Computational and Experimental Flow Field Analyses of Separate Flow Chevron Nozzles and Pylon Interaction

12 Pages·2003·7.7 MB·English

by  Massey, Steven J.

AIAA 2003–3212
Computational and Experimental
Flow Field Analyses of Separate
Flow Chevron Nozzles and Pylon
Interaction
Steven J. Massey
Eagle Aeronautics, Inc., Hampton, VA 23669
Russell H. Thomas
Aeroacoustics Branch, MS 166, NASA Langley
Research Center, Hampton, VA 23681
Khaled S. Abdol-Hamid
Configuration Aerodynamics Branch, MS 499, NASA
Langley Research Center, Hampton, VA 23681
Alaa A. Elmiligui
Analytical Services & Materials, Inc.,
Hampton, VA 23666
9th AIAA/CEAS Aeroacoustics
Conference and Exhibit
May 12–14, 2003/Hilton Head, SC
Forpermissiontocopyorrepublish,contacttheAmericanInstituteofAeronauticsandAstronautics
1801AlexanderBellDrive,Suite500,Reston,VA20191–4344
Computational and Experimental Flow Field Analyses
of Separate Flow Chevron Nozzles and Pylon
Interaction
StevenJ.Massey∗
EagleAeronautics,Inc.,Hampton,VA23669
RussellH.Thomas†
AeroacousticsBranch,MS166,NASALangleyResearchCenter,Hampton,VA23681
KhaledS.Abdol-Hamid‡
ConfigurationAerodynamicsBranch,MS499,NASALangleyResearchCenter,Hampton,VA23681
AlaaA.Elmiligui§
AnalyticalServices&Materials,Inc.,Hampton,VA23666
Acomputationalandexperimentalflowfieldanalysesofseparateflowchevronnozzlesispresented. The
goalofthisstudyistoidentifyimportantflowphysicsandmodelingissuesrequiredtoprovidehighlyaccurate
flowfielddatawhichwilllaterserveasinputtotheJet3Dacousticpredictioncode. Fourconfigurationsare
considered:abaselineroundnozzlewithandwithoutapylon,andachevroncorenozzlewithandwithoutapy-
lon.Theflowissimulatedbysolvingtheasymptoticallysteady,compressible,Reynolds-averagedNavier-Stokes
equationsusinganimplicit,up-wind,flux-differencesplittingfinitevolumeschemeandstandardtwo-equation
k−εturbulencemodelwithalinearstressrepresentationandtheadditionofaeddyviscositydependenceon
totaltemperaturegradientnormalizedbylocalturbulencelengthscale.ThecurrentCFDresultsareseentobe
inexcellentagreementwithJetNoiseLabdataandshowgreatimprovementoverpreviouscomputationswhich
didnotcompensateforenhancedmixingduetohightemperaturegradients.
Introduction from the isolated case, the aerodynamic and noise reduc-
Typically for modern commercial aircraft, engine in- tion performance of the device or strategy. This focus on
stallation involves the engine-under-the-wing or the tail boththeaerodynamicaswellasacousticinteractioneffects
mounted configuration. However, even within those two of installation and propulsion airframe aeroacoustics, will
basic categories there are many design variables includ- becomemoreimportantasnoisereductiontargetsbecome
ing structural, aerodynamic, and operational factors. For moredifficulttoachieve.
thesestandardengineinstallationsanddesignrequirements
Theworkinthispaperisacontinuationofanon-going
theindustryhashighlydevelopeddesignandanalysispro-
efforttostudytheeffectofthepylononseparateflownoz-
cesses.1
zles including those equipped with the chevron jet noise
The impact on the net radiated noise of the aircraft is
reduction device. Building on preliminary work,2 the pri-
an additional challenge that is emerging as increasingly
mary objective of this work is to improve the capability
importantinpropulsionairframeintegrationandisthegen-
to simulate installed jet configurations and to develop un-
eral motivation for the work reported here. One example
derstanding of the characteristics of the flow field of the
of an aeroacoustic effect of propulsion airframe integra-
selected installation configurations through computational
tion could be the effect of the pylon on the development
solutionscomparedwithflowfieldexperimentsperformed
of the exhaust plume and on the resulting jet noise. An-
at the NASA Langley Jet Noise Laboratory. In parallel
otherarea ofinstallation effectonnoise is theimpact that
research, Hunter3 is developing an installed jet noise pre-
installationhasonnoisereductiondevicessuchaschevron
diction method that uses the flow field information from
nozzles. Many noise reduction devices are studied funda-
thesecomputationalsolutionsandcompareswithacoustic
mentally on isolated components. In general, installation
experimentsthathavealsobeenperformedattheJetNoise
effectsmustbeconsideredbecausetheseeffectsmayalter,
Laboratory on these same configurations. Together, these
∗SeniorResearchScientist,AIAAMember. three tools are being used to develop an understanding of
†AerospaceEngineer,SeniorMemberAIAA. theacousticinteractionbetweenpylonandchevronnozzles
‡AerospaceEngineer,AssociateFellowAIAA. andthemoregeneralinteractionofpylonandjetwiththe
§SeniorScientist.
aim of developing flow and acoustic prediction capability
Copyright(cid:176)c 2003bytheAmericanInstituteofAeronauticsandAstronautics,
Inc. NocopyrightisassertedintheUnitedStatesunderTitle17,U.S.Code. The andnoisereductiontechnologyforinstalledjetconfigura-
U.S.Governmenthasaroyalty-freelicensetoexerciseallrightsunderthecopyright tions.
claimedhereinforGovernmentalPurposes. Allotherrightsarereservedbythe
copyrightowner.
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and pylon design combined with no added design feature
forthejunctionsimilartothejunctioninthepreviouscon-
figuration4.
ExperimentalFlowConditions
Surveys of the flow fields of configurations 1, 3, and
4Fareusedtocomparewiththeresultsofthesimulations
in subsequent sections. The surveys were performed in
theNASALangleyLowSpeedAeroacousticWindTunnel
a)Config.1 b)Config.6 with a traverse apparatus moving a single rake of probes
(see Figure 2). Mean total pressure and total temperature
were measured with a rake that was populated with three
total pressure and three total temperature probes and tra-
versed in cross-sectional planes at x/D = 2, 5, 10, and
17.Ateachcross-sectionagridwasmappedwithmeasure-
mentstakentypicallyin0.64cmincrementsatx/D=2and
5andin1.27cmincrementsatx/D=10and17.Thegrids
were sized at each axial station to cover most of the core
andthefanplume. Asaresult,severalhundredincrements
andsamplesweretakeninordertocompleteasurveyata
c)Config.3 d)Config.4F
single axial station. Maintaining the core and fan jet op-
Fig.1 Surfaceandsymmetryplanegridlines. erating condition was critical to obtaining a good survey.
Table1liststhemeanvaluesofthecoreandfanoperating
Configurations
conditions and the standard deviation of those conditions
The baseline configuration is a separate flow nozzle of
foratypicalsurveyatasingleaxialstation,indicatingthat
bypassratiooffivewithanexternalplug. Thenozzleand
theoperatingconditionswereinfactmaintainedwellover
pylon designs are from a nozzle study performed by Mc-
the more than an hour of run time required for each axial
Donnell Douglas (now Boeing) in 1996 and represents a
station.
generic design. The chevrons were designed for the core
nozzleusingguidelinessimilartothoseusedintheNASA Table1 Meanandstandarddeviationvaluesforthecoreand
AdvancedSubsonicTransportprogram. Thechevronsare fanoperatingconditionsduringthesurveyofconfiguration3
atx/D=5.
designed to penetrate into the core flow by approximately
thethicknessoftheboundarylayer.Thetrailingedgeofthe Mean StandardDev.
baselinenozzleischosentocorrespondtothemid-pointof NPRCore 1.557 0.004
thechevronaxiallength. Thefourconfigurationsanalyzed T Core 826.1K 3.3K
t
inthisstudyare: NPRFan 1.747 0.005
T Fan 358.7K 0.8K
Configuration 1: Baseline round core and fan nozzle t
withnopylon(Figure1a).
ComputationalFlowConditions
Configuration 6: Baseline core and fan nozzle with
Theflowconditionsforbothexperimentsandcomputa-
pylon(Figure1b).
tions are set at the take-off cycle point. The free stream
Configuration3: Eightchevroncorenozzleandbase- Mach number is 0.28 with total pressure and tempera-
linefannozzlewithnopylon(Figure1c). ture set to standard atmospheric conditions at sea level of
101353Paand 295Krespectively. Thefanpressureratio
Configuration4F:Eightchevroncorenozzleandbase-
is1.75withtotaltemperatureof359K.Thecorepressure
line fan nozzle with pylon with the tip of a chevron
ratiois1.56withtotaltemperatureof828K.
alignedwiththepylon(Figure1d).
NumericalMethod
The configuration numbering scheme is consistent with
previouslyusedconfigurationnumbers.2 Thecurrentcon- Thefluidflowissimulatedbysolvingtheasymptotically
figurations 1 and 3 are identical in geometry to the same steady, compressible, Reynolds-averaged Navier-Stokes
configurationssimulatedpreviouslyonlyinthisworkthey equationsusinganimplicit,up-wind,flux-differencesplit-
are simulated with the results of the improved computa- ting finite volume scheme and standard two equation k-ε
tionalformulationtobedescribedbelow. Thepyloninthe turbulence model4 with a linear stress representation and
currentworkhasa divergingshelfangle of 1.5◦ (configu- theadditionofaneddyviscositydependenceontotaltem-
rations6and4F)whilethepyloninthepreviousconfigu- peraturegradientthroughthevariationtheC closurecoef-
µ
rations2,4,and5hadacurvedshelfline. Thejunctionin ficient,seeAbdol-Hamidetal.5 Allcomputationsareper-
configuration4Fissimplytheresultofaseparatechevron formedusingtheparallel,multiblock,structuredgridcode
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Fig.2 Photograph,lookingupstream,oftheflowfieldsurveyexperimentintheNASALangleyLowSpeedAeroacousticWind
Tunnel.Configuration1isinstalledonthejetenginesimulatorsurroundedbythewindtunnelnozzle.Rakeofprobes(centerof
photo)isseenmountedonatraversemechanism.
PAB3D.6 Viscous diffusion terms are modeled as uncou- chevron nozzle without pylon provide confidence that the
pledintheflowdirectionandfullycoupledinthecrossflow azimuthaldirectionisalsofullyresolvedwith40cellsper
directionanda3-factorschemeisusedfortheapproxima- chevron or 1.125◦ resolution. Grid sizes range from less
tionofimplicitterms. than 300,000 cells for a 6◦- two cell wedge grid to over
Grid sequencing is used to accelerate convergence by 16 million cells for the full 180◦ chevron/pylon grid, see
solving 1/4 then 1/2 of the grid in each of the three com- Table 2 and Figure 1. All surfaces are gridded and run as
putational directions. The general solution procedure fol- viscous with the exception of the lower bifurcator and a
lowedistosolvetheregionnearthenozzleviatimemarch- verysmalltipregionoftheplug. Theaveragevalueofthe
ing,thensolvetheplumeblocksviaspacemarching,then lawofthewallcoordinate,y+,ofthefirstcellcenterisap-
finally run at least 200 time marching iterations on just proximately one with a minimum of 0.4 and a maximum
theplumeblocksandadjacentupstreamblocksinorderto offive. Thesolutiondomainextendsoversixcorediame-
smooth any inflections at the time/space marching block ters,(D = 12.8cm)upstreamofthefanexit,nearly32D
boundary. Typical iteration counts for 3-D grids at each downstream and six D radially. In all plots, the origin of
gridlevelare5,000, 4,000, 3,000and2,000. Axisymmet- the x-axis, x/D = 0.0, is set to the fannozzle exit, which
ric cases are stiffer and require 10,000 iterations per grid putsthecoreexitatx/D=0.83andtheplugtipatx/D=
level. A sample convergence history, Figure 3, in terms 1.87.
of flow and turbulence residual is shown for four grid se-
quence levels, where 0.5 denotes half of the spacing used Typicalruntimesforthefullyconvergedsolutionatthe
fortheproductionruns. Convergedsolutionsforcenterline finegridlevelarelessthan40hoursfor16.2millioncells
totaltemperature,showninFigure4,areessentiallyidenti- using up to 21 2-GHz Pentium 4 nodes on an unbalanced
calatallgridlevelsanddemonstratenumericalverification grid. Balanced computations using 8 CPU’s for the eight
for the axial and radial directions. Consistency between plumeblockscontaining600,000cellseach,yieldparallel
theaxisymmetricsolutionsandtheperiodicsolutionsofthe efficienciesofupto97%oraspeedupfactorof7.8.
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Modifiedk−εModel
Thek−εmodelisthemostpopulartwo-equationturbu-
10›5 10›7 lencemodelandiswidelyusedacrossmanyflowregimes,
qResidual eventhoughitwasdevelopedandtunedprimarilyfortwo-
kResidual
dimensional, incompressible flows. Thus, it is suspected
10›6
10›8 thatobservederrorsinresolvinghightemperaturejetmix-
ing is a result of the model being applied outside of its
al10›7 44 al envelope. The physical mechanism for the missing quan-
Residu 22 11 10›9Residu toiftythoeftduernbsuilteynctomnitxriibnugtiiosnthtooutghhetKtoelbveind-uHeetlomthhoeltazbisnesntcae-
q10›8 k bility. Experimentally7,8 ithasbeenshownthatthespatial
.5.5
growthofatwo-dimensionalshearlayerisproportionalto
10›10 thesquarerootofthedensityratioofthetwomixingfluids.
10›9 InarecentstudybyTamandGanesan,9adensitybasedcor-
rectionwasappliedontopoftheThiesandTam10modified
10›10 10›11 k−ε model, however it is strictly intended for free shear
0 20000 40000 60000 80000
flows and therefore not applicable to the current configu-
Iterations
rations. Withinstalledjetsitisparticularlyimportantthat
themodelapplytobothfreeshearandwallboundedflows.
Fig.3 Config. 1-axi,RoundNozzle:Residualhistoryatfour
Forthepurposeofthepresentstudy, aminimallyinvasive
levelsofgridrefinement.
correctiononlytoturbulenteddyviscosityisusedtorectify
themixingdeficiencyforhightemperaturejets. Toinsure
thatthemodifiedk−εmodelreturnstotheoriginalmodel
forcoldjetsandthatitremainsaccurateforwallbounded
1 flows,turbulencescaledtotaltemperature,T¯,ischosenas
the variable for the additional eddy viscosity dependence,
Coarse(44) where
0.9
Medium(22)
Fine(11) k3/2(cid:107)∇T (cid:107)
e) ExtraFine(.5.5) T¯ = t . (1)
or0.8 JNLDATA ε Tt
c
(
TT The functional relationship was determined by the best
T/T0.7 match to experimental data for the baseline round nozzle
e
rlin andisasfollows,
e
nt0.6 (cid:183) (cid:184)
Ce C =C 1+ CTT¯3 (2)
0.5 µ µ0 1+CMMt2
wherethestandardk−εclosurecoefficientisC =0.09.
0.4 µ0
0 5 10 15 20 25 30 Thetemperaturegradientcoefficient,C ,issetto24.33by
T
X/D
bestfittodataafterassigningtheturbulenceMachnumber
coefficient, C to 4. Turbulence Mach number, M , is
Fig.4 Config.1-axi,RoundNozzle:Centerlinetotaltemper- M t
definedby
atureatfourlevelsofgridrefinement.
M2 =2k/a2 (3)
t
where a is the speed of sound. For this study no attempt
Table2 Zonalgridcellcounts. ∗Config. 1-axiisaxisymmet-
wasmadetoconstructageneralfunctionaldependenceon
ricandfullytimemarched.
turbulenceMachnumber,henceEq.2shouldonlybeused
Time Space for subsonic jet flows. However, this has now been suc-
Marched Marched cessfullyaddressedinAbdol-Hamidetal.5
Config. x/D ≤14 x/D >14 Total
1−axi∗ 2x148,464 2x148,464
Results
1 4,083,072 1,797,120 5,880,192
6 7,805,440 3,594,240 11,399,680 The three issues to be addressed in this section are as
3 10,125,312 3,594,240 13,719,552 follows;1)therectifiedCFDresultsusingthemodifiedk−
4F 12,620,096 3,594,240 16,214,336 ε model versus the original CFD results, 2) the validation
ofCFDresultswithexperimentaldata,and3)explanation
ofthephysicalcharacteristicsoftheflows.
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1
1:BaselineRound(stdk›e)
1:BaselineRoundNozzle
6:RoundNozzlew/Pylon
0.9 3:ChevronNozzle Config.1,RoundNozzle.
4F:ChevronTipunderPylon
1:Data
3:Data
0.8 4F:Data
e)
or
c Config.6,RoundNozzlew/Pylon.
T(t0.7
/
Tt
0.6
Config.3,ChevronNozzle.
0.5
0.4
0 5 10 15 20 25 30 Config.4F,ChevronTipunderPylon.
X/D Fig.6 CFD:C factoronsymmetryplane.
µ
Fig.5 Totaltemperaturealongjetaxis.
CFDRectification
The effect of the temperature gradient modified k − ε
model over the standard k − ε model for the round noz-
Config.1,RoundNozzle:Standardk-εmodel.
zle is to increase turbulent mixing and hence decrease the
potential core length by 3.4 core diameters, D. The core
lengthsaretabulatedinTable3andaredefinedforthex/D
inwhichTt = 0.995Tt∞ alongtheaxisofthejet,seeFig- Config.1,RoundNozzle.
ure 5. The action of the modified k −ε model in terms
Table3 CFDPotentialCoreLength
Config. Corelength,D Config.6,RoundNozzlew/Pylon.
1-stdk−ε 12.5
1-modk−ε 9.1
6 8.1
Config.3,ChevronNozzle.
3 4.6
4F 5.4
Config.4F,ChevronTipunderPylon.
Fig.7 CFD:Totaltemperatureonsymmetryplane.
oftheincreasededdyviscosityclosurecoefficientisshown
in Figure 6, where the ratio of the actual to the standard
value of 0.09 is plotted. In the code, the maximum ratio
issetto5,however,mostoftheflowfieldsarewellbelow
3. Asaresultoftheundisturbedshearlayers,whichcreate
strong temperature gradients, the round jet configuration
Config.1,RoundNozzle:Standardk-εmodel.
exhibitsthehighestamountofC amplification. CFDso-
µ
lutionsofthegeneralflowfieldaredepictedfortheround
nozzle, Figures 7-10, with the standard k −ε model fol-
lowedbyallconfigurationswiththemodifiedk−εmodel. Config.1,RoundNozzle.
Note, for configuration 3., the symmetry plane was plot-
ted for the solution rotated by 22.5◦ to be consistent with
experimentalcrossflowplots.
Config.6,RoundNozzlew/Pylon.
CFDValidation
As previously discussed, the present model was tuned
on the axisymmetric grid to the round nozzle experimen-
Config.3,ChevronNozzle.
tal results. Particular attention was paid to matching the
axial total temperature at x/D = 5 and 10. The model
was then frozen for the other cases. Computed total tem-
peraturealongtheaxisisplottedwithexperimentaldatain Config.4F,ChevronTipunderPylon.
Fig.8 CFD:Totalpressureonsymmetryplane.
Figure 5. Comparing the data points at x/D of 5 and 10,
configuration 1 is on data, configuration 3 is less than 1
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a result of the under prediction of mixing. For configura-
tion1,T isinnearperfectagreementandp iswithinone
t t
contourlevelofagreement,seeFigures11and12.Forcon-
Config.1,RoundNozzle:Standardk-εmodel.
figuration3showninFigures14and15,themixinglobes
total temperature and pressure differ by only two contour
levels. With the addition of the pylon, configuration 4F
Config.1,RoundNozzle. shows a slightly larger deviation from measured data, see
Figures16and17. Focusingonthechevroninducedcross-
flowplumesatx/D = 5,T istwotofourlevelsoff,with
t
thehighestdifferencebeinginasmallregionnearthelower
Config.6,RoundNozzlew/Pylon.
bifurcator. Thehigherthanexpectedtemperaturenearthe
lower bifurcator is likely a result of not modeling it as a
viscous surface, hence there is a lower level of turbulent
Config.3,ChevronNozzle. mixing in this region. For total pressure, the contours are
againseentobetwolevelshigherthanmeasured. Theper-
cent error in terms of the contour range is summarized in
Table 4. Calculated mass flow is also in good agreement
Config.4F,ChevronTipunderPylon.
Fig.9 CFD:Machnumberonsymmetryplane. withmeasureddata,seeTable5.Experimentally,therewas
somediscrepancybetweentwomethodsofmeasurementof
up to 0.36 kg/sec, however, in both sets of measurements
the trend was the same, so the comparison of normalized
valuesisvalidandinexcellentagreementwithCFD.
Config.1,RoundNozzle:Standardk-εmodel.
Table4 RelativeCFDCrossflowError
Config. T Error p Error
t t
1 ≈0% <5.5%
Config.1,RoundNozzle. 3 12.0% 11.0%
4F 12.0-24.0% 11.0%
Config.6,RoundNozzlew/Pylon.
Table 5 Mass flow Comparison. ∗Config. 6 was estimated
basedonarearatio.
Config. CFD Exp. Error
Config.3,ChevronNozzle. 7.835kg/s 7.902kg/s
1 1.000 1.000 0%
6 0.940 0.94∗ 0%
3 0.993 0.994 -0.1%
Config.4F,ChevronTipunderPylon.
4F 0.939 0.936 0.3%
Fig.10 CFD:Turbulentkineticenergyonsymmetryplane.
D under mixed, and configuration 4F is between 1 and 2
D undermixed. Relativeerrorscomparedtothepredicted FlowPhysics
roundcorelengtharelessthan11%forconfiguration3and
Thepurpose of creating a chevroncore nozzle is to en-
11%to22%forconfiguration4F.
hancemixingandhencereducenoisewithverylittlethrust
Incomparisonswithcrossectionaldatafortotaltemper- loss. Preliminarycalculationsforthecurrentchevronnoz-
ature and pressure, see Figures 11 - 17, the thickness and zlesshowathrustlossoflessthanonepercent. Toclearly
shapeoftheshearlayersareseentobeinexcellenttogood showthemixingeffectsofthechevroncoreandthepylon,
agreementwithmeasureddata. Note,noexperimentaldata a non-dimensionalized, mass averaged turbulence kinetic
was taken for configuration 6. Also, for configuration 3. energy and total temperature expressions are introduced,
theCFDsolutionwasrotatedintheazimuthaldirectionby showninFigures18and19respectively. Theexpressions
22.5◦ to align it with the experimental data. For the total follow those published by Kenzakowski et al.11 and are
temperature plots, the contour range extends from 0.39 to definedasfollows:
0.99withalevelspacing,∆Tt,of0.04. Fortotalpressure, (cid:82) (cid:113)
therangeisfrom1.00to1.72withspacingof∆pt =0.04. kρudA
In the experimental data plots, the data points were taken kˆ = A(cid:82) q (4)
ρudA
at ∆x and ∆y = 0.1D intervals and are marked with a (cid:82) A
smallblackdot. Thistendstosmearoutthinshearlayers, φρudA
Tˆ = (cid:82)A (5)
butdoesnotaccountforthemismatchwithCFD,whichis t ρudA
A
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Experiment CFD Experiment CFD
T /T p /p
t tCORE t t∞
Fig. 11 Config. 1, Round Nozzle: Total temperature cross Fig.12 Config. 1, RoundNozzle: Totalpressurecrosssec-
sectionsatx/Dof2,5,10and17. tionsatx/Dof2,5,10and17.
where flow velocity vectors at x/D = 2, shown in Figure 20.
T −T
φ= t tFAN (6) Intheseplots,uniformlyspacedvectorswereplottedwith
T −T
tCORE tFAN the length proportional to the magnitude over contours of
withintegrationonlyperformedoverareaswhere the axial velocity component, u. In both cases, as the py-
lonandplugcloseout,thecrossflowvelocityvectorsshow
0.005≤φ≤1. (7)
flow moving in the direction to fill in the wake. For the
From the figures it is clear that the introduction of the roundnozzlewithoutapylon,anoverallinwardflowisob-
chevron core nozzle greatly enhances turbulent mixing, servedduetothesecondaryflowsetupbytheplug. With
while the pylon installation contributes to the mixing by theadditionofthepyloninconfiguration6,astrongerover-
onlyasmallamountfortheroundnozzleandevenlessfor all vertical flow toward the pylon is setup. Also, because
the chevron nozzle. Chevrons are seen to be an excellent the pylon is also tapered in the horizontal direction, an
method to enhance mixing without introducing much tur- additional horizontal velocity is induced. This flow then
bulenceinthenear-fieldcomparedtotheroundnozzlewith separatesatthesharpbottomedgeofthepylonandrollsup
pylonandactuallyreducingitinthefar-field,seeFigure18. into a small vortex. For the chevron nozzle without a py-
The mechanism for the enhanced mixing due to both lon, configuration3, anoctagonalshapedinfluenceonthe
pylon and chevrons can be seen by examining the cross- plug flow at the jet center is seen in the crossflow as well
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Tt/TtCORE,CFD pt/pt∞,CFD Experiment CFD
T /T
t tCORE
Fig.13 Config.6,RoundNozzlew/Pylon:Totaltemperature
andpressuresectionsatx/Dof2,5,10and17. Fig.14 Config. 3,ChevronNozzle: Totaltemperaturecross
sectionsatx/Dof2,5,10and17.
as the axial flow. However, the strongest effect by far is carriesturbulenceenergy2fromboththeboundarylayerof
onthecore/faninterface. Note,inthisfigure,configuration thepylonaswellasthecore/fanshearlayer,itisexpected
3 has not been rotated as in the previous plots, therefore tobeanadditionalsourceofnoise.
its chevrons are oriented as shown in Figure 1c, and are
ConcludingRemarks
aligned with configuration 4F, where the chevron tip is at
the z/D = 0. It is observed that the chevrons allow the The purpose of this study was to provide insight into
core flow to stream out in a strong crossflow plume much the flow physics of pylon-jet interactions and to provide
likeamushroomcloud,wherethehotcoreflowrushesup the input mean flow field to acoustic prediction methods
whiledrawingthecoolerflowdownarounditsbase. When for installed jet noise. Important flow phenomenon were
theeffectofthepylonisaddedinforconfiguration4F,two identifiedandthemodelingtechniquesrequiredtoprovide
notableeffectsareobserved;1)becauseofthepylonblock- highlyaccuratemeanflowfielddataspecificallyforuseas
age, no fan flow can be drawn down near the pylon, and inputtoacousticpredictionmodelswereestablished. Four
2)thevortexonthecrossflowplumeadjacenttothepylon configurations were considered; a baseline round nozzle
constructively interferes with the separation vortex com- with and without a pylon, and a chevron core nozzle with
ing from the bottom edge of the pylon and forms a much andwithoutapylon.Theflowwassimulatedbysolvingthe
stronger vortex than in configuration 6. Since this vortex asymptotically steady, compressible, Reynolds-averaged
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Experiment CFD Experiment CFD
p /p T /T
t t∞ t tCORE
Fig.15 Config. 3,ChevronNozzle: Totalpressurecrosssec- Fig.16 Config.4F,ChevronTipunderPylon:Totaltemper-
tionsatx/Dof2,5,10and17. aturecrosssectionsatx/Dof2,5,10and17.
Navier-Stokesequationswithatemperaturegradientmodi- less than 11% for configuration 3 and 11% to 22% for
fiedtwo-equationk−εturbulencemodel.ThecurrentCFD configuration 4F. This study has also clearly shown that
results are seen to be in good to excellent agreement with installation effects are significant and introduce local and
JetNoiseLabdataandshowgreatimprovementoverprevi- global changes to the flow. Of critical importance is the
ouscomputationswhichdidnotcompensateforenhanced interface between the chevron induced vortical flow and
mixingduetohightemperaturegradients. Intermsofthe the bottom edge of the pylon which in the configuration
potentialcorelength,whichistheclearestsingleindicator 4F interferes constructively to produce a potential source
of error, the new round nozzle computations are in com- of noise. With a firm understanding of the flow physics
plete agreement with experimental data. This is in sharp androbustnumericalmodel,futureresearchwillaimtode-
contrasttoinitialcomputationsusingtheunmodifiedk−ε signmoreaffectivenoiseattenuatingnozzlemodifications,
model, which over predicted potential core length by 3.4 whilefurtherrefiningCFDpredictioncapabilities.
corediametersor37%.Currentresultsforthechevroncore
Acknowledgments
nozzlewithoutthepylonshowapotentialcorelengtherror
oflessthanonecorediameter. Theinclusionofthepylon ThecontributionsoftheentireJetNoiseLabtothePy-
increasestheerrortobetweenoneandtwocorediameters. lon Effects Experiment are gratefully acknowledged. The
Relative to the round nozzle core length, these errors are authorsalsowishtothankS.PaulPaoandCraigHunterof
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AMERICANINSTITUTEOFAERONAUTICSANDASTRONAUTICSPAPER2003–3212