Transcript No Slide Title

33rd Turbomachinery Research Consortium Meeting
Identification of structural stiffness
and material loss factor in a
shimmed (generation one) bump
type foil bearing
TRC-B&C-04-2013
Luis San Andrés
Mast-Childs Professor
Joshua Norsworthy
Graduate Research Assistant
May 2013
TRC Project 32513/1519 FB
Metal Mesh Foil Bearings: Operation at high temperatures
1
Bump-type foil bearing (BFB)
BFB components: bearing cartridge,
bump Foil strip (compliant), and top foil
Hydrodynamic air film pressure develops
between the rotating shaft and the top foil
Top Foil Fixed
End
Top Foil
Bearing
Cartridge
Bump
Foil
Applications: ACMs, micro gas turbines,
turbo expanders, turbo compressors, turbo
blowers, soon in automotive turbochargers
 Adequate load capacity provided by
the bump foil strip (compliant)
 Frictional damping (due to relative
motion of bump foils) dominates
 Tolerant to misalignment
Bump Foil
Bearing
Cartridge
2
Issues with foil bearings
 Endurance: performance at start up & shut down
 Little test data for rotordynamic force coefficients
 Thermal management for high temperature
applications (gas turbines, turbochargers)
 Prone to subsynchronous whirl and limit
cycle operation –
Example subsynchronous motions
RudDloff, L., Arghir, M., et al., 2011,
“Experimental Analysis of a First
generation foil Bearing. Start-Up
Torque and Dynamic Coefficients,”
ASME GT2010-22966
Unloaded FB: “Self-Excited” whirl motions at speed 30 krpm (500
Hz) with whirl frequency=165 Hz (WFR=0.33)
Original and shimmed GFBs
Thin foil
Structural bump
Θl
Θl
Ω
Ω
Y
Journal
Y
Journal
Θp
g
Θs
Housing
X
(a) Gas
foil bearing
Original
GFB
Original GFB
ts
Shim
X
(b) Gas foilShimmed
bearing with
GFBthree shims
Shimmed GFB
Inserting metal shims underneath bump strips introduces a
preload (centering stiffness) at low cost – typical industrial
practice. Preload produces centering stiffness at small loads
Kim, T.H., and San Andrés, L., 2009, Trib. Trans.
5
Test BFB specifications
Parameters
Bearing cartridge outer diameter, DO
Bearing cartridge inner diameter, DI
Bearing axial length, L
Top foil thickness (Inconel X750), tT
foil length , 2πDI
Number of bumps, NB
Bump foil (Inconel X750)
Thickness, tB
Pitch, s0
Length, lB
Height, hB
Shim (AISI 4140) length
Length
Thickness, ts
Width
Angular extent
Shaft diameter, Ds
Measured inner diameter of the FB
(assembled)
Magnitude
50.74 mm
37.98 mm
38.10 mm
0.1 mm
110 mm
26
Nominal FB radial clearance, cnom=(DI -Ds)/2
0.120 mm
Weight of test bearing and outer cartridge
0.112 mm
4.3 mm
2.1 mm
0.50 mm
38.1 mm
50 µm
7.87 mm
11.8°
36.5 mm
36.74 mm
1.1 kg (10 N)
Di
L
2cnom
Do
L/D = 1.03
Shimmed bump-type foil bearings
Bump
Foil
The shims have an
adhesive glue layer
on the bottom
Top Foil
Shims are added at
discrete locations
circumferentially
and stretch axially
Metal Shim
Bearing
Cartridge
Shimmed bumps are
pressed closer to the rotor
than other bumps
7
Clearance in a shimmed BFB
Clearance profile:
cnom: Nominal
bearing clearance
tS : Shim thickness
NS : Number of shims
θ : Angular coordinate
θp : Angular distance
between consecutive
shims
θ1 : Angular coordinate
of the first shim
(all angular coordinates
taken from the middle
of the shim)
8
Static load test rig
Lathe chuck holds shaft & bearing during loading/unloading cycles.
Load cell
Lathe saddle
Eddy Current sensor
Load cell
•
•
Eddy current
sensor
Test bearing
Lathe chuck
Lathe tool holder
Dr. Chirathadam, TRC 31st (2011)
Shaft affixed in lathe chuck
Test bearing
Stationary shaft
Load-deflection results for original BFB
Region of
bump
compression
x
4 cycles of push and
pull loads directed
90o to top foil fixed
end
Regions with bump
compression are
fitted to a third order
polynomial
Bearing reaction force:
F = K 0 + K 1x + K 3 x 3
Nonlinear F(X)
Region of
bump
compression
Small BFB
hysteresis loop :
little mechanical
energy dissipation
Regions of low load (<50 N) evidence the diametral clearance region
10
Load vs. deflection – compare
Applied load vs BFB deflection
250
200
Bearings with
100µm shims
150
Load [N]
100
-200
50
0
-100
-50 0
-100
-150
100
Bearings
without shims
200
Push Loads
Pull Loads
Bearings with
50µm shims -200
-250
Deflection [μm]
Original and Shimmed BFBs show nonlinear force behavior.
Shims effectively reduce bearing clearance.
11
Estimated bearing structural stiffness
Bearing structural
stiffness:
Bearing
with 50μm
shims
Push/Pull
K( x)
F

 K1  3K3 x 2
x
Bearing
with 100μm
shims
Push/Pull
Original
bearing
Push/Pull
Bearing with 100µm shims
K ≠0 at x=0: assembly
interference fit (no
clearance)
Bearing stiffness increases with bearing deflection and shim
thickness
12
Loss factor estimation
Loss factor g =
E dis
p K ed
2
=
1
p K ed
2
ò F dx
BFB with 100µm shims
Bearing Configuration
45º
90º
Original
0.07
50µm shims
0.20
100µm shims
0.07
Original
0.02
50µm shims
0.13
100µm shims
0.053
Largest loss
factor for the
50µm shim
bearing due to
increased
sliding friction
13
Predictions (90º orientation)
Load vs BFB deflection
50 µm shims
100 µm shims
Original
Stiffness
Predictions from a simple model agree well with experimental
results for all test configurations
14
Conclusions
Bearing structural stiffness increases with increasing shim
thickness and hardens with bearing displacement.
• The loss factor for the test (generation one) BFB is small.
• Highest loss factor g ~0.20 for bearing with 50 µm shims
due to increase in sliding of foil strips wit bearing cartridge.
• Predictions from model agree well with experimental
results.
Shimmed BFB (without an assembly interference
fit) shows larger energy dissipation than original
BFB.
Proposal to TRC (1 year)
Objective: Quantify rotor lift off and shut down events for
shimmed BFBs, as well as determine force coefficient
a) Install and test the original and shimmed BFB in a rotordynamic test
rig.
b) Conduct dynamic load tests to determine force coefficients over a
range of excitation frequencies
c) For increasing static loads, conduct rotor speed start-up and shut
down tests and record drag torque and lift-shaft speed.
Oil inlet
Eddy current sensor
Static
load
TC center housing
Journal
BEARING
Shaft
stub
Accelerometer
Oil outlet
Air outlet
Turbine
housing
Static load
BEARING
(force gauge)
5 cm
X
Thermocouple
Y
Squirrel
Thermocouple cage (Soft
elastic
support)
Stinger connection
to shaker
Load sensor
Accelerometer
New Proposal
Effect of Shimming on the
Rotordynamic Force
Coefficients of a Bump-type
Foil Bearing
Luis San Andrés
Mast-Childs Professor
Joshua Norsworthy
Graduate Research Assistant
May 2013
17
TRC budget
Shimmed bump foil bearings
Year I
Support for graduate student (20 h/week) x $ 2,050 x 12 months
$ 24,600
Fringe benefits (0.6%) and medical insurance ($185/month)
$
2,378
Travel to (US) technical conference
$
1,200
Tuition three semesters ($362 credit hour x 24 h/year)
$
8,688
Supplies for test rig (machine parts $1,000 + portable data
storage $140)
$
1,140
$ 37,996
Research will characterize, qualitatively and
quantitatively, shimming as a cheap and
effective way of improving rotordynamic
performance of rotors supported on BFBs.The
work is important for manufactures of
turbochargers, turboexpanders and micro gas
turbines