Transcript Slide 1

Gas
Bearings
for Oil-Free Turbomachinery
29th
Turbomachinery
Consortium
Meeting
Dynamic Response of a Rotor-Air
Bearing System due to Base
Induced Periodic Motions
Yaying Niu
Research Assistant
Luis San Andrés
Mast-Childs Professor
Principal Investigator
TRC-B&C-1-09
Start date: Oct 1st, 2008
2009 TRC Project
GAS BEARINGS FOR OIL-FREE TURBOMACHINERY
Micro Turbomachinery (< 0.5 MW)
Gas Bearings for Oil-Free Turbomachinery
Turbo Compressor
100 krpm, 10 kW
Advantages
• Compact and fewer parts
• Portable and easily sized
• High energy density
• Lower pollutant emissions
• Low operation cost
http://www.hsturbo.de/en/produkte/turboverdichter.html
Micro Turbo
500 krpm, 0.1~0.5 kW
http://www.hsturbo.de/en/produkte/micro-turbo.html
Oil-free turbocharger
120 krpm, 110 kW
http://www.miti.cc/new_products.html
Gas Bearings for Oil-Free Turbomachinery
Gas
Bearings for MTM
Metal Mesh Foil Bearing
Advantages
• Small friction and power losses
• Less heat generation
• Simple configuration
• High rotating speed (DN value>4M)
• Operate at extreme temperatures
Issues
GT 2009-59315
Gas Foil Bearing
AIAA-2004-5720-984
• Small damping
• Low load carrying capacity
• Prone to instability
Flexure Pivot Bearing
GT 2004-53621
Gas Bearings for MTM
Gas Bearings for Oil-Free TurbomachineryGT 2009-59199
2008: Intermittent base shock load excitations
Drop induced shocks ~30 g. Full recovery within ~ 0.1 sec.
Ps=2.36 bar (ab)
Alignment Bolt
Accelerometer (A2)
Load cell
Eddy current
sensors
Accelerometer (A1)
Rotor
Gas bearing
Pressurized air
supply
Base
plate
Rubber pad
Load cell
cm
Plastic pad
Test table
Hinged fixture
Hitting rod
Plunger
Solenoid
Rotor motion amplitude increases largely. Subsynchronous
amplitudes larger than synchronous. Excitation of system
natural frequency. NOT a rotordynamic instability!
2008-2009 Objectives
Gas Bearings for Oil-Free Turbomachinery
Evaluate the reliability of rotor-air bearing systems
to withstanding base load excitations
• Set up an electromagnetic shaker under the base
of test rig to deliver periodic load excitations
• Measure the rig acceleration and rotordynamic
responses due to shaker induced excitations
• Model the rotor-air bearing system subject to
base motions and compare the predictions to test
results
2009 Gas bearing test rig
Gas Bearings for Oil-Free Turbomachinery
Accelerometer
Alignment bolts
Rubber O-rings
Eddy current
Load cells
sensors
Imbalance
plane
Trust pin
Rotor
The rod merely pushes on the base plate!
Infrared tachometer
Test bearings
Motor
cm
Air supply
Test rig base
Oscilloscope
Rotor
y
Hinged
fixture
x
Coil
spring (9 kN/m)
Rubber
pad
Support springs
10°
Electromagnetic
shaker
28 cm
Test rig
Function
generator
Power
amplifier
Test table
Rotation
direction
Bearing
Electromagnetic shaker
Gas Bearings for Oil-Free Turbomachinery
Test
rotor and gas bearings
Flexure Pivot Hybrid Bearings: Improved stability, no pivot wear.
Rotor
Eddy current sensor probe
Vertical
Horizontal
Vertical
Horizontal
Left bearing
Right bearing
• 0.825 kg in weight
• 190 mm in length
• Location of sensors and
bearings noted
A
Gas bearing
Air supply
45 Flexure web
°
Pad
Load cells
Φ0.5 feed
hole
33.2
X
2.0
10°
7 2°
43°
Y
5
Static Load
62.48
6.0
A
Rota
tion
direc
tion
Section A-A
Clearances ~42 mm, Preload ~40%. Web rotational stiffness = 62 Nm/rad.
Test rig tilts by 10°. NOT Load-on-Pad (LOP) !
Shaker delivered accelerations
Gas Bearings for Oil-Free Turbomachinery
3
Rotation
direction
Bearing
Rotor
Excitation frequency: 6 Hz
Acceleration [g]
x
Hinged
fixture
Coil
spring (9 kN/m)
Rubber
pad
Rotor speed:
34 krpm (567 Hz)
0.17 sec (6 Hz)
2
y
Acceleration
1
0
-1
10°
-2
28 cm
0
0.1
0.2
0.3
0.4
0.5
Time [sec]
0.3
0.3
Excitation frequency: 6 Hz
Excitation frequency: 6 Hz
0.25
Excited
frequencies
Excited frequencies
Acceleration [g]
Acceleration [g]
0.25
6 Hz12 Hz 18 Hz 24 Hz
0.2
Acceleration
Acceleration
51 Hz
0.15
0.1
0.2
6 Hz
0.15
Due to electric motor
12 Hz
624 Hz
0.1
18 Hz
51 Hz
0.05
0.05
0
0
0
20
40
60
Frequency [Hz]
80
100
0
200
400
600
800
1000
Frequency [Hz]
Shaker transfers impacts to the rig base! Super harmonic frequencies are
excited.
Rotor speed coast down tests
Gas Bearings for Oil-Free Turbomachinery
0.05
0.045
1X
LV
Amplitude [mm]
0.04
RV
Rotor
LH
0.035
Left bearing
No base excitation
RH
Right bearing
Ps = 2.36 bar (ab)
2krpm
0.03
0.025
Rotor coasts down
from 35 krpm
0.02
0.015
0.01
30krpm
0.005
2X 35krpm
No added imbalance
0
0
100
200
300
400
500
600
700
800
900 1000
1100 1200
1300
1400
Frequency [Hz]
Subsynchronous whirling
starts beyond 30 krpm,
fixed at system natural
frequency 193 Hz
Amplitude (pk-pk) [μm]
25
Pressure
2.36bar 3.72bar 5.08bar
Natural Freq 192Hz 217Hz 250Hz
LV_2.36bar (ab)
Slow roll compensated
Synchronous response
20
LV_3.72bar (ab)
LV_5.08bar (ab)
15
250Hz (15krpm) @ 5.08bar
10
217Hz (13krpm) @ 3.72bar
5
192Hz (11.5krpm) @ 2.36bar
0
0
5
10
15
20
Speed [krpm]
25
30
35
40
Rotor speed coast down tests
Gas Bearings for Oil-Free Turbomachinery
Ps = 2.36 bar (ab)
0.05
LV
1X
0.045
0.04
Left bearing
0.035
0.3
RH
Excitation frequency: 12 Hz
Acceleration
0.25
Right bearing
2krpm
Acceleration [g]
0.03
0.025
0.02
0.015
0.2
Excited
frequencies
0.15
51 Hz
12 Hz 24 Hz 36 Hz 48 Hz
0.1
0.01
0.05
2X
0.005
35krpm
0
0
100
200
300
400
500
600
Natural freq-193Hz
20
700
800
900
1000
1100 1200
Frequency [Hz]
1300
0
1400
0
20
40
60
80
100
Frequency [Hz]
Amplitude_LV
Synchronous response
Subsynchronous response:
1) 24 Hz (Harmonic of 12 Hz)
2) Natural frequency 193 Hz
15
Amplitude [μm]
Amplitude [mm]
Rotor
LH
24Hz (2X12HzExcitation freq)
Shaker input frequency: 12Hz
RV
10
212 Hz
5
Natural frequency
0
0
100
200
300
400
Frequency [Hz]
500
600
Synchronous Dominant!
Excitation of system natural frequency
does NOT mean instability!
Fixed speed, increasing pressures
Gas Bearings for Oil-Free Turbomachinery
LV
RV
LH
Rotor
Left bearing
0.07
Amplitude [mm]
Offset by
0.01 mm
RH
Right bearing
LV_2.36bar
LV_3.72bar
LV_5.08bar
Excitation frequency: 12Hz; Speed: 34krpm
0.06 Excited
0.05
Shaker input frequency: 12Hz
Rotor speed: 34 krpm (567 Hz)
12Hz, 24Hz, 36hz, etc
frequency
and harmonics
70~90Hz
0.04
NOT due to base motion!
Natural
frequency
Synchronous
frequency 567Hz
(34 krpm)
Pressure
increases
0.03
243Hz
5.08 bar
0.02
215Hz
3.72 bar
0.01
193Hz
2.36 bar
0
0
100
200
300
400
500
600
700
Frequency [Hz]
Rotor response amplitude at the system natural
frequency decreases, as the feed pressure increases.
Gas Bearings
for Oil-Free Turbomachinery
Fixed
pressure,
increasing speeds
LV
RV
Rotor
LH
Left bearing
0.07
Right bearing
Excitation frequency: 12Hz; Feed pressure: 2.36bar (ab)
Excited frequency
12Hz,
and harmonics
Natural
frequency
0.06
0.05
Amplitude [mm]
Shaker input frequency: 12Hz
Feed pressure: 2.36 bar (ab)
RH
0.04
LV_26krpm
LV_30krpm
24Hz, 36hz, etc
LV_34krpm
567Hz (34krpm)
500Hz (30krpm)
70~90Hz
Speed
increases
433Hz (26krpm)
0.03
193Hz
34 krpm
0.02
180Hz
30 krpm
0.01
180Hz
26 krpm
0
0
100
200
300
400
500
600
700
Frequency [Hz]
Rotor response amplitude at the system natural
frequency increases, as the rotor speed increases.
Gas Bearings
Oil-Free
Turbomachinery
Fixed
speed for
and
pressure,
increasing input frequency
LV
RV
Rotor
LH
Left bearing
0.07
Rotor speed: 34 krpm (567Hz)
Feed pressure: 2.36 bar (ab)
RH
Right bearing
Feed pressure: 2.36bar (ab); Speed: 34krpm
Excited frequency
and harmonics
0.06
Natural
frequency
193Hz
Synchronous
frequency 567Hz
(34 krpm)
0.05
Amplitude [mm]
LV_W/O
LV_6Hz
LV_12Hz
LV_5Hz
LV_9Hz
Frequency
increases
0.04
12Hz
0.03
9Hz
0.02
6Hz
0.01
5Hz
70~90 Hz
NOT due to base motion!
No excitation
0
0
100
200
300
400
Frequency [Hz]
500
700
Same600
excitation
magnitude
for 6, 9, and 12 Hz
Rotor response amplitude at the system natural
frequency increases, as the input frequency increases.
Gas Bearings2for Oil-Free Turbomachinery
XLTRC prediction
FE rotor model
LV
5
10
15
RV
20
Shaft1
23
Shaft1
1
Shaker input frequency: 12Hz
Feed pressure: 2.36 bar (ab)
LV
RH
LH
RV
Rotor
LH
Left bearing
RH
Right bearing
0.8
Right bearing support
Test rig base
System Natural Freq
Base
motion
Natural freq=13,338cpm (222Hz)
Damping ratio=0.044
Rotor speed=34 krpm
Conical
XLTRC2
26 krpm
30 krpm
34 krpm
Conical
202 Hz
212 Hz
222 Hz
Cylindrical
185 Hz
193 Hz
201 Hz
Rotor speed
Measured
Rotor speed
Cylindrical
26 krpm
30 krpm
34 krpm
180 Hz
180 Hz
193 Hz
Conical mode
Input acceleration
12 Hz
0.7
Acceleration [m/s2]
Left bearing support
0.6
24 Hz
0.5
36 Hz
0.4
201 Hz
222 Hz
48 Hz
0.3
60 Hz
0.2
0.1
0
0
Cylindrical
50
100
150
200
250
Frequency [Hz]
Input acceleration
in XLTRC2, simulate
actual acceleration.
XLTiltPadHGB™
Prediction uses synchronous speed bearing force coefficients. In
actuality, gas bearing force coefficients are frequency dependent!
300
Gas Bearings2for Oil-Free Turbomachinery
XLTRC prediction
LV
Shaker input frequency: 12Hz Input acceleration
Feed pressure: 2.36 bar (ab)
only on VERTICAL
Rotor speed: 34 krpm (567 Hz) direction
RV
LH
Rotor
Left bearing
RH
Right bearing
0.8
LV_34krpm_measurement_relative
LV_34krpm_XLTRC2 prediction_absolute
100
Measured N.F. component
Amplitude [μm]
12Hz
567Hz
70~90Hz
10
193Hz
24Hz
Input acceleration
12 Hz
0.7
Acceleration [m/s2]
1000
0.6
24 Hz
0.5
36 Hz
0.4
201 Hz
222 Hz
48 Hz
0.3
60 Hz
0.2
0.1
201 & 222Hz
36Hz
0
0
1
48Hz
0.1
100
150
200
250
Frequency [Hz]
Predicted natural frequency
component
60Hz
0.01
10
50
100
1000
Prediction frequency step:
1.25 Hz.
Frequency [Hz]
XLTRC2 predicts absolute rotor motions! Measured rotor response is
relative to bearing housing.
300
Rigid rotor model prediction
Gas Bearings for Oil-Free Turbomachinery
Equations of Motion:
Rotor 1st bending mode:
1,917 Hz (115 krpm)
&
& GU
& CU
& KU = W  F  CU
&  KU
ΜU
imb
b
b
Shaker input frequency: 12Hz
Feed pressure: 2.36 bar (ab)
LV
1
Z  K   2Μ  i   G  i  C F
Steady-State!
LH
Absolute rotor response
Zr  Z  Ub
RV
Left bearing
Relative rotor response
System Natural Frequency:
Rigid rotor model
34 krpm
Conical
191 Hz
200 Hz
208 Hz
Cylindrical
184 Hz
192 Hz
200 Hz
XLTRC2
Conical
202 Hz
212 Hz
222 Hz
Cylindrical
185 Hz
193 Hz
201 Hz
0.6
24 Hz
0.5
36 Hz
0.4
200 Hz
48 Hz
209 Hz
0.3
60 Hz
0.2
0.1
0
Measured
Cylindrical
Acceleration [m/s2]
30 krpm
Right bearing
Input acceleration
12 Hz
0.7
26 krpm
RH
Input acceleration in rigid rotor model,
VERTICAL direction only!
0.8
Rotor speed
Rotor
180 Hz
180 Hz
193 Hz
0
50
100
150
200
250
300
Frequency [Hz]
System response equals to the superposition of unique single frequency
responses.
Gas Bearings for Oil-Free Turbomachinery
Rigid
rotor model prediction
Shaker input frequency: 12Hz
Feed pressure: 2.36 bar (ab)
Rotor speed: 34 krpm (567 Hz)
RV
Rotor
LH
Left bearing
RH
Right bearing
1000
0.8
LV_34krpm_code prediction_relative
LV_34krpm_measurement_relative
100
Measured N.F. component
Amplitude [μm]
567Hz
70~90Hz
193Hz
10
Input acceleration
12 Hz
0.7
Acceleration [m/s2]
LV
0.6
24 Hz
0.5
36 Hz
0.4
200 Hz
48 Hz
209 Hz
0.3
60 Hz
0.2
0.1
0
200 & 208Hz
0
50
100
150
200
250
300
Frequency [Hz]
1
Above the natural frequency,
the system is isolated!
12Hz
24Hz
0.1
36Hz
Predicted natural frequency
component
48Hz
60Hz
0.01
10
100
Frequency [Hz]
1000
Relative rotor motion
Rigid rotor model predicts relative rotor motions!
The test rotor-bearing system shows good isolation.
Conclusions
Gas Bearings for Oil-Free Turbomachinery
• The recorded rotor response contains the main input frequency
(5-12 Hz) and its super harmonics, and the rotor-bearing system
natural frequency.
• The motion amplitudes at the natural frequency are smaller
than the components synchronous with rotor speed.
• The rotor motion amplitude at the system natural frequency
increases as the gas bearing feed pressure (5.08~2.36bar)
decreases, as the rotor speed (26~34krpm) increases, and as
the shaker input frequency (5~12 Hz) increases.
• Predicted rotor motion responses obtained from XLTRC2® and
an analytical rigid rotor model show good correlation with the
measurements. The system shows reliable isolation.
Reliability of rotor-air bearing system to
withstanding base load excitations demonstrated