2009-59919

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

AHS 2009 paper

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

ASME GT2009-59920

San Andrés, L., Ryu, K., and Kim, T.H., 2011, “Identification of Structural Stiffness and Energy Dissipation parameters in a 2nd Generation Foil Bearing; Effect of Shaft Temperature”, ASME J. Eng. Gas Turbines Power, vol. 133 (March) , pp. 032501

J Eng Gas Turbines & Power

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.)

8th IFToMM Int. Conf. onRotordynamics

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

ASME GT2011-46767

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 GT2011-45763

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, v 133

ASME GT2010-22508NASA/TM 2010-216354

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, v 133

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, v 133

ASME GT2010-22981

7

References Foil Bearings

Rubio, D., and L. San Andrés, 2007, “Structural Stiffness, Dry-Friction Coefficient and Equivalent Viscous Damping in a Bump-Type Foil Gas Bearing,” ASME J. Eng. Gas Turbines and Power, v 129 2005 Best PAPER Rotordynamics IGTI Structures and Dynamics Committee

ASME GT2005-68384

San Andrés, L., and Kim, T.H., 2008, “Forced Nonlinear Response of Gas Foil Bearing Supported Rotors,”Tribology International, 41(8), pp. 704-715.

Tribology International

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

ASME GT2004-53611

Kim, T-H, and L., San Andrés, 2007, “Analysis of Gas Foil Bearings with Piecewise Linear Elastic Supports.” Tribology International, 40, pp. 1239-1245.

Kim, T.H., Breedlove, A., and San Andrés, L., 2009, “Characterization of Foil Bearing Structure at Increasing Temperatures: Static Load and Dynamic Force Performance,” ASME Journal of Tribology, v 131(3)

J of Tribology

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 GT2006-91238

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 GT2005-68486

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

AIAA-2007-5094

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

ASME GT2007-27249

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 GT2008-50571IJTC2007-44047

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

IJTC2008-71195

8

References

Kim, T.H., and L. San Andrés, 2006, “Limits for High Speed Operation of Gas Foil Bearings,” ASME Journal of Tribology, 128, pp. 670-673

Journal of Tribology

San Andrés, L., and Chirathadam, T., 2011, “Metal Mesh Foil Bearings: Effect of Excitation Frequency on Rotordynamic Force Coefficients

ASME GT2011-45274

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.”

ASME DETC2007-34136

Other

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

AHS Paper

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

ASME GT2009-59315

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

ASME GT2010-22440

Metal mesh foil bearings

9

10

Topic• Statement of Work & Sources for Presentation

• Objectives and accomplished work in 07-08Computational model. Validation with published data. Rotordynamic measurements at TAMU





11

Research Objectives (2007-08)THD model for prediction of GFB performance

• Perform physical analysis, derive governing equations, and implement numerical solution.

• Develop GUI for User ready use

• Compare GFB predictions to limited published test data (NASA mainly)

• Revamp existing test rig with cartridge heater, acquire new bearings, machine new rotor

• Perform structural tests on bearings and measure rotordynamic response for increasing shaft temperatures

12

Scheduled Timeline & completion

Rotordynamic Measurements for increasing shaft temperatures (max 500 C), identification of GFB synchronous force coefficients

Reception of parts and assembly of components, troubleshooting, connection to static loader and shaker

Planning of modifications to existing, selection of instrumentation and cartridge heater, design of insulation cover and rotor

Rotordynamic-GFBs Test rig (High Temperature)

Measurements of load & bearing deflection for increasing shaft temperatures (max 500 C), identification of FB structural parameters

Reception of parts and assembly of components, troubleshooting, connection to static loader and shaker

Planning of modification, selection of instrumentation and cartridge heater, design of insulation cover

Test rig for identification of FB structure (High Temperature)

Prediction of performance and comparisons to available rotordynamic test data

Development simple NONLINEAR physical model for foil bearings

Nonlinear analysis GFBS

Comparison of GFB predictions to measured performance from TAMU test rig

Predictions of GFB performance for parametric studies

Integration of thermal model with GFB FD computational code (gas film)

Implementation thermal model (Finite Element Based) and coupling to existing STRUCTURAL MODEL

Development physical model for thermal transport in foil bearings

Computational analysis GFBS

Q8Q7Q6Q5Q4Q3Q2Q1Task

Luis San Andres MS student

Tae Ho Kim UG worker

13

Accomplishments: Proposed & Actual

Completed Dec 2010100%

Design & construction; selection & procurement of instrumentation and bearings; assembly, troubleshooting and operation at high temperature rotor-bearing test rig. Measurements of temperatures and rotordynamic performance with Foster-Miller GFBs completed (see Q7). Tests with MiTi® bearings at higher temperatures in progress. Validation of computational model also in progress.

Rotordynamic-GFBs Test rig (High Temperature)

See Q4, Q7 reports

Design & construction; selection & procurement of instrumentation and bearings; assembly, troubleshooting and operation at high temperature. Measurements of static load performance & comparison to predictions

Test rig for identification of FB structure (High Temperature)

Implementation in XLTRC2 for ready rotordynamic analyses

Development simple NONLINEAR physical model for foil bearings. Prediction of performance and comparisons to rotordynamic test data

Nonlinear structural analysis of GFBS

See Q4 & Q7 reportsValidation of GFB predictions with measured temperatures from NASA & TAMU published research

Analysis completed. Code delivered on June 10, 2009

Physical model for thermal transport in foil bearings. Integration of thermal model with GFB FD computational code (gas film). Prediction of GFB performance: parametric study

Thermohydrodynamic Analysis of GFBS

commentPlanned &

ActualTask

1st & 2nd Years

14

Thermohydrodynamic model in a GFB

ρ= ℜg

PT

μ α= v T

- Ideal gas with density,

- Gas viscosity,

- Gas Specific heat (cp) and thermal conductivity (κg) at an effective temperature

Ω

Bump strip layer

Top foil

Hollow shaft

Bearing housing

External fluid medium

Inner flow stream

Outer flow stream

Thin film flow

X

Y

X=RΘSide view of GFB with hollow shaft

Reynolds equation in thin film3 3

( )12 12f f f f f f f f

m zf g f f g f g f

h P P h P P P hU

x T x z T z x Tμ μ⎛ ⎞ ⎛ ⎞ ⎛ ⎞∂ ∂∂ ∂ ∂

+ =⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜ ⎟ ⎜ ⎟∂ ℜ ∂ ∂ ℜ ∂ ∂ ℜ⎝ ⎠ ⎝ ⎠ ⎝ ⎠

15

THD model

GFB with cooling flows (inner and/or outer)

Outer flow stream Top foil

Bearing housing “Bump” layer

zxPCo, TCo

X

YZ

Bearing housing

PCi, TCi

Inner flow stream

ΩRSo

Hollow shaft

PaThin film flow

z=0 z=LT∞

Convection of heat by fluid flow +

diffusion to bounding surfaces

= compression work + dissipated

energy

( ) ( ) ( ) ( )

( )2212 13

ρ ρ

μ

⎛ ⎞∂ ∂⎜ ⎟+ + − − −⎜ ⎟∂ ∂⎝ ⎠

∂ ∂⎛ ⎞ ⎧ ⎫= + + + + −⎜ ⎟ ⎨ ⎬⎜ ⎟∂ ∂ ⎩ ⎭⎝ ⎠

f i o

f f f f f f f fp fF f F Sf S f

f f ff f f f f m f m

f

h U T h W Tc h T T h T T

x z

P PU h W h W U U U

x z h

Bulk-flow temperature transport equation

16

T∞

TBo

TBi

TFo

TSo

TSi

TFi

TCi

TO

Tf

→S CQ

SoQ

→BQ

→∞BQ

→F BiQ

→f FQ→S fQ

FQ→F OQ

→O BiQ

Top foil

Bump layer

Hollow shaft

Bearing housing

External fluid

ΩdӨ

RSi RSo RFi RFo RBi RBo

SiQ

Q =Rq

QCi

Heat carried by thin film

flow

Heat carried by outer flow

stream: Heat

(-): Heat

(+)

QB

QCo

Drag dissipation power (gas

film)

Heat carried by inner flow

stream

Heat conduction through shaft

TS

Heat flow paths in rotor - GFB systemHeat flows &

thermal resistances in a

GFB & hollow shaft

Heat conducted

into bearing

Cooling gas streams

carry away heat

1710.4 GN/m3Bump foil stiffness

0.31Bump foil Poisson’s ratio

200 GPaBump foil Young’s modulus

Assumed39 x 1 Number of bumps x strips

Assumed0.580 mm Bump height

Assumed4.064 mm Bump pitch

Assumed1.778 mm Bump half length

Ref. [21]127 μmBump foil thickness

Ref. [21]127 μmTop foil thickness

Top foil and bump strip layerAssumed20 μmNominal radial clearance

Assumed5 mmBearing cartridge thickness

Ref. [7]41 mm Bearing length

Ref. [7]25 mmBearing inner radius

Bearing cartridge

Value / commentParameters ValueParameters

1.014 x 105 PaAmbient pressure

1,020 J/kg°KSpecific heat

1.164 kg/m3Density

0.0257 W/m°KConductivity

10-5 Pa-sViscosity

287 J/(kg-°K)Gas Constant

Gas properties at 21 °C

Generation I GFB with single top foil and bump strip layer

THD Model Validation

Gas viscosity & density & conductivity, foil Young’s modulus, and clearance

change with temperature.

Radil and Zeszotek, 2004Dykas and Howard, 2004

Published data

18

Peak film temperatureSupply air (TSupply),

shaft (TS), and bearing OD (TB)

temperatures at 21 °C.

Film temperature + higher than ambient, even for small load of 9 N. Good agreement preds with test data

0

40

80

120

160

200

240

0 50 100 150 200 250 300

Static load [N]

Peak

tem

pera

ture

[° C

]

TSupply=21°CTest data

(Mid-plane)Predictions(Mid-plane)

30,000 rpm

40,000 rpm

50,000 rpm

20,000 rpm

Predictions & test data Radil and Zeszotek, 2004Read more in ASME Paper GT2009-59919

Predictions & test data

19

2008 rotor-GFB test rig

Drive motor (25 krpm).

Cartridge heater max.

temperature: 300F

Air flow meter (Max. 100

L/min at 14 psig)

Driving motor

GFB housing

Tachometer

Flexible coupling

Electromagnet loader

Strain gage load cell

Test rotor

Eddy current sensor

Cooling air hose

Infrared thermometer

Cartridge heater

Max. temp. 130 °C

20

Numbers in circles show locations of temperature measurement.

2 Bearing outer surface temperature (Drive and bearing and free end bearing)1 Bearing sleeve temperature (at five locations along circumference)

3 Rotor surface temperature (Drive end and free end)4 Bearing support (housing) surface temperature (Drive end and free end)

Cooling air

Eddy current sensor(Max. 177 ºC)

Speed sensor

Cartridge heater

Flexible couplingHollow test

rotor

DC router motor

(25 krpm)

Infrared Thermometer (Max. 540 ºC)

3 3

2 2

4 4

Infrared Thermometer gun(Max. 500 ºC)

cm

0 10

1

K-type thermocouples(Max. 480 ºC)

Ambient temp. (Ta)~ 22 °C (71 ° F)

2008 hot rotor-GFB test rig

21

THD Model Validation Bearings at TAMU

585968Bump arc angle [deg]4.0794.1615.581Bump arc radius0.5100.5400.468Bump height3.9502.1003.742Bump length4.6404.3004.581Bump pitch

24 × 3 axial 26 × 1 axial 25 × 5 axial Number of Bumps0.1020.1200.100Bump foil thickness0.1270.1200.100 Top foil thickness25.438.138.2Top foil axial length

Top foil and bump strip layer37.92137.9539.36Inner diameter44.57550.8050.85Outer diameter

Bearing cartridge

MiTi(2nd gen.)

KIST(1st gen.)

Foster-Miller(2nd gen.)Parameter [mm]

Elastic Modulus 214 GPa,Poisson ratio=0.29

Foster-Miller FB with Teflon®coating (Generation II)

22

Waterfall plots:

(a) Case 1

0 200 400 600 800 10000

16

32

48

64

80

Frequency [Hz]

Am

plitu

de [m

icro

ns]

Am

plitu

de [μ

m, 0

-Pk]

Frequency [Hz]

1X 25 krpm

4 krpm

15 krpm

Tc = 22 °C

0 200 400 600 800 10000

16

32

48

64

80

Frequency [Hz]

Am

plitu

de [m

icro

ns]

Am

plitu

de [μ

m, 0

-Pk]

Frequency [Hz]

(b) Case 2

25 krpm

4 krpm

15 krpm

1X

Tc = 93 °C

0 200 400 600 800 10000

16

32

48

64

80

Frequency [Hz]

Am

plitu

de [m

icro

ns]

Am

plitu

de [μ

m, 0

-Pk]

Frequency [Hz]

(c) Case 3

25 krpm

4 krpm

15 krpm

1X

Tc = 132 °C

Cartridge temperature (Ths) increases

1X component dominant, i.e., no subsynchronous motion,

during coastdown tests

FE – vertical planeCase 1-3 without cooling flow, Ta ~ 22°C, and Ths = 22°C, 93 °C, and 132°C

coastdown responses

23

0

20

40

60

80

100

0 5000 10000 15000 20000 25000 30000

Rotor speed [rpm]

Am

plitu

de [μ

m, 0

-pk]

(22 °C)

(93 °C)

(132 °C)

Speed - up


Rotor speed up 1X responseW/o cooling flow, Ta ~ 22°C, and Ths = 22°C, 93 °C & 132°C

Above critical speed ~ 14.5 krpm, amplitude drops. A nonlinearity! As Ths increases, the peak amplitude decreases.

DE – vertical plane

24

W/o cooling flow, Ta ~ 22°C, and Ths = 22°C, 93 °C, and 132°C

As Ths increases, critical speed raises by ~ 2 krpm and the peak amplitude decreases. Nonlinearity absent!

0

20

40

60

80

100

0 5000 10000 15000 20000 25000 30000

Rotor speed [rpm]

Am

plitu

de [μ

m, 0

-pk]

(22 °C)

(93 °C)

(132 °C)


Coastdown

Rotor coastdown 1X response

DE – vertical plane

Read more in AHS-65 2009 Paper

25

26

Topic• Statement of Work & Sources for Presentation• Objectives and accomplished work in 07-08



coastdown speed and rotor motionsEffect of cooling flow on bearing and shaft

temperatures. Validation of computational model* The computational code

Graphical User Interface. Further predictions• GFB thermal management tests and preds.• Closure & added value

27

Research Objectives 2008-09Model validation with TAMU FB test data

• Complete test rig using cartridge heater for high temperature operation (up to 360C)

• Measure rotordynamic performance during speed coastdown from 30 krpm and for increasing shaft temperatures

• Quantify effect of side flow on cooling bearings (max. 150 LPM per bearing)

• Benchmark model predictions

28





Bearing cartridge

MiTi(2nd gen.)

KIST(1st gen.)



29

2009 hot rotor-GFB test rig

Gas flow meter (Max. 500 LPM). Drive motor (max. 65 krpm) )

Instrumentation for high temperature. Insulation casing

Insulated safety cover


Flexible coupling

Drive motor

Cartridge heater

Test GFBs

Test hollow shaft (1.1 kg, 38.1mm OD,

210 mm length)

TachometerEddy current

sensorsHot heater inside rotor spinning 30

krpm

Max. 360 °C

30

Thermocouples in test rotor-GFB rig

Foil bearings

Cartridge heaterHeater stand

T14

T10

T12

T13

Coupling cooling air

Drive motor

T15T16Th

Hollow shaftT5

T11

TambΩ

T1

T4

T3

T2

45º

Free end (FE) GFB

g

45º

Ω

T6

T7

T8

T9

Drive end (DE) GFB

g

Insulated safety cover

Cooling air

Overall 15 thermocouples for GFB cartridge outboard, Bearing support housing surface, Drive motor, Test rig ambient, and Cartridge heater temperatures Two noncontact infrared thermometers for rotor surface temperature

31

50 ° 5 thermocouple locations:Θ = 22°, 94°, 166°, 238°, 310° along bearing mid-plane

Θ

Bearing sleeve Top foilBump strip layer

Ω

Spot weld

310°

94° 166°

22° 238°

X

Y

g Machined axial slot Bearing mid-plane

Oblique view

Thermocouples in test GFB

five (5) thermocouples placed within machined axial slots.

at

Foster-Miller FB uncoated (Generation II)

32

1

10

100

0 10 20 30 40 50 60 70 80Coast down time [sec]

Rot

or s

peed

[krp

m]

No heatingThs=100ºCThs=200ºCThs=300ºCThs=360ºC

Time to coast down rotorBaseline,

Heater up to 360C.No forced cooling

Coastdown time lesser as rotor heats (reduced clearance)


Exponential decay

Long time to coastdown :

very low viscous drag

(no contact between rotor and

bearings)

Test Data

Effect of shaft temperature

Coastdown time (s)

Speed (krpm)

0

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25 30 35Rotor speed [krpm]

Tem

pera

ture

rise

[°C

]

No cooling

50 LPM

Test data

Predictions

Error bar

Max.Avg.Min.

predictions & test data

FB OD temperature rises with rotor speed and decreases with forced cooling stream ~ 50 LPM. Predictions agree with test data

Room temperature 21 °C.

static load ~ 6.5N

Test data & predictions

Bearing outboard temperatureDrive end FB

Heater OFF

Rotor speed : 30 krpmw/o and w low cooling

Free End Drive End

T11 T12

T1 T6

rotor speed (krpm)

45 °

Bearing cartridge

Top foil

Bump strip layer

Spot weld

X

Y

g

Θ

Ω

Hot shaft (Isothermal)

Heat flux (Shaft → bearing)

34

Free End Drive EndNo heating

T11=37º C T12=26º C

Free End Drive End

T11=157º C T12=107º C

Ths=360º C

Free End Drive End

T11=92º C T12=70º C

Ths=200º C

FH

FV

DH

DVg

DH

0

10

20

30

40

50

0 5 10 15 20 25 30

Speed [krpm]

Am

plitu

de [μ

m, 0

-pk]

No heatingThs=100ºCThs=200ºCThs=300ºCThs=360ºC

Baseline. Heater to 360C. No forced cooling


As heater T increases to 360ºC, peak motion amplitude decreasesin speed range 7 krpm to 15 krpm

System natural frequency

Rotor 1X motionsD

H

Drive End (H)

Test Data

1X response as rotor heats

speed (krpm)

Tests

35

predictions & tests

As heater temperature raises, rotor amplitude decreases for speed < 15 krpm & the critical speed increases from 14 krpm to 17 krpm

0

10

20

30

40

50

0 5 10 15 20 25 30

Rotor speed [krpm]

Am

plitu

de [μ

m, 0

-pk]

Cartridge heater temperature increasesThs=360ºC

Ths=200ºC

No heating

Predictions

Test data

Baseline. Heater to 360C. No forced cooling

Drive End (H)

Rotor speed (krpm)

1X rotor response


predictions & tests

FB cartridge temperature increases linearly with shaft temperature

Supply air (TSupply) ~ 21 °C.0

20

40

60

80

100

0 25 50 75 100 125

Shaft temperature rise [ºC]

Bea

ring

tem

pera

ture

rise

[ºC

]

0

20

40

60

80

100

0 25 50 75 100 125


Bea

ring

tem

pera

ture

rise

[ºC

]

Test dataPredictions

DE Bearing Temp

Test data

Predictions

FE Bearing Temp

static load ~ 6.5N

static load ~ 3.5N

Test data & predictionsShaft temperature rise (C)

Heater up to 360C.

Rotor speed : 30 krpmNo cooling flow

Bearing outboard temperature

Free End Drive End

T11 T12

T1 T6

37

AIR SUPPLY

Gas pressure Max. 100 psi

Cooling flow needed for thermal

management: to remove heat from

shear drag or to reduce thermal

gradients in hot/coldengine sections

Cooling gas flow into GFBs

heater

38

AIR SUPPLY


Heater warms unevenly rotor.

Side cooling cools unevenly

rotor and also heater


heater

39

Free End Drive End

No heating

T11 T12

T1 T6

Heating of rotor

0

2

4

6

8

10

12

14

16

0 10 20 30 40 50 60Time [sec]

Tem

pera

ture

rise

[ºC

]

Baseline imbalance, No side flow & 50 L/min

T1-Tamb

T11-Tamb

T6-Tamb

T12-Tamb

10 krpm 20 krpm 30 krpm

: Temp. drop due to 50L/min cooling flow

Bearing cartridge and rotor temperatures

increase steadily with time

Rotor speed makes rotor and bearings hotter

Cooling flow removes heat from shear dissipation in rotor, most

effective at high speedHeater OFFTest Data

Rotor speed : 10, 20, 30 krpm

Test time (min)

Effect of rotor speed and side cooling

40

0

50

100

150

200

250

300

350

400

0 20 40 60 80 100 120

Time [min]

Hea

ter

tem

pera

ture

, Th

[ºC

] Free End Drive End

T11 T12

T1 T6Th

Heater power is limited

Cooling>100 LPM cools both rotor & HEATER!

21C 100C 200C 300C 360C

No cooling & 50L/min

100L/min

150L/min

Effect of cooling flowHeater temperature

Test Data

Heater up to 360C

Rotor speed : 30 krpmw/o & w cooling flowsHeater temperature increases

Test time (min)

41

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120

Time [min]

Tem

pera

ture

ris

e [º

C]

Free End Drive End

T11 T12

T1 T6Th

High temp. (heater up to 360C).Cooling flow up to 150 L/min

rotor speed : 30 krpm

Cooling effective > 100 LPM and when heater at highest temperature

T1-Tamb

T1-Tamb

T1-Tamb

T6-Tamb

T6-Tamb

T6-Tamb

21C 100C 200C 300C 360C

Cooling flow increases

Effect of cooling flowBearings OD temperatures

Test Data

Heater temperature increases

Test time (min)

42

0

5

10

15

20

25

30

35

0 50 100 150

Cooling flow rate [L/min]

Tem

pera

ture

rise

[ºC]

Free End Drive End

T11 T12

T1 T6Th

Effect of cooling flow

Cooling flow increases

T1-Tamb

T6-Tamb


200C

100C

No heating

Bearing OD temperature decreases with cooling flow

Turbulent flow > 100 LPM

Bearing cartridge temperature

Test Data

Cooling flow (LPM)

High temp. (heater up to 360C).Cooling flow to 150 LPM

rotor speed : 30 krpm

43

1

10

100

0 10 20 30 40 50 60 70 80

Coast down time [sec]

Rot

or s

peed

[krp

m]

Cond. #7: No cooling, No heatingCond. #8: 50 L/min cooling, No heatingCond. #9: No cooling, Ths=360ºCCond. #10: 50L/min cooling, Ths=360ºC

Effect of cooling flow

No heating

360C

50 L/min

No cooling

Coastdown time down by 20% (13 s) with cooling at 50 LPMTest Data

Coastdown time (s)

Rot

or s

peed

(krp

m)

Time to coast down rotor

As cooling flow rate increases, FB cartridge temperature decreases. Predictions agree with test data.

0

10

20

30

40

50

60

0 20 40 60 80 100


Bea

ring

tem

pera

ture

rise

[ºC

]

Test data

Predictions

No cooling

50LPM

150 LPM

125LPM100LPM

static load ~ 6.5N

Supply air (TSupply) ~ 21 °C.

Heater up to 360C.

Rotor speed : 30 krpmw/o & w cooling flow


DE Bearing temperature rise

Predictions & testsBearing cartridge temperature

Shaft temperature rise (C)

Free End Drive End

T11 T12

T1 T6Th

45

Post-test condition of rotor and GFBsBefore operation

Before operation

FE DEAfter extensive heating with rotor spinning

After extensive hearing with rotor spinning tests

FE DE

UNCOATED top foil !

Wear marks on top foils are at side

edges

Rotor shows polishing marks at bearing

locations. Deep wear marks at outboard edges

Static load directionStatic load

direction

46Test foil bearings continue to survive high temperature & high vibration operation!

Test data & predictionsAmplitudes of rotor synchronous motion proportional to

added imbalances.

Thermal management with axial cooling streams is beneficial at high temperatures and with large flow rates ensuring turbulent flow conditions.

As rotor and bearing temperatures increase, air becomes more viscous and bearing clearances decrease; hence coastdown time decreases.

For operation with hot shaft, amplitude of rotor motion drops while crossing (rigid body mode) critical speed.

47

48







49

The computational program

Code: XL_GFB_THD

• Windows XP 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

Delivered on June 2009

50

Graphical User Interface

Worksheet: Shaft & Bearing models (I)

51


Worksheet: Shaft & Bearing models (II)

52


Worksheet: Top Foil and Bump Models

Box 8

Box 9

Box 10

53


Worksheet: Foil Bearing (Operation and Results)

54

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35 40 45 50

Rotor speed [krpm]

Jour

nal e

ccen

trici

ty [μ

m]

-100

-80

-60

-40

-20

0

20

40

60

80

100

Jour

nal a

ttitu

de a

ngle

[deg

]

Cartridge heater temperature increases

No heating

Ths=360ºC

Ths=200ºC

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40 45 50

Rotor speed [krpm]M

inim

um fi

lm th

ickn

ess

[μm

]0

2

4

6

8

10

12

14

16

18

20

Dra

g to

rque

[N-m

m]


No heating

Ths=200ºC

Ths=360ºC

Static load parametersstatic load ~ 6.5 N

No cooling flow

As temperature increases, journal attitude angle and drag torque increasebut journal eccentricity and minimum film thickness decrease due to reduction in operating clearance

Drive End FB

Predictions

Predictions

Rotor speed (krpm) Rotor speed (krpm)

Free End Drive End

T11 T12

T1 T6Th

55

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

0 5 10 15 20 25 30 35 40 45 50

Rotor speed [krpm]C

ross

-cou

pled

stif

fnes

s [M

N/m

]

0

1

2

3

4

5

6

7

8

0 5 10 15 20 25 30 35 40 45 50

Rotor speed [krpm]

Dire

ct s

tiffn

ess

[MN

/m]

No heating

KXY

KYX


Ths=200ºC

Ths=360ºC

No heating

KXX

KYY


Ths=200ºC

Ths=360ºC

As temperature increases, stiffnesses (KXX, KYY) increase significantly, while difference (KXY-KYX) increases slightly at low rotor speeds and decreases at high rotor speeds

static load ~ 6.5 NNo cooling flow

Drive End FB

Predictions

Bearing stiffnesses Predictions


56

0

0.5

1

1.5

2

2.5

3

0 5 10 15 20 25 30 35 40 45 50

Rotor speed [krpm]

Dire

ct d

ampi

ng [k

N-s

/m]

-1.5

-1

-0.5

0

0.5

1

1.5

0 5 10 15 20 25 30 35 40 45 50

Rotor speed [krpm]C

ross

-cou

pled

dam

ping

[kN

-s/m

]

As temperature increases, damping (CXX, CYY) increase. Cross damping (CXY,CYX) change little above 30 krpm.

CYX

CXY

No heatingThs=200ºC

Ths=360ºCNo heating

CYY

CXX


Ths=200ºC

Ths=360ºC


static load ~ 6.5 NNo cooling flow

Drive End FB

Bearing damping Predictions

Predictions


57

0

50

100

150

0 100 200 300 400

Cooling flow rate [lit/min]

Peak

tem

pera

ture

[° C

]

40,000 rpm

20,000 rpm

Outer cooling flow

Inner and outer cooling flows

Laminar flow Turbulent flow

Re D

= 23

00

Cooling flow rate increases

No cooling flow

Predictions on effect of cooling flow

Peak temperature drops with strength of cooling stream. Sudden drop at ~ 200 lit/min b/c of transition from laminar to turbulent flow

Supply air (TSupply), shaft (TS), and bearing OD (TB)

temperatures at 21 °C.

Static load =89 N (180°).

TSupply=21°C

Predictions

Rotor speed : 20 & 40 krpm

58

0

20

40

60

80

100

Tem

pera

ture

rise

[°C

]

Top foil

Bump layer

Hollow shaft

Bearing housing

External fluid dӨ

RSi RSo RFi RFo RBi RBoTCi T∞

TBoTBiTFoTSoTSi TFi

Tf

Radial directionTCo

With forced cooling, GFB operates 50 °C cooler. Outer cooling stream is most effective in removing heat

Predictions radial temperature

Natural convection on

exposed surfaces of bearing OD and

shaft ID

Mean temperature

No coolingShaft temp. rise=79 °C

50 L/minShaft temp. rise=67 °C



Cooling stream increases

DE FB

Rotor speed : 30 krpmw/o & w cooling flow

Model

Model predictions

59

60






• Work with MiTi Bearings• Closure & added value San Andrés, L., Ryu, K., and Kim, T.H., 2011, “Identification of Structural Stiffness and Energy

Dissipation parameters in a 2nd Generation Foil Bearing; Effect of Shaft Temperature”, ASME J. Eng. Gas Turbines Power, vol. 133 (March) , pp. 032501

61

Top foil

Cartridge sheet

Bumps

FB nominal dimensions

0.160CNominal radial clearance [mm]

36.84DJShaft diameter [mm]

38.135DTBearing Top foil inner diameter [mm]

5.08rBBump arc radius [mm]

0.127tTTop foil thickness [mm]0.394hBump height [mm]

0.102tBump foil thickness [mm]

3.3022loBump length [mm]

4.318sBump pitch [mm]

24× 3NBNumber of bumps

25.40LAxial bearing length [mm]

44.64DOCartridge outer diameter [mm]

37.98DCartridge inner diameter [mm]

ValueSymbolParameter [Dimension]

Two generation II GFBsThree (axial) bump strip layers, each with 24 bumps.Korolon® 800 coating (up to 800°F) on top foil surface.

MiTi Korolon® foil bearing

62

-30

-20

-10

0

10

20

30

-200 -150 -100 -50 0 50 100 150 200

Static load [N]

Bea

ring

disp

lace

men

t [µm

]

Test 1Test 2Test 3

e

Push load

Release

Pull load

Release

Tests 1-3: Three cycles

MiTi® FB deflection versus static load

Top foil spot weldg

Direction of static load

Displacement sensor

F ≠ K XNonlinear F(X)

: Stiffness hardening

Large hysteresis loop : Mechanical energy dissipationdue to dry-friction between top foil contacting bumps and bump strip layerscontacting bearing cartridge sheet

Room temperature testsLathe chuck

Live center

Test bearing

Rotor

Load cellEddy current

sensor

90° bearing orientation

Shaft OD 36.56 mm: Highly preloaded FB

FB fitted smoothly into 3.08 mm thick bearing shell

63

MiTi® FB structural stiffness

0

5

10

15

20

25

-30 -20 -10 0 10 20 30

Bearing displacement [µm]

Stru

ctru

al s

tiffn

ess

[MN

/m]

Pull load

Push load

y = 0.015x3 + 0.0604x2 + 2.7284x + 39.694R2 = 0.9718

y = 0.0127x3 + 0.0872x2 + 3.761x + 2.3845R2 = 0.987

-200

-150

-100

-50

0

50

100

150

200

-30 -20 -10 0 10 20 30


Stat

ic lo

ad [N

]

Pull loadPush loadPoly. (Pull load)Poly. (Push load)

e

Cubic polynomial curve fit over span of applied loads

F=F0+K1X+K2X2+K3X3

K=K1+2K2X+3K3X2

Distinctive hardening effect as FB deflection increases

Room temperature tests

64

Room temperature tests

-120

-90

-60

-30

0

30

60

90

120

-200 -100 0 100 200

Static load [N]

Bea

ring

disp

lace

men

t [µm

]

Test 1Test 2Test 3

Push load

Release

Pull load

Release Tests 1-3: Three cycles

MiTi® FB deflection versus static loadLathe chuck

RotorDE Test bearing

Eddy current sensor

Live center

FE Test bearing

Load cell

FB sliding fit without play in 3.08 mm thick bearing shell!

Top foil spot weldg

Direction of static load

Displacement sensor

0

1

2

3

4

5

6

7

8

-120 -90 -60 -30 0 30 60 90 120


Stat

ic lo

ad [N

]

Pull loadPush load

ROTOR OD 36.46 mm

90° bearing orientationIdentified from Cubic polynomial curve fit

65

MiTi® FB test setup for dynamic loads

Bearing housing

Eddy current sensor

Load cell

Test shaft

Cartridge heaterThermocouples

Shaker

Single frequency dynamic load in

horizontal direction

Test bearing

Bearing housing

Index fixture


Uncoated rigid, non-rotating, hollow shaft supported on FB.

0.785 (load cell + attachment hardware)Bearing Mass M, kg23, 103, 183, and 263Shaft Temperature, °C

50-200 (increment: 25 Hz)Frequency Range, Hz7.4, 11.1, 14.8, and 18.5FB Displacement controlled [µm]

FB press fitted onto 15.5 mm thick bearing

housing!

Shaft OD 36.56 mm

66

134 mm

Ø 25 mm

Indexing fixture chuck

76 mm

Ø 25.4 mm

Shaft heating using electric heater

Ø 36.56 mm

Th

Th

Th

T1

T1

T1

T2

T2

T2

T4

T4

T4

T3

T3

T3

0

50

100

150

200

250

300

1 2 3

Heater set temperature (Th) [°C]

Tem

pera

ture

[°C]

Th=103°C Th=183°C Th=263°C

T1T2T3 Th

Significant temperature

gradient along shaft axis.

Cartridge heater warms unevenly

shaft

T4

Steady state temperature (heater 1 hr operation)

MiTi BBearing housing

67

Parameter Identification (no shaft rotation)

( )eq tM x K x C x F+ + =

Meq

Keq

Ceq

Fext

x

Equivalent Test System: 1DOFK stiffness, Ceq viscous damping OR γ loss factor

Harmonic force & displacements

Impedance Function

( ) i tx t X e ω=( ) i tOF t F e ω=

2( )Oeq

FZ K M i CX

ω ω= = − +

Viscous Dissipationor dry-friction Energy

2dis eqE C Xπω=

2disE K Xπ γ=

68

Effect of temperature on dynamic stiffness

Th = 23°C Th = 263°C

-4

-2

0

2

4

6

8

10

0 100 200 300 400

Frequency [Hz]

Real

par

t of i

mpe

danc

e F/

X [M

N/m

]

7.4 µm11.1 µm14.8 µm18.5 µm

7.4 µm

18.5 µm

FB motion amplitude increases

-4

-2

0

2

4

6

8

10

0 100 200 300 400

Frequency [Hz]

Rea

l par

t of i

mpe

danc

e F/

X [M

N/m

]7.4 µm11.1 µm14.8 µm

7.4 µm

14.8 µm

FB motion amplitude increases

2Re ( )OF K MX

ω⎛ ⎞ = −⎜ ⎟⎝ ⎠

Motion amplitude increases




Real (F/X) decreases with FB motion amplitude & increases with shaft temperature.

69

Th = 23°C, 90° bearing orientation

Highly preloaded FB: K decreases as FB motion amplitude increases due to decrease in # of active bumps

4

4.5

5

5.5

6

6.5

7

7.5

8

8.5

9

0 50 100 150 200 250

Frequency [Hz]

Stru

ctur

al s

tiffn

ess

[MN

/m]

7.4 µm11.1 µm14.8 µm18.5 µm

0

2

4

6

8

10

12

14

16

18

20

0 5 10 15 20


Stru

ctru

al s

tiffn

ess

[MN

/m]

Static pull loadStatic push loadDynamic load at 50 Hz

2Re OFK MX

ω⎛ ⎞= +⎜ ⎟⎝ ⎠

2Re 50OFK M at HzX

ω⎛ ⎞= +⎜ ⎟⎝ ⎠

Dynamic structural Kcompared to static structural K


Dynamic load

Static load

At larger FB deflections, static K is larger than dynamic K

Effect of temperature on structural stiffness

70

FB stiffness & viscous damping

4

4.5

5

5.5

6

6.5

7

7.5

8

8.5

9

0 50 100 150 200 250

Frequency [Hz]

Stru

ctur

al s

tiffn

ess

[MN

/m]

23ºC103ºC183ºC263ºC

2Re OFK MX

ω⎛ ⎞= +⎜ ⎟⎝ ⎠

FB motion amplitude: 14.8 µm

TEST FB cartridge OD is constrained within bearing housing.FB radial clearance decreases as shaft temperature raises!

FB stiffness and viscous damping increase with shaft temperature and decrease with excitation frequency.


0

1

2

3

4

5

6

7

8

0 50 100 150 200 250

Frequency [Hz]

Equi

vale

nt v

isco

us d

ampi

ng [k

Ns/

m]


Im O

eq

FXC

ω

⎛ ⎞⎜ ⎟⎝ ⎠=


Effect of temperature on stiffness & damping

71

Loss factor vs frequency

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100 150 200 250

Frequency [Hz]

Stru

ctur

al lo

ss fa

ctor


FB motion amplitude: 14.8 µm


Structural (material) loss factor best represents energy dissipation in FB

The FB loss factor increases with excitation frequency and decreases slightly with shaft temperature. More damping expected in rotordynamic measurements

eqCK

ωγ =

Effect of temperature on loss factor γ

72

This material is based upon work supported by NASA GRC and the TAMU Turbomachinery Research Consortium (TRC)

EFFECT OF COOLING FLOW ON THE OPERATION EFFECT OF COOLING FLOW ON THE OPERATION OF A HOT ROTOROF A HOT ROTOR--GAS FOIL BEARING SYSTEMGAS FOIL BEARING SYSTEM

Texas A&M University Mechanical Engineering Department

Chair of Advisory Committee: Dr. Luis San Andrés

Ph. D. Final Exam

Keun Ryu

Nov. 23, 2010

74

Objective

Quantify effect of cooling flow and shaft temperature on the rotordynamic performance of a GFB supported rotor. Investigate adequate thermal management strategies using forced cooling flow into the GFBs

75

Research tasks• Revamp a GFB rotordynamic test rig for operation at high speed and extreme temperatures• Measure temperature of bearings and rotor and the motions of rotor for increasing rotor speeds, shaft temperatures, and cooling flow rates• Quantify effect of gas flow on cooling bearings (max. 500 L/min)• Compare the experimental results (rotor responses and bearing temperatures) to predictions from an in-house computational program

76

TAMU Hot rotor-GFB test rig

Gas flow meter (Max. 500 LPM). Drive motor (max. 50 krpm)

Instrumentation for high temperature

Free end rotor temperature (TrFE)

Free end rotor temperature (TrDE)

T5

Drive motor

Infrared thermometers

Flexible coupling

GFB support housing

FEGFB

Hollow rotor

Th (Reference thermocouple to

control heater temperature)

Infrared tachometer

Cartridge heater

Displacement sensors

DEGFB

T10

Cooling air supply for coupling

Td (under cover)

Tout

77

AIR SUPPLY


Cooling flow needed for thermal

management: to remove heat from

shear drag or to reduce thermal

gradients from hotto cold engine

sections


heater

78

AIR SUPPLY


Heater warms unevenly test

rotor.Side cooling

flows cool unevenly the

rotor.


heater

79

Dykas (2006): Investigates thermal management in foil thrust bearings. Cooling flow rates, to 450 L/min, increase bearing load capacity at high rotor speeds. Inadequate thermal management can give thermo-elastic distortions affecting load capacity of test FB

Overview – Thermal management

Radil et al (2007): Evaluate effectiveness of three cooling methods (axial cooling, direct and indirect shaft cooling) for thermal management in a hot GFB environment

Component-level tests

DellaCorte (1998): No cooling flow. 3rd gen. GFB up to 70 krpm (2.4 MDN) at 700C. Bearing load capacity and torque decrease with temperature because of reduced bearing preload.

Ruscitto et al (1978): Perform load capacity tests on 1st gen. GFB up to 45 kprm (1.7 MDN) and static load 111 N with 110 L/min cooling flow at 315Cbearing temperature.

80

Heshmat et al (2005): Demonstrates hot (650C) GFB operation in a turbojet engine to 60 krpm. Cooling flow rates to 570 L/min still give large axial thermal gradients (13ºC/cm)

Overview – Thermal management

San Andrés et al (2009): Forced cooling flow has limited effectiveness at low rotor temperatures. At high test temperatures, large cooling flows (turbulent) remove heat more efficiently.

Gases have limited thermal capacity, hence (some) bearings demand large cooling flows to remove heat from hot rotor sections.

System-level tests

LaRue et al (2006): Oil-free Turbocharger. Thermal management achieved by cooling the TC rotor and FBs.

Lubell et al (2006): Commercial oil-free micro-turbines. Cooling air flows axially through hollow rotor ID remarkably decrease rotor temperature.

81

Why thermal effects are important?

Gas bearings (when airborne) are nearly friction free, hence the show small (drag) power loss and temperature raise. With hot rotors the “lubricant” in the bearings must also cool components. But gases have small thermal capacity and conductivity, and hence, get hot! Rises in temperature change material properties (solids and gas), and most importantly, change bearing clearance!

82

0

50

100

150

200

250

300

350

400

450

500

550

600

650

0 20 40 60 80 100 120 140 160 180 200Time [min]

Tem

pera

ture

[ºC

]

FE rotor (TrFE)DE rotor (TrDE)Heater (Th)

RBS failureFree end rotor OD

(Tr FE)

Drive end rotor OD (Tr DE)

Heater(Th)

Heater off Ths=200ºC Ths=400ºC Ths=600ºC

0

20

40

60

80

100

120

0 20 40 60 80 100 120 140 160 180 200Time [min]

Tem

pera

ture

[ºC

]

T1

T2

T3

T4

T4

T2T1

T3 RBS failure

Heater off Ths=200ºC Ths=400ºC Ths=600ºC

Pressure

Lesson from previous demonstrationNO COOLING FLOW!!

Damaged foil bearing

12/2009: HT GFB test

83

Test Gas Foil Bearing

Test Gas Foil Bearing (Bump-Type)1st Generation. Diameter: 36.63 mm

Foil material: Inconel X-750

Reference: DellaCorte (2000)Rule of Thumb

2010: GFBs donated by KIST

Bumps Top foil

Hollow rotor (Inconel 718): 1.360 kg. Length: 200.66 mm. OD36.51 mm and ID 17.9 mm. HT Coating up to 400C

UNCOATED TOP Foil !

84

Foil Bearing Dimension

67Bump arc angle [deg]2.25Bump arc radius, rB

0.50Bump height, hB

2.5Bump length, lB

4.4Bump pitch, So

26 × 1 axial Number of Bumps0.12Bump foil thickness0.12Top foil thickness38.1Top foil axial length

Top foil and bump strip layer37.95Inner diameter50.8Outer diameter

Bearing cartridgeParameter [mm]

Foil material: Inconel X-750

KIST FB uncoated (Gen. I)

Top foil

Bearing sleeve

Bump strip layer

lB

rB

hBsO

αRuler: 0.5 mmEach graduation

85

FB deflection versus static load

Hysteresis loop : Mechanical energy dissipationdue to dry-friction between top foil contacting bumps and bump strip layerscontacting bearing cartridge

Room temperature tests: Estimation of bearing clearance

-350

-300

-250

-200

-150

-100

-50

0

50

100

150

-200 -150 -100 -50 0 50 100 150

Static load [N]

Bea

ring

dis

plac

emen

t [um

]

DE bearing

FE bearing

FB diametrical clearance~ 200 µm

Load – deflection tests(Cyclic loading & unloading)

F ≠ K XNonlinear F(X)


86

Oblique view

Thermocouples in test GFB

Four (4) thermocouples placed within machined axial slots.KIST FB uncoated (Generation I)

Thermocouple (Bearing mid-span)

3 m

m5 mm

g

Free end (FE) bearing

45º

T4

T1

T2

T3

Drive end (DE) bearing

g45º

T9

T6

T7

T8

TrFE

T1~T4

Th GFBs

Free End (FE)

Drive End(DE)

TrDE

T6~T9

87

Thermocouples in bearing housing

1 in housing duct + 1 at outboard plane of free end bearingForced cooling stream temperature

Rotor (free end)

ToutBearing support housing

Heater

Gas foil bearing(Rotor free end)

Bearing housing

Duct Thermocouple (Td)

Rotor free end (FE)

Rotor drive end (DE)

Thermocouple (T5)Thermocouple (T10)

88

Hot rotor-GFB test rig

Dimensions

44.4

5

62.23

19.69

153.

04

144.78

15.9

0

17.9

0

254

50

180

200.66

DuctHollow rotor

Cartridge heater

15.90

17.90

44.45

36.51

Side viewHollow rotorCartridge

heater

GFB support housing

Free endGFB

Drive endGFB

Duct

5

Front view

Td

Th

Dimension [mm]

89

Hot rotor-GFB test rig

Instrumentation

Foil bearings

Cartridge heater Drive motor

Mass flow meterPressure gauge 2

Valve 2

FB Cooling flow path Shop compressed air

(up to 1 MPa)

Valve 1Valve 3

Pressure gauge 1

Pressure gauge 3

Heater temperature

controller

~208 V AC

Temperature digital panel meter

Thermocouples (K-type)

Displacement sensors

FFT Analyzer

Oscilloscopes

Signal conditionerTachometer

Data acquisition board

PC

Cooling air supply to coupling

FB Cooling air supply



~460 V AC

Motor controller

Tin

Thermocouples: 1 x heater, 3 x cooling air

2 x 4 FB outboard, 2 x Bearing housing2x Drive motor, 1 x ambient

+ infrared thermometers 2 x rotor surface (Total = 19)

90

Test Cases

Overall 1049 min

30503010010

30350301009

3035030658

3035030Off7

136350 → 250 → 150 → 50101506

266350 → 250 → 150 → 5010→ 20 → 301005

248350 → 250 → 150 → 5010→ 20 → 30654

108350 → 250 → 150 → 50 → 001503

84350 → 250 → 150 → 50 → 001002

87350 → 250 → 150 → 50 → 00651

Time [min]

Set cooling flow rate(into two bearings) [L/min]

Rotor speed [ krpm]

Heater set temperature [ºC]

Test case #

91

Rotor OD Temps. vs Time

Heater set temperature = 150ºC

Test cases #1 and #4

Temperatures on shaft ODincrease steadily with

elapsed test time at each rotor speed and

cooling flow rate condition

No rotor spinning

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120

Time [min]

Tem

pera

ture

ris

e [ºC]

-1600-1450-1300-1150-1000-850-700-550-400-250-10050200350500

Coo

ling

flow

rat

e [L

/min

]

Tr FE

Tr DE

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120 140

Time [min]

Tem

pera

ture

ris

e [º

C]

-1600-1450-1300-1150-1000-850-700-550-400-250-10050200350500

Coo

ling

flow

rat

e [L

/min

]Tr FE

Tr DE

10 krpm

TrFE

T1~T4

Th GFBs

Free End (FE)

Drive End(DE)

TrDE

T6~T9

The rotor is a source of HEAT!

Thermal gradientHot to cold

FE rotor >DE rotor

92

Duct & Outboard temperature rises vs time



Tin ~ TambTd > Tout > Tin

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120

Time [min]

Tem

pera

ture

ris

e [ºC]

-1600-1450-1300-1150-1000-850-700-550-400-250-10050200350500

Coo

ling

flow

rat

e [L

/min

]

T out

T d

T in

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120 140

Time [min]

Tem

pera

ture

ris

e [º

C]

-1600-1450-1300-1150-1000-850-700-550-400-250-10050200350500

Coo

ling

flow

rat

e [L

/min

]

T outT d

T in

10 krpm

No rotor spinning

TrFE

Td

TrDE

DuctTh

Bearing housing

Tout

93

FE bearing temperature rise vs time

Heater set temperature = 150ºCFree End Bearing

Mid-plane

T1 T3

T4

T2

T1 T3

T4

T2

T1 T3

T4

T2


0

10

20

30

40

50

60

70

0 20 40 60 80 100 120 140

Time [min]

Tem

pera

ture

ris

e [º

C]

-1600-1450-1300-1150-1000-850-700-550-400-250-10050200350500

Coo

ling

flow

rat

e [L

/min

]

T 1

T 3

T 2

T 4

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120

Time [min]

Tem

pera

ture

ris

e [º

C]

-1600-1450-1300-1150-1000-850-700-550-400-250-10050200350500

Coo

ling

flow

rat

e [L

/min

]

T 4

T 3

T 1

T 2

No rotor spinning

T3>T2>T4>T1 due to differences in rotor OD temp. along its circumference

Rotor speed makes bearings slightly hotter (a few deg C)

10 krpm

94

Bearing temperature rise vs duct temp.


Free end BearingTemperatures on bearings ODs linearly

increase with duct air temperature as the cooling flow rate into the bearings

decreases


30 krpm0

5

10

15

20

25

30

0 5 10 15 20 25 30

Duct air temperature rise [ºC]

Bea

ring

tem

pera

ture

ris

e [ºC]

No cooling flow

230~280 L/min350~420 L/min

50~65 L/min150~170 L/min

No rotor spinning

0

5

10

15

20

25

30

0 5 10 15 20 25 30

Duct air temperature rise [ºC]

Bea

ring

tem

pera

ture

ris

e [ºC]

TrFE

Td

TrDE

DuctTh

Bearing housing

T1~T4 T6~T9

230~300 L/min

350~450 L/min

50~80 L/min

150~190 L/min

Cooling flow decreases


95

Rise in temperatures: Duct vs Rotor OD


TrFE

Td

TrDE

DuctTh

Bearing housing

Test cases #2 and #5 No rotor spinning

0

5

10

15

20

25

30

0 20 40 60 80 100

Rotor OD temperature rise [ºC]

Duc

t air te

mpe

ratu

re ris

e [ºC]

0

5

10

15

20

25

30

0 20 40 60 80 100

Rotor OD temperature rise [ºC]

Duc

t air te

mpe

ratu

re ris

e [ºC]

No cooling flow

230~280 L/min350~420 L/min

50~65 L/min

150~170 L/min

30 krpm



230~300 L/min

350~450 L/min

50~80 L/min

150~190 L/min

Td decreases with cooling flowdue to longer residence of air

particles in the duct

Td increases with rotor speeddue to windage effect

Td

Td

96

Bearing OD temperature rise vs. cooling flowTest cases #2 and #5

-10

-5

0

5

10

15

20

0 100 200 300 400 500


Tem

pera

ture

ris

e [º

C]

No rotor spinning10 krpm20 krpm30 krpm

T 1~4 -T d

Temperature difference (T-Td) is invariant

while increasing cooling flow rate!

Bearing temperature is a small fraction of the heat

source temperature (heater and duct air).

TrFE

Td

TrDE

DuctTh

Bearing housing

T1~T4 T6~T9

Free end Bearing


?

97

Rotor OD temp. vs heater temp. (- duct ???)Test cases #1~#3

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100 120 140

Temperature difference, (T h -T d ) [ºC]

Tem

pera

ture

diff

eren

ce [º

C]

350 L/min250 L/min150 L/min50 L/minNo cooling flow


No rotor spinning

The cooling gas flow removes heat from the top foil back

surface, thus cooling the

rotor OD

TrFE-Td

TrDE-Td

TrFE

Td

TrDE

DuctTh

Bearing housing

98

Rotor OD temp. vs heater temp.Test cases #4 and #5

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100 120 140

Temperature difference, (T h -T d ) [ºC]

Tem

pera

ture

diff

eren

ce [º

C] ~350 L/min

~250 L/min~150 L/min~50 L/min

Rotor OD temp (relative to duct

temp Td)decrease with

cooling flow

30 krpm

TrFE-Td

TrDE-Td

Cartridge temperature (Ths) increases TrFE

Td

TrDE

DuctTh

Bearing housing

99

Cooling Capability: Bearing OD temp.Test cases #2 and #5

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0 100 200 300 400 500



[ºC

/L/m

in]

Tem

pera

ture

ris

e C

oolin

g flo

w r

ate


The cooling capability of the forced axial flow

on the bearing temperatures

changes little with flow rate

~ Constant


Free end Bearing

TrFE

Td

TrDE

DuctTh

Bearing housing

T1~T4 T6~T9

100

Cooling Capability: Rotor OD temp.Test cases #2 and #5

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 100 200 300 400 500



[ºC

/L/m

in]

Tem

pera

ture

ris

e C

oolin

g flo

w r

ate


The cooling capability of the forced axial flow on the rotor temperatures appears

to have an exponential decay character.

The cooling effectiveness of the forced cooling

stream is most distinct at the free end rotor OD.

TrFE

Td

TrDE

DuctTh

Bearing housing


Free end rotor

101Cooling flow rate does not affect amplitude and frequency contents of rotordynamic displacement

Waterfalls of rotor motion

Test case #4

1X

~250 min

2X3X

1X 2X 3X

1X 2X 3X

~350 L/min

~50 L/min

Cooling flow

~350 L/min

~50 L/min ~350 L/min

~50 L/min

30 krpm

20 krpm

10 krpm

Baseline, Ths=65C

Drive End (Horizontal)

FV

GFBs

DV

FH DH

g

Free of sub synchronous whirl motions

102

Rotor motion measurements

103

Baseline, Ths=150C

Rotor OD temperature does not affect rotor dynamic displacements!

Waterfalls of rotor motion Drive End (Horizontal)

Test case #6

1X

~135 min

2X 3X

~350 L/min Cooling

flow

10 krpm

DH

~50 L/min FV

GFBs

DV

FH DH

g

104

Synchronous rotor response: effect of shaft temp.

FV

GFBs

DV

FH DH

g Free End Drive End

TrFE=87º C TrDE=54º C

Ths=100ºC, 30 krpm, 350 L/min Free End Drive End

TrFE=33º C TrDE=32º C

Heater off, 30 krpm, 350 L/min

Test cases #7~#9

Flexible rotor mode at ~90 krpm (rap test)Critical speed (Rigid body mode) ~ 5 and 8 krpm

No major differences in responses between cold and hot Test cases #7~#9

0

10

20

30

40

50

60

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Speed [krpm]

Am

plitu

de [μ

m, 0

-pk]

Heater offThs=65ºC Ths=100ºC

0

10

20

30

40

50

60

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Speed [krpm]

Am

plitu

de [μ

m, 0

-pk]

Heater offThs=65ºC Ths=100ºC

DV DH

Speed down (16.7 Hz/s) Speed down (16.7 Hz/s)


105

GFB TEHD model By San Andrés and Kim (2008)

Material properties (gas & foils) = f (Temperature)Shaft thermal and centrifugal growthBearing thermal growth

Bearing clearance

Thermo-elastic deformation eqns.Finite Elements and discrete parameter for bump strips.Thermal energy conduction paths to side cooling flow and bearing housing.

Top foil & underspring

Reynolds eqn. for hydrodynamic pressure generation Energy transport eqn. for mean flow temperatureVarious surface heat convection modelsMixing of temperature at leading edge of top foil

Gas film

Excel GUI + executable licensed by TAMU

106106

Recap: test rotor and FB

Outer flow stream Top foil

Bearing housing “Bump” layerzx

PCo , TCo

Bearing housing

PaThin film flow

z=0 z=LT∞

Ω RSo

Heatsource

Th

Cooling stream

Hollow rotor

Hot air (out)

ambient

Schematic view of rotor and heater cartridge + side cooling stream

Natural convection on exposed surfaces

of bearing OD and shaft ID

107107

T∞

TBo

TBi

TFo

TSo

TSi

TFi

TCi

TO

Tf

→S CQ

SoQ

→BQ

→∞BQ

→F BiQ

→f FQ→S fQ

FQ→F OQ

→O BiQ

Top foil

Bump layer

Hollow shaft

Bearing housing

External fluid

ΩdӨ

RSi RSo RFi RFo RBi RBo

SiQ

Q =Rq

QCi

Heat carried by thin film

flow

Heat carried by outer flow

stream: Heat

(-): Heat

(+)

QB

QCo

Drag dissipation power (gas

film)

Heat carried by inner flow

stream

Heat conduction through shaft

TS

Heat flow paths in rotor - GFB systemHeat flows &

thermal resistances in a

GFB & hollow shaft

Heat conducted into

bearing

Cooling gas streams

carry away heat

108

Input:Measured ambient,

rotor OD & inlet cooling flow

temps.

Free end FB

0102030405060708090

100

0 25 50 75 100 125 150 175 200

Cooling flow rate per each bearing [L/min]

Tem

pera

ture

[ºC

]

30 krpm: Test30krpm: Prediction20 krpm: Test20 krpm: Prediction10 krpm: Test10 krpm: Prediction

predictions & testsBearing temperature

static load ~ 5.94 N

X

Y

Ωg

Heat fluxShaft OD → Bearing

Shaft OD → Cooling stream

Hot shaft(isothermal)

45º

Θ

Top foil leading edge

Top foil trailing edge

Thin film flow

Bump strip layer

Top foil

Bearing housing

External fluid Load

Predictions agree with test data!!

Test data

Predictions

109

predictions & testsBearing temperatureDrive end FB

X

Y

Ωg




45º

Θ



Thin film flow

Bump strip layer

Top foil

Bearing housing

External fluid Load

0102030405060708090

100

0 25 50 75 100 125 150 175 200

Cooling flow rate per each bearing [L/min]

Tem

pera

ture

[ºC

]

30 krpm: Test30krpm: Prediction20 krpm: Test20 krpm: Prediction10 krpm: Test10 krpm: PredictionTest data

Predictions

static load ~ 7.39 N

Predictions follow test data: better at DEB since smaller temperature gradient along heater axial length

110110

Predictions: Temperature fields

Shaft = 80CCooling stream inlet = 33C

1.0

14.0

27.0

40.053.0

66.079.0

S1 S5 S9S1

3

36.0038.0040.0042.0044.0046.0048.0050.0052.0054.0056.0058.0060.00

Circ coordinate [deg]

Axial coordinate

Circumferential angle [deg]

104163

225281

34040

Axial node number

1 5 10 15

45

Film

tem

pera

ture

[ºC

]

Test case #5Ths=100C,30 krpm, Free end bearing

Cooling flow 175 L/min

X

Y

Ωg




45º

Θ



Thin film flow

Bump strip layer

Top foil

Bearing housing

External fluid Load

14.0

27.0

40.053.0

66.079.0

S1 S5 S9 3

36.0038.0040.0042.0044.0046.0048.0050.0052.0054.0056.0058.0060.00

Circ coordinate [deg]

Circumferential angle [deg]

104163

225281

34040

Axial node number

1 5 10 15

45

Film

tem

pera

ture

[ºC

]

Cooling flow 25 L/min

Shaft = 56CCooling stream inlet = 41C

Fresh gas enters

Fresh gas enters

Shear mechanical energy generated

Shear mechanical energy generated

111111GFB rotorydnamic force coefficients do not change with the strength of cooling flow rate

static load 5.94 NFree End FB

Bearing stiffnesses predictions

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

5 10 15 20 25 30 35

Rotor speed [krpm]

Dir

ect s

itiff

ness

[MN

/m]

Kxx, 175 L/min Kxx, 125 L/minKxx, 75 L/min Kxx, 25 L/minKyy, 175 L/min Kyy, 125 L/minKyy, 75 L/min Kyy, 25 L/min

K xx

K yy

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

5 10 15 20 25 30 35

Rotor speed [krpm]

Cro

ss-c

oupl

ed s

itiff

ness

[MN

/m]

Kxy, 175 L/min Kxy, 125 L/minKxy, 75 L/min Kxy, 25 L/minKyx, 175 L/min Kyx, 125 L/minKyx, 75 L/min Kyx, 25 L/min

K xy

K yx

X

Y

Ωg




45º

Θ



Thin film flow

Bump strip layer

Top foil

Bearing housing

External fluid Load

Kxx > Kyy

112112

Free End FB

Bearing damping predictions

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

5 10 15 20 25 30 35

Rotor speed [krpm]

Dir

ect d

ampi

ng [k

N-s

/m]

Cxx, 175 L/min Cxx, 125 L/minCxx, 75 L/min Cxx, 25 L/minCyy, 175 L/min Cyy, 125 L/minCyy, 75 L/min Cyy, 25 L/min

C x

C yy

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

5 10 15 20 25 30 35

Rotor speed [krpm]

Cro

ss-c

oupl

ed d

ampi

ng [k

N-s

/m]

Cxy, 175 L/min Cxy, 125 L/minCxy, 75 L/min Cxy, 25 L/minCyx, 175 L/min Cyx, 125 L/minCyx, 75 L/min Cyx, 25 L/min

C yx

C xy

X

Y

Ωg




45º

Θ



Thin film flow

Bump strip layer

Top foil

Bearing housing

External fluid Load

static load 5.94 N

GFB rotorydnamic force coefficients do not change with the strength of cooling flow rate.

Cxx > Cyy

113A linear rotordynamics software (XLTRC2®) models test rotor – GFBs system and predicts the rotor synchronous responses

Shaft11 2 3

4

5 6 7 8 9 10 11 12 13 14 15Shaft1

16

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0 0.04 0.08 0.12 0.16 0.2 0.24Axial location [m]

Shaf

t rad

ius

[ m]

Flexible coupling

Foil bearingsupports

Foil bearingsDrive end Free end

Imbalance planes

Coupling added mass and inertia

XLGFBTHpredicts synchronous bearing

force coefficients

FE Model of Test Rotor-Bearing System

114

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35Rotor speed [krpm]

Nat

ural

freq

uenc

y [k

rpm

]

Cylindrical mode

Conical mode

1st critical speed

2nd critical speed

Damped Eigenvalue Mode Shape Plot

f=4215.2 cpmd=.0468 zetaN=4200 rpm

Damped Eigenvalue Mode Shape Plot

f=7146.3 cpmd=.5915 zetaN=7200 rpm

Damped Natural Frequency MapTest case #7, Heater off

115115

predictions & tests

The predicted rotor responses reasonably correlate with the measurements.

Forced cooling 175 L/min per bearing

1X rotor response

02468

101214161820

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Speed [krpm]

Am

plitu

de [μ

m, 0

-pk]

Test data

PredictionFree End (H)

FV

GFBs

DV

FH DH

g

Test cases #7~#9

116116

- GFB temperatures linearly increase with the inlet cooling air temperature.

- When the rotor spins, the bearing sleeve temperatures do not change with the cooling flow rate; albeit the rotor OD temperature increases with the strength of the cooling stream,

- The cooling effect of the forced external flows is most distinct when the rotor is hottest and at the highest rotor speed.

- Forced cooling flows do not affect the amplitude and frequencycontents of the rotor motions. The test system (rigid-mode) critical speeds and modal damping ratio remain nearly invariantfor increasing the rotor temperature and cooling flow strength.

Conclusions

117117

-A physics-based computational THD model predicts accurately measured FB OD temperatures for increasing shaft temperatures with cooling flow

- Rotordynamic analysis integrating predicted FB force coefficients reproduces recorded rotor dynamic responses with increasing cooling flow rate and shaft temperature.

Predictive tool validated & benchmarked to reliable test data base !!!

Conclusions

118

Major contribution

The present work provides the most complete to date measurements of GFB temperatures and rotordynamic response thereby extending the GFB knowledge database. Comprehensive experiments and benchmarking of predictive toolserve to advance GFB applications for use intohigh temperature microturbomachinery.

119






• Current work with MiTi Bearings• Added value & closure

120

NSF-Research Undergraduate Experience in Microturbomachinery & ManufacturingTo conduct hands-on training and research in mechanical, manufacturing, industrial, or materials engineering topics related to technological advances in microturbomachinery

To develop microturbines to enhance defense, homeland security, transportation, and aerospace applications.

(10 students /year) x 3 y NSF (06-09) $ 259 k

Added value to NASA Project

121

2009 REU MTM Program

Calvin CollegeMechanical EngineeringShane MullerREU student

Experimental Identification of Structural Stiffness and Damping in a 1st Generation Gas Foil Bearing for Oil-free MTM

Project #1

U. of Texas, San AntonioMechanical EngineeringJose CameroREU student

Measurement of Drag Torque, Power Loss, Friction Coefficient, Temperature, and Wear in a Foil Bearing & Coated Rotor System

Project #2

KIST FB

KIST FB (1st generation)

Oil inlet

Valve Open Valve Close

Rotor starts

Rotor stops

Constant speed ~50 krpm

Valve Open Valve Close

Rotor stops

Rotor starts

122

- To develop a physics-based computational modelof GFB including thermal effects

-To develop a fully tested and experimentally verified design tool for predicting GFB performance

- To measure the rotordynamic performance of aHOT rotor supported on GFBs

- To quantify the effect of feed gas flow on cooling GFBs

Closure: objectives accomplished

Predictive tool validated & benchmarked to reliable test data base !!!

123

Acknowledgments• NASA GRC: Drs. S. Howard & Dr. C. DellaCorte• Turbomachinery Research Consortium• NSF REUP• Capstone Turbine, Inc.• MiTi©, Foster-Miller• KIST: Korea Inst. Science & Technology• Honeywell Turbocharging Technologies

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

124

Back up slides

125





Bearing cartridge

MiTi(2nd gen.)

KIST(1st gen.)



126

Static load test setup

Lathe chuck

Test bearing

Eddy current sensor

Strain gauge type load cell

Test shaft

Cartridge heater

Steady static load (or unload) proportional to linear movement of lathe tool holder

Thermocouples

127

High temperature rotor

Inconel 718 shaft: photos taken by manufacturer (KIST) prior to machining of threaded holes at rotor ends and coating shaft at bearing locations.

KIST proprietary solid lubricant (400 ºC)

NO COST!

128

Closure Y2

ADDED VALUE: 08 & 09 Summer NSF-REU in microturbomachinery

educated six undergraduate students (US citizens).

Assess effects of temperature (to 160 C) on the structural properties of FB from static load (250 N) tests:

Loading and unloading tests show hardening nonlinearity and mechanical hysteresis.

FB structural stiffness reduces with temperature due to increase in bearing radial clearance (atypical).

Model predictions reproduce test data, when accounting for thermal effects in materials properties and components’expansion.

129

0

10

20

30

40

50

0 5 10 15 20 25 30

Speed [krpm]

Am

plitu

de [μ

m, 0

-pk]

DVDHFVFH

0

10

20

30

40

50

0 5 10 15 20 25 30

Speed [krpm]

Am

plitu

de [μ

m, 0

-pk]

DVDHFVFH

Baseline coastdown, No forced cooling

1X response with cold and hot rotor

Heater OFF Heater Ths=360C

Elastic rotor mode at 29 krpm (480 Hz) : soft coupling and connecting rodCritical speed (rigid body mode) ~ 13 krpm

Similar rotor responses for cold and hot rotor operation

Free End Drive EndNo heating

T11=37º C T12=26º C

Free End Drive End

T11=157º C T12=107º C

Ths=360º C

Test Data

speed (krpm) speed (krpm)

Documents

Thermohydrodynamic Analysis of Bump Type Gas Foil Bearings: A … · 2020-03-16 · San Andrés, L., and Chirathadam, T., 2011,“Metal Mesh Foil Bearings: Effect of Excitation Frequency