The document summarizes the journey to developing ultra-high temperature compliant foil bearings capable of operating at 870°C for application in gas turbine engines. Key points: - Foil bearings were tested on a simulated gas turbine engine rig with a 17 kg rotor, achieving steady operation with inlet air at 900°C and measured foil temperatures over 815°C. - Advances in materials, coatings, analysis, and system integration enabled the breakthrough, including a polymer coating that allows operation to 480°C and an elastic ceramic coating to over 1000°C. - Testing validated that foil bearings can accommodate high temperature applications in gas turbines and meet the goal of the International High Performance Turb

1. GT2018-75555
ULTRA-HIGH TEMPERATURE COMPLIANT FOIL BEARINGS – THE JOURNEY TO
870°C AND APPLICATION IN GAS TURBINE ENGINES: EXPERIMENT
ASME Turbo Expo 2018
June 11-15, 2018, Oslo, Norway
1
Hooshang Heshmat,
James F Walton II and
Brian Nicholson

2. MITI Oil-Free Bearings and Seals
2
6-150 mm
690 kPa/100 psi / 870°C
Journal Foil Bearing Thrust Foil Bearing Foil Face Seal Foil Radial Seal
15-250 mm 25-1300 mm 20-250 mm
550 kPa/80 psi / 650°C 550 kPa/80 psid / 650°C 690 kPa/100 psid / 870°C

3. MITI Oil-Free Turbomachinery –
Power & Propulsion
3
60 kWe
Flywheel Energy Storage
8 kWe
180,000 rpm
Gas Turbine Generator ORC Turbogenerator
65 kWe
30,000 rpm60,000 rpm
Turbine Engine
135 to 4500 N
60,000 rpm

4. Objectives
• Demonstrate That Compliant Foil Bearing Technology Is
Suitable for Gas Turbine Engines
– Temperatures ≥ 815°C
– Rotor Weights ≥ 50 kg
4

5. The Motivation - IHPTET
• Established 1987 to Double Propulsive Capability of GTEs
• Component Goal for 815°C/1500°F High Temperature
Bearings Established
• Numerous Approaches Attempted
– REBs w/Different Materials & Lubrication Schemes
– Magnetic Bearings
– Compliant Foil Bearings
– Hybrid Foil/Magnetic Bearings
5

6. The Final Result Foil Bearing Operating with 870°C Film
Time (Minutes)
0 50 100 150 200 250 300 350
Temperature(C)
0
200
400
600
800
1000
Speed(krpm)
0
5
10
15
20
25
30
35
T4_C Inlet Cavity
T5_C Inlet TDC
Bearing
Chamber
Bearing Inboard
Speed
Bearing Free End
20269-T16R3ABCD
6
815°C Bearing
Chamber
Air 900°C

7. Background – 30 Years Later
• Enabling Technologies Include
– Foil Bearing Design Capabilities
• FD-FE Coupled Elasto-Hydrodynamic Analysis
– Hydrodynamic Stiffness and Damping
– Structural Compliance & Damping
– Thermal Effects
– Coatings & Materials
• Polymer Based Coating - 480°C
• Elastic Ceramic Coating - 1000°C+
• High Temperature Foils
– Modulus
– Strength
– Oxidation Resistance
– System Integration Methodologies
• Rotor-Bearing Dynamics
• Thermal Management
• Static Structures
7
eo
θ
W
φ0
hmin
Coating
KHydro
KStruct
BHydro
BStruct
CompliancyDamping

8. Historical Advancements
8
1970 1980 1990 2000 2010
Year Advancement Made
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
Air Cycle Machines,
Turboexpanders
Automotive Turbocharger
Gas Turbine Engines
03-0052

9. Progress  GTEs (Red emphasizes key elements)
Application Output
(Nthrust orKwe)
Speed
(rpm * 103 )
Rotor
Weight
(kg)
Bearing Temp
(°C)
FESS 10 kPa (1.5 psia) 62.5 kWe 60 100 100
Turboalternator 50 kWe 30 7 175
Turbojet Engine 1.35 KNt 60 12 650
GTE Simulator 55 KNt 30 48 675
Turboalternator 8 kWe 180 1 705
Turbojet Engine 0.135 KNt 120 1 815
GTE Simulator 4.5 KNt 50 17 870
9

10. Tribological coatings need these characteristics
10
Good Friction & Wear
Elasticity
Coefficient of Expansion
Thermal Conductivity

11. Simulator Rig #1 – 50.5 kg Rotor w/ Overhung Turbine
11
330 N
Brg Load

12. The rest of the presentation focuses on the
17 kg GTE Simulator Rotor
12
60 N Brg
Load

13. Assembled Simulator Rig #2 - w/Insulation
13

14. Y2
Drive Turbine Pressure
Speed
REB (T1)
Heat
Shield
Y1
X1
X2
Heat Shield Cold
Side (T2)
Sensor Temp
(T14)
Sensor Temp
(T15)
Housing Coil
Heater (T3)
Heater Outlet
(T12)
CFB Inlet Cavity (T4)
CFB Exit TDC (T9)
CFB Exit 270o (T8)
CFB Exit BDC (T10)
CFB Inlet TDC (T5)
CFB Inlet BDC (T6)
CFB Mid-Length 90o (T7)
CFB Upstream (T11)
Housing Temp (T13)
CFB Foil BDC (T16)
14

15. Bearing Instrumentation
Heat
Shield
CFB Exit TDC
(T9)
CFB Exit 270o
(T8)
CFB Exit BDC
(T10)
CFB Inlet TDC (T5)
CFB Inlet BDC
(T6)
CFB Mid-Length
90o (T7)
CFB Foil BDC
(T16)
15

16. Thermocouple Instrumentation at axial locations
16
Inboard Midspan Outboard
T5
T6
T4
T7
T9
T10
T8
I M O

17. Design - Foil Bearing
17
L=50.8 mm
D = 38.1

18. Initial High Temperature Test vs Time
18
T11 R8, 900
o
C (1650
o
F) Heater Setting
Time (sec)
0 1000 2000 3000 4000 5000 6000
Temp
o
C
0
200
400
600
800
1000
Speed(KRPM)
0
2
4
6
8
10
12
14
16
18
20
Speed
900°C Heater Set Point
CFB
Outboard
CFB Inboard
& Midspan
CFB
Chamber
T11R8
Chamber
Inlet

19. Dynamic Speed Cycling (note: transient speed test)
Time (Minutes)
275 300 325 350 375 400
Temperature(C)
0
125
250
375
500
625
750
Speed(krpm)
0
5
10
15
20
25
30
35
T14_R0-4

20. Final Result Foil Bearing Operating with 870°C Film
Time (Minutes)
0 50 100 150 200 250 300 350
Temperature(C)
0
200
400
600
800
1000
Speed(krpm)
0
5
10
15
20
25
30
35
nlet Cavity
nlet TDC
nlet BDC
Mid Brg 90o
TDC
Outlet BDC
Upstream
D
Bearing
Chamber
Bearing Inboard
Speed
Bearing Free End
20269-T16R3ABCD
20
Time (Minutes)
150 160 170 180 190 200
Speed(krpm)
15
16
17
18
19
20
21
22
23
24
25
Temperature(C)
600
700
800
900
1000 SPEED
T4_C Inlet Cavity
T5_C Inlet TDC
T6_C Inlet BDC
T7_C Mid Brg 90o
TDC
T8_C Outlet 270o
TDC
T9_C Outlet TDC
T10_C Outlet BDC
T16_C Foil
T11_C Upstream
T12_C Heater Setpoint

21. T5
T6
T4
T7
T9
T10
T8
Middle OutboardInboard
Maximum Measured Bearing Shell Temperatures
795°C
803°C
791°C
796°C
788°C
785°C
787°C
21

22. Differential Shaft and Bearing Temperatures
22
Time (Minutes)
300 305 310 315 320 325 330 335
Temperature(C)
0
50
100
150
200
Speed(krpm)
0
10
20
30
T4_C Inlet Cavity
T5_C Inlet TDC
T6_C Inlet BDC
T7_C Mid Brg 90o
TDC
ΔT ~ 32°C
ΔT ~ 25°C
T16-Bump
Foil Temp
T4-Bearing
Chamber
ΔT ~ 90°C
Heater Set Point
T11-Upstream
of Chamber
Speed
Korolon k = 2 W/m-K
Air k = 0.026-0.04 W/m-K
For Applied Thickness
Delta-T = 80-110°C
Foil
Shaft
TC
Korolon

23. High-Temp Foil Bearing (Gas film temps based on previous slide)
Copyright © 2011-2018 MiTi® 23
870°C
815°C
6/12/2018

24. T5
T6
T4
T7
T9
T10
T8
Middle OutboardInboard
Maximum Estimated Foil Temperatures
795°C
819°C
806°C
811°C
804°C
802°C
801°C
24

25. Material Modulus vs Temperature
25
50
100
150
200
250
0 200 400 600 800 1000
ElasticModulus(Mpa)
Temperature(°C)
IN718 MPA IN X750 MPA Ni-Cr-CO

26. Simulator Model
26

27. Rotor System Conical Critical Speed
7687 rpm
27

28. 8547 rpm Conical Mode
21000 rpm Spin Speed
28

29. Critical Speed Map showing potential impact of high temperature on bearing stiffness
Critical Speed Map
Stiffness (N/m)
1e+5 1e+6 1e+7
CriticalSpeed(rpm)
1e+3
1e+4
1e+5
MiTi Proprietary Information Do Not Disclose 29
5500 < ωn < 8500 rpm
1.5 < K <
5.5e6 N/m

30. Comparison of Predicted vs Measured Natural Frequencies
For All Tested Temperatures and Speeds
30
4000
5000
6000
7000
8000
9000
10000
11000
5000 10000 15000 20000 25000 30000 35000 40000 45000
NaturalFrequency
Spin Speed (rpm)
ComparisonMeasuredvs Predicted
Predicted CS_RT-815C Sub-Sync (425-480C) SubSync _RT CS_50-to-650C Sub-Sync_650C
Measured Critical Speeds
20-to-815oC
SubsynchronousFrequencies 20-to-815oC
Thermal
Effect

31. Summary & Conclusions
• IHPTET Goal Achieved
• Bearing Tested To Temperatures ≥ 815°C
– Inlet Airflow Temperatures 900°C
– Fluid Film Temperatures to 870+oC
– Foil Temperatures to >815oF
• High Temperature Impacts Modulus/Stiffness
• Necessary High Temperature Coating Demo’d
• Foil Bearings Accommodate Rotors >50 kg
• Enabling Technology for Future High
Temperature Engine Integrations Established
31

32. • For Oil-Free Foil Bearing Systems it’s
Integration
Integration
Integration
32
In Real Estate They Say It’s All About
Location, Location, Location…

33. Advanced Rotating Machinery Development
33
Station: 2
X disp: Min = -9.8857, Max = 10.977
Y disp: Min = -16.753, Max = 40.591
0.00 0.07 0.14 0.21 0.28 0.35
-25
0
25
50
-25
0
25
Damping Ped1 = 20 lb-s/in
Damping Ped 2 = 130 lb-s/in
Unbalance = 0.001 oz-in left plane
= 0.002 oz-in right Plane
Time (sec)
AMB
Deactivated
AMB
Reactivated
ZCAB Opening
ZCAB Open
98-0229
AMB Vertical
Reaction Force
ZCAB Vetical
Reaction Force
Rotor-Bearing Model
Bearing Analysis
ω
W
e
Thermal Models
Transient Shock
Contour Stability Map Plotting Log Decrement as a Function
of Spin Speed and Damping for Rigid Mode 2 Aluminum Compressor
All Bearings Have The Same Damping
2.5
2.52.5
2.5
2.0
2.02.0
2.0
1.5
1.5
1.5
1.5
1.5
1.0
1.0
1.0
1.0
0.5
0.5
0.5
0.5
0.0
0.0
-0.5
3.0
0.5
Spin Speed (rpm)
2.0e+4 4.0e+4 6.0e+4 8.0e+4 1.0e+5 1.2e+5 1.4e+5 1.6e+5 1.8e+5
Damping(N-s/mm)
0.000
0.025
0.050
0.075
0.100
0.125
0.150
0.175
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Unstable
Log Decrement
Stability Analysis
DISTRIBUTION C. Distribution authorized to US Government agencies and their
contractors

34. Questions?
34
If you are REALLY Serious about Using Extreme High
Temperature Foil Bearings, get in touch with me:
James Walton
jwalton@mohawkinnovative.com