[American Institute of Aeronautics and Astronautics 10th Atmospheric Flight Mechanics Conference - Gatlinburg,TN,U.S.A. (15 August 1983 - 17 August 1983)] 10th Atmospheric Flight Mechanics Conference - An investigation of the breakdown of the leading edge vortices on a delta wing at high angles of attack
May 9, 2018 | Author: Anonymous |
Category: Documents
AIAA-83-2114 An Investigation of the Breakdown of the Leading Edge Vortices on a Delta-Wing at High Angles of Attack J.F. McKernan and R.C. Nelson, Univ. of Notre Dame, Notre Dame, IN +, *, AlAA Atmospheric Flight Mechanics Conference August 15-17,1983/GatIinburg, Tennessee -~ ~ ~~ ~~~ for permission to copy or republish, contact the American Institute of Aeronautics and Astronautics 1633 Broadway, New York, NY 10019 AN INVESTIGATION O? ViF. RRCAKDOWN OF VIE 1.F.ADlNC EDCi VORTICICS ON A DIII.TR WING AT tiicii .WCI.ES or ATTACK John I:. McKcman" and Robert C . Nelson" Rcrospacc and Mechanical :>,nginecr ing Department U n i v e r s i t y of : lotre D a m e S o t r e Dime, I n d i a n a A b s t r a c t __- An investigation o f t h e Arrakdown of t h e l ead - i n g edge v o r t i c e s t h a t form on d e l t a wings a t h i g h a n g l e s o f a t t a c k is p r e s e n t e d . A l a se r i l l u m i n a - t i o n technique was used f o r fl.ow v i s u a l i z a t i o n . P i c t u r e s were taken a t 1!4-, m i d - , a n d 3 !4 - chord p o s i t i o n s f o r s i d e s l i p a n g l e s of 0 , - 4 , and -8 d e g r e e s a t 10 d i f f e r e n t angles of a t t a c k from 0 to 4 5 d e g r e e s i n increments of 5 d e g r e e s . In a d d i t i o n t o o b t a i n i n g t h i s se r i f s of q u a l i t y photo- g r a p h s , t h e s t r u c t u r e of t h e v o r t i c e s and t h e p r o g r e s s i o n of t h e b u r s t p o i n t as a f u n c t i o n of a n g l e of a t t a c k and s i d e s l i p a n g l e was s t u d i e d . S u r f a c e pressure measurements y i e l d e d l i f t , p i t c h - i n g moment, and r o l l i n g moment curves as f u n c t i o n s of a n g l e of a t t a c k and s i d e s l i p a n g l e . P l o t s o f pressure c o e f f i c i e n t s across t h e span a t v a r i o u s chord l o c a t i o n s , s i d e s l i p a n g l e s , and i n c i d e n c e a n g l e s are a l s o p r e s e n t e d . Nomenclature b c C 1 cM - cP KP K V P 'ATM 'PORT x Y w i n g span Wing r o o t chord R o l l i n g moment coef f i c I C 11 t ( a b o u t c e n t e r l i n e ) L i f t c o e f f i c i e n t P i t c h i n g moment c o e f f i c i e n t ( a b o u t 114 chord) Pressure c o e f f i c i e n t [(I' P o t e n t i a l l i f t c o n s t a n t from Polhamus theo ry Vor tex l i f t c o n s t a n t from Polhamus theo ry Pressure Atmospheric pressure Pressure a t s u r f a c e p o r t on model Free s t r e a m s t a t i c p r e s s u r e F ree stream dynamic pressure Reynolds number (based on m o t chord , P V d i I ) Wing planform area Wing l o c a l semi-span Thickness t o m o t chord r a t i o Free s t r e a m v e l o c i t y Chordwise c o o r d i n a t e Spanwise c o o r d i n a t e PORT - p - ) / q m l - *Graduate Research A s s i s t a n t , L i e u t e n a n t United s t a t e s xavy **Associate P r o f e s s o r , A s s o c i a t e Fellow AIAA a Angle or a t t a c k (3 Sid r . s l i p a n g l e A sweep ang le 0 Dcnsi ty il Viscosiity I n t r o d u r Lion e a r l y i n t h e h i s t o r y o f a e r o n a u t i c s , t h e a d v a n t a g e s of a t t a c h e d flow over n wing were r e c o g n i z e d . I n f a c t , i t became one of t h e major c o n s i d c r a t i o n s i n wing d e s i g n . Howcver, w i t h t h e a d v e n t of s u p e r s o n i c f l i g h t and t h e accompanying wing d c s i g n , t h i s c o n d i t i o n became i n c r e a s i n g l y more d i f f i c u l t to m a i n t a i n . In t h e l a t e 1950 ' s D r i t i s h r e s e a r c h e r s began work on t h e d e s i g n of a s u p e r s o n i c t r a n s p o r t a i r c r a f t which, d e p a r t i n g from t h e t r a d i t i o n a l " a t t a c h e d flow" c o n c e p t , used a. s l a n d e r , sharp-edge wing i n which t h e f low s e p a r a t e d a l o n g t h e e n t i r e l e a d i n g edge producing two s t r o n g s p i r a l v o r t i c e s . ( ' ) has c o n t i n u e d i n t h e s t u d y of t h o s e v o r t i c and t h e i r e f f e c t on t h e aerodynamics of S i n c e thcn i n t e r e s t The flow structure on t h e upper s i d e of a d e l t a wing is ext remely complex. A t moderate a n g l e s o f a t t a c k t h e leeward f low f i e l d f o r t h e s e planforms is dominated by .e h i g h l y o r g a n i z e d v o r t i - c a l f low s t r u c t u r e emanat ing from t h e sharp l e a d i n g edge. A s k e t c h of t h e classtc l e a d i n g edge f low f i e l d s t r u c t u r e on a d e l t a wing is shown i n F i g u r e 1. The v o r t e x s h e e t s shed from t h e l e a d i n g edge r o l l s up i n t o a p a i r o f pr imary v o r t i c e s . The pr imary v o r t i c e s , i n t u r n , c r e a t e secondary "or- [ices near t h e upper s u r f a c e of t h e wing. There i s a s t r o n g f low on t h e s u r f a c e benea th t h e pr imary v o r t i c e s . T h i s outward f low s e p a r a t e s from t h e s u r f a c e forming a smaller secondary v o r t e x o u t b o a r d and below t h e l e a d i n g edge v o r t e x . I t is p o ~ s i h l e t h a t t h e r e are a d d i t i o n a l v o r t i c e s near t h e s u r f a c e i n t h i s r e g i o n . S u r f a c e o i l f low p a t t e r n s have shown e v i d e n c e o f secondary and p o s s i b l y t e r t i a r y s e p a r a t i o n l i n e . The v o r t i c a l f low f i e l d on t h e l e e w a r d s i d e of a d e l t a wing is c h a r a c t e r i z e d hy l a r g e v e l o c i t y v a r i a t i o n s . Near t h e v o r t e x core, a x i a l v e l o c i t i e s n e a r l y f i v e t imes t h e f r e e s t r e a m v e l o c i t y have been measured. The s t r u c t u r e o f t h e l e a d i n g edge v o r t e x can undergo a s u b s t a n t i a l change which i s r e f e r r e d to as " v o r t e x b u r s t i n g " or "breakdown." Vortex b u r s t i n g i s c h a r a c t e r i z e d by t h e sudden d e c e l e r a - t i o n o f t h e a x i a l f low i n t n e v o r t e x core, a decrease i n c i r c u m f e r e n t i a l v e l o c i t y and an i n c r e a s e i n t h e s i z e of t h e v o r t e x . F i g u r e 2 i l l . u s t r a t e s t h e t r a n s f o r m a t i o n t h a t t h e l e a d i n g edge v o r t e x undergoes d u r i n g breakdown. The p o s i t i o n along t h e wing where b u r s t i n g occurs h a s been shown e x p e r i m e n t a l l y t o depend upon t h e l ead - i n g edge sw2ep a n g l e , a s p e c t r a t i o , a n g l e o f a t t a c k and a n g l e o f s i d e s l i p . When v o r t e x b u r s t i n g coccurs t h e prc~:;surc d i s - t r i b u t i o n i s modif ied i n t h e r eg ion wlierc t h c v o r t e x breaks down. 'The l a r g e s u c t i o n prrssures a s s o c i a t e d w i t h t h e l e a d i n g edge V O ~ ~ P X iirr diminished when t h e vortex breaks down. Iirraune o f t h e r e d u c t i o n i n t h e upper surrace s w l ion pressure a f t of t h e b u r s t p o i n t , t h c r e is r i 106s of l i f t , d r a g and t h e nose-dawn p i t c h i n g m ~ m m t . The i n t h e s u c t i o n prcssures. The r e d u c t i o n i n d r a g can be i n t e r p r e t e d as a r e d u c t i o n i n tlw induced d r a g . Recause t h e l o s s i n l i f t occiirs l ~ c ~ l i i n t l the b u r s t p o i n t t h e r e is a r e d u c t i o n i n thv nasc-down p i t c h i n g moment. l o s s i n l i f t is d i r e c t l y r e l a t c d t o t h e rrrlL,rti"" A s i n d i c a t e d by t h e s h o r t i n t r o d w t ion, t h e aerodynamic c h a r a c t e r i s t i c s o f a d e l t a wing are ve ry dependent upon t h e s t r u c t u r e of t h r l e a d i n g edge v o r t i c e s . of an i n i t i a l exper imenta l i n v e s t i g a t i o n of t h e breakdown o f t h e l e a d i n g edge vortices o n n t l c l t a wins a t h i g h a n g l e s of a t t a r k . T h i s paper w i l l p r e s e n t f l i t , resul ts &KT.i!>F t a l A p p r a t!?. A l l of t h e exper iments d e s c r i b e d i n t h i s paper were conducted a t t h e U n i v e r s i t y of Notrc' Ilame Aerospace L a h o r a t o r y . E i t h e r one of twc i d c n t i c a l low t u r b u l e n c e subsonic wind t u n n e l s werr used f o r bo th t h e f low v i s u a l i z a t i o n and p r c s s ~ i r c ~ t c s t i n g . f o r each phase o f t e s t i n g . For t h e smoke-flow v i s u a l i z a t i o n p o r t i o n , t h i s c o n s i s t e d of n smoke g e n e r a t o r , smoke r a k e , laser, G r a f l e n Cr ; iph ic V i e w camera, a Canon AI p o s i t i o n and 3 manual changes o f s w i t c h p o s i t i o n would complete t h e run o f 147 p o r t s . The o u t p u t from t h e S c a n i v a l v e u n i t went t o one of t h e S e t r a - Systems Model 33911 h i g h range e l e c t r o n i c manometers d e s c r i b e d p r e v i o u s l y . The o t h e r e l e c t r o n i c manom- d e t e r r e c e i v e d an i n p u t of s t a t i c pressure from t h e tes t s e c t i o n . Both manometers were a l s o open t o a tmospher ic pressure. The a n a l o g o u t p u t from b o t h manometers went to t h c minicomputer through t h e A I D c o n v e r t e r . Thus t h e computer r e c e i v e d t h e f o l l o w i n g : (PKrM- Pm) and (PATM- Ppor t ) . Th i s i n f o r m a t i o n w a s used t o d e f i n e t h e pressure c o e f f i c i e n t C = (P - PmVQm). A schemat ic of t h i s pressure measuring sys tem i s shown i n FiBurc 7 . P PORT Data A c q u i s i t i o n System The Data A c q u i s i t i o n System used i n t h e p r e s s u r e s t u d i e s was developed a t t h e U n i v e r s i t y o f Not re Dame Aerospace Lab. The main component w a s an Apple I1 P l u s minicomputer , w i t h 64-K b y t e s o f RAM. i n c r e a s e t h e f l e x i b i l i t y of t h c sys tem as wel l as i n c r e a s i n g t h e s t o r a g e c a p a c i t y (270-K b y t e s p e r d i s k ) . Four mini - f loppy d i s k d r i v e s g r e a t l y To f u n c t i o n in i t s r o l e of "experimenter" t h e computer needed several a d d i t i o n s . The d e v i c e s added e n a b l e d the machine t o read a n a l o g i n p u t s th rough a 12-h i t a n a l o g to d i g i t a l ( A I D ) conversion and t o send a n a l o g o u t p u t s t o l a b equipment via a 8 - b i t d i g i t a l t o a n a l o g ( D I A ) c o n v e r s i o n . Thus f a r t h e d a t a has been c o l l e c t e d and s t o r e d by t h c Apple. Through n Hayes Microcomputer P r o d u c t s Smartmodem i n s t a l l e d i n t h e sys tem, i n t e r c o m p u t e r communica- j t i o n between t h e Apple and t h e U n i v e r s i t y I B M 370 Model 168 was e s t a b l i s h e d and t h e d a t a could h e e l e c t r o n i c a l l y t r a n s f e r r e d to t h e I B M 370 t o t a k e advantage of i t s g r e a t l y s u p e r i o r c a p a b i l i t i e s f o r d a t a r e d u c t i o n . Models Two s i m i l a r models were b u i l t , one w i t h pres - sure t a p s f o r t h e pressure s t u d i e s and t h e o t h e r w i t h o u t , f o r smoke-flow v i s u a l i z a t i o n . Roth models had a l e a d i n g edge sweep o f 70 d e g r e e s , a 406.4mm (16 i n ) chord l e n g t h , which y i e l d e d a 2 9 6 m (11 .647 i n ) span a t t h e t r a i l i n g e d g c , and an a s p e c t r a t i o o f 1 . 4 6 . Each were beveled on t h e lower s u r f a c e t o a d i s t a n c e 9.525mm (0.375 i n ) from t h e l e a d i n g edge. The models were made 19mm ( 0 . 7 5 i n ) t h i c k p r i m a r i l y t o house t h e n e c e s s a r y t u b i n g a s s o c i a t e d w i t h t h e pressure taps on t h e pressure model. Th i s y i e l d e d a 0.047 t h i c k n e s s t o chord r a t i o . A s k e t c h of t h c model is shown i n F i g u r e 8 . Exper imenta l R e s u l t s - rlow V i s u a l i z a t i o n The l a se r l i g h t s h e e t technique was a l so used t o s t u d y t h e l e a d i n g edge v o r t e x s t r u c t u r e OD a 70' swept d e l t a wing model a t a Reynolds numher hased upon t h e mid-chord of 225,000. An example of t h e v i s u a l i z a t i o n d a t a o b t a i n e d i n t h i s s t u d y are shown i n F i g u r e s 9 and 1 0 . F i g u r e 9 shows t h e l e a d i n g edge v o r t e x p a t t e r n when t h e model i s - a t 2 5 d e g r e e s a n g l e o f a t t a c k and Zero degree s i d e - s l . i p . The laser l i g h t s h e e t is i l l u m i n a t i n g t h e v o r t e x s t r u c t u r e a t t h e 112 chard p o s i t i o n . The vortex core r e g i o n s are c l e a r l y i n d i c a t e d by t h e v o i d o r d a r k s p o t s i n t h e smoke p a t t e r n . When t h e vortex b u r s t s , t h e v o i d r e g i o n d i s a p p e a r s and t h e s i z e of t h e v o r t e x i n c r e a s e s . F i g u r e 10 shows t h e d e l t a wing model at a s i d e s l i p a n g l e of +8 d e g r e e s . The laser s h e e t is i l l u m i n a t i n g t h e vor- t ex structure a t t h e 314 chord p o s i t i o n . I n t h i s example, t h e r i g h t or windward v o r t e x h a s e n p e r i - enced vor tex b u r s t i n g . The o c h e r p o r t i o n of t h e f low v i s u a l i z a t i o n tests c o n s i s t e d of measur ing tlic p r o g r e s s i o n of t h e h u r s t p o i n t as a f u n c t i o n o f a n g l e of a t t a c k and s i d e s l i p a n g l e . The b u r s t p o i n t was l o c a t e d i n terms of an XlC d i s t a n c e on t h e wing. Th i s was accomplished by t h e i n s t a l l a t i o n o f a g r i d on t h e l e f t s i d e of t h e model. The b u r s t p o i n t could he p laced t o w i t h i n 0.0125 chord l e n g t h on t h e model.. Thc weak l i n k i n t h i s p r o c e s s was t h e d e t e r m i n a t i o n of e x a c t l y what c o n s t i t u t e d t h e b u r s t p o i n t . AB d i s c o v e r e d by Lambourne and R r ~ e r ( ~ ) , t h e breakdown p r o c e s s c o n s i s t e d of t h r e e s t a g e s and d i d n o t happen i n s t a n t a n e o u s l y . I n e f f e c t t h e r e e x i s t s a b u r s t r e g i o n i n s t e a d o f a b u r s t p o i n t . Forward o f t h i s r e g i o n , t h e v o r t e x i s v e r y w e l l d e f i n e d . A f t of t h e r e g i o n , t h e c h a r a c t e r h a s changed dramat i - c a l l y . I n between, though, can he c o n s i d e r e d a' t r a n s i t i o n r e g i o n , ana logous t o t h e laminar t o t u r b u l e n t boundary l a y e r t r a n s i t i o n on an a i r f o i l . So an " e y e b a l l " judgment had t o be made hy t h e ob- server as t o what p o i n t t h e v o r t e x was t o he con- s i d e r e d b u r s t e d . Th i s i n t r o d u c e s an i n a c c u r a c y , e s t i m a t e d t o be a b o u t 5 p e r c e n t , which should bc taken i n t o a c c o u n t when comparing d a t a . F i g u r e 1 1 shows a p l o t of t h e de tc rmincd break- down p o s i t i o n a s a f u n c t i o n o f a n g l e of a t t a c k . The v a l u e a t 2 5 d e g r e e s a n g l e of a t t a c k was es t ima- t e d t o b e a t 114-chord l e n g t h behind t h e model, as no g r i d s y s t e m was a v a i l a b l e h e r e . A f a i r l y smooth curve r e s u l t s . N o t i c e t h a t from 25 d e g r e e s t o 26 d e g r e e s a n g l e of a t t a c k t h e b u r s t p o i n t moves from 114-chord behind t h e wing t o about t h e 0 .88 chord p o s i t i o n on t h e wing. s i m i l a r , evcn more severe, jump f o r h i s 70 d e g r e e model , f rom w e l l a f t of t h e t r a i l i n g edge t o about the 0 . 8 chord p o i n t . Wentz(15) found a From 20 d e g r e e s , where breakdown was f i r s t o b s e r v e d t o occur over t h e wing when a s i d e s l i p a n g l c was induced, to 40 d e g r e e s , where t h e b u r s t p o i n t was so c l o s e t o t h e l e a d i n g edge as t o he non-moasurable, p l o t s were made of breakdown p o s i t i o n of t h e windward v o r t e x as a f u n c t i o n of t h e s i d e s l i p a n g l c . These arc shown i n F i g u r e 1 2 The l eeward v o r t e x is n o t p l o t t e d because i t q u i c k l y moved o f f of t h e wing and i n t o t h e wake. F i n d i n g s from t h i s breakdown p o s i t i o n v i e u a l i - z a t i o n a n a l y s i s b e a r o u t t h e p r e v i o u s l y known rela- t i o n t o a n g l c of a t t a c k . AS i n c i d e n c e i n c r e a s e s t h e breakdown occurs f a r t h e r forward on t h e wing. A s i d e s l i p a n g l e induces an asymmetr ica l b u r s t c o n d i t i o n where t h e windward v o r t e x b u r s t p o i n t moves forward and t h e leeward v o r t e x b u r s t p o i n t moves a f t as s i d e s l i p is i n c r e a s e d . The symmetri- cal c o n d i t i o n compared w i t h o t h e r i n v e s t i g a t i o n s i n F i g u r e 13.(") D i f f e r e n c e s can be accounted f o r severa l ways. p o i n t , as p r e v i o u s l y d i s c u s s e d , c o u l d l e a d t o d i s c r e p a n c i e s . A l so , i t i s known t h a t wing t h i c k - Observer d e t e r m i n a t i o n o f b u r s t ness d e l a y s t h e b u r s t i n g phenomenon. Thi ~n~odcl used h e r e w a s much t h i c k e r than Wentz's m d o c ~ l . pressure Measurements A s w i t h the flow v i s u a l i z a t i o n tCSt6, d l 1 C U ~ S were made a t a Reynolds number o f approxinmtely 225,000. The model used was t h e 70 deg rcc s v r e p a n g l e , 0 , 0 4 7 t h i r k n e s s t o chord r a t i o modcl w i t h 1 4 7 s u r f a c e pressure t a p s . L o c a t i o n s of p r r s s u r e t a p s on thc model are g iven i n Table 1. The p r e s s u r e over t h e e n t i r e model. was surveycr i for 50 d i f f e r e n t c o n d i t i o n s , namely, 10 a n g l e s o f a t t a c k from 0 t o 4 5 deg rees i n inc remen t s o f 5 degrees, and 5 s i d e s l i p a n g l e o f 0 , 4, +R, degrees f o r each a n g l e of a t t a c k . T h c pressirc , r o i - l e c t e d was c o n v r r t e d t o pressure c o e f f i c i c i i t s ant1 was t hen used t o c a l c u l a t e t h e l i f t , p i t c h i n g moment, and r o l l i n g moment. r i g u r e 14 i s a p l o t o f t h e l i f t c w f f i r i e n t versus a n g l e of a t t a c k . The curve shows t h e non- l i n e a r l i f t produced by t h e v o r t e x system. A t abou t 2 5 d e g r e e s angle o f a t t a c k t h e l i f t curve s l o p e d e c r e a s e s and t h e l i f t value r e a c h e s a maximum a t aiiout 35 d e g r e e s a n g l e of a t t a c k and then d e c r e a s e s . The o n s e t o f t h i s d e v i a t i o n from i n c r e a s i n g 1 . i f t c o i n c i d e s w i t h t h e c r o s s i n g o f tlie t r a i l i n g edge by the b u r e t p o i n t . On thr .same graph is p l o t t e d t h e value o f l i f t as pre i i i c t cd by Polhamus, u s i n g h i s l ead ing -edge s u c t i o n znnalogy a n a l y t i c a l method. Th i s method is desc r ibvd i n r f f e r r n c e ( 1 1 , 2 2 C = K SINa COS a + K V SIN a COSa L P where K p is a p o t e n t i a l f l o w c o n s t a n t and K V is a v o r t e x flow c o n s t a n t used t o p r e d i c t t h e l i f t on a s l e n d e r sharp edged wing w i t h no camber o r t w i s t From h i s d a t a , K was determined t o be 1 . 8 a n d P K was equal t o TI V I t shou ld be no ted t h a t values o b t a i n e d by e x p e r i m e n t a t i o n c o i n c i d e well w i t h a c c e p t e d theo ry u n t i l t h e 25 degree angle of a t t a c k p o i n t is reached. This is t o he expec ted s i n c e thi: Polhamus theo ry does n o t accoun t f o r t h e l o s s of l i f t doe t o the b u r s t i n g phenomenon. The p i t c h i n g moment curve is shown i n Figure 15. I t can he seen t h a t as t h e b u r s t p o i n t moves onto t h e wing t h e nose down p i t c h i n g m o m r n t t h a t was p r e s e n t i s l e s s e n e d , c r e a t i n g an " c f f o c t i v e " p i t c h u p . This fo l lows due t o t h e l o s s of l i f t on t h e rear p o r t i o n of t h e wing, a f t o f t he liiirst p o i n t . The r o l l i n g moment curves show t h e e f f e c t of These curves are t h e asymmetr ical b u r s t i n g case. shown i n F i g u r e s 1 6 through 18. Figure 16 is a p l o t o f r o l l i n g moment ( a b o u t c e n t e r l i n e ) v e r s u s angle o f a t t a c k . For t h e zero s i d e s l i p c o n d i t i o n t h e r o l l i n g moment is c l o s e t o zero through the range o f a n g l e o f a t t a c k . The p o s i t i v e and nega- t i v e s i d e s l i p cases are symmetr ical t o each o t h e r , bu t show t h e asymmetr ical b u r s t i n g c o n d i t i o n . For example, -4 degree s i d e s l i p curve shows a p o s i t i v e r o l l i n g moment i n i t i a l l y . Around 15-20 degrees a n g l e o f a t t a c k t h e p o s i t i v e r o l l i n g moment s t a r t s L c dccrease. Th i s i s t h e e f f e c t o f t h e windward v o r t e x s t a r t i n g t o b u r s t over t h e wing. A s t h e windward v o r t e x b u r s t p o i n t moves f u r t h e r f o w a r d with a n g l e of a t t a c k , t he r o l l i n g moment a c t u a l l y Ihnnges s i g n due t o t h e extreme l o s s of l i f t on ~ i i i i ~ s i d e of t h e wing. H O W B V B ~ , a s angle of a t t a c k is f u r t h e r i n c r e a s e d , t h e leeward v o r t e x b e g i n s t o ihiirst over t h c wing. Thus t h e r o l l i n g momcnt curve lh ~ 5 ~ maxi I . 2. 3. 4 . 5. 6 . 7 . 8 . 9. 10. 11. 1 2 . 1 3 . fol lowing concl .us ions were dram. Using t h e laser i l l u m i n a t i o n t e c h n i q u e , a s e r i e s o f smoke photographs o f t he l e a d i n g edge v o r t l c F s a t v a r i o u s combinat ions o f a n g l e o f a t t a c k and s i d e s l i p angle were o b t a i n e d . The photographs appear t o show t h r e e s e p a r a t e r e g i o n s similar t o Earnshaw's v o r t e x model. The l a s e r s h e e t was a l s o used t o de t e rmine t h e v o r t c x b u r s t l o c a t i o n . A s e x p e c t e d , breakdown p o s i t i o n was found t o move f o r - ward w i t h i n c r e a s i n g angle o f a t t a c k and an asym- m e t r i c a l b u r s t c o n d i t i o n developed w i t h s i d e s l i p , where the windward v o r t e x b u r s t e d e a r l y . Comparison w i t h o t h e r d a t a , though c l o s e , ex- h i b i t e d enough of a d i f f e r e n c e t o y i e l d t h e f o l l o w i n g c o n c l u s i o n s . The s o - c a l l e d b u r s t p o i n t is i n a u t a l i t y a b u r s t r e g i o n . Lambourne and Bryer('? s e p a r a t e d t h e phenomenon i n t o t h r e e s t a g e s o f f low d e c e l e r a t i o n , s p i r a l d e f l e c t i o n , and breakdown t o f u l l scale t u r b u l e n c e . From t h e p r e s e n t i n v e s t i g a t i o n i t is sugges t ed t h a t t h i s p rocess t a k e s p l ace over a l a r g e enough area t o cause s u b s t a n t i a l d i f f e r e n c e s i n tlhe d e t e r m i n a t i o n o f b u r s t p o i n t . T h i s problem is compounded by the f a c t t h a t n o s t a n d a r d d e f i n i t i o n of b u r s t p o i n t e x i s t s and consequen t ly d i f f e r e n t i n v e s t i g a t o r s may be u s i n g d i f f e r e n t c r i t e r i a to choose t h i s p o i n t . Again, i n t h e s e p r e s e n t t e s t s u s i n g a laser which o n l y i l l u m i n a t e d one t h i n p l ane of smoke a t m y t ime , t h e p o i n t j u s t p r i o r t o t h e d i sappea rance o f t h e v i s c o u s sub -co re , was t a k e n as b u r s t p o i n t . r i n a l l y d i f f e r e n c e s i n d a t a can be a t t r i b u t e d t o wing t h i c k n e s s . T h i s p a r t i c u l a r d e l t a wing, 19mm t h i c k . was t h i c k e r than most wings t e s t e d by o t h e r s . Th ickness h a s been documented as d e l a y i n g b u r s t and, i n g e n e r a l , r e t a r d i n g v o r t e x development. R e s u l t s from pressure measurements showed t h e e f f e c t o f t h e s e v o r t i c e s on t h e aerodynamic param- e t e r s of l i f t , p i t c h i n g moment, and r o l l i n g moment. The presence o f t h e v o r t i c e s d i d i n c r e a s e t h e l i f t u p t o t h e p o i n t of v o r t e x breakdown on t h e wing. L i f t t a p e r e d o f f , e v e n t u a l l y d e c r e a s i n g , and t h e nose-down p i t c h i n g moment dec reased i n magnitude. Both o f t h e s e e f f e c t s are due t o t h e l o s s o f l i f t over t h e rear p o r t i o n o f t h e wing, beh ind t h e b u r s t p o i n t . R o l l i n g moment a t s i d e s l i p a n g l e s showed an o s c i l l a t i o n as a f u n c t i o n of angle of a t t a c k . T h i s t oo was expec ted due t o the asymmetr ical con- d i t i o n induced by t h e s i d e s l i p . Examinat ion o f t h e pressure c o e f f i c i e n t d i s - t r i b u t i o n s can e x p l a i n a g r e a t d e a l abou t v o r t e x behav io r . The s u c t i o n peaks a s s o c i a t e d w i t h the vortex are e v i d e n t on C p l o t s . Though n o t as d e f i n i t e , o c c a s i o n a l ev rdence o f t h e secondary v o r t e x was present. The peaks a s s o c i a t e d w i t h t h i s v o r t e x , however, are much s m a l l e r , can sometimes be comple t e ly missed, and were n o t e v i d e n t a t all i n flow v i s u a l i z a t i o n t e s t s . A f t e r t he b u r s t p a s s e s th rough a p a r t i c u l a r chord p o s i t i o n , a f l a t t e n i n g of t h e spanwise d i s t r i b u t i o n was n o t e d . Unfortu- n a t e l y t h e b u r s t p o i n t i n s e l f cou ld n o t be p r e c i s e - l y l o c a t e d from t h e s e p r e s s u r e p l o t s as was o r i g i n - ally hoped. Again, t h e a r b i t r a r y n a t u r e o f v i s u - a l l y choos ing t h e b u r s t p o i n t and t h e e x i s t e n c e o f a b u r s t r e g i o n cou ld l e a d t o d i f f i c u l t y i n c o r r e l a t i o n between t h e two forms o f d a t a . E f f e c t s o f v a r i a t i o n s o f t h e p r e s s u r e c o e f f i - c i e n t s along rays as f u n c t i o n s oE a n g l e of a t t a c k and chord p o s i t i o n were seen in t h e l i f t and moment p l o t s . Peaks i n s u c t i o n corresponded to p o i n t s o f mi im l i f t and n c g a t i v c p i t c h i n g moment References Polhamus, E . C . , " P r e d i c t i o n s of Vor t ex - i , i f t C h a r a c t e r i s t i c s hy a Leadins-Edce S u c t i o n . - Analogy," J o u r n a l of A i r c r a f t , V o l . 8 , A p r i l 1 9 7 1 , pp. 193-199. Kulfdn, R . M . , "Wing Geometry E f f e c t s on I .eading Edge V o r t i c e s , " AIM Paper 79-1872, Arigus t 1979. n e r t i n , .J. J . , ,and S m i t h , M . I . . , Aerodynamics f o r Eng inee r s , Englewood C l i f f s , X . J . : P r c n t i c e - B a l l , I n c . , 1979. Earnshaw, P. B . , " A n Expcrimental I n v e s t i g a Lion of t he S t r u c t u r e o f a Leading-Edge I.ambourne, N . C . , and Rryer , D . W . , "The B u r s t i n g of Leading-Edge Vortices-Some Obse rva t ions and Di scuss ion of the Phenomenon," A e r o n a u t i c a l Research Counc i l , Repor t s and Memoranda, N O . 3282, 1962. E l l e , B . J . , "On t h e Rreakdown a t l l igh I n c i - dences o f t h e Leading-Edse V o r t i c e s on n o l t a Glings," J o u r n a l of t h e Riyal Aero%- S u , Vol 64, 1960, pp . 491-493. E l l e , B . J . , "An I n v e s t i g a t i o n a t Low Speed o f t he Flow near t h e Apex o f Thin De l t a Wings w i t h Sharp Leading Edges," A e r o n a u t i c a l Research Counc i l , Reports and Memoranda, No. 3176, 1961. Peckham, D. â¬I., "Low Speed Wind Tunnel T e s t s on a S e r i e s o f Uncambered S l c n d e r P o i n t e d Wings w i t h Sharp Edges," A e r o n a u t i c a l Research Counc i l , Reports and Memoranda, No. 3186, 1958. E r i c k s o n , 6. E . , "Water Tunnel S t u d i e s o f Leading Edge V o r t i c e s , " J o u r n a l o f A i r c r a f t , Vol 1 9 , June 1982, p p . 442-448. Benjamin, T. B . , "Theory of t h c Vor t ex Break- down Phenomenon,'' J o u r n a l o f F l u i d Mechanics, Vol. 1 4 , 1963, pp. 593-629. Lowson. M. V . . "Some E m e r i m e n t s w i t h Vortex ~~ ~~ Breakdown," J o u r n a l o f t he R o ~ A e r o n a u t i c a l w, V o l . 6 8 , 1964, pp . 343-346. Eamshaw, P. B . , and Jawford , J . A , , "LOW Speed Wind T u n n e l Experiments on a S e r i e s of Sharp-Edged De l t a Wings," A e r o n a u t i c a l Research Counc i l , Repor t s and Memoranda, No. 3 4 2 4 , 1966. Hummel, D . , and S r i n i v a s a n , P . S . , "Vortex Breakdown E f f e c t s on t h e Low Speed Aerodynamic C h a r a c t e r i s t i c s of S l e n d e r De l t a Wings i n Symmetrical Flow," Journal of t h e Royal Aero; n a u t i c a l S o c i e t y , Vol. 71, 1967, pp . 319-322. 1 4 1 5 16 . 17, 18. 19. 2 0 . 21. P a r k i n s o n , 6 . V . , Sun , Y . C . , a n d D a v i s , 11. R., "Observa t ions on Low Asnect R a t i o W i n w a t High I n c i d e n c e , " $&an Aeronaut ics -~ ;incj Space J o u r n a l , Vol. 1 3 , March 1967 , 1pp. 111 116. Wentz, W . H . . "Wind Tunnel I n v e s t i g a t i o n s of Vortex Breakdown on S l e n d e r Sharp-I F i g u r e 5 Smoke Hake Figure 8 Specifications of Delta Wing Model Figure 9 Leading Edge Vortices on a 70 Degree ?iz.urc 5 Zkctc'i of F l o w Visualization Experimental Delta Wing a = 25', B = 0", X = c / 2 set up F i g u r e 10 Leading Edge Vortices on a 70 Degree Figure 7 Pressure Measuring System with Computer Delta Wing a = 2 5 ' , B = a*, X = 3 c / 4 7 Figure 11 Vortex Breakdown P o s i t i o n Versus Angle o f A t t a c k BURST POINT- TRAILING EDGE f CROSSES 1 ni n -r-~- ~ n - a i 200 A 0 0 D 0 0 0 0 0 0 0 0 0 0 0 0 0 v) T.E. 0.8 0.6 0 4 0.2 APEX X I C Figure 1 2 Vortex Breakdown P o s i t i o n Versus Side- s l i p Angle (Windward Vortex Only) -e----=--- W 0.03 + 0.02 w - u t 0 0 1 - x 5 0 - z " w I 0 5 0 J J -001 f 8-0 02 -0.03 - A a.o* . 0 0 = 5 0 0 0 (I 40" 0 a = z o o ~ g 0 0 ~ 1 5 ~ - 0 8 A A , t A - 0 0 0 8 ~ 0 8 -a -4 o w 4 a ~ u -. Figure 1 7 C 1 R o l l i n g Moment C o e f f i c i e n t Versus S i d e s l i p Angle. a - 0 - 20' 1 0 02 -4.0- + z $ -3.0- LL Y W 0 w n 3 m m W 0 -2.0- n a t 001- w u 0 0 > -001 - LL LL w " + z w 0 I -- -5.0--1 A 01 IO' 0 a Z 2 0 " o a = 4 0 ° 0 Q 30" X /C = 0.5 O p o O 8 %,egg- i300008 0". A :j: n +O-,ann 0 0 a 0 ncbn; o n A b . 0 J 8 -Oo3 -a - 4 0 4 a i ' igrn Y I S ( X 1 -e 20 c = Pressu re C o e f f i c i e n t D i s t r i ! > u t i o n P Versus Wing Semi-span at 35' Anglc of At t ack f o r Various Chord L o c a t i o n s n a = 150 + -4.0- 0 k -3.0- 5 w 0 " w Ln m w a 5 -2.0- a -1.0- n a = 25" 0 (I i 35" 0 a = 45" Y / S l r l i 0.6 0 0 0 0 l-L-d~~ 0.2 0.4 0.6 0.8 1.0 X / C i 'igure 21 C Pressure C o e f f i c i e n t D i s t r i h u t i o n P v e r s u s Chord Loca t ion a t y/s(x) = 0.6 f o r Various Angles o f A t t a r k -5.0 1 1 1 1 1 1 1 1 1 Y / C : 0 3 n X I C ~ 0 . 5 CROSSES 0.3C x,c io,7 BURST POINT BURST POINT CROSSES 0.5C W m W a Y / S ( x l = 0.6 IO 20 30 40 50 fiNGLE OF fiTTfiCK (DEGREES) F i g u r e 22 C 1 Pressure C o e f f i c i e n t D i s t r i b u t i o n Versus Angle of A t t a c k a t y / s ( x ) = 0.6 f o r Various Chord L o c a t i o n s P
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Report "[American Institute of Aeronautics and Astronautics 10th Atmospheric Flight Mechanics Conference - Gatlinburg,TN,U.S.A. (15 August 1983 - 17 August 1983)] 10th Atmospheric Flight Mechanics Conference - An investigation of the breakdown of the leading edge vortices on a delta wing at high angles of attack"