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28 th 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

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TAMU past work on 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 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

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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/ A1 Turbocharger with hydrodynamic foil bearings Ref. Patent No. US B2 Foil Journal Bearings Thrust foil Bearing

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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

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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

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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

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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

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MMFB dimensions and specifications Dimensions and SpecificationsValues Bearing Cartridge outer diameter, D Bo (mm)58.15±0.02 Bearing Cartridge inner diameter, D Bi (mm)42.10±0.02 Bearing Axial length, L (mm)28.05±0.02 Metal mesh donut outer diameter, D MMo (mm)42.10±0.02 Metal mesh donut inner diameter, D MMi (mm)28.30±0.02 Metal mesh density, ρ 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 ºC110 Poissons ratio of Copper, υ0.34 Bearing mass (Cartridge + Mesh + Foil), M (kg) ± PICTURE

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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

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

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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

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

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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

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

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

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

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Al-Khateeb & Vance model : reduction of stiffness with force magnitude (amplitude dependent) MMB structural stiffness vs excitation frequency At low frequencies ( 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

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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) 12.7 μm 25.4 μm 38.1 μm Motion amplitude increases

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

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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.

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Design equation: Metal mesh stiffness/damping Functions of equivalent modulus of elasticity (E equiv ), hysteresis coeff. (H equiv ), axial length (L), inner radius (R i ), outer radius (R o ), axial compression ratio (C A ), radial interference (R p ), motion amplitude (A), and excitation frequency (ω) Empirical design equation for stiffness and equivalent viscous damping coefficients (Al-Khateeb & Vance, 2002)

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

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Predictions compared to test data: Damping Amplitude increases 12.7 μ m 25.4 μm 38.1 μm Markers: 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

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Metal Mesh Foil Bearing Rotordynamic Test Rig (a) Static shaft 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 TC cross-sectional view Ref. Honeywell drawing # Twin ball bearing turbocharger, Model T25, donated by Honeywell Turbo Technologies

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Positioning table Torque arm Squirrel cage (b) Front view (a) Right side view Weight Static load TC driving system Load cell Eddy current sensor Spring Rotating journal Static load applies upwards : using weights & pulleys Arm and load cell to measure bearing torque measurement Metal Mesh Foil Bearing Rotordynamic Test Rig

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Positioning table : Max load 110N Max 3X 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

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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

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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 (20h/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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