The foil bearing (FB) is one type of hydrodynamic bearing using air or another gas as a lubricant. When FBs are designed, installed, and operated properly, they are a very cost-effective and reliable solution for oil-free turbomachinery. Because there is no mechanical contact between the rotor and its bearings, quiet operation with very low friction is possible once the rotor lifts off the bearings. However, because of the high speed of operation, thermal management is a very important design factor to consider. The most widely accepted cooling method for FBs is axial flow cooling, which uses cooling air or gas passing through heat-exchange channels formed underneath the top foil. The advantage of axial cooling is that no hardware modification is necessary to implement it, because the elastic foundation structures of the FB serve as the heat-exchange channels. Its disadvantage is that an axial temperature gradient exists on the journal shaft and bearing. In this paper, the cooling characteristics of axial cooling are compared with those of multipoint radial injection, which uses high-speed injection of cooling air onto the shaft at multiple locations. Experiments were performed on a three-pad FB 49 mm in diameter and 37.5 mm in length, at speeds of 30,000 rpm and 40,000 rpm. Injection speeds were chosen to be higher than the journal surface speed, but the total cooling air flow rate was matched to that of the axial cooling cases. Experimental results show that radial injection cooling is comparable to axial cooling at 30,000 rpm, in terms of cooling performance. Tests at 40,000 rpm reveal that the axial cooling performance reaches saturation when the pressure drop across the bearing is larger than 1000 Pa, while the cooling performance of radial injection is proportional to the cooling air flow rate and does not become saturated. Overall, multipoint radial injection is better than axial cooling at high rotor speeds.

References

References
1.
DellaCorte
,
C.
, and
Edmonds
,
B. J.
,
1995
, “
Preliminary Evaluation of PS300: A New Self-Lubricating High Temperature Composite Coating for Use to 800 °C
,” NASA Technical Report No. NASA TM-107056.
2.
DellaCorte
,
C.
,
1996
, “
The Effect of Counterface on the Tribological Performance of a High Temperature Solid Lubricant Composite from 25 to 650 °C
,”
Surf. Coat. Technol.
,
86–87
(
2
), pp.
486
492
.10.1016/S0257-8972(96)02959-3
3.
Stanford
,
M. K.
,
Yanke
,
A. M.
, and
DellaCorte
,
C.
,
2004
, “
Thermal Effects on a Low Cr Modification of PS304 Solid Lubricant Coating,
” NASA Technical Report No. NASA TM-2003-213111.
4.
Ku
,
C.-P. R.
, and
Heshmat
,
H.
,
1992
, “
Compliant Foil Bearing Structural Stiffness Analysis: Part I—Theoretical Model Including Strip and Variable Bump Foil Geometry
,”
ASME J. Tribol.
,
114
(
2
), pp.
394
400
.10.1115/1.2920898
5.
San Andrés
,
L.
, and
Kim
,
T. H.
,
2007
, “
Improvements to the Analysis of Gas Foil Bearings: Integration of Top Foil 1D and 2D Structural Models
,” Turbo Expo 2007, Montreal, Canada, May 14–17, ASME Paper No. GT2007-27249.
6.
San Andrés
,
L.
, and
Kim
,
T. H.
,
2009
, “
Analysis of Gas Foil Bearings Integrating FE Top Foil Models
,”
Tribol. Int.
,
42
(
1
), pp.
111
120
.10.1016/j.triboint.2008.05.003
7.
Kim
,
D.
,
2007
, “
Parametric Studies on Static and Dynamic Performance of Air Foil Bearings With Different Top Foil Geometries and Bump Stiffness Distributions
,”
ASME J. Tribol.
,
129
(
2
), pp.
354
364
.10.1115/1.2540065
8.
Kumar
,
M.
, and
Kim
,
D.
,
2008
, “
Parametric Studies on Dynamic Performance of Hybrid Air Foil Bearings
,”
ASME J. Eng. Gas Turbines Power
,
130
(
6
), p.
062501
.10.1115/1.2940354
9.
Lee
,
D.
,
Kim
,
Y.
, and
Kim
,
T.
,
2009
, “
The Dynamic Performance Analysis of Foil Journal Bearings Considering Coulomb Friction: Rotating Unbalance Response
,”
STLE Tribol. Trans.
,
52
(
2
), pp.
146
156
.10.1080/10402000802192685
10.
Kim
,
D.
, and
Park
,
S.
,
2009
, “
Hydrostatic Air Foil Bearings: Analytical and Experimental Investigations
,”
Tribol. Int.
,
42
(
3
), pp.
413
425
.10.1016/j.triboint.2008.08.001
11.
Kim
,
D.
, and
Lee
,
D.
,
2010
, “
Design of Three-Pad Hybrid Air Foil Bearing and Experimental Investigation on Static Performance at Zero Running Speed
,”
ASME J. Eng. Gas Turbines Power
,
132
(
12
), p.
122504
.10.1115/1.4001066
12.
Lez
,
S. L.
,
Arghir
,
M.
, and
Frene
,
J.
,
2007
, “
A New Bump-Type Foil Bearing Structure Analytical Model
,”
ASME J. Eng. Gas Turbines Power
,
129
(
4
), pp.
1047
1057
.10.1115/1.2747638
13.
Lez
,
S. L.
,
Arghir
,
M.
, and
Frene
,
J.
,
2007
, “
Static and Dynamic Characterization of a Bump-Type Foil Bearing Structure
,”
ASME J. Tribol.
,
129
(
1
), pp.
75
83
.10.1115/1.2390717
14.
Radil
,
K.
,
DellaCorte
,
C.
, and
Zeszotek
,
M.
,
2007
, “
Thermal Management Techniques for Oil-Free Turbomachinery Systems
,”
STLE Tribol. Trans.
,
63
(
10
), pp.
319
327
.10.1080/10402000701413497
15.
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
16.
Radil
,
K.
,
Howard
,
S.
, and
Dykas
,
B.
,
2002
, “
The Role of Radial Clearance on the Performance of Foil Air Bearings
,”
STLE Tribol. Trans.
,
45
(
4
), pp.
485
490
.10.1080/10402000208982578
17.
Salehi
,
M.
,
Swanson
,
E.
, and
Heshmat
,
H.
,
2001
, “
Thermal Features of Compliant Foil Bearings – Theory and Experiments
,”
ASME J. Tribol.
,
123
(
3
), pp.
566
571
.10.1115/1.1308038
18.
Peng
,
Z. C.
, and
Khonsari
,
M.
,
2006
, “
A Thermohydrodynamic Analysis of Foil Journal Bearings
,”
ASME J. Tribol.
,
128
(
3
), pp.
534
541
.10.1115/1.2197526
19.
Feng
,
K.
, and
Kaneko
,
S.
,
2008
, “
A Study of Thermohydrodynamic Features of Multiwound Foil Bearing Using Lobatto Point Quadrature
,”
Proceedings of ASME Turbo Expo 2008: Power for Land
,
Sea and Air
,
Berlin, Germany
, June 9–13, ASME Paper No. GT2008-50110.
20.
San Andrés
,
L.
, and
Kim
,
T. H.
,
2009
, “
Thermohydrodynamic Analysis of Bump Type Gas Foil Bearings: A Model Anchored to Test Data
,” Turbo Expo 2009, Orlando, Florida, June 8–12, ASME Paper No. GT2009-59919.
21.
Lee
,
D.
, and
Kim
,
D.
,
2010
, “
Thermo-Hydrodynamic Analyses of Bump Air Foil Bearings With Detailed Thermal Model of Foil Structures and Rotor
,”
ASME J. Tribol.
,
132
(
2
), p.
021704
.10.1115/1.4001014
22.
Lee
,
D.
,
Kim
,
D.
, and
Sadashiva
,
R. P.
,
2011
, “
Transient Thermal Behavior of Preloaded Three-Pad Foil Bearings: Modeling and Experiments
,”
ASME J. Tribol.
,
133
(
2
), p.
021703
.10.1115/1.4003561
23.
Kim
,
D.
,
Lee
,
D.
,
Kim
,
Y. C.
, and
Ahn
,
K. Y.
,
2010
, “
Comparison of Thermo-Hydrodynamic Characteristics of Airfoil Bearings With Different Top Foil Geometries
,”
Proceedings of the 8th IFToMM International Conference on Rotordynamics
, Seoul, Korea, Sept. 12–15, Paper No. WeD1-4.
24.
Kim
,
D. J.
,
Ki
,
J. P.
,
Kim
,
Y. C.
, and
Ahn
,
K. Y.
,
2012
, “
Extended Three-Dimensional Thermo-Hydrodynamic Model of Radial Foil Bearing
,”
ASME J. Eng. Gas Turbines Power
,
134
(
5
), p.
052501
.10.1115/1.4005215
25.
Kim
,
Y. C.
, and
Lee
,
D. H.
,
2010
, “
Air Foil Bearing for High Temperature Cooling
,” Patent No. KR20120017637.
26.
Ponnappan
,
R.
, and
Leland
,
J. E.
,
1999
, “
External Condenser Design for Cooling of Rotating Heat Pipe in MEA Applications
,” SAE Paper No. 1999-01-1360.
27.
Radil
,
K.
, and
Batcho
,
Z.
,
2011
, “
Air Injection as a Thermal Management Technique for Radial Foil Air Bearings
,”
Tribol. Trans.
,
54
(
4
), pp.
666
673
.10.1080/10402004.2011.589964
You do not currently have access to this content.