Boundary layer suction configurations with minimal pump requirements for multi-element airfoils

109 Pages·2016·7.43 MB·English

by  Jorik Van Craenenbroeck

Boundary layer suction con-
figurations with minimal
pump requirements for
multi-element airfoils
Thesis
Jorik Van Craenenbroeck
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B
OUNDARY LAYER SUCTION
CONFIGURATIONS WITH MINIMAL PUMP
-
REQUIREMENTS FOR MULTI ELEMENT
AIRFOILS
THESIS
by
JorikVanCraenenbroeck
inpartialfulfillmentoftherequirementsforthedegreeof
MasterofScience
inAerospaceEngineering
attheDelftUniversityofTechnology.
Studentnumber: 4047125
Projectduration: August3,2015-30/05/2016
Supervisor: Prof.dr.ir.L.Veldhuis
Thesiscommittee: Prof.dr.ir.L.Veldhuis, TUDelft
Prof.dr.ir.B.vanOudheusden, TUDelft
Ir.N.Timmer TUDelft

S
UMMARY
High lift systems are complex and heavy systems but despite that they are still indispensable to reconcile
optimalcruiseperformanceoftheaircraftwithanacceptabletake-offandlandingperformancewithregard
torequiredrunwaylength. However,adefinitivetrendtowardslowercomplexityhighliftsystemsisalready
ongoing for quite some time ([1]) and new methods to allow lighter and simpler high lift systems are ac-
tivelysoughtafter. Oneofthemethodsthathasalreadyproventobeabletoincreasehighliftperformance
isboundarylayersuction. Themaindisadvantageofaboundarylayersuctionhoweveristhatitisaformof
activeboundarylayercontrolwithoftenhighpowerrequirements. Inanattempttomakeupforthepower
requirementsandminimizetheweightpenaltyofaboundarylayersuctionsystem,systemsthatuseanal-
readyexistinglow-pressureareaintheengine([2])areinterestingtopursue; neverthelesstheystillrequire
extrapowergeneration. AlongthesamelineofreasoningaBLSsystemcanbeenvisagedthatisdrivenby
a‘naturallyoccurring’lowpressurezone,suchasthelowpressurezonenearthewing-tipgeneratedbythe
wing-tipvortex. Theunderpressurethatcanbeexpectedfromthishoweverisnotverylow,certainlynotin
theorderofmagnitudethatisnecessaryforatypicalBLSsystem.Thereforetherequirementsforthebound-
arylayersuctionsystembecomeaveryimportantaspect.Whiletheresearchinthepresentedareaisusually
focusedonmaximizingthemaximumliftcoefficientatthecostofhighsystemrequirements(suchasthere-
quiredunderpressure)theaimofthepresentedprojectistolookatthepossiblegainsduetoboundarylayer
suctiononamulti-elementairfoilwhileminimizingtherequirementsfortheboundarylayersuctionsystem.
Losingtheadditionalliftthatcouldbeachievedwithamoredemandingsystemshouldbecompensatedby
areductionincomplexity,weightandtheabsenceoftheneedforadditionalpowergeneration.
Inordertoperformthisinvestigationasimulationplatformisrequired. Anumericalapproachisused:
theflowfieldissimulatedwiththeinviscid-viscidinteractionflowsolverMSESwhichissuitableformulti-
elementairfoils.Thiscodehoweverwas(re-)adaptedtoincludethesimulationofBLS,whichwaspartofthe
work. Thereportthereforeincludesapartdescribingthisworkaswellasapartdescribingthevalidation
oftheappliedchanges. TheadaptionofthecodetoincludethesimulationofBLSreliedheavilyuponthe
workofMerchantandalsodeOliveiraAndradeandmainlyinvolvedchangingtheintegralboundarylayer
formulationandclosurerelationsinMSES[3,4].Validationofthisworkyieldedthefollowingobservations:
• Thesimulationoflargerareasofcontinuoussuctioniswellpredicted,theerrorforthesuctioncasesis
onthesameorderasthenon-suctioncase.AgreementwithrFoilsuc(alsoaninviscid-viscidflowsolver
adaptedforBLS,althoughforsingleelements)isexcellent.
• Inthecaseofslotsuctiontheeffectoftherecirculationzonesattheslotentrancecannotbecaptured
andthisresultedinanunderpredictionofθ.Comparisonwithexperimentaldatashowedthatthisdid
notaffectthepredictionofthe‘outerflow’verymuch, buttheunderestimationofθ maybecomea
problemincaseswithsevereadversepressuregradientswhereseparationbecomesanissue.
• ThereliabilityoftheflowpredictionnearC isunclearandvariesfromcasetocase. Thereforeitis
lmax
advisabletoavoidusingresultsnearthisarea.
Shiftingthefocusbacktotheinvestigationforalow-requirementBLSdesignagain,thequestionofwhat
definestherequiredpowerofaBLSsystemisaddressed. Withthehelpoftheequationforanidealpump
onecanconcludethatthisconsistsattheonehandoftherequiredincreaseintotalpressurethatmustbe
overcomeandontheotherhandthesuctionlevelandarea.Torelaxtherequirementsfortheincreaseintotal
pressureitisinterestingtoapplysuctionatalocationwitharelativelyhighstaticpressure.Itwasconcluded
thatthemostpromisingsuctionlocationwhiletakingthisintoconsiderationistowardsthetrailingedgeof
anelement,largelytotrytoinfluencethewake;thefocusofthestudyislargelyconcentratedonthissubject.
Inthepresenceofanadversepressuregradientthewaketendstogrowthickerandthiscanescalatetoa
situationwherethewakedominatestheflowfield,alossofliftcanbeobservedandevenflowreversaloccurs
inthewake: ‘wakeburst’. Makingtheboundarylayerthinnerwiththehelpofsuctioncandelaythisand
iii
iv SUMMARY
increasetheoverallliftagain. Acriticalfactorinthedetectionofthisso-calledwakeburstisthegrowthrate
ofthedisplacementthickness dδ∗: basedonexperimentaldatafoundinliteratureandthesimulationswith
ds
MatSESuctionitwasfoundthatifitreachesacriticalvalueof0.23wakeburstislikelytohappen.
SimulationsontheNLR7301andMFFS026multi-elementairfoilsystemsinaconfigurationwherewake
burstoccursshowthattheoverallliftcanbesuccessfullyincreasedbyapplyingsuction.Aclearlinkbetween
suctionandthegrowthrateofδ∗ inthewakecanbedistinguished; andbykeeping ddδs∗ belowthecritical
valuewakeburstisavoided.InthecaseoftheNLR7301theliftcoefficientisincreasedfrom3.064to3.196(or
anincreaseof4.31%)andfortheMFFS026itisincreasedfrom3.5to3.6(3%).
Thesimulationsshowedthattheinvestigatedsuctionconfigurationsdonotyieldasignificantbenefitover
earlierinvestigatedBLSconfigurations, nordoesitperformsignificantlyworsebutwiththeconsideration
thatitonlymakessensewhenwakeburstispresent. However,thisdoesnottakeintoaccounttheeffectof
thesuctionlocation.TypicalBLSconfigurationsallfeaturesuctionatlocationswherethepressureisalready
verylow,whichwillinpracticerequirealotofpowertogeneratetheincreaseintotalpressurethatisrequired
tomaintainthesuctiondistribution.Thisagaincallsforapowerfulpump,letalonemakingitpossibletouse
anaturallyoccurringlowpressurezonetodrivetheBLS.Itbecomesthenaquestionofbalancingthe‘power’
thatiswillingtobe‘invested’intheBLSsystemwiththesuctionlocationandstrength.
P
REFACE
Thisreportisagraduatethesis, writtenasapartoftheMaster’sdegreeinAerodynamicsattheFacultyof
AerospaceEngineering,DelftUniversityofTechnology.Abasicknowledgeofaerodynamicsisrecommended,
althoughthenecessarykeyideasareexplainedinchapters2(and5).
WiththisthesisIwillfinishmystudieshereinDelftandthisseemslikeanappropriatetimeandplace
to thank some people. First and foremost my parents, who have supported me for all these years — also
financially(thankyou!) —andgavemetheopportunitytostudyhereinDelft. Thanksforbeingsopatient
andunderstandingeverytimeIannouncedplans—academicandsometimesnon-academic—thatdelayed
mygraduationalittlebit.Youmadethisparteasyforme.
WhenthinkingaboutmytimehereinDelft,mythoughtsgoimmediatelyouttothegreatgroupoffriends
Ihavemadehere.Notonlywereyouabigsupportforstudyrelatedissues,butyouwerealsoveryimportant
forthepersonaldevelopmentIhavegonethroughduringalltheseyears.Icouldn’thavedoneitwithoutyou
anditcertainlywouldnothavebeensuchanamazingtime!
TesamenmetdezethesiszalikookmijnstudieshierinDelftafrondenenditlijktmeeengoedmoment
om even wat personen te bedanken. Eerst en vooral mijn ouders die mij al deze jaren gesteund hebben —
ookfinancieel(danku!) —endiemedemogelijkheidhebbengegevenomhierinDelfttekomenstuderen.
Bedanktomzogeduldigenbegrijpendtezijniederekeerikplannen—academischeensomsnon-academische
—aankondigdediemijnafstuderenzoudenuitstellen.Julliemaaktenhetmeopditvlakergmakkelijk.
AlsikaandevoorbijetijdhierinDelftdenkgaanmijngedachtendirectuitnaardegeweldigegroepvrien-
dendieikhierhebgemaakt.Julliewarennietalleeneengrotesteuntijdenshetstuderen,maarjulliewarenook
ergbelangrijkvoordepersoonlijkeontwikkelingdieikhebdoorgemaaktdooraldezejaren. Zonderjulliezou
hetnietgeluktzijnenhetzouzekernietzo’nfantastischetijdgeweestzijn!
IalsowouldliketothankmysupervisorsL.VeldhuisandB.vanOudheusdenfortheirsupportduringthe
project,aswellasG.deOliveiraAndradewhohelpedmewithsomeoftheproblemsIencounteredwiththe
MSEScode.
JorikVanCraenenbroeck
Delft,May2016
v

C
ONTENTS
1 Introduction 1
2 Theoreticalbackground 3
2.1 Highliftsystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1 Introductiontohighliftsystems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.2 Multi-elementairfoilflowfields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.3 Workingprinciplesofmulti-elementairfoils. . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.4 Flowseparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.5 Wake. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.2 Boundarylayersuction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.2.1 Historicalbackgroundandflyingexamples . . . . . . . . . . . . . . . . . . . . . . . . 16
2.2.2 Suctiontype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2.3 Boundarylayersuctiononmulti-elementairfoils . . . . . . . . . . . . . . . . . . . . . 20
3 BoundarylayersuctionforMSES 25
3.1 MSESinshort. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.1.1 Newtonsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.2 Codestructure&summaryofmodifications . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.3 Momentumintegralrelations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.3.1 vonKármánintegralboundaryrelation . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.3.2 Kineticenergyshapeparameterequation . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.4 Closurerelations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.4.1 Laminarclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.4.2 Turbulentclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.5 Couplingcondition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.6 The‘mat’inMatSESuction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4 ValidationMSESadaptionforsuction 37
4.1 PorousflatplateexperimentbyFavreetal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.1.1 DevelopmentoftheBLparameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.2 SlotsuctionexperimentbyvanderHoeven. . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.2.1 Differentsuctionmodels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.2.2 Slotsuctionfordifferentsuctionlevels. . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.3 ComparisonwithrFoilsuc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5 Role,importanceandassessmentofthewake 45
5.1 TheactivepartinaBLSsystem:thepump . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.2 Wakeflowinamulti-elementairfoilsystem. . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.2.1 Wakeinanadversepressuregradient . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
5.2.2 Wakeburst:aquestionofsemantics? . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
5.3 Assessmentofthewake. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
5.3.1 Gartshore’scriterion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
5.3.2 Wakeburstdetection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
6 BLSconfigurationswithminimalpumprequirementsformulti-elementairfoils 59
6.1 NLR7301 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
6.1.1 Comparisonwithexperiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
6.1.2 NLR7301withsuction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
vii
viii CONTENTS
6.2 MFFS026 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
6.2.1 MFFS026withsuction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
6.3 Theapplicationofsuctiontoavoidwakeburst:thegeneralcase . . . . . . . . . . . . . . . . . 68
7 Conclusion&Recommendations 73
Bibliography 77
A Closurerelations 81
A.1 Laminarclosure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
A.2 Turbulentclosure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
B ChangelogMSEStoMatSESuction 83
C MSES&convergence 89
C.1 ConvergenceoftheNewtonsolver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
C.2 Aflapdeflectionof26◦ontheNLR7301airfoil . . . . . . . . . . . . . . . . . . . . . . . . . . 90
C.3 TheNLR7301airfoilatα 15◦ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
=
C.4 TheNLF22airfoil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92