1. Thomas Abraham Chirathadam
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

2. 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
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

3. Recent Patents: gas bearings & systems
Turbocharger with hydrodynamic
foil bearings
Ref. Patent No. US B2
Foil Journal
Bearings
Thrust foil
Bearing
‘Air foil bearing having a porous foil’
Ref. Patent No. WO 2006/ A1
A metal mesh donut is a cheap replacement to “porous foil” 3

4. 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

5. 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

6. 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

7. 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

8. MMFB dimensions and specifications
Values
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)
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) ±
PICTURE

9. 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

10. Static Load vs bearing deflection results
MMFB wire density ~ 20%
3 Cycles: loading & unloading
Nonlinear F(X)
Large hysteresis loop : Mechanical energy dissipation
Push load
Start
Pull load
Hysteresis loop
Displacement: [-0.06,0.06] mm
Load: [-130, 90 ]N

11. Derived MMFB structural stiffness
MMFB wire density ~ 20%
During Load reversal : jump in structural stiffness
Push load
Pull load
Start
Max. Stiffness ~ 4 MN/m

12. Dynamic load tests MMFB motion amplitude (1X) is dominant.
Motion amplitude controlled mode
12.7, 25.4 &38.1 μm
Accelerometer
Force transducer
MMFB
Frequency of excitation :
25 – 400 Hz (25 Hz interval)
Waterfall of displacement
Eddy Current sensors
Electrodyamic shaker
Test shaft
Test shaft Fixture
MMFB motion amplitude (1X) is dominant.

13. Amplitude of Dynamic Load vs Excitation Frequency
Dynamic load decreases with increasing frequency and decreasing motion amplitudes
38.1 μm
Motion amplitude decreases
25.4 μm
12.7 μm
At higher frequencies, less force needed to maintain same motion amplitudes

14. Identification Model Equivalent Test System 1-DOF mechanical system
F(t)
X(t)
Equivalent Test System 14

15. Parameter Identification (no shaft rotation)
Harmonic force
& displacements
Impedance Function
Viscous Dissipation
Or Hysteresis Energy
Material
LOSS FACTOR 15

16. Real part of (F/X) vs excitation frequency
Frequency of excitation :
25 – 400 Hz ( 25 Hz step)
12.7 μm
Motion amplitude increases
25.4 μm
38.1 μm
Natural frequency of the system
Real part of (F/X) decreases with increasing motion amplitude 16

17. K MMB structural stiffness vs excitation frequency
Frequency of excitation :
25 – 400 Hz (25 Hz step)
At low frequencies ( Hz), Stiffness decreases fast.
At higher frequencies, Stiffness levels off
Motion amplitude increases
12.7 um
MMFB stiffness is frequency and motion amplitude dependent
25.4 um
38.1 um
Al-Khateeb & Vance model : reduction of stiffness with force magnitude (amplitude dependent) 17

18. Imaginary part of impedance (F/X) vs frequency
Frequency of excitation :
25 – 400 Hz ( at 25 Hz interval)
Motion amplitude increases
12.7 μm
Im (F/X) decreases with motion amplitude, little frequency dependency
25.4 μm
38.1 μm

19. Loss factor vs excitation frequency
Frequency of excitation :
25 – 400 Hz ( at 25 Hz step)
Structural damping or loss factor increases with frequency ( Hz)
But, remains nearly constant for higher frequencies ( Hz)
25.4 μm
38.1 μm
12.7 μm
Loss factor ~ frequency independent at high freqs. 19

20. 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.

21. Design equation: Metal mesh stiffness/damping
Empirical design equation for stiffness and equivalent viscous damping coefficients (Al-Khateeb & Vance, 2002)
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)

22. Stiffness: prediction & test data
MMFB structural stiffness decreases
as frequency increases and
as motion amplitude increases
Amplitude increases
Markers: Test data
Lines: Prediction
12.7 μm
25.4 μm
38.1 μm

23. Predictions compared to test data: Damping
Amplitude increases
MMFB equiv. viscous damping decreases
as the excitation frequency increases and
as motion amplitude increases
Markers: Test data
Lines: Prediction
12.7 μm
25.4 μm
38.1 μm
Predicted equivalent viscous damping coefficients in good agreement with measurements

24. Metal Mesh Foil Bearing Rotordynamic Test Rig15 10 5 cm
Journal press fitted on Shaft Stub
(a) Static shaft
TC cross-sectional view
Ref. Honeywell drawing #
Max. operating speed: 120 krpm
Turbocharger driven rotor
Regulated air supply:9.30bar (120 psig)
Twin ball bearing turbocharger, Model T25, donated by Honeywell Turbo Technologies
Test Journal: length 55 mm, 28 mm diameter , Weight=0.22 kg 24

25. Metal Mesh Foil Bearing Rotordynamic Test Rig
Static load
Load cell
Eddy current sensor
Torque arm
TC driving system
Weight
Rotating
journal
Spring
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 25

26. 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
Supports squirrel cage
Provides motion in two horizontal directions
COST of positioning TABLE: $3631 26

27. 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 ( g ~ 0.50 ) at high frequencies
Predicted stiffness and equivalent viscous damping coefficients are in agreement with test coefficients: Test data validates design equations 27

28. 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
TASKS B
UDGET 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