Aircraft. Corporation and the Ames ...... in shapewith or without camber. With blowing, the flows revealed a very high streamwise pressure gradient at the trailing.
Nsi-e944 /ore 4,'.S_
W. D. Bachalo and M. J. Houser
Aercmetrics,
Inc.
P.O. Box 308 Mountain
.._
-'"
:"':-_
View, CA
_LA/_K
NOT
193
94042
FILMED
Abstract
Optical
interferGmetry
investigation tunnels. study
of
DSMA671
airfoil
Tur_,el.
were
compared
agreement
a to
speed
obtained
with and
extracted
agreement
the
measurements.
spatially
for
large
scale
point
diffraction
_ _2;_:_llqG
Ames
was
of
Transonic
PAGE
the
supercritical
_*_-=_=_-_=_= excellent
flow
the
visualization scalar
inviscid
flow
to
Doppler
were
laser
also
in good
sufficiently
two-
quantitative by
the
This
method
successfully
Tunnel.
NOT
FILMED
data
from
interfercmeter.
interfercmetric
195
Transonic
quantitative of
the
compared
provided
BLANK
in
were
developed.
Wind
used
wind
profiles
was
was
and
scale
velocity
(visual),
interfercmeter
were
The
acquiring
real-time
large
,-L_. uL=
results
flow
in
to the
2-by-2-foot
data.
and
results
acquiring
facilities
2-by-2-foot
the
reliable
integrated
NASA
and wake
These
that
to obtain
64A010
Measurements
interferograms
indicating
N_A
the accuracy
layer
applied
techniques
pressure
for
been
fields
UL,U=_L=U
potential
boundary
A method
Ames
surface
verified the
from
dimensional
data
interfercmetry.
the
velocimeter
the
the
in the
ve
have
flow
symmetric
performance
demonstrated
results
airfoil
interfercmetry
t_o-dimensional
Wind
and
transonic
Holographic
of
techniques
data
in
based
on
the
tested
in
the
The holographic applied
to
utilizing of the
the
the the
jet
other
and
real-time
investigations Coanda
effect.
interaction parameters
of
with
interfercmetry circulation
These the
affecting
results
trailing the
lift
methods
control
airfoils
revealed
edge
were
the
boundary
details
layer
and
augmentation.
K_ interfer_metry, transonic, effect,
holography,
supercritical
laser
Doppler
airfoils,
point
diffraction
circulation
velocimeter.
196
interferometry,
control,
Coanda
1.0
Introduction Optical
fluid the
dynamics
work
also plasma
by
research
of Ernst
been
that
interfercmetry
used
the
be
However,
addressed of
These
development
of
Brooks
[2,
3]
method
could
pulsed
associated
with
a diagnostic
a century
beginning
recently,
the
transfer, the
of
was
the
partially
with
flow
fields limited
sensitivity
alleviated
has
and
severely
extreme
in
method
combustion,
scale
and
tool
by
to
the
laser. of
holography
represented
by
vibration
the and
by
means optical
[i]
and
the
Heflinger,
advance
Holographic
provided
Horman
measurements a notable
applied.
lasers
More
source
were
aerodynamic
be
as
interfercmetry
light
problems
the
to
with
the
introduction
applications
(1838-1916).
research.
vibration.
and
Mach
used
approximately
in heat
coherence
The
for
been
effectively
dynamics could
has
in
light
terms
wave
through
Wuerker of
where
and the
reconstruction
which
quality
initial
were
the
limitations
essentially
eliminated. Trolinger _lall
scale
suggested
[4]
applied
supersonic
the
possibility
and
the
method
hypersonic of
utilizing
197
to
the
flow the
visualization
fields. method
These in
large
of results scale
transonic flow field
investigations.
was developed and installed
A holographic interferometer
on the NASAAmes2-by-2-foot
transonic
wind tunnel for this purpose by the author in 1974. Extensive testing and evaluations of the results subsequent years.
were undertaken over the
During that time, the method was proven capable
of acquiring detailed
flow visualization
data in the NASAAmes2-by-2-foot,
and accurate quantitative
6-by-6-foot,
and ll-foot
transonic wind tunnels [5, 6, 7, 8, 9]. Transonic flows proved to be especially application
of interferGmetry
whereas in supersonic
flows, the density changes occur primarily
through shocks.
the shocks that are present in the transonic
are weak so the entire
to the
since compression of the fluid
occurs continuously throughout the field,
addition,
suitable
In
flow fields
flow can be ass_ned to be isentropic.
Thus, in the t_o-dimensional flows studied, the interference fringes were at the sametime a mapping of the isopycnics, constant static
pressure, flow speed, and Mach contours.
These
data could readily be reduced with the use of other wind tunnel flow conditions to obtain the quantitative The strong phencmena observation local
in
coupling
transonic of
the
layer
flows
global
viscous-inviscid
boundary
between
the
inviscid
predicates
features
of
interactions.
interaction,
results.
the the
and
simultaneous
flow
Conditions
turbulence-induced
198
viscous
fields such
and as
ccm_pression
the the
shock
waves,
and pressure gradients generated by the
character
of
interfercmetry
of
By
using
ph_
in
the
are
flow
data
regions.
very flow
often
flow
the
these
quantitative
details
entire
furnished
visualization scalar
the
model
field.
means
in both
for
could
the
profiles
influence
Holographic obtaining
chracteristics
short
lost
the
and
inviscid
duration
detailed for
and
exposures,
be recorded
and
i_n time-_averaged
producing viscous the
time-varying
analyzed.
surfa_
These
pr_,_r_
_nd
p__robe
measurements. Several
twp-dimensional
investigated
using
helicopter airfoil to
the
rotor flows
interfercmetry
flows
[5,
of
interfercm_eter velocimeter goals.
(IDV) of
to
fluid
experimental
the
range
interferc_etry
directing
LDV
measurements
the
turbulence
quantities
visualization contribution dynamics
provided toward
which
the
data to
were
by
the
the
as
regions The
flows.
199
challenge required
the
holographic laser
attain
Doppler
these
conditions
proved
of
such,
to
on
symmetric
shifted
interferc_eter
these
emphasis
of
The
effort
needed.
understanding
characterize
and
of parametric
the
The
data.
in an
were
a significant
frequency
investigated, the
posed
dynamicist,
combined
fields
investigation
flows
t%_>-_ent were
flow
techniques.
the
These
detailed and
Because
led
6].
computational
acquisition
transonic
the
effective where
in
flow
detailed
angle
flow
made
a significant
_lex
fluid
and
Supercritical program
with
Research program and
the
with
of
Douglas
Center
[7].
the
providing
class
airfoils
operating
at
by
interactions.
design
regions
These
As
such,
conventional
airfoil
calculations
were
that
convergence
occur. the
The intended numerical phase in
to
edge
to
pressure
interferumeter
tests.
to
by
Ames
of
these
an
design
lift
overall
flow of
supercritical
fields this
airfoils
coefficient
characterized
procedures
failed
because from
realistic
were
covered
data
program_,
were
part
improved
and
also
a physically
computations.
data
were
the
are
viseous-inviscid
are
methods
and
a cooperative
used
by
for
the
initial
the
actual
for
inviscid
did
the
aft
calculating
flow
solution
required
large
field
not
treatment
of
region.
provide
of the
strong
so different
investigations
subsequent
flow
often
the
ntwnber
iterative
flows
Simiempirical
trailing
of
tests
produced
Mach
under
documenting
for
airfoils
the
of
completely
fields
studied
Corporation
series
insights
Flow
their
characterized
loading.
of
further
also
Aircraft
The
goal
airfoil.
were
for
under
the
compariscn
Based
on
the
research
with data
the
were
Laser
velocimeter,
combined provide
with an
data
unusually
fields.
200
made
from
results
obtained
modifications Doppler
program
the
complete
to
the
in
were of
the
first
airfoils
surface
and
used pitot
holographic description
of
the
Research circulation
on
control
interferometry [i0].
on
an
increases
the The
jet.
of
added
method
because External
using
holographic
real-time
conducted
configurations
control
airfoils
in
the
over
transonic
when
slot
reduced
and
and
remains
by
period
transonic
Coanda
effect
flow
fields
which
predicting
these jet
attached
jet
three
the
produced
the
for
of
at
_ _-ve!ocity 7
pressure
is entrained
a
operating
understanding
occurs
blowing
interferometry
utilizing
to the
a surface
fluid
for
were
effect
of
Coanda
airfoil
difficulty
from
utilizing
supported
complexity
e_nda
tangentially surface
also
a new
Circulation
introduce
flows.
rotorcraft
investigations
a number
speeds.
was
and
These
years
advanced
emits
to
the
beneath
assisting
the the
flow
in
t
remaJ_ning of
the
attached
well-around
a complete
regarding
neighborhood conditions
of were
detachment.
elucidating
the
other
at
of
the
some
of the
training
investigated
Because
flows
initiation
and
visualization
questions
airfoil
typically
blunt
trailing
edge
airfoil.
Interferometry
the
the
the
program, the
the
flow
flow
behavior
edge.
A
including
speeds these
ccmplex
were
which
understanding
transonic
of
techniques
was
helped
range
of
the
stall
of
the
rather
phenomena.
to
generate
resolve
particularly
investigations
201
applied
in
some
of
the
operating condition
circulation primitive were
and
jet
control at
needed
the for
In this bringing for
report,
the
large
the
interfemumetric
scale
transonic
_ative
measurements
reliability
of
the
Application
of
a new
data
in large
which
2.O
in
tunnel
to
to
visualization for
will
be
reviewed. the
quantitative
obtaining
data.
real-time
interfercmetry
described.
under
development
by
Ames
2-by-2-foot
Transonic
the
required
as diagnostics
demonstrate
and
is also
were
fruition
testing
presented
method
that
The
Aercmetrics
method
has
Wind
been
Tunnel.
Techniques
Ln_ez_met_r
As
a flow
technique method.
does
diagnostic,
the
not
in principle,
frcm
holographic
method
differ,
In comparison,
interference followed
between
similar
interferes time.
wind
facilities
Imerf_
-nl_c
efforts
techniques
are
flow
scale
is currently
demonstrated
development
Tnis
two
recordings
light
in are
two
paths
distinction
imperfections
the
the
holographic
reconstructed
at
different
waves is optical
reconstructed
from
interferometry
light times
because
path
to
and
interfered.
202
waves
paths
important
Mach-Zehnder
creates
whereas
dissimilar
tend
the
which the at
have
Mach-Zehnder
tb_
same
component
cancel
when
holographic
in
Although there are several ways in which holography can be used
as
an
intermediary
for
exposure,
real-time,
and
was
to be
useful
found
this
most
method,
an
plate
while
there
later
used
p!ates
to
are
processing,
plate
holder,
be
aligned used
the
in
the
displacements
reconstruction
technique. entire ascertain fringe a
when
the
of
wave.
under in of
mode. at
on
the
the
the
is
Subsequent
reconstruction
reference
One
reference
the
test
because
plates
hologram
investigation.
20 nanoseconds).
the
alignment
criteria
of
when
the
is often
interfercmeter
changes
of
results
as
That
knowledge
produced
light
taken
arises
density
view,
a)ndition. result
This
tunnel.
beam, plate
can
conditions. the
exposure
Random
are
accounted
for
in
process.
the
of
(
With
wind
insignificant
images
difficulty
If
field
are
technique
(photographic)
a duplicate fringe
latter
a holographic
conditions
plates
short
between
major
by
the
double
applications.
are positioned
infinite
is extremely
One
plates
with
on
reference
flow
system
metlxx_s,
in the
the
the
including
in aerodynamic
flow
illLm%inated
consecutively
duration
as
the
for
Vibrations
the
is no
at
plate
is made
reconstruct
After
and
dual
exposure
exposed
interfercmetry
is,
transonic have in good
flow
flow
led
flow the
case,
it
case
density.
to aocurate with
203
dual
plate
over
the
is difficult
to
wherein
characteristics
agree,ent
the
is disturbed
is aligned
to the
in the
utilizing
the
infinite
fringes
a
other
reconstructions other
only
Fortunately, and
to
that
measurements.
occur
The
first
holography for
conversion
utilized
alignment.
pulses
"freeze"
flow
the
lasers
produce
length
alignment
requirements.
good
tended
be
relatively laser
long
firing
Optical
path
optical
system
Based
lengths
on
the
a makeshift
and
installed
capable 22/sec line has
of at
in the was
(0.532
to m).
a so-called
cavity's
unstable
required
to
with
the
order
Ames
pulse
80 n1_ of
transform
a quasi-gaussian
this
alignment
of
a the
ruby the
primarily
separate
laser system to
the
between
CW
laser.
investigations
using
the
ruby
a permanent
instrument
the
the
source.
repetition
Ray
in
problem.
facility.
light
rates the
DCR-I
laser
configuration.
shape.
204
A The
profile
was
Quanta Nd:YAG
between
frequency
distribution
intensity
50
to
have
required
(
makeshift
intensity
resonator
the
a
energy
simplified
with
due
laser
the
energy
Quanta
which
30 meters
2-by-2-foot
as
also
to
and
system,
"donut"
of
high
lasers
was
with
neon
nanoseconds)
seconds)
exacerbated
used
The
the This
align
feasibility
producing _
but
need on
20
meter
system
a helium
produced
(30-60
to
(
one
periods
optics
laser
of
cons_ning.
supports
and
1 Nd:YAG
the
with
These
Holograms
time
time
and
order
schlieren
sufficiently
duration
efficiency
very
tunnel
laser
recorded.
the
diffraction
to
short
being
coherence
had
wind
ruby
of
on
the
a pulsed
Ruby
millijoules)
of
i/sec
doubled
produces due Thus, into
the
a means a
designed Ray
DCR-
laser
is
and green
a beam to
laser
that
laser was
filled-in
beam
The optical stage
is
shown
intensity a 150 two
system in
Figure
profile,
a
micrcmeter
paths
consisting 1.
of
In order
combination
aperture
a transmitter
was
of
to
transform
a lens
used.
The
and
beam
with
a beamsplitter.
The
object
reflected
from
the
and
expanded
schlieren
mirror.
schlieren
mirror
transmitted which
was
46
the
and was
light
the
wind
a beam
at
tunnel
collimating
mirrors
to
the
was
receiver The at
the
fold
expanded and
and
directed
angle
of
resolution
plate
fringes of
the
that
film.
stage.
the
at
beam
provided
length
matching
was
kept
were Beam
the
in
within
205
An
was long
to control achieved The
diameter
and
enough
the
intersection
beam
passed optical the
beam
with reference at
the
plate.
object
small
object
an appropriate
the
trench.
the holographic of
of
was
mm
and
holder.
was
to 90
the
spherical
beamsplitter
the
was
and
The
second
into
beam
formed
receiver
system
within
lens
was
with
split
information
a
Because
collimated onto
by
a trench.
beam
filter
then
section.
the
beam
to overfill
plate
through
intersection
holographic
interference
holographic
via
path
the
was
or
receiver
spatial
beam
received to
the
expansion
test
collimate
tranmnitted
Optical
beam
was
to
the
the
tunnel
refocused used
of
a collimated
wind
divergence. used
f0ci
in diameter
recording
Laser
paths,
an
lens
for
the
coinciding,
mirror
additional
under
With
through
schlieren
size
beamsplitter
and
to
spatial angle
reference
beams
produce frequency determines
the
spatial field
carrier
frequency
superimposed
on
frequency the
is
required
Dif_
Thus,
to
variations
an
ensure
adequate
adequate
due
to
margin
the
On
diffraction
flow
the
efficiency
of
Interferumeter
A relatively feasibility
time
in
that
Smartt
[Ii]
light
reference PDI
it presented
is like
the
quantitative With diffraction The
opaque
disk.
aperture
other as
into
PDI,
the
a point
Figure (or
to be in
2
method
for was
of
providing
real-
as
described
by
be
light
absorbing
film
of
wave
the located
principle
embodiment or
an
206
in
the
and
llm_ever, the directly.
is generated the
path
aperture of
by
of
the or
an
operation.
image
proposed
otherwise
wherein test
field,
distortion
a circular
at
the
producing
wave
located
either
the
configuration
test
reference
illustrates
In
the
capable
is
shear
to produce
discontinuity
analyzed.
unique
through
spherical
disk)
radial
_nts
the
can
(PDI)
of
the
concept on
opaque
an
investigated The
possibility
forms
it has two
known
discontinuity
aperture
the
afte_____r passing only
at
beam.
wavefront
scme
information the
was
applications.
interfercmeter
insofar
waves,
concept
results.
is divided
is
flow
diffraction
interfercmeters
the
interfercmetry
interfercmetric The point
the
new
in compressible
attractive
an
it.
has
holograms.
Point
The
which
of
the
by
Smartt,
ncndiffracting
substrate
was
transmitted produces
with a
then
the
a
plane
will
aperture
c_n
fringe
operation.
reduce
the
reduces
minimun the
case are
along
circular
be
to
of
the of
are
the
transmittances. in
the
system.
fluid
beccme Another
applications
of
dynamics to be
the
is
produced
the
axis
away
Lateral
!Ln___r
fringes of
wave
for
the
which,
in
the
visibility
and
the
The
angle
be
requirenents
can
size.
applications,
by
be
where
the
will
of
the film
than
in the wave
that
of
with
the
special
distortions
the
fulfillment
of
these
requirements
requirement
that
is specific
to
fluid
dynamics
is
for
more
and
first
satisfied
However,
of
turn,
the
greater
the
finite
relative
defined
should
from
aperture
effecting size
which
movement
fringes.
aperture
is
wave.
optical
is
aperture
resulting
cone
aperture
aperture
wave
fringes.
pattern
large,
the
and
test
diffracted
These the
If
aperture
diffraction
while
displacement
the
film
transmitted
pr_u_ce
parameters
fringes
expected
will
aperture
Deliberate
selection of
entire
visibility
receiver
proper
the
used
the
diffracted
produce
important
resulting aperture
the
wave.
spherical
with
intensity
the
The
a
upon
in amplitude
diffracted
interfere of
incident
reduction
small,
Movement focal
Light
spherical
sufficiently will
used.
difficult.
the
freeze
the
motions
demand
the
use
of
need in
high
the
very
flow
pincer
short
field.
continuous
207
duration Short wave
exposures
exposures, (C_)
or
to
in turn,
pulse
lasers.
The
withstand
use
such
of
substrates
high
energy
demonstrated
that,
even
laser
holes
in
burned
at
the
with
apertures
levels.
Our
very
energy
low
substrates
or
disks
preliminary
tests
levels,
rendering
cannot
the
the
pulsed
device
inoperable. Because fluid
of
dynamics
diffracted energy when
and
upon
focused and
relatively
weak
energy
of
the
relative
will
reduce
possibly Sane of
be
the
of these
light
will
appear
on
to onto
focused
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the be
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diffracted
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of
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flow.
amount
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absorption
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be
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of
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With
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reference
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2O8
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in
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diffracted
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inviscid
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object
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of
in
amplitudes
The
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The
present
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visibility
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wave.
difficulties
the aperture if
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extent
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as
of
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intensities
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However,
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the
wave
a greater
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of
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refractive
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amplitude
range
transmitted
incident the
large
applications,
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of
could
absorption
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the substrate the possibility there
may
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insufficient
Clearly, relative the
the
modify
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research
similar
system
receiver light
with
the
was the
section.
source.
must
mirrors
Because
field
a white
be
of
tested
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the
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schlieren light the
beam
beamsplitter. remove
the
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The high
system.
transmitted
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split
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can
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dynamics
_
_h_
in Figure The up
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in the
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receiver
through
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into
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beam
optical
was
spatially
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section.
2O9
were
This
The
or The
a to At
with
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a
filtered
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mirror
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A
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3.
layout
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to
The
.method
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attempts
fluid
[13].
laser
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expanded
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and
system
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include
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Howes
lengths
source
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transmitter
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ope _=_"
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in
configuration
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to be
Either
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_he
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The
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to vibration,
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Ln
increased
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same
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high
technique
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it out
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worthy
solved of
in principle, beam
real-time
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concept
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for
to
A great was
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energy
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simplicity
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information produced by the refractive
then reccmbined with system
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aligned
interferometer. section
were
vibration
method two
was
very
as
this
configuration
in fluid
optical the
pinholes
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ccmmerically
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light.
visibility
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used
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light can
be
description
scattered
by
approximated
high
Because
Both
viewing of
the
the
be
fringe
of
reduction
use
the
introduced pattern
the
trans_nitted
may
be
amplitude aperture
Fraunhofer
210
other and
and
and
of
which in
instead
hence,
of
angular the
image
the
the
reflected One
diffraction
of
available
and,
in
use
consist
used
is being
used
the
to maximize
exploited.
the
the
involved
was
it
energy
now
losses
of
of
all,
levels
the
that
technique,
of
could
such
system.
application
energy
the
receiver
the
First
of
the
may
while
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the
of
mounted
beamsplitter
to maximize
produced
the
for
a variable
ratio.
the
complicates
the
interference
on
It was
Mach-Zehnder
schlieren
apertures
withstand
signal-to-noise by
a
The
attenuation
the
for
the
available.
Additional
than
section
rigidly
allowed
aperture.
substrate
were
field.
a common
investigations.
paths
process,
as
flexibility
dynamics
This
ccmp3nents
and
serious
upon
the
optical
compact
needed
wave.
manner
more
incident
were
same
no
the
separate
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made
offered
the
However,
Inasmuch also
beamretains the wave
images can
be
recorded.
distribution interfercmeter theory
as
of
jt(- sinO) J
where e is the IO
is
the
aperture order the of
incident
Bessel's
the
function
of
collimating
The shifts the
method
in
the
filtered
appropriate. under
relative
incident
upon
increase
the
pinhole.
On
pinhole
this
transmission
analysis.
would
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test
of
the
was
controlling A
but
the
hand,
other
require
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and
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focal
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expression, aperture relative made.
or
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was
planar
as
evaluated waves.
The
Several were the
length the
considered
in
intensity lens
would
burnout
of
long
focal
length
lens
and
longer
focal
length
lens
to
211
first
interfering
incident
measured.
short
would
the
was
the
spherical
was
parameter
is the
introducing
filtering on
beam,
is the
this
of
by
wave
the
Jl
were
it and
lenses
intensity
wave
that
d
numerical
Estimates
laboratory
distortion
pinhole.
the
filtering
efficiency
transform The
the
incident
Using
to
object
procedure,
levels
of
in
and
kind.
3.
the
aperture,
wavelength,
Figure and
from
the
matched
optically
with
With
ccmbinations
of
at
first
be
tested
beam,
oontrolled
the
reference
was
wave
laser
can
lens
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measured
intensity
pattern
of
angle
A is
diffraction the
beam
damager,
intensities
the
scattering
the larger
collimate
the
filtered
the
object
reference or
These
data
considerations media.
polaroid,
4" X
Estimates
of
_rk
holographic
spacing
approximately
lines of
5"
in the
(450ram),
On
approximately
resolution
limit
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large Thus,
in order
media.
In
an
angular
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is
L_
also
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that
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If the was
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upon
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X
used. the
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film
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High
movie ram.
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recorded
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16 mm
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airfoil
view
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example,
4"
Using
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resolution film,
This
speed
i0
is
film
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resolution. maximize
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increases known
for
films.
to the
based
field
60
to mitigate
beam
).
made
suparcritical
ram.
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recognize
distribution
( eE" _ _ point
It
a
this
per
important
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diameter.
to overlap
investigation,
35ram film
For
resolution
conventional
effort
to
enough
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the
and
entire
approximately
to
of
were
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the
lines
of
it was
instructive
layer If
size
pLnhole
the
resolution
35ram film,
be
grain
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interfercmetry.
30
must
stages
16ram movie,
approximate
resolution
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affected
early
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boundary
ram.
a diameter
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the
per
In
the
at
beam.
recording
with
beam
from
square
light
212
a
it was
of
(intensity
the
factor
of
aperture
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as
I/d
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to
decreases
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diameter by
on
intensity
diffraction
aperture
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requirement,
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increased
on
scattered as
intensity
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area
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the
intensity
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limited
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the
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%Duld
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intensity,
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of on
to
4.
the
the
same. The
aperture
incident
focused
a distorted
However, size
beam.
If
incident
ounponent
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beam,
the
the
studies
filtering
of
the
optical
aperture
survival,
susceptibility
filtering
requires
spatial
are
being
considerations
filtering,
reference
beam
to misalignment.
ReductUm Obtaining
quantitative
straightfcward wind
for
tunnel
changes
at
optimtwa
number
mode.
the
Using
fringes
using
produce
the field
test
the
present
flow
Mach
infinite a direct of
from
the
phase
mode of change
relationships. of
the
61
_n
has
light
213
an
the
the
through
density to produce fringe
advantage
that
fringe
density can
in_eneous
wave
is
infinite
constant
per In
so
sufficient
in the
the
interferograms
'I_e pathlength
was
fringes
mapping
shift
was
numbers
fringe
density
the
flows. case
interference
following the
results
two-dimensional
in the
of
Evaluation
test
a factor
distortion
large
Optimization
the
by
essentially
wave.
Further
Data
remain
is
be
an
the
contours. determined density
where
is the laser wavelength
refraction.
When
fringe
the
mode,
the
N
is an
relating
equation
of
the
[n(x,y)
integer.
phase
n is
interferometer
_I
where
and
variation
to density,
in
of the
infinite
is
no]dz
the
index
aligned
fringes
-
Applying
is
the
= NA
Gladstone-Dale
Constant
the
relationship
integrated
is
0(x,y) - 0o + N-! KL
The
constant
values
used
in
the
L=
tests
609.6
to be
0.226
0.226
Combining result
the
constants
and
m
(gm/_3)
0.532
-1
x I0-3
(gmlcm3)
adjusting
in:
214
were:
mm
= 0.532 Z =
described
for
-I
the
,m 609.6
wall
mm
boundary
layers
01
It
several
with ways.
of
If
view,
surface
F_w
this
and
with
the
This
of
was
be
case.
converted
to
from
in
flow
in
the
This
tunnel
with
21%
which
in the
Ames
produced 2-by-2-fcot
is a closed-return,
open The
porous-slotted airfoils
tested
Corporation
DSMA671
circulation
control
airfoils
tunnel
conditions
test
the
the
by
using
Another flow
example.
ranged
examples Transonic
variable upper were
and
lower
a NACA
64/K)IO, airfoil
utilizing
Coanda
a
215
the
free-stream
paper
Wind
Tunnel.
flow
facility
walls
supercritical
from
in this
density
the
a
inviscid
for
as
used.
Instead,
Po"
velocimeter,
used
done
density
pressure,
be obtained laser
was
could
the
the total
to be
_disturbed
conditions generally
could
experiments
conducted
Aircraft
To,
density.
a region
not
fringe
Luv__
were
testing.
was
measurement
measured
The
was
ibm/ft3 fringe
a particular
wind-tunnel
reference
nekm
x I0 -_
identify
there
temperature,
velocity
2.46
corresponding
the
pressure
independent
=
to its
Unfortunately,
total
00
remained
reference
field
-
for
transonic
a Douglas and
several
effect. Mach
number
Wind of
the
0.3 to 0.9 and chord Reynolds number of 106 to 2 x 106 . Transition airfoils
3.0
strips were used on the upper and lower surfaces of the to ensure fully
Results
and
the
other
aligrm_/%t de_ned
Because
of
to
the
the
of
exposed
two mode
view.
Typically,
the
waves
ideally
This
was
considering
the
number
range
how
uncertainties waves,
a
accurately
series the
by
tests could
were be
mode. conducted
no
in
wind
tunnel.
flow
the
aligrm_nt
of
the
result
no
fringes
in
fringes
considered of
of
waves
was
two
conditions
in the
system
or
of
obtained
optical
should
aligrmm_%t.
a
to measurements
light
fringe
and
one
over
possible
determine
with
light
fringe
ccmpared the
infinite
Evaluation holograms
of
obtained
reconstructed to
the
were
results
necessary
aligned
of
data
quantitive
means.
flows.
Discussiuns
Interfercmetry and
developed turbulent
fringes
waves
to
over
occur
an
acceptable
present
under
pairs
the
infinite
the
field
after
level
the
could
visualization
in the
development.
With
disturbed
due
initial
the
to the
not
light
flow,
be
trusted
phase
of
wave
over
Figure
4,
216
even
the
of
error
test
flow
instrumentation
the
the
for
entire
alignment
field of
of
careful
conditions. Interferograms
of
Reconstruction
would
to be
using
of
the
view
interfercmeter were
reduced
with
other
the
means.
With
uncertain.
to basic
surface
measured
was
The
pressure the
the
by
interfercmetric
and
readily
available
compared
results
to measurements
and
reliable
data
is
distribution. of
isentropic
interferograms
the
the
parameters
most
assunKstion
from
coefficient
flow
Tnus,
were
flow,
the
reduced
densities
to
surface
pressure
relationship
2
P
Pt
y_2
and
where are
Moo the
density
is
the
flow
of
one at
frcm
and of
the
one
the
Mach
density
at the
fringes
point
in
reference
number,
_s the
to
y = 1.4,
stagnation
identified flow.
obtain
Pt
and
conditions. using
Fringes the
and
Pt The
a pressure
were
then
simply
at
each
point
pressure
and
density
field.
A_re_nent interfercmetric confirmed
freestream
pressure
measurement counted
the
the
between
the
data,
Figure
interfe_ic
measured 5 was
surface generally
results.
217
It
very should
good be
the
which
recognized
in
corrected downstream total improvement
in the
Experiments the
Douglas
airfoils
were
flow edge
relatively
had
a
the
closed
in the
interferograms local
concavity
and
near
The at
the
which static
surface were
edges
in the
boundary
measurements
well
contours to
pressure
the
both
trailing
airfoil.
produced
the
64A010
primary
below
were
to maintain
the
which
the
trailing
displaced
edge
a
inviscid
the
the
The
airfoil
streamwise
supercritical
in
for
Supercritical
on
to
and
airfoils
surfaces
aft
in
above
the
8.
concavity
contours
of
to
the
near
wake
using
boundary
flows
in
the pitot
the
other to
the
produced also lower
boundary and
static layer
by
normal
variations
layer
correct
provided
to measure
gradients
Pressure
used
of
data
of
difficult
pressure
airfoils.
upper
corresponding
downstream
slight
airfoils,
icwer-surface
on
the
upper
surface
wake.
outer
present
flat
Oumparisons
closed
maxima
a
supercritical
Figure
shock
located
the
on
[7],
surface
fringe
interferogram
are
the
loading.
symmetrically
indicating
have
lower
aft
By contrast,
the
conducted
to hold
edge.
of
also
Corporation
large
that were
or
only
distribution.
characteristically
trailing
flow
pressure
Aircraft
shock-free
showed
pressure offered
static
and
wake,
by
and
pressure
Figure
9,
Significant
streamlines
surface
218
near
distributions
techniques.
occurred
layer
pressure
could
be
supercritical across
the
concavity. wake
lowerThese
profile
probe
measurements.
data
that
the
surface
obtained
at
pressure
points
cn
the
interfercmetric
results
the
recorded
airfoil
agreement
but in the
dimensionality occurred
the
of
the
interaction
typically
of
time-averaged
the
airfoil.
were
spatially
averaged
at
an instant
in time.
also
confirmed
flow.
A small
neighborhood
interaction
represents
midspan
results
of
in the
data
shock
the
causes
the
shock.
the
Thus,
relative in
This
sidewall shock
The over
difference
of the
with
the
results
the
of
good
twothe
was
boundary
to move
span
data
due
have
to
the
layers.
forward
at
The the
sidewalls. At
an
relatively
airfoil
angle
of
strong,
there
was
pressure
across
the
agreement
good
pressure was
loss
the
with
across
insignificant.
Figure
outer
as
edge
of
the
However,
the
obtain
an
results
achieved An
the
and,
with
estimation
estimation
of
the
the
that
loss
total
attack
to 6.2 ° , There
provide in
and
strength
such the
severe was
pressure.
was
obtained
7 demonstrated
219
the
of
pressure
in total
However,
in entropy,
would
shock
total
change
Occurred.
layer
was
the
data
shock
of
verified
interf_tric
a strong
of
loss
shock
data.
separation
in Figure
the
the
angle
the surface
shown
the in
hence,
boundary
of
even
data
increased
separated
representation
separation.
an
with
errors
pressure
shock
to whether
accurate
agreement
the
3.5 ° wherein
a concern
shock-induced
the
of
producing
With
6, massive
uncertainty
shock
attack
at
the
an cases. very
good
flow made Using
to the
Once the confirmed,
relative
the
Mach
accuracy
contours
of
the
interferGmetry
determined
data
was
from
1
0t
were
traced
from
the
interferograms.
quantitative
mapping
valuable
comparisons
flow
for
of
the to
The
global
Mach
features
numerical
of
contours
provide
the
and
predictions
flow of
the
a
are
inviscid
field. The
using
flow
the
speed
was
determined
from
the
assu_pticn
of
isentropic
flow
of
density
distribution
a perfect
gas
and
the
relationship
