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Gas Bearings for Oil-Free Turbomachinery28th Turbomachinery Consortium Meeting
Dynamic Forced Response of a Rotor-Hybrid Gas Bearing System
due to Intermittent Shocks
TRC-B&C-1-08
2008 TRC Project
GAS BEARINGS FOR OIL-FREE TURBOMACHINERY
Keun RyuKeun RyuResearch Assistant
Luis San AndrésLuis San AndrésMast-Childs ProfessorPrincipal Investigator
Gas Bearings for Oil-Free TurbomachineryMicro 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
Gas Bearings for Oil-Free Turbomachinery
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
Gas Bearings for MTM
Gas Bearings for Oil-Free Turbomachinery
Thrust in TRC 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
Gas Bearings for MTM
Gas Bearings for Oil-Free Turbomachinery
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
Gas bearing test rig
Gas Bearings for Oil-Free Turbomachinery
2007: 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
Gas Bearings for MTM GT 2008-50393
Gas Bearings for Oil-Free Turbomachinery
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.
2007-2008 Objectives
Gas Bearings for Oil-Free Turbomachinery
Clearances Cp =38 & 45 m, Preload =7 & 5 m (~20%)Web rotational stiffness=20 Nm/rad
TEST 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
worn pads surfaces
Flexure Pivot Hybrid Bearings: Promote stability, eliminate pivot wear, engineered product with many commercial applications
TEST gas Bearings
Gas Bearings for Oil-Free Turbomachinery
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
Gas Bearings for Oil-Free Turbomachinery
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
Gas Bearings for Oil-Free Turbomachinery
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)
Gas Bearings for Oil-Free Turbomachinery
-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
Gas Bearings for Oil-Free Turbomachinery
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
Gas Bearings for Oil-Free Turbomachinery
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
Gas Bearings for Oil-Free Turbomachinery
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
Gas Bearings for Oil-Free Turbomachinery
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)
Gas Bearings for Oil-Free TurbomachineryRotor 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
Gas Bearings for Oil-Free Turbomachinery
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)
Gas Bearings for Oil-Free Turbomachinery
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
Gas Bearings for Oil-Free Turbomachinery
• 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
Gas Bearings for Oil-Free Turbomachinery
TRC Proposal: Gas Bearings for Oil-Free Turbo-
machinery – Identification of Bearing Force Coefficients from Base-Induced Excitations
• Set up an electromagnetic shaker to deliver excitations (periodic loads of varying frequency) to the test rig.
• Measure the rotor response due to base induced excitations.
• Identify frequency dependent bearing stiffness and damping coefficients from measured rotor transient responses at increasing rotor speeds.
• Compare the identified bearing force coefficients to predictions from XLTRC2 computational models.
TA
SK
S
BUDGET FROM TRC FOR 2008/2009: Support for graduate student (20h/week) x $ 1,600 x 12 months,
Fringe benefits (2.5%) and medical insurance ($194/month) $ 22,008 Tuition & fees three semesters ($3,996x3) + Supplies for test rig $ 17,992 Total Cost: $ 40,000
Gas Bearings for Oil-Free Turbomachinery
Electromagnetic shakerShaker force peak amplitude (sine): 98 N (22 lbf)Useful frequency range: 5 ~ 9000 Hz
Identify frequency dependent bearing force coefficients at increasing rotor speeds
Operating rotor speed range: 170 Hz ~ 1 kHz 10 krpm ~ 60 krpm
Z
X
Y
LDS V406/8 – PA 100E
Low frequency excitations: simulate roadsurface effect on MTM