Luis San Andrés Mast-Childs Professor Fellow ASME ASME GT2011-45257 ASME J. Eng Gas Turbines & Power (in print) Thomas Abraham Chirathadam Research Assistant Texas A&M University ASME TURBO EXPO 2011, Vancouver, Canada (June 2011) Presentation available at http://rotorlab.tamu.edu Metal Mesh Foil Bearing Effect of Motion Amplitude, Rotor Speed, Static Load, and Excitation Frequency on Force Coefficients
ASME TURBO EXPO 20 11 , Vancouver, Canada (June 2011). Metal Mesh Foil Bearing Effect of Motion Amplitude, Rotor Speed, Static Load, and Excitation Frequency on Force Coefficients. Thomas Abraham Chirathadam Research Assistant. Luis San Andrés Mast-Childs Professor Fellow ASME. - PowerPoint PPT Presentation
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Luis San AndrésMast-Childs Professor
Fellow ASME
ASME GT2011-45257ASME J. Eng Gas Turbines & Power (in print)
Presentation available at http://rotorlab.tamu.edu
Metal Mesh Foil BearingEffect of Motion Amplitude, Rotor Speed, Static Load, and Excitation Frequency on
Force Coefficients
Oil-Free Bearings for Turbomachinery
JustificationCurrent advancements in vehicle turbochargers and midsize gas turbines need of proven gas bearing technology to procure compact units with improved efficiency in an oil-free environment.
DOE, DARPA, NASA interests range from applications as portable fuel cells (< 60 kW) in microengines to midsize gas turbines (< 250 kW) for distributed power and hybrid vehicles.
Gas Bearings allow• weight reduction, energy and complexity savings• higher temperatures, without needs for cooling air • improved overall engine efficiency
Ideal gas bearings
Simple – low cost, small geometry, low part count, constructed from common materials, manufactured with elementary methods.
Load Tolerant – capable of handling both normal and extreme bearing loads without compromising the integrity of the rotor system.
High Rotor Speeds – no specific speed limit (such as DN) restricting shaft sizes. Small Power losses.
Good Dynamic Properties – predictable and repeatable stiffness and damping over a wide temperature range.
Reliable – capable of operation without significant wear or required maintenance, able to tolerate extended storage and handling without performance degradation.
+++ Modeling/Analysis (anchored to test data) available
Gas Foil Bearings
Used in many oil-free rotating machinery: high load capacity (>20 psig), rotordynamically stable, tolerance of misalignment and shocks…….
: Bump spot weld X
Rotor spinning
Housing
Bump strip layer
Top foil
Gas film
Y
Top foil spot weld
Ω
Ө
…… but expensive with intellectual property restrictions. A low cost proven alternative needed.
Metal Mesh Foil Bearing (MMFB)
MMFB COMPONENTS: Bearing cartridge, metal mesh ring and top FoilHydrodynamic air film develops between rotating shaft and top foil.
Large damping (material hysteresis) offered by metal mesh
Tolerant to misalignment, and applicable to a wide temperature range
Coatings needed to reduce friction at start-up & shutdown
Metal mesh foil bearing5 cm
Metal Mesh Ring
Top Foil Coated with MoS2
Bearing Cartridge
Rotor spinning
Slot
MMFB components
Top Foil
0.12 mm top foilChrome-Nickel alloyRockwell 40/45
Heat treated at ~ 450 ºC for 4 hours and allowed to cool. Foil retains arc shape after heat treatment
Sprayed with MoS2
sacrificial coating
Metal mesh pad
Compressed weave of copper wires
Compactness (density)=20%
Stiffness and damping of MMFB depend on metal mesh compactness
Bearing cartridge (+top foil+ metal mesh)
Metal mesh pad and top foil inserted in steel bearing cartridge.
Top foil firmly affixed in a thin slot made with wire-EDM machining
Simple to manufacture and assemble
Zarzour and Vance (2000) J. Eng. Gas Turb. & Power, Vol. 122Advantages of Metal Mesh Dampers over SFDsCapable of operating at low and high temperaturesNo changes in performance if soaked in oil
Al-Khateeb and Vance (2001) ASME GT-2001-0247Test metal mesh donut and squirrel cage( in parallel)Metal Mesh damping not affected by modifying squirrel cage stiffness
Choudhry and Vance (2005) ASME GT-2005-68641Develop design equations, empirically based, to predict structural stiffness and viscous damping coefficient
METAL MESH DAMPERS provide large amounts of damping. Inexpensive component.
Past work in Metal Mesh Dampers
Ertas &Luo (2008) ASME J. Gas Turbines Power, 130MM damper force coefficients not affected by shaft eccentricity (or applied static load)
Ertas (2009) ASME J. Gas Turbines Power, 131Two metal mesh rings installed in a multiple pad gas bearing with flexural supports to maximize load capacity and damping. Bearing stiffness decreases with frequency & w/o external pressurization; and increases gradually with supply pressure
Ertas et al. (2009) AIAA 2009-2521Shape memory alloy (NiTi) shows increasing damping with motion amplitudes. Damping from NiTi larger than for Cu mesh (density – 30%) : large motion amplitudes (>10 um)
Recent work by OEM with MM dampers to maximize load capacity and to add damping in gas bearings
Metal Mesh Dampers in Hybrid bearings
Past work in MMFBsSan Andrés et al. (2010) J. Eng. Gas Turb. & Power, 132(3)Assembled the first prototype MMFB (L=D=28 mm). Load vs Deflection with hysteresis shows large structural damping 0.7). Frequency dependent stiffness agree with predictions.
San Andrés et al. (2009) ASME GT2009-59920Demonstrated operation to 45 krpm with early rotor lift off. Educated undergraduate students.
San Andrés et al. (2010) J. Eng. Gas Turb. & Power, 132Start and shut down to measure torque and lift-off speed. Low friction factor ~ 0.01 at high speed 60 krpm.
San Andrés and Chirathadam (2011) J. Eng. Gas Turb. & Power, 133Rotordynamic coefficients from unidirectional impact loads. Estimated stiffness and damping force coefficients at 50 krpm.
EXPERIMENTS with a PRIOR MMFB (larger mesh thickness)
1. Structural stiffness and damping
2. Friction factor with airborne operation
0
0.5
1
1.5
2
2.5
0 100 200 300 400Frequency [Hz]
Str
uctu
ral s
tiffn
ess
[MN
/m]
12.7 um25.4 um38.1 um12.7 um Prediction25.4 um Prediction38.1 um Prediction
Al-Khateeb & Vance model
MMFB structural stiffness vs. freq.
At low frequencies (25-100 Hz), stiffness
decreases
At higher frequencies, stiffness
gradually increases
Bearing stiffness is frequency and
motion amplitude dependent12.7 m
25.4 m38.1 m
Motion amplitude increases
San Andres et al., 2010, ASME J. Eng. Gas Turbines Power, 132 (3)
10
100
1000
10000
100000
0 100 200 300 400Frequency [Hz]
Equi
vale
nt v
isco
us d
ampi
ng [N
s/m
]
12.7 um25.4 um38.1 um12.7 um Prediction25.4 um Prediction38.1 um Prediction
MMFB eq. damping vs. frequency
Amplitude increases
12.7 μm25.4 μm38.1 μm
MMFB equiv. viscous damping
decreases as the excitation
frequency increases and
as motion amplitude increases
Al-Khateeb & Vance modelSan Andres et al., 2010, ASME J. Eng. Gas Turbines Power, 132 (3)
Test MMFB is structurally soft with large damping: Mid-range of rule of thumb (ROT)
Net static load (applied load-bearing weight) 22 N ( W/LD=0.16 bar) and 36 N ( W/LD=0.26 bar)
Acknowledgments/ Thanks to
http://rotorlab.tamu.eduLearn more at:
Honeywell Turbocharging Technologies
Turbomachinery Research Consortium
Questions (?)
Extra slides - >
Rotor acceleratesRotor accelerates
Comparison: MMFB&BFB Friction factor vs rotor speed
f = (Torque/Radius)/(Static load)
f ~ 0.03
f ~ 0.03
Friction coefficient decreases with increasing applied static loads and rotor speed (due to lift-off)
MMFB BFB
Static load
0.01
0.1
1
0 10 20 30 40 50 60 70
Rotor speed [krpm]
Fri
ctio
n f
acto
r [-
]
35.6N
26.7N
17.8N
0.01
0.1
1
0 10 20 30 40 50 60 70
Rotor speed [krpm]
Fri
cti
on
facto
r [-
]
35.6N
26.7N
17.8N
Future work: MMFB force coefficient prediction
Θ
Θl
Θt
Θp
X
Y
eY
eX
h
r
r
p
r+c
m
r+c
Metal mesh
Rotor
Top foil radius with assembled clearance
Top foil
Fixed end
Rectangular finite element with 4 nodes
1 2
4 3
Km w
p
x
y
z
Metal mesh
Top foil
Analysis steps:1. Obtain stiffness matrix for MMFB structure + top foil using FEM.2. Assume small amplitude motions about a static position.3. Solve Reynolds equations for isothermal, isoviscous ideal gas.4. Predict force coefficients using dynamic (perturbed) pressure fields
Unwrapped Metal mesh and top foil
Demonstrate high temperature reliable operation of MMFB with adequate thermal management.
a) Construct two MMFB fitting existing test rig dimensions. b) Measure rotor response for temperature as high as 200 ºC, rotor speed up to 50
krpmc) Compare thermal performance of MMFBs with Gen. I bump-foil bearings