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29 th Turbomachinery Research Consortium Meeting Measurements of Drag Torque, Lift-off Speed and Identification of Structural Stiffness and Damping in.

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Presentation on theme: "29 th Turbomachinery Research Consortium Meeting Measurements of Drag Torque, Lift-off Speed and Identification of Structural Stiffness and Damping in."— Presentation transcript:

1 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 Andrés 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

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

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

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

5 MMFB assembly BEARING CARTRIDGE METAL MESH RING TOP FOIL Simple construction and assembly procedure

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, 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 ºC 110 Poissons ratio of Copper, υ0.34 Bearing mass (Cartridge + Mesh + Foil), M (kg) PICTURE

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 # Twin ball bearing turbocharger, Model T25, donated by Honeywell Turbo Technologies MMFB

8 Positioning (movable) table Torque arm Calibrated spring MMFB Shaft (Φ 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

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.

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

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 – krpm Side load = 8.9 N W D = 3.6 N

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

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

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) 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

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)

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

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

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)

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 : 21°C

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)

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

22 Impact force Shaft not rotating Frequency domain averages of 10 impacts along vertical (Y) direction Y Time domain Frequency domain

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]

24 Bearing acceleration Journal not rotating TC shaft stub is flexible A Y - ω 2 Y Acceleration derived from relative displacement of bearing cartridge and shaft Measured acceleration Y Time domain Frequency domain

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 = * 10 5 N/m Me st = kg Curve fit Critical damping C crit =2*( K Y M ) 0.5 = 423 N.s/m

26 Identified MMFB structural stiffness Journal not rotating Structural stiffness decreases (10%) initially ( Hz), but increases with further increase in frequency. K est = * 10 5 N/m K Y = Re {(F - M est A y )/Y}

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

28 Aluminum foam bearings ParametersBearing 1Bearing 2 Bearing Cartridge Outer Diameter [mm]58.03 ± ± 0.01 Bearing Cartridge Inner Diameter [mm]42.11 ± ± 0.01 Aluminum Foam inner Diameter [mm][28.20, 29.30][28.04, 28.15] Bearing Axial Length [mm]28.07 ± ± 0.01 Bearing Mass [kg] ± ± Porosity %8693 DONATED by CIATEQ A.C. Aluminum foam is stiff & brittle – Not recommended for use as structural support of foil bearing

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

30 Backup Slides

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 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

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 Static Load Test Setup

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

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

35 Motion amplitude controlled mode Electrodyamic shaker MMFB AccelerometerForce transducer Test shaft Fixture Test shaft Eddy Current sensors 12.7, 25.4 &38.1 μm Frequency of excitation : 25 – 400 Hz (25 Hz interval) 08 TRC: MMFB Research Dynamic Load Test Setup

36 Structural stiffness decrease with increasing motion amplitudes Stiffness increases gradually with Frequency 08 TRC: MMFB Research

37 Eq. Viscous damping decreases with increasing motion amplitudes Damping decreases rapidly with frequency 08 TRC: MMFB Research


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