NASA/CR-2001-210841 ICASE
Interim
Report
Turbulence Edited
Langley
M.D.
NASA
Modeling
Workshop
and
C.L. Rumsey
Research
Center,
Hampton,
Virginia
Center,
Hampton,
Virginia
Salas
ICASE, J.L.
37
by
R. Rubinstein NASA
No.
Hampton,
Virginia
Thomas Langley
March
2001
Research
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ICASE
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Edited
No.
Modeling
and
Langley
M.D.
/
/
37
Workshop
by
R. Rubinstein NASA
_
/
Report
Turbulence
C.L.
Rumsey
Research
Center,
Hampton,
Virginia
Hampton,
Virginia
Salas
ICASE, J.L.
.... 2_
Hampton,
Virginia
Thomas
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Research
Center,
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Center
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TURBULENCE
MODELING
EDITED BY R. RUBINSTEIN_,C.L.
number
Executive
Summary.
flows near
the onset
following
be established.
taken
of other efforts Combustion
advances existing quality
understood
model
The
provide
models.
mixing
for analysis
Key words,
turbulence,
them as follows. and forming
we cannot
understanding
of turbulent
"Rational
do
flows
some
turbulent
has been modeling
achieved
validating DNS,
number,
priority
(DNS) new
computer
be given
to document
Models
and Reynolds
since
it is the least be given
Eddy
require
to the
Simulations
Navier-Stokes currently
represent
the use of RANS
a balanced
these approaches DNS,
as
issues such as grid
methods
future,
be
as well
Large
limitations
should include modeling,
Turbulence,
Reynolds-averaged
in the foreseeable
separation,
on Flow,
should
and
LES, and hybrid
although
number
by Lumley
restricted Aerospace with
capabilities
effort
in
and our ability
to
as well.
LES
is correct,
classes
there
of flows.
Technology
unable
respects,
fluid dynamics
to reliably
predict
have
Committee
1999
us very good
in accurately separation
us the ability
progress report
(ASTAC)
concluded
Indeed,
reliably. qualitative
to calculate
in the calculation
of the
predicting
onset.
of industrial
of turbulent transport
brought
considerable
flows
and all sorts
but have not brought
December
Advisory
reactors
the effects
effort
has been
The
of turbulent
nuclear
to calculate
of intense
all practical
computational are
years
the importance
automobiles,
on an ability
hundred
in nearly
summarized
of aircraft,
are dependent
flows
turbulent
success
and
should
equation,
Second
Simulations
and implementation
design
that. One
this view
of NASA's
Reynolds
In 1996 John Lumley
[1] While
Subcommittee
at high
length-scale
models.
Advantage
implementation Stress
assessment
be needed,
should
on Algebraic
the
Numerical
will
the
Fluid Mechanics
reliably."
for
research
and higher
basis. Therefore,
experiments
made
modeling
Community
numerical
high Reynolds
in this workshop
and categorized.
A high priority
on improving
Direct
high Reynolds
process ....
Unforttmately,
long-term
to calculate
for turbulence
Research
"unit"
datasets.
of this workshop,
validation,
classification.
be reviewed
selected
in developing
on a limited
configurations
Introduction.
models.
not the focus
development,
1.
he placed
guidance
modeling
Subject
support
in order
and standards
form, including
of two-equation
near-wall
valuable
for realistic
turbulence
calculate
should
should
Although
approaches
methods
emphasis
of improved
would
(RANS)
(2) NASA
in a standard
AND J.L. THOMAS 4
the participants
such as that of the European Carefully
s,
are needed
database
to fill the gaps in existing capabilities
SALAS
To this end,
data sets should
consortium.
and is a key component
development (LES)
underway,
in instnmaentation,
Models.
and beyond.
experimental
already
and resolution.
Stress
viable
Existing
2, M.D.
modeling
(1) A national/international
(ERCOFTAC)
turbulence
in turbulence
of separation
recommendations.
should
and
Advances
RUMSEY
WORKSHOP
Airframe that
attached the
report
of
Systems
while flow,
great current
considered
l NASA Langley Research Center, Hampton, Virginia 23681-2199. 2NASA langley Research Center, Hampton, Virginia 23681-2199. 3 ICASE, NASA Langley Research Center, Hampton, Virginia 23681-2199. This research was supported by the National Aeronautics and Space Administration under NASA Contract No. NAS1-97046 while the third author was in residence at ICASE, NASA Langley Research Center, Hampton, Virginia 23681-2199. 4 NASA LangleyResearch Center, Hampton, Virginia 23681-2199.
separation onsetaspresenting a greater challenge than debatable
conclusion
future needs
(see Bradshaw's
for accurate
turbulence-modeling NASA
Langley
presentation
computations
workshop
Research
of high Reynolds
(LaRC)
and organized
wide range of knowledge,
were invited
by establishing
and the expectations
Airframe
Systems
turbulence
Subcommittee
modeling.
Boeing,
Brian
perspectives Katepalli
Later that morning
Smith,
Lockheed
Tech,
spoke
about
around group discussions
number
in turbulence
issues
on January
committee
modeling,
by the attendees.
In order to provide
capabilities
experts,
and
talks were presented. NASA
LaRC,
to the discussions,
by a
the workshop Chair of the
shortcomings Philippe
separated
and Roger
of
Spalart, their
The rest of the workshop
some structure
a
covering
presented
number
of this flow regime
methods.
and
was sponsored
Mark Anderson,
capabilities
a
at flight conditions,
LaRC, opened
high Reynolds
of the physics
with experimental
NASA
Gatski,
emphasizing
our current
40 technical
on current
Thomas
This is perhaps
flows
participants.
five summary
and
gave an overview
associated
representing
flows.
The workshop
Approximately
views
afternoon,
separated
12-13, 2001.
he had from the workshop the
separated
In order to assess
turbulent
by ICASE.
Aeronautics,
Yale University,
C).
Ajay Kumar,
and early
Martin
of the state-of-the-art Sreenivasan,
Virginia
to participate.
presented
with massively
in Appendix
was held in Reno, Nevada
Center
its purpose
dealing
own
flows. 5 Simpson,
was planned
the following
three
topics were chosen: a)
turbulence
modeling
for vortical
b)
turbulence
modeling
for time dependent
c)
turbulence
modeling
for juncture
However, divided
the three topics
into three
experimental document
groups
difficulties,
summarizes
and
the results
The organization
of the modeling conclusions assessment
of turbulence,
issues,
from the workshop,
methods
flows, and
and mixing flows.
was
in any sense to limit the discussion.
asked
to discuss
and alternative
approaches
the adequacy
The 40 participants
of current
as they related
turbulence
to the three topics
were models,
above. This
of the workshop.
are given. assessment
and recommendations. of current
group
of this document
held in each of the three groups
separated
were not intended
each
numerical
flows,
is as follows. These summaries of current
Section
5 gives
and recommendations
a list of participants,
methods, final
In Sections are broken directions overall
for future
2 through
into the following for improvement
conclusions
development.
and a copy of the workshop
4, summaries
from
of the discussions
subsections:
importance
of turbulence the workshop,
The appendices
models,
and
including
an
include
an agenda
presentations.
5Afourth talk by PeterBradshaw was planned, however Bradshaw was unable to attendthe workshop. His slides are included in Appendix C.
2.
Group
I - Summary
Findings
and Recommendations.
Facilitators:
C.L
Rumsey
(LaRC) and J.B.
Andcrs (LaRC) 2.1.
Importance
2.1.1.
Vortical
flows.
the aeronautics/aerospace •
Wing
•
of the Modeling
The following
of different types of vortical flows of interest to
tip vortex Interaction
o
Far downstream
with tail
Chine vortex Interaction
•
Strake
•
Vortex
•
Fuselage
•
Vortex
generators
•
Internal
vortices
•
Vortex
instabilities
•
Flap/junction
effects
flow
so important
to compute
be important
when
enhancers
(Chevrons)
types
this
on
upon
layer. The strake (sometimes
wing, body, or tail boundary that burst induce unsteady
layer.
fall
industry
into
one
design).
or come near of the engine called
that creates
the following
easier to compute,
For example,
nacelle
that passes
on fighters
3
body (horizontal a vortex
shear
comes near a surface,
wing tip vortices tail, following that can interact
edge piece near the wing-body back over the body
have been associated
tails as they pass near).
free
flow
or
but also tends to be less important
computing
that generates
is a leading
a vortex
categories:
unless a free vortex
a downstream
strakelet)
Strake vortices
loads on the vertical
of
(in other words,
for aircraft
on the outside
for example,
list
on engines
Free shear flow is generally
it accurately
they impinge
chine is a protuberance
layer
vortex breakdown
layer interaction.
aircraft,
gradient
vortex
Mixing
vortical
in boundary
from the point of view of the aerospace
fighter
pressure
(separation)
Including
vortex/boundary
layer, including
at high alpha and ogive cylinder
o
Most
with wing boundary
bursting
o
some
list gives examples
community:
o
o
boundary
of Turbulence
accurately
can
aircraft).
The
with the wing intersection
and can interact
with vertical
it is not
on
with the
tail buffet (vortices
It can be more instructive
to redefine
•
Free vortex zero pressure
gradient
•
Free vortex with pressure
gradient
•
Free vortex with and without
•
Vortex
interaction
with boundary
•
Vortex
interaction
with shock
•
Interacting
•
Smooth
Predicting
vortex
vortices
and counter-rotating)
details is not always important
(SA) turbulence
are often looking absolute
representation
of the types of vortical
from the point of view of the aerospace
when there is an interaction
for accurate
were accurately
of trends,
and not absolute
manufacturing
industry.
predicted
in the vicinity
with the tail. Also, it is important
predictions
flows that can occur.
of a vortex with a downstream
model (which adds too much eddy viscosity
levels of drag is critical to airplane
aerospace
and represents
surface.
on the
An
in spite of the Spalart-
of vortices)
to note that engineers
levels.
It depends
diffusing
the
in the aircraft
industry
On the other hand, the prediction one of the most difficult
challenges
of in the
industry. Generally,
Reynolds
flows, the Reynolds
laminar,
layer (BL), with and without separation
gives a broader
vortex prior to the vortex interaction
decay
(ZPG)
was given from Boeing for which loads and moments
Allmaras
as follows:
separation
categorization
case, and tends to be more important
categorizations,
axial flow
(co-rotating
body cross-flow
This physical
example
the above list in terms of physical
in a vortex,
number
is not too important
of the vortex-forming
then viscous
the Reynolds
2.1.2.
number
number
transport
becomes
physical
(response
•
Unsteady
(hysteresis,
•
Post-separation
•
Post-curvature
•
2-D smooth
separation
•
3-D smooth
surface separation
•
2-D shock-induced
separation
•
3-D shock-induced
separation
•
Vortex/BL
gradient
affects the initial vortex important.
flows.
However,
formation.
Far downstream,
for free vortex
If there
is turbulence
as the flow becomes
quasi-
flows.
The category
of separated/time-accurate
flows
can be broken
categorizations:
Curvature
Most separated
more
free shear
important.
•
to pressure
becomes
Separated/time-accurate
down into several
device
in turbulent
to normal straining)
and pressure gradient
time lag)
physics physics
interaction flows can be categorized
effects,
curvature
in terms of one or more of these physical
can affect separation
location from a smooth
categories.
body. Convex
surface
In addition curvature
reduces turbulence whereas concave curvature enhances turbulence. Beyond and "recover"
from separation.
it is often possible and possible recovery interest
to predict
reattachment
downstream
location
2.1.3.
to suggest
Juncture
computation
of secondary
flows of importance 2.2.
the turbulence
model
grid refinement
to achieve
more accurate Nonetheless,
modeling
Often,
vortical
many model
Other
insufficient
grid resolution. "Pros
is presented
the problem
(putting
to correctly
with capturing
models
(EVM),
which
causes
and Cons"
represent cannot
are of particular
The comment
vehicles.
was made that
issue.
example,
jets and mixing
industrial
industry.
needs.
layers)
Accurate
A prioritized
and Recommendations
are
list of
section below.
vortex
interaction
in the region
effects
has less to do with
where the vortex exists. In this regard,
grid in the right place) might go a long way toward helping
do this well.
Many models
model
types
vortical
+ suppresses
diffused
here,
produce
at the correct rate (v'w'
- needs curvature
as related
radial vs. u'v'
correction
normal
stress differences
- cost/robustness + can reproduce
correct behavior
- cost + should correctly (no consensus
predict any free shear flow on this "pro" statement)
Many models, eddy viscosity
above and beyond
the effects
to vortical
diffusion
- not necessarily
To get the details
stress and curvature. erroneously
is given
flows.
pro):
EVM+suppression
+ represents
between
to be excessively
list for turbulence indicates
for turbulent
the relationship
the vortices
•
LES/DES
(for
for most typical
models are deficient
- too diffusive
•
up.
modeling
in the Conclusions
enough
EVM
RSM
was brought
of flows
not important
turbulence
con, and "+ (plus)"
ASM/EASM
separation
of these flow types for aerospace
is a turbulence
types
physics refers to
flows from the point of view of the aerospace
•
•
scaling
its extent
flow computations.
existing
needs
of free vortices,
•
number
For example,
separation,
well. Post-curvature
occurrence
scaling
accurately.
Methods
or adaptation
the vicinity
indicates
is probably
flows.
eddy viscosity
(minus)"
flows.
than that of juncture
of Current
particularly
A general
number
to compute
and shock-induced
than it does with lack of grid refinement
automatic
fight, a turbulence
that Reynolds
for turbulence
Vortical
of the frequent
region, a flow may reattach
but if there is shock-induced
surface separation
the issue of Reynolds
mixing
is often important
are often not predicted
because
vortices
Assessment
2.2.1.
Smooth
and
far more important
physics
on a wing correctly,
downstream
community,
this discussion,
there is no evidence
probably
shock location
of curvature.
to the aerospace During
This post-separation
a separated
axial)
flows
in of
("-
Key: EVM=eddy viscosity model,EVM+suppression indicates eddyviscositymodelswithoneofmany available simplefixesthatmakethe model"turnoff" withinvortices,ASM=algebraic stressmodel, EASM=explicit algebraicstressmodel,RSM=Reyaolds stress model, LES=large eddy simulation, DES=detached Based here
eddy simulation.
on the breakdown
to list the model
framework
only.
of vortical
flows into physical
types that are capable
The group
of solving
mark was used when there was some uncertainty.
a single
specific
case (and some uncertainty
limited
yet being
validated
opinions
success
in a validation
also earned
given by members
flows,
sufficiently
for which
is known,
if a model remains)
The two items with "N / Y?"
work for all cases
DES defaults
fine grid, regardless
condition
validity
necessary
a table is presented
should
to adequately
be viewed
as a
complete
it. A
type has been validated
then that model
earned a "Y?" and a belief that a model should
a "Y?"
earlier,
Note that this table
For example,
as to the model's
given
was assigned
be capable
are labeled
as such
only for "Y?"
in spite of its not
because
of differing
of the group.
Note that DES should shear
each category.
did not have the time or all the information
question
Similarly,
categorizations
to LES.
content
boundary
layer interaction.
And for any free shear
of the Reynolds
or that the spectral
except
number (assuming
The other
flow, LES should
that the spectral
flows
yield
content
good
are all free results
of any inflow
on a
boundary
is not important). TABLE 2.1 EVM
EVM with
ASM/EASM
RSM
suppression A. Free vortex with zero pressure
N
Y
Y
Y
N
Y?
?
Y
N
_
?
Y?
with BL (with and without
N / Y?
Y?
Y with tweak
Y
with shock
N
?
9
y?
N
?
?
Y?
N / Y?
Y?
?
Y?
B. Free vortex with pressure
gradient
C. Free vortex with and without D. Vortex interaction
gradient
axial flow
separation) E. Vortex interaction F. Interacting
vortices (co-rotating
and counter-
rotating) G. Smooth
body cross-flow
separation
The fixes used in "EVM+suppression" Richardson However,
number) they
environments stream-wise
do not work (such
strain,
one such complex so a nearly
may work well for vortices in general
as in adverse
pressure
i_ntropic
turbulence
(tuning
in which
for vortices gradients,
or when there are circulation flow is an internal
models
to be sensitized
straining
interacting
in the stream-wise
with a boundary
in the presence
changes)
these simple
flow in which the shear stresses
results
downstream.
to a curvature
In this region,
of additional
direction
layer. shear,
parameter is relatively
Also,
in more
when there
fixes may not work either. decay rapidly, the turbulent
but the normal kinetic
such as
energy
weak.
complex
is significant An example
stresses
of
do not,
is fairly
high.
"EVM+suppression" maygettherepresentation of theshearstresses right,butit will notbeableto high turbulent
seven flow categories, stresses
even though
and strains
For example,
(as implied
in simplifying
between
and strains
In general, However,
of vortices.
which
validation
requires
that include
studies
in this area (both DNS studies
additional many
attention.
experimental
existing
flows,
datasets
the following
physics
and post-curvature
separation,
to post-separation
physics. to assess the capability whether
is often a big problem;
turbulent
CFD can cause discrepancies.
For example,
for improving models
geometrically
easier to grid-converge.)
data.
Clearly,
including
term
the interaction
seven
There
flow
categories.
are many experimental
numerical
simulation
this is an area that could
vortex
Langley
breakdown.
models.
region
Aeroelasticity,
facility
(DNS) use some
data).
A thorough
Also,
survey
of
for separated/time-accurate
of solving
Question
marks
physics
stand
each category.
indicate
uncertainty,
Simple
out as a challenge
so they remove
turbulence
models
is unknown
to be helpful
is case-dependent.
As with the
and boxes
geometric
to most
with
modeling
models,
but the separated It may in part be
for separated/time-accurate
flows,
or other issues.
it is
For example,
then comparing
using
fully
for, can also lead to discrepancies.
toward
isolating
specific
for validation,
are most useful for isolating
(Unit problems
accurately,
in the experiment,
will likely be useful
unit problems
improvements.
This behavior
if not accounted
wing experiment
toward
simple
categorizations
are due to turbulence
is too complex
the trapezoidal
and guiding modelers
also usually
if the transition
experiment
turbulence
(LES/DNS)
theses).
predicted.
of existing
poor predictions
transition
models.
of the above
models ot_en can get the shock location
related
a given
term and the
offered by the group.
of the shock) may be poorly
Often
be
is made.
The diffusion
does capture
data are very old (for example,
as a fi-amework only.
itself (downstream
to separate
should
to the equations the diffusion
ASM/EASM
on many
Using the physical
region
often difficult
Ph.D.
relationship
then that model
circumstances.
knew of only two direct
for delta wings,
flows.
opinions
For shock-induced
In attempting
in certain
table lists the model types that are capable
that post-separation
RSM.
the correct
and quality would be helpful.
both N and Y indicate differing
including
equation),
all of the above
terms.
or full simulation
experimental
have been taken
provides
are made regarding
However,
validation
are unpublished
this table should be viewed
Note
CFD
but the group participants
Separated/time-accurate
given earlier,
table above,
enough
Many of the existing
data and its relevance
2.2.2. flows
vortical
assumptions
of the vortex.
either experimental
studies
stress transport
of solving
One pays a price each time a simplification
in the stress generation
has not been
capable
If a model
can lead to misrepresentation
as embodied
there
that is generally
of terms is required.
in the exact Reynolds
in the region of the centerline
stresses
order model
from RSM to ASM/EASM,
terms for the stresses,
can be important
is the lowest some modeling
able to yield a good representation
convective
the
kinetic energy.
As seen in Table 2.1, RSM
between
compute
isolate
a specific
fidelity considerations
failings
of turbulence
but is not simple
specific aspect
failings
enough
of turbulence
of turbulence
and are
from the CFD modeling,
and are
TABLE 2.2 EVM
EVM+ ASM/EASM RSM fixes
A.Curvature (response tonormalstraining) including pressure gradient B.Unsteady (hysteresis, timelag) C.Post-separation physics D.Post-curvature physics E.2-Dsmooth surface separation F.3-Dsmooth surface separation G.2-Dshock-induced separation
N
N/Y
Y
Y
Y N N N/Y N Y?
Y N N Y N/Y Y?
Y N N Y Y Y
Y N/Y? N/Y Y Y Y
H.3-Dshock-induced separation Ii Vortex-BL interaction
? N/Y?
? Y?
? Y
? Y
In theareaof unit helpful
for exploring
on simple defining
problem
shock-induced
problems
Juncture
axisyrmnetric
However,
turbulence
challenging.
models
are the type that may be
have been very successful
in the past
in spite of the difficulty
the turbulence
modeling
community
inherent
in
is definitely
in
experiments.
and
mixing
flows.
There
is a lot of evidence
for many of these types- of flows (for example, in a turbulence
stress differences.
In other words, if a turbulence
are proportional
bump experiments
Therefore,
for 3-D separation,
terms are required
stresses
further
are more
out good unit problems
need of more "3-D unit problem"
are required
separation.
like this. 3-D flows
and carrying
2.2.3.
experiments,
model
to the strain
horseshoe
for it to be able to compute model
(Boussinesq
that full Reynolds
vortices). secondary
and the model
(RSM)
It is also well known that nonlinear motions
is a linear eddy viscosity
assumption)
stress models
induced
model
cannot
by turbulent
(LEVM),
predict
normal
then the turbulent
turbulent
normal
stress
differences. 2.3. addressed
Directions
directions
for improvement
separated/time-accurate Turbulence
modelers
fluctuating)
profiles,
flows, generally
helpful,
and may benefit
(LDV),
oil film, liquid crystal,
obtaining
length-scale
like
coefficient,
scale would be extremely
uncertainties
in turbulence
exploitation
are:
and any other non-intrusive
information),
full simulations
three
itself
helpful,
image
technique.
to improve
because
Where
models
(both
that
(PIV), laser Doppler experiments
for
mean and
of the length
techniques
only
hand-in-hand.
Also, although
the modeling
may be the only way to move forward.
8
turbulence
of velocity
coefficient.
Experimental velocimetry
the group
must move forward
components
and pressure
modeling.
particle
In order
modeling
an experiment:
skin friction
Due to time constraints,
flows.
and turbulence
to have, from
profiles,
from further
Models.
of separated/time-accurate
of the length
one of the biggest
of Turbulence
both experiments
temperature
to obtain, some measure currently
for Improvement
are lacking
are
difficult scale is currently
velocimetry (such as in
Some goalsforimprovement inprediction ofseparated flowsarelistedhere: •
Increase
generality
ofturbulence
•
Need naturally
•
Must include
•
Separation
control into modeling
•
Continued
exploration
•
Overall,
good behavior
The issue of turbulence
may be used). are referred Langley,
of DES the role of DNS/LES
modeling
(for example,
Or sometimes,
different
different
of a given
It is not a trivial
although
model
[2].
It is difficult
a much greater problem
For example,
delay the location
some major of transition
in use in industry
compared
three
constants,
uniformity,
existing
individuals
and/or
damping
such
functions
yet, when implemented,
however.
In an effort
codes to have identical
when
implement
differences
they
at NASA
implementation
exist.
(This
employ
version.
an unpublished
modification
of
problem,
like EASM and RSM, even exists for simple models
today
to the published
different
exist in the literature,
models
models
Often,
limiters,
task to ensure
to validate/improve
codes
methods, model
to modify
for more complex
modeling
is also important.
numerical
versions
to by the same name.
for prediction
implementation
it took one month for three individuals
an EASM
SA.
near walls
effects of curvature
should increase
a given model differently
model formulation
like
to SA that can
Most users are not aware that this modification
has been employed.) 2.4. general,
Conclusions
and
not specifically
prioritize
Recommendations.
geared
toward
various flow categories,
of the participants,
Separation
•
Vortex
•
Jets and mixing
•
Unsteady
•
Other
is (starting
(including
and recommendations
any one of the flow categories.
for which turbulence
this prioritization
•
The conclusions
incipient
modeling
efforts
First
given
of all, it is important
should be focused.
here are fairly to attempt
to
From the point of view
with the most important):
separation)
flows layers
flows
(Juncture
flows,
Heat transfer
(scalar
transport),
Flow-induced
is subjective.
What areas are considered
noise,
Compressibility,
Cavity
flows) Naturally, prioritizing. importance
this prioritization
However,
the top four
items
to a great number of people Some
implementations
specific
by ERCOFTAC
recommendations
details
completeness on proper
seem to the group
to represent
depend flows
on who is doing the of interest
and of
in many disciplines. follow.
for RSM (and other models)
set up to guarantee Furthermore,
in this list
important
efficient
First,
an
(so people
effort
details
on how turbulence
use of models
should
be published.
[3].
9
be
undertaken
will want to use them).
in reporting
are a step in this direction
should
numerical
There should be standards
models are implemented
For example,
to make
the guidelines
(for repeatability). document
published
An organized validation turbulence
modeling After
turbulence
modeling
it necessary? thorough
community
two days
goal is appropriate
effort
of discussion,
efforts
should
or desirable.
validation
or poor geometric
will require
considerable
A large ERCOFTAC). serve
The group
may be required.
wing, ROCK
wing,
of unit problem
The
experiments
group
made
modeling
methods.
It is imperative needed
coefficient,
The following discussed
final
from existing
some
areas
2.
improvement
is particularly
These included
use of PIV for spatial
boundary velocity
summary
represents
old data
•
Quantify
uncertainty
•
Correlate
data to particular
3.
Develop
4.
Assess,
5.
Collaboration
needed.
(such
as
old ones exist that new
databases:
an experimental
database,
or updated trapezoidal a good set
Some suggestions
conditions
profiles
be given,
(mean
that
correlations,
would
LDV,
included
be most
helpful
for
and other non-intrusive
for use in CFD
and fluctuating),
a "balanced
plan"
for turbulence
physical
phenomena
instrumentation
effort to assess/screen
•
databases
where
experimental
approaches
For both wind tunnel and flight? (no consensus
improve,
This
computations.
temperature
profiles,
modeling.
These
Key surface
skin friction coefficient.
Validate
•
A
bump.
for experimental
•
advanced
Is
What are specific
experimental
be evident
some existing
Mine old experiments
Develop
this
or is it too much?
when so many
may
more fully below: 1.
up as to whether
and not some other factor like grid resolution
recommendations
are three-component
which
Can this state of affairs be improved?
As a part of compiling
axisymmetric
that well-defined
and surface
and select
evaluation,
for validation/model
validation.
goal toward
I.e., is it do-able,
a slew of new experiments
swept bump in channel.
some
as an unspoken
models.)
of the group mentioned
bump or a modified
turbulence
measurements
to evaluate
a thorough
Members
and plane
some sort of axisymmetric
is needed
After
cases.
before they are discounted.
model
the
and/or simulations.
did not want to advocate
weU.
models.
In addition,
stood out as one that really needs a lot more focus in the future.
help from experiments
perfectly
experiments
to all turbulence
cases.
the issue was brought
an "abyss"?
models
due to turbulence
modeling
effort
simpler
standard
set of standard
to RSM,
However,
stress modeling
for the existing
(This applies
concerted
given
less robust than simpler
that are unambiguously
fidelity?
was
in the future.
Is full Reynolds
The issue of length-scale
pressure
a lot of attention
be directed
effort is necessary
failings
on a set of simple
also needs to build up to a more complex
RSM has been traditionally
documentable
might
should be undertaken
and document
existing
models
numerical
implementation
needed Funding
commitment
required
10
here)
items
are
6.
Continue
model development •
After needed.
Maintain
assessing
All old and new (proposed) out of this workshop.
relevance
old datasets,
In new experiments,
targeted
experiments
be organized
to whatever
should
be placed
should
European
ERCOFTAC
conditions
(e.g., actual wing shape in flight, transition
consortium
In the effort assessment
to assess/screen
proceed?
Should
one code, but probably has not worked
both
to calibrate
the models
numerical
implementation
Model and implementation
adequately those
represent
determined
propulsion
certain
may be needed.
from experimental 3.
around
codes?
Opening
in some
It is probably
CFD
with
boundary
way. best
How should
the
to have more than
up this type of effort to too many codes domain?
Grid resolution
(although
boundary
complex
between
different
people
It might
and quality
old models
issues must be can be useful
As a part of the
of the same model
should
be a
industry.
Other areas
the collaboration
current
people
may not
priorities
working
any collaborative
of the "group."
participants
might have different
of more
and developed,
outside
The
than
in the area
effort
Also, new models
is indicated prediction
Importance below
of the Modeling
for transport
needs in the current •
Reynolds
•
Control
may arise both
and theory.
and Recommendations.
•
3-D High-Lift
These areas are discussed
of Turbulence.
vehicles
CFD environment
Number Surface
aircraft
of
needs to make
Facilitators:
J.L. Thomas
(LaRC)
and R.A.
(LaRC) 3.1.
to
in the Navier-Stokes
and new ones.
implementations
be helpful
layer codes
implementation
need to be involved.
to be refined
from people
Findings
to the existing
should be assessed.
As models continue
II - Summary
provide
need to be classified
the assessment.
among
data as well as from mathematics
Group
carefully
similar
etc.).
multiple
have a balance
For example,
new ideas that come
database,
effort fall under NASA's
of the aerospace
venue.
data should
on the more
consistency
to engineering
or international
be unmanageable.
the "right"
segments
in the current
sure not to suppress
Wahls
effort,
Data for
as a check
robustness
In any collaborative
efforts both in flight as well as in wind tunnels.
be employed
should
assessment,
that arise
codes should
and to serve
The validation/assessment
challenges
models
to devise a strategy for performing
in any study, and Navier-Stokes
particularly
where
3-D data.
location,
Does the validation
fill in, or replace for obtaining
a national
models,
there be collaboration
solvers).
goal.
existing
in the past.
on unit problems,
All experimental
more than three would
in Europe
form a sub-committee included
effort.
into
for to supplement,
as to their relevance
to have experimental
validation
plan evolves
may be called
should be assessed
and collected
flows
collaborative
new experiments
an emphasis
It is important
to relevant
The general importance
and then for more for transport
Effects on Separation
Effectiveness
more fully below.
11
general
aircraft are:
vehicle
of the modeling types.
The
of turbulence
key engineering
3.1.1. increased
Reynolds
performance
Transonic
wings
conditions.
number
is tied to designs
are
typically
increase
order of 1.3.
Correspondingly
at transonic maximum
Many
at the shock.
discrepancies
times,
between
testing
pitching
C).
(see
Appendix
pronounced
break
comparison
to the flight test results
Johnson-King
change
moment
increment)
that wing-body
at angles
gradient
k-omega
however,
are quite good. Reynolds
problems,
number
typified
and shock-induced
separations.
in effectiveness
design tradeoffs
than can be made at lower Reynolds
testing
because
spanwise
Reynolds
number
were cited for the MD-11
3.1.3. involved
confluent
wing.
boundary
flows.
three-component
are sensitive
reliance
Separation high-lift
effects
outboard
aileron
tuff observations
Reynolds
number
to Reynolds off-body
on experiments
prediction
number
effects,
separation,
comer/juncture
is necessary,
Chines/strakes
challenge
12
in
and
number
effect
this effect limits the facilities.
with significant
wing,
whereas
spanwise
cited an favorable
component
of
in 2-D. of the many leading
and strake/chine
conditions,
create vortices,-which
flow physics
edge
separations,
flows.
of the lack of confidence
driver at approach
on the nacelle
intersections)
of Boeing-retired
greater
trailing flows,
largely because
to
is made on ground-based
F. Lynch
because
are not
important
Reynolds
on the DC-10
including
especially
is in 3-D applications
a significantly
the
of 3-D separated
ground-based
effects have not been encountered
on the flap is the most important configurations.
also
heavy reliance
effectiveness
indicated
are
with these flows;
For example,
results;
flow with both
that modeling
in transonic
deficiency
occur.
This area is the ultimate
layers and wakes,
area where extensive separated
The adverse
3-D high-lift. that
wing;
The biggest
model
of separated
is an adverse
associated
of Boeing-
with the trend from
(wing-nacelle-pylon
there
loss of lift in
for the full configuration
agreement
(~6 million)
agreed
at this
a much more
F. Lynch
turbulence
comparisons
This is an area in which
number
effect as regards
increase)
numbers
in CFD.
Reynolds
In general,
number
effectiveness.
of the lack of confidence
flow on the DC-10
issues
surface
flow for which adverse
adverse effects
Control
with a Reynolds
model
of the
of Boeing
and CFD show
(SST)
regions
the
either by high Reynolds
with a consequent
on separation
by juncture/comer
number
to be the root cause
generated
and, thus, results
effects
forward,
of separation;
and M. Anderson
transport
is general
moves
on the
to Reynolds
flight buffet onset.
since some
There
separation
by some
with the Johnson-King
to full configurations
Mach numbers
from the trailing edge reaches the
edge separation,
shear-stress
at cruise
aft, with a corresponding
occurs at the onset
both wind tunnel
of attack near the observed
(i.e., a decrease
3.1.2.
slope
of NASA
airframe,
section
and quite sensitive
is believed
by A. Kumar
is not universal,
experiments
integration
pressure
number
on the MD-11
has not been extended
area of uncertainty.
airframe-propulsion
edge
since
angles of attack.
an aft-loaded
occurs at shock
the trailing
performance,
or higher
moves
occurs as the separation
at the onset of trailing
calculations
The MD-I 1 experience
is a major
downstream
is increased,
with the MD-11
from the SA and Menter's
model
and
the shock position
in lift curve
to Reynolds
presentations
For example,
flight test and ground-based
adverse
of attack
a definite
in the lift curve slope
flight and differed
cruise,
position
the lift levels at buffet onset in flight with the lift levels
or computation
observed
shock
for cruise
Mach numbers
These two effects are compensatory
This sensitivity
workshop,
flows
a mid-chord beyond
as the angle
lift (and a positive
separation
available.
with
is important
to higher
bubble with reattachrnent
in lift coefficient.
speeds.
This area
that delay separation
designed
in lift; a separation
leading to a decrease
retired
on separation.
As the angle of attack is increased
nonlinear
number
effects
especially interact
This is an
in predicting for advanced beneficially
with the uppersurfaceviscousflow to controlseparation at high-liftconditions; thesedevicesaregenerally !
determined
through
nacelle-pylon
vehicles,
cut-and-try
integration
the basis
variations
are the most important
The key engineering
prediction
etc.) are summarized
as follows:
needs
•
Vortex Flow Breakdown
•
Buffet
•
Active Flow Control
•
Store Separation
•
Manuever-induced
•
Jet Impingement
and Ground
•
Ducts (including
Unsteady
•
Cavities
•
Rotor Blades
•
High Lift
•
Transitional Flows
•
High Freestream Turbulence
•
Wake Interactions
•
Shock Boundary
•
Wall Heating
Unsteadiness
for multiple
vehicle
the maximum
chines
and the wing-
lift.
types (i.e., military,
rotorcraft,
reusable
(Time Lags and Hysteresis)
Layer Interactions
(Heat Transfer)
these areas
in detail.
to classify existing
cut across
onset, progression, crossflows, encountered
surface),
and shock-induced
vehicle
experiments
number,
needs
list is below.
can be translated These
for new key experiments
including
(backward-facing Topologies
prediction
A partial
and shock strength
are geometry-driven separations.
lines.
or advocate
and reattachment,
Reynolds
typically
The above engineering
pressure
The three types of separation
steps), adverse
of open and closed
•
Transient
evolution
of transonic
separated
flows, including
number,
shock variations,
and corner/juncture
flows
Vortical
flows, especially
vortex breakdown,
including
breakdown,
and the impact
of unit Reynolds
numbers
13
control
stability
pressure
separation
surface
drivers
form
to be conducted.
a range of onset conditions, variations.
into a
issues could
gradient
(smooth
should be
considered. •
launch
Helicopters)
for a framework
gradients,
to determining
These
Separation)
issues, which
Separation
drivers
and flight tests.
Interactions
set of flow physics
•
in ground-based
and Interactions
(Turbomachinery,
We do not discuss general
parameter
deflections,
for different
Reynolds
modes
of
Passive andactiveflowcontroldevices, suchasvortexgenerators andzeromass flow(synthetic) jets, including detailed dataforturbulence modelenhancements andthedevelopment ofglobal,ratherthan local,models •
Mixinglayers, including merging boundary layers andwakes fromthemainelement, flap,andslat, withadverse pressure gradient andReynolds number effects
•
Curvature effects, especially recovery from
curvature
•
Transition
trip and roughness
prediction
and control,
including
tunnel to flight and for lower Reynolds 3.2.
Assessment
calculations process
involve
(i.e.,
calculation. various
a multitude
numerical
R. Cosner
of Boeing
cited
have a significant
ground-based
lift curve slope at transonic
Reynolds showed
number
and the turbulence
much
more
CFD
gave
experience
satisfactorily results
closures
flow.
in applications
situations additions
models
there is growing
to baseline
efforts
give quite similar
showed
success
of the
of the interaction
of the
through
flight tests;
was addressed abrupt
tests before
change
flight.
The phenomena
with in the
However,
turned
it
out to be
of the lift loss that the wind tunnels
doubling
the entire
during
The problem
numbers.
of the overall
the
the problem--an
only a fraction
However,
the grid produced the program
wing
drop
are often blamed
no
confidence
experimental
models
(k-epsilon
turbulent
with the EASM
defmitive
results
managers
phenomena.
in practice
layers.
and elsewhere,
less expensive
that agreed
indicated This
for insufficient
predicts
Studies
that
particular resolution
assessment in the ability exists.
maximum
of the turbulence of Reynolds
for M=5. The results in both the length
14
that the EASM
sidewall model
stress
systematic
conducted
of separation
boundary
and either
this may be
layer
to be applicable comparisons
increase
and the variation
SA or
should
be
for this particular
by A. Johansson
show a quantum
of second
and validation
although
capabilities
models
As an example,
have been recently
development
lift very closely,
the
capability
such as SA or SST for many
high-lift
have shown
to simulate
the current
models
two-dimensional
and NASA
Neither
or k-omega)
additions,
extensive
by Boeing
information
separations
at this workshop
than the simpler,
results.
boundary
to make a more
for which
methods
Reynolds
inadequacies
For instance,
cooperative
of sidewall
series of shock-induced baseline
model
are no better
predictions.
through
in order
However,
turbulence
accuracies
determines
and cost.
At the end of the study,
as noted in the talks presented
to the influence
completed
tunnel
that
noted in wind tunnel
at flight
it is clear the
link in the elements
as an example
that caused
of wind
computations.
conducted
SST turbulence due
wind
needs,
schedules
lift--was
tests.
prediction
that was only uncovered
The anomaly
was the chief suspect.
(UAV)
difficulty
on program
disappear
modeling)
drop phenomena
control
maximum
with ground-based
of the key engineering studies
model
is not uncommon;
In general, moment
turbulence
Initial CFD computations
to within
of three-dimensional
before
that would
insensitive.
impact
and flight tests.
speeds
to be a problem
is a flight
negative
experiments,
method,
for correlation
air vehicles
of vehicle
and it is often the weakest
the F-18 wing
The wing drop problem
such as uninhabited
From the standpoint
of fluid interactions
modeling,
elements.
was judged
Methods.
geometry
such surprises CFD,
of Current
vehicles,
calculations
to general of EASM
of KTH [4] for a
of accuracy
over the
of separation
with
shockstrength.Inthesecomputations, muchof theimproved resultis attributed to improvements inthenearwall asymptotic behavior gainedthroughEASM.Thecomment wasmadethattheseflowscouldalsoprobablybe accurately computed withtheSSTor SAmodels, in whichcasetheimprovement is attributed tothevariable eddy viscosity coefficient termratherthanthenonlinear terms.Additionalexamples werecitedof engineers atEuropean carcompanies routinely usingEASM-type models in calculations usingtensof millionsofgridpointswithnotable improvements overlineareddyviscosity models (LEVM)forseparated flows. Asencouraging astheresultsusingthesesecond-moment closure methods havebeen,thepossibility was discussed to circumvent theEASMclassof modelsin favorof goingdirectlyto theRSMclass.However, the numerical difficultieswereconsidered sogreatwiththisclassthattheEASMapproach shouldnotbe bypassed, since EASM allows many additional Until recently systematic tests, which
intended
such as pressures,
to be representative
that involved can
for turbulence
supply
development
of a limited
more detailed global
measurements
or local
or simpler
information
method and the Johnson-King benchmark
In this respect, development
of specific
of flow physics
model.
models.
models,
since most of the modeling
of these methods;
to hold in many
limited
are unit problem
shear stresses.
the Bradshaw
to surface
experiments, in application,
These experiments
models,
as in integral
structural
coefficient
method
of the ratio
flows and is used by the lag entrainment
experiments
can be quite expensive
to conduct,
integral but serve
models.
closure-type
the last ten years
For example,
are usually
wings,
These tests are
issues encountered
of turbulent
was through
or multi-element
of methods.
type
or turbulent
to the development
These unit problem
tests of turbulence
profiles
models
The ftrst are application
such as wing-bodies
The second
has been observed
For the second-moment verification/assessment,
useful
categories.
and oil flows. types
formulations.
turbulence
since the measurements
such as velocity
half- or one-equation
of shear stress to kinetic energy
as definitive
number
numerical
for the acceptance/verification
development,
skin friction,
fall into two
configurations,
as a basis
model
easily into current
the only way to assess
experiments
aerospace
engineer
rather
simulations,
These
of specific
to the practicing
not appropriate
measurements,
of direct
with experiments.
measurements
are useful
generally
with the advent
comparisons
involving
effects to be included
have seen
experiments
not used
is done for homogeneous
an increased
this trend should
are
increase
usage
flows
of information
proportionally
for development, or low Reynolds from
direct
to the computational
but only number
simulations capability
for
flows. in the
available
for direct simulations. The turbulence limitations
modeling
issues are listed
below
followed
in these areas. •
Separation
and Post-separation
•
3-D Effects
•
Unsteadiness
•
Length-scale
•
Role of Curvature
Equation
15
by a discussion
of the current
capabilities
and
•
Reynolds
•
Vortical
3.2.1.
improve
Scaling
Flows
Separation
few two-dimensional coefficient
Number
and post-separation.
test cases available;
in the formulation, the correlation
downstream
of separation separation
including
has the effect of reducing
predicted
of the models.
reattachment
seem to do reasonably
in the models
through a variable
shear stress levels
Current
(see [5]).
models
models
Although the Bachalo
Likewise,
to be predicted
reasonably
for the backward-facing well by some models,
well for the
eddy viscosity
at separation,
do not uniformly
quite well in terms of pressures (and skin friction),
are underpredicted. seems
this has been achieved
with experiment
of separation,
flow [6] is generally
which
Many of the current
which tends to
predict the
region
and Johnson axisymmetric
burap
the shear stress levels downstream
step computations, but all models
the
overall
underpredict
extent
of
the shear stress
levels. 3.2.2. effects
3-D effects.
to make a definite
no boundary
assessment
measurements
to be a universal Thus, models However,
There is insufficient
are available
this limitation,
nearly
if it exists,
Unsteadiness.
the biconvex
airfoil
alternating
noted
Reynolds
that unsteady
at transonic
turbulence
Averaged
of the current
3.2.5. required without
Length-scale
speeds,
models.
modeling
changed
characterized
be less accurate. crossflow
effects.
with experiments
(RANS)
to date,
two-equation,
or
in flow visualizations.
This equation
deficiencies As noted
The inclusion
the character
of curvature
of the results
[9].
16
of
using
becomes
larger,
as in spoiler
there is not consensus
can be pushed.
F. Lynch
or bluff
on the extent to of Boeing-retired
with small upper surface curvatures,
on modem
afMoaded
transport
RSM
but
sections.
ad hoc, even in attached
flows and the
unknown.
at this workshop,
for EASM.
calculations
[7, 8], which show improvements
flows is currently
in the talks presented
recent
with
which
although
is viewed as quite
for separated
The general
in the time scales associated Several
of
interactions
zones
for airfoils
such as encountered
layer to chord ratios
by shock/boundary-layer
by itself
conditions
but appear to be less important
modeling.
with boundary
evident
have shown results
DES models increases,
Navier-Stokes
equation.
models,
any additional
not appreciably
would
with one-equation,
of the aircraft motion.
As the separation
to occur at transonic
Role of curvature.
for LEVM
motions
frequencies
separations,
of incorporating
flow tended
flows over airfoils
with no large-scale
that it was only a small effect for curved sections,
contribution
of calculations
do quite well when there is a large distinction
upper and lower surface
the importance
3.2.4.
Since there is thought not
based upon such an assumption
by the comparison
separated
with the reduced
of McDevitt
SA and EASM over algebraic
unsteady
is not confirmed
steady
models
and that associated
which
methods
that use wall functions either in combination
as quite
is that the current
body flows,
high aspect ratio wings,
near the trailing edge, even for attached flows.
Some transonic
the turbulence
induce
for transonic
and separation
closures.
a half were cited
consensus
For example,
upon this law would have a major limitation in flows with significant
including those of 3-D calculations
3.2.3.
data for wings with strong crossflow
various models.
3-D law of the wall behavior,
that depended
second-moment
between
experimental
additional
can handle
terms in 2-D multi-element
curvature
the effects
terms are
of curvature
high-lif_ computations
has
3.2.6. conduct
Reynolds
an experiment
the computation
number
tunnel
usually
that reproduces
to flight
is present, airframe
from establishing
Vortical
such
except
or chine/strake
vortex
3.3. Directions separated
number
scaling
In production
flow; for instance,
it is common
wind tunnel
and breakdown. is generally
for Improvement
numbers;
number,
can be
problem
is associated
testing,
the objectives
with are
to locate the trips to match
and flight. models
fail when streamwise
Even though
not a significant
vortices
vorticity
are present
driver for airframe
with the flow field, such as in vortex breakdown
with high-lift
to
for all
performance
for low aspect ratio wings
configurations.
of Turbulence
Models.
The goals
for improvement
of predictions
in
flows are listed below: •
Increased
generality
•
Naturally
good behavior
•
Curvature
corrections,
•
Improved
modeling
•
More extensive
•
Increased
To obtain of the improved
funding
more
high-lift
and to the assessment
should
be conducted
of our current
investment
of other
3.3.1.
Eddy Simulation
for prediction
should
capabilities.
government
across
agencies
models and a discussion
Improved
turbulence
in turbulence advances
through
consensus
in turbulence
models.
Pressure-strain
•
Near-wall
experiments
designed
and
Direct/ons
for improvement
Modeling
Modeling
]7
efficient
Simpler
on the basis wing designs
and cheaper
of active flow control needed
- Unsteady
canonical
needed experiments
three areas below: •
computations
are expensive
prediction
of additional
prediction.
from RANS
and carefully
to advocate
For example,
in separation
on a few
experiments
it is necessary
modeling.
improved
the spectrum
with modelers
The required
methods
along these fronts,
be tied to the validation
to get a national jointly
(DES)
modeling
through
can be attained
of capabilities
is a need
turbulence
of Detached
flow control devices
for the improvement
improvement
assessment
improved
evaluation
performance
efforts
experiments
of active and passive
cruise Mach numbers
of the modeling
There
in EASM
that is tied to the advances
Much
- DNS.
near walls especially
support
capability to higher
effective
of the formulation
role of DNS/LES
can be pushed
LES
at high Reynolds
are paramount.
rollup
it is more important
at less than flight Reynolds
is that all of the LEVM
of these vortices
strongly
interactions
consensus
of vortex
the resolution
if they interact
effects
at the shock between
A general
as in the computation
albeit
modeling,
an experiment
Most of the Reynolds
fully turbulent
thicknesses
flows.
configurations,
prediction
with confidence.
of turbulence
than to conduct
interaction,
in which transition
layer displacement
3.2.7.
turbulence
the fully turbulent
number
scaling,
quite different
the boundary
From the standpoint
with fully established
made at higher Reynolds wind
scaling.
to assess
benchmark to provide
irrefutable
modeling.
are presented of current
LES
- DES -
experiments.
and should capitalize turbulence
devices.
ongoing
RANS (URANS)
and
These
data for the
on the sizeable Directions
for
below.
turbulence
models
are in the
•
Length-scale
Equation
The pressure-strain modeling
modeling
and length-scale
are discussed
equation modeling
Pressure-strain
modeled
modeling.
term in homogeneous
of the three areas, although
3.3.1.2. integration
Near-wall
significant
approach
is to model
the equation
At separation,
this law breaks
of confidence from
a solid
to higher
appropriate
scaling
method
number
flows
should be in pressure-strain
is highly
for example,
a separated
equation
airfoil
with k-epsilon, algebraic
the length scale equation. production
terms
directly).
length-scale Advancements computations
These areas
The length
Flows in which
equation
deficiency
could
be made
or experiments
turbulent
region,
for model
stress never
energy
layer
methods
are known
do with one- and two-equation and testing
modeling
transport
DNS
validation.
is important
spectral
that
The main concern
18
with
should
theory
across
[10].
This
that this
to the dissipation
the shear
clearly
require
since RSM
be otherwise
to suggest
formed
stress
by the
is predicted is consistent
indicating
a problem
some
to EASM
accurate
however,
and
accompanied
with this area, as with all methods
in
to RSM
of the terms
approaches;
models
as
coefficient
from LEVM
RSM
uncertainty.
scales that interact,
the wake
the eddy viscosity
clearly
terms
was made
refers
length
where
as the models are changed
effects or
transfer
better
a second-moment
It is the area of greatest
epsilon to get k correct,
slightly
as to
is that the equations
The comment
equation
Thus,
of these
in other parts of the equations.
is an example
(k) is not.
high
of information
no wall damping
in the future.
with momentum
flows.
with a smooth
Extension
source
in deriving
or higher models.
mixing
be masking
using
flows
The general
for attached
simulation.
an excellent
with
The length-scale
scale model changes
may by
kinetic
terms
to provide
behavior
in the
robustness
in practice.
have been completed
in the
considerations
but one has to change
diffusion
DNS simulations velocity
difficulty
to be used with a reasonably
flows or for any flows with disparate
edge
it is the
as the most mature
as an observed
models
DNS is expected
only; one still needs damping
fluid. A simple
stress model
closure
has been made
for more complex
modeling.
trailing
but turbulent
and
progress
because
as the
in computations
of the wall, which one could
for separated
is defined
in favor of the Reynolds
to all of the two-equation
questionable
upper and lower surface
with an explicit
computed
The near-wall
attention
thus, it can be judged
such as the log-law
normal
on realizability
models
which is a key ingredient
The modeling
(i.e.,
equations.
extensive
problem
arising
behavior,
be expected
recent
based
approach
has received
of second-moment
An argument
but will be tested
Length-scale
usually
the outer
would
of KTH indicated
is preliminary
accurately
stress
the latter, pertain to most models.
modeling
and validation.
independent
approach
merging
on Reynolds
is still in question.
This is an area in which
separation.
for simple
3.3.1.3.
to usage
improvement
to be entirely
region
near-wall
based upon a known
down.
Reynolds
A. Johansson
equation,
aspect
wall by prescribing
through
be formulated
closure
This modeling
This difficulty,
limitation
for model
simulations
models.
especially
The
to the wall.
is the most
could
based
difficulties,
in the near-wall
modeling.
of the equations
separation
to models
flows and can be studied in detail;
the modeling
problem,
degree
pertains
below.
3.3.1.1. principal
Modeling
are the
computable. by
LES
based on
DNSor LES,is thescalingof theresultsto flightReynolds numberassociated with flightvehicles, sincethese simulations will notbepractical formanyyears. 3.3.2.Needed experiments. Theneedof measurements in unitproblems wasdiscussed atlength.These unit problems
are used to demonstrate
post-separation that
are
regions.
There
not plagued
axisymmetric
by
three-dimensional
to simulate
with Navier-Stokes
inverse
techniques
to determine
axisymmetric
These
experiment
is characterized
shock
experiments
to include (through
addition
enough
in complexity
at lower Reynolds There datasets.
used
were no specific
numbers
is available.
high-lift
validation,
The NASA
Adaptive
discretization specified
computations determining
trapezoidal
Bachalo
and
by Rumsey
and Gatski
using
[13]. Two-
since there is less influence
flows, and the data collection
It could
Johnson
but could be computed
axisymmetric
using
to induce
controlled
for example).
experiment;
moves
be expanded
upstream
current
this to the
CFD design
three-dimensional
The experiment
DNS and, thus, serve as a validation
of 3-
is easier than a
bump
in which the separation
generator,
would
be simple
case for such approaches
of a given turbulence
the accuracy
complex
flow applications
physical
error embodied
rigging
to serve
at transonic
flows with strong
integrations
of the high-lift
as definitive
speeds
test case is viewed
zonal
turbulence
benchmark
at reasonable
3-D effects
encountered
Reynolds
at high Reynolds
as a step along
configuration
would
the way for 3-D
on realistic
and small
be quite
useful.
equations
being pursued.
Also,
Establishment Methods
airframes.
adjustments
in the solution
separated
can
number,
of a basis to determine
guidelines/standards
there
seems
of a given set of turbulence
19
for adapting
to ensure
[3] referenced
above.
as
turbulence
knowledge
of
the capability
associated
with the
the grids to attain a
sufficiently
accurate
3-D
However,
capabilities
for
Moreover,
for
are just in their infancy.
to be nothing models.
the error
models
purpose
there is no a priori
to determine
flow computations
turbulence
the lack of a general
and use that as a basis
as noted in the recent ERCOFTAC
at high Reynolds
various
are not widely used largely because
differential
of complex-geometry
models)---using
way to circumvent
model in a given situation.
in a calculation
are now emerging,
high-wing,
a possible
Such techniques
are now
information
of nacelle-pylon-chine
(also called
to the local physics--are
tolerance
for 3-D experiments
flow interactions.
models
to all flows.
layer
wing,
to the component
of a given set of partial
error
used
Johnson
or shear stress data for transonic
intended
turbulence
they are appropriate
model
conditions,
or modified
proposed
boundary
but lacks the key element
or mask certain
of a given
models.
separation
by LES and/or
recommendations
no velocity
the flow is quite sensitive
the capabilities
different layer
and
for flow separation
[12]. The latter two flows are very
as unit problems
experiment
suction, or a vortex
arise in measuring
In this regard,
model applicable
as that
the
such as in
number.
Difficulties
accentuate
such
the Bachalo
separation
boundary
of sweep,
shape,
models,
models
include
flow of Simpson of boundary
of current
turbulence
These
layers and secondary
upon
to compare
to be computed
numbers.
Also,
boundary
could build
shock-induced
effects
effects.
because
wall
deficiencies
to assess
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TURBULENCE A NASA
MODELING: PERSPECTIVE
T. B. Computational
Gatski
Modeling
NASA
Langley
Hampton,
Turbulence
_z Simulation Research
VA
23681,
Modeling
January 1213, Reno, Nevada
107
Center USA
Workshop 2000
Branch
OBJECTIVE • Identify' deficiencies
in predictive
• Develop improved/new
capabilities
models
• Capable
of more accurate
predictions
of flows currently
, Capable
of solving more complex flows which become of interest APPROACH
Model
Development
(DNS/LES)
Appl
108
of interest
HIERARCHY
OF SOLUTION
METHODS
Ij Direct Numerical Simulation I Computer Numerical Capacity Issues/ II
I
I
I ] I I INumerio_,,_sue_ I I_O'_O'NT_LOSU_ESi iS'"OL_-PO'"T_LOS I I I
I Large-Eddy Simulation I
I lSubGrid Scalel Models I
I
Reynolds-Averaged
Navier-Stokes
I
I Analytic Theories [Stochastic Models I
I Second Moment .II Closures
I
' I.
I Numericallssues I gmD==.=9 I
I Two-Equation Models
r/lAIgebraicStressl 1 Models
I One-Equation Models
I
I
I
I Zero-Equation Half-Equation
• RANS
approach
turbulent • RANS
formulations
appear
that
RANS
the turbulent • A separate
moment require
issues
for calculating
to the closure
are derived,
problem
higher-order
moments
closure level of sophistication
used
in developing
varies widely
related
issue is the numerical
needed
in RANS
associated
with
RAN S equations
methodology
susceptible
equations
framework,
though
common
flow fields
inherently
closures
set of equations • CFD
most
(aerodynamic)
• As statistical
• Within
currently
Modelsl Models I
depend
solution
of the closed
formulation accuracy
on closure
109
and etticiency level
of solution
of
TURBULENCE • Single-point
MODELING
FOCUS
(space and time) correlations
, Linear eddy viscosity model (LEVM) • Nonlinear
eddy viscosity model (NLEVM)
§ Algebraic
stress model (E)ASM
, Second moment § Reynolds
closure (SMC)
stress model (RSM) SINGLE-POINT
CLOSURES
COST, COMPLEXITY
f
REYNOLDS STRESS
ALGEBRAIC
STRESS
I
SOLUTION OF TENSORIAL EQUATION
FORMAL
NON-LINEAR EDDY T" GENERAL EXPRE_tON LINEAR
VISCOSITY
_
EXPLICIT
ALGEBRAIC
STRESS
EDDY-VISCOSITY "PHYSICS';
• Closure model development • Mean variable
focused in incompressible
density extensions
, Role of compressible , Direct numerical
"DYNAMIC
used mainly
correlations
simulation
regime
in compressible
flows
uncertain
of supersonic
110
RANGE"
flow (Ames, Langley)
LINEAR
EDDY
• The momentum
equation
VISCOSITY is
P D----(: • Turbulent
closure
model
MODELS
Oxi
t- Oxj
is taken
as
(# + #t) cgxj]
2 -fiTij =
bij
* #t is the turbulent , _- is a turbulent * bij
absorbed • Coupling
-ij
3
viscosity
time scale stress
anisotropy
to the kinetic
into the pressure
between
5ij _ -C. -Sij
-- 2K
eddy
is the Reynolds
, Term proportional
--_--fi K S ij -- 2 lzt S ij
term
tensor
energy for
mean flow and turbulence
111
K is (formally)
is through
#t
TWO-EQUATION • Many two-equation • K-
MODEL
models
c model
• K - _ model • Shear
Stress
Transport
model (Ames)
, More .......... ONE-EQUATION • Transport • Popular
equation
for the turbulent
among industrial
atively inexpensive
MODEL eddy viscosity
users due to its ease of implementation,
rel-
cost, and good performance HALF-EQUATION
MODEL
• Outer eddy viscosity is modified to account for the effect of streamwise evolution of the flow on the turbulence • Ordinary evolution
differential
equation
of tile maximum
ZERO-EQUATION • Based on Prandtl's • Isotropic
is solved for the streamwise
shear stress (Ames) (ALGEBRAIC)
(1925) mixing length theory
eddy viscosity
112
MODEL
LIMITATIONS • LEVM
AND
are a proven
• Inherent
tool in turbulent
in the formulation
§ Isotropy
direct
of Boussinesq
• Consequence Insensitivity Need
secondary
(ASMs)
rate
tensor
be fixed in a rigorous models extend
the Boussinesq
and EASM
§ Any other (lower) could be connected
(NLEVMs)
the range
in ducts
Wij
manner andtheir
Tij
=
Tij(Sij,
for the characteristic
formulations
based
subset
algebraic
of LEVMs T)
with
turbulent
on a two-equation
closure (zero-, half-, one-, to a NLEVM or ASM.
113
SiN
effects
of applicability
approximation
equations
motions
on (frame-indifferent)
to noninertial
on rotation
eddy viscosity
assumes
of the models
of turbulence
cannot
which
TiN and Sij
of sole dependence
• Need for transport • NLEVM
deficiencies
of turbulent
indifference
dependence
• Such defects
• Replace
LEVMs
predictions
approximation
between
prediction
§ Material-frame
models
flow-field
are several
proportionality
• Precludes
stress
TO
of the eddy viscosity
• Consequence
• Nonlinear
ALTERNATIVES
scales closure
or two-equation)
7
NONLINEAR ALGEBRAIC • Class
of nonlinear
tensor
eddy
representation
EDDY VISCOSITY/ STRESS MODELS viscosity
in terms
models
coefficients
• For general
Reynolds
can be either through
through
a modified P D_i Dt
, $ represents tion • Generally
basis,
to
N finite
need to be determined
representations,
the direct
coupling
to mean
use of Tij in momentum
flow
equation
or
form given by Op Oxi
-
nonlinear
assumed
which
stress
one-term
+
N) is a given tensor
I expansion
the
N
= Of n
extend
of Sij used in LEVMs
2
* T/__) (n = 1...
that
O[ L(# + #t) OxjJ O_i] + $ t Oxj
(source)
in developing
terms
closures
from the
tensor
for Reynolds
, Functional
dependency
on the characteristic
, Functional
dependency
on the mean velocity
turbulent
representa-
stresses scales
gradient
b_ = b_j(Sk_,W_t,_-) • Tensor
representations
basis also assumed
114
to be functions
of S and W
• For b(S, W, _-) this basis consists T (_) = S
T(6)
T (2) = SWWS T(3) _ S 2 - 5{S 1 2 }I T (4) = W 2 1 a{W2}I T (5) = WS 2 - S2W • Nonlinear
eddy viscosity
• Expansion
coefficients
§ Calibrations
algebraic
• Expansion
T (7) =
W2S
+ SW
2
WSW
2 --
W2SW
{SW2}i
T(9) = W2S 2 + S2W 2 2 {S2W2}i 3 T (lo) = WS2W 2 _ W2S2W. models
(NLEVMs)
determined
from or numerical
data
constraints
stress models (EASMs) derived
consistent
from the full differential
with the results of tensor RSM
• In both models • Explicit
23
T (s) = SWS 2 - S2WS
consistency
coefficients
representations
_--
with experimental
§ Some physical • Explicit
of the elements
tensor representation
for b is obtained
§ Subset of full representation
basis
115
SOME • Quadratic
NLEVM
EXAMPLES
(Glenn)
• RDT (rapid distortion
theory) result for rapidly rotating
turbulence
(no shear) used • c_i coefficients
determined
the cases of axisymmetric • Coet_cients optimized ical simulation • Quadratic
by applying expansion
realizability
constraints
and contraction
by comparison
with experiment
and numer-
EASM (Langley)
• Extracted model • Enhancements • Rotational
form from RSM with SSG pressure-strain
to improve and curvature
• Wall proximity
predictive
capability
effects (CTR, Langley)
effects (CTR, Langley)
116
to
rate correlation
10
LIMITATIONS
AND
• NLEVM/EASMs • Inherent
ALTERNATIVES
are now being
in the formulation
• Weak
equilibrium
• Assumed • Such defects
can be addressed
in a rigorous
assumed
• Close linkage
between
• Directly
incorporate
and anisotropic
property
models
dissipation
not all features
effects
deficiencies
diffusion
manner
with
of formulation transport
EASMs (Langley)
strain
stress
equations
rate correlation
rate of differential stress
components
only partially
117
SMC
taken
model
model
and the Reynolds
for the pressure
effects of individual transport
applications
and viscous
form for turbulent the (E)ASMs
NLEVM/EASMs
= O)
transport
, Modifying
, Turbulent
(Dbij/Dt
form of turbulent
frame-invariance
, Relaxation
in many
are two (possible)
assumption
• Improving
• Unfortunately
used
TO
retained precluded into account
11
SECOND • Reynolds
stress
, Structure
model
based
• Calibrations • Applied
MOMENT
CLOSURES
(RSM)
models
extensively
most
common
account
based
!
--
SMC at this
for dimensionality
on homogeneous
to inhomogeneous
time
of turbulence
flows
flows
Incompressible • Tij
(SMCs)
Flow
!
UiU j --
Pij
f_ij
+
Hij
+
O_y
Dij
-
cij
0_
= --TikOx k
_-Jkox k
0 Dij
=
UjU k
OXk
-1-
nt-
•
,(CrikUj
turbulent-transport
eij
--
_e(_ij
• Development
-'1- 2edij
of improved
§ Pressure-strain § Anisotropic § Turbulent
-
rate
closure
correlation
dissipation transport
§ Wall proximity
• -_'kOxk
effects
rate term
viscous _tiffusion
+ cr}k
models
118
_
_
(Langley)
2z,,
for
(Langley,
(Langley)
(CTR)
nt- 6rjkUi!
Glenn)
OzkOxk
12
Compressible II II
" fi_-ij = pui uj (Favre
Flow
variables)
-DT-ij
--
P Dt
P_:)ij
-t-
pHij
q-
flDij
-
O_j -#['gj = --prik oXk
P_-ij
-Jr pMij
O_i -_7jkOzk
_,Ozj + Oxi 2 p, OU'_
-
3
_z_
5ij 7
II
II
If
!
I
I
!
l
turbulent
transport
viscous
2 -ficij
2_-fieSij + 2-fiedij
-pMg5= put • Development • Dilatation • Pressure
of improved
_
Oxj
closure
dissipation dilatation
• Mass flux model • Wall proximity
l.,g-
o jk Oxk
effects
119
I
l
y
models
for
diffusion
13
SUMMARY
OF
CURRENT
Theoretical • Half;equation
coordinate
for SST model , Extend
range
regime
(Glenn,
• Improve • Improve
dependence
of applicability
algebraic
sensitivity
• Structure • Length-scale • Generalized
properties
models
of current terms
wall proximity modeling
equation
of model
function"
to transition
terms
(CTR, (Langley)
(Langley)
effects
(CTR)
(Ames)
(Glenn)
120
analysis
flows (Ames) CTR)
(Langley)
RSM closures
from multi-point
wall functions
(Langley,
and curvature
for compressible
modeling
function
"switching
and free shear
formulations
to rotation
to account
transport
in APG
stress
• Improve
• Turbulent
in required
of turbulence
capability
frame-invariance
• Some selective
improvements
Langley)
• Improve
• Formulate
model
(Ames)
predictive
explicit
• Improve
Approaches
and two-equation
• Eliminate
ACTIVITIES
(Glenn)
Langley)
14
SUMMARY
OF
CURRENT
ACTIVITIES
Applications • Variety
of aerodynamic
• High-lift
flows
flow field prediction
• Transonic
buffet
• Trap-wing
onset
vortex
• Variety
flowpath
of separated
• Flows
in pressure
(Ames,
Langley)
wing
analysis
(Glenn,
Langley)
flow studies
of unit problems
• Wakes
Langley)
(Langley)
flow over delta
• Ramjet/scramjet • Variety
analysis
CFD validation
• Transonic
(Ames,
(Ames,
Langley)
gradient
with curvature
• Deficiencies
in model
performance
cycled
back
into
improved
model
development Other • Multi-scale
turbulence
• Non-equilibrium • Dynamic
RANS
Modeling
Areas
models
effects
zonal modeling
• Linkage • Heat transfer
between
LES and non-stationary
and reacting
flow modeling
121
RANS-type
closures
_,_,
2_ j / /'
STANFORD Thermosciences Stanford,
ICASE/LaRC
Division,
Reynolds
modeling
Modeling
Number
Peter
M.E.
Dept
CA 94305-3030
Turbulence
Turbulence High
UNIVERSITY
for
Separated
Bradshaw
bra dsh aw_vk.sta 12 Jan.
nford .ed u 2001
(no oral presentation)
1 122
workshop
Flows
MY
• (I)
Virtually
models)
TAKE
ON
SEPARATED
all Reynolds-averaged
are calibrated
in flows
FLOWS-I
turbulence
dominated
models
(or SGS
by shear layers (in suit-
able axes) • (II) (i.e. • (III)
There
is no guarantee
that
reliable in flows very different (important
any model will be "universal" from those used for calibration)
parts of) Separated
flows are not dominated
by
shear layers • (IV)
Therefore
in separated
Reynolds-averaged
flows.
Ever.
2 123
models cannot
be guaranteed
MY
• The problem • (A)
TAKE
ON
of predicting
predicting
SEPARATED
separated
the separation
line*
FLOWS-II
flows has two parts:with
a more-or-less
given
region with
a more-or-less
given
pressure distribution • (B) predicting separation line
the separated
•.. "more or less" because there is strong upstream initial
tests of a model
influence
could and should be divided
into (A)
- but and
(B) * "line"
not "point":
all real-life separated flows are three-dimensional,
some with very strong streamwise
124
vorticity
TEST
CASES
FOR
• Predicting reversed-flow still a useful test... ...because
• The
by a low-Re
largely-neglected
severe test far from
skin friction
it goes as Re -°'5
be reproduced
of models
"still air".
SEPARATED
FLOWS
in the 2D backstep
approx.
(0.5 _ 1/2)
(wall-layer)
model
flow
over a cone
for the separated
(Calvert,
JFM
flow is
and this should
at zero incidence
region
because that
21, 273 (1967):
probably
is a is so only
the base pressure is reliable). • In both these cases separation are several aration
"boat
from
tail"
a smooth
test
is forced
cases (mainly
surface,
generally
regions.
4 125
at a sharp edge. There axisymmetric) with
small
with sepseparation
WHY
...because,
of course,
MODEL
we are too cheap to solve the exact equa-
tions like the structures •
"Turbulence
.lack Nielsen • Stan
people do
modeling
is the
pacing
item of CFD"
- the late
and many others
Birch of Boeing
power, not turbulence • Rightly models
TURBULENCE?
or wrongly,
said -
"what
limits
you is computing
models" industrial
users stick with
5 126
eddy-viscosity
"BEST
• Correct
BUY"
-
- remembering
WHAT
that even testing
be limited by available/affordable • There
I HAVE
NOW
of existing models can
computing
is an urge to say "if my model does thin
my pet N-S case (even the backstep) • Large eddy simulation eddies which
just
do not carry
• But near a solid surface
it must
shear layers and
be OK".
models the smallest
(sub-grid-scale)
much stress or momentum all eddies are small
6 127
EDDY
"Glushko intensity
that
uses the TKE q2
and
the eddy
( Reynolds • Therefore
only to calculate highly
the
the turbulent
questionable
_T is given by (_)]/2L/_T
assumption
=
constant"
28, 593 (1967)
was implementing
• Eddy viscosity a turbulence
equation
makes
viscosity
PB et al. JFM ...(Glushko
then
VISCOSITY-I
Prandtl-Wieghardt
is easy to define
quantity
to a mean-flow
stress)/(Mean it should
(and
strain
measure).
(1945)) It is the ratio of
quantity,
rate)
not be treated
(like TKE say)
7 128
as a pure turbulence
quantity
EDDY
• It may be better
VISCOSITY-II
behaved / easier to correlate
than
Reynolds
stress - but no guarantees • In self-similar (e.g.
flows with one velocity
vr and 5) eddy viscosity
(and in slowly-changing
flows
scale and one length
scale
must scale as
near a solid surface
f(y/5)
= _y/5
SO vt = _;ury) • In such flows,
(production
/ dissipation)
solid surface g = 1
8 129
= g(y/5
and near a
UNSTEADINESS
-
• Reynolds averaging does not and cannot unsteadiness and turbulence •
Neither
can any other
sort of averaging
ness is periodic or otherwise structured frequency,
or wavelength,
AND
I
distinguish
between
unless the unsteadioccupies a different
range from the turbulence.
• Unsteadiness in a separated flow can very sensitive to boundary, or initial, conditions. • This makes me pessimistic averaged models in separated
about flow...
9 13o
the reliability
of (Reynolds-)
UNSTEADINESS - II ...and
of course we often
estimate
structural
want
are ill-posed problems, Better-posed
DNS,
predict
the
buffeting or low-frequency
• Flows which are very sensitive
•
to
to boundary
unsteadiness,
to
noise or initial
conditions
and there's an end of it!
problems
need 3D time-dependent
simulations,
LES, DES or whatever
• DES, fed by a Reynolds-averaged
model
only if the boundary layers at separation of the turbulence don't matter
10 131
is likely to be reliable are so thin that
details
MY
• (1) Direct
TAKE
ON
effects of viscosity on Reynolds
flow are small for u_y/v time.
N _ 200 at lit
• (2)
However,
mension fraction
much of the
Re, leading • (3)
and KTH
than
intermittent
to "direct
via d_/dx
"high"
wisdom is that
(at
the surface of the greater
Re, (1)
NUMBER
stress in fu//y-turbulent
< N where N is a function
of space and
present!). "viscous
superlayer"
2 and its volume outer
has a di-
occupies a large
layer at low (i.e.
laboratory)
viscous effects".
Indirect effects of viscosity
ary layers) • At
REYNOLDS
can enter (e.g. flat-plate
bound-
or du_-/dx and (2)
are not a concern.
neither is (3)...
11 132
The
received
MY
TWO
• The bare-bones
CENTS
ON
derivation
THE
LOG
LAW-I.,.
of the log law, due to Landau,
is that
if u = f(u_, y, ") then
du
Ury
dy ...
and we expect f -_ i/_
• Obviously the "if"
a necessary,
y
-7-)
(say) as its argument but
maybe
tends to infinity.
not sufficient,
condition
for
to be true is y plane Pols.+ine f1_w, Thoma. 180. ForMldJUcoLlJymlx_e
L
J
I
i
l
I
I
I
I
J
I
!
J
I
|
_
i
J
vldueof_/_
Z. FZpm frun F=zd_is &
i
i
i
i
J
i_
j l pmse_l_
(u'rms}_
3
0 0
0
3
•
O0
•
o : _oo::,,=0,:..°._1_. .•=
, •
0
0
O
• .'
lowdec
_.3t. _60
leej_
|4,
o 1-10 • 11-20 o 21 - 30 • 31 - 66
,.
L.igrr,i L Bradshaw I151tW)
• a
102
Figure
20:
]
J
J
t
I
_
(
_
103
TSe iait1_eo
ofi + and ]_y_dds
I
I
_
I
l
Reiz
numberon
i
I
I
t
J
t
I
_
10 &
the maximum
vadue of _/u.,..
178
i
_
I
10
_
from 13
LASER
DOPPLER
VELOCIMETRY
Advantages: • •
Linear
frequency
- velocity
Miniature
3-velocity-compponent
uncertainties
of each velocity
•
Fine spatial
30im spherical •
Doppler
resolution
measurement
Rate of strain,
volume
vorticity,
relationship
probes
with low
component measurements within
dissipation
-
30im of wall
measurements
possible
Disadvantages: • •
Low data
Flow
•
Probe
required
rate - 103 to 10 4 coincident •
•
seeding
Setup
Single
restricted
179
per sec.
point data
and data acquisition
hardware
signals
time
to model
interior
o=
180
t
=
G
m
"0 .ira
G
m
0 0
oR
o
E 0
E m
0
_u
w
w
181
182
I
I
I
I
I
TABLE 3. 20:1 odds +2o" uncertainties of means velocities, Reynolds' stresses and triple products. I
I II
Term
I
Uncertainty I
II
II
I
I
I
I!
Term
0.033
0.082
_lU
s.
0.04
0.07 0.025
0.144
0.051
0.097
0.062
U-'_l U.3.
0.055
_W"Z/U_
0.165
_-_/U_
0.053
uvw/
0.05
0.037
0.254
0.019
0.043
0.424 i na
183
|
Uncertainty
I
0.148
u/u,
I
0
p_
ib
0
0
0
°_-
]84
185
3O
t.
2O
100
2 3
101
2 3
102
2 3
Re, = z s, ooo, U/
u,
mean veloc41typrofiled" in tunnel coordinates.
2
W/
u,
mean velocity profiles in tunnel coordinates.
M;_ffo_,s I- ¥ rh,_/o_s s'- 9
186
# PI#_ :"o 0 p/=le < o
4
Receiving
optics for &UI_,
AU/Ay,
AUI_
._
_--_\
Transparent wall
\\
........
,
'_-
-z// / bo/u,. ,_ a.j Receiviug
_
for fur AVIAx, AV/&y,
AVIAz
Figure 1. Schemtic of AU and AV inddemt and receiving optics for ROSVOR LDV. AW incident and receiving optics same as arrangement for AU, but lying in the YZ plane.
187
i
PARTICLE
IMAGE
VELOCIMETRY
Advantages: • •
Faster
Global
measurements
data acquisition
time for one plane
Disadvantages: • • •
Higher
Setup
Only
(out of plane
Flow
seeding
required
and data processing
planar
data
data with much
time
with lower uncertainties higher
uncertainties)
uncertainties
for u', v' than hot-wire
much
higher
triple
product
Multiple
fields
of view required
188
and LDV;
uncertainties to resolve
various
scales
REPORT
DOCUMENTATION
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Report 5. FUNDING
NUMBERS
ModeLing Workshop C NAS1-97046 WU 505-90-52-01
6. AUTHOR(S) Edited by R. Rubinstein,
7. PERFORMING
C.L. Rumsey, M.D. Salas, J.L. Thomas
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NAME(S)
AND ADDRESS(ES)
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NOTES
Langley Technical Final Report 12a.
Report
Monitor:
Dennis M. Bushnell
DISTRIBUTION/AVAILABILITY
STATEMENT
12b.
DISTRIBUTION
CODE
Unclassified-Unlimited Subject Category 34 Distribution: Nonstandard Availability: 13. ABSTRACT
NASA-CASI
(Maximum
(301) 621-0390
200 words)
Advances in turbulence modeling are needed in order to calculate high Reynolds number flows near the onset of separation and beyond. To this end, the participants in this workshop made the following recommendations. (1) A national/international database and standards for turbulence modeling assessment should be established. Existing experimental data sets should be reviewed and categorized. Advantage should be taken of other efforts already underway, such as that of the European Research Community on Flow, Turbulence, and Combustion (ERCOFTAC) consortium. Carefully selected "unit" experiments will be needed, as well as advances in instrumentation, to fill the gaps in existing datasets. A high priority should be given to document existing turbulence model capabilities in a standard form, including numerical implementation issues such as grid quality and resolution. (2) NASA should support long-term research on Algebraic Stress Models and Reynolds Stress Models. The emphasis should be placed on improving the length-scale equation, since it is the least understood and is a key component of two-equation and higher models. Second priority should be given to the development of improved near-wall models. Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) would provide valuable guidance in developing and validating new Reynolds-averaged Navier-Stokes (RANS) models. Although not the focus of this workshop, DNS, LES, and hybrid methods currently represent viable approaches for analysis on a limited basis. Therefore, although computer Limitations require the use of RANS methods for realistic configurations at high Reynolds number in the foreseeable future, a balanced effort in turbulence modeling development, validation, and implementation should include these approaches as well. 14. SUBJECT
TERMS
turbulence,
high Reynolds
15.
number,
separation,
modeling,
NUMBER
DNS, LES
OF PAGES
193 16. PRICE
CODE
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