GAS FOIL BEARINGS FOR OILFREE ROTATING MACHINERY

1
29th Turbomachinery Research Consortium Meeting
MEASUREMENTS OF ROTORDYNAMIC PERFORMANCE IN A HOT
ROTOR-GAS FOIL BEARING SYSTEM
Keun Ryu Research Assistant
Luis San Andrés Mast-Childs Professor Principal
Investigator
Tae Ho Kim Post-doctorial Research Associate
TRC-BC-2-09
This material is based upon work supported by
NASA Research Announcement NNH06ZEA001N-SSRW2,
Fundamental Aeronautics Subsonic Rotary Wing
Project 2 32525/39600/ME and the Turbomachinery
Research Consortium
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Gas Foil Bearings Bump type

• Series of corrugated foil structures (bumps)
  assembled within a bearing sleeve.
• Integrate a hydrodynamic gas film in series with
  one or more structural layers.

Applications APUs, ACMs, micro gas turbines,
turbo expanders

• Reliable (large load capacity to 100 psi)
• Tolerant to misalignment and debris, also high
  temperature
• Need coatings to reduce friction at start-up
  shutdown
• Damping from dry-friction and operation with
  limit cycles

3
Gas Foil Bearings (/-)

• Increased reliability large load capacity (lt 100
  psi)
• No lubricant supply system, i.e. reduce weight
• High (up to 2,500 K) and low temperature
  capability No scheduled maintenance
• Ability to sustain high vibration and shock load.
  Quiet operation

• Less load capacity than rolling or oil bearings
• Wear during start up shut down
• Little data for rotordynamic performance
• Thermal management issues
• Predictive models need anchoring to reliable test
  data

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Foil Bearing Research at TAMU
Reference DellaCorte (2000) Rule of Thumb

• Test Gas Foil Bearing (Bump-Type)
• Generation II. Diameter 38.1 mm
• 25 corrugated bumps (0.38 mm of height)

2009 GFBs with UNCOATED TOP Foil for HT operation
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Rotordynamic tests for hot rotor operation
2008 Effects of hot rotor axial cooling flow
Rotor coastdown test
Drive end vertical plane
As Tc increases, critical speed increases by 2
krpm and the peak amplitude decreases.
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Research objectives 08/09
Rotordynamic Measurements on a High Temperature
Rotor Supported on Gas Foil Bearings

• Revamp test rig using cartridge heater for high
  temperature operation (up to 360C)
• Measure rotordynamic performance from 30 krpm
  speed coastdowns and various shaft temperatures
• Quantify effect of gas flow on cooling bearings
  (max. 150 L/min per bearing)

Funding from TRC start date on February 2, 2009
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Rotordynamic test rig setup GFBs
Rotordynamic test rig revamped with a cartridge
heater and instrumentation for operation at high
temperature.
Insulated safety cover
Infrared thermometer
Tachometer
Eddy current sensors
Hot heater inside rotor spinning 30 krpm
Drive motor
Cartridge heater
Flexible coupling
Test hollow shaft (1.1 kg, 38.1mm OD, 210 mm
length)
Test GFBs
Drive motor (max. 65 krpm). Cartridge heater max.
temperature 360C Air flow meter (Max. 500
L/min),
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Operation of hot rotor supported on GFBs
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Schematic view of instrumentation setup
45º
Insulated safety cover
Hollow shaft
Coupling cooling air
Drive motor
Cartridge heater
Heater stand
Foil bearings
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
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Rotor OD Temperature at increasing heater
temperature
T11
TFEB
Tc
TDEB
T12
T13
Cartridge heater loosely installed inside the
hollow rotor
Cartridge heater location
Ambient temp. (Ta) 22 C Rotor out of its
bearings
Significant temperature gradient along rotor axis
Heat source warms (unevenly) rotor and its
bearings
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Verification of rotor-bearing system response
Operating condition Room temp. Baseline, No
cooling, No heating
Normalized rotor synchronous response amplitudes
(coastdown)
Proportional to added mass imbalance

Rotordynamic model with linearized GFB force
coefficients will predict the rotor behavior
correctly
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Rotor 1X motions for cold and hot conds
High temp (heater up to 360C). Baseline, No
cooling
Rotor synchronous response amplitudes (coastdown)
No heating
Ths360C
Flexible rotor mode at 29 krpm (480 Hz) Soft
coupling and connecting rod Critical speed (Rigid
body mode) 13 krpm
No major differences in rotor response between
cold and hot rotor operation
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Rotor 1X motions for cold and hot conds
High temp (heater up to 360C). Baseline, No
cooling
DH
Rotor synchronous response amplitudes (coastdown)
Drive End (Horizontal)
DH
Cartridge temperature (Ths) increases
System natural frequency
As Ths increases to 360ºC, peak motion amplitudes
between 715 krpm decrease.
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Effect of shaft temperature
High temp (heater up to 360C). Baseline, No
cooling
Recorded coastdown rotor speed versus time
Long time to coastdown very low viscous
drag (no contact between rotor and bearings)
Exponential decay
Cartridge temperature (Ths) increases
Overall coastdown time reduces as rotor becomes
hotter!
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Cooling gas flow into GFBs
Side feed gas pressurization (Max. 100 psi)
Typically foil bearings DO not require
pressurization. Cooling flow needed for thermal
management to remove heat from drag or to reduce
thermal gradients in hot/cold engine sections
AIR SUPPLY
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Heating of rotor as speed time increase
Baseline imbalance, No side flow and 50 L/min
Temp. drop due to 50L/min cooling flow
20 krpm
30 krpm
10 krpm
Bearing cartridge and rotor surface temperatures
steadily increase with time larger rotor speed
makes rotor and bearings hotter. Side flow
removes heat from shear dissipation in rotor,
most effective at high speed
Fixed rotor speed of 10, 20, 30 krpm
Heater cartridge OFF
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Heating of rotor at steady state
Baseline imbalance, No side flow and 50 L/min
Temp. drop due to 50L/min cooling flow
Side flow removes heat from shear dissipation
in rotor. Thermal gradient Hot to cold FE rotor
gtFEB gt DEB gt DE rotor
Heater cartridge OFF
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Effect of cooling flow on heater temperature
High temp. (heater up to 360C). Cooling flow up
to 150 L/min
Fixed rotor speed 30 krpm
heater temperature
360C
300C
21C
100C
200C
No cooling 50L/min
100L/min
Due to limited heater power
150L/min
Cooling rates gt 100 LPM cool the heater!
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Effect of cooling flow on bearing temperatures
High temp. (heater up to 360C). Cooling flow up
to 150 L/min
Bearings temperature raises
Fixed rotor speed 30 krpm
360C
Cooling method is effective for flows above 100
L/min and when heater at highest temperature
300C
T1-Tamb
21C
100C
200C
T6-Tamb
T1-Tamb
Cooling flow increases
T6-Tamb
T1-Tamb
T6-Tamb
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Effect of cooling flow on rotor temperature
High temp. (heater up to 360C). Cooling flow up
to 150 L/min
Fixed rotor speed 30 krpm
Cooling flow increases
200C
T6-Tamb
T1-Tamb
100C
No heating
Cartridge temperature (Ths) increases
Turbulent flow gt 100 LPM
Bearing cartridge temperature
Rotor OD temperature decreases with cooling flow
rate.
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Effect of shaft temp. and cooling flow
Recorded coastdown rotor speed versus time
50 L/min
No cooling
No heating
360C
Overall coastdown time reduces by 20 (13 s) with
cooling flow of 50 LPM.
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Post-test condition of test rotor and GFBs
Before operation
After extensive hearing with rotor spinning tests
FE
DE
Static load direction
Static load direction
UNCOATED top foil !
Majority of polished (wear) marks on the top foil
are at its axial edges
Before operation
FE
DE
After extensive hearing with rotor spinning tests
Rotor shows wear marks at locations in contact
with bearings, in particular bearings outboard
edges
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Conclusions

• Amplitudes of rotor synchronous motion are
  proportional to added imbalance masses.

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

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

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

• Foil Bearings continue to survive high
  temperature operation Still working !

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Tae Ho Kim leaves TAMU (Farewell to TRC!)
Thanks TRC members for your continued support
and interest!
Tae Ho Kim
EDUCATION at TAMU (Supervisor Dr. Luis San
Andrés) Ph D. Texas AM Univ. College Station,
TX, Sept. 2003 Aug. 2007 Dissertation Analysis
of Side End Pressurized Bump Type Gas Foil
Bearings A Model Anchored to Test Data
Postdoc. Texas AM Univ. College Station, TX,
Sept. 2007 May 2009 Research Topic
Thermohydrodynamic Analysis of Bump Type Gas Foil
Bearing and Experimental Validations
Career Change to KIST Korea Institute of
Science and Technology (KIST), Seoul,
Korea Senior Research Scientist , June. 2009
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TRC acknowledged publications

• ASME Journal of Tribology, 2006, 128, pp. 670-673
• Tribology International, 2007, 40(8), pp.
  1239-1245
• ASME Journal of Eng. Gas Turbine Power, 2007,
  129, pp. 850-857
• ASME Journal of Eng. Gas Turbine Power, 2008,
  130, pp. 012504
• Tribology International, 2008, 41(8), pp. 704-715
• ASME Journal of Eng. Gas Turbine Power, 2009,
  131, pp. 012501
• Tribology International, 2008, 42(1), pp. 111-120
• ASME Journal of Tribology, 2009 (In-press)
• STLE Tribology Transactions, 2009 (In-press)
• ASME Journal of Eng. Gas Turbine Power, 2009
  (Accepted)
• ASME Journal of Eng. Gas Turbine Power, 2009
  (Accepted)
• ASME GT Paper GT2009-59920, 2009 (To be
  presented)
• AHS Rotorcraft conference, 2009 (To be
  presented)
• AHS Rotorcraft conference, 2009 (To be
  presented)
• World Tribology Congress (WTC), 2009 (To be
  presented)

Honor Finalist in the ASME Tribology Division
Young Engineer Short Paper Contest, November,
2006.
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Short Introduction to KIST GFB Research Facilities
(a) Dynamic load shaker test rig and (b) High
temperature test rig.

• Thrust foil bearing static load test rig and
• Test foil bearing

(a) AMB-GFB hygrid bearing dynamic load test rig
and (b) AMB-GFB hybrid bearing supports
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Short Introduction to KIST GFB Research Facilities

• 300 Hp high speed oil free motor (50 krpm) and
• Process fluid GFB dynamic load test rig

KIST seeks fruitful collaborations with TRC
members! Thank you! Tae Ho Kim thk_at_kist.re.kr
(a) Oil-free turbocharger engine test rig and (b)
Variable geometry oil-free turbocharger

• Fuel cell turbo-blower and
• Palm size microturbine rotordynamic test rig

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Rotordynamic Performance of Foil Gas Bearings
Test Analysis
STRUCTURAL STIFFNESS OF THREE KIST FOIL BEARINGS
Dr.Luis San Andrés Mast-Childs Professor Chunliu
Mao Research Assistant
TRC Project 32513/1519 C4
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Donated KIST bearings rotor
10,000
Do50.8mm DI37.95mm DT36.63mm
L38.1mm
Three bearings differ in clearance only Cnom
(DT- Ds)/2
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Static Load Test Rig Setup
Eddy Current Sensor
Lathe Chuck
Test KIST Bearing
Live Center
Load Cell

• Mount (floating) foil bearing on a rigid shaft
• Both ends of shaft are fixed
• Tests at room temperature

Top foil leading edge is installed 45 away from
horizontal (load direction)
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Static load test setup
Lathe chuck holds shaft bearing during
loading/unloading cycles.




Eddy Current sensor


Stationary shaft
Lathe tool holder
Test FB
Lathe tool holder moves forward and backward
push and pull forces on foil bearing
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Static load vs deflection
PULL LOADS
PUSH LOADS
Radial Clearances Cnom (DT- Ds)/2
V1-10.0375mm V2-10.0525mm V2-20.1325mm
Force F(x) is nonlinear, modeled as an odd power
polynomial F(x)k0k1xk2x2k3x3k4x4k5x5 Find
structural stiffness from dF/dx
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Bearing structural stiffness
KSdF/dxk12k2x3k3x24k4x35k5x4
PUSH LOADS
PULL LOADS
Radial Clearances Cnom (DT- Ds)/2
V1-10.0375mm V2-10.0525mm V2-20.1325mm

• KIST foil bearing structural stiffness
• Highly asymmetric with respect to the null
  deflection condition
• Bearing with lowest radial clearance has highest
  stiffness

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TRC Proposal Gas Bearings for Oil-Free
Turbomachinery
COMBINE ALL THREE TRC PROJECTS INTO ONE

• Revamp test rig and conduct experiments
• Two MiTi Korolon coated foil bearings for
  cartridge heater temperatures to 400 C and with
  rotor speed to 50 krpm.
• - Rotor lift off and touch down speeds, load
  capacity and drag power, synchronous speed force
  coefficients, and regimes of stability and limit
  cycle operation. Perform comparisons with
  predictions
• Conduct dynamic load tests in KIST bearings
• - Identification of structural stiffness and
  damping coefficients and correlation with
  predictive tool.
• Install automatic open/close valve to operate
  multiple start stop cycles in turbocharger
  driven gas bearing test rig.
• KIST bearings, Lift off and touch down
  speeds, load capacity and drag power.

TASKS
Budget from TRC for 2009/2010 Support for
graduate student (20 h/week) x 1,600 x 12
months 19,200 Fringe benefits (2.5) and
medical insurance (194/month)
2,808 Tuition three semesters (3,996 x 3),
11,988 Supplies test rig (thermocouples
and thermometers)
6,004 Total Cost

40,000
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TC driven Rotor for Gas Bearing Rotordynamic Tests
(a) Static shaft
TC cross-sectional view Ref. Honeywell drawing
448655
Max. operating speed 120 krpm Turbocharger
driven rotor Regulated air supply9.30bar (120
psig)
Twin ball bearing turbocharger, Model T25,
donated by Honeywell Turbo Technologies