Computer Simulation of Aircraft Aerodynamics

C NASA Technical Memorandum 102221

Computer Simulation

of Aircraft Aerodynamics

Mamoru lnouye

October 1989 .

._- __ - _ _ ~ ( N A S A - T M - 1 0 2 2 2 1 ) COMPUTER S I M U L A T I O N OF N90-11699 A T H € & A F T A E R d D Y N A H I C S ( N A S A ) 4i$ C S C L 0 1 A

.5-& 7’97

Uncl a s G3,/02 0 2 3 9 2 8 7

NASA

National Aeronautics and Space Administration NASA Technical Memorandum 102221

Computer Simulation

of Aircraft Aerodynamics

~~~ ~ Mamoru Inouye, Ames Research Center, Moffett Field, California October 1989

NASA

NationalAeronautics and Space Administration Ames Research Center Moffett Field, California 94035 COMPUTER SIMULATION OF AIRCRAFT AERODYNAMICS Mamoru I n o u y e A m e s Research C e n t e r SUMMARY T h e r o l e o f A m e s R e s e a r c h C e n t e r i n c o n d u c t i n g basic a e r o d y n a m i c s r e s e a r c h t h r o u g h c o m p u t e r s i m u l a t i o n s is described. The c o m p u t e r f a c i l i t i e s , i n c l u d i n g s u p e r c o m p u t e r s and p e r i p h e r a l e q u i p m e n t , r e p r e s e n t t h e s t a t e o f t h e a r t . The methodology of c o m p u t a t i o n a l f l u i d d y n a m i c s is e x p l a i n e d b r i e f l y . F u n d a m e n t a l s t u d i e s of t u r - b u l e n c e and t r a n s i t i o n a r e b e i n g p u r s u e d t o u n d e r s t a n d t h e s e phenomena and t o d e v e l o p models t h a t can be u s e d i n t h e s o l u t i o n o f t h e R e y n o l d s - a v e r a g e d N a v i e r - S t o k e s e q u a t i o n s . Four a p p l i c a - t i o n s o f c o m p u t e r s i m u l a t i o n s f o r a e r o d y n a m i c s p r o b l e m s a r e described: s u b s o n i c f l o w a r o u n d a f u s e l a g e a t h i g h a n g l e o f a t - t a c k , s u b s o n i c flow t h r o u g h a t u r b i n e s t a t o r - r o t o r s t a g e , t r a n - s o n i c f l o w a r o u n d a f l e x i b l e s w e p t w i n g , and t r a n s o n i c f l o w a r o u n d a wing-body c o n f i g u r a t i o n t h a t i n c l u d e s a n i n l e t and a t a i l .

I NTROD UCT I ON S i n c e t h e i n t r o d u c t i o n o f j e t a i r c r a f t t o r e g u l a r c o m m e r c i a l s e r v i c e 30 y e a r s a g o , t h e w o r l d ' s f l e e t h a s grown t o o v e r 7 , 0 0 0 a i r p l a n e s . A l t h o u g h t h e U n i t e d S t a t e s market share h a s e r o d e d o v e r t h e y e a r s , most of t h e s e a i r c r a f t were m a n u f a c t u r e d i n t h e U n i t e d S t a t e s . N e w a i r c r a f t a r e n e e d e d now t o r e p l a c e a g i n g a i r f r a m e s , t o comply w i t h noise r e s t r i c t i o n s , and t o improve o p e r a t i n g e f f i c i e n c i e s . M a n u f a c t u r e r s p l a n t o b u i l d o v e r 8,000 new a i r c r a f t d u r i n g t h e n e x t 1 5 years. One of N A S A ' s o b j e c t i v e s is t o p r o v i d e t h e a i r c r a f t i n d u s t r y w i t h t h e basic t e c h n o l o g y re- q u i r e d t o d e s i g n new a i r c r a f t t h a t will m a i n t a i n t h e c o u n t r y ' s p r e e m i n e n c e i n t h e world marketplace.

F AC I L I T I E S COMPUTER A m e s R e s e a r c h C e n t e r h a s two c o m p u t e r f a c i l i t i e s a v a i l a b l e f o r t h e s i m u l a t i o n o f a i r c r a f t a e r o d y n a m i c s . The C e n t r a l Comput- i n g F a c i l i t y s e r v e s t h e g e n e r a l research n e e d s of t h e C e n t e r w i t h a C r a y Y-MP/832 s u p e r c o m p u t e r . The N u m e r i c a l A e r o d y n a m i c S i m u l a t i o n ( N A S ) f a c i l i t y p r o v i d e s a c o m p u t a t i o n a l c a p a b i l i t y t o t h e whole c o u n t r y , i n c l u d i n g researchers i n i n d u s t r y , u n i v e r - s i t i e s and g o v e r n m e n t a g e n c i e s . T h e h i g h - s p e e d p r o c e s s o r s i n t h e N A S f a c i l i t y a r e c u r r e n t l y a C r a y - 2 a n d a C r a y Y-MP/832.

T h i r t y - f i v e s c i e n t i f i c w o r k s t a t i o n s are d i s t r i b u t e d among u s e r s a t t h e C e n t e r ; o t h e r w o r k s t a t i o n s a r e d i s t r i b u t e d a r o u n d t h e c o u n t r y . T h e c o m p l e t e s y s t e m i n c l u d e s mass s t o r a g e , s u p p o r t p r o c e s s i n g , and l o n g - h a u l c o m m u n i c a t i o n s s u b s y s t e m s c o n n e c t e d b y a h i g h - s p e e d d a t a n e t w o r k . T h e l o n g - t e r m g o a l is t o replace t h e h i g h - s p e e d p r o c e s s o r s p e r i o d i c a l l y w i t h t h e f a s t e s t a v a i l a b l e s u - p e r c o m p u t e r s .

COMPUTATIONAL F L U I D DYNAMICS The N a v i e r - S t o k e s e q u a t i o n s which d e s c r i b e t h e b e h a v i o r of v i s c o u s f l o w s h a v e b e e n known f o r o v e r 1 5 0 y e a r s . C o m p u t a t i o n a l f l u i d d y n a m i c s is t h e r e l a t i v e l y new f i e l d i n which t h e s e p a r t i a l d i f f e r e n t i a l e q u a t i o n s a r e s o l v e d u s i n g h i g h - s p e e d c o m p u t e r s .

T h e flow f i e l d , i n c l u d i n g a n y s o l i d b o d i e s or b o u n d a r i e s , is e n - c a s e d w i t h i n a g r i d of mesh p o i n t s . D i f f e r e n c e methods are t h e n u s e d t o s o i v e t h e f l o w p r o p e r t i e s f o r t h e s p e c i f i e d b o u n d a r y and i n it i a l cond it i o n s .

TURBULENCE N e a r l y a l l p r a c t i c a l a e r o d y n a m i c s p r o b l e m s i n v o l v e t u r b u l e n t f l o w n e a r s u r f a c e s and i n wake r e g i o n s . The c o m b i n a t i o n of t h e f i n e g r i d r e q u i r e d t o r e s o l v e t h e t u r b u l e n c e and t h e p r o c e s s i n g s p e e d r e q u i r e d t o p e r f o r m t h e c a l c u l a t i o n s r u l e s o u t e x a c t s o l u - t i o n s of t h e N a v i e r - S t o k e s e q u a t i o n s f o r complex c o n f i g u r a t i o n s .

I n o r d e r t o o b t a i n s o l u t i o n s , t h e t u r b u l e n c e terms a r e t i m e - a v e r a g e d and a p p r o x i m a t e d w i t h empirical m o d e l s .

The most commonly u s e d t u r b u l e n c e model is t h e Baldwin-Lomax a l g e b r a i c e d d y v i s c o s i t y model ( R e f . l), which w o r k s w e l l f o r f l o w s w i t h l i t t l e o r n o s e p a r a t i o n . Improved m o d e l s are n e c e s - s a r y f o r f l o w s w i t h l a r g e s e p a r a t e d r e g i o n s and steep p r e s s u r e g r a d i e n t s . Computer s i m u l a t i o n of t u r b u l e n c e is b e i n g u s e d t o s t u d y t h e d e t a i l e d s t r u c t u r e f o r t h e purpose of d e v e l o p i n g n e / t u r b u l e n c e m o d e l s . S p a l a r t ( R e f . 2 ) r e c e n t l y p e r f o r m e d d i r e c t s i m u l a t i o n s o f a t u r b u l e n t b o u n d a r y l a y e r on a f l a t p l a t e f o r R e y n o l d s n u m b e r s , R e e , b a s e d on momentum t h i c k n e s s , u p t o 1 4 1 0 .

The d e t a i l e d q u a l i t y o f t h e c a l c u l a t i o n s may b e o b s e r v e d i n t h e v o r t i c i t y c o n t o u r s shown i n F i g . 1.

APPLICATIONS C u r r e n t c a p a b i l i t i e s f o r c o m p u t e r s i m u l a t i o n o f a e r o d y n a m i c s p r o b l e m s a r e d e m o n s t r a t e d by t h e f o l l o w i n g a p p l i c a t i o n s made by inenibers of t h e A m e s A p p l i e d C o m p u t a t i o n a l F l u i d s B r a n c h . The e q u a t i o n s s o l v e d are u s u a l l y t h e t h i n - l a y e r , R e y n o l d s - a v e r a g e d N a v i e r - S t o k e s e q u a t i o n s , and t h e Baldwin-Lomax model is u s e d f o r t u r b u l e n t f l o w .

I

I I 1 1 ' - - - T - I I . I ' I '

0 1000 2000 Moo 4MM 5ooo 6ooo 7000 8ooo pooo X' F i g . 1 V o r t i c i t y c o n t o u r s on f l a t p l a t e , R e o = 1 4 1 0 ( R e f . 2 ) t f o r e b o d v S u b s o n i c f l o w a r o u n d a s l e n d e r f u s e l a g e a t a h i g h a n g l e o f a t t a c k was c a l c u l a t e d by S c h i f f , Cummings, S o r e n s o n , a n d Rizk ( R e f . 3) t o s t u d y t h e v o r t i c a l f l o w on t h e l e e w a r d s i d e , which a f f e c t s t h e m a n e u v e r a b i l i t y o f t h e a i r c r a f t . A c l o s e u p of t h e two-block g r i d is shown i n F i g . 2; t h e i n t e r f a c e is l o c a t e d a t t h e b e g i n n i n g o f t h e wing l e a d i n g - e d g e e x t e n s i o n (LEX). The a f t b l o c k h a s a l a r g e r number o f c i r c u m f e r e n t i a l p o i n t s t o d e f i n e t h e LEX. N e a r l y a q u a r t e r o f a m i l l i o n g r i d p o i n t s were u s e d .

F i g . 2 Two-block g r i d a r o u n d F i g . 3 S u r f a c e f l o w p a t t e r n on a i r c r a f t f o r e b o d y a i r c r a f t f o r ebod y ( R e f . 3) ( R e f . 3) The s u r f a c e flow p a t t e r n is shown i n F i g . 3 f o r M , = 0 . 2 , a = 30°, and p y n o l d s number b a s e d on mean a e r o d y n a m i c c h o r d , R e c = 11.5 x 1 0 . The p r i m a r y and s e c o n d a r y s e p a r a t i o n l i n e s on t h e f o r e b o d y and t h e s e c o n d a r y c r o s s f l o w s e p a r a t i o n l i n e on t h e LEX are i n good a g r e e m e n t w i t h f l i g h t - t e s t d a t a . ' S u b s o n i c f l o w t h r o u g h a t u r b i n e s t a t o r - r o t o r s t a g e was cal- c u l a t e d by R a i ( R e f . 4 ) t o u n d e r s t a n d t h e flow processes i n o r d e r t o d e s i g n more e f f i c i e n t t u r b o m a c h i n e r y . A p a t c h e d - g r i d s y s t e m was u s e d w i t h t h e g r i d a b o u t t h e r o t o r moving r e l a t i v e t o t h e g r i d a b o u t t h e s t a t o r . T h i s is shown i n F i g . 4 f o r a m i d s p a n l o c a t i o n . T h e c o m p l e t e g e o m e t r y i n c l u d e d t h e h u b a n d o u t e r c a s i n g w i t h some t i p c l e a r a n c e . E q u a l number o f r o t o r and s t a t o r b l a d e s were u s e d t o r e d u c e t h e c a l c u l a t i o n s t o o n e r o t o r and o n e s t a t o r b l a d e . The t o t a l number o f g r i d p o i n t s was 2 0 0 , 0 0 0 .

ZONE 3 ZONE 4 F i g . 4 P a t c h e d g r i d a r o u n d F i g . 5 I n s t a n t a n e o u s p r e s s u r e s t a t o r and r o t o r a t c o n t o u r s a t midspan midspan ( R e f . 4 ) ( R e f . 4 ) C a l c u l a t i o n s were p e r f o r m e d f o r a n i n l e t Mach n u m b e r , M i = 0.07, and R e = l o 5 per i n c h . I n s t a n t a n e o u s p r e s s u r e c o n - t o u r s a t midspan are shown i n F i g . 5.

f l o w a r o u n d a f l e x i b l e swept wing was c a l c u l a t e .

T r a n s o n i c b y Guruswamy ( R e f s . 5'6) t o d e m o n s t r a t e t h e c o u p l i n g b e t w e e n t h e v o r t i c a l flow and t h e wing d e f o r m a t i o n . The u n s t e a d y N a v i e r - S t o k e s e q u a t i o n s were s o l v e d s i m u l t a n e o u s l y w i t h t h e s t r u c t u r a l e q u a t i o n s of m o t i o n . A new g r i d was g e n e r a t e d a t e a c h t i m e s t e p t o c o n f o r m w i t h t h e d e f o r m e d w i n g . The i n i t i a l and d e f o r m e d g r i d s a t t h e 50% s e m i s p a n a i r f o i l s e c t i o n are shown i n F i g . 6.

C a l c u l a t i o n s were performed f o r ramp m o t i o n of a r e c t a n g u l a r w i n g , u s i n g a NACA 0015 a i r f o i l s e c t i o n w i t h a n aspect r a t i o of 4 and a sweep a n g l e o f 3 0 ' . The e f f e c t s o f f l e x i b i l i t y on un- s t e a d y l i f t c o e f f i c i e n t s a t f o u r s p a n l o c a t i o n s a r e shown i n F i .

7 f o r M, = 0 . 5 , R e y n o l d s number b a s e d on c h o r d , Re, = 2 x 1 0 % , and p i t c h i n g r a t e A = 0.1. The h i g h e r l i f t f o r t h e f l e x i b l e wing is a t t r i b u t e d t o t h e i n c r e a s e i n a n g l e of attack c a u s e d by t h e f l e x i b i l i t y .

I 75% SEMISPAN ,.----.

,_.__.--.._ RIGID ; 1 -I ROOT .- - - - - - - - FLEXIBLE 0 2.5 5.0 7.5 10.0 12.5 TIME F i g . 7 U n s t e a d y l i f t c o e f f i - F i g . 6 I n i t i a l and d e f o r m e d g r i d a t 50% s e m i s p a n of c i e n t f o r r i g i d and f l e x i b l e wing ( R e f . 5) f l e x i b l e wing ( R e f . 6) C o m p l e t e a i r c r a f t T r a n s o n i c f l o w a r o u n d a wing-body c o n f i g u r a t i o n , i n c l u d i n g a n i n l e t and a t a i l , was c a l c u l a t e d b y F l o r e s a n d C h a d e r j i a n ( R e f . 7). The p u r p o s e was t o d e m o n s t r a t e t h e a b i l i t y t o c a l c u l a t e t r a n s o n i c v i s c o u s f l o w o v e r a complete a i r c r a f t . The flow f i e l d was d i v i d e d i n t o 2 7 z o n e s , d e t e r m i n e d b y g e o m e t r i c a l or f l o w c o n - d i t i o n s , f o r a t o t a l of h a l f a m i l l i o n g r i d p o i n t s . The s u r f a c e g r i d c o v e r i n g t h e f o r w a r d p o r t i o n o f t h e f u s e l a g e , i n c l u d i n g t h e i n l e t and w i n g , is shown i n F i g . 8.

Q = 6 : . a n d R e y n o l d s n u m b e r C o m p u t a t i o n s f o r M , = 0 . 9 , based on wing r o o t c h o r d , Rec = 4.5 x 1 0 8 r e q u i r e d 25 h o u r s f o r 5 , 0 0 0 i t e r a t i o n s , u s i n g o n e processor of a C r a y X-MP/48. P r e s - sure c o e f f i c i e n t s on t h e v e r t i c a l t a i l a t t h r e e - q u a r t e r s h e i g h t a r e shown i n F i g . 9. C o m p a r i s o n w i t h e x p e r i m e n t a l r e s u l t s ( R e f . 8) shows good a g r e e m e n t . C a l c u l a t i o n s f o r t h e wing and f u s e l a g e w i t h o u t t h e t a i l surfaces ( R e f . 9 ) a l s o show good a g r e e - ment ( F i g . 1 0 ) .

-0.1 0.0 0.1 0 3 0.3 0.4 0.5 0.1 0.7 0.1 0.0 1.0 x / c F i g . 8 G r i d f o r f u s e l a g e F i g . 9 P r e s s u r e c o e f f i c i e n t on f o r e b o d y ( R e f . 7) v e r t i c a l t a i l ( R e f . 7 ) A A V a A

\ \

\ \

\ \ K l

\ 7 7

I 77 = 0-45

d m i

I - F i g . 1 0 P r e s s u r e c o e f f i c i e n t on wing and upper f u s e l a g e center- l i n e ( R e f . 9 ) CONCLUDING REMARKS Many c h a l l e n g e s s t i l l r e m a i n i n c o m p u t a t i o n a l f l u i d d y n a m i c s . S t e a d y - s t a t e s o l u t i o n s are s o u g h t u s i n g t i m e - d e p e n d e n t m e t h o d s t h a t r e q u i r e t h o u s a n d s of steps f o r c o n v e r g e n c e . The e f - f i c i e n c y of n u m e r i c a l methods m u s t be improved t o m a k e t h e b e s t u s e of a v a i l a b l e c o m p u t e r s . N e w t u r b u l e n c e m o d e l s are n e e d e d ; t h e most commonly u s e d model--the Baldwin-Lomax model--is o v e r t e n y e a r s o l d and is i n a d e q u a t e f o r s e p a r a t e d flows. S i n g l e - p r o c e s s o r s u p e r c o m p u t e r s are a p p r o a c h i n g t h e i r i n h e r e n t perf or- mance l i m i t s , and multiprocessors o f f e r a means f o r i n c r e a s i n g p e r f o r m a n c e . A l g o r i t h m s and c o d e s m u s t be c o n s t r u c t e d t o take a d v a n t a g e of t h e s u p e r c o m p u t e r a r c h i t e c t u r e . F i n a l l y , a e r o d y - n a m i c s must b e combined w i t h o t h e r aspects of a i r c r a f t d e s i g n .

m a t e r i a l s , c o n t r o l and g u i d a n c e , and p r o p u l s i o n S t r u c t u r e and s y s t e m s are e q u a l l y i m p o r t a n t , and c o u p l i n g b e t w e e n d i s c i p l i n e s w i l l b e r e q u i r e d i n f u t u r e d e s i g n s .

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8. R e u e , G.L., D o b e r e n z , M.E. , and W i l k i n s , D.D., Component

Aerodynamic Load from 1 / 9 - S c a l e F-16A Loads Model, G e n e r a l Dynamics Rep. 16PR316, F o r t Worth, TX, May 1 9 7 6 .

9. R e z n i c k , S.G., and F l o r e s , J . , Strake-Generated Vortex I n t e r - a c t i o n s for a Fighter-Like Configuration, J . A i r c r a f t , Vo1.26, No.4, Apr. 1989, pp.289-294.

Report Documentation Page 2. Government Accession No. 3. Recipient's Catalog No.

1. Report No.

NASA TM- 102221 5. Report Date 4. Title and Subtitle Computer Simulation of Aircraft Aerodynamics October 1989 8. Performing Organization Report No.

7. Author@) A-89227 Mamoru Inouye 10. Work Unit No.

505-60-01 9. Performing Organization Name and Address 1 1. Contract or Grant No.

Ames Research Center Moffett Field, CA 94035 13. Type of Report and Period Covered 12. Sponsoring Agency Name and Address Technical Memorandum National Aeronautics and Space Administration 14. Sponsoring Agency Code Washington, DC 20546-0001 I 15. Supplementary Notes Point of Contact: Mamoru Inouye, Ames Research Center, MS 202A-1, Moffett Field, CA 94035 (415) 694-5126 or FTS 464-5126 Presented at JSASS 27th Aircraft Symposium, Fukuoka, Japan, Oct. 18-20, 1989.

16. Abstract The role of Ames Research Center in conducting basic aerodynamics research through computer simulations is described in this paper presented at the International Sessions of the 27th Aircraft Symposium, sponsored by the Japan Society for Aeronautical and Space Sciences and held at Fukuoka, Japan, during October 18-20, 1989. The computer facilities, including supercomputers and peripheral that represent the state of the art, are described. The methodology of computational fluid equipment dynamics is explained briefly. Fundamental studies of turbulence and transition are being pursued to that can be used in the solution of the Reynolds- understand these phenomena and to develop models averaged Navier-Stokes equations. Four applications of computer simulations for aerodynamics problems are described: subsonic flow around a fuselage at high angle of attack, subsonic flow through a turbine stator-rotor stage, transonic flow around a flexible swept wing, and transonic flow around a wing-body configuration that includes an inlet and a tail.

7. Key Words (Suggested by Author(s)) 18. Distribution Statement Aerodynamics Unclassified-Unlimited Computational fluid dynamics Subject Category - 02 20. Security Classif. (of th~

9. Security Classif. (of this report) 121. No. o f ; F I 22. Price

A02 Unclassified Unclassified I I I 4SA FORM 1626 OCT 86 For sale by the National Technical Information Service, Springfield, Virginia 22161