Transcript Slide 1

Gas
Bearings
for Oil-Free Turbomachinery
28th
Turbomachinery
Consortium
Meeting
Dynamic Forced Response of a
Rotor-Hybrid Gas Bearing System
due to Intermittent Shocks
Keun Ryu
Research Assistant
Luis San Andrés
Mast-Childs Professor
Principal Investigator
TRC-B&C-1-08
2008 TRC Project
GAS BEARINGS FOR OIL-FREE TURBOMACHINERY
Gas Bearings
for Oil-Free Turbomachinery
Micro
Turbomachinery
(< 0.5 MW)
ADVANTAGES
• High energy density
• Compact and fewer parts
• Portable and easily sized
• Lower pollutant emissions
• Low operation cost
ASME Paper No. GT2002-30404
http://www.grc.nasa.gov/WWW
/Oilfree/turbocharger.htm
Gas bearings
Gas Foil Bearing
• Oil-Free bearing
• High rotating speed (DN value>4M)
• Simple configuration
• Lower friction and power losses
• Compact size
Flexure pivot Bearing
AIAA-2004-5720-984
GT 2004-53621
Gas Bearings
for Oil-Freefor
Turbomachinery
Gas
Bearings
MTM
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 Oil-Freefor
Turbomachinery
Gas
Bearings
MTM
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 rubfree 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 Oil-Free
Turbomachinery
Gas
bearing
test
rig
Max. operating speed: 100 kpm
3.5 kW (5 Hp) AC integral motor
Rotor: length 190 mm, 28.6 mm diameter,
weight=0.826 kg
Rig
housing
Bearing shell and
Load cells
Bearing
cover
Gas bearing
Shaft and DC motor
Components of high-speed gas bearing test rig
Gas Bearings
for Oil-Freefor
Turbomachinery
GT 2008-50393
Gas
Bearings
MTMSupply
pressure
2007: Control of bearing stiffness / critical speed
20
Amplitude [μm, pk-pk]
5.08 bar
Displacements
at RB(H)
15
10
V: vertical
H: horizontal
2.36 bar
5.08 bar
Blue line: Coast down
Red line: Set speed
2.36 bar
5
R
L
0
0
5000
10000
15000
20000
Speed [rpm]
25000
30000
35000
40000
Controller activated system
Peak motion at “critical speed” eliminated by
controlling supply pressure into bearings
2007-2008 Objectives
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.
TEST gas bearings
Bearings
Gas Bearings for Oil-Free Turbomachinery
Flexure Pivot Hybrid Bearings: Promote stability, eliminate pivot wear,
engineered product with many commercial applications
33.2
A
Pressurized
air supply
Shaft
rotation
16.6
Air
Feeding
hole
φ0.62
Flexure web
Pad
7.0
120°
1.0
Ω
Rotor
LOP
16.5
Web length
Y
φ62.48
Casing
43.2°
A
72°
X
28.56
worn pads
surfaces
Load Cells
Section A-A
Clearances Cp =38 & 45 mm, Preload =7 & 5 mm (~20%)
Web rotational stiffness=20 Nm/rad
2008 Gas Bearing test rig layout
Gas Bearings for Oil-Free Turbomachinery
Accelerometer
Eddy current
sensors
Alignment Bolts
Load cells
Flexure pivot pad bearing
RB: Right bearing
LB: Left bearing
Thrust pin
Rotor
Imbalance
plane
LB
Pressurized air
supply
Rubber pad
Infrared tachometer
RB
Electric
motor
Base plate
cm
Supporting stand
Accelerometer
Lifting handle
Load cell
Test table
Plastic pad
Hitting rod
Plunger
Solenoid
Electromagnetic
pusher
E-pusher
: Push type solenoid
240 N
at 1 inch stroke
Electromagnetic pusher tests
Gas Bearings for Oil-Free Turbomachinery
25
Alignment Bolt
Accelerometer (A2)
Acceleration [g]
Eddy current
sensors
Multiple impact
20
Load cell
Accelerometer (A1)
Rotor
Gas bearing
15
Impact from e-pusher
10
Shock after dropping
5
0
Pressurized air
supply
0
plate
Base
Rubber pad
0.1
0.2
0.3
0.4
0.5
-5
Load cell
cm
Time [s]
1.6
Plastic pad
Hinged fixture
Hitting rod
Plunger
Solenoid
Acceleration [g]
Test table
1.2
0.8
0.4
Impact duration ~20 ms
E-force ~400 N (pk-pk)
0
0
200
400
Frequency [Hz]
600
800
Manual lift & drop tests
Gas Bearings for Oil-Free Turbomachinery
25
Shock from dropping
Alignment Bolt
Accelerometer (A2)
20
Multiple impact
Eddy current
sensors
Accelerometer (A1)
Rotor
Gas bearing
Acceleration [g]
Load cell
15
10
Shock from bounce
5
Manual lifting
0
0
0.1
0.2
0.3
0.4
0.5
-5
Pressurized air
supply
Time [s]
plate
Base
1.6
Lifting handle
Test table
Hinged fixture
Lift off to 5~15 cm
(10~30° rotation)
cm
Acceleration [g]
Rubber pad
1.2
0.8
0.4
0
0
200
400
Freqeuncy [Hz]
600
800
Coast down: E-pusher tests
Gas Bearings for Oil-Free Turbomachinery
Ps=5.08 bar (ab)
Impact force from e-pusher
50
Rotor speed
400
40
Measured impact force
300
30
200
20
100
10
0
0
Rotor speed [krpm]
500
20
40
60
80
100
120
Coast down time [sec]
V: vertical
H: horizontal
Intermittent shocks
Acceleration
on test rig100~400
base plate
Impact
force
N
Acceleration on left bearing housing
Rotor response at LH
Impact from e-pusher
0
R
L
20
15
Test rig base plate
Left bearing housing
46 krpm
0.2
Shock ~15 g
Transient rotor
response ~ 40 µm
Acceleration [g]
10
5
0.15
Shock from dropping
0
-5 0
0.1
0.05
0.1
0.15
0.2
0.05
-10
-15
0
-20
-25
-30
Rotor response at LH
Time [s]
-0.05
Rotor response [mm]
Rotor speed [krpm]
Force [N, pk-pk]
Displacements
at LB(H)
60
600
Mea
sure
d
acc
eler
atio
n on
test
rig
bas
Gas Bearings
for Oil-Free
Turbomachinery
Coast
down:
manual
lift & drop tests
Measured acceleration on test rig base plate
Acceleration on test rig base plate
Acceleration [g, pk-pk]
20
Shock induced
acceleration
At base 5~20 g
15
10
Chart Title
At housing
5~10 g
5
Ps=3.72 bar (ab)
0
10000
20000
30000
40000
50000
60000
Rotor synchronous response
25
No shock
Lift-drop test
Coast down time (lift-drop test)
Beyond critical speed:
Synchronous frequency is isolated
from shocks
Below 20 krpm:
Large fluctuation of synchronous
response
R
L
V: vertical
H: horizontal
Displacements
at LB(H)
Amplitude [μm, pk-pk]
Rotor speed [rpm]
20
Coast down time
(lift-drop test)
15
100
80
60
Lift-drop test
10
40
5
20
No shock
0
0
0
10000
20000
30000
40000
Rotor peed [rpm]
50000
60000
Coadt down time [sec]
0
Gas Bearings for Oil-Free
Turbomachinery
Waterfall:
manual
lift & drop tests
Displacements
at LB(H)
Ps=2.36 bar (ab)
0.04
R
L
V: vertical
H: horizontal
0.03
2 krpm
0.02
Rotor
speed
decreases
0.01
2X
1X
60 krpm
0
0
250
500
750
1000
1250
1500
1750
2000
Frequency [Hz]
Excitation of rotor natural frequency. NOT a
rotordynamic instability!
Rotor response: manual lift & drop tests
8 bar (ab) feed pressure
o bearings
Gas Bearings for Oil-FreeChart
Turbomachinery
Title
Ps=2.36 bar (ab)
No shock
Synchronous
125
Lift-drop test
Subsychronous
Lift-drop test
15
Amplitude [μm, RMS]
Amplitude [μm, pk-pk]
Rotor overall response
140
No slow roll compensation
110
95
80
Subsynchronous
10
Synchronous
(slow roll
compensated)
5
65
No shock
50
0
10000
20000
30000
40000
50000
Rotor speed [rpm]
60000
0
0
10
20
30
40
50
Rotor speed [krpm]
Shock loads applied
Shock loads applied
Overall rotor amplitude increases largely.
Subsynchronous amplitudes larger than synchronous
60
Rotor response: manual lift & drop tests
Gas Bearings for Oil-Free Turbomachinery
Subsychronous
Subsychronous
Ps=2.36 bar (ab)
Natural frequency of
rotor-bearing system
(150~190 Hz)
300
15
Whirl amplitude [μm, RMS]
250
Whirl frequency [Hz]
Subsychronou
s
Subsychronou
s
200
150
Natural frequency of
test rig (~40 Hz)
100
50
0
10
5
0
0
10
20
30
40
Rotor speed [krpm]
50
60
0
50
100
150
200
250
300
Whirl frequency [Hz]
Rotor-bearing natural frequency increases with rotor
speed. Natural frequency of test rig also excited.
Rotor response: manual lift & drop tests
Acceleration on test rig base plate
Gas Bearings
for Oil-Free Turbomachinery
Acceleration on left bearing housing
Rotor response at LH
Shock from dropping
30
Acceleration [g]
Test rig base plate
0.25
Left bearing housing
Shock from bounce
10
0.2
0.15
0
0
0.05
0.1
Rotor response at LH
0.15
0.2
0.1
-20
0.05
-30
0
-40
-0.05
Time [s]
Rotor response [mm]
15 krpm
20
-10
Ps=2.36 bar (ab)
0.3
Drop induced
shocks ~30 g
Transient response
Full recovery within
~ 0.1 sec.
Rotor speed vs time (No shocks)
Gas Bearings for Oil-Free Turbomachinery
70
5.08 bar, No shock
Rotor speed [krpm]
60
3.72 bar, No shock
2.36 bar, No shock
50
40
5.08 bar
3.72 bar
30
20
2.36 bar
10
0
0
20
40
60
80
Coast down time [sec]
100
120
Dry friction
(contact)
With feed pressure: long time to coast down
demonstrates very low viscous drag!
Gas Bearings
for Oil-Free
Rotor
speed
vsTurbomachinery
time (Manual lift-drop tests)
3.72 bar (ab) feed pressure into bearings
60
50
Rotor speed [krpm]
40
40
Exponetial decay,
R2=98.99%
30
30
Measured shock on
test rig base plate
Linear decay,
R2=99.03%
20
20
10
10
0
0
0
10
20
30
40
50
60
70
80
Overall coast down
time reduces with
shock loads (~ 20 sec)
No shocks
2.36 bar (ab) feed pressure into bearings
60
90
Drop-down test
Coast down time [sec]
Rotor speed [krpm]
Exponential decay (No
rubs) even under
severe external shocks
Rotor speed [krpm]
50
60
Rotor speed
Shock to test rig
50
Exponetial decay,
R2=98.45%
40
40
Linear decay,
R2=98.33%
30
30
Measured shock on
test rig base plate
No shocks
20
20
10
10
0
0
0
10
20
30
40
50
60
Coast down time [sec]
70
80
90
Acceleration [g, pk-pk]
Rotor speed [krpm]
50
60
Rotor speed
Shock to test rig
Acceleration [g, pk-pk]
Drop-down test
Conclusions
Gas Bearings for Oil-Free Turbomachinery
• Under shock loads ( up to ~30 g), natural frequency of rotorbearing 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
Bearings for Oil-Free
Turbomachinery
TRCGas
Proposal:
Gas Bearings
for Oil-Free Turbo-
machinery – Identification of Bearing Force
TASKS
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.
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)
Tuition & fees three semesters ($3,996x3) + Supplies for test rig
Total Cost:
$ 22,008
$ 17,992
$ 40,000
Gas Bearings for Oil-Free Turbomachinery
Electromagnetic shaker
LDS V406/8 – PA 100E Shaker force peak amplitude (sine): 98 N (22 lbf)
Useful frequency range: 5 ~ 9000 Hz
Operating rotor speed range: 170 Hz ~ 1 kHz
10 krpm ~ 60 krpm
Y
X
Z
Low frequency excitations: simulate road
surface effect on MTM
Identify frequency dependent bearing force
coefficients at increasing rotor speeds