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
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 AndrésTae-Ho Kim
Thomas Abraham ChirathadamAlex 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
Zarzour and Vance (2000) J. Eng. Gas Turb. & Power, Vol. 122
Advantages of Metal Mesh Dampers over SFDsCapable of operating at low and high temperaturesNo 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
METAL MESH DAMPERS proven to provide large amounts of damping. Inexpensive. Oil-free
Recent Patents: gas bearings & systems
A metal mesh donut is a cheap replacement to “porous foil”
‘Air foil bearing having a porous foil’Ref. Patent No. WO 2006/043736 A1
Turbocharger with hydrodynamic foil bearingsRef. Patent No. US7108488 B2
Foil JournalBearings
Thrust foilBearing
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) Top foil within Metal Mesh Donut
MMFB
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.
ApplicationReplace 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 ValuesBearing 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
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) 0.3160 ± 0.0001
PICTURE
Bearing cartridge
Top foil
Donut shaped metal mesh
Rotating shaft
Gas film
Ω
Static load test setup
Lathe tool holder moves forward and backward : push and pull forces on MMFB
Lathe chuck holds shaft & bearing during loading/unloading cycles.
Lathe tool holder
Eddy Current sensor Load cell
Test MMFB
Stationary shaft
-150
-100
-50
0
50
100
150
-0.07 -0.02 0.03
Displacement, X (mm)
Stat
ic lo
ad,
F (N
)
Push Load
Pull Load
Static Load vs bearing deflection results 3 Cycles: loading &
unloading
Nonlinear F(X)
Large hysteresis loop : Mechanical energy dissipation
MMFB wire density ~ 20%
Displacement: [-0.06,0.06] mmLoad: [-130, 90 ]N
Start
Push load
Pull load
Hysteresis loop
MMFB wire density ~ 20%
Derived MMFB structural stiffness
During Load reversal : jump in
structural stiffness
Max. Stiffness ~ 4 MN/m
Start
Push load
Pull load
Dynamic load tests Motion amplitude controlled mode
Electrodyamic shaker
MMFB Accelerometer Force transducer
Test shaft FixtureTest shaftEddy Current sensors
MMFB motion amplitude (1X) is dominant.
Waterfall of displacement
0
20
40
60
80
100
120
140
160
180
200
0 100 200 300 400 500 600
Frequency [Hz]
Dis
pla
cem
ent [
um
]
1 XIncreasing frequency
12.7, 25.4 &38.1 μm
Frequency of excitation :
25 – 400 Hz (25 Hz interval)
0
10
20
30
40
50
60
70
80
90
0 100 200 300 400Frequency [Hz]
Dyn
amic
load
[N]
12.7 um25.4um38.1 um
At higher frequencies, less force needed to maintain same motion amplitudes
Amplitude of Dynamic Load vs Excitation Frequency
Dynamic load decreases with
increasing frequency and
decreasing motion
amplitudes
38.1 μm
25.4 μm
12.7 μm
Motion amplitude decreases
Identification Model
( )tM x K x C x F
Equivalent Test System
Meq
Keq
Ceq
Fext
x Lf =244 mm Lf =221 mm L= 248 mm
F(t)
X(t)
1-DOF mechanical system
Harmonic force & displacements
Impedance Function
MaterialLOSS FACTOR
Viscous DissipationOr Hysteresis Energy
( ) i tx t X e ( ) i tF t F e
2( )F
Z K M i CX
2
disE K X
2
disE C X
Parameter Identification (no shaft rotation)
KC
1
ImF
K X
-1
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
0 100 200 300 400
Frequency [Hz]
Re
al
pa
rt o
f F/X
[M
N/m
]
12.7 um25.4 um38.1 um
Real part of (F/X) decreases with increasing motion amplitude
Real part of (F/X) vs excitation frequency
Natural frequency of the system
Frequency of excitation :
25 – 400 Hz ( 25 Hz step)
2( )K M
12.7 μm
25.4 μm
38.1 μm
Motion amplitude increases
0
0.5
1
1.5
2
2.5
3
3.5
4
0 100 200 300 400
Frequency [Hz]
Str
uc
tura
l Sti
ffn
es
s [
M N
/m]
12.7 um25.4 um38.1 um
Al-Khateeb & Vance model : reduction of stiffness with force magnitude (amplitude dependent)
MMB structural stiffness vs excitation frequency
At low frequencies (25-100 Hz), Stiffness
decreases fast.
At higher frequencies, Stiffness
levels off
MMFB stiffness is frequency and
motion amplitude dependent
Frequency of excitation :
25 – 400 Hz (25 Hz step)K
12.7 um
25.4 um
38.1 um
Motion amplitude increases
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 100 200 300 400Frequency [Hz]
Imag
inar
y p
art
of
F
/X [
MN
/m]
12.7 um25.4 um38.1 um
Im (F/X) decreases with
motion amplitude, little
frequency dependency
Imaginary part of impedance (F/X) vs frequency
Frequency of excitation :
25 – 400 Hz ( at 25 Hz interval)C K
12.7 μm
25.4 μm 38.1 μm
Motion amplitude increases
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 100 200 300 400Frequency [Hz]
Str
uctu
ral L
oss
Fact
or
12.7 um25.4 um38.1 um
Loss factor ~ frequency independent at high freqs.
Loss factor vs excitation frequency
Structural damping or loss factor increases
with frequency ( 25-150 Hz)
But, remains nearly constant for higher
frequencies ( 175-400 Hz)
Frequency of excitation :
25 – 400 Hz ( at 25 Hz step)
12.7 μm
25.4 μm
38.1 μm
Model of Metal Mesh damping material
As force increases, more stick-slip joints between wires are freed, thus resulting in a greater number of spring-damper systems in series.
Stick-slip model (Al-Khateeb & Vance, 2002)
Stick-slip model
arranges wires in series connected by dampers and
springs.
Design equation: Metal mesh stiffness/damping
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)
, ,equiv o i A pK E f L R R f C f R f A f
, ,equiv o i A pC H g L R R g C g R g A g
2/325 21 4 10 1 2.96 10 1pA
equiv k ko i o i o i
RCL AK E
R R L R R R R
3/ 2 2/325 21 8.7 10 1 1.8 10 1
cpA
equiv co i o i o i n
RCL AC H
R R L R R R R
Empirical design equation for stiffness and equivalent viscous damping coefficients (Al-Khateeb & Vance, 2002)
Stiffness: prediction & test data
Amplitude increases
12.7 μm
25.4 μm
38.1 μm
Markers: Test data
Lines: Prediction
MMFB structural stiffness
decreases as frequency
increases andas motion amplitude increases
Predictions compared to test data: Damping
Amplitude increases
12.7 μm
25.4 μm38.1 μmMarkers: Test data
Lines: Prediction
MMFB equiv. viscous damping
decreases as the excitation
frequency increases and
as motion amplitude increases
Predicted equivalent viscous damping coefficients in good agreement with measurements
Metal Mesh Foil Bearing Rotordynamic Test Rig
(a) Static shaft
Max. operating speed: 120 krpmTurbocharger driven rotorRegulated air supply:9.30bar (120 psig)
Test Journal: length 55 mm, 28 mm diameter , Weight=0.22 kg
Journal press fitted on Shaft Stub
TC cross-sectional viewRef. Honeywell drawing # 448655
Twin ball bearing turbocharger, Model T25, donated by Honeywell Turbo Technologies
Positioning table
Torque arm
Squirrel cage
(b) Front view(a) Right side view
Weight
Static load
TC driving system
Load cellEddy current sensor
Spring
Rotatingjournal
Static load applies upwards : using weights & pulleysArm and load cell to measure bearing torque measurement
Metal Mesh Foil Bearing Rotordynamic Test Rig
Positioning table: Max load 110N Max 3”X 3” travel in two directions Resolution of 1μm
- Supports squirrel cage- Provides motion in two
horizontal directions
Squirrel Cage: - Provides soft support to
MMFB- Maintains concentricity
(prevents tilting) of MMFB with test journal
Metal Mesh Foil Bearing Rotordynamic Test Rig
COST of positioning TABLE: $3631
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
Large MMFB structural loss factor ( ) at high frequencies
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
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
TA
SK
S
BUDGET FROM TRC FOR 2008/2009: Support for graduate student (20 h/week) x $ 1,600 x 12 months $ 22,008 + Fringe benefits (2.5%) and medical insurance ($ 164/month) Tuition three semesters ($ 3996x3) + Supplies for test rig($ 6004) $ 17,992 Total Cost: $ 40,000