Implementing gas foil bearings (GFBs) in micro gas turbine engines is a proven approach to improve system efficiency and reliability. Adequate thermal management for operation at high temperatures, such as in a gas turbine or a turbocharger, is important to control thermal growth of components and to remove efficiently mechanical energy from the rotor mainly. The paper presents a test rotor supported on GFBs operating with a heated shaft and reports components temperatures and shaft motions at an operating speed of 37 krpm. An electric cartridge heater loosely inserted in the hollow rotor warms the test system. Thermocouples and noncontact infrared thermometers record temperatures on the bearing sleeve and rotor outer diameter (OD), respectively. No forced cooling air flow streams were supplied to the bearings and rotor, in spite of the high temperature induced by the heater on the shaft outer surface. With the rotor spinning, the tests consisted of heating the rotor to a set temperature, recording the system component temperatures until reaching thermal equilibrium in  ∼ 60 min, and stepping the heater set temperature by 200 °C. The experiments proceeded without incident until the heater set temperature equaled 600 °C. Ten minutes into the test, noise became apparent and the rotor stopped abruptly. The unusual operating condition, without cooling flow and a too large increment in rotor temperature, reaching 250 °C, led to the incident which destroyed one of the foil bearings. Post-test inspection evidenced seizure of the hottest bearing (closest to the heater) with melting of the top foil at the locations where it rests on the underspring crests (bumps). Analysis reveals a notable reduction in bearing clearance as the rotor temperature increases until seizure occurs. Upon contact between the rotor and top foil, dry-friction quickly generated vast amounts of energy that melted the protective coating and metal top foil. Rather than a reliability issue with the foil bearings, the experimental results show poor operating procedure and ignorance on the system behavior (predictions). A cautionary tale and a lesson in humility follow.

References

References
1.
Agrawal
,
G. L.
,
1997
, “
Foil Air/Gas Bearing Technology: An Overview
,” ASME Paper No. 97-GT-347.
2.
DellaCorte
,
C.
, and
Valco
,
M.
,
2000
, “
Load Capacity Estimation of Foil Air Journal Bearing for Oil-Free Turbomachinery Applications
,”
STLE Tribol. Trans.
,
43
(
4
), pp.
795
801
.10.1080/10402000008982410
3.
DellasCorte
,
C.
, and
Pinkus
,
O.
,
2000
, “
Tribological Limitations in Gas Turbine Engines: A Workshop to Identify the Challenges and Set Future Directions
,” Report No. NASA/TM-2000-210059/REV1.
4.
Walton
,
J. F.
,
Heshmat
,
H.
, and
Tomaszewki
,
M. J.
,
2004
, “
Testing of a Small Turbocharger/Turbojet Sized Simulator Rotor Supported on Foil Bearings
,”
ASME
Paper No. GT2004-53647.10.1115/GT2004-53647
5.
Heshmat
,
H.
, and
Walton
,
J. F.
,
2000
, “
Oil-Free Turbocharger Demonstration Paves Way to Gas Turbine Engine Applications
,” ASME Paper No. 2000-GT-620.
6.
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. Tribol.
,
132
(
1
), p.
011701
.10.1115/1.4000279
7.
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 Power
,
132
(
4
), p.
042504
.10.1115/1.3159386
8.
San Andrés
,
L.
,
Ryu
,
K.
, and
Kim
,
T. H.
,
2011
, “
Thermal Management and Rotordynamic Performance of a Hot Rotor-Gas Foil Bearings System. Part I: Measurements
,”
ASME J. Eng. Gas Turbines Power
,
133
(
6
), p.
062501
.10.1115/1.4001826
9.
Ryu
,
K.
, and
San Andrés
,
L.
,
2012
, “
Effect of Cooling Flow on the Operation of a Hot Rotor-Gas Foil Bearing System
,”
ASME J. Eng. Gas Turbines Power
,
134
(
10
), p.
102511
.10.1115/1.4007067
10.
Dykas
,
B. D.
,
2006
, “
Factors Influencing The Performance of Foil Gas Thrust Bearings For Oil-Free Turbomachinery Applications
,” Ph.D. thesis, Case Western Reserve University, Cleveland, OH.
11.
Dykas
,
B. D.
,
2003
, “
Investigation of Thermal and Rotational Contributions to the Catastrophic Failure Mechanism of a Thin-Walled Journal Operating With Foil Air Bearings
,” M.S. thesis, Case Western Reserve University, Cleveland, OH.
12.
Heshmat
,
H.
,
Hryniewicz
,
P.
,
Walton
,
J. F.
,
Willis
,
J. P.
,
Jahanmir
,
S.
, and
DellaCorte
,
C.
,
2005
, “
Low-Friction Wear-Resistant Coatings for High-Temperature Foil Bearings
,”
Tribol. Int.
,
38
, pp.
1059
1075
.10.1016/j.triboint.2005.07.036
13.
San Andrés
,
L.
,
Kim
,
T. H.
, and
Ryu
,
K.
,
2009
, “
Thermohydrodynamic Analysis of Bump Type Gas Foil Bearings: A Model Anchored to Test Data
,” Final Project Report to NASA SSRW2-1.3 Oil Free Engine Technology Program.
14.
San Andrés
,
L.
,
Ryu
,
K.
, and
Kim
,
T. H.
,
2011
, “
Identification of Structural Stiffness and Energy Dissipation Parameters in a Second Generation Foil Bearing: Effect of Shaft Temperature
,”
ASME J. Eng. Gas Turbines Power
,
133
(
3
), p.
032501
.10.1115/1.4002317
15.
Timoshenko
,
S. P.
, and
Goodier
,
J. N.
,
1970
,
Theory of Elasticity
,
McGraw-Hill
,
New York
.
16.
Radil
,
K.
, and
Zeszotek
,
M.
,
2004
, “
An Experimental Investigation Into the Temperature Profile of a Compliant Foil Air Bearing
,”
STLE Tribol. Trans.
,
47
(
4
), pp.
470
479
.10.1080/05698190490501995
17.
San Andrés
,
L.
,
Ryu
,
K.
, and
Kim
,
T. H.
,
2011
, “
Thermal Management and Rotordynamic Performance of a Hot Rotor-Gas Foil Bearings System. Part II: Predictions Versus Test Data
,”
ASME J. Eng. Gas Turbines Power
,
133
(
6
), p.
062502
.10.1115/1.4001827
18.
Radil
,
K. C.
,
DellaCorte
,
C.
, and
Zeszotek
,
M.
,
2007
, “
Thermal Management Techniques for Oil-Free Turbomachinery Systems
,”
STLE Tribol. Trans.
,
50
(
3
), pp.
319
327
.10.1080/10402000701413497
19.
Radil
,
K. C.
, and
DellaCorte
,
C.
,
2009
, “
A Three-Dimensional Foil Bearing Performance Map Applied to Oil-Free Turbomachinery
,” U.S. Army Research Laboratory, Cleveland, OH, Report No. ARL-TR-4473.
20.
Radil
,
K.
, and
Batcho
,
Z.
,
2011
, “
Air Injection as a Thermal Management Technique for Radial Foil Air Bearings
,”
STLE Tribol. Trans.
,
54
(
4
), pp.
666
673
.10.1080/10402004.2011.589964
21.
Lee
,
D.
, and
Kim
,
D.
,
2010
, “
Thermohydrodynamic Analyses of Bump Air Foil Bearings With Detailed Thermal Model of Foil Structures and Rotor
,”
ASME J. Tribol.
,
132
, p.
021704
.10.1115/1.4001014
You do not currently have access to this content.