1.. , )
N~TIONAL ADVISOhY CO MM ITTEE FOR AERONAUTICS
x o. 672
T~~ ST~~LI~G OF FO UR TYPIC~L ~lRFOIL SE~TION S
r~ TrlE N .A. C . A . VARI~31~-~E~ SI~Y TU~NEL
By I r a :r. :~ b bot tall d .Al"O e r t S ~l e r (' a ~ Leu g l ey Je.nor ial Aer o!luutical Laooratory
7i ~ s h in :: tOll
October 1 938
GOVT. DOC.
BU::, .. . ,-.~ _ . ..J ,cNCE
& TECHNOLOGY DEP'T.
https://ntrs.nasa.gov/search.jsp?R=19930081486 2020-06-17T13:09:20+00:00Z
NATIONAL ADVISORY COMMITFEE FOR AEROIAUT ICS
TEC3N ICAL NOTE no . 672
FLOW OESERVA 'rIO IS WITH TUFTS AND LA;',IP BLACK OF
T3E STALLI - G OF FOUR TYPICAL AIRFOIL SECTIONS
In THE N. A. C.A . VAR I, B1E-DENSITY TUNNEL
By Ira a . Ab bot t a nd Albert Sherman
A p reliminary i nvestjgati o n of the sta llin~ processes of f our typ ica l ai~foil sec ti o s was made over the critical r ange of the Reyn ol d , I)'uifiber . l\'otion pictures were taken o f the move : ents of s . all silk tufts o n th e airfoil surface as the ang le o f attack increased through a range o f angl es including the s tall . T~e b oundn y -layer flow also at certain a ng les of a ttack ~as i ni ic a ted by tho pat torns for med by a suspension of l a!llpb lack in oil brushed o nto the airfoi l surface . These observ a tio ns were anal yze d to g ether wi th correspoJdiu . force-test measure ments to e rive a picture o f the stalli ng processes of airfoils .
I~:TR OJTJ CT I O ~
Fue stallin characteri~tics of an airfoil section arE: amon g its most i mp ortant aero dyna m·.c p roperties, not only because the value of tho maxi mum lift coefficient deter~ines the win~ loading pe rmissible for a g iven stall ing s p eed but also because ~hese c haracteristics influence t he manner of stall of tape red wi ng s, vh ich is i nt i mate ly connected with lateral stability and damping in roll at the s t all . A disc u ssion of the me chanis m of the stall is g i v en i n ref e r e n c e 1 , in Vil i c 11. t he s tall i s con sid ere d t 0 b e caused by laminar or turbulent separation result i ng in gen eral fl07 breakdo n ; t he type of s oparation is g overned by ta e airfoil section and t he Reynolds 'umb er a nd is in fluenced by the general bo~ .dary-layer conditions . Although uch experiillcntal and theoret ica l st u y has been devoted to the mechanism of the stall , the phenomena wh ich occur are so comp lex that the understandi ng of the s ubje ct remains unsatisfactory .
L
2 _' .A . C.A. Techn ical No te No . 672
The p r esent p rel iminari inve st i g ation wa s u nde rt aken t o study the stalling of fou r t yp ical airfoil sections over the critical rang e o f the Reynolds Nuob er in the N . A . C.A . variabl e~density tunnel . This inve~ti ~a ti o n is to be e x te nd e d t o include t t e st a lli n g o f tape r ed wings in the r .A.C.A. v ariable-den si ty tunnel a nd of airfoil s ections in f li g ht and in win d tunnel s of mu c h l ess tur bulence than that of th e N . A.C. A . vari a bl e - d ensit y tun nel . I t is expected that t he re sults of t h~ se investigation s , togeth er wit h a ~van ces in boun d ar y -layer theory, will p rovide so me additiona l i nforma tion l eadin5 to a better und ers t andin~ o f the nature of the s tal l and of the efrects of wind -tun nel turbul~ n ce on air f oil d ata.
~ot io n p ic tures o f the move me nts of sma ll s ilk tufts on the ai r foi l surfac e were ma de as the ai ~f o il passed thr ough the stall . As a~ ind ication of t he boundary-layer flow , p attern s fo r med by a suspens io n of l ampb lack in oil brushed onto the ai r foi l surfac e we r o observed at c erta in angles of a tt ack . Th ose o bse rv ations we re corrolated wit h fo rce-test measu r ements to p rovi d e a parti~l p ict ure of the s t alli ng p r oce s ses of th e air foil sections under the f l o l conditions of t he v ariab l e-densit y wind tunnel .
MET1.~O D
The models emp lo y ed were the N . A . C.A . OG09 and 83 1 8 r ectan g u l a r, square - tip air f oils and the N .A.C . A . 0012 and 4 4 1 2 r e ctan gular , rounded-tip a i r foils . The tests were sLaila r to the usua l fo rce tests (reference 2 ) oxcept that two ang le - of -at tack stings i n stead o f th e usua l single sti n we re used to. eli mi nate i nterfe r ence at the mid section of the air f oi l. The on l y force mea s urem e nts made we r e readin~s of the lift coeffic i ents n e a r t he s tall.
For the ob se rv ations of the g enera l flow above the airfoil surface, f in e s i lk tufts wer e employ ed ; their l ength a nd s p aci ng were o f the order of 1 / 4 inch . They were affixed b y their f ro nt ends t o the airfo il upper sur face near t h e mid s ection a nd th e ir posit i ons were sta g ge r ed to mi nimize mutu~ l interferenc e . A remo tely ope r ated 1 6 - mi lli meter moti on - pictur e ca _e ra We S u sed to take t he p i cture r eco rds, the tunnel li ghts bei ng dimmed mo men t ar ily a t specified val ues of the co nt inuou~ l y increasing angle of attack to i nd icat e the a ng le o f att ack on each f il m.
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3
For the Dound.ar y - lay er patt.erns, l.3. mrJ bla~}: was su s ~ended in · oil of various viscosities , t . e viscos i ty be i ng cha~b ed to suit the tunnel o pe r at i ~g copditions , and was b r us he don tot: e air f 0 iIi n a s t h ina f i 1 !.l asp 0 s s i -0 1 e . Tne observations were rne de at fixed angles of attack to obta i n patterns of the flow f o r steady c onditions . Motionpi c ture records , su~p leillE n t e j bJ visua l obs e rv a t i on s whcn possible , were obtained of t ~no;) f or::mtio:1 of the patterns . Po s ition mea ure~ents of the prom i n ent l in e s RId regions in the l ampblack patte r ns were obtaine1 af ter eacnr~n . A lthoug~ some features of most of t he pattern g chan~cd
slow~y with time afte r the 8~r f l ow was stopp ed because t ... le oil ran over t 'le surface , it is believed tha.t the se measu r e1ents represo nt t~e patte rn wit h a fair degree of accur a c y .
T.he tufts were exp cted t o descri-::Je the gen era l f10'.'7 ov er t~e airfoi l , and the lampblack in oil was expec ted to indicate the nature of the f l ow in the boundary layer ~
It_ is imp ortant to reco f~ nizG the possibil it y tha.t the tuf t S .01' the lamp-Dlack may :18ve chango:! he c haracter of the f l ow by th eir p resen~e . This effe=t, ho wever , is be lieved to have b eon s~~ll , inasmu_h as the va l ues of t _ o max i 'mu;:n li ft coef ~.'·~_ c i" nt a greed wi 11 '';:'l e va'_uC's previously obtain ed without tufts .
Fi gures 1 to 4 p rese nt th e resul ts of t~e tuft obser vations co related with the corresponiing section lift curves derived f ro m fo!'c e - test d.ata . ~:ae flow rep resentations are group ed in co:u· ns corr esron~ ing to the dif ~ er
ent valu es of tne effectivG Eeyrtol slumber Re ; the ordi nate position of each repre enta~ion orresponds to the sec.tion angle of att a c: :Xo ' I mpo rta:l t feat -u.res of ti.le flow in tha Doun ary laye:- as de dL!. ced. fro:n the l ampblack patte ns ar c indicated on t' c fi eu~ es "y appropriate symbols . Where symbols o re lock ing , n o mea sure~cnt s were made .
Interpretation of data . - In t h e in te ~r etation of the tu.ft obse:-vationr- , the two conditions t·er.· ed ~ l unsepaC'a ed" a nd "fully separated ll flo qere easil Jr distir_guishable . For unsepara ted flow , the tufts ~ould ordi nar ily l i e flat on the ai.rfoi l surface without movement ; fo r separated f lo w', the t.uftl? fl.uctuated vio l ently in direction , sorne'-
4 N . A . C. A . Tec~nical Note No . 6 72
times disappearing entir e ly from the pictures but g eneral ly ind. icating a stro ng reversed flow . The details of the transition from unseparated to fully separated flow varied wit h the different airfoils and with the va lues of the Reyno lds Number .
In some cases , such as for the N . A . C . A . 4412 airfoil, the fi r st fluctuat i ons of the tufts as the angle of attack of t he airfoi l was increased were small uncertain movements of those nearest the tra i ling edge . Such move ments were conside r ed to be caus e d by the r ela tively thick turbulent bounda r y l aye r . and the f l ow i s conside r ed to be unsepa rated .
In other cas e s , the first movements of the tufts were sudden , violent flicks in wh ich the flow i ndicated by the tufts completely change d direct i on . The se flicks might occur ove r either a sma l l or a large r eg ion . Sometimes these flic k s were of v ery short duration , occurring only for the length of time required for the air to travel two or th r ee chord lengths . As the angle of attack increased , these flic k s commonl y became more fre uent and of longe r duration . The flow in this ca s e is represe nt ed in fi gures I to 4 as Itmomentari l;~r separated . 11
As the flic k s beca me more frequent and of longer dura tion , a point was reached whe re the time during which the flo w was separated was of the same order as the time of unseparated flow . Such a condition is defined as being lIintermittently separated . 1I This condition often occurred witho u t the i ntervention of the s udden short flicks previously mentioned .
In the case of t he lampblac k -in-oil observations , st udy of motion- picture records and visual o bse rvat i on indi cat ed t1at t he first movements of th e ver ' thin film usually consisted of a downstream flow from the leadi ng edg e and a cleaning out of the film by both upstream an d downstream movements fro m so me po int down str eam f rom the location of th e peak negative pressure . In the inter mediate region , two sharp lin e s of lamp black and oil devel oped . These lines might either be merged or be separated by an appreciable distance , in which case the film between them r emained undisturbed by the flow . In a ll cases , the distan c e between the fi r st s ha rp line and the downstream point from which the film moved in both direct ions de creased at i ncreased Reynolds Numb e r s or r educed angles of attack , the entire pattern disappearing at sufficiently
N . A.C . A, Technical Rote No . 67 2 5
l ow an g les . Th e distance bet we en th e two s h ar p lin e s vari e d ac coriing l y . Th e gen eral a ppea r a nce of a pattern is sho'n i n figure 5 , T~e sket c h (fi g . 5a) poin ts out the most definite feat ure s usua lly observ e d in a la mp black pat t e r n as t hey occ ur r ed on t he N. A. C, A. 83 1 8 air fo il . (Se e fi g . 5b . ) Be for e the photograph (fi g . 5b) was tak e n , i ncidental l y , the p a tt ern had run a pp reCi a bly , losi ng it s or i ina l sharpne ss .
Th e prope r i nt erpretati on of s u ch pa tter ns is doubt ful , but th e va ria tions of t he pattern with an g l e of at tac ~ and Re y nolds Number corresp ond close ly to what would b e exp ected from considera tion of the boundary - layer condi tio ns on the basi s · of the following tentat ive i n terpre t ation .
T ~l e fir s t , 0 r u p s t rea m , s h a r p 1 i n e i s tho '.11.; h t t 0 b e a ssoc i a t ed with a l oca l red~ction in tnc s h e a ring fo rces at the sur face of the airfoil . Such a reduct ion i n the s near in g forces may be c au sed by l aminar sepa atio n and , for brevi ty , t he locat i on of th i s l ine wi ll be r e fe rred to a s " po i nt of laminar separat ion . 11 '!:' he poin t f ro m wh ich t he f il m moved in both the u p str eam and the downstr e a m di r e c t ions i s c onsid.e od to be he p o int ",he re thc flow re t urns to t he surfacc as the r esu l t of the for ma tion of t urbu le n ce , T_ e second sharp line tlen becomes th e up st ream li mit o f t he reg ion o f st ro ng reversed flow under t he overrunni ng boundary laye r .
On th e basis of t " i . i nte r p r et atio n , th e p a ttern s sn ow tn e increased. diff i cult y . experienced by the flow i n re t u rni ng to th e su r f ace aft e r laminar sep aration at hi g h an ~ le~ of at tack or at lo w v alues of the Reynolds Number . Even tually t hi s p roces s , i n ~he case of the ! . A. C.A . 0 009 a nd 0 0 12 air f oils, l eads to co~p l ete f lo w sep aration fro m' near t he leadin~ edg e, as i ndicated by the tuft obse rva tions . In t he case of t h e N.A . C. A. 44 1 2 and 83 1 8 airfoils, t he stall occurs by p ro ~ress ive sepa ra tio n fr om n ca r tho traili ng e dge be fo re t he l aminar sep aration beco mes s uffi Cient l y s e v e re t o cau se co mpl .ete flo -o r eakd own .
T~e p .ositions of thE ~i r s t sha r p line of the pa tt e rns ar e tab~ l ated in t ab le I together with so me the or et ica l sep aration pOints co mput e d for the sa me con~itions b y the meth o d of re fe re n c e 3 . rh e mo t i mp o rtant iea t ures o f the b oundar y -lay er flow, as indicated by t h e f ore g oing inter p retation, a r e shown in fi gur e s 1 to 4 . So me features have been o mitted fro m t he p r e s e _ tation b ecaus e o f difficulty in
6 N . A • C • • l... Tee h n i c a J. ].IT 0 t 0 No . . 6 72
me a sll ri ng or i nte r p r et ing the p8.tterns . I n part ' cular , tne point whe e tnA f lo ~ is cons id ered to r et urn to the surface i s often omit t ed bec a"-lse too li ttle l a.mp b lack re li1ain ed in t h is re Gion to pe r mit measure l eEt after t he patte r n .as for med . On account of tu ose difficulties and t~e poss i bil ity tl: at the a c cumul <l.t ion of t l G la npb l ack may affect the .("10'.7, thE) '.lS0 or t h i s Eethod f or tho study of the bound.ary l ay~r i s not advo cated .
E..:..! ..:...C ... h_000L~ir i9..il...:...- The results for the N . A . C . A . 0009 airfoil are p re sented in figure 1 . This airf~il is an exa,np le of t he type i n whic h the stall is influenced p r iaari l y by the l aminar separa t ion o ccurrin g n ear the lead ing edge . In t h0 l ower critical range of the Reyn olds i: u~nber, t he first eviclenJ9 S!10W~1 by the tufts of t e a.p proach i ng stall i s U!cuentary se1J aration occurring .'it the lead ing edge f ollo wed b y inte r mi ttent separation eithe r spr ead ing down strea m fro m th e leadinf ed ~ e or occurr ing simultaneousl y over the wlo l o upp er " u r fa c e . The co mp letely separated rc gj on grows bac·ward to cov a r tho en tir e uppe r surface . If t 'l e lift i s sufficient l y 10'''', h owever , it continues t o increase to about thE) maximun lift co effi cient for a flat ~ l a to .
At a v ~ lue o f t ~ e e f fective ROY~ 0 l is Nu~bo r of 3 , 400 , 000. t ho a ct i o n i s simila r t o that in t ho l owe r r ange except t hat momen t a r y sep a rati on first oc curs near t he traili ng edge , which p r obab l y i nd icates sepa ra tion of t h e turbule n t bo u nda ry l et;r c r. The s epa r ated re g io _ do es not g r ow f o r wa r d bu t p r o bab l y i nflu e n ces t he moment a r y sep arati on t hat s udd e n l y occurs ove r t he e nti r e uppe r surf a ce ; the st a ll the n d evelop s much the samo as at t he l orre r val u es of t he Rey nol ds Num ber . At the h i g her valu es of the ReynolQs Number, i n termittent separation o cc u rs si ;m lta c ously over the en tire u.:,-pe r surfa c e .
R~!~Q..!..~~.!.._Q.Q.1.? ___ ~iI.iQ..tJ.:. .!.. - At t he l owe r end 0 f the c r i t i-cal Reyno lds Numbe r r a ng e , the stal li ng p roces s for t h e N. _4. . C. A . 0012 airfoi l (fig . 2) is similar to that for t h e N . R . C. A. 0009 airfoil, in that sepa r ation g rows back f ro m t he leading edg e to cov er t he entire u p er surfa ce and then i r creases in in te n sit y wit h incr easing ang l e of attack . At the h i gh er Reyno l ds Numbers in the critica l range , the s ep arat ion starts at the trai l in g ed b e and p robably i nf lue n ces the com · l et e f 10 Vf b re a k do tv n fro m the I e ad i ng e d g et hat 0 ccur s at larg er a ngles of att a ck.
N ,A, C-. A. . Tee hn i cal Not e }if o . 672 7
stall 'in g p rocess for th e ~ , A . C.A .. 44 12 airfoil ( fig . 3) a'pp, ear to b e opp osit e to th o se f o r t he N.A . C.A. 0009 airfo il . Sepa ration grows forward from the trai l ing edge wita inc r easin~ ang l e of at t ack , evidently as a re s u lt of p ro gre ssi v e separation of th e turbule n t bOlndary' laye r . Ss parat ion o ri ~i nateq at lo wer angles of attac~ as t h e Reynolds Number is i n creas e d and the stalling pro ce ss cov ers a larg er range of a ng les, the ma xi u m li f t coe.fficie n t bein ~ h i ~he r at t h e h i gher values of the Reynolds Nu~ber . TDe re ar e no sudden cha n g e s in the c ha r a cter of t hE! ' flow in t he re g io n of the stall . The overrunnin c::; flow a pp ears to be unaffected by th e laminar s eparation i nd icat ed by the la mp black t e sts, ~u t the p r esen ce of this la minar separation pro babl~ in fluen ces t~e turbul ent sep a I' a t io n n e a I' the t I' a il i n ~; e d 5 e . ( C 0 mp a I' e r e fer en c c 1.) '
li..:..A . C..: A . ~.;p8~irfoi,h- Fi gure -± ZJ.1 0WS he st al li n g p r oc e sses f or the . C , A . 83 1 8 a ir f o:!.l, w1ic h a r e s omewhat s i milar to those fo r the N. A .C , A. 4412 . At a v a lue of tne ef fe ct ive Rey olds IUillb e r of 200 , 0 00 , a sudden sharp drop i n lift occu.rs at t '1e maxi mu m a Yld i s acco :npani e by a corr esp onding sudd e n change i n th e c~aracter 0 th e fl ow . At all values of the e f fect iv e Reynol , s ~umbe r for which t ests were maie, exc ep t for a v a lue of 800 , 000 , the tufts sh owed s epa ra t i on phonomena at the midd le of th e section corre sp ond ing ro ughly wit h t he r eg io n of rev ersed f lo i indicate by th e l a:npblack at t h e lower val u es of the R eyn ol~ ~u!niJ e r . In gene ral, h owever, the stall r e~ults f ro n p rog r essi ve separation of t " e turbulent b ounda r y l ayer, the s e'parated re gi on g ro ' L.g forward fro m t l1e t r ailing edge . Tn 6 16ad ing edg e r e s is ts the proc es s of s eparation much more mar~edly than does tha t of t h e J .A . C,A , 4412 .
G e n e I' a 1 s ta ll in g: p ro c e,~~~..:.. - Tn est a 11 i n g p I' 0 C e s s e s s . OWl b y t h ese t e sts are in agree ment with the discussion of s talling presented i n refer~n c e 1 . T~e f i nal flow
· br eakdown occurs eit he r ~s l eading-edge separa i on , caused b y sep aration of th e la:ni na r b ounda r y laye r and f ~ ilure to re establish th e ~w thr ough t~e for mat ion of turbulence, o r a s sepa ration of the t'rbulent " oundary layer n ea r the trai li ng edg e . Thes e tw o st lling p ro c e sses a r e n o t , hpw ever, sepa rat e pneno h1 e na occurri~g inde:genden tl y but are i ntimatel ~ re la ted , the a ct ua l p oi n t of s epa ration a nd i ts g r ow th bei ng inf l uenced by t he gene r a l bounda r y-lay c r c on ditions .
~hen sepa ratio n o ccurs nca r the l e ad in ~ edge (f i gs . 1 a nd 2) , it usua lly cau s e s a sudden d ro p in likt either 7ith
8 N . A . C . A . Technir a l :N ot e No . 672
o r without vi ol en t . fl u ctua t ions b etw een t he two co ndi t ions of stalled a n d unst a ll e d f l o w . . In t 4e c a s e o f the N . A . C . A . 0 009 a ir fo i l (fi g . 1 ) , this type o f s eparat io n occurr e d at all v a lue s of t h e Re y n ol d s Nu mb e r ; but , a t the lower valu es , t he f lo w was p a rtl y r e establishe d ov e r a l a r g e portion of t h e c h ord and th e stall was p ro g re ss iv~ . ~h e r eestab l ishrr.e nt o f t h e f l o ~ was fa cilit a ted b y the l o ~ lift c oeffi cient at t he stall , which i nd ic ate s r e lat ive l y lo w adver se p r es 8u ~ e g r a die n ts .
Whe n sep ara t io n o cc u rr e d n ea r t he tra iling e d g e (fig s . 3 a n d 4) , it pro g res s ed f o r ~a rd with o~t an~ s udden fl ow c h a ng e s or dro p s in the li f t e xc ept i n t ~e cas e o f t he N . A . C . A . 831 8 a i rfoil at the lowest va lue of t h e Re y no l ds Numb e r test e d , f or wh ich the fi nal f l o ~ bre akd ow n a ppa rent l y oc cu rred as the r esult o f for~a rd s epa r~t i o n.
'lhe que sti o n ar i s e s a.s t o th f; e x tent to whi c h the ge n e r a l fl o w is s epa rated an d to ~ich the l ift is af fe cte d wh en s epa r a t i on is sho wn by the t l1ft s o n t he su r face , particularl y wh e n the s epara tion sho\n by the tufts is of short du r ation . I n t '18 pr e sent tests , t h e t u ft s often f ailed to sh o w the l ocal s 0pa ra ti on i nd i c a te d by the lamp bl a ck , whi c h ind ic at3d t ha t t ~e r eg ion of r e ver s ed flo u was v e r y s h allo w an d had l it tle e f fe c t o n the gene r a l flo w. Simila rl y , l e s s s h all o w r e g io n s of r e v e r se d flow mi g ht b e i n di c ate d by t he s u rf a ce t u ft s bu t ha v e l i tt le effect on t h e li ft coeff ici en t . Jones (r e fere nc e 4 ) st u d i ed t he flow by mean s of tufts attac h ed to s mal l r o ds e xt e ndi ng so me d i s tan ce fro m t he air f oil surface, bu t .lit t le ha s b e e n do ae to co r rela te t h e result s of s lc h stud. i e s 1.'f ith t he eff e cts on i n s tan tan e 0 us Ii f t for pa r tic u I a r air f 0 i 1 s e c t ion s • F u r t h er st udy c f the det a il e d flo w c hange s an d t he a cco mpa nyi no f luctu atio ns oft ha f o r c es at t he s tall appears to off e r a promising fiel d of resea rc h l ead i ng to a b e tter und e rstandin g of the effe c ts o f s c a l e and t u r bulence a s well as o f t he effect of t he t yp e of st a ll o n airp l a n e pe r f o r ma n ce .
Lang l ey lemorial Ae r o na utical La bor a to r y , Natio na l Ad visory Committe e for Ae r o nautics ,
Langl e;r Pie ld , V8 . • , Sept e mber 7 , 1938 .
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N . A • C • A . Tee hn i cal ~T 0 t e IT 0 • 6 7 2 9
I , J acobs, EasLilan _ . . and Snerman, Albert : irfoil Sec -tio n Characteristics as Affected by Variations of the Reynolds ~urnbe _ , T . R . No . 586 , N . A . C . A. , 1 937 .
2 . ,Tacobs , East . lan i";- . , anc'l. Ab -oott , I r;:.. d .: The :t;r . ~\' . C . A ,
Variable-Density Wi ~ d TU;'1ne: l. T . R . Fo , 416 , N . .A . C . A . • 1 932 .
, , 3 , Von Karman, Tr.t . , ar.d ~,[i llikan , C. 3 .: On t ile Theory
of La mi:1ar 30 ·:nda.r y La y eTS Involving Separa.tion . T . R . No . 504 , ~ . A . C . ~ ., 1 934 .
4 . Jones, B . 'Aelvill : Stall i ng . R . A . S , Jour . , v o l. XXX' III , no . 2 85 , S (.; ~ t . 1934 , pp . 753 - 76 9 .
N . A . C . A . Tee h n i cal }: 0 teN 0 • 67 2 1 0
TABLE .1
r~e oretica1 aLd ~ e a sured La mi nar Se p arat ion Points
( iv-easured p oints obt ained fro m lampb lack p 3.tterns) -,-----J-- - ----,---- - -------N . ~l . C . A . R e ao C L iLa mina r separation p oin ts air f oi l ( millions) (deg . ) (p ercent of chord fro m
I leading edge)
---rheoretical ivlea sur ed
------- -------f-----------1-----0 . 4 6 . 2 0 . 5 000 9 6 . 1 1 1 . 0 1 . 080 I O~ 3 . 3
8 . 2 11 . 0 1 . 0801 . 3 ? I I
. 4 I 6 . 3 I
3 . 2 I I . 4 I 9 . 0 I 1 . 0 . 4 11. 6 I . 5
00 12 1.7 9 . 4- . ~ :o I 1 . 6 1 . 3 1.7 11. 1 1 . 0 50
, 1 . 2 1.0 I
1 . 7 11 . 9 1 . 1 00 I 1. 2 r= • v
3 . 4 9 . 4 . 9 10 ! 1. 5 1.4 3 . 4 1 4 . 2 1 . 3'~9 !
I . 8 . 4
. 4 1 0 . 3 I 1 . 0 , 1. 4 I 44 1 2 1.7 10 . 2 I 1 . 2 3 . 4 13 . 5 I . 9
. 2 8 . 3 I ",1 . 5
83 1 8 . 4 8 . 0 1 . 420
I 22 . 6 21 . 6
. 8 8 . 0 1 . 445 22 . 1 26 1.7 8 . 0 I None
~ 20 ou
-3 Ii J 16
~ 'H o
• 'i 12
1:1 o .... .. o • CD 8
4.
o
oJ
Re- 0.4
..
50 11><> Per ent hOrc1
~-
J I
I
1.7 3.4
0.4 \ \' \3.'
\ \ \ "-
// /
• / ..-.. ~/ ~/
A / P 50 1~0 V Per pent hord 2
I k::2-V 50 1~0 ~ Per ent phord ~
/ V
o .2 .4 .6 .8 1.0 Section lift coefficient, cl
figure la .- rlow obeervatione on the N.A.C,A. 0009 airfoil. (See figure lb for key)
1.a 1.4
III
~
o
~ .. 3 ~ o ~
~ .. co
~
0> ~ ru
... .. GIl
~
L
28
24
~20 ., -0
~ »j'
~ 16 +> +>
'" 'H o .,
i 1 2
R o ... +> o .,
<1l 8
4
o
Re- 6 .1
p 50 Per ent
8.2 )( 106
s
s
1 0 P 50 hord Per ent phord
/'
V /
./ 7
o .2 .4
I
6 . --\ ~~. I
s t;i V Key for la and lb
a Tuft observat10no of the flow
V over the a1rfoil upper s<U'face -. --
V =U ••• par,," fl~. tt= lPO /
/' == llomentarily eeparated.
V ~ Interm1ttently eeparaied •
V - Separated. _ _
/" s Sudden estab11shment of new state of flow. +-- t---
Lampblack-1n-01l observat10ns .
t I Po1nt of lam1nar separat10n. -
I t P01nt of reestablished flow. - -
I ~ Region of revereed flow . I I I I
. 6 _8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 Sect10n lift coeff1c1ent , cz
F1gu'e lb . - Flow obser vations on t",le N.A _C.A. 0009 a1rfoil.
z ;.. ()
»
>-)
<> o
[ o III .... z o .. <> z o
a> --> t\l
"'l ... ~
~
33
38
34
bII ~ 30
'ff .Ii ~ !: 16 II ... o .. .... ! 13
II o .... .. o ..
!D 8
4
o
h
-, I .....
P
t::==-- '-
Re- 0 . 4
Nt.
• ~
50 lOp Pero ent 0 obo d
t Ipoin~ of {amma.; sep~rat1~n. I I I I I I Tuft observations of tbe flow --
t Point of rsestablisbed flow. oyer the airfoil Upper surfaoe.
I- Region of reversed flo • • r------~Un.eparated flow. --
~Koaentarily separ ated. --
~Intermittently separated.
-Separated. --~ V ~ Sudden establisbaent of r-- s
ne. state of f lo •. --1.7 3.~ )( 10
Lampblaok-in-oil observations . --
3.4
-- --~ • 1\ 0 .4 1.7 / -. \ /
S \ 7,/ // ) ~/-;
//
~ / ,/
/ 50 1 )0 ) 50 1 0
V ~
Per ent f ob rd Pero ~nt 0 obo d
/ V
,/ /
/ V
-
o . 2 . 4 .6 . 8 1.0 1.2 1 . 4 Seoti on li f t obefficient , oz
Figure 3.- 11911' obs ervat ions on tbe I.A.C.A. 0012 ·airfoi l.
l1li
~
o ~
~ C» o
[ o ~ tz: o c+ C»
,z: o
en ~ 0.>
... ... ~
t\)
to ., 'tI
28
24 ~
I 20
·1, i ~
~. III ... '.ii 1 :
""' o .,
i a o ..... .. o .,
II)
I
I
-4 ~
r--r-- ~
Re- p.4
50 1 0 Per ent hord
p
~t oLervluonl of Le f l ow over the airfoil upper surface . I--
= Unseparated flow. r---Intermittently separated. ............
r--- ,-- -- I--- -- Separated. 1.7 3.4 106
Lampblack- in--oil observations. I--
t oint of l~ina sep ration.
1\ "-
0 . 4 1 . 7 05 . 4- "-
-"" \ \ , J
) /
/ /'
V v/ /' / ~ v./
~~ ~
~
V ~ 50 1 0
100 V V Per pent chord p 50
V V
./ V
/ V
./ V
0 .2 .4 .6 .8 1.0 1.2 1.4 1.6 Section 11ft coefficient, 0z
rlgure 3.- rlow observations on the N.A.C . A. 4412 airfoil.
'"' ~
o
~
.... .. o
[ o
~ ~ ... <D
~
Ol ~ N
'" ... (Jq
(,0
110 C>
3
2
l' 6
"'!.1 a ~ .w~
~ .. .. .. ~ o
j Q o .. .. o C>
<D
B
"
)
-4 f
-a :
1/
0
I---
- I---- 1/ r----. Re- 0 .3
1-- - ~ ..
• -
~ i"' /? ...... 7
50 1 a Perc nt c ord
l-
-t---- V - I----~ r--0.4 0.8
1\
/ -f-
/ ( :Y
r--- - - -- -..., 0.3 0.4) ><- 0 I
1/ v"'" , ?
t+ l .~ /'
~ r + r t r
V ~I/ r /
? ~ V /
50 1 a 50 1(>0 V/ Pero nt c pOrd Pero ~nt c ord V; V v
......-;
/ 'P'"
J V
/ / V
V j::::Y
V - - . o .( .2 .6 .8 1.0 1.2 1.4 1 .6
Section lift coefficient, 01
Figure 4 • . - Flow obaerTatlona on the B.A.C . A. 8318 airfoil. (Sea figure 4b for key)
I
\\1 )/
/ V
8
1.8
III
~
a ~
... 3 [ o
e. ~ etC)
~ 0> ~ t\)
... ... Oil
:
3'
v --- /' ---Re- 1.7
ao
16
; 'd - 12 ~ .w~
I / ?
50 1 0 Per ent phord
!i .. ~ 8 ... 0
• i , g ~ ..
D 0
" CD
0
-4
./ /
-
/ V
-8
o .2
------- --.........
3.4 106
" 3.4 - \ '1.7
\ 1\ \ ) ) vi
~ V ,/
,/' Key for 4a and 4b.
/ Tuft observatione of the flow
/:/ over the airfoil upper surfaoe •
~ ::?' = Unseparated flow.
= Momentarily separated.
./ V
I ~ Interalttently separated.
50 IPO ./ - Separated. • Per ~ent hord / s Sudden eetablisn.snt of new
/' state of flow.
/ Lampblaok-in-oil obeervations .
/' V , Point of la.1nar separatio •• .
4 Point of turbulent separation. T
+ Point of ress tabll ehed flow . . t- Region of revereed flow .
? Observat ion doubtful .
., .6 .8 1 .0 1. 2 1.4 1.6 1 .8 2.0 a.a Seotion lift ooeffioient , ~
Figur e 'b .- Flow obs ervati ons on the N.A.C.A. 8318 airfoil.
-
... ~
o .. ... 8 ~ o e t' .. It
~
m ~ t\I
.... .. ~ tf
N.A.C.A. Technical Note No. 672
Figure 5a.- Sketch indicating general appearanoe of 1ampb1aok pattern on forward
portion of H.A.C.A. 8318 airfoil. Arrows show direction of motion of 1ampb1aok.
Fig . 5a,b
Figure 5b.- Lampblack pattern on H.A.C.A. 8318 a irfoil. Photograph of pattern; ao , 8.30 , Re , 200,000.
