NAOA-c¢-t4_,loci
NASA-CR- 178109
NASA Contractor Report a78109
19860018903
FEASIBILITY STUDYOF OPTICALBOUNDARY
LAYERTRANSITIONDETECTIONMETHOD
M. Azzazy, D. Modarress,
and J. D. Trolinger
SPECTRON
DEVELOPMENT
LABORATORIES,INC.
Costa Mesa, California
Contract NAS1-17293
June 1986
LI_,_ARY, N_SA
NationalAeronauticsand
SpaceAdministration
LangleyResearchCenter
Hampton,Virginia23665
I:......... !, WRt'-_r_EA
3 1176 01315 4241
TABLE OF CONTENTS
NO.
PAGE
TABLE OF CONTENTS ............................................
LIST
1.0
2.0
3.0
4.0
i
OF FIGURES ..............................................
iv
LIST OF TABLES ...............................................
xi
INTRODUCTION
................................................
I.I
Theoretical
1.2
Survey
1.3
High
1.4
Organization
CHAPTER
Basis ......................................
of Boundary
Sensitivity
Layer
Transition
Differential
Detectors ..........
Interferometry
...........
of the Report .............................
II - INSTRUMENT
DESCRIPTION ..........................
1
2
4
5
6
2.1
Optical
2.2
Compensator
System .....................................
I0
2.3
Electronics
System .....................................
II
CHAPTER
System .........................................
1
III - SYSTEM
3.1
Mathematical
3.2
Uncertainty
3.3
Speckle
CHAPTER
4.1
4.2
6
ANALYSIS ................................
14
Analysis ..................................
14
Due to Misalignment
........................
Analysis .......................................
IV - OPTICAL
DIAGNOSTICS
ACCESS
IN WIND
TUNNELS ......
17
19
22
Introduction ...........................................
22
4.1.1 General
22
Background ...............................
4.1.2 The Problem ......................................
22
Methods
24
for Getting
4.2.1 Using
Existing
Light
Model
-i-
In and Out ...................
Surface
Optical
Properties..
26
TABLE
OF CONTENTS
CONTINUED
NO.
PAGE
4.2.1.1
Mirror
4.2.1.2
Diffuse
4.2.2 Changing
Surface ...........................
26
Surface ..........................
28
Surface
Optical
4.2.2.1Retroreflective
4.2.2.2
4.3
4.4
4.5
5.0
Holographic
Materials ................
31
of Surface
Elements
Preparation .......
(HOE) .....................
42
43
43
4.3.2 Conceptual
46
Application ...........................
4.3.3 Construction of a HOE for High Efficiency
Indirect Shadowgraph or Holographic
Interferometry ...................................
50
Preparation of Surfaces for Differential
Interferometry .........................................
57
Recommendations
60
........................................
V - EXPERIMENTAL
Low Speed Wind
TESTS ...............................
Tunnel
61
Tests ............................
61
Experiment ...........................
62
5.1.2 Turbulent
Spot Experiment ........................
62
Supersonic
Tunnel
67
5.1.1
5.2
Optical
Forms
28
4.3.1 General ..........................................
CHAPTER
5.!
Other
Properties ..............
Shear Layer
Wind
5.2.1 Tunnel
Conditions ................................
5.2.2 Instrument
5.2.3 Unitary
Tests ...........................
Conditions ............................
Wind
Tunnel
-ii-
Tests ........................
67
69
69
TABLE
OF CONTENTS
CONTINUED
NO.
6.0
PAGE
RESULTS ......................................................
71
6.1
Shear Layer
Experiment .................................
71
6.2
Turbulent
Spot Experiment ..............................
73
6.3
Supersonic
Wind
Tunnel
VII RECOMMENDATIONS
Results .........................
..................................
80
7.0
CHAPTER
8.0
REFERENCES ...................................................
88
APPENDICES ....... ............................................
91
-iii-
87
LIST OF FIGURES
NO.
PAGE
I
Block
2
Schematic
3
Coordinate
4
Block Diagram
5
Schematic
6
Relationship
Between
7
Transmitting
Light
8
Enhancing
9
Retroreflective
Coatlngs-Glass
I0
Retroreflective
Materials-Corner
II
Experimental
Geometry ........................................
35
12
Retroreflection
- Intensity Profiles for a
Number of Materials ..........................................
37
Reflectivity
vs. Angle of Incidence of Various
Retroreflective
Materials ....................................
38
13
14
Beam
Diagram
Describing
Diagram
the Instrument ......................
of the Optical
System ............................................
of Compensator
of Electronics
Surface
Profile
20 ° Angle
System ......................
System ..............................
13
the Signal
and Phase ....................
18
Into or From a Model ......................
27
Spheres .......................
Embossings ..................
of the Retroreflective
15
Beam of Retroreflection
16
Diffraction
17
Producing
18
Example
19
Laser
20
Multiple
21
Flow Visualization
at 45 ° Angle .........................
Reflectors ...............
a HOE on an Arbitrary
- In Wind
Velocimetry
Made
Point LDV Systems
in Model
Surface ............
Tunnels ....................
Possible
Generated
Blocked
-iv-
30
32
33
Beam for a
of the Various
HOE Application
Doppler
9
12
of Incidence .......................................
and Using
8
System ..........................
Reflectivity ...............................
Patterns
7
39
40
41
45
47
by HOE ...............
48
by HOE'S ................
49
Regions
by HOE ...........
51
LIST
OF FIGURES
CONTINUED
NO.
PAGE
22
Geometry
Selection
for the HOE ...............................
53
23
Exposure Geometry for Experimental
Nonspecular
Holographic
Pupil-Forming
Screen .............................
54
24
Computer
55
25
Creating a High-Galn Projection Screen From Glass
Plate Holograms ..............................................
56
26
Holoscreen
58
27
Photograph of the Uncoated Holoscreen at the
Center and Near the Edge of the Aperture .....................
59
28
Schematic
Assembly ........................
64
29
Schematic Illustration of the Optical Setup of the
Reflecting Mirror/Scattering
Surface .........................
65
30
Schematic
66
31
Laser
Controlled
Hologram
Measurement
Experimental
of the Shear
Layer
of the Turbulent
Interferometer
Generation
Signal
Station ..............
Configuration
............
Spot Experiment ...................
RMS as a Function
of
Temperature
Fluctuations for Both the Reflecting
Mirror and the Scattering Surface ............................
72
Temperature
Profile of the Pulsed Jet Measured by
the Cold Wire ................................................
74
33
Vibration
75
34a
Spectrum of the Laser Interferometer
Signal for
Pulsating Frequency ef 305 Hz ................................
77
Spectrum of Cold Wire Data For Pulsating Frequency
of 305 Hz ....................................................
77
The Digitized Interferometer
Signal After Filtering
Out the Effect of Vibration ..................................
77
Spectrum of Laser Interferometer
Signal for Pulsating
Frequency of 120 Hz Using Scientific Retro-Reflector .........
77
Spectrum of Cold Wire Signal For Pulsating Frequency
of 120 Hz ....................................................
77
32
34b
34c
35a
35b
Level
as Detected
by the Laser
--V--
Interferometer
......
LIST OF FIGURES
CONTINUED
NO.
35c
36
PAGE
The Digitized Interferometer
Signal After Filtering
Out the Effect of Vibration ..................................
Signal/Noise
Ratio
of Both the First
Using Retro-ReflectingMaterial
and Second
77
Harmonics
on the Surface ...............
78
The Digitized Frequency Spectrum of the Interferometer
Signal Under Window Boundary Layer Disturbance ...............
79
The Digitized Frequency Spectrum of the Interferometer
Signal After Filtering Out the Effect of Window Boundary
Layer .......................................................
79
38
Time Averaged
82
39
Areas
40a
Digital
Signal
40b
Digital
40c
Digital
41
Signal Spectrum at x = 8", and Re = 2 x 106 , After
Using the Filter .............................................
37a
37b
Signal of Natural
of Applicability
Transition ...................
for Differential
Interferometer
.......
83
Spectrum
at x = 8", and Re = 2 x 106 ..........
84
Signal
Spectrum
at x = 8", and Re = 3 x 106 ..........
85
Signal
Spectrum
at x = 8", and Re = 4 x 106 ..........
86
87
APPENDICES
A(1)
X
A(2)
x = 4" Re = 2 x 106 Be fore Filte r............................
A2
A(3)
x = 4" Re = 2 x 106 After
A3
A(4)
X
A(5)
x = 5" Re = 2 x 106 After
_
_
2" Re
5 o° Re
_
_
2 x 106 Filter
2
X
106 Before
ooooooooooooeoooooooooooooooooooooo
Filter .............................
Filter
oooooooooooooooooooooooooeoo
Filter .............................
-vi-
A1
A4
A5
"
LIST OF FIGURES CONTINUED
NO.
PAGE
A(6)
x = 6" Re = 2 x 106 Before
Filter ............................
A6
A(7)
x = 6" Re = 2 x 106 After
Filter .............................
A7
A(8)
x = 8" Re = 2 x 106 Before
Filter ............................
A8
A(9)
x = 8" Re 2 x 106 After
Filter ...............................
A9
A(10)
x = 9" Re = 2 x 106 Before
Filter ............................
AIO
A(II)
x = 9" Re = 2 x 106 After
Filter .............................
All
A(12)
x = 12" Re = 2 x 106 Before
A(13)
x = 12" Re = 2 x 106 After
A(14)
x = 2" Re = 3 x 106 Filter ...................................
AI4
A(15)
x = 4" Re = 3 x 106 Before
Filter ............................
AI5
A(16)
x = 4" Re = 3 x 106 After
Filter .............................
AI6
A(17)
x = 5" Re = 3 x 106 Before
Filter ............................
AI7
A(18)
x = 5" Re = 3 x 106 After
A(19)
x = 6" Re = 3 x 106 Before
A(20)
x = 6" Re = 3 x 106 After
A(21)
x = 8" Re = 3 x 106 Before
A(22)
x = 8" Re = 3 x 106 After
A(23)
x = 9" Re = 3 x 106 Before
A(24)
x = 9" Re = 3 X 106 After
A(25)
x = 12" Re = 3 x 106 Before
A(26)
x = 12" Re = 3 x 106 After
A(27)
x = 2" Re 4 x 106 Filter .....................................
Filter ...........................
AI2
Filter ............................
AI3
Filter .......................
...... AI8
Filter ............................
AI9
Filter .............................
A20
Filter ............................
A21
Filter .............................
A22
Filter ............................
A23
Filter .............................
A24
Filter ...........................
A25
Filter ............................
A26
-vli-
A27
LIST OF FIGURES
CONTINUED
NO.
PAGE
A(28)
x = 3' Re = 4 X 106 Before
A(29)
x = 3" Re = 4 x 106 After
A(30)
x = 4" Re = 4 x 106 Before
A(31)
x = 4" Re = 4 x 106 After
A(32)
x = 5" Re = 4 x 106 Before
A(33)
x = 5" Re = 4 x 106 After
A(34)
x = 6" Re = 4 x 106 Before
A(35)
x = 6" Re = 4 x 106 After
A(36)
x = 8" Re = 4 x 106 Before
A(37)
x = 8" Re = 4 x 106 After
A(38)
x = 9" Re = 4 x 106 Before
A(39)
x = 9" Re = 4 x 106 After
A(40)
x = 12" Re = 4 x 106 Before
A(41)
x = 12" Re = 4 x 106 After
A(42)
x = 5" y = 1.0" Filter .......................................
A43
A(43)
x = 5" y = 0.875"
Filter ..............................
A44
A(44)
x = 5" y = 0.875" After
Filter ...............................
A45
A(45)
x = 5" y = 0.75"
Filter ...............................
A46
A(46)
x = 5" y = 0.75" After
Filter ................................
A47
A(47)
x = 5" y = 0.675"
Before
A(48)
x = 5" y = 0.675"
After
A(49)
x = 5" y = 0.5"
Before
Before
Before
Filter ............................
A28
Filter .............................
A29
Filter ............................
A30
Filter .............................
A31
Filter ............................
A32
Filter .............................
A33
Filter ............................
A34
Filter .............................
A35
Filter ............................
A36
Filter .............................
A37
Filter ............................
A38
Filter .............................
A39
Filter ...........................
A40
Filter ............................
A41
Filter ..............................
A48
Filter ...............................
A49
Filter ................................
A50
-viii-
"
LIST OF FIGURES
CONTINUED
NO.
PAGE
A(50)
x -- 5" y = 0.5" After
A(51)
x --5" y = 0.375"
A(52)
x = 5" y = 0.375"
A(53)
Filter .................................
A51
Before
Filter ...............................
A52
After
Filter ...............................
A53
x -- 5" y = 0.25"
Before
Filter ...............................
A54
A(54)
x = 5" y = 0.25"
After
Filter ................................
A55
A(55)
x -- 5" y = 0.125"
Before
A(56)
x = 5" y = 0.125"
After
A(57)
x = 5" y = 0.0"
A(58)
x = 5" y = 0.0" After
A(59)
x -- 4" y -- 1.0" Filter .......................................
A60
A(60)
x = 4" y = 0.875"
Filter ..............................
A61
A(61)
x = 4" y = 0.875 .°After
Filter ...............................
A62
A(62)
x = 4" y = 0.75"
Before
Filter ...............................
A63
A(63)
x = 4" y = 0.75"
After
Filter ................................
A64
A(64)
x = 4" y -- 0.625"
Before
A(65)
x = 4" y = 0.625"
After
A(66)
x = 4" y = 0.5" Before
A(67)
x = 4" y = 0.5" After
A(68)
x = 4" y = 0.375"
Before
A(69)
x -- 4" y = 0.375"
A(70)
A(71)
Filter ..............................
A56
Filter ...............................
A57
Filter ................................
A58
Filter .................................
A59
Before
Before
Filter ..............................
A65
Filter ...............................
A66
Filter ................................
A67
Filter .................................
A68
Filter ..............................
A69
After
Filter ...............................
ATO
x -- 4" y = 0.25'
Before
Filter ...............................
AT1
x = 4" y = 0.25"
After
Filter ................................
A72
-ix-
LIST OF FIGURES
CONTINUED
NO_____.
PAG E
A(72)
x
4" y
A(73)
x = 4" y = 0.125"
A(74)
X
_
4" y
_
0 • 0" Before
A(75)
X
_
4'O y
_
0 • 0 oe After
=
0 • 125" Before
After
Filter
Filter
Filter
Filter
-ooooeeeoeeeooeeeeeeeeeeeelee.
eeeooeeeoeeeoeeoeeee.eeeeoeeoe.
ooeeooeoooooooooooooeoooeoooooeo
..ooeoo.oeoooooooeoooooooooooo.ot
--X--
A73
A74
A75
A76
LIST
OF TABLES
NO.
PAGE
1
OPTICAL
ACCESS
RESTRICTIONS
2
OPTICAL
ACCESS
SOLUTIONS .....................................
3
MODEL
4
SUMMARY
CONDITIONS .................................
68
5
BOUNDARY LAYER THICKNESS AND OPTICAL PATH DIFFERENCE
AS A FUNCTION OF REYNOLDS NUMBER .............................
68
SURFACE
PREPARATION
OF TUNNEL
IN WIND
TUNNELS ..................
OPTIONS ............................
-xi-
23
25
29
1.0
INTRODUCTION
I.I
Theoretical
Numerical
Basis
validation
types tested
in wind
region where
transition
Boundary
model
layer
surface
Reynolds
sition
wind
depends
conditions
other applications
used extensively
Hefner,
region
the level
on the fluid
affect
to reduce
payload
et al, and Hough
independent
of several
region
(LFC) which
and fuel consumption
in the boundary
and its relation
layer,
to turbulent
methods
still
and
Determinato
has been
and to improve
however,
flow
of tran-
important
of long range
the different
such as
the flow
as well.
Control
drag,
place.
but the model
is also
friction
of the
takes
the region
transition
Flow
reviewed
flow
turbulence,
flow parameters,
layer
proto-
knowledge
parameters,
Therefore,
the transition
the skin
aerodynamic
to turbulent
... etc.
of boundary
of transition
flow
around
of freestream
such as Laminar
endurance,
transition
requires
is a function
and Mach number
tion of the location
range,
often
from laminar
roughness,
not only
tunnel
tunnels
transition
number
of the flow field
the
aircraft.
of delaying
the anatomy
requires
the
of
more
research.
The transition
region
turbulent
spots which
turbulent
boundary
transition
Schubauer
al, called
play a key role
layer flows.
received
special
and Klebanoff.
at constant
is generally
pressure
attention
vortex
spots
since
A turbulent
of
of laminar
to
spot
structure
and their
the classical
in a laminar
a single
--I--
by the onset
in the evolution
Turbulent
is essentially
it A-shaped)
recognized
relation
experiments
boundary
large horseshoe
which
moves
to
layer
(Perry,
downstream
of
with
et
its
ends slipping
Coles,
along
the surface
et al, showed
that
the llne of symmetry,
lag behind
at 0.64
speed flows,
vlz.,
characterized
increase
tion region.
prototypes.
techniques
fluctuations)
such techniques
transition
based
layer
transfer.
pathlength
of a small
fraction
more modifications
transi-
the heat
due to high
trans-
tempera-
on measuring
the
the transi-
to implement
and use
to measure
small
transition
provide
Holographic
optical
has
a tremendous
are difficult
boundary
as velo-
layer
tool in detecting
techniques
is
an
and interfero-
variations
(density
of a wavelength,
to be applied
density
however,
to boundary
layer
detection.
Survey
of Boundary
Layer
for detection
for tests in transonic
intrusive
gages
the heat
on the order
Techniques
used
detect
gages
a popular
Optical
can measure
need
surface
flow value
region
fluctuations
Since
experiences
on
At high
as well
to a boundary
speeds.
region
or turbulent
surface
to measuring
leading
and supersonic
became
and, hence,
alternative
methods
rests
of that vortex
the transition
the density
et al, and
which
velocity.
fluctuations
measuring
in the flow,
However,
fluctuations
1.2
and temperature
Therefore,
transfer
on aerodynamic
the tails
or supersonic,
its laminar
of heat
vortex
transonic
in the transition
ture fluctuations
A-shaped
of the
U= is the freestream
at transonic
over
Wygnanskl,
at 0.77 U=, while
the focus of several
fer coefficient
metic
moves
by density
tion detector
amount
the apex
et al).
U®, where
city fluctuations.
become
(Cantwell
Transition
of boundary
and supersonic
and model dependent.
Detectors
layer
wind
Oil sublimation
transition
presently
tunnels
are generally
methods
(Cassels
et al),
and smoke wire
locate
techniques
the region
although
(Betill
of transition.
providing
valuable
the laminar
results
about the transition
influences
and turbulent
the transition
of transition,
they suffer
measures
transition
region,
scopic
fluctuations
the frequency
serious
description
mentation
in the flow
to detect
A large
surface
in order
temperature
fluctuations
to erroneous
of the thin
at the
results.
Moreover,
layer
transition
is
A detailed
referred
1980 and 1982, and Stalllngs,
specific
to exactly
the micro-
due to boundary
(sometimes
of thin
about
area of the thin film.
film techniques
the region
number
large area
of the signal
techniques
without
dent of the test model.
provide
disturbing
Havener
based on holographic
applicable
grated
how
to as hot film)
et al).
and require
In sum-
additional
instru-
for every model.
transition
detector
any quantitative
The relatively
lead
gages are model
Nonintruslve
layer
on the model
which might
can be found in Fancher
mary, thin film
used
and does not give any information
of the large
of thin
separation
it is not certain
or the wire
drawbacks.
the macroscopic
content
lost as a result
do not yield
are routinely
of transition.
film gages
techniques,
the interface
and moreover,
to visually
zone.
thin film gages
the region
about
on the model
film gages has to be installed
locate
as a tool
visualization
regions,
area,
of the pigments
Although
Flow
information
between
the presence
et al) were used
fluctuations
along
to detect
boundary
the flow and are generally
developed
a boundary
Interferometry.
only to 2-dimenslonal
density
a capability
The method,
or axlsymmetrlc
the beam
-3-
layer
path,
flows,
indepen-
transition
however,
is
and the inte-
i.e. pathlength
difference,
should
detectable
eter
fringes.
to detect
nique,
et al, developed
fluctuations
more sensitive
drawbacks
developed
than the laser wavelength
Laderman,
density
although
the same
be higher
a technique
in the boundary
to detect
boundary
cone in a supersonic
results
that the interferometer
frequency
technique,
cannot
domain
which
although
readily
be extended
aerodynamic
models.
dimensional
flow models
has the capability
direction
the stringent
holography
1.3
of measuring
condition
or common
small
of high
beyond
flows,
over
a technique
fluctuations
This
interferometry
The
3-dimenslonal
transition
to the flow model.
sensitivity
peak in the
over
requires
density
O'Hare's
or axlsymmetric
layer
shapes
over an
of transition.
the transition
of arbitrary
suffers
0'Hare
flow.
has a sharp
to 2-dimensional
of boundary
The tech-
Recently,
number
to the region
to detect
Detection
perpendicular
signal
layer.
transition
high Reynolds
corresponds
applicable
layer
interferom-
interferometry,
interferometry.
axisymmetric
show
an optical
than holographic
as holographic
to produce
threethat
in a
configuration
imposes
the capability
of
techniques.
High Sensitivity Differential Interferometry
The method developed in this study is based on differential
interferometry, which is capable of detecting optical pathlength difference in the order of 1/1000 in a direction normal to the aerodynamic
model, where I is the laser wavelength.
The method, which is a
variation of the Smeets and George interferometer, utilizes two beams of
orthognal polarization.
surface.
The two beams are incident normal to the model
The reflected beams are made to interfere at the plane of a
-4-
detector
via a Wollaston
between
the two planes
comprises
power
a Pockels
supply
vibration.
to compensate
intermittent
Organization
signals
II, the optical
mathematical
description
and data reduction
reflecting
materials
to validate
detector
voltage
due to model
into
the
relevant
of Chapter
while
a series
are described
Langley
obtained
VII.
-5-
transition
of tests
the development
Recommendations
in Chapter
documented
of
in
of retrodetector.
V deals
Research
with
Center.
and verification
at the Unitary
for future
The
and experiments
part of Chapter
at NASA
as well as the results
VI.
The effects
layer
for
interpretation
of the characteristics
the second
supporting
results
are also
developed
in detail.
signal
III.
to the boundary
The experimental
in Chapter
including
uncertainty
V describes
systems
are described
in Chapter
Wind Tunnel
activities
difference
and electronics
the tests at the Unitary
presented
loop which
fluctuations.
IV is an analysis
the system,
the instrument
the angle
and a high
are then converted
are considered
Chapter
The first part
amplifier,
of the system
and the misalignment
III.
bisects
of the Report
layer transition
Chapter
axis
A phase-lock
the phase
density
the boundary
speckles
optical
of polarization.
The detector
In Chapter
whose
cell, a difference
is used
corresponding
1.4
prism
tests
tunnel
of
are
and research
2.0
INSTRUMENT
DESCRIPTION
The design
and development
interferometer
was the major
reported
in earlier
Although
the instrument
sition
surface
detector,
height
applications
beyond
papers
by Modarress,
concept
to measure
of the high
sensitivity
the scope of this report.
The instrument
(Azzazy).
layer
tran-
roughness
and
A full discussion
differential
of the
interferometer
In this chapter,
and electronic
et al.
as a boundary
the surface
was
detailed
systems
is
descriptions
of the differential
are presented.
The instrument
It has the ability
the instrument
developed
to detect
in a direction
three major
differential
et al, and Azzazy,
was developed
of camshafts
compensator,
sensitivity
of this study.
profiles
interferometer
tronics
focus
it was applied
of the optical,
%/I000
of a high
optical
A detailed
embodies
phase
in Figure
system,
description
several
variations
to the model.
is shown
elements:
system.
weak
normal
concept
here
novel
in the order
A schematic
I.
block
The system
compensator
of each
features.
diagram
of
encompasses
system
system
of
and elec-
will
follow
herein.
2.1
Optical
System
The instrument
Wollaston
prism,
laser beam into
polarization
various
optical
Wollaston
two-plane
directions
components
interferometer.
system
is illustrated
(I), is used
polarized
to split
beams
In the present
are crucial
configuration
--6--
a linearily
2.
A
polarized
(S and P polarizations).
and the orientation
in the system
in Figure
of the optical
axes of the
to the performance
the original
The
of the
polarization
_
Input: Laser
Illumination
Optics
r
--
Boundary Layer
Around the Model
--
Detection
System
Beam
Electronic Signal
Processing
|
_
i
i[
Output:
Density
Fluctuation
Signal
I
Compensator Loop
Figure (i)
Block Diagram Describing
the Instrument
Reflecting
Polarizer
He-Ne
Beam
Splitter
Wollaston
(1)
7
Laser
f
I
i
Pockels
Cell
!
oo
I
Wollaston
[Detectors
Figure
(2)
Schematic
Diagram
of the Optical
System
(2)
Surface
direction
plane,
of the laser beam was at 45 ° with
which
laser beam
is defined
propagation
(I) and the Pockels
The two beams were
as the plane
opposite
another
then focused
polarizations.
at 45 ° with
interference
illustrates
Wollaston
respect
since
of the two beams
the coordinate
(2), whose
system
plane.
The scattered
by Wollaston
system
optical
plane.
(I).
are of
includes
axis
This orientation
at the detector
of
of Wollaston
the two beams
The rest of the detection
(I).
axis
model.
and recombined
at this stage
to Wollaston
the direction
to the scattering
on the aerodynamic
prism, Wollaston
to the scattering
The optical
cell were perpendicular
is possible
Wollaston
that contains
and the detector.
light of the two beams was collected
No interference
respect
is oriented
results
Figure
used and the orientation
in
(3)
of the
prisms.
Y
S Polarization,
Pockels Cell,
Wollaston (1)
Y"
/
%
/
\
f
\
/
/
\
/
X" Direction
of Original
Laser Polarization,
Wollaston (2)
/
\
/
\
/
\
/
f
w
j
f
t
F
J
X (P Polarization)
Figure
(3) Coordinate
-9-
System
2.2
Compensator
System
The interference
Wollaston
pattern
(2) are detected
of the two beams
by a quadrant
and B, are 180 ° out of phase;
SA = So + S 1 cos(6
emanating
detector.
from
The two signals,
A
that is,
+ _v + Y)
(1)
SB = So + S 1 cos[_
where
6 is the phase
+ (6 + _v+ _)] = So - S I cos(6
difference
tude and large frequency),
amplitude
6v' the phase
and low frequency)
cell.
The amplitudes
fringe
visibility.
ential
amplifier
to produce
difference,
that is
phase
The signals
The quadrature
amplifier
error
signal.
thus driving
combined
power,
is achieved
classified
The phase
et al).
loop used
in a differ-
to the cosine
when
of the
_ + _v + y = _ + mz,
to realize
as a phase-tracking
The output
y can be made
signal
and
(2)
by the sum of the signals
the error
by the Pockels
to the laser
proportional
(large
+ _v + Y)
(Giallorenzi
normalized
(low ampli-
vibration
introduced
SA and SB were
The feedback
is generally
(PTDC)
due to model
y the phase
a signal
condition
(m = 0, i, 2, .... ).
system
and
fluctuations
So and S 1 are proportional
S C = 2S 1 cos(_
condition
due to density
+ _v + Y)
to zero.
-i0-
the quadrature
homodyne
detection
from the differential
A and B, is defined
to exactly
For small
cancel
as an
the signal
excursions
from
6v'
the
quadrature
feedback
condition
system,
vibration
2.3
the system
which
induced
of Figure
attenuates
(4) is a simple
low frequency
linear
signals,
i. e.,
signals.
Electronics
System
The electronics
system
designed
to meet
compensator
system
is shown
in Figure
(5).
electronics
system
embodies
the following:
the requirements
Special
features
i.
Minimum
voltage
to the divider
numerator
2.
Maximum
voltage
to the divider
denominator
3.
Frequency
4.
Correction signal
quency ~ 7 kHz.
5.
Output
bandpass
signal
of the system
to the Pockels
frequency
-II-
of the
is #250 mV.
is #I0 V.
is 200 kHz.
cell is low fre-
is > 7 kHz.
of the
Detector Signal A
Differential
Detector Signal _
Amplifier
Correction
'
_
Detector
Detector
Divider
['-_.
-'I
L__" _
Normalized
Signal
Low-Pass
Filter
Signal
v
to Pockels Cell
Signal
.[A
Signal_B
Sum Amplifier
High-Pas s
Filter
v
Signal Out
Figure (4)
Block Diagram of Compensator System
l
15k
150k
Modulator
lK
9K
SPF
7 kHz Low-
Pass Filter
.-I
W
I
lK
7 kHz High_
Pass Filter
9K
+ 15v 50k
Figure (5)
-15v
Schematic of Electronics System
Signal Out
3.0
SYSTEM
ANALYSIS
The present
foundation
interpret
the signal.
cal element,
performance.
analysis
The electric
field amplitude
since
the electric
part of the chapter
of each polarization
are orthogonal
of each other.
field entering
-- ei(mt + kz)
m
of each optisystem
consti-
is a discussion
Using
through
Jones'
can be treated
and,
therefore,
calculus
Wollston
(I) can be
introduced
{[a
Ill
l
s
0
+
(3)
ap
_ is the laser
frequency,
by the Pockels
in the S and P polarization
through
of the overall
is not
as
E
where
of the system
the two polarizations
feel the presence
presented
analysis
of the functions
then used to
on the signal.
Analysis
(Swindell)
outlined,
of the system misalignment
part, and the third
and their effect
The mathematical
is first
to the understanding
Mathematical
independently
cannot
system
The mathematical
Uncertainty
of the speckles
into 3 parts.
to the full understanding
but also
the second
3.1
is divided
of the interferometer
only imperative
tutes
chapter
Wollaston
cell,
k the wave
number,
y the phase
as and ap the electric
directions,
(I), the electric
respectively.
field
-14-
amplitude,
field
amplitude
After
passing
Em, remains
the
same provided
that the optical
cell are parallel.
given
A complete
in the next section.
can be represented
the reflectance
axes of Wollaston
analysis
of misallgnment
The scattered
by a deterministic
of the surface
(I) and the Pockels
is
light, Esc , from the surface
complex
(amplitude)
uncertainties
function,
and profile
p, describing
(phase),
such
that
E SC
where
= p: E m
the complex
p=
(4)
function,
p, is defined
as
[ikx
01
(5)
ik6
e YJ
where
6x and 6y are the disturbances
the passage
of the laser beams
Since Wollaston
ference
of the scattered
in the optical
through
(2) is oriented
beams
the fluid
pathlength
flow.
at 45 ° to Wollaston
can be achieved
due to
in the plane
(I), interof the
s
photodetectors.
plane,
Esig,
field such
Therefore,
electric
can be represented
field
amplitude
as a function
at the detector
of the scattered
electric
that
Eslg
= _
_
(6)
-15-
Since the detector
field amplitude,
signal
is proportional
the detector
signals
to the square
after
algebraic
of the electric
manipulation
become
where
So = a2
s + a p2 is the laser
visibility.
The phase
I.
Vibration
2.
Phase difference
induced
Therefore,
further
reduced
difference
phase
and V = 2 asap/S o is the fringe
6X - 6y can be divided
difference,
due to density
the signals
such
power,
into 2 parts:
6v , at low frequency.
fluctuations
in the flow field,
A and B of the two detectors
6.
can be
that
SA = So + So V sin
[_2- k (6 + 6v + _)]
(8)
SB = So - So V sin
The quadrature
condition
[_2
k (6 + 6 + y)]
v
is achieved
k (5 + y) = _ + m_,
v
2
when
m = O, I, 2 ...
(9)
S
An error
signal
S (S is defined
as S = _where
and S+ = SA + SB) is used as a feedback
-16-
control
S
= SA
to the Pockels
SB
cell.
The Pockels
such
cell
controller
that Equation
signal
(9) is realized.
S can be used
(density
to interpret
fluctuations)
signal
Uncertainty
Serious
differential
respect
deficiencies
presentation
in the operation
interferometer
arise
of the two signals
A and B
cell.
of the high sensitivity
due to mlsaligning
For a small
cell and Wollaston
(II) has complex
signal.
When
to the familiar
desirable
interferometer
angle,
Wollaston
= between
(I), the quadrature
(I) with
the optical
condition,
multiple
the angle
quadrature
roots
(II)
which
= tends
condition,
lead
to zero,
to a diminished
Equation
Equation
(II)
(9), which
of the dlffuse-point
and
is
differential
system.
it does
does Wollaston
cos k(6 - y)
for the performance
Misaligning
however,
variation
(9) becomes
discretlzed
highly
pathlength
(I0)
cos k(6 + y) = 2
reduces
the optical
interferometer
Due to Misalignment
axes of the Pockels
Equation
The normalized
y, at all times
S.
to the Pockels
Equation
shift,
the relation:
(6) is a schematic
and the error
3.2
through
a phase
6
_
S = V sin 2_
Figure
introduces
Wollaston
not affect
(2) will
only result
the performance
(I).
-17-
in a decreased
of the interferometer
signal,
as
SignalAmplitude
(a)
3
4
2
I
6IX
(b)
Figure (6) Relationship Between the Signal and Phase
18
3.3
Speckle
When
Analysis
an object
is illuminated
wavefront
appears
structure
of this granularity
microscopic
properties
be chaotic
theory
properties
uniform
ular
surface).
made
to interfere
pattern
carries
object.
phase
pattern
resulting
In general,
signal
However,
vibration
causes
speckles,
the signal
is done
Gaussian
can vary
from
to a delta
function
(spec-
wavefront
and the resultant
height
to show that
can be
interference
of the diffuse
the interference
can be used to measure
of aerodynamic
the interferometer
roughness
is static
can produce
the interferometer
laser
beams
due to speckles
as the model
through
distribution
function
of the surface
roughness
the focused
of
the statistical
the circular
that a speckled
wavefronts
to
the two waves.
speckles
affect
information
surface),
two speckled
that influence
obeys
appear
by the methods
studied
density
a plane wavefront
surface
which
a signal
diffuse
between
vibration
quency
probability
demonstrated
due to the surface
is dynamic.
intensity
to the
Speckles
The probability
was extrapolated
from
the phase difference
duce speckles
light
information
The analysis
Goodman,
patterns.
(totally
with
relationship
described
the phase
Azzazy
The detailed
no obvious
and statistics.
statistics
(speckles).
and can be best
of the scattered
while
bears
the reflected
surface.
of laser speckle
statistics,
in shape
beam,
of the illuminated
and unordered
probability
function
to be granular
by a laser
models
performance
the compensator
-19-
since
and the signal
dynamic
signals
performance.
of interest
model
off different
the same fre-
Discrimination
system.
the
due to model
Since
to be scattered
has approximately
vibration.
does not pro-
against
It is also
of
such
importance
to note
visibility
fringe
that the effects
contrast
The characteristic
correlation
function
expression
where
and hence,
smaller
of the reflected
is illuminated
result
is measured
intensities.
function
in decreasing
slgnal-to-nolse
size of the speckles
for the autocorrelatlon
the surface
of speckles
Goodman,
intensity
ratio.
°
by the auto-
of the scattered
by a uniform
the
derived
an
intensity
beam of diameter
D such that
Rl(r)
where
Jl is Bessel
between
tion
= <1> 2
the lens
spatial
frequency
f
where
function
(12)
order,
and f is the distance
pattern
expressed
up of a set of gratings
The maximum
spatial
by the interference
of the illuminated
area.
frequency,
of the light
Therefore,
by Equaof
fmax,
is
scattered
the maximum
spatial
is
1
max
(13)
%f
- a
a is the diameter
length.
2
The speckle
to be made
frequencies.
formed
j
of the first
and the object.
that of the grating
the edges
Jl_f
-_
2
(12), can be considered
varying
from
+
of the viewing
It is interesting
tion of the surface
to note
roughness,
that
lens aperture
the speckle
but rather
-20-
a function
and f is the focal
size
is not a func-
of the optics.
In conclusion,
between
the speckle
the two scattered
information
Speckles
lead
visibility.
cast beam
about
beams.
the pathlength
to smaller
The maximum
effects
The interference
difference
signal-to-noise
speckle
do not prevent
size
between
ratio
interference
pattern
-21-
phase
the two beams.
through
the reduction
is in the same order
diameter.
carries
of
as the broad-
4.0
OPTICAL
DIAGNOSTICS
4.1
Introduction
4.1.1
General
electromagnetic
front.
wave
A receiving
wavefront
may require
ity.
an optical
is either
negligible
system
4.1.2
NASA
information
scatters
the wave-
amount
of the
information.
to the outside
that noise
which
onto
the desired
in a way
access
problem
is often
The major
of the differential
layer transition.
personnel
This
of the test
added
drastically
facil-
to the signal
focus
different
for
of this program
has
interferometer
Therefore,
a separate
for the differential
extended
case of all optical
the objective
diagnostic
to the locatask was
interferometer.
of the task to cover
the
instruments.
The Problem
The basic
optical
to a location
a conditioned
or accountable.
to treat this problem
Moreover,
back
by passing
a sufficient
to extract
the radiation
been on the application
general
then collects
types of instruments.
tion of boundary
works
or impresses
be accomplished
The optical
defined
TUNNELS
into a test facility
from which
passing
This must
different
instrument
from the wavefront
modified
IN WIND
Background
In general,
radiation
ACCESS
access
problem
is caused
is severely
for five different
classes
by the fact that in most wind
restricted.
of optical
Table
1 summarizes
instruments.
-22-
tunnels
the problem
The types
of
TABLE
TYPE OF DIAGNOSTIC
LDV!LTA
Forward
I
i
Scatter
I.
OPTICAL
ACCESS
RESTRICTIONS
IN WIND TUNNELS
REQUIREMENT
RESTRICTION
High resolution access to point of
interest.
Large collecting access
for output.
Nearly straight through
optical access.
Input and output window size,
quality, location.
Access
blocked by model.
Schlieren
Shadowgraph
Interferometry
Deflectometry
High optical quality access in and
out.
Straight through access.
Size of either input or output equal
to field of view.
Window
Access
size, quality, location.
blocked by model.
Photography
Access to point photographed.
Illumination access.
Window
Access
size, quality, location.
blocked by model.
Holography
(Transmission)
Straight through access.
Size of either input or output
to field of view.
Window
Access
size, location.
blocked by model.
Reflection
ferometry
Holography
Input/output access
model reflectivity
Window
location.
Inter-
equal
restictions
model
include
or other
window
the model
when
the light wave
eter.
tion
can pass
not always
a trivial
considered,
the region
without
between
through
at no more
and blockage
to probe
to the sample
by the
bearing
wave.
imposing
the sample
volume
than two points
ways
In fact,
of the wind
tunnel
and the sample
each
to optimize
the window
perim-
collec-
the light
upon
to the
it is
be carefully
boundary
volume
when
to the
along
getting
In the
exists
information
Not only must
the instrument
volume.
case
unlnterpretable
the affect
boundary
the optimum
is to find other
problem.
but also
adjacent
straight
the problem
of the information
volume
quality,
is used
interferometer,
This case exists
Therefore,
sample
an instrument
is immediately
case of the differential
detector.
location,
components.
Specifically,
layers,
size,
layer
must
and
be under-
stood.
4.2
Methods
for Gettln_
Light
Table 2 summarizes
the problem.
wrong
wind
When
place,
input or output
wall
itself
optics
of the wall
lent boundary
must
the model
of methods
blocks
to conduct
element.
the
the light
and aero-
For example,
modulation
been devised
to deal with
the transmitted
The
The aero-
unacceptable
-24-
inside
then be considered.
as an optical
to either
to solve
or are in the
of the aerodynamics
not be overlooked.
have
access
be used
the flow must
be used
layer can impress
A number
which
itself
part of the optics
The problem
inside
may sometimes
are too small,
that mirrors
volume.
of the components
that can be exercised
windows
is to install
This may require
to or from the sample
optics
the approaches
one approach
tunnel.
In and Out
a turbu-
on the beam.
the case
or received
for
TABLE
RESTRICTION
2.
OPTICAL
ACCESS
SOLUTIONS
CONDITION
point
APPROACHES
Input window
location
Cannot access
from window.
of interest
Mirrors inside tunnel.
Transmitter inside tunnel.
Input window
size
Insufficient
input beam size.
Optics
location
Radiation
window,
interest
Mirrors
light
size
Insufficient
!
inside
tunnel.
l
Output
window
Output window
Access
blocked
by model
Radiation
model.
of
output
misses
beam size.
of interest
strikes
Inside
tunnel.
Use
scattered from tunnel wall.
Optics
inside
tunnel.
Prepare
model
surface.
-
Use light scattered from model
Make model reflective
-
Make model
transparent
Put receiver in model.
Put transmitter in model.
light.
Fiber optics
to convey
cept.
optics
the diagnostics
trated
also can be used
device
4.2.1
Using
Existing
Mirrored
Model
Surface
the model
surface
optical
simplest
approach
optical
properties
radiation
Optical
addressed
properties
part
of
it inside
approaches
transparent
illus-
or inserting
in this program
or preparing
surface
depending
equivalent
with
side.
on the opposite
For a surface
face smoothness
Any curvature
to act as a mirror,
of the same order
of the surface
phase modulation.
polished
the surface
will
This approach
or when
a mirror
is tilted
then it reflects
between
If the mirror
to having
it must
be impressed
is useful
when
be retrieved.
26
the forward
a transparent
the surface
direction
qualsurface
being
used.
as a
can be
on the surface
to allow
to
to a sur-
on the light wave
can be replicated
in the proper
from the
is of high
of light
to
The
the normal
be polished
as the wavelength
surface
access.
or scattered
on the angle
ity, then this is essentially
is that of using
the model
optical
reflected
and the angle of incidence.
a window
Properties
that aid in the desired
is a mirrored
in a direction
the surface
when
to locate
Other
the model
of these is to use the light
If the model
highly
the sensing
possible
itself.
the con-
Surfaces
A particular
model.
making
7 illustrates
to miniaturize
in the model
include
role in this regard;
in the model.
4.2.1.1
have
Figure
so that it becomes
tunnel or even
in the figure
windows
an ever-lncreaslng
light into or out of a model.
Fiber
the wind
are playing
and
the light
to
TRANSPARENT MODEL
MODEL
SURFACE
MODEL
SURFACE
RECEIVER IN MODEL
"__. I/7,
_
I
TRANSMITTER IN MODEL
-'_--"
/
Figure
(7)
Transmitting
Light
Into or From a Model
FIBER
/OPTIC
Since it is not always
have examined
alternative
in an unprepared
state
Table 3 summarizes
4.2.1.2
Diffuse
which
problem
with
in the reflected
in both amplitude
the light
source
light
The problem
beam.
and phase,
which
large spatial
of the reflected
a condition
Surface
properties
optical
available
or to use it
For all the
to be a laser.
which
surface
those
that
focus
in the speckle
spatial
the model
pre-
distribution
is not easily
as the illuminated
occur
presents
handled
by
is vibrating
area.
in the amplitude
In
and phase
light.
Optical
components
the surface
properties.
in detail
to alter
with a film,
into the surface.
and their
materials
Properties
it is advantageous
by coating
of the possibilities
cially
especially
true when
fluctuations
For some applications,
inserting
we
function.
is considered
The light has a random
is in the same order
optical
optical
is manifested
by an amount
Changing
criteria,
surface
from a diffuse
many instruments,
This is especially
4.2.2
the model
the required
many instruments.
such a case
the above
have been considered.
of coherent
light onto the surface.
sent
to prepare
to achieve
here
to meet
Surfaces
The reflection
a difficult
ways
methods
cases to be discussed
possible
Figure
-28-
a paint,
their
or by
8 summarizes
We have examined
to determine
ties.
the surface
some
commer-
optical
proper-
TABLE 3.
CONDITION
WANTED
MODEL
SURFACE
PREPARATION
TYPE OF PREPARATION
OPTIONS
LIMITATION
Wide angle scattering
Etched to provide
surface,
Specular
Polished to % smoothness.
Replicated mirror.
Curved surface aberration.
Flat surface required.
Spherical (cats eye) coating
add surface roughness.
_I00 micron
diameter
Corner,
Diffraction
noise
reflection
diffuse
Speckle pattern induced
scattered radiation.
on
!
l
Retroreflection
Preferential
direction
Forward
reflection
scattering
cube
coating.
spheres.
added
to beam.
Mirror inside model.
Diffraction
grating on surface.
Holographic optical element.
Curved surface aberration.
Limitation on angular access.
Mirror inside model.
Transparent model.
Receiver in model.
Transmitter in model.
Curved
surface
aberration.
MODEL SURFACE
RETROREFLECTIVE PAINT COATING
/
100 MICRON SPHERES
BONDER
100-500 MICRON
_/CORNER
_/BONDER
-_-CORNERCUBE REPLICA COATING
CUBES
_
___..._
'\'_"L_MODEL
SURFACE
!
ol
BONDER
"_'_
DIFFRACTION GRATING COATING
MODEL SURFACE
1-500 MICRON SPACING
/
WINDOW
INTERNAL MIRROR
_
MIRROR
/
"_t-----MODELSURFACE
Figure
(8)
Enhanclng
Surface Reflectivlty
4.2.2.1
Retroreflective
Commercially
Materials
available
retroreflective
ety of mterials.
Figures
of some of these.
Retroreflectlve
and glass spheres
properly
of nominally
applied
portion
the spheres
of clear
photograph
this material
Such procedures
paints
are nested
However,
distance
requires
heat
care
drying
Other retroreflectlng
paints
since the number
The so-called
can be seen
slightly
chosen
that
scientific
in these figures,
larger.
Also,
the reflection
A major
concern
to the spheres,
fact, applies
above have
expressed
An alternative
material
containing
in diameter.
about
The other
protective
corner
mounted
the pigment
these
adding
cube
types
which
as
and
backing
optimum.
of coatings
roughness
heights
argument
is
due
in
described
would
problem
reduce
is an embossed
of nominal
of the material
-31-
since,
in a pigment
two mterlals
reflectors
than the
more uniform
This
this
backing
is much higher.
of the sphere
coating
relieves
surface
better
are somewhat
roughness,
which
The outer
that
is the most efficient
of 25 to 50 micrometers.
plastic,
spheres
results.
to adhesive
per unit area
from the back
to the paint.
a smooth,
their effect.
meters
typically
only
spheres
material
the surface
to insure
are significantly
the spheres
often
the glass
acceptable
are applied
they are accurately
to make
they may change
plastic
grade
from this
sphere.
These
of glass
with a significant
between
to achieve
coatings
9b and c).
When
is not retroreflecting.
the paint
does not cover the retroreflecting
of pigment
in diameter.
it can be seen
exists
a vari-
of the surfaces
a mixture
in pigment
much of the surface
include
(shown in Figures
contain
50 to I00 micrometers
that a significant
comprise
I0 are microphotographs
glass exposed.
and that on a microscale
Applying
9 and
coatings
200 micro-
is flat and
(a) 3-M "Codit Paint
(b) 3-M Scotchlight Engineering Grade
(c) 3-M Scotchlight
F'igure (9)
Scientific
Retroreflective
-32-
Grade
Coatings-Glass
Spheres
(a) Front Surface
(b) Rear Surface
Figure(10)
Retroreflective
Materials-Corner
-33-
_mbossings
would
not disturb
photomicrographs
material.
flow
in a boundary
layer.
Figure
of the front and rear surface
This represents
the most
efficient
I0 contains
of a sample
material
of this
tested
in this
study for retroreflection.
Because
these are candidates
we were not able to find published
number
of critical
ties.
Properties
areas,
which
for use in wind
properties
and since
of the materials
a study was completed
were considered
tunnels,
to measure
to be important
in a
such proper-
were
the
following:
I.
Reflection
2.
Angular
3.
Reflection
4.
Angular spread
of incidence
5.
Intensity distribution
of angle of incidence
These
properties
strated
and were
surfaces.
Figure
first series
mount
center
of the reflected
by a beam splitter
the results
of incidence.
to a detector
beam by a linear
should
beam as a function
geometry
reported
were
illu-
and diffuse
used
mounted
white
to make the
on a rotary
The retroreflected
beam was
that was traversed
through
translator.
here were
to differ
at other
not vary drastically
-34-
of angle
beam as a function
of mirrors
The materials
are likely
of incidence
for all of the materials
the experimental
that all measurements
of angle
in the reflected
to the properties
the angle
beam
as a function
were measured
II shows
and the results
However,
of the reflected
efficiency
compared
of the reflected
emphasized
meters
spread
of measurements.
to control
directed
efficiency
It should
be
done at 633 nanowavelengths.
for Argon-ion
lasers
the
Retrorefleetive
Material
r9
.;.1._--
r--- 14 em - - - I....;
;-.._
. - - 16 em --...,
em--
~12cm1
(10
~)
I.
17 cm
--...-.I
(40X)
I~
f
I
=
12 em
D ::; 4 em
Vol
V1
1
On ,+ranslation Stage (It!)
Power Meter Detector (coherent radiation power meter 212)
On
Rotary Stage
Figure (11) Experimental Geometry
BESF
Laser
5 mvJ
Figure
mirror
12 shows the resulting
and to each other
of course,
corner
the most
efficiency
by comparing
Beam-spread
the process
if half
changes
power points
almost
by the
The reduced
can
the one for the
for all materials.
this is difficult
Because
to quantify,
then the retroreflecting
the same apparatus
retroreflected
the materials
(Figure
materials
incidence
as high
of the materials
The profiles
corner
but
are
Finally,
results
depicted
indicates
beams
Figures
were
at angles
of
the applicability
excels.
However,
then measured
14 and 15 show
At 20 degrees
angle
as a
the results
of incidence
at 45 degrees
of the diffraction
at 0 and 45 degrees
are illustrated
in
little
off the
the
the 3M scien-
is best.
photographs
materials
falls
models.
of incidence.
still
tific grade material
different
curved
of the
of incidence
cube material
This graph
and at 45 degrees.
cube material
of angle
fall off surprisingly
of the retroreflected
of the angles
at 20 degrees
The corner
as 40 degrees.
to highly
at the center
as a function
13).
Two of the materials
function
the intensity
beam was measured
fastest.
since
is,
The beam-spread
with
to a
as good as the mirror.
Using
onto
are chosen
The mirror
ten percent.
curves
small
as compared
is followed
effects.
the individual
the beam profile
beam.
This
of about
to diffraction
is surprisingly
profiles
incident
in this case.
at an efficiency
is due largely
be observed
mirror.
for a normally
efficient
cube material
intensity
(a) since
there is a beam
in Figure
the reflector
splitter
16.
angles
pattern
is a mirror.
-36-
made
of incidence.
The appearance
in the setup
were
with
for the
The
of the raw beam
The two spots
two reflecting
result
is
Mirror
Corner
Cube
Material
;cier
Scotch
Engineering
_
O
.I
NRC
Paint
Paint
.01
0
.25
.5
.75
1
1.25
1.5
Translation
Figure (12)
Retroreflection
1.75
2.0
2.i5
2.'5
(CM.)
- Intensity Profiles for a Number of Materials
-37-
Corner Cube Material
3M
Scientific Grade
3M
Engineering Grade
Paint
o
.1
.01
,
0
!
i0
I
20
Angle
I
30
I
40
I
50
!
60
(Degrees)
Figure (13) Reflectivity Vs. Angle of Incidence of Various RetroreflectiveMaterials
-38-
Corner Cube Material
3M
ientific
3M
Engineering
Grade
Paint
.]
O
Beam Profiles of Retroreflection
.01
_
0
.25
.50
.7"5 1.0
1.25 1.50
Translation
Figure (14)
1.75
2]0
2.25
2.50
(CM.)
Beam Profile of the Retroreflected
-3g-
at 20° Angle
Beam for a 20° Angle of Incidence
3M
Scientific
Grade
.I
Paint
>
3M
,-,
mngineering
Grade
Corner Cube
Material
.01
i
0
i
;
i
.25
.5
.75
I
1.0
I
1.25
Translation
Figure
(15)
Beam
z
i
;
I
;
1.5
1.75
2.0
2.25
2.5
X (CM.)
of Retroreflection
-40-
at 45 ° Angle
(a)
. .. ,!',,.A.._.]I..... ._ _"]I.R_,4.I'<
_'c
"
CORNER LL,_:_!,_IATER.IAL•
(b)
"r, SC 11ENTI FI C (I:;RADE
...d
(d)
..
3H EM_I[t'_E!!;RING (:,_.,.A._;)
........
' '"_[:_
CORNER Ct!._i:_:_.{...,,
1_'_
I:.,.
i[AL
'
Figure (16)
Diffraction Patterns of _he Various Reflectors
at Normal Incidence Angles.
-41-
surfaces.
The diffraction
the glass spheres
disperse
pattern
Theory
concludes
of a large number
and of equal
diameter
Figure
engineering
grade material
to the fact
apertures
that
are relatively
that the Fraunhofer
which
mono-
diffraction
are randomly
form as that of one of the
that the sphere
are rather
from
material
has the same
16 suggests
to be drawn
in (b) attest
grade
of circular
apertures.
conclusion
shown
in the scientific
in size.
oriented
pattern
widely
used
to make the 3M
dispersed
(e) is that the paint
in size.
uses
The
more monodlsperse
spheres.
Except
reflecting
face.
made
a specular
in each
of typically
case,
thicker
the thinner
the angle
nated
by tilting
tually unchanged.
can be observed
4.2.2.2
Other Forms
Rarely
does
a mirror
face requires
same techniques
of Surface
or a diffuse
slightly
is
than that
must be considered
the normal.
angles
as shown
of incidence
is vir-
the diffraction
in Figure
15h.
Preparation
surface.
surface
mirrors
-42-
exhibit
To make a mirror
be ground
for grinding
cube material
but it can be elimi-
of incidence,
machined
that the surface
used
angle
to change
a normally
away from
sur-
its optical
is better
90 degrees,
at 20 degree
At 45 degree
the corner
This reflection
to a retro-
from a first
material,
its reflection
slightly
pattern
pattern
Since
is nearly
the material
in addition
property
this is a plastic
plastic,
of incidence
have,
reflecting
3M materials.
The diffraction
either
the materials
is not as good as the mirror.
seen with
when
property,
Since,
quality
for the paint,
and polished.
on glass,
the properties
of such a surBy using
an essentially
the
of
perfect
mirror
can be produced
buffing
wheels
and grits of various
surface
is produced,
until
ready
unless
dielectric
made
for mirrors
diffuse
An untreated
grating
increase
most
of the scattered
placed
as the tool marks
light
The condition
could be ruled on the model,
places
In principle,
as desired
The most
general
reflection
case
hologram,
4.3
Holographic
4.3.1
General
the subject
Optical
of diffraction,
into a second wavefront
used
orders
location
to form the hologram.
a
by angles
This can cause
if not taken
into
if the receiver
is
or if the machine
material
In fact,
which
gratings
is attached
can be directed
by the correct
the surface
to
to as many
ruling.
is converted
into
a
section.
(HOE)
or transmitting
converts
common
can be
llke
separated
together.
orders,
of the next
Elements
which
orders
to advantage
or on another
A HOE is a reflecting
process
closer
is that in which
oxidize
The most
optically
for the application.
and to any desired
coatings
The surface
acts
the receiver,
diffraction
such a
polishing.
diffraction
tailored
will
coating.
monoxide.
diffraction
become
After
removable
most metal
commonly
can be used
marks are deliberately
the model.
after
to miss
in one of the strongest
easily
dielectric
surface
8), producing
that
account.
by etching
machined
(see Figure
with
is silicon
the use of
of coarseness.
such coatings,
a gold or proper
coating
optically
Without
This includes
degrees
it can be protected
for use.
coated with
on any metal.
film which,
an illuminating
emulates
whatever
The surface
-43-
through
wavefront
of one form
form of wavefront
of the hologram
the
can have
was
any
shape whatever
formed.
so long as it remains
Therefore,
hologram,
if the surface
then any known
other desired
wavefront
fixed
after
of the model
illuminating
wave
and directed
the hologram
is
is converted
to a
can be converted
to any desired
into any
direction
regardless
of the shape of the model.
Figure
17 illustrates
trary surface.
One method
the production
for forming
arbitrary
shape is to first
material,
such as a photographic
make
the recording.
chosen
during
the instrument
used
desired
for which
to produce
If a photographic
procedures
be bleached
sion were
sary.
after
emulsion
like a photographic
and fixing
later
were
This would
used,
After
be used.
on a mlrror-like
of
wave
to illuminate
to
is
the
the characteristics
constructed.
of
The object
like the one which
is
it is illuminated.
the entire
exposure,
reflection
surface
form a good optical
hologram.
would
but it would
would
be
development
hologram
bleaching
surface
model
normal
The developed
to form a high efficiency
placed
upon
is a wavefront
plate.
would
in which
the reference
be used
is being
surface
a photosensitive
or photoresist,
and depends
the hologram
on a metal
with
the hologram,
the surface
to leave the surface
treated
emulsion
that will
the application
a hologram
the surface
In producing
to be like the wave
surface
wave
coat
and use of a HOE on an arbi-
would
then
If the emulnot be necesbe rather
fragile.
Alternatively,
After exposure,
hologram.
the photosensitive
the surface
This also
face can be metal
would
be etched,
is an extremely
coated,
making
material
fragile
it a more
-44-
can be photoresist.
forming
a surface
surface;
however,
rugged
surface.
relief
the sur-
The latter
STEP ONE - RECORDING
STEP TWO - ETCHING/
CONJUGATE DESIRED
OUTPUT WAVE
PHOTORESIST
COAT ING
,
_
SILVER OR NICKLE PLATING
RECONSTRUCTED
WAVE
MODEL
MODEL
REFERENCE_I"
WAVE
WAVE
REFERENCE
REFLECTIVE_ SURFACE
RELIEF HOLOGRAM
Figure
(17)
Producing
and Using
a HOE on an Arbitrary
Surface
type of HOE was produced
relief
holograms
pressing
4.3.2
can be used
into plastics
Conceptual
Before
during
this program.
to replicate
of potential
applications
will
applications
in a wind
mated
desirable
window
There
that
can be made
Figure
Velocimetry.
limated
LDV sample
optics,
operating
immediately
are set between
in the forward
Figure
20 carries
face with
a more
complex
converted
into a number
as a colli-
In example
to a focus
B, a
at some
be a small
emerges
to the number
application
is coated with
waves
a HOE which
an angle
interference
fringes
Therefore,
at the surface
as a
of waves
mode - the most
a step
In this
of output waves
-46-
between
case,
which
them.
in
one has created
an
beams,
Detecting
will
applied
by coating
a collimated
focus
a col-
encountered
easily
further
Doppler
reflects
of the model.
the two reconstructed
the concept
in Laser
with
be found.
scatter
HOE.
on a
be put to use in flow dlgnos-
a potential
will
emerges
for example,
no limit
a set of
is formed
C, an input wave
might
the familiar
Veloclmetry
a discussion
the surface.
two collimated
region,
volume
which
from
surface
comes
This might,
In example
wave
angle.
which
is, in principle,
19 illustrates
input wave as
Doppler
by
18 illustrates
element
input
as a wave
how such waves
A model
In the overlap
Laser
emerges
to emerge
Now consider
Figure
at some convenient
at the point.
of waves.
holograms
of HOE's,
The holographic
point near the model.
pair
tics.
be given.
A, a collimated
directed
input wave
located
surface
later).
the production
tunnel.
In example
output wave
collimated
metal
Application
further
model.
identical
(to be discussed
discussing
curved
These
mode.
the sur-
input
and cross
be
wave
is
at points
MODEL SURFACE
MODEL COATED WITH HOLOGRAPHIC OPTICAL ELEMENT
INPUT WAVE:
ANY KNOWN FORM
_"
HOLOGRAPHIC
OPTICAL ELEMENT
OUTPUT WAVE:
ANY DESIRED FORM
EXAMPLES
I
'
(A)
(C)
(B)
FOCUSED WAVE OUT,
HOE
COLLIMATED
WAVE IN
_--
_ /
WAVES OUT
/
_/
.#MODEL
/_
ANY SHAPED
_@
ANGL/E
COLLIMATED
WAVE IN_
\ MODEL
I SURFACE
_.__Y"
_//__./
COLLIMATED WAVE OUT
AT ANY ANGLE
TWODIVERGING
MODEL
FOCUSED
WAVE IN
Figure
(18) Example
HOE Application
- In Wind Tunnels
OUTPUT WAVE 1
/
/
/
OUTPUT WAVE
2
VIRTUAL FRINGES FROM
INTERFERENCE OF 2 OUTPUT
_
WAVES
TO BE USED
INTERFEROMETRY
ORFOR
FOR LDV
I
Oo
,
/
/
/
INPUT WAVE
f
/P
Figure
(19)
Laser Doppler
Velocimetry
MODEL SURFACE
Made
Possible
by HOE
TWO BEAMS CROSS
AND FOCUS FOR LDV
i
-_-,HOE
MODEL
]
II
COLLIMATEDINPUT WAVE
]
,,'1-_
]
MULTIPLE LDV SAMPLE VOLUMES
Figure
(20)
Multiple
Point
LDV Systems
Generated
by HOE's
near
the surface.
sample
volume.
at the same
with only
Each
point where
In this way,
instance.
a single
mny
points
A striking
input wave
two waves
cross
could
feature
becomes
be sampled
an LDV
for velocity
of such an application
the equivalent
is that
of many LDV systems
is
achieved.
Figure
zation
using
21 illustrates
possible
in regions
conventional
limated
wave,
model surface
mated,
on which
and to direct
would have
been
that would have
4.3.3
the region
where
makes
flow visuali-
otherwise
a badly distorted,
diverging
prevents
In this case,
of interest,
to keep
the HOE,
a col-
strikes
the wave
it can be recorded
Without
the
colli-
in the form
the reflected
and astlgmtic
wave
wavefront
been uninterpretable.
can be used wherever
exists
shadowgraph
in the optical
HOE can be introduced
of this
to provide
is the diagnostics
A potential
application
or holographic
and laboratory
a HOE which
an aberrating
train,
or LDV from being
of a HOE for High
Interferometry.
producing
produce
across
Construction
Holographic
shadowgraph
blockage
or interferogram.
schlieren,
prime example
which
from applicability.
it to a place
such as a curved window
correcting
the model
a HOE has been formed
The same principle
venting
where
techniques
which passes
of a shadowgraph
a HOE application
otherwise
used.
Efficiency
testing
Indirect
would receive
was carried
the the HOE.
light
-50-
from
wavefront.
in cylindrical
of HOE for high-efficiency
interferometry
pre-
An aberration
the required
of flows
element
pipes.
Shadowgraph
or
indirect
to the point
The objective
a projector
A
was
of
to
at some angle,
a,
SHADOWGRAPH OF WING
@
COLLIMATED OUTPUT
i
I
'
COLLIMATED INPUT WAVE
FLOW OUT OF PAGE
Figure
(21)
Flow Visualization
in Model
Blocked
Regions
by HOE
and concentrate
angle,
the reflected
0, not the specular
light
in an aperture
angle.
around
an axis
Figure 22 illustrates
at an
the
requirement.
In a separate
program,
U.S. Naval Training
or embossed
Equipment
screen
material
contract
number
Center,
NG1339-84-C-0026,
the production
for accomplishing
of sample
a similar
for the
replicas
task was an
objective.
Large
hologram
arrays were
ual hologram
geometry
is illustrated
traverse
array
was assembled
production
photoresist
thick.
a conductive
A 0.024"
layer of nickel
off the photoresist,
the process.
This surface
"matrices"
resulting
ration
plate.
Replication
layer
master
duced at a moderate
by coating
the
one or two molecules
the photoresist
of the hologram.
this negative
layer
Next,
in
posi-
and peeling
plates can be made before
is used
Large
cost.
in a hot press
quantities
Alternative
and plastic
methods
casting.
perfect
to produce
Casting
replica.
heated
The acrylic
to produce
of aluminized
This material
that it can be fixed onto another
_ximum
hologram
of the
deterio-
is observed.
nized mylar replicas.
nearly
to automate
25) is electro-deposited
destroying
twenty
The individ-
A computerized
begins
about
(see Figure
by plating
Up to about
The nickel
such
Figure 23.
is a negative
are produced
by replication.
was developed
silver
and is peeled
tive
in
and software
(see Figure 24).
with
produced
comes
with
the alumi-
mylar
can be pro-
a peel-off
backing
surface.
replicas
acrylic
must
efficiency.
-52-
include
injection
onto a master
then be aluminized
molding
can produce
to attain
a
Side
I
View
Geometry
of
Application
•
Projector
HOE
8"
Center
II"
Hologram
Construction
Reference
Beam
Photoresist
Plate
Obj ec t
Beam
]==._________=._
_ _'-._-_'_ ..-..-.
_
Hologram
Reconstruction
gram
I
Figure
(22)
Geometry
-53-
Selection
for the HOE
5.3m
_'_i_
I
APERTURE
2mm
SOURCE
OBJECT
REFERENCE
SOURCE
I
4°
30
_
_
.,,I--
_o
EMULSION
PHOTORESIST
1.9cm
\
GLASS PLATE
i
PUPIL
LOCATIOt,I
Figure
(23) Exposure Geometry for Experimental
Pupil-Forming
Screen.
-54-
Nonspecular
Holographic
•
- t.. ."1'
.:.{.~ .)"
Fig_""!J_~AJ.:.<
.
CGmpur.(~r
L()n.troIled
~
PHOTORESIST
CLASS PLATE
i
Photoresist
PHOTORESIST
_
Exposure
GLASS
]]
the
photoresist.
The irregularities
causes
permanent surface
deformation wil!
in
diffract light to recreate the original
image.
plate.
I
PLATE
PHOTORESIST
GLASS PLATE
NICKEL PLATE
NICKEL
is spun onto a glass
_STER
followed
by development
Nickel is p!ated on the deformed
photoresist
to create a master plate.
_______J
The photoresist
removed.
blYLAR
PRESSINGS
ALUMINIZED
PIIOTORESIST
to light
and glass
plate
are
bIOSAIC
H
MASTER
_
ST,_IPER
NICKEL
ALUMINIZED
PRESSINGS
_
Figure
a High-Gain
MOSAIC
LARGE
STAMPER
MOSAIC
.ACRYLIC
Creating
_
Projection
-56-
ACRYLIC
MYLAR
(25)
Screen
From Glass
PRESSING
Plate
Holograms
The final product
embossed
on aluminized
Corporation,
mylar.
the same
cards and produced
was a 6-inch
by 50-foot
roll of hologram
This was produced
company
that produces
the holographic
cover
by American
holographic
of National
arrays
Banknote
VISA and Master-
Geographic
Magazine.
In total,
in size
seven different
from 3" x 4" to 5" x 7".
7,000 holograms
six to eleven
arrays
Each array
and the time required
had been
contained
to produce
produced
ranging
from 4,000
each array
to
ranged
from
hours.
Tests were performed
detail
master
herein.
Figure
on the best samples.
26 illustrates
These
are included
in
one such test of the master
hologram.
Figure
27 is a resulting
screen
near
the desired
dent.
Screen
4.4
Preparation
of Surfaces
surface
no surface
at all,
the region
of interest
ratio.
mirror
surface
surface
The high
For Differential
for differential
is a perfect
This provides
When
and when
this should
mirror
be done.
When
gain is evi-
is the case of
directly
being
of highest
from it,
influenced
possible
the model
of this
reflects
this is not possible,
by the
signal-to-
surface
axis can be oriented
-57-
through
The equivalent
and the light
to prepare
the optical
and holo-
Interferometr_
interferometry
information
a signal
it is possible
screen
the light passes
with phase
white
measured.
and on to the receiver.
to the detector
flow field only.
noise
aperture.
that is, wherein
the surface
returning
of a combined
gains as high as 20 were
The ideal
is when
viewing
appearance
normal
to a
to the
alternative
"_
HOLOSCREEN
_
• CAMERA
ZEROTH
ORDER
U,
_o
,
'
El
IT
CENTER.
_r_
•
18'
_
12"
I
"
i
PROJECTOR
WItlTE
SCREEN
Figure
(26) Holoscreen
Measurement
Experimental
Configuration
ALL EXPOSURES
ARE THE SADIE.
,- • U.S. NAVAL
TRAINING
E_ENT
CENTER
I_
.....................
•
!
_NOTE
- ZERO POSITION IS IN TIIE CENTER
z
:_
OF THE VIEWING APERTURE 18 FEET
._
FROM I_]E SCREEN°
+14"
TR_ING
' "
CENTER
':_i':"""::TRAIN!NG
:i
"'!':i I:
TRA'INING":!:_:_I
.......
i!..:..!.
: ..E_
::;!
ENT.:i:i.
]
CENTER
."_".:::"_CENTER .,:,:I
-17"
Figure
(27) Photograph
-3"
of the Uncoated
0
Holoscreen
+3"
at the Center
+23"
and Near
the Edge of the Aperture
approaches
described
as good have
been
above which
ior.
reflecting
material
the scope
approach
of incidence
produced
up to about
less
by Avery
45 degrees
produced
The production
beyond
angles
cube material
At angles
signal-to-noise
ratios
almost
tested.
For cases with
the corner
provide
than about
International
the scientific
by 3M Company
20 degrees,
proved
grade
retro-
excelled.
and testing
of HOE's
for this application
of this project;
however,
in theory,
the mirrored
surface
for signal
super-
quality
these
were
could
regardless
of the sur-
face shape.
4.5
Recommendations
The use of mirrored
to be adequate
ometry.
for surface
However,
HOE application
extremely
through
surfaces
preparation
in this study,
in the general
exciting
the investigation
problems
area
it would
and could
of this concept
in experimental
represent
-60-
a major
of
break-
locations.
importance
and its application
aerodynamics.
interfer-
has led to
inaccessible
to be of great
appear
of the principle
of flow diagnostics
in otherwise
seem
materials
for the differential
the introduction
possibilities
in the study of flows
Therefore,
and retroreflective
to continue
to important
5.0
date
EXPERIMENTAL
TESTS
This chapter
describes
the interferometer
in low-speed
used
to simulate
flows.
and
wind
system.
tunnels.
the density
2) turbulent
spot.
i.e.,
the optical
dow.
The turbulent
a window,
two wind
layer
to the point
of interest
involved
were
in supersonic
experiments:
experiment
to vali-
were performed
fluctuations
encountered
tunnel
spot experiment
where
temperature
intermittency
The shear
access
performed
The first set of tests
Controlled
The tests included
through
two sets of experiments
I) shear
layer
was an open system,
did not require
propagating
a win-
the laser
the effects
of window
boundary
layer have
set of tests were
performed
in a supersonic
beam
been
assessed.
The second
nel
(NASA Langley
I) turbulent
Unitary
tripping
3) natural
transition.
procedures
will
5.1
wire
ddx (_)
where
freestream
experiment,
Tunnel
2) turbulent
embodied:
wedge,
of the apparatus
and
and experimental
Tests
optical
difference,
path,
AT, such
Ap, can be expressed
in terms
constant
density
along
(14)
the beams'
line of sight,
(Kai r = 2313 x 10 -7 m3/kg),
and temperature
of
that
= K_ • !_) • AT(x)
x is the distance
Gladstone-Dale
The experiments
tun-
herein.
The differential
the temperature
Tunnel).
A description
follow
Low Speed Wind
Wind
wind
respectively.
-61-
K is the
0 and T are the
5.1. I
Shear Layer Experiment
A shear
layer assembly
I cm x [0 cm, as shown
Variable
temperature
plate was produced
element.
caused
in Figure
by applying
splitter
plate.
one beam was
underneath
used
diffuse
of the reflecting
no overheat
stream
perature
5.1.2
along
Turbulent
or diffuse
across
focused
the heating
point
was then
plate.
at
2.5 cm behind
the
by 2 mm in such a way that
and the second
beams,
have
beam was
prototypes)
illustration
1 mmm
been performed,
and the other
were
measured
The cold wire was
measurement
the splitter
one
used a
to scatter
back the
of the optical
setup
surface.
fluctuations
the optical
behind
to the flow and parallel
Two experiments
aerodynamic
(cold wire).
difference
plate
back the laser
mirror
of the optical
profile
were
of
the system.
the splitter
normal
29 is a schematic
The temperature
with
plate.
(simulating
Figure
voltage
separated
the splitter
to reflect
surface
laser beams.
positioned
The two beams were
1 mm above
layer
at the measurement
The two beams
the splitter
a mirror
a variable
section
to calibrate
of the flow behind
The laser beams were
plate.
cross
in the shear
fluctuation
by the fluctuation
an output
28 was used
differential
Temperature
to the splitter
with
station.
path was measured
into pathlength
using
a Tungsten
installed
2 mm down-
The temperature
to reduce
difference
wire
fluctuation
the measured
via Equation
tem-
(14).
Spot Experiment
The turbulent
20 x 20 cm suction
spot experiment
type low speed
was performed
subsonic
-62-
wind
in a test section
tunnel.
A flat plate
was placed
in the test section
laser beams at
pressible
perpendicular
[3 cm from the window
boundary
layer flow over
city of 4.3 m/sec was disturbed
an orifice
in the surface
9 cm behind
originated
the leading
passed
through
ator.
The two output
tude setting
air through
inlet
the port.
layer
signal
air into
about
the temperature
such
to measure
to the test section
layer 0.63
B.L. was controlled
ture fluctuations
focused
and ampli-
flow of heated
the penetra-
did not exceed
on the machined
The beams
along
the
behind
path.
vertical
heating
tunnel
the window.
pass
and also
by connecting
63
as
fluctuations
(14).
access
disturbance
be obtained
to
at the entrance
the rod to a rheostat.
15 °C could
beams
to measure
of Equation
the optical
Temperature
only
The cold wire has
rod was placed
inside
of
by
through
the laser
of the temperature
via the integration
surface
were separated
air would
the beam
the profile
up to about
to the ambient
0.45 cm.
in the wind
cm from
air
gener-
frequency
layer
of the interferometer,
the phase difference
and located
was set such that
the boundary
air through
by a signal
connected
velo-
It was then
in a periodic
that the heated
fluctuations
The incom-
The heated
Proper
A cold wire was placed
A 0.5 cm diameter
outer
chamber.
resulted
beams were
a check on the performance
dary
a heating
1 cm from the orifice.
one of the two beams.
quantify
30.
was driven
of the
freestream
in Figure
The line pressure
thickness,
0.2 cm and positioned
also been used
through
with
cm in diameter
in the flat plate.
The interferometer
the flat plate
0.32
30.
flow of heated
of the valve were
of the driver
tion depth of the heated
boundary
by a periodic
valve, which
ports
in Figure
the flat plate,
edge as shown
a solenoid
and to the orifice
as shown
of the plate
from a compressor,
to the direction
through
boun-
to the
Temperasuch an
THERMOCOUPLE
SCREEN
SPLITTER
PLATE
I
HEATING ELEMENT
PLACE OF TWO BEAMS
_
_I
_
2.5cm_.
PLENUM
CHAMBER
THERMOCOUPLE
Figure
(28) Schematic
of the Shear
Laver Assembly
_._The
InterferometerBeams
SCATTERING
SURFACE
REFLECTI_G
MIRROROR
WOLLASTON I
I I I I
AIR FLOW
I
Figure
(29) Schematic Illustration of the Optical
Reflecting Mirror/Scattering
Surface
Setup
of the
HEATED
AIR
DRIVER
SIGNAL
_
\ \
\ \
SOLENOID
\ \ \ \ \ \
\ x \ \ \ \ \ \ \ \ \ ,)-
>-\ \ \ \ \ \
VERTICAL
Figure
(30)
HEATING
Schematic
_I
\ \I
SURFACE
:HI _ \ \ \ \ \ \ \
ROD
of the turbulent
-66-
spot experiment.
arrangement.
The laser beams
at 12.5 cm from the optical
B.L.
to get
window
to the flat plate.
disturbance
created
of interest
were
5.2
Supersonic
5.2.1
Tunnel
A parametric
through
study
prism
located
the outer
of the effects
limit
of the
of the signal
performed.
Wind
Tunnel
Tests
Conditions
Plan Wind
conducted
The tunnel
a
Mach number
o
Stagnation
•
Stagnation
•
Reynolds
and the wavelength
II at the Langley
pressure
continuous
flow
were:
=
2.36
temperature
=
339 °K
pressure
=
38 to 189 KN/m 2
(m-1)
=
3.3(10) 6 to 1.6(I0) 7
(ft-I)
=
(10) 6 to 5(10) 6
number
used
Section
is a variable
conditions
range
range
Table (4) is a summary
coefficient
at Test
Tunnel which
facility.
Dale
propagated
by the rod on the detectability
The tests were
Unitary
out of the first Wollaston
of the tunnel
corresponds
is tile He-Ne
conditions.
The Gladstone-
to that of air, K = 0.0002317
red line,
-67-
% = 6328
°A.
m3/Kg,
TABLE 4.
SUMMARY
Relft
Po
KN/m 2
Po
O
K01%
Kglm 3
Kglm 3
.m-I
38
0.39
0.06
22
2(10) 6
76
0.78
0.12
43.97
3(10) 6
114
1.17
0.18
65.95
4(10) 6
152
1.56
0.24
87.94
is a list of the boundary
Ap/_.
~ over half
CONDITIONS
(10) 6
The model was a flat plate
length,
OF TUNNEL
The density
the boundary
TABLE
layer
5.
with
a zero angle
thickness,
fluctuations
layer
_, and the difference
Ap/<p> has been assumed
thickness.
BOUNDARY LAYER THICKNESS
DIFFERENCE AS A FUNCTION
Re/ft
of attack.
_(mm)
Ap/%[at
AND OPTICAL
OF REYNOLDS
x = 4"]
(10) 6
I.23
1/3690
2(10) 6
0.871
1/2611
3(10) 6
0.7112
1/2132
4(10) 6
0.616
1/1846
68
PATH
NUMBER
Table
5
in path
to be
1%
5.2.2
Instrument
Conditions
The instrument
A)
parameters
as follows:
Optical
Wollaston
•
(I) divergence
Beam expander
Focal
length
B)
angle
=
1°
=
3
lens
=
30"
plane
=
5 mm
=
32 _m
=
83%
magnification
of the focusing
Beam separation
of the focal
Beam
diameter
at the focal
Beam
coincidence
plane
at the window
boundary
layer
Electronics
o
Signals
were
Frequency
•
5.2.3
experiment
leading
Tunnel
5 mm beam
numbers
conducted
used
at the focal
(Re/ft
at 2.4" from
wedge
1.25"
the beams
0.125"
between
stream
from the roughness,
done
200 kHz
=
7 kHz
experiment.
located
the turbulent
The turbulent
at 3.75"
where
from
were horizontal
plane.
different
Three
and 3.25"
edge.
were
from
involved
installing
were
69
with
Reynolds
Scans
were
a roughness
scans
at the
every
at 1.6" and 2.6" down-
y = 0 is the roughness
experiment.
the
5 mm apart
Vertical
conducted
for the same Reynolds
wire
the wire.
The beams
vertical.
y = +i" and y = -I" were
were
=
the two beams
experiment
the leading
focal plane, however_
attempted:
= 2 x 106 , 3 x 106 and 4 x 106).
at 0.0", 0.25",
measurements
were
wedge
In this experiment
The turbulent
element
transition
a size 30, sand-wire
separation
were
recorder
Tests
and the turbulent
involved
edge.
drive
filter
Wind
experiment
on a direct
bandpass
Low-pass
Unitary
recorded
Two tests simulating
wire
were
number
location.
as the previous
The
A natural
horizontal
transition
configuration.
test was attempted
Measurements
were
I", 2", 3", 4", 5", 6", 8", 9" and 12" from
Reynolds
numbers
Concurrent
which
were
measure
were
the same as previously
with
installed
the interferometer
with
the beams
conducted
the leading
location.
-70-
at 0.25",
edge.
0.375",
The flow
stated.
measurements,
at 4", 5" and 6" from the leading
the transition
in the
thin film gages
edge were
used
to
6.0
RESULTS
The experimental
chapter
wind
are presented
tunnel
tunnel
Figure
abscissa
the reflecting
tional
in the shear
surface.
to pathlength
surface.
presented,
31 shows the strength
and the scattering
second
mirror
31.
is about
also
shows
to small temperature
the signal
ture differences,
temperature
nonlinearity
results
followed
of the low speed
by the unitary
layer
using
super-
5 times
that the signal
fluctuations,
becomes
layer becomes
in the transverse
-71-
while
have
back
off
off the diffuse
is linearily
for large
nonlinear.
propor-
temperature
For large
3-dimensional
direction
been
by the
reflected
scattered
of tem-
the mirror
14 as shown
strength
that
for both
fluctuations
Equation
effects.
as a function
experiment
The signal
strength
the shear
fluctuations
of the signal
The temperature
differences
in Figure
The figure
fluctuations,
The laboratory
in the previous
Experiment
fluctuations
reduced
of the tests described
results.
Shear Layer
perature
herein.
tests are first
sonic wind
6.1
results
which
giving
tempera-
results
rise
in
to the
mV (rms)
• REFLECTING
MIRROR
& SCATTERINC
SURFACE
500 I
A
400
3OO
I
200
I
i
100
0
0
2.5
5.0
7.5
TEMPERATURE
I
I
•0113
Figurei31)
!
0.0225
FLUCTUATION
I
0.0338
10.0
I
12.5
I
I
f
15.0
AT °C
0.045
0.0563
Laser Interferometer
Signal RMS as a Function of Temperature
Fluctuations for Both the Reflecting Mirror and the Scattering
Surface.
I
0.0675
6.2
Turbulent
Spot Experiment
Three experimental
performance
of the high
(I) diffuse
surface,
reflecting
access
optical
reflect
back
the signal
eliminate
reflecting
corner
which
surface
laser beams
due to tooling
were
characteristics
the output
on the model.
32.
enhance
effects
and
Several
retro-
was obtained
"scientific
signal
from
retroreflector",
system
have
of the interferometer
fluctuations
coating,
profile
measured
of the interferometer
is shown in Figure
Figure
the speckle
at the
surface
beam,
of the interferometer
The temperature
path
disturbance
of the model
performance
as
the
study.
and retroreflecting
the optical
spot experiments
known
the present
by comparing
surface
the best
generically
throughout
of the cold wire.
experiment,
tried;
layer
the incident
reduce
marks
to evaluate
and (3) retro-
coatings
along
diffraction
was used
with
for both
by the cold
in the turbulent
The air velocity
spot
in all turbulent
was 4.3 m/sec.
33 shows
a no heating
dominant
Retroreflecting
used
interferometer:
surface,
of boundary
and the S/N ratio,
the diffuse
under
in the presence
cubes coating,
along
differential
strength
coatings
have been
(2) retroreflecting
the incident
been examined
wire
sensitivity
window.
_le response
that
configurations
natural
the frequency
condition
spectrum
as measured
frequencies
of the vibration
level
by the interferometer.
The
of the low-speed
wind
tunnel were
64, 78,
and 245 IIz.
Figures
34a and 34b represent
off the diffuse
respectively,
heated
surface
of the flate
in the frequency
air through
the orifice,
the interferometer
signal
scattered
plate and the cold wire,
domain.
The frequency
in this case,
-73-
of the pulsating
was 305 Hz.
The other
Velocity
0.5
0.4
r-t
Boundary
Layer
-
0.3 -
o
I
f
u
0.2 -
0.1
J
, I
1.0
1.5
Temperature
Figure (32)
Temperature
Profile
I
Fluctuation_
of the Pulsed
2.0
AT °C
Jet Measured
by the Cold Wire
16.0 --
14.4 --
12.8 --
I.
25
50
L
I
!
75
I00
125
Frequency
Figure
(33) Vibration
Level
150
175
L
L
200
225
in Hz
as Detected
by the Laser
Interferometer.
J
250
peaks in the frequency
attributed
spectrum
to the vibration.
tion noise because
of the interferometer
No attempt
the vibration
fundamental
same order as the jet pulsations.
used
to mathematically
shows
reduce
the interferometer
ter to reduce
Figures
interferometer
35a, 35b and 35c show
system
using
signal,
reducing
the vibration
effects,
a second
frequency
harmonics
signal
also shows
Figure
fluctuations.
fundamental
orifice
figure
shows that
corresponds
confirm
amplitude
ratio
the ability
perturbations
been
34c
the numerical
fil-
on the flat plate
AT = 1.4°C.
The laser
after
flow
The cold wire
shows
system
35a and 35c.
ratio
and second
first
signal
interferometer
in Figures
detected
of the
The orifice
of 115 Hz are shown
to a phase difference
has a signal-to-noise
figure
respectively.
Both the first
the minimum
have
Figure
strength
coating
the signal/noise
frequency
of the
filters
and the interferometer
as shown
36 illustrates
temperature
the signal
at 230 Hz.
the vibra-
frequencies.
115 Hz and
the same behavior
using
are
were
of vibrations.
retroreflecting
the cold wire
were:
numerical
after
due to vibration
surface,
conditions
strength
to filter
frequencies
However,
the effects
signal
the peaks
was made
system
as a function
harmonics
of the
for a
in the figure.
harmonics
signal
The
which
of 1.41 x 10-3 , the laser wavelength,
of about
150.
The results
of the interferometer
in the fluid
system
flow with high
shown
in this
to follow
small
signal-to-noise
ratios.
Figures
disturbance
ential
37a and 37b show the effects
on the detectability
interferometer.
Figure
limit
boundary
of the high sensitivity
37a shows
-76-
of the window
the signal
superimposed
layer
differon the
Figure 34a
Spectrum of the laser interferometer
signal for pulsating frequency of 305 Hz
Figure 35a
CoLd vtre
6ee
Spectrum of laser Interferometer signal
for pulsating frequency of 120 Hz using
s=lentlfic retro-reflector
e_o
AT " 2°C
s_e
€old VLre SLier).
AT I Io_,°C
su
! _..
!
ie
I_
_e
Figure 34b
Figure 34e
_e
_oo
_
_
|50
_
_o
5ae
SpecLrum of cold wire data for
pulsating frequency of 305 Hz
The dIRLtized interferometer signal
after filtering out the effect of vibration
-77-
Figure 35b
Figure
35c
Spectrum of cold wire signal for pulsating
frequency of 120 Hz
The digitized interferometer signal after
filtering out the effect of vibration
f = 115 Hz
175
_-A
Ist Harmonics
150
125
-
I00
-
o
o
o
z
J
=
m
75
-
50
-
25
2nd
Harmonics
-
I
1.25
I
I
1.5
1.75
Temperature
j
_
1.2653
I
I
2.0
Fluctuations
I
1.5183
1.77i4
l
2.25
I
2.0245
I
2.2775
(36) Signal/Noise Ratio of Both the First and Second Harmonics
Using Retroreflecting
Material on the Surface.
78
2.5
AT °C
_/l x 103
FiKure
e
t
2.53
Figure
,.. .........
(37a) The Digitized Frequency Spectrum of the Interferometer
Signal Under Window Boundary Layer Disturbance.
,. _1,), ,t.. 1-.; or
)_
[
: _ I-I-,:'_i,
uumm_h:_*_:_"|::i:_h_;5_|rme|i_!_'.;i_-'ii_;;'_i_`_!_;_i_i_ij;_ii_ii_
Figure
;
:
,_
,_'_"._':
:,'VI',
.r,.
I
_:"
,' hl,h IL,li,_I _il','ii "_'._I..|% ;,,,ll|,i,,I'il] _ldlhi!;_l;lli;llliiili_i:l;,llh.'.lA_llliihU_'.l!Ui_
(37b) The Digitized Frequency Spectrum of the Interferometer
Signal
After Filtering Out the Effect of Window Boundary Layer.
-79-
disturbance,
window
and Figure
disturbances
condition
have
corresponds
detected
signal
37b shows
been numerically
to a phase
has a phase
layer thickness
for both
disturbance
fail to recover
6.3
Supersonic
Wind
The dominant
Therefore,
Tunnel
frequency
dominant
layer thickness,
for
1 mm boundary
frequency
nals obtained
was
in the course
on the oscilloscope.
300 kHz,
beyond which
evident
spectrum
obtain
transition
in Table
tial
37.
X, while
and simple
the
The thermal
boundary
were
the ratio
in the transition
of disturbances
23 mm
of the
region
is on the
mathematical
of transition
that the flow disturbance
and travels
layer
with
thickness
Figures
and
experiment
were
peaks
observed
were
Lack
the areas
-80-
sigas they
was
drops
in the time domain
observed
of clear
as
in the frequency
signals
ratio
of applicability
interferometer.
the
band of the instrument
gain of the electronics
analyser.
velocity.
U= = 600 m/sec,
of the low signal-to-noise
39 shows
is as large as
the freestream
transition
The frequency
signals
was calcu-
38 are the time averaged
of the natural
by a spectrum
Figure
that when
dominant
No distinct
is an artifact
5.
shows
the amplification
No transition
in Figures
The rod heating
Results
600 kHz.
appeared
drastically.
X.
of the
the signal.
lated based on the assumptions
the boundary
out.
of 0.01
of 0.00!
to the disturbance
becomes
the effects
rod and the flat plate
The figure
order of 60:1, the noise
filters
difference
after
filtered
difference
the heating
and 4 mm, respectively.
window
the signal
due to
as calculated
of the differen-
The second
possibility
that led to the low signal
is the beams coincidence
as they travel
layer.
is defined
Beam coincidence
beams coincide
the optical
to a high
to the beam area.
access
window
level of noise.
in the window
boundary
It was established
to signal
that
disturbance
Azzazy,
et al, showed
can annihilate
the dominant
destroy
frequency
is substantially
different
The full details
of the window
attention.
The supersonic
Lecroy
digitizer
fast
system
data was then recorded
transform
data.
techniques
Figure
transition
disturbance
agreed
boundary
still
need more
was set at 2 MHz sample
rate.
of memory.
power
Numerical
the power
spectrum
layer
at transition.
using
to obtain
spectrum
effects
data were
at 8" from the leading
is the power
frequency
leading
signals.
O'Hare
window
at
disturbances
digitized
on 266 kbytes
40, shows a sample
that large
the
layer
of the two beams
developed
layer
tunnel
which
were used
experiment
The abscissa
wind
boundary
However,
than the dominant
boundary
of the area where
of 60:1 unwanted
the signal.
ratio
boundary
the interferometer
threshold
of the fully
the window
turbulent
can cause
layer
totally
as the ratio
The fully
that a cut-off
ratio,
through
to noise
spectrum
during
the
The
Fourier
of the
the natural
edge at Re = 2 x 106 •
and the ordinate
is the frequency
scale 0-400kHz.
A numerical
noise
and window
at 2" from
Figure
filter
boundary
the leading
41 shows
natural
transition
to reduce
the effects
layer.
The filter
is taken
edge for the natural
the power
plete set of the power
is used
spectrum
spectrum
transition
at x = 8" using
before
and the turbulent
and after
wedge
-81-
of background
to be the spectrum
experiment.
the filter.
the filter
experiments
A com-
for both
are presented
the
in
Appendix
with
A.
The ordinate
a scale
arbitrary
capability
in all the figures
0-400 kHz and the abcissa
units.
More
research
of the technique
is the power
work will
to measure
order of 1/2500.
-82-
represents
be carried
pathlength
the frequency
spectrum
in
out to assess
differences
the
on the
Figure
L_8)"_'
"_ Time Averaged Si<<na.].s_
of Natural Transition
-83,-
• (Areas of Applicability
for Differential
Interferometer)
1.0
•
igh
Speed
•
_Subsoni
0.75
g
0.50
kKUnitary'
s Test_
/
/
0.25
Section 2
K Unita[y's
(August
85 Test
Test)
!
!
a
l
l
t
|
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Boundary
Figure(39)
Layer
Thickness
Areas of Applicability
for
Differential
Interferometer.
-84-
in mm
4.0
Figure
(40) Digital
Signal
Spectrum
at x = 8", and Re = 2 x 106 .
-85-
Figure
(41) Signal
the
Spectrum
at x = 8", and Re = 2 x 106, After
Filter.
-_6-
Using
7.0
RECOMMENDATIONS
The following
features
test of the differential
I.
Increase
Section
increase
vide
2.
larger
the signal-to-noise
Adapt
better
Polish
Use flow
or both
Using
in a factor
wind
tunnel
of .56
to pro-
ratio
has the advantage
as well
of
as decreasing
the
of transition.
boundary
of the beams
as they propagate
through
layer.
to achieve
better
flatness
and reduce
the noise
roughness.
visualization
the flow field,
either
thickness.
result
Use another
layer thickness
coincidence
the model
layer
tunnels:
for the density.
increasing
due to surface
5.
density.
the boundary
frequency
Plan will
a successful
wind
by increasing
and the boundary
I at the Unitary
values
to achieve
in supersonic
ratio
Increasing
the window
4.
density
in freestream
dominant
3.
interferometer
the signal-to-noise
the freestream
Test
are recommended
prior
techniques
to have
to the interferometry
-87-
better
understanding
measurements.
of
8.0
REFERENCES
Azzazy, M., Modarress, D. and Hoeft, T., "High Sensitivity
Boundary
Layer Transition Detector," SPIE 29th International
Symposium, SPIE
569-08 (1985).
Also
Instruments
(1985).
submitted
to the Journal
of Physics
E, Scientific
Azzazy, M., "Suface Topography Using Diffuse Point Differential
Interferometry",
to be submitted to Applied Optics (1986), also Azzazy, M.,
"Diffuse Point Differential
Interferometry
for Contouring the Surface
Profile of Camshafts",
Final Report SDL No. 85-2431-02F
(1985), Submitted to Cummins Diesel Engine, Co.
Batill, S. M. and Mueller, T. J., "Visualization
of Transition in the
Flow Over an Airfoil Using the Smoke-Wire Technique,"
AIAA Journal,
Vol. 19, No. 3, pp. 340-345, March 1981.
Cantwell, B., Coles, D., and Dimotakis,
in the Plane of Symmetry of a Turbulent
pp. 641 (1978).
P., "Structure
Spot," J.F.M.,
and Entrainment
Vol. 87, Part 4,
Cassels, W. A. and Campbell, J. F., "Boundary Layer Transition Study
Several Pointed Bodies of Revolution at Supersonic Speeds," NASA TN
D-6063 (1970).
of
Coles, D. and Barker, S. J., "Some Remarks on a Synthetic Turbulent
Boundary Layer," in Turbulent Mixing in Nonreactive
and Reactive
Flows,
ed. S. N. B. Murthy, Plenum (1975).
Fancher, M. F., "A Hot-Film System for Boundary Layer Transition
Detection in Cryogenic Wind Tunnels," presented to Euromech Colloquium
132 on
Hot-Wire, Hot-Film Anemometry and Conditional Measurement,
Lyon, France,
July 1980.
Fancher, M. F., "Aspects of Cryogenics Wind
Douglas," AIAA Paper No. 82-0606, 1982.
Tunnel
Testing
Technology
at
Giallorenzi,
T. G., Bucaro, J. A., Dandridge, A., Sigel, Jr., G. H.,
Cole, J. H., Rashleigh, S. C., and Priest, R. G., "Optical Fiber Sensor
Technology",
IEEE Journal of Quantum Electronics,
Vol. QE-18, No. 4,
pp. 626 (1982)
Goodman, J. W., "Statistical Properties of Laser Speckle Patterns,"
"Laser Speckle and Related Phenomena,"
J. D. Dainty, ed., SpringerVerlag (1976).
Havener,
graphy,"
A. G., "Detection of Boundary-Layer
Transition Using HoloAIAA Journal, Vol. 15, No. 4, pp. 592-293, April 1977.
-88-
in
Havener,
A. G., "Holographic
Bursting
83-1724,
in Supersonic
1983.
Measurement
Axisymmetric
Hefner, J. N. and Bushnell,
Drag Reduction,"
Von Karman
Hough, G., ed., "Viscous
nautics and Aeronautics,
of Transition
Boundary
Layers,"
and Turbulent
AIAA
Paper
D. M., "An Overview of Concepts
Institute, AGARD-R-654
(1977).
Flow Drag Reduction,"
Vol. 72 (1980).
Laderman, A. J. and Demetriades,
sition with a Laser Beam," AIAA
January 1976.
AIAA
progress
No.
for Aircraft
in Astro-
A., "Detection of Boundary-Layer
TranJournal, Vol. 14, No. I, pp. 102-104,
Modarress,
D., Doty, J. L., Trolinger, J. D., and Hoeft, T., "High Sensitivity Laser Interferometry
for Detection of Boundary Layer Transition," AIAA 17th Fluid Dynamics and Laser Conference, AIAA-84-1640
(1984).
O'Hare, J., "A Nonperturbing
Boundary Layer Transition
29th International
Symposium, SPIE 569-07 (1985).
Detector,"
Perry, A. E., Lim, T. T., and Teh, E. W., "A Visual Study
Spots," J. Fluid Mech., Vol. 104, pp. 387-405, 1981.
of Turbulent
Saric, W. C. and Reed, H. L., "Effect of Suction and Blowing
dary-Layer Transition," AIAA Paper No. 83-0043, 1983.
Schubauer, G. B., and Klebanoff, P. S., "Contributions
of Boundary Layer Transition",
NACA TN3489 (1955).
Smeets, G., "A High Sensitivity
Laser Interferometer
Objects," Proceedings of the 8th International
Shock
London 1977.
SPIE
on Boun-
on the Mechanics
for Transient Phase
Tube Symposium,
Smeets, G. and George, A., "Investigation
of Shock Boundary Layers with
a Laser Interferometer,"
Proceedings
of the 9th International
Shock Tube
Symposium, Stanford, July 1983.
Stallings, Jr., R. L., and Lamb, M., "Effects of Roughness Size on the
Position of Boundary Layer Transition and on the Aerodynamic
Characteristics of a 55 ° Swept Delta Wing at Supersonic Speeds," NASA Technical
Paper 1027 (1977).
Swindel, W., Polarized Light,
Huchinsen and Ross (1978).
Benchmark
Papers
in Optics,
Vol.
I, Dowden
Wygnanski,
I., Sokolov, M., and Friedman, D., "On a Turbulent Spot in a
Laminar Boundary Layer," J.F.M., Vol. 78, Part 4, pp. 785 (1976).
-89-
APPENDIX A
-91-
I.
NATURAL
TRANSITION
-92-
DATA
il!ii!_
Figure
A(1) x = 2" Re = 2 x 10 6 Filter
-AI-
Figure
A(2)
x = 4" Re = 2 x 10 6 Before
-A2-
Filter
H_illl_llilfll|l
fllllillWl
Figure
A(3) x = 4" Re = 2 x 10 6 After
-A3-
Filter
Figure
A(4) x = 5" Re = 2 x 106 Before
-A4-
Filter
, _.i'.7_---,,+.,,
, IIiZ
J
Figure
A(5) x = 5" Re = 2 x 10 6 After
-A5-
Filter
Figure
A(6)
x = 6" Re = 2 x 106 Before
-A6-
Filter
£IIi_! 6,i!_ _'_
_
_t _t' _._
It'_ °
|_lfl_flllli1111L_111t_|lUlll_IHll_lll!lUllnlHlltlllHll|llllBlilllt_llllmlNHll
l|lll|Im
Figure
A(7) x = 6" Re = 2 x 10 6 After
-AT-
Filter
Figure
A(8) x = 8" Re = 2 x 106 Before
-A8-
Filter
' it,_,'!1
.,,,.+" --
' _',,, ,"It
,i_
II11IItlHIIIIIII]
_,t_
',;'"tJ]t_,,_
.....
'''+'
'IL ,Ui
_:l_,,If
IItlIILI_IIIII_I
Figure A(9) x = 8" Re = 2 x 10 6 After
-Ag-
Filter
Figure
A(10) x = 9" Re = 2 x 10 6 Before
-AI O-
Filter
_,..,
111
,,llLJ
I
+lll_lllltll'_llllfll
Figure A(II) x = 9" Re = 2 x 10 6 After
-AIi-
Filter
Figure
A(12) x = 12" Re
2 x 10 6 Before
-AI2-
Filter
Figure
A(13) x = 12" Re = 2 x 10 6 After
-AI3-
Filter
Figure
A(14) x = 2" Re = 3 x 10 6 Filter
-AI4-
- _,,,.
1 _[]Nz
Figure
A(15) x = 4" Re = 3 x 10 6 Before
-AI5-
Filter
:llilmllllllllllllllt|INUllidllllllUlLlllllllti
llll2lUllllillllilltllllltlLLlll
Figure
A(16) x = 4" Re = 3 x 10 6 After
-AI 6-
Filter
Figure
A(17)
x = 5" Re = 3 x 10 6 Before
-AI7-
Filter
Figure
A(18)
x = 5" Re = 3 x 10 6 After
-AI8-
Filter
Figure
A(I9) x = 6" Re = 3 x 106 Before
-AI 9-
Filter
Figure A(20)
x = 6" Re = 3 x 106 After
-A20-
Filter
lill I_,
]. ,rl
I,
i{I
!Ig
IIL1llil_Itl
rillll
I_:t
I_L
IL__.J,:i
Figure
A(21) x = 8" Re = 3 x 106 Before
-A21-
Filter
Figure
A(22) x = 8" Re = 3 x 106 After
-A22-
Filter
;_'7_
_I._
z
_. Li_._
_I,-'.%u":"
,_
,_i!-_;..It
m,_i_,n
Figure
A(23) x = 9" Re = 3 x 106 Before
-A23-
Filter
'!Itt_
l+.e ,_+_I
.1,' ._+I
a,,.+.
p+ ++
,.Jll1_.
h.,_.n'._P'
'iLt,+i,..
IIIInlIIIIHHIII
unlUUllnfl
lllUl
IHIlIIIIIIIlIIIUH
llmlllll
Figure A(24)
x = 9" Re = 3 x 106 After
-A24-
Filter
Figure A(25)
x = 12" Re = 3 x 106 Before
-A25-
Filter
Figure A(26)
x = 12" Re = 3 x 106 After
-A26-
Filter
Figure
A(27)
x = 2" Re 4 x 106 Filter
-A27-
,p_q
Figure
A(28) x = 3" Re = 4 x 106 Before
-A28-
Filter
ttltllt|
Figure
A(29) x = 3" Re = 4 x 106 After
-A29-
Filter
Figure
A(30) x = 4" Re = 4 x 106 Before
-A30g
Filter
Figure
A(31)
x = 4" Re = 4 x 106 After
-A3 i-
Filter
q
Figure
A(32)
x = 5" Re = 4 x 106 Before
-A32-
Filter
'! ,
_
"II.
roll
,II
,dll._l
IIIIIHHIII_III_IInlIIIIIIII
I IIIIIII
1!lllllllllllUlli_
Figure
A(33) x = 5" Re = 4 x 106 After
-A33-
Filter
Figure A(34) x = 6" Re = 4 x 106 Before
-A34-
Filter
Figure
A(35) x = 6" Re = 4 x 106 After
-A35-
Filter
Figure
A(36_ x = 8" Re = 4 x 106 Before
-A36-
Filter
l
Figure
A(37)
x = 8" Re = 4 x 106 After
-A37-
Filter
Figure
A(38)
x = 9" Re = 4 x 106 Before
-A38-
Filter
lllllllMllllllnlU_llilliflltlllHIMlll
Figure
A(39)
x = 9" Re = 4 x 106 After
-A39-
Filter
I ''q
Figure
A(40) x = 12" Re = 4 x 106 Before
-A40-
Filter
m,
q
,
II
fllllill
Iltllllllllf:flll
mlllllllillll
IIMI
Figure A(41) x = 12" Re = 4 x 106 After
-A41-
Filter
II.
Wedge
TURBULENT
WEDGE
at x = 2.75" from
Re = 2 x 106
-A42-
DATA
L. E.
Figure
A(42)
x = 5" y = 1.0" Filter
-A43-
Figure
A(43) x = 5" y = 0.875"
-A44-
Before
Filter
Figure
A(44)
x = 5" y = 0.875" After
-A45-
Filter
Figure
A(45) x = 5" y = 0.75" Before
-A46-
Filter
Figure
A(46) x = 5" y = 0.75" After
-A47 -
Filter
Figure
A(47)
x = 5" y = 0.675"
-A48-
Before
Filter
II_,dU
_
J_Jl
_'_I
r'
JIl 'g,,d_l lil d|t,_
Figure
A(48)
x = 5" y = 0.675"
-A49-
After
Filter
ill."_I,,'.l)_
-" 8
Ib-l,_,,,,._.,:
Figure
A(49) x -- 5" y = 0.5"
-A50-
Before
Filter
A
HII!!
lllllllnl_HliUilllllllllltllLtllllllUlllltlll|lllliL1111!lllllllll
Figure
A(50)
x = 5" y = 0.5" After
-A5I-
Filter
Figure
A(51) x = 5" y = 0.375"
-A52-
Before
Filter
Figure
A(52) x = 5" y = 0.375"
-A53-
After
Filter
Figure
A(53) x = 5" y = 0.25"
-A54-
Before
Filter
Figure
A(54) x = 5" y = 0.25" After
-A55-
Filter
Figure
A(55) x = 5" y = 0.125"Before
-A56-
Filter
Figure
A(56) x = 5" y = 0.125" After
-A57-
Filter
£_,,_::8
Jk.h,m
Figure
A(57) x = 5" y = 0.0" Before
-A58-
Filter
Figure A(58)
x = 5" y = 0.0" After
-A59-
Filter
Figure
A(59)
x = 4" y = 1.0" Filter
-A60-
Figure
A(60)
x -- 4" y = 0.875"
-A6 i-
Before
Filter
Figure
A(61) x = 4" y = 0.875"
-A62-
After
Filter
Figure
A(62) x = 4" y = 0.75"
-A63-
Before
Filter
_" ,:r_
IIL-. "1 '!j_
......
| II||l}l|l!
Figure
A(63)
x = 4" y = 0.75"
-A64-
After
Filter
tll_llllllillil|lllllilllilll
Figure
A(64)
x = 4" y = 0.625"
-A65-
Before
Filter
"-
,*,,..'..,i_, i_ ':"_ _'''
tl
11
:lllltilltlfl
llilLiULt
ItlHlt
!
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Figure
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A(69) x = 4" y = 0.375" After
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Standard
1. Report
NASA No.
CR-178109
Bibliographic
Page
] 2. Government Accession No.
3. Recipient's Catalog No.
I
4. Title and Subtitle
"Feasibility
Detect
ion
5. Report Date
Study
blethod"
of
Optical
Boundary
Layer
Transitior_
June
6.
1986
Performing
Organization
Code
7. Author(s)
M. Azzazy,
D.
Modarress,
and
J.
D.
8. Performing Organization Report No.
SDL No. 85-2285-47F
Trolinger
9. Performing Organization Name and Address
10. Work Unit No.
Spectron Development
Laboratories,
3303 Harbor Blvd. , Ste. G-3
Costa
Mesa,
CA 92626
Inc.
11.
12. Sponsoring Agency Name and Address
Contract or Grant No.
NAS1-17293
13. Type of Report and Period Covered
National Aeronautics
and Space Administration
Washington,
DC 20546
Contractor Report
14.Sponsoring AgencyCode
505-60-21-02
15. Supplementary Notes
Langley
Technical
Monitor:
Final Report for the period
Robert
M. Hall
22 February
1983 - 15 November
1985
16. Abstract
A high sensitivity differential
interferometer
was developed to locate
the region where the boundary layer flow undergoes transition from laminar to
turbulent.
Two laboratory experimental configurations
were used to evaluate
the performance of the interferometer:
open shear layer, and low speed wind
tunnel turbulent spot configuration.
In each experiment, small temperature
fluctuations were introduced as the signal source.
Simultaneous cold wire
measurements were compared with the interferometer data.
The comparison
shows that the interferometer
is sensitive to very weak phase variations
in
the order of 0.001 the laser wavelength.
An attempt to detect boundary layer transition over a flat plate at
NASA-Langley Unitary supersonic wind tunnel using the interferometer
system
was performed.
Tile phase variations during boundary layer transition in the
supersonic wind tunnel were beyond the minimum signal-to-noise
level of the
instrument.
17. Key Words(Suggestedby
Boundary
Layer
Authors(s))
-
18. DistributionStatement
Transition
Interferometry
Unclassified
- Unlimited
Subject
19. Unclassified
Security Cla.ssif.(ofthis report)
For sale by the National
NASA
Langley
Form
63
(June
1985)
J20. Security
Unclassified
Clazsif.(of this page)
Technical
Information
Service,
Category
121. 180
No. of Pages 22. Price
A09
Springfield,
Virginia
22161
34
_ENTER
3 1176 01315 4241
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