Transcript No Slide Title

Dual-Pump CARS and OH PLIF
PI: Andrew Cutler
PhD Students: Gaetano Magnotti, Luca Cantu, Emanuela Gallo
The George Washington University
Collaborators
Paul Danehy (ASOMB), Craig Johansen (NIA)
NASA Langley Research Center
June 16, 2011
National Center for Hypersonic Combined Cycle Propulsion
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Background
• CFD methods employing semi-empirical models used in analysis of
hypersonic airbreathing engine flow paths
– RANS (or Favre averaged) codes have models for turbulent stresses, mass and
energy transport, turbulence chemistry interactions
– LES methods have models for subgrid scale turbulence
• Models depend upon experimental data for validation
– Information on mean flow and statistics of the turbulent fluctuation in flow
properties
• Data requirements
– Simple well defined supersonic combustion flows with well-known boundary
conditions
– Time and spatially resolved
– Good instrument precision
– Converged statistics
• Approach
– Dual-pump CARS
• T, mole fraction species
– Planar laser-induced fluorescence imaging of OH radical (PLIF)
• Flow-visualization
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Flow Fields
Laboratory supersonic flame
with 10 mm center jet
University of Virginia’s DualMode Scramjet
Supersonic free jet flames (hot
center jet with H2 co-flow)
Scramjet combustor
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Dual-Pump CARS
Virtual states
P1
S
P2
AS
Rot.-vib. states
Process 1 (N2, H2)
•
Process 2 (O2, H2)
Two narrowband pump (Green+Yellow) + broadband Stokes (Red) laser
Probe molecular Raman transitions
Two simultaneous processes
Coherent signal beam (Blue)
–
–
•
AS
Four-color mixing process at beam focus / intersection
–
–
–
•
P2
S
P1
Analyze with spectrometer
Fit spectra to theory to obtain T, mole fraction species
Measurement time ~10 ns, volume ~50 µm x 1.5 mm
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“Mobile” CARS System
Narrowband and broad-band dye laser
beams on top of each other
Laser cart
Flame
Transmission
Collection
Detection
Beam Relay System (BRS)
•
Laser cart
–
–
–
–
–
•
Detection system
–
–
–
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Nd:YAG (532 nm,1.2 J, 20 Hz, seeded) =
Green
YAG-pumped broad-band dye laser (~9.6
nm or 263 cm-1 at 605 nm) = Red
YAG-pump narrow-band dye laser (~ 0.07
cm-1 at 553 nm) = Yellow
Remote beam steering (picomotor mounts)
Control of beam size (telescopes) and
energy (polarizers/waveplates)
Focusing lens, polarizer, remote beam
steering
1 m monochromator
Cooled CCD
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Beam Relay System at UVa
• Moves beam crossing within flow field; 3 components, typically 2
motorized
Measurement point
5’x8’ optical table
Transmission
Detection
Beams from
laser
cart
CARS
window
Collection
Linear bearings/rails*
Dual mode combustor
*Horizontal motions are
motor driven
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Transmission and Collection Optics
•
•
Laser beams focused and combined with separate mirrors and lenses
Focal plane imaging system
–
–
Beam focusing
Beam crossing
Measurement volume
Lenses
Uncoated glass splitter
Multi-pass
dichroic
splitter
ND filter
From BRS
and Cart
Focal plane imaging
system: microscope
objective and CCD
camera
Signal beam
To BRS and
Detection
Focal plane images
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Optical Implementation at UVa
Transmission optics platform
Monochrometer
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Method for Fitting Spectra
• Sandia CARSFT code
– Computes theoretical spectra
• New algorithm* fits spectra by interpolating from
library of pre-computed spectra
• Novel feature is structure of library (sparsely
packed) and method for interpolation of spectra
from library
– Smaller libraries, faster library generation, faster fitting
• Allows fitting of more chemical species and
no.
sparse regular
faster turn around
chem library library
– Enables “WIDECARS”
*Cutler, A.D., Magnotti, G., J. Raman Spectroscopy, 2011.
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size
species size
size
ratio
1
10
10
1.00
2
60
100
1.67
3
270
1000
3.70
4
1080
10000
9.26
5
4050 100000 24.69
6
14580 1000000 68.59
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Measurements in Hencken Burner
• Hencken flat flame burner
– H2-air flame
– Flame temperature and composition known from theory
• Computed from gas flow rates assuming adiabatic reaction to equilibrium
100,000
N2
10,000
Intensity (counts)
H2 S(5)
O2
H2 S(6)
H2 S(9)
1,000
100
 =1.17
 =2.34
Hencken burner
 =0.23
10
0
200
400
600
800
1,000
1,200
Pixel
Average DP CARS spectra at 3 equivalence ratios
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(a)
CARS Intensity/Arbitr. Units
100000
Theory
Experiment
10000
1000
100
10
2050
2100
2150
2200
2250
2300
2350
Wavenumber/cm-1
Theory
Experiment
1000
100
10
2050
2100
2150
2200
2250
2300
2350
-1
Wavenumber/cm
(c)
CARS Intensity/Arbitr. Units
100000
N2
Theory
Experiment
10000
O2
1000
100
10
2050
2100
2150
2200
Wavenumber/cm
(d)
2250
2300
2350
-1
10000
CARS Intensity/Arbitr. Units
Typical spectra
normalized
and fitted
(a) =0.23
(single shot)
(b) =1.17
(single shot)
(c) =0.23
(mean)
(d) =1.17
(mean)
10000
CARS Intensity/Arbitr. Units
(b)
Theory
Experiment
1000
H2
100
11
10
2050
2100
National Center for Hypersonic Combined Cycle Propulsion
2150
2200
Wavenumber/cm
2250
-1
2300
2350
Fitted Temperature in Hencken Flame
– Mode noise in broad band dye
laser, camera noise, photon shot
noise
• SD of fitted parameters
depends on selection of
residual minimized by fitter
– R2 = noise-weighted least squares
fit to signal intensity (Snelling et al,
1987)
– (R1, R3 commonly used in the
literature)
• We found R2 < R3 < R1
• Similar results for fitted N2, O2,
H2 mole fractions
2000
Temperature (K)
• Means agree well with theory
• Actual standard deviation (SD)
in flame due to unsteadiness is
unknown but believed small
• Fitted parameters have noise
2500
Fitted mean
Theory
1500
R1
1000
R3
500
Standard deviation of fit x10
R2
0
0
0.5
1
1.5
2
2.5
3
3.5
Equivalence ratio
SD in T reduced x2 by proper
selection of residual!
Important for turbulence
studies
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Saturation Effects
Saturation effects in Hencken
burner flame  = 0.3
Sqrt of CARS intensity (arbitrary units)
• Signal  Ip1 Ip2 IS d2 L2
– Want to minimize L
– Must maximize Ip1 Ip2 IS to maintain
signal
– Saturation effects limit Ip1 Ip2 IS
• Saturation effects studied in
Hencken flame
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N2
Mean spectra
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4
O2
2
2200
2250
2300
Raman Shift (cm-1)
• Fitted mole fraction more
sensitive than temperature
0.16
Fitted O2 mole fraction vs. irradiance
0.15
O2 mole fraction
Error in O2 up to 30%
H2 most sensitive to saturation
Saturation thresholds determined
We now know how to avoid
saturation
Ip2=400 GW/cm2
0
2150
– Mixture of Stark shift and
stimulated Raman pumping
–
–
–
–
Ip2=100 GW/cm2
10
Ip1=40 GW/cm2
0.14
Ip1=140 Gw/cm2
0.13
0.12
850 mm f.l
500 mm f.l
300 mm f.l
0.11
0.1
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10
100
1000
10000
Ip2*Is
(GW2/cm4)
100000
1000000
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Status of CARS
• CARS data base in laboratory supersonic flame
– Data acquisition completed
– Data analysis in progress
• CARS system currently installed at UVa
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Supersonic Flame*
• Center jet 10 mm, hydrogen vitiated air,
variable Mach (0.75-2.0) and temperature
• Unheated, low-speed coflow
• 10 test cases; variables
– Nozzle exit Mach number (Me)
– Center jet temperature (equivalent flight Mach
Mh)
– Coflow gas
• C = H2 coflow, combustion
• M = N2 coflow, mixing but no combustion
• Nominally 100,000 spectra for each test
case, fitted for T, and mole fractions N2,
O2, H 2
– Sampled at 5 axial locations, 23-30 radial
locations at each
• Will be used by NCHCCP modelers
Equivalent flight
Mach number (Mh)
Me/Mh 5 6
7
0.75
C+M
1
C+M
1.6
C C+M C+M
2
M
Exit Mach number (Me)
*This work mostly supported by NASA Hypersonics NRA grant (NNX08AB31A)
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Typical Results in Supersonic Flame
Plots of mean T vs. radial distance at several axial locations
Mixing
(coflow = N2)
Me=1.6
Mh=7
2400
2000
1
1600
15
2400
Combustion
(coflow = H2)
Me=1.6
Mh=6
2000
2
1600
16.2
36.6
35
1200
65
100
800
-20
-10
1200
400
0
0
10
20
98.9
800
400
0
63.4
-40
-30
-20
-10
0
10
20
30
40
Center jet diameter = 10 mm, surveys are at ~1, 15, 35, 65, and 100 mm
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“WIDECARS”*
• Enable DP CARS in C2H4 +
H2 – air flames
• New broadband Stokes laser
– 2x increase in spectral width allows
additional chemical species to be
simultaneously probed
• Temperature, mole fraction
N2, O2, CO2, C2H4, H2 and
CO measured at 300 K.
– Most species ever simultaneously
measured with CARS!
– Fit with new software
• Future development required
– Validate at flame temperature
– Modeling/calibration for C2H4
*Collaboration with Tedder and Danehy (LaRC)
Tedder et al., Appl. Optics, 2010
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Stokes laser Spectrum
3% CO2, 5% CO, 5% C2H4, 25% H2, 62% N2
CO2
N2
H2 S(3)
C2H4
H2 S(4) CO2
CO
Demonstration in a
room T gas cell
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OH PLIF Preliminary Setup
• Modified CARS laser cart to produce UV light
needed for OH PLIF
– Installed doubling crystal
– Optimized laser for power
• Performed OH PLIF measurements in laboratory
–
–
–
–
Set up sheet forming optics
Set up laminar OH combustion with water welder
Investigated camera settings
Determined optimal PLIF transitions
• Flow visualization only
– Signal roughly ~ OH density (not calibrated)
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Laser sheet
excites molecules
Tunable Laser
H2
O2
Water welder
provides reactants
for combustion
λ = 281.135 nm
Planar Laser-Induced Fluorescence (PLIF)
Excited molecules
fluoresce
CCD camera
detects
A2∑+←X2ΠΩ(1,0)
Excited state
Gas
Ground state
flow
LIF ~ nOH
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Ongoing Work and Future
• Summer 2011
– Acquire CARS data bases in UVa Dual Mode Scramjet
Configuration B (no isolator) and C (with isolator)
– OH PLIF flow visualization (same cases)
Config. B
Combustor
TDLAT
Extender
Config. C
Isolator
Combustor
TDLAT
Extender
• 2011-2013
– Develop and validate “WIDECARS” for C2H4 (+ H2) in Hencken
flame
– Acquire CARS data base supersonic flame with C2H4 + H2 coflow
– Acquire CARS/PLIF data base in UVa scramjet with ethylene
flame/cavity flame holder
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Summary
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•
•
•
•
•
•
•
•
•
Motivation
Dual pump CARS
“Mobile” system and implementation at UVa
Method of fitting spectra
Measurements in a Hencken burner (H2-air) and
supersonic jet
Saturation effects
Measurements in a supersonic flame
WIDECARS
OH PLIF setup and preliminary data
Ongoing and future work
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