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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
• 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 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
• 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 bearing and shafttemperatures. Validation of computational model
* The computational codeGraphical User Interface. Further predictions
• GFB thermal management tests and preds.• Closure & added value
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
Cartridge temperature (Ths) increases
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)
Cartridge temperature (Ths) increases
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
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 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
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
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
Infrared thermometer
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)
Cartridge temperature (Ths) increases
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
Cartridge temperature (Ths) increases
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
Test data & predictions
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
Shaft temperature rise [ºC]
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
Gas pressure Max. 100 psi
Heater warms unevenly rotor.
Side cooling cools unevenly
rotor and also heater
Cooling gas flow into GFBs
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
Cartridge temperature (Ths) increases
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
Shaft temperature rise [ºC]
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
Test data & predictions
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
Topic• Statement of Work & Sources for Presentation• Objectives and accomplished work in 07-08
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 bearing and shafttemperatures. Validation of computational model
* The computational codeGraphical User Interface. Further predictions
• GFB thermal management tests and preds.• Closure & added value
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
Graphical User Interface
Worksheet: Shaft & Bearing models (II)
52
Graphical User Interface
Worksheet: Top Foil and Bump Models
Box 8
Box 9
Box 10
53
Graphical User Interface
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]
Cartridge heater temperature increases
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
Cartridge heater temperature increases
Ths=200ºC
Ths=360ºC
No heating
KXX
KYY
Cartridge heater temperature increases
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
Rotor speed (krpm) Rotor speed (krpm)
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
Cartridge heater temperature increases
Ths=200ºC
Ths=360ºC
Cartridge heater temperature increases
static load ~ 6.5 NNo cooling flow
Drive End FB
Bearing damping Predictions
Predictions
Rotor speed (krpm) Rotor speed (krpm)
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
125 L/minShaft temp. rise=39 °C
150 L/minShaft temp. rise=32 °C
Cooling stream increases
DE FB
Rotor speed : 30 krpmw/o & w cooling flow
Model
Model predictions
59
60
Topic• Statement of Work & Sources for Presentation• Objectives and accomplished work in 07-08
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 bearing and shafttemperatures. Validation of computational model
* The computational codeGraphical User Interface. Further predictions
• 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
Bearing displacement [µm]
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
Bearing displacement [µm]
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
90° bearing orientation
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
Motion amplitude increases
System natural frequency
System natural frequency
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
Bearing displacement [µm]
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
Motion amplitude increases
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.
Heater temperature increases
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]
23ºC103ºC183ºC263ºC
Im O
eq
FXC
ω
⎛ ⎞⎜ ⎟⎝ ⎠=
Heater temperature increases
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
23ºC103ºC183ºC263ºC
FB motion amplitude: 14.8 µm
Heater temperature increases
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
Gas pressure Max. 100 psi
Cooling flow needed for thermal
management: to remove heat from
shear drag or to reduce thermal
gradients from hotto cold engine
sections
Cooling gas flow into GFBs
heater
78
AIR SUPPLY
Gas pressure Max. 100 psi
Heater warms unevenly test
rotor.Side cooling
flows cool unevenly the
rotor.
Cooling gas flow into GFBs
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)
45° bearing orientation
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
Infrared thermometer
Infrared thermometer
~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
Heater set temperature = 150ºC
Test cases #1 and #4
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
Test cases #1 and #4
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.
Heater set temperature = 100ºC
Free end BearingTemperatures on bearings ODs linearly
increase with duct air temperature as the cooling flow rate into the bearings
decreases
Test cases #2 and #5
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
Cooling flow decreases
95
Rise in temperatures: Duct vs Rotor OD
Heater set temperature = 100ºC
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
Cooling flow decreases
Cooling flow decreases
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
Cooling flow rate [L/min]
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
Heater set temperature = 100ºC
?
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
Cartridge temperature (Ths) increases
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
Cooling flow rate [L/min]
No rotor spinning10 krpm20 krpm30 krpm
[ºC
/L/m
in]
Tem
pera
ture
ris
e C
oolin
g flo
w r
ate
Heater set temperature = 100ºC
The cooling capability of the forced axial flow
on the bearing temperatures
changes little with flow rate
~ Constant
Cooling flow rate increases
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
Cooling flow rate [L/min]
No rotor spinning10 krpm20 krpm30 krpm
[ºC
/L/m
in]
Tem
pera
ture
ris
e C
oolin
g flo
w r
ate
Heater set temperature = 100ºC
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
Cooling flow rate increases
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)
Cartridge temperature (Ths) increases
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
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
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
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
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
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
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
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
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
Topic• Statement of Work & Sources for Presentation• Objectives and accomplished work in 07-08
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 bearing and shafttemperatures. Validation of computational model
* The computational codeGraphical User Interface. Further predictions
• 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
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- 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 !!!
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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:
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Back up slides
125
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
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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!
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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.
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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)
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