FFA TN 1990-15

239 Pages·2014·4.81 MB·English

FFA TN 1990-15
FLY GTEKNISKA
FORSOKSANSTALTEN
TheA eronautRiecsaela rch
InstiotfuS twee den
COORDINATESA ND CALCULATIONFSO RT HE
FFA-Wl-xFxFxA,- W2-xAxNxD FFA-W3-xSxExR IES
OF AIRFOILSF ORH ORIZONTAL AXISW IND
TURBINES
by
AndeBrjso rck
Stockh1o99l0m
FlYGTEKNISKFAO RSOKSANSTALTEN FFA TN 1990-15
TheA eonauticRaels earch
Instituotfe S weden
AerodynamDiecpsa rtment
Coordinataensd Calculatiofnosrt heF FA-Wl-xxx,
FFA-W2-xxaxn d FFA-W3-xxSxe rieosf Airfoiflosr
HorizontAaxli sW ind Turbines
by
AnderBsj orck
SUMMARY
Airfoilfso ru se ohno rizontaaxli sw indt urbinehsa ve bedeens igned.
Thea irfoilasr ed ivideidn tot hreed ifferesnetr ies:
Thef irsts eriesF,F A-Wl-xxcxo,n stitutaeisr foilwsi tht hicknetsos
chordr atiofsr om1 2.8%t o 27.1%. Thed esiglni ftc oefficiefnotrs
theF FA-W1-xsxexr iersa ngef rom0 .9f ort he1 2.%8 airfoil1,.0 5 for
a 15.%2 airfoitlo 1.2 fort he2 7.%1 airfoi.l
Twoa irfoilisn a seconsde rieFsF A-W2-xaxrxe d esignewdi thd esign
liftc oefficieanptpsr oximat0e.1l5y u nitsl owert hant hatf ort he
FFA-W1-xsxexr ie.s
Thet hirds erieosf airfoilcso nstitutaeisr foilwsi tht hicknetsos
chordr atiorsa nginfgr om1 9.%5 to 36%.T he2 1.%1 and 19.t5h%i ck
airfoilasr ed esignetdo conformt o thinneNrA CA6 3-60a0i rfoils
whicha ret hent o be usedf ort heo uterp artso f thew indt urbine
bladeT.h et hickeari rfoilasr ed esignetdo offerb etteare rodynamic
performanfcoera given thicktnoe cshso rdr atio than NtAhCiAc6 k3 -
600a irfoils.
SponsoriAngge ncyT:h eN ationaEln ergy Administ(rSaTtEiVo)n
FFAT N1 990-15
CONTENTS Page
1. INTRODUCTION 5
2. ANALYTICAL TOOLS 5
2.1C omparison with Wind TunnelT ests 6
2.2Ap plicatioonf theC alculalated Airfoil Data
to HorizontalA xis Wind Turbines 8
. CHARACTERISTICS OF THE AIRFOILS 9
3
3.1T he1 5.2%T hickA irfoilFsF A-W1-1a5n2d F FA-W2-152
10
3.2T hickerA irfoilsi n the FFA-W1 Series 12
3.3T heF FA-WS2e ries 14
3.4 TheF FA-WS3e ries 14
4 . COMPARISON WITH OTHER AIRFOILS 15
5. PRESENTATATION OF DATA OF THE FFA AIRFOILS 17
6. CONCLUDING REMARKS 18
REFERENCES 19
TABLES 22
FIGURES 37-148
FFAT N 1990-15 5
l.INTRODUCTION
A numbeorf a irfoilfso rH orizontAaxli sW indT urbineHsA,W Tsh,a ve
beend esigneadt FFA.T hea irfoilwse rei nitialdleys ignefdo ra 45
meterd iameteHrA WT.T hatw indt urbinwee re bteo operateadt con­
stantt ip speed arnadtt ioob e powerc onrtollebdy yawinogu to f
wind.W itht his rotino rm ind the airifno tihlesF FA-W1-xsxexr ies
wered esigneDde.s irabclhea racterisotfi tchse sea irfoilasr e
discussiend [1]a nd [2].T heF FA-airfoairlesd esignetdo produce
strucutralleyf ficient airfoial sd eswiigtCnh1 t hati s highetrh na
forc ommogne neraalv iatioani rfoils.
Thist echnicnaolt em ainlpyr ovidecso ordinataensdc alculated drag
polarfso rt heF FA-airfoiAl ssh.o rtd escriptiiosng iveno f the
computeprr ogramtsh atw ereu sedf ort hed esigpnr ocesasn dc al­
culationasn,d s omeo f thec haractiesrticso f thea irfoilasr ed is­
cussedO.n lyc alculataeedr odynamdiact af ort heF FAa irfoilasr e
presenteAd 2.- Dw indt unnelt esto f the 15.t2h%i ckF FA-W1-152
airfoihla sb eenc arrieodu ta ndr esluts fromt hist esta rep re­
senteidn [3].
ANALYTICAL TOOLS
2.
Thea irfoidle sigann da nalysicso desI SESa ndX FOILh aveb eenu sed
fort hed esigann da nalysiosf the FFA-airfIoSiElSs,d. e velopaetd
MITb y Drelaa ndG iles[ 4,5]i,s basedo n a streatmu beE ulere qua­
tion solvefro rt hei nviscifdl owf ieldA. two equatbioounn dary
layerf ormulatiiosn u sedt o calculatthee b oundarlya yerw hichi s
coupletdo thien viscifdl ow fievlidat he boundlaaryye rd isplace­
mentt hicknessB.o undarlya yert ransitioins determinbeyd t hee n
method[ 5]( ni n thee nm ethoids designatAecdr it.)
TheI SESp rograims capabloef calculatisnmga llr egionosf sepa­
ratedf low.T heo nseto f separatioonn t hea irfoislu ctiosni dea nd
the accompanydirnagg i ncreassee em btoe relativewleyl lp redicted.
Thed e-cambereifnfge cotf a thickb oundarlya yero r separatiiosn
alsor epresentiend t heC 1/a-curFvoer.s omea irfoilasn dR eynolds
numberesv enC lmaaxn ds talls eemst ob e rathewre lle stimated.
MarkD relah asr ecentldye velopae dn ewp rograXmF OIL.X FOILu ses
ssentialtlhye s ameb oundarlya yerf ormulatiaosn I SES,b utt hei n­
e
viscifdl owf ieldi s calculatbeyd a linear-viocrittys treafmu nc­
tionp anelm ethodT.r ansonfilco wa nalysiwsi ths hockiss notp os­
siblew itht hep anelm ethoodf XFOILb ut the pmaentehlo ids a p­
preciabflays tetro r unt hant hes treamlinEeu lerm ethoodf ISES.
Calculiaotnsf orw indt urbinea irfoilasr ew elli ntot hes ubsonic
regimwee ren o shockasp peaarn dc alculatiwointsh X FOILi nsteaodf
ISESh aso fferedc oan sidarerbeldeu ctiionn c omputitnigm e.
FFAT N 1990-15 6
BothI SESa ndX FOILh avei nversdee sigmno desw,h eret hev elocity
distributoivoenr a parto f thea irfoicla nb e changeadn dt he
correspondcihnagn gien airfoigle ometrcya lculeadt.X FOILa lsoh as
veryn icef eaturessu cha s modifying mtehaenl ineb ya ddinag �Cp
(asf unctioonf thec hordt)o thep ressurdei stribution.
2.1C omparisons with Wind TunnelT ests
------- ---
EvangelisatnadV emuru[ 7]s how comparisobnest weeInS ES-
calculatiaonndsw indt unnelr esultfso ra n EPPLE3R8 7,a NASA
NLF(1)-10a1n5d a NASAN LF(1)-04a1i6r foilC.o mparisobnest ween
ISES-calactuilonasn dw indt unnelr esultfso rt heF FA-W1-1a5i2r foil
aref oundi n [3.)
Resultfsr omI SESa ndX FOILw erec heckeadg ainswti ndt unnelr esults
fora numbeorf airfoilFsi.g .1 -7s howX FOILc alculaticoonmsp ared
withw indt unnel resfuolrtt shr eea irfoilfsr omt he NACA6 3-series
anda NASAL S(1)-04a2i1r foil.
XFOILc alculatiwoenrse m adew ithf reet ransitioann df orcetdr an­
sitionI.n r ealittyra nsitioins affectebdy suchf actorass surface
qualityf,r ees treatmu brulencaen dn oiseC.o rreliaotnw itht ran­
sition studies ldouwtr uirnbgu lenceen vironmeanntdsv erys mooth
wavef ree surfaicnedsi catteh atv alueosf Acrit=1s4h oulbde used
tor epresefnrte ef lighati rcrafcto nditionAs c.o mmonluys edv alue
of Acrits eemst o be 9, whichh asb eenu sedf ora llf reet ransition
calculatiporness entiend t hisr eport.
Fig.l-s7h owt hat tmhien imudmr agl evela,s calculatbeydX FOILi,s
lowert han tvhael uetsa kenf romw indt unnelt estsT.h eg eneral
characterisotfi tchse d ragp olari s,h oweverr,a thewre llr epre­
sented.
In ordert o carryo utc omparisoofn o thera irfoilwsi tht heF FA­
airfoilcsa lculatiwointsh X FOILh aveb eenm adef or1 5%a nd2 1%
thicka irfoilfsr omt heN ASAL S(1)s eriest,h eF X 84-Ws.e rieasn d
NACA 63-400 airsfeoepi alrsa,g ra4p.h R esultwsi tht heo nea irfoil
testeidn differewnitn dt unnelosf tens hows omev ariationI.t
threeforsee emsm ostj ust ctoom pardei ffereanitr foiltse steidn
thes amew ay,o r in thisc aset o comparceo mpuattionmsa dew ith the
samep rograums ingt hes ameb oundarlya yerp arameters.
Calculatiaornesa lsom adeu sing fitxreadn sitioTnh.i si s donei n
ordert os imulatae r oughl eadinegd ge.T hee ffecotf roughness
arountdh el eadinegd gei s dependeonnt t hes evereneses.,g .h eight,
andt he extensoifo tnh e roughnIetsi ss. i n no wayo bviouhso wt o
simulatreo ughneisns c alculatioannsd,w hatd egreoef roughness
that is tob e simulatedO.n ew ayo f simulatirnogu ghneisns c alcula­
tionsw ouldb e toi ntorducea jumpi n theb oundarlya yerm ometnum
thicknesisn additiotno forcintgr ansitioTnh.i s has pbreaecntc eid
FFAT N 1990-15 7
by Hilla ndG arrad[ 8]a nds eemss oundH.o weverf,o rt hep resent
studyo nlyf orcetdr ansitiowna su sed.T het rnasiitonh asb een
forceadt x/c=1a%t the suctsiiodne a nd1 0%a t thep ressursei de.
Thed esirhea sb een to reprae "sweonrts t cawsiet"hX FOILa ndI SES.
As the angolfe a ttacckh angest,h es tagnatipooni ntw illm ove
arountdh el eadinegd ge.T o be suret hatt hef ixedt ransition
positiowno uldb e downstreoafm t he stagnatipooni ntf,o rt hea ngle
of attacrka ngeu sedi n thec alculatio1n0s%,w asc hooseant the
pressursei dea nd1 % at thes uctiosni de.T ransitiaosn f arf orward
as 1% mightn otb e realistaincd h aso nlyb eenu sed rtoe presetnhte
menitoned" worscta se".
TheF FA-W1-1a5i2r foihla sb eenw indt unnetle stewdi thl eadinegd ge
roughnesRso.u ghnesstsr ipwsi tha heighotf =0.7 at x/c=5w%e re
mm
usedo n an airfoitlh ath ada 700 chord [R3e]s.u ltfsr omt his
mm
testc omparrea thewre llw ithI SESc alculations fowrictehtd r an­
sitioant 1% on the suctsiiodne a nda t 10%o n the pressure side.
Calculatreeds ultwsi thf orcetdr ansitiocno mpared witnod t unenl
testr esultwsi thN ACAs tandarrdo ughneisnsd icatteh att hed etri­
mentaelf fecotn thed ragl evelo f theN ACAs tandarrdo ughneisss
worset hant hato f soleltyr ippintgh e boundary layer.1 5%F or the
thickN ACA 63-airfoils sah arrapst uhcetri opne ako ccurast the
leadinegd gea t higha ngleosf attack.T hef reet rnasitiopno int
thereformeo vesf orwardasl mostto the1 % pointf ora ngleosf attack
arounds tallF.i xintgr ansitioant x /c=1t%h erefohraes v eryl ittle
effecto n theC lma·x Otherai rfoilpsr oducae d istincttra ilinegd ge
separatisounb jectteod a n increasien angleo f attacbke forae high
leadinegd ges ucitonp eaka ppeasr.Them aximulmi ftw ithf reet ran­
sitioins thenr eachewdi th tthrea nsitiopno sitiorne arwarodf the
1% point.e fTfheec otf forcintgra nsitioant x/c=1i%s thenl arge,
whichi s showni n e.g.F ig.8a nd9 .
Resultasr es hownf ort heN ASAL S(1}-04M2O1D a irfoiiln Fig.7.
XFOILc alculatiaornesm adew ithf ixedt ransitioant x /c=7% atb oth
thes ucitona ndt hep ressursei de.T hew indt unnetle sts with
"roughneosns" a rem adew ithr oughnesstsr ipast x/c=7.5a%t both
sides[ 10.] T hisr oughneisss s izedo nlyl argee nougtho provoke
transitioann dn ott o simulataen yh eavy insceocntt aminatiTohne.
dragi ncreasdeu et ot her oughnesstsr ip( trpipings tripi)s rather
wellc apturebdy XFOILf ort hisc ase.T hisa lsoe xemplifiheoswd if­
ferent tehfef ectosf theN ACAs tandarrdo ughneasnsd t hem ilder
NASAr oughneasrse .A revieowf the effectosf roughneosns a irfoils
hasr ecentlbye eng ivenb y Bragga ndG regoreck w[e1r2et] h el ift
lossd uet or oughnesosn, a NASAL S(1-)0413a irfoili,s shownt o be
substantiiafl t estewdi thm ores everreo ughness.
Fig.7a lsos howst hatt hem aximulmi fta nds tlal characterisatriec s
notc orrectrleyp resentedt hebX yF OILc alculatioTnhse.l ift-ucrve
s�opedC,1d/a,d ecreasaess t heb oundarlya yerg etst hickera ndt he
trailinegd ges eparatiporno gressfeosr ward. Tihsi qsu itew ell
FFAT N 1990-15 8
reproduciend X FOILc alculatioen.sg,.F ig.6H.o wevert,h em agnitude
of dCld/a takenf romX FOIL( andI SES)c alculatisoenesm t o be
slightlhyi ghetrh anv alueosb tainefdr omw indt unnetle stsW.h en
thes epartaedr egiongse tm oree xtensiavned t hel iftr eacheist s
maximuvma lueo r drop( stal,l X)FOILc alculatioofntse na ppeatro
oversetimatlei ft.I nXF OIL, thew aket rajectorfyo ra viscous
calculaticoans ei st akenfr oma n inviscisdo lutioant thes amea .
Thisi s nots trictlcyo rrecsti ncev iscouesf fecst decreaslei fta nd
changteh ew aket rajectroy.I ti s believetdh att hise ffecits the
causeo f thed ifferencsehso wni n Fig.8.
2.2A pplicatioofn t heC alculated AiDraftoati olH orizontAaxli s
WindT urbines
Three-dimensional seufcfhea cst ssp,a n-wipsree ssurger adients,
centrifugfaolr ceasn dC oriolfiosr cewsi llb e presenotn a wind
turbineb ladeT.h isw illr esulitn differenciens,e .g.,C1 max and
lift-cursvleo peD.i fferencbeest weetnw o-andt hreed imensional
calculatiaorness hownb y S0rense[n1 3][,1 4]E.x perimaeln wtorki s
donei n Denmar[k1 5][,1 6]i,n theU .S.A[ 17][,1 8]i,n England
[19][,2 0]a ndi n Hollan[d2 1]W.o rki s alsoc urrentdloyn ea t FFA.A
5.35m eter diamweitnedrt urbineh asb eenw indt unnetle steidn a
largew indt unnela t CARDiCn China[ 22]O.n eo f the bladewse re
equippewdi th2 32p ressurtea pss o thatC p/x recordincgosu ldb e
obtainefdo r8 differernatd iaslt atoins.T hisb ladeh asr ecently
beent esteddu rinngo n-rotatcionngd itioants F FA.R esultfsr omt his
testw illb e usedt oo btaiqnu anittativaen dq ualitatidvief ferences
in e.g.C 1 between rtohtea tinagn dn on-raottingc ase.
It seemst o be welle stablishetdh atC 1max is increasfeodr t he
innerp artso ft heb ladeR.e sultfsr omM adseann dR asmusse[n1 6]
indicathei ghlrye duceldi ftc-urvsel opea ndC 1max towardst het ip.
The angolfe a ttacikn thesed atai s derivefdr omb ladee lement­
/momentmuemt hod(sS trimpe thods.) T he chanigne l ift-cursvleo pe
betwee2n- Da nd3 -Dd atac ant herefovreer yw ellb eo riginatifnrgo m
an incompleteniens tsh ee stimatioofn t he angolfea ttacbky t he
bladee lement/momemnettuhmo dR.e sultfsr om [18] show frroems ults
testswi tha rectanguluanrt wistbelda dee quipped wtihteSh 8 09
airfoidle velopaetd S ERI[ 23]P.r essure measurweemreemn atdse a t
the8 0%r adiusst atioonf the blaadned t hel ocal anogfl aet tack
wasm easurebdy a windv anea heado f the bladTeh.e sem easurements
werec omparetdo 2-tDe stasn dr elativegloyo da greemeinsts hown
betweetnh e2 -Da nd3 -Dc ase.
Manyo f thes tudieosf 3-De ffectasr eo nlyy eti n thes ta�ting
phasea ndr eliabldea taa re stitlolb e awaitedI.n the ligohft t he
differenciens,e .g.,C1 max betweetnh e 2c-aDs ea ndt he3 -D the
uncertainitny C1 max as predictbeyd X FOILa ndt hed ifferences
betweeXnF OILa-ndI SESc alculatisoenesm t o beo f lessi mporatnce.
Fort heF FA-Wa1i rfoilasn dt heF FA-W2-1a5i2r foicla lculatiwointsh
ISESa rem ade.D ifferencien sC1 max betweeInS ES aXnFdO ILc alcula-
FFAT N 1990-15 9
tionsa res howni n Fig.31-3I6t. i s believetdh atI SESc alculations
arem orer eliablHeo.w everc,a lculatiaotn tsh eseh igha ngleosf at­
tackm ustb e vieweudp onw iths omewhactr iticaely es.F ort het hick­
esta irfoils utnhcee ratintyi s theg reatesbtu,t t hena gaint,h e
uncertaintayb outt hed ifferencbeest wee2n- Dd ataa nd3 -Dd ata is
largef ort her ootr egion.
No attemptsa rem adet o makec orrectiotnos thpeo larsso thatt hey
applyt o the 3-Dc aseo f a windt urbine.
Furtheurn certadiant aa reC m. Thec alculatveadl ueosf Cm drop( the
absolute valwuheesnt) h et railinegd ges eparatiporno gressfeosr ­
ward. Thiiss s eeni n, e.g., Fig.3 wphietrceh itnmhgoe m endtr ops
from= -0.0f8o ra ttachedf lowt o =-.f0o4r h igha ngleosf atatck.C m
takenf romt hew indt unnetle sts howt heo pposittere nd.T hisd rop
in Cm which seembse ptroe senotf allX FOIL( andI SES)c alculations
of the FFA-airfoainldsm ustb e considerteod b e unrealistic.
At higha ngleosf attack tChctv ea luemsu sta lsob e viewewdi ths ome
caution.
CHARACTERISTICS OF THE AIRFOILS
-3.
Airfoilasr ed esignewdi thv aryintgh icknetsosc hordr atios re­
flectintghe needf ord ifferesntta tionosn the blade.
Theh elixa nglei s smallf ort heo uterp artso f theb lade( the lift
vectoirs directeadl mospte rpendicutloa r the turpbliannee a)n d
theL /D ratiios of utmositm portancAes. t heh elixa ngleg ets
largetro wardst he roott,h eL /Dr atiog raduallloyo seism portance.
Towards rtohoet t herei s insteadf,o rs tructurraels onssu cha s
highc rosss ectiohne ighatn dr easonabslmya llc hordsa, n eedf or
thicka irfoilfso ro peratiaotn h ighl iftc oefficients.
TheF FA-Ws1e rieiss designewdi thb estL /Dr atioast rathehri gh
liftc oefficnites.H owevert,h e1 2.8%p ercentth icka irfoidle signed
fort heb ladet iph asa slightllyo werd esigcn1 than the 15.2%
thick airfTohielr .e asownh yt het ip airfoihla sa lowerd esigCn1
is mainltyh ef ollowinIgf: t he blaidse g ivene,. g.,a lineatra per
planf orm,t hent hel ocall iftc oefficiesnhto uldf,o ro ptimum
performandceec reasteow ardst het ip. Also,a irfoidlr agw itha
roughl eadinegd gew ouldb e higheirf thea irfoiwle red esigned for
a highedre sigCn1 , andl owd ragi s of highesti mporatncea t the
bladet ipw hert he helixangilse s malla ndt he velocitiaerse l arge.
Theu nderlyisnpge cificatisoentus p for the deosfi tghne F FA-W1
andF FA-Wa2i rfoils daersec ribiend [2)a nda fulld iscussioofn
thea irfoiclh aracteriswtiilclst herefonroet b e givenh ere.
FFAT N 1990-15 10
3.1 The 15.2% ThicAki rfoilFFsA -W1-152a nd FFA-W2-152
The1 5.2% thicka irfoilFsF A-W1-1a5n2d F FA-W2-1a5r2e d esignetdo
haveh ighL /D ratios. Hirgaht ioLas/r De e asiesatt atinedb y a rel­
ativelhyi ghC 1d esignI.t i s thep roducCt1 *Ct hati s thei mportant
characterisatti eca chb lader adiuosf a windt urbineD.e signgi tnhe
bladef ora lowerC1 thereforree sultisn largecrh ordsL.a rger
chordgsi vel argeRre ynoldnsu mberwsh ichf avourtsh eL /D ratio.
Also,i f the crosss ection heoifg thhte blaidse k eptc onstantth,e
relativtehi cknesdse creasweist hd esigCn1 a ndt hinneari rfoils
generalhlayv el owerd rag.T ogehtert hism akesL /Da rathewre ak
functioonf desigcnl .
Thec hoicoef desigCn1 c ant hereforbee madeo n structurcaoln sid­
erationTso. s upportth eb laded esignewri tha irfoilosp timized at
differednets igCn1 thea imh asb eent o desigdni fferesnetr ieosf
airfoilcsh aracteribzye tdh eb estL /Da t differeCn1t. S o faro nly
a 15.2% and2 1%t hicks ecitoni s designeidn thel owerC1 design
serieFsF A-W2-xxx.
If a bladee lement/momemnettuhmo ids usedt oo btaionp timumc hord
andt wistd istributiito ins in factt hep roducCt1 *Ct hati s
determinaetd e achb lader adiusA. l argec hordc anb e chooseinf a
lowd esigCn1 is chooseno,r thec hordc anb e decreasiefd t he
desigCn1 is increase(dm orcea mbereadi rfoilosr localt wist
towardas h ighearn gleo f attack.) Differecnhto iseosf desigCn1 ,
i.e. desigann gleo f attackf,o rt hes amea irfoiwli llr esult in
differevnatl ueosf thel ocabll adec hordw,h ichw illr esulitn d if­
ferenRte ynoldnsu mberfso rt hed esigcna se( Winds peeda ndt ip
speedr atio.) Therefore, calcsuhloautlibdoe n csa rrieodu ta t con­
stantC 1*Cf ord eterminatioofn a t whatl iftc oefficiebnets tL /D
willb e obtainefdo ra givena irfoiflo ru seo n horizontaaxli sw ind
turbines.
Fig1.0 and1 1 showc alculatifoonrst he1 52.% thicka irfoilast b oth
constanRte ,a ndw ithR e varying inverselCy1 .I wti itsh s eent hat
by makintgh et hec alculatiaotn cso nstanCt1 *ci; .e.a t constant
C1*Rei,n comparisona ctoon stanRte ,t he angleo f attacrka ngef or
a givenh ighL /Di s increaseFdi.g 1.2 showst hat a highL /Dc anb e
achievebdo thf ort hel owerd esigCn1 o f theF FA-Wa2i rfoials well
as fort heF FA-Wali rfoilF.i g1.3 showsb otha irfoilpsl otted
superimpoosne eda cho ther.( Thed esigcn1 f ort heF FA-Wa2i rfoils
cann otb e characteriazse ldo w,b utt heird esigCn1 i s lowert han
thatf ort heF FA-Wa1i rfoils)
Ifa irfoislu rfaceasr es ufficiently stmhoeol tahm,i nabro undary
layerw illu ndergo separiant tihoena dversper essurger adient
beforter ansitioonc cursT.r ansititohne no ccurisn thef rees hear
layer aan tdr ansitionbaulb blies formedT.h isi s then ormawla y
transitioonc curast airfoilast lowR eynolds numb(eRrels e sst han
FFAT N 1990-15 11
= 5 millio.n T)h em ainp roblem withb utbhbilsie s t he associated
dragi ncreasTeh.i sd ragi ncreasies proportionatlh eth oe ighotf
theb ubble(* B) andt hem agnituodfe t hep ressurjeu mpa t ther ear
parto f theb ubblweh erer eatatchmenotc curs( see e.g.a nd[ 5]
[25].)
Fort het hninerF FA-airfoiwlhse,r el owd ragi s importanatn,
"instabilriatnyg e" hbaese ni ncorporaotne tdh e airfoil suction
side.A n instabilirtayn gei s a regioonf weak adverse pressure
gradientthsa tw illp romote gtrhoew tohf boundarlya yeri nstability
andt ransitiobnu,t w eret heg radienatrse s malle nougtho a void
laminasre paratioTnh.e" instabilriatnyg eo"n the1 5%a irfoilasr e
designetdo minimdirzaeg a tR eynoldnsu mberosf theo rdero f 3 mil­
lionsT.h ei nstabilirtayn gei s roundeodf fa t thea ftp artb ute x­
tendss omed istancbee yontdh ep ointo f laminasre paratioInn. t his
wayt hep ressurjeu mpa t ther earo f theb ubblea,n d thtuhse d rag
increaswei,l lb e kepts malle veni f transitiodno esn oto ccur
beforsee paratioInf. t heR eynoldnsu mbeirs decreased, letnhget h
of thel aminabru bblwei lli ncreasaen,d t hep ressurjeu mpw ill be
largearn dc ausea dragp enaltyF.o rt hes mootshu rfacceo ndition of
thea irfoil, tehfifse cste tst hel owerR e rangef ort hea irfoitlo
Re=2m illion.
Onep urposwea st o desigtnh e1 5.2%t hicka irfoilsso thath ighL /D
ratiocsa nb e realiseOdp.e rationeaxlp erience witthu rbwiinned
bladesh,o weveri,n dicattehsa t thep roblewmi tht oo longt ransit­
ionalb ubblewsi lln otb e the primparroyb lemS.u rfacmea nufacturing
irregulariteireoss,i oonf thel eadinegd ge,o r thea ccumulatoifo n
dirto r insectasr el ikeltyo caupsree matutrrea nsitioAn s.tu dyo f
thee ffectosf differeLn/tD r atioosn thep owerc oefficie[n2t] ,
showst heu tmositm portanocfe a n airfoiflo rw hicht hed egradation
of the L/Dr atiow ith,e .g.,a roughl eadinegd gei s keptt o a
minimumC.a rei s theerforet akent og ivet hea irfoilgso od,o r at
leasta cceptablpee,r formanacse " rougahi rfoils".
Thel owers urfacies designesdo that= 90%l aminafrl ows houlbde
achievabilfe t hes urfacies smoothT.h eu ppers urfacies designed
witha rooft op follobwye tdh e" instabilriatnyg ea'n'd a mainp res­
sure recovertyh et traoi linegd gep ressurTeh.e l engtohf ther oof
topi s,h oweverm,a tcheidn sucha wayt hate ven itfh eb oundary
layeir ss ubj�ctto prematutrrea nsitioann dt hickenindgu et o a
roughs urfacet,he pressurreec oversyh oulbde milde nougtho avoid
boundarlya yers eparatifoonr licfote fficie=n0t.s1 u nitsa bovet he
design lciofetf ficieIntt i.s believetdh att hisg ivest heb est
combinatioofnh ighL /Dd uet ol aminafrl owf ort hes mooth surface
case,a nda cceptabLl/eD wirtohu ghs urfaces.
Iti sp ossiblteha tb etterro ugha irfoiple rformanccaenb e achieved
ift hea irfoiils given moarfetl oadinlgi kee .g.a NACA6 3-615
(a=l.Oa)i rfoilI.n troudcinga certaianf tl oadinwgi lld ecreasteh e
velocitlye velo f ther ooft opa ndr educe tahvee ragaed versper es-