29 th Turbomachinery Research Consortium Meeting Measurements of
Drag Torque, Lift-off Speed and Identification of Structural
Stiffness and Damping in a Metal Mesh Foil Bearing Luis San Andrs
Thomas Abraham Chirathadam Tae-Ho Kim Project title : Metal Mesh
Foil Bearings for Oil-Free Turbomachinery: Test Rig for prototype
demonstrations TRC Funded Project, TEES #32513/1519 V2
TRC-B&C-3-09 May 2009 Slide 2 TRC Project: Tasks 08/09
Construction of Metal Mesh Foil Bearing (MMFB) Test Rig MMFB
performance characteristics Bearing drag torque Lift- Off Speed Top
Foil Temperature Identification of force coefficients (Impact load
tests) with and w/o shaft rotation Structural stiffness and
equivalent viscous damping Current research builds upon earlier
work on metal mesh dampers conducted by Prof. John Vance and
students Slide 3 Metal Mesh Foil Bearing (MMFB) MMFB COMPONENTS:
Bearing Cartridge, Metal mesh ring and Top Foil Hydrodynamic air
film develops between rotating shaft and top foil. Potential
applications: ACMs, micro gas turbines, turbo expanders, turbo
compressors, turbo blowers, automotive turbochargers, APU Large
damping (material hysteresis) offered by metal mesh Tolerant to
misalignment, and applicable to a wide temperature range Suitable
tribological coatings needed to reduce friction at start-up &
shutdown Cartridge Metal mesh ring Top Foil Slide 4 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 to bump-type foil
bearings) Cost effective, uses common materials Metal mesh creeps
or sag with operation & time Near absence of predictive models
(bearing mainly) Damping is NOT viscous. Modeling difficulties
Slide 5 MMFB assembly BEARING CARTRIDGE METAL MESH RING TOP FOIL
Simple construction and assembly procedure Slide 6 MMFB dimensions
and specifications Dimensions and Specifications Bearing Cartridge
outer diameter, D Bo (mm)58.15 Bearing Cartridge inner diameter, D
Bi (mm)42.10 Bearing Axial length, L (mm)28.05 Metal mesh donut
outer diameter, D MMo (mm)42.10 Metal mesh donut inner diameter, D
MMi (mm)28.30 Metal mesh density, MM (%)20 Top foil thickness, T tf
(mm)0.076 Metal wire diameter, D W (mm)0.30 Youngs modulus of
Copper, E (GPa), at 21 C 110 Poissons ratio of Copper, 0.34 Bearing
mass (Cartridge + Mesh + Foil), M (kg) 0.316 PICTURE Slide 7 MMFB
rotordynamic test rig (a) Static shaft Max. operating speed: 75
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 TC cross-sectional view Ref.
Honeywell drawing # 448655 Twin ball bearing turbocharger, Model
T25, donated by Honeywell Turbo Technologies MMFB Slide 8
Positioning (movable) table Torque arm Calibrated spring MMFB Shaft
( 28 mm) String to pull bearing Static load Eddy current sensor
Force gauge Top foil fixed end Preloading using a rubber band 5 cm
Test Rig: Torque & Lift-Off measurements Thermocouple Slide 9
Test procedure Sacrificial layer of MoS 2 applied on top foil
surface Mount MMFB on shaft of TC rig. Apply static horizontal load
High Pressure cold air drives the ball bearing supported Turbo
Charger. Oil cooled TC casing Air inlet gradually opened to raise
the turbine shaft speed. Valve closing to decelerate rotor to rest
Torque and shaft speed measured during the entire experiment. All
experiments repeated thrice. Slide 10 Shaft speed and torque vs
time Rotor starts Constant speed ~ 65 krpm Valve open Valve close 3
N-mm Rotor stops Applied Load: 17.8 N Manual speed up to 65 krpm,
steady state operation, and deceleration to rest Startup torque ~
110 Nmm Shutdown torque ~ 80 Nmm Once airborne, drag torque is ~ 3
% of Startup breakaway torque Top shaft speed = 65 krpm Iift off
speed Lift off speed at lowest torque : airborne operation W D =
3.6 N Slide 11 Varying steady state speed & torque Rotor starts
61 krpm Rotor stops 50 krpm 37 krpm 24 krpm 2.5 N-mm 57 N-mm 45
N-mm 2.4 N-mm2.0 N-mm 1.7 N-mm Manual speed up to 65 krpm, steady
state operation, and deceleration to rest Drag torque decreases
with step wise reduction in rotating speed until the journal starts
rubbing the bearing Shaft speed changes every 20 s : 65 50 37 - 24
krpm Side load = 8.9 N W D = 3.6 N Slide 12 Startup torque vs
applied static load Worn MoS 2 layer Fresh coating of MoS 2 Top
foil with worn MoS 2 layer shows higher startup torques Larger
difference in startup torques at higher static loads Startup Torque
: Peak torque measured during startup Dry sliding operation Slide
13 DRY friction coefficient vs static load Worn MoS 2 layer Fresh
MoS 2 layer With increasing operation cycles, the MoS 2 layer wears
away, increasing the contact or dry-frictioncoefficient. Enduring
coating on top foil required for efficient MMFB operation! Friction
coefficient f = (Torque/Radius)/(Static load) Dry sliding operation
Slide 14 Bearing drag torque vs rotor speed 8.9 N (2 lb) 17.8 N (4
lb) 26.7 N (6 lb) 35.6 N (8 lb) Rotor not lifted off Dead weight (W
D = 3.6 N) Increasing static load (W s ) to 35.6 N (8 lb) 0 0.5 1
1.5 2 2.5 3 3.5 4 4.5 20304050607080 Rotor speed [krpm] Bearing
torque [N-mm ] Steady state bearing drag torque increases with
static load and rotor speed airborne operation W D = 3.6 N Side
load increases Data derived from bearingtorque and rotor speed
vstime data Slide 15 Friction coefficient vs rotor speed Dead
weight (W D = 3.6 N) Increasing static load (W s ) to 35.6 N (8 lb)
f decreases with increasing static load Friction coefficient f
increases with rotor speed almost linearly airborne operation
Friction coefficient f = (Torque/Radius)/(Static load) 8.9 N (2 lb)
17.8 N (4 lb) 26.7 N (6 lb) 35.6 N (8 lb) Slide 16 Bearing drag
torque vs rotor speed Lift-off speed 8.9 N (2 lb) 17.8 N (4 lb)
26.7 N (6 lb) 35.6 N (8 lb) Max. Uncertainty 0.35 N-mm Rotor
accelerates Bearing drag torque increases with increasing rotor
speedand increasing applied static loads. Lift-Off speed increases
almost linearly with static load Slide 17 Lift-Off speed vs applied
static load Lift-Off Speed increases ~ linearly with static load
Lift-Off Speed : Rotor speed beyond which drag torque is
significantly small, compared to Startup Torque W D = 3.6 N Side
load increases Slide 18 Rotor accelerates 8.9 N (2 lb) 17.8 N (4
lb) 26.7 N (6 lb) 35.6 N (8 lb) Friction coefficient vs rotor speed
f ~ 0.01 Friction coefficient ( f ) decreases with increasing
static load f rapidly decreases initially, and then gradually
raises with increasing rotor speed Dry sliding Airborne
(hydrodynamic) Slide 19 Top foil temperature (bearing outboard) 8.9
N (2 lb) 17.8 N (4 lb) 26.7 N (6 lb) 35.6 N (8 lb) Top Foil
Temperature increases with Static Load and Rotor Speed Top foil
temperature measured at MMFB outboard end Only small increase in
temperature for the range of applied loads and rotor speeds
INCREASING STATIC LOAD Side load increases Room Temperature : 21C
Slide 20 Test Setup : Impact Load Test Positioning table MMFB
Journal (28 mm) Flexible string Force gauge Top foil fixed end 5 cm
(TOP VIEW) Accelerometer Eddy current sensor MMFB Journal (28 mm)
TC Accelerometers (Not visible in this view) (FRONT VIEW) IMPACT
HAMMER (SIDE VIEW) Slide 21 Identification model Assembly mass, M =
0.38 kg Impact along Y direction only 1-DOF mechanical system In
frequency domain Identification model, in frequency domain SHAFT
STATIONARY: NOT ROTATING Slide 22 Impact force Shaft not rotating
Frequency domain averages of 10 impacts along vertical (Y)
direction Y Time domain Frequency domain Slide 23 Bearing
displacement Shaft not rotating Frequency domain averages of 10
impacts along vertical (Y) direction Rapidly decaying amplitude
shows large damping from MMFB Y Time domain Frequency domain Time
[s] Slide 24 Bearing acceleration Journal not rotating TC shaft
stub is flexible A Y - 2 Y Acceleration derived from relative
displacement of bearing cartridge and shaft Measured acceleration Y
Time domain Frequency domain Slide 25 Curve Fit Identifying Static
Stiffness and Mass Journal not rotating Estimated test system
natural frequency f n = (K Y /M) 0.5 = 89 Hz Re (F/Y) = K est + M
est * Re (A/Y) K est = 1.179 * 10 5 N/m Me st = 0.379 kg Curve fit
Critical damping C crit =2*( K Y M ) 0.5 = 423 N.s/m Slide 26
Identified MMFB structural stiffness Journal not rotating
Structural stiffness decreases (10%) initially ( 50-85 Hz), but
increases with further increase in frequency. K est = 1.179 * 10 5
N/m K Y = Re {(F - M est A y )/Y} Slide 27 Identified eq.viscous
damping Journal not rotating Equivalent viscous damping decreases
with increasing frequency C YY = Im MMFB shows lots of damping,
making test system just below critically damped C crit =2*( K Y M )
0.5 = 423 N.s/m Slide 28 Aluminum foam bearings ParametersBearing
1Bearing 2 Bearing Cartridge Outer Diameter [mm]58.03 0.0158.02
0.01 Bearing Cartridge Inner Diameter [mm]42.11 0.0141.60 0.01
Aluminum Foam inner Diameter [mm][28.20, 29.30][28.04, 28.15]
Bearing Axial Length [mm]28.07 0.0128.15 0.01 Bearing Mass
[kg]0.1027 0.000050.1017 0.00005 Porosity %8693 DONATED by CIATEQ
A.C. Aluminum foam is stiff & brittle Not recommended for use
as structural support of foil bearing Slide 29 Conclusions TC
driven MMFB rotordynamic test rig to measure bearing drag torque,
bearing displacements and acceleration. Operates up to 70 krpm
Bearing startup torque, increases with applied static loads. A
sacrificial coating of MoS 2 reduces start up torque Bearing drag
torque, while bearing is airborne, increases with static load and
rotor speed Top foil steady state temperature increases with static
load and rotor speed Impact tests: shows MMFB has large damping;
its stiffness gradually increases with frequency, except while
traversing the bearing natural frequency Slide 30 Backup Slides
Slide 31 TAMU past work (Metal Mesh Dampers) 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 METAL MESH DAMPERS
provide large amounts of damping. Inexpensive. Oil-free Slide 32 08
TRC: MMFB Research at TAMU Lathe tool holder moves forward and
backward : push and pull forces on MMFB Lathe tool holder Eddy
Current sensor Load cell Test MMFB Stationary shaft San Andres, L.,
Chirathadam, T.A., and Kim, T.H., (2009) GT-2009-59315 Static Load
Test Setup Slide 33 3 Cycles: loading & unloading Large
hysteresis loop : Mechanical energy dissipation MMFB wire density ~
20% Displacement: [-0.06,0.06] mm Load: [-130, 90 ]N Start Push
load Pull load Hysteresis loop 08 TRC: MMFB Research at TAMU Slide
34 MMFB wire density ~ 20% During Load reversal : jump in
structural stiffness Max. Stiffness ~ 4 MN/m Start Push load Pull
load 08 TRC: MMFB Research Slide 35 Motion amplitude controlled
mode Electrodyamic shaker MMFB AccelerometerForce transducer Test
shaft Fixture Test shaft Eddy Current sensors 12.7, 25.4 &38.1
m Frequency of excitation : 25 400 Hz (25 Hz interval) 08 TRC: MMFB
Research Dynamic Load Test Setup Slide 36 Structural stiffness
decrease with increasing motion amplitudes Stiffness increases
gradually with Frequency 08 TRC: MMFB Research Slide 37 Eq. Viscous
damping decreases with increasing motion amplitudes Damping
decreases rapidly with frequency 08 TRC: MMFB Research
