gt2009-59199 flexure pivot hybrid gas bearings keun ryu research assistant asme turbo expo 2009,...
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GT2009-59199 Flexure Pivot Hybrid Gas Bearings
Keun RyuKeun RyuResearch Assistant
ASME TURBO EXPO 2009, Orlando, Fla
Dr. Luis San AndrésDr. Luis San AndrésMast-Childs Professor
Fellow ASME
TURBOMACHINERY LABORATORYTEXAS A&M UNIVERSITY
Supported by TAMU Turbomachinery Research Consortium
ASME paper GT2009-59199
Dynamic Forced Response of a Rotor-Hybrid Gas Bearing System
due to Intermittent Shocks
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
Micro Turbomachinery (< 0.5 MW)
• High energy density • Compact and fewer parts• Portable and easily sized• Lower pollutant emissions• Low operation cost
ADVANTAGES
• Oil-Free bearing • High rotating speed (DN value>4M)• Simple configuration• Lower friction and power losses• Compact size
Gas bearings
AIAA-2004-5720-984
Gas Foil Bearing
GT 2004-53621
Flexure pivot Bearing
ASME Paper No. GT2002-30404
http://www.grc.nasa.gov/WWW/Oilfree/turbocharger.htm
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
Ideal gas bearings for micro turbomachinery (< 0.5 MW ) must be:
Simple – low cost, small geometry, low part count, constructed from common materials, manufactured with elementary methods. Load Tolerant – capable of handling both normal and extreme bearing loads without compromising the integrity of the rotor system.
High Rotor Speeds – no specific speed limit (such as DN) restricting shaft sizes. Small Power losses.
Good Dynamic Properties – predictable and repeatable stiffness and damping over a wide temperature range.
Reliable – capable of operation without significant wear or required maintenance, able to tolerate extended storage and handling without performance degradation.
+++ Modeling/Analysis (anchored to test data) readily available
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
Thrust of research program:
Investigate conventional bearings of low cost, easy to manufacture (common materials) and easy to install & align.
Combine hybrid (hydrostatic/hydrodynamic) bearings with low cost coating to allow for rub-free operation at start up and shut down
Major issues: Little damping, Wear at start & stop, Instability (whirl & hammer), & reliability under shock operation
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
Max. operating speed: 100 kpm3.5 kW (5 Hp) AC integral motor
Rotor: length 190 mm, 28.6 mm diameter, weight=0.826 kg
Components of high-speed gas bearing test rig
Rig housing
Bearing shell andLoad cells
Gas bearing
Bearing cover
Shaft and DC motor
Test rig
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
Test rig
Positioning Bolt
X
Y
Load
LOP
Rotor/motor
Bearing
Sensors
Load cell
Air supply
Thrust pin
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
Air Feeding
holeφ0.62
33.2
Section A-A
16.5Web length
16.6
φ62.48
A
A
120°
28.56
Load Cells
Pressurized air supply
PadFlexure web
Ω
Shaft rotation
1.0
7.0
43.2°72°
LOP
X
YRotor
Casing
Promote stability: no cross-coupled stiffnesses Eliminate pivot wear, contact stresses, pad flutter Minimize manufacturing and assembly tolerances’ stack-up
Flexure pivot tilting pad hybrid bearing
Clearances Cp =38 & 45 m, Preload =7 & 5 m (~20%)Web rotational stiffness=20 Nm/rad
worn pads surfaces
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
Zhu & San Andres (2004) GT 2004-53621 Gas bearing for oil-free applications. Good comparisons with:
TAMU work on flexure pivot tilting bearings
Delgado & San Andres (2004)Computational model for hydrodynamic operation, with application to hybrid brush seals
San Andres (2006)Computational model for hybrid operation validated by Zhu (2004) measurements. Code used by 20+ companies
Stable to 99 krpm
60 KRPM
GT 2004-53614
GT 2004-53621
Journal of Tribology, 129
San Andres & Ryu (2007)Operation with worn clearances and LOP/LBP configuration
J. Eng. Gas Turbines and Power, 2008, 130
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
2008: Control of bearing stiffness / critical speed
Peak motion at “critical speed” eliminated by controlling supply pressure into bearings
Controller activated system
Displacements at RB(H)
L R
V: verticalH: horizontal
5.08 bar
2.36 barBlue line: Coast down
Red line: Set speed
2.36 bar5.08 bar
J. Eng. Gas Turbines and Power, 2008, v. 130
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
Objectives:
Demonstrate the rotordynamic performance, reliability, and durability of hybrid gas bearings
•Rotor motion measurements for increasing gas feed pressures and speed range to 60 krpm.
•Install electromagnetic pusher to deliver impact loads into test rig.
•Perform shock loads (e-pusher & lift-drop) tests to assess reliability of gas bearings to withstand intermittent shocks without damage.
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
cmcmElectricmotor
Load cells
Infrared tachometer
Pressurized air supply
Thrust pin
Flexure pivot pad bearing
Eddy current sensors
Alignment Bolts
Imbalance plane
RB: Right bearingLB: Left bearing
LB RB
Base plate
Hitting rod
Test table
Electromagnetic pusher
Load cellRubber pad
Accelerometer
Accelerometer
Plunger
Solenoid
Lifting handle
Rotor
Plastic pad
Supporting stand
E-pusher: Push type solenoid
240 N at 1 inch stroke
2008 Gas bearing test rig layout
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
Load cell
Pressurized air supply
Eddy current sensors
Alignment Bolt
Base plate
Hitting rod
Test table
Load cell
Rubber pad
Accelerometer (A1)
Accelerometer (A2)
Plunger
Solenoid
RotorGas bearing
Hinged fixture
cmcm Plastic pad
-5
0
5
10
15
20
25
0 0.1 0.2 0.3 0.4 0.5
Time [s]
Acc
ele
rati
on
[g
]
Impact from e-pusher
Shock after dropping
0
0.4
0.8
1.2
1.6
0 200 400 600 800
Frequency [Hz]
Ac
ce
lera
tio
n [
g]
Electromagnetic pusher tests
Impact duration ~20 msE-force ~400 N (pk-pk)
Multiple impact
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
Load cell
Pressurized air supply
Eddy current sensors
Alignment Bolt
Base plate
Test table
Rubber pad
Accelerometer (A1)
Accelerometer (A2)
Manual lifting
RotorGas bearing
Lifting handle
Hinged fixture
cmcm
-5
0
5
10
15
20
25
0 0.1 0.2 0.3 0.4 0.5
Time [s]
Acc
ele
rati
on
[g
]
Shock from dropping
Shock from bounce
0
0.4
0.8
1.2
1.6
0 200 400 600 800
Freqeuncy [Hz]
Ac
ce
lera
tio
n [
g]
Manual lift & drop tests
Multiple impact
Lift off to 5~15 cm (10~30° rotation)
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
-30
-25
-20
-15
-10
-5
0
5
10
15
20
0 0.05 0.1 0.15 0.2
Time [s]
Acc
ele
rati
on
[g
]
Ro
tor
res
po
ns
e [m
m]
0
-0.05
0.05
0.1
0.15
0.2Test rig base plate
Left bearing housing
Rotor response at LH
Shock from dropping
Impact from e-pusher0
100
200
300
400
500
600
0 20 40 60 80 100 120
Coast down time [sec]
Fo
rce
[N
, p
k-p
k]
Impact force from e-pusher
Rotor speed
Rotor speed [krpm]
Measured impact force
Ro
tor
sp
ee
d [
krp
m]
60
50
40
20
30
10
0
Shock ~15 gTransient rotor response ~ 40 µm
46 krpm
Intermittent shocksImpact force 100~400 N
Displacements at LB(H)
L R
V: verticalH: horizontal
Ps=5.08 bar (ab)
Coast down: E-pusher tests
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
0
5
10
15
20
0 10000 20000 30000 40000 50000 60000
Rotor speed [rpm]
Acc
eler
atio
n [
g,
pk-
pk]
Acceleration on test rig base plate
Shock induced acceleration
At base 5~20 gAt housing 5~10 g
Beyond critical speed: Synchronous frequency is isolated from shocks
Below 20 krpm:Large fluctuation of synchronous response
Ps=3.72 bar (ab)
Displacements at LB(H)
L R
V: verticalH: horizontal
Coast down: manual lift & drop tests
Chart Title
0
5
10
15
20
25
0 10000 20000 30000 40000 50000 60000
Rotor peed [rpm]
Am
plit
ud
e [μ
m, p
k-p
k]
No shock
Lift-drop test
Coast down time (lift-drop test)
No shock
Lift-drop test
Coast down time (lift-drop test) 60
40
20
0
Co
adt
do
wn
tim
e [s
ec]
80
100
Rotor synchronous response
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
0.04
0.03
2 krpm
0.02
0.01
1X 2X
0 60 krpm0 250 500 750 1000 1250 1500 1750 2000
Frequency [Hz]
Rotor speed
decreases
Excitation of rotor natural frequency. NOT a rotordynamic instability!
Ps=2.36 bar (ab)Displacements
at LB(H)
L R
V: verticalH: horizontal
Waterfall: manual lift & drop tests
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
Overall rotor amplitude increases largely. Subsynchronous amplitudes larger than synchronous
0
5
10
15
0 10 20 30 40 50 60
Rotor speed [krpm]A
mp
litu
de
[μm
, R
MS
]
Synchronous
Subsychronous
Subsynchronous
Synchronous(slow roll
compensated)
Rotor response: manual lift & drop tests
Ps=2.36 bar (ab)
Shock loads applied Shock loads applied
Chart Title
50
65
80
95
110
125
140
0 10000 20000 30000 40000 50000 60000
Rotor speed [rpm]
Am
plitu
de [μ
m, p
k-pk
]
No shock
Lift-drop test
5.08 bar (ab) feed pressure into bearings
No shock
Lift-drop test
Rotor overall response
No slow roll compensation
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
0
5
10
15
0 50 100 150 200 250 300
Whirl frequency [Hz]
Wh
irl
amp
litu
de
[μm
, R
MS
]0
50
100
150
200
250
300
0 10 20 30 40 50 60
Rotor speed [krpm]
Wh
irl
freq
uen
cy [
Hz]
Natural frequency of rotor-bearing system (150~190 Hz)
Natural frequency of test rig (~40 Hz)
Rotor-bearing natural frequency increases with rotor
speed. Natural frequency of test rig also excited.
Rotor response: manual lift & drop tests
Ps=2.36 bar (ab)
GT2009-59199 Flexure Pivot Hybrid Gas BearingsRotor response: manual lift & drop tests
15 krpmDrop induced shocks ~30 g
Transient responseFull recovery within
~ 0.1 sec.
Ps=2.36 bar (ab)
-40
-30
-20
-10
0
10
20
30
0 0.05 0.1 0.15 0.2
Time [s]
Ac
ce
lera
tio
n [
g]
Ro
tor
res
po
ns
e [
mm
]
Test rig base plate
Left bearing housing
Rotor response at LH
Shock from bounce
Shock from dropping
0.2
0
0.05
0.1
-0.05
0.15
0.2
0.25
0.3
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
With feed pressure: long time to coast down demonstrates very low viscous drag!
0
10
20
30
40
50
60
70
0 20 40 60 80 100 120
Coast down time [sec]
Ro
tor
sp
ee
d [
krp
m]
5.08 bar, No shock
3.72 bar, No shock
2.36 bar, No shock
5.08 bar
2.36 bar
3.72 bar
Dry friction
(contact)
Rotor speed vs time (No shocks)
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70 80 90
Coast down time [sec]
Ro
tor
sp
ee
d [
krp
m]
Rotor speed
Shock to test rig
Measured shock on test rig base plate
Acc
eler
atio
n [
g,
pk-
pk]Rotor speed [krpm]
60
50
40
20
30
10
0
3.72 bar (ab) feed pressure into bearings
Drop-down test
Exponetial decay,
R2=98.99%
Linear decay,R2=99.03%
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70 80 90
Coast down time [sec]
Ro
tor
sp
eed
[k
rpm
]
Rotor speed
Shock to test rig
2.36 bar (ab) feed pressure into bearings
Measured shock on test rig base plate
Acc
ele
rati
on
[g
, pk
-pk
]
Rotor speed [krpm]
60
50
40
20
30
10
0
Drop-down test
Exponetial decay,
R2=98.45%Linear decay,
R2=98.33%
Overall coast down time reduces with
shock loads (~ 20 sec)
Exponential decay (No rubs) even under severe external shocks
Rotor speed vs time (manual lift-drop tests)
No shocks
No shocks
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
• Under shock loads ( up to ~30 g), natural frequency of rotor-bearing system (150-200 Hz) and test rig base (~ 40 Hz) excited. However, rotor transient motions quickly die!
• For all feed pressures (2-5 bar), rotor transient responses from shocks restore to their before impact amplitude within 0.1 second. Peak instant amplitudes (do not exceed ~50 µm)
• Even under shock impacts, viscous drag effects are dominant, i.e., no contact between the rotor and bearing.
• Hybrid bearings demonstrate reliable dynamic performance even with WORN PAD SURFACES
Conclusions:
GT2009-59199 Flexure Pivot Hybrid Gas Bearings
Dominant challenges in gas bearing technology
Current research focuses on coatings (materials), rotordynamics (stability) & high temperature (thermal management)
– Bearing design & manufacturing process better known. Load capacity needs minute clearances since gas viscosity is low.
– Damping & rotor stability are crucial – Inexpensive coatings to reduce drag and wear at
low speeds and transient rubs at high speeds
– Engineered thermal management to extend operating envelope to high temperatures
Need Low Cost & Long Life Solution!
GT2009-59199 Flexure Pivot Hybrid Gas Bearings2009 Gas bearing test rig layout
Oscilloscope
Functiongenerator
Power amplifier
Test rig
Electromagnetic shakerTest table
Alignment bolts Rubber O-ringsEddy current
sensors
Trust pin
Imbalance plane
Infrared tachometer
Load cells
Test bearings Motor
Accelerometer
Support springs
Electromagnetic shaker
Test rig base
Air supply
Rotor
cm
connecting rod pushes base plate!
Rubber pad
Hingedfixture
Rotor
Bearing
y
x
Rotationdirection
10°
Coilspring (9 kN/m)
28 cm
GT2009-59199 Flexure Pivot Hybrid Gas BearingsRotor speed coast down tests
2X
1X
Natural freq-193Hz
24Hz (2X12Hz-Excitation freq)
35krpm
2krpm
Frequency [Hz]
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400
Am
pli
tud
e [m
m]
0.05
0.045
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0
0
5
10
15
20
0 100 200 300 400 500 600
Frequency [Hz]
Am
pli
tud
e [μ
m]
Amplitude_LV
Synchronous response
Natural frequency
212 Hz
Left bearing
Rotor
Right bearing
LH RH
LV RV
0
0.05
0.1
0.15
0.2
0.25
0.3
0 20 40 60 80 100
Frequency [Hz]
Acc
eler
atio
n [
g]
Acceleration
12 Hz 24 Hz 36 Hz
51 HzExcited frequencies
Excitation frequency: 12 Hz
48 Hz
Ps = 2.36 bar (ab)
Subsynchronous response:1) 24 Hz (Harmonic of 12 Hz)2) Natural frequency 193 Hz
Shaker input frequency: 12Hz
Synchronous Dominant! excitation of system natural frequency
is NOT an instability!
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