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OVERVIEW OF ADVANCED WING DESIGN Raymond M. Hicks NASA Ames Research Center ABSTRACT Several recent examples of experiment-theory correlation are presented to givean indicationof the capabilities and limitations of wing design and analysis for transonic applications by potential-flow theory. The examples include correlations of experimental pressure distributions with theoretical results from isolated wing codes and wing-body codes. Both conservative and non-conservative differencing as well as body and boundary layer corrections are considered. The results show that a full potential isolated wing code correlates well with data from an isolated wing test but may give poor prediction of the aerodynamic characteristics of some wing-body configurations.
Potential-flow wing body codes were found to improve the correlation for the wing-body configurations considered.
ISOLATED WING W I N D TUNNEL MODEL Thesweptwingshown i n F i g u r e 1 w a s t e s t e d i n t h e A m e s 12-foot p r e s s u r e t u n n e l a t Mach .8 and a t Reynoldsnumber of 2 m i l l i o n b a s e d on t h e M . A . C . ( r e f . 1). The model was mountedonthetunnel w a l l and hence i s u s e f u lf o re v a l u a t i n gi s o l a t e dw i n gc o d e s .
S = 0. 77M2 (8.283 ft2) A3 =6.04 TAPER RATIO = 0.5
NACA 641 - 212 SECTION
NORMAL TO L.E.
b/2 = 1.52M (5 ft) F i g u r e 1 1 58 II EXPERIMENT-THEORY CORRELATION FOR A N ISOLATED WING The experiment-theory correlation for the isolated wing is shown in Fig. 2. The code FL022NM solves the transonic potential equation in non-conservative form with an iterated Nash-McDonald boundary layer correction. The boundary layer subroutine was coupled with FL022 by P. A. Henne of Douglas Aircraft Company. The results shown in the figure indicate that good experiment-theory correlation of wing pressures can be expected for most isolated wings with 6-series sections at span stations greater than q. % .15. The correlation mightbe expected to be less satisfactory at span stations closer to the wall due to the close proximity to the tunnel wall boundary layer.
Figure 2 1 59 VOUGHT A-7 FIGHTER W I N D TUNNEL MODEL A model of the Vought A-7 fighter was tested in the Ames 11-foot transonic wind tunnel to evaluate the capability of FL022 to predict the surface pressures for a low aspect ratio wing mounted in the high position on a low fineness ratio body. A sketch of the wind tunnel model is shown in Figure 3. The wing has an average thickness of 12 percent of the chord.
Figure 3 1 60
I
EXPERIMENT-THEORY CORRELATION FOR THE A-7 FIGHTER The experiment-theory correlation for the A-7 fighter at Mach .85 and a Reynolds number of 8.7 million is shown in Figure 4 . Note that FL022 predicts a shock position which is farther forward than the experiment at all span stations. The FL022 calculation includes a passive boundary layer correction but no body correction.
us LS 11 ci us LS CP 0 0 EXPERIMENT 0.400 0.335 0 0 EXPERIMENT 0.246 - FLO22 0.390 0.292
- FLO22 0.231
r
-.4 -.4 CP .4 .4
77 = 0.146 77 - 0.4
us LS c\ us LS C ( 0 0 EXPERIMENT 0.343 0 0 EXPERIMENT 0.386 - FLO22 0.277
-
FLO22 0.320 . I I I I .8 .2 .4 .6 .a 1 .o xle 77 = 0.634 q = 0.878 Figure 4 1 61 EXPERIMENT-THEORY CORRELATION FOR THE A-7 FIGHTER A comparison of t h e A-7 w i n d t u n n e l d a t a w i t h c a l c u l a t i o n s o b t a i n e d from the wing-body code, FL028, is shown i n F i g u r e 5. N o t et h a tt h e s h o c k p o s i t i o n a n d s t r e n g t h p r e d i c t e d byFL028 a g r e e w e l l w i t h t h e e x p e r i m e n t a lv a l u e s . The most s e r i o u sf l a wi nt h e FL028 c a l c u l a t i o n s is t h ep r e s s u r eo s c i l l a t i o n so nt h eu p p e rs u r f a c e a t t h e two i n b o a r d s t a t i o n s .T h i sr e s u l ti n d i c a t e st h ei m p o r t a n c e of i n c l u d i n gt h e body e f f e c ti nc a l c u l a t i o n si n v o l v i n gt h i st y p eo fc o n f i g u r a t i o n .
iJs LS T I c , 0 0 EXPERIMENT 0.400 0.335 us LS c\ - FL028 0.396 0.346 0 0 EXPERIMENT 0.246 - FL028 0.279 -.4 CP O .4 I I I I I .e 0 .2 .4 .6 .e 1.0 0 .2 .4 .6 .e 1 .o x l c x l c
77 - 0.4
77 = 0.146 us LS ' I C( us LS T I c , 0 0 EXPERIMENT 0.878 0.343 0 0 EXPERIMENT 0.634 0.386 - FL028 0.856 0.345 - FLO28 0.621 0.377 -.8 -.4 .4 1 ,*L- ~ L . .1.- . . 1 -1". " 0 .2 .4 .6 .8 1 .o .2 .4 .6 .8 1.0 x l c x IC
Q - 0.63 F i g u r e 5 77 - 0.86
1 62 TRANSONIC WING-BODY WIND TUNNEL MODEL Thewind tunnelmodel shown i n F i g u r e 6 was t e s t e d i n t h e Ames 1 4 - f o o tt r a n s o n i cw i n dt u n n e l .T h i sc o n f i g u r a t i o n has b e e ni n c l u d e dt o show t h a t t h e r e s u l t s shown p r e v i o u s l y f o r t h e A-7 f i g h t e r are n o t p e c u l i a r t o h i g h w i n g , l o w a s p e c t r a t i o f i g h t e r a i r c r a f t .
LR = 6.0 (tfc)maxroot = 0.13 (tfC)maxtip = 0.09 F i g u r e 6 1 63 EXPERIMENT-THEORY CORRELATION FOR A TRANSONIC WING-BODY A comparison of experimental wing pressures with those predicted by FL022 for Mach .8 and a Reynolds number of 2 . 3 million is shown in Figure 7 for a transonic wing-body configuration. The calculations included an iterated boundary layer correction and a twist distribution determined by a panelcode analysis to correct for body effects. The poor correlation at the inboard stations indicates an inadquate body correction.
Figure 7 1 64 I -- EXPERIMENT-THEORY CORRELATION FOR A TRANSONIC WING-BODY The experimental pressures f o r t h e t r a n s o n i c wing-body c o n f i g u r a t i o n are compared w i t h c a l c u l a t i o n s f r o m t h e wing-body code, FL030, i n F i g u r e 8.
Note t h a t t h e c o r r e l a t i o n i s s u b s t a n t i a l l y improvedoverthatobserved w i t h FL022 i n F i g u r e 7 , p a r t i c u l a r l y f o r t h e i n b o a r d s t a t i o n s .
F i g u r e 8 1 65 TRANSONIC BIZ-JET WIND TUNNEL MODEL Tests of the transonic biz-jet configuration shown in Figure 9 permitted an evaluation of the ability of the wing-body code, FL028, to predict the effect of body mounted engines on thewing pressure distribution .
c
Figure 9 1 66 TRANSONIC BIZ-JET MATHEMATICAL MODEL The mathematical model used to describe the transonic biz-jet configuration for input to FL028 is shown in Figure 10. The engine installation was simulated by a large "bump" on the side of the body with a cross-sectional area equal to the engine plus pylon minus capture area.
Figure 10 1 67 EXPERIMENT-THEORY CORRELATION FOR A TRANSONIC BIZ-JET The experimental and theoretical pressure distributions with and without the engine installation are shown in Figure 11. The predicted pressures show the correct trend with engine installation but the magnitude of the effect is underestimated.
EXPERIMENT us L S us LS 0 8 N X E L L O F F 0 0 NACELLOFF 0 0 NIICTLLOr. 8 NACELLON - NACELLOFF "" NACELL ON q = 0.27 77 = 0.55 = 0.85 Figure 11 1 68 REFERENCE I 1 . Edwards, George G.; a n d B o l t z , F r e d r i c k W.: An A n a l y s i s of t h eF o r c e s a n d P r e s s u r e D i s t r i b u t i o n o n a Wing withtheLeadingEdge Swept Back 37.25". NACA RM A9K01, Mar. 1950.
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