Transcript GAS FOIL BEARINGS FOR OIL

28th Turbomachinery Research Consortium Meeting
Development of a Test Rig for Metal Mesh
Foil Gas Bearing and Measurements of
Structural Stiffness and Damping in the
Metal Mesh Foil Bearing
Luis San Andrés
Tae-Ho Kim
Thomas Abraham Chirathadam
Alex Martinez
Project title : Metal Mesh-Top Foil Gas Bearings for Oil-Free Turbomachinery:
Test Rig for Prototype Demonstration
TAMU past work on Metal Mesh Dampers
METAL MESH DAMPERS proven
to provide large amounts of
damping. Inexpensive. Oil-free
Zarzour and Vance (2000) J. Eng. Gas Turb. & Power, Vol. 122
Advantages of Metal Mesh Dampers over SFDs
Capable of operating at low and high temperatures
No changes in performance if soaked in oil
Al-Khateeb and Vance (2001) GT-2001-0247
Test metal mesh donut and squirrel cage( in parallel)
MM damping not affected by modifying squirrel cage stiffness
Choudhry and Vance (2005) Proc. GT2005
Develop design equations, empirically based, to predict structural
stiffness and viscous damping coefficient
Recent Patents: gas bearings & systems
Thrust foil
Bearing
Foil Journal
Bearings
‘Air foil bearing having a porous foil’
Ref. Patent No. WO 2006/043736 A1
A metal mesh donut is a
cheap replacement to
“porous foil”
Turbocharger with hydrodynamic
foil bearings
Ref. Patent No. US7108488 B2
TRC Project: Tasks 07/08
Construction of Metal Mesh Foil Bearings
-Assembly of top foil and metal mesh donut inside a
cartridge
•Identification of structural force coefficients
-Static load-deflection tests for structural stiffness
-Dynamic load tests for stiffness and structural loss factor
-Effects of frequency
•Construction of test rig for demonstration of
MMFB Performance
-Turbocharger (TC) driven system
Metal Mesh Foil Bearing (MMFB)
Molding of top foil
(Heat treatment)
Top foil (An initial flat strip
and a curved, heat treated foil)
MMFB
Top foil within Metal Mesh Donut
Metal Mesh Foil Bearings
 Metal mesh donut and top foil assembled inside a
bearing cartridge.
 Hydrodynamic air film will develop between rotating shaft
and top foil.
 Metal mesh resilient to temperature variations
 Damping from material hysteresis
 Stiffness and viscous damping
coefficients controlled by metal
mesh material, size (thickness, L,
D), and material compactness
(density) ratio.
Application
Replace oil ring bearings in oil-free PV
turbochargers
Metal Mesh Foil Bearings (+/-)
 No lubrication (oil-free). NO
High or Low temperature limits.
 Resilient structure with lots of
material damping.
 Simple construction ( in
comparison with other foil
bearings)
 Cost effective
 Rotordynamic force
coefficients unknown
 Near absence of predictive models
 Damping NOT viscous. Modeling
difficulties
MMFB dimensions and specifications
Dimensions and Specifications
Values
Top foil
Bearing Cartridge outer diameter, DBo(mm)
58.15±0.02
Bearing Cartridge inner diameter, DBi(mm)
42.10±0.02
Bearing Axial length, L (mm)
28.05±0.02
Metal mesh donut outer diameter, DMMo (mm)
42.10±0.02
Metal mesh donut inner diameter, DMMi(mm)
28.30±0.02
Ω
PICTURE
Rotating shaft
Gas film
Bearing cartridge
Metal mesh density, ρMM (%)
20
Top foil thickness, Ttf (mm)
0.076
Metal wire diameter, DW (mm)
0.30
Young’s modulus of Copper, E (GPa), at 21 ºC
110
Poisson’s ratio of Copper, υ
0.34
Bearing mass (Cartridge + Mesh + Foil), M (kg)
Donut shaped
metal mesh
0.3160 ±
0.0001
Static load test setup
Lathe chuck holds shaft & bearing during loading/unloading cycles.
Load cell
Eddy Current sensor
Stationary shaft
Lathe tool holder
Test MMFB
Lathe tool holder moves forward and backward : push and pull forces
on MMFB
Static Load vs bearing deflection results
MMFB wire density ~ 20%
150
Push Load
Pull Load
Static load, F (N)
100
Nonlinear F(X)
50
Push load
0
-0.07
3 Cycles: loading &
unloading
-0.02
-50
Start
0.03
-100
Hysteresis loop
-150
Displacement, X (mm)
Displacement: [-0.06,0.06] mm
Load: [-130, 90 ]N
Pull load
Large hysteresis
loop : Mechanical
energy dissipation
Derived MMFB structural stiffness
MMFB wire density ~ 20%
6
Push load
Pull load
Stiffness [MN/m]
5
D
Push load
4
Pull load
B
3
A
2
C
1
Start
0
-0.08 -0.06 -0.04 -0.02
0
0.02 0.04 0.06 0.08
Displacement [mm]
Max. Stiffness ~ 4 MN/m
During Load
reversal : jump in
structural stiffness
Dynamic load tests
12.7, 25.4 &38.1 μm
Motion amplitude controlled mode
MMFB
Accelerometer Force transducer
Frequency of excitation :
25 – 400 Hz (25 Hz interval)
Waterfall of displacement
200
180
Electrodyamic shaker
Test shaft
Test shaft Fixture
Eddy Current sensors
Displacement [um]
160
Increasing
frequency
1X
140
120
100
80
60
40
20
0
0
100
200
300
Frequency [Hz]
MMFB motion amplitude (1X) is dominant.
400
500
600
Amplitude of Dynamic Load vs Excitation Frequency
90
38.1 μm
Dynamic load [N]
80
Dynamic load
decreases with
increasing
frequency and
decreasing
motion
amplitudes
12.7 um
25.4um
38.1 um
70
Motion amplitude decreases
60
50
40
25.4 μm
30
12.7 μm
20
10
0
0
100
200
300
400
Frequency [Hz]
At higher frequencies, less force needed to maintain same
motion amplitudes
Identification Model
Fext x
1-DOF mechanical system
Ks
ss
F(t)
Keq
Fext
Meq
L Lf L s
Ceq
z
Lf =244 mm
X(t)
Lf =221 mm
L= 248 mm
x
Equivalent Test System
M x  K x  C x  F(t )
Parameter Identification (no shaft rotation)
it
F (t )  F e
x(t )  X e
it
F
2
Z   (K   M )  i  C
X
Edis  C X
2
Edis    K X
2
1
F
  Im  
K X
Harmonic force
& displacements
Impedance Function
Viscous Dissipation
Or Hysteresis Energy
Material
LOSS FACTOR
C 
K

Real part of (F/X) vs excitation frequency
(K   M )
2
Frequency of excitation :
25 – 400 Hz ( 25 Hz step)
4
Real part of F/X [MN/m]
3.5
12.7 um
25.4 um
38.1 um
12.7 μm
3
Motion amplitude
increases
2.5
2
1.5
1
25.4 μm
0.5
38.1 μm
0
Natural frequency
of the system
-0.5
-1
0
100
200
300
400
Frequency [Hz]
Real part of (F/X) decreases with increasing motion amplitude
MMB structural stiffness vs excitation frequency
K
4
Motion amplitude
increases
3.5
Structural Stiffness [M N/m]
12.7 um
25.4 um
38.1 um
12.7 um
3
2.5
Frequency of excitation :
25 – 400 Hz (25 Hz step)
At low frequencies
(25-100 Hz), Stiffness
decreases fast.
At higher frequencies,
Stiffness levels off
2
1.5
1
38.1 um
25.4 um
0.5
0
0
100
200
300
400
MMFB stiffness is
frequency and
motion amplitude
dependent
Frequency [Hz]
Al-Khateeb & Vance model : reduction of stiffness with force
magnitude (amplitude dependent)
Imaginary part of impedance (F/X) vs frequency
 C  K
Frequency of excitation :
25 – 400 Hz ( at 25 Hz interval)
Imaginary part of F/X [MN/m]
2
12.7 um
25.4 um
38.1 um
1.8
1.6
1.4
12.7 μm
Motion amplitude
increases
Im (F/X)
decreases with
motion
amplitude, little
frequency
dependency
1.2
1
0.8
0.6
0.4
25.4 μm
0.2
38.1 μm
0
0
100
200
Frequency [Hz]
300
400
Loss factor vs excitation frequency
Structural Loss Factor

Frequency of excitation :
25 – 400 Hz ( at 25 Hz step)
1
0.9
0.8
12.7 um
25.4 um
38.1 um
Structural damping or
loss factor increases with
frequency ( 25-150 Hz)
25.4 μm
0.7
0.6
38.1 μm
But, remains nearly
constant for higher
frequencies ( 175-400 Hz)
0.5
0.4
0.3
0.2
0.1
0
12.7 μm
0
100
200
300
400
Frequency [Hz]
Loss factor ~ frequency independent at high freqs.
Model of Metal Mesh damping material
Stick-slip model (Al-Khateeb & Vance, 2002)
Stick-slip
model
arranges
wires in series
connected by
dampers and
springs.
As force increases, more stick-slip joints between wires are
freed, thus resulting in a greater number of spring-damper
systems in series.
Design equation: Metal mesh stiffness/damping
Empirical design equation for stiffness and equivalent viscous damping
coefficients (Al-Khateeb & Vance, 2002)
 
K  Eequiv  f  L, Ro , Ri   f C A   f R p  f  A  f  
2


Rp
L
5  C A 
2 

K  Eequiv 
 1  4 10 

1

2.96

10



 R R
 Ro  Ri  
 L   
i
 o
2 / 3 
 
 A 
   k  
   1   k 


 
 Ro  Ri 
  

 
C  Hequiv  g  L, Ro , Ri   g CA   g Rp  g  A  g  
2 

Rp
L
5  C A 
2 


C  H equiv 
 1  8.7 10 

1

1.8

10


 Ro  Ri  
 L   
 Ro  Ri




2 / 3  


 A 
   c
  1   c 
  

 
 
R

R




i 
 o
  n  
 
3/ 2 
Functions of equivalent modulus of elasticity (Eequiv),
hysteresis coeff. (Hequiv), axial length (L), inner radius (Ri),
outer radius (Ro), axial compression ratio (CA), radial
interference (Rp), motion amplitude (A), and excitation
frequency (ω)
Structural stiffness coefficient [MN/m]
Stiffness: prediction & test data
MMFB12.7structural
um
25.4 stiffness
um
38.1
decreases
um
as Series4
frequency
Series5
increases
and
Series6
as motion
amplitude
increases
4
Amplitude
increases
3.5
3
2.5
12.7 μm
2
25.4 μm
1.5
38.1 μm
1
Markers: Test data
0.5
Lines: Prediction
12.7 μm
0
0
100
200
300
400
500
Frequency [Hz]
25.4 μm
38.1 μm
Markers: Test data
Lines: Prediction
Predictions compared to test data: Damping
Viscous damping coefficient [N-s/m]
12.7 um
10000
25.4 um
38.1 um
Amplitude
increases
1000
12.7 μm
25.4 μm
38.1 μm
Markers: Test data
Lines: Prediction
100
0
100
200
300
400
500
Series4
MMFB
equiv.
Series5
viscous
damping
Series6
decreases
as the excitation
frequency
12.7 μm
increases
and
25.4 μm
38.1 μm
as motion
amplitude
increases
Frequency [Hz]
Markers: Test data
Lines: Prediction
Predicted equivalent viscous damping coefficients in good
agreement with measurements
Metal Mesh Foil Bearing Rotordynamic Test Rig
(a) Static shaft
TC cross-sectional view
Ref. Honeywell drawing # 448655
Max. operating speed: 120 krpm
Turbocharger driven rotor
Regulated air supply:9.30bar (120
psig)
Test Journal: length 55 mm, 28
mm diameter , Weight=0.22 kg
Journal press fitted on Shaft Stub
Twin ball bearing turbocharger,
Model T25, donated by
Honeywell Turbo Technologies
Metal Mesh Foil Bearing Rotordynamic Test Rig
Static load
Load cell
Torque arm
TC
driving
system
Rotating
journal
Spring
Eddy
current
sensor
Weight
Squirrel cage
Positioning table
(a) Right side view
(b) Front view
Static load applies upwards : using weights &
pulleys
Arm and load cell to measure bearing torque
measurement
Metal Mesh Foil Bearing Rotordynamic Test Rig
Squirrel Cage:
- Provides soft support to
MMFB
- Maintains concentricity
(prevents tilting) of MMFB
with test journal
Positioning table:
Max load 110N
Max 3”X 3” travel in two directions
Resolution of 1μm
COST of positioning TABLE: $3631
- Supports squirrel cage
- Provides motion in two
horizontal directions
Conclusions
TC
driven MMFB rotordynamic test rig under
construction
Static and dynamic load tests on metal mesh
bearings show large energy dissipation and
(predictable) structural stiffness

MMFB
stiffness decreases with amplitude of
dynamic motion
MMFB structural loss factor ( ~0.50 ) at
high frequencies
Large
Predicted stiffness and equivalent viscous damping
coefficients are in agreement with test coefficients: Test data
validates design equations
TRC Proposal: Metal Mesh Foil Bearings for Oil-Free
TASKS
Turbo-machinery : Rotordynamic performance
Complete construction of turbocharger driven
MMFB test rig : squirrel cage, static loading device
and torque measurement device
Conduct experiments on test rig
Rotor lift off and touch down speeds, measurements of
torque & load capacity, vibration and stability (if any)
Identification of dynamic force response
Impact loads on test bearing + more measurements of
structural stiffness and loss factor
BUDGET FROM TRC FOR 2008/2009:
Support for graduate student (20 h/week) x $ 1,600 x 12 months
+ Fringe benefits (2.5%) and medical insurance ($ 164/month)
Tuition three semesters ($ 3996x3) + Supplies for test rig($ 6004)
Total Cost:
$ 22,008
$ 17,992
$ 40,000