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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

Interim

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

NASA

Langley

Research

Center,

Langley

Research

Center

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Hampton, Operated

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Virginia by Universities

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Service

(NTIS)

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

PAGE

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for

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DATE

AND

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including Send Services,

Reduction

TYPE

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SUBTITLE

Turbulence

the time for reviewing instructions, searching existin K data sources, comments reKard ng th s burden est mate or any other aspect of this Directorate 1"or information Operations and Reports, 1215 Jefferson

Paperwork

3. REPORT

March 2001 4. TITLE

per response, of information. Headquarters

Project

AND

(0704-0188),

DATES

Washington,

DC

20503.

COVERED

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

ORGANIZATION

NAME(S)

AND ADDRESS(ES)

8. PERFORMING ORGANIZATION REPORT NUMBER

ICASE Mail Stop 132C NASA Langley Research Center Hampton, VA 23681-2199

ICASE Interim

9. SPONSORING/MONITORINGAGENCYNAME(S)AND ADDRESS(ES) National Aeronautics and Space Administration Langley Research Center Hampton, VA 23681-2199

11. SUPPLEMENTARY

No. 37

10. SPONSORING/MONITORING AGENCY REPORT NUMBER

NASA/CR-2001-210841 ICASE Interim Report

No. 37

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

A09 17. SECURITY CLASSIFICATION OF REPORT

Unclassified _ISN 7540-01-280-5500

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19. SECURITY CLASSIFICATION OF ABSTRACT

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i