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Thomas Abraham Chirathadam

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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 Rig
15 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

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