Document
UNIVERSITY O F WASHINGTON
AERONAUTICAL LABORATORY
REPORT 801 An Experimental Investigation of Feasibility of t V/STOL ~ a e t section in UWAL 8 x 12 Wind Tunnel by Using a 1/8 Scale Model of the T u n n e l - * c .
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TABLE OF CONTENTS Paqe Photo Index Figure Index 2, 3 Summary R e p o r t 3ody Introduction Description of Model Tunnel and Equipment Testing Procedure 13 R f t 6 U l t S and Discurtsion Conclusions References 2 0 . c L 801 I .
PXUTO INDEX Title Photo Paqe
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1 Basic 8 x 12 Model Tunnel Without Extension 2 1 2 Model Tunnel With 7 5 Foot Extension Added 21 3 Survey Probe in 8 x 12 Test Section 22 4 Survey Probe in 2 1 x 19 T e s t Section 22 FIGURE INDEX T i t l e Paqe Fisure
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B a s i c Dimensions of the Large T e s t S e c t i o n 2 3 Probe C a l i b r a t i o n Curves 2 4 Model Tunnel P r o p e l l e r Performance 25 4 Upflow i n Vertical P l a n e of Trunnion E x 12 Te s t S e c t i o n 26 5 C r o s s f l w i n Vertical Plane of Trunnion 8 x 1 2 Test Sect i o n 27 6 Dynamic P r e s s u r e D i s t r i b u t i o n i n Vertical Plane of Trunnion 8 x 12 T e s t S e c t i o n 28 7 Flaw Angles i n 2 1 x 19 T e s t S e c t i o n , S t a t i o n 1 29 Flow Angles i n 2 1 x 19 T e s t S e c t i o n , S t a t i o n 3 30 Flow Angles i n 2 1 x 19 T e s t S e c t i o n , S t a t i o n 5 3 1 1 0 Dynamic Pressure D i a t r i b u t i o n i n S t a t i o n 1, 2 1 x 19 T e s t S e c t i o n 32 11 Dynamic P r e s s u r e D i s t r i b u t i o n i n S t a t i o n 3 , 2 1 x 19 T e s t S e c t i o n 33 1 2 Dynamic P r e s s u r e D i s t r i b u t i o n i n S t a t i o n 58 21 x 19 Test S e c t i o n 34 13 E f f e c t of P r o p e l l e r Anti-swirl Vanes on V e l o c i t y Profile at 117 i n . Model Scale Downstream of P r o p e l l e r 35 , .
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FIGURE INDEX Fiqure T i t l e PaQe 14 E f f e c t of Propeller Anti-swirl Vanes on V e l o c i t y Profile at 187 in. Model S c a l e Downstream of Prepeller
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SUMMARY
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F e a s i b i l i t y of adding a large test s e c t i o n u p s t r e a m of the 8 x 13 test s e c t i o n of t h e F. K. K i r s t e n wind t u n n e l was experimentally i n v e s t i a a t e d by a scale model of the e x i s t i n g wind tunnei. The v a l i d i t y of the unmodiir'ied m o d e l w a s r'irsi verified by comparing m o d e l t u n n e l f l o w w i t h f u l l scale 8 x 12 t u n n e l flow. F i n a l l y , the model t u n n e l was m o d i f i e d
by adding a 21 x 19 - 60 foot test s e c t i o n upstream of t h e 8 x
1 2 test s e c t i o n . Corner vanes and propeller a n t i - s w i r l vanes were shown to have s u f f i c i e n t effectiveness t a contrzl flow angles and velocity distribution in both test sections. A f i n a l sdjustment was achieved which 5ave s a t i s f a c t o r y flow i n b o t h test s e c t i o n s .
It is coneluded t h a t the pzcposed modification of t h e p r e s e n t 8 x 12 t e s t section wind t u n n e l to accomadate a larse test section for V/STOL aircraft wind t u n n e l testing is feasible.
- - 5 8 1 1 I. I n t r o d u c t i o n V/STOL* a i r c r a f t at low forward speeds have t h e unique characteristic of causing l a r g e downwash a n g l e s ,
apprsachfng !?no at the hovering conditiol?. x C G i i S e q i i i e E Z e
is t h a t t h i s type of a i r c r a f t experiences l a r g e changes i n p i t c h i n g moments i n t h e t r a n s i t i o n region between t h e hovering and c r u i s i n g c o n d i t i o n thus i n t r o d u c i n g untlsual handling problems. Such d i f f i c u l t i e s must be f u l l y i n v a s t i c a t e d before f l i q h t , p r e f e r a b l y by u s i n g a model i n a wind t u n n e l which h a s t h e c a p a b i l i t y of providing an aerodynamic environment e q u i v a l e n t t o the t r a n s i t i o n c o n d i t i o n s of the aircraft. Consequently t h e wind t u n n e l must be able t o provide an a c c u r a t e l y c o n t r o l l e d l o w test air v e l o c i t y (approaching r e r o ) , and a minimum w a l l i n t e r - f e r e n c e error.
The problem of the wall i n t e r f e r e n c e can be r e l i e v e d by r e q u i r i n g a s m a l l r a t i o of t h e model t o test s e c t i o n si7e.
The d i f f i c u l t y and high c o s t of c o n s t r u c t i n g a c c u r a t e small models, together w i t h t h e l o w Reynolds number re- s u l t i n g , makes it either impractical o r unacceptable t o use the n o m a 1 si7e wind tunnel. Thus t h e only w a y t o o b t a i n a small r a t i o of t h e model t o test s e c t i o n sipe is t o b u i l d a l a r g e test s e c t i o n . F a c i l i t i e s w i t h l a r g e r * V e r t i c a l o r S h o r t Take-Off and Landing I . .
test s e c t i o n s have been developed and used by t h e NASA and .
some a i r c r a f t companies throughout the country. b u t t h o s e f e w f a c i l i t i e s now e x i s t i n g w i l l n o t be able t o m e e t the demands of t h e i n d u s t r y f o r a r o u t i n e development wind tunnel +astin9 nf their V ! S T O T , aircraft d e s i q .
The p r e s e n t UWAL** 8 x 17 f o o t , 2 5 0 mph, wind t u n n e l could be modified t o add a large t e s t s e c t i o n by r e l o c a t - i n g t h e bellmouth of the e x i s t i n g t u n n e l f u r t h e r up- stream. A l a r g e test s e c t i o n could be produced i n t h i s manner w i t h a cross s e c t i o n of 3 0 3 or 439 square f e e t upstream of the e x i s t i n g 8 x 1 2 test s e c t i o n . The v e l o c i - t y i n t h i s large test s e c t i o n would be very low (7ero t o 6 ' 3 or 8q mph) and would be a c c u r a t e l y c o n t r o l l e d , i n s p i t e of model power i n p u t , due t o the r e l a t i v e l y large power r e q u i r e d by the whole t u n n e l c i r c u i t . Such a modi- f i c a t i o n was proposed i n WAL Rep. 744.
A f i r s t s t e p i n t h e proposed modification program was t o b u i l d a p i l o t model of t h e p r e s e n t wind t u n n e l , and t o t r y t h e s e changes i n t h a t model- The value of such a model t u n n e l has b e e n s u b s t a n t i a t e d by t h e NASA i n t h e i r study of t h e 7 x 19 f o o t t u n n e l modification a t Langley.
and by t h e Boeing Company's e x t e n s i v e use of t h e i r model tunnels. A t t h e same t i m e , an a n a l y t i c a l s t u d y o f t h e **University of Washington Aeronautical Laboratory c 7 ~ above proposed modification w a s made t o explore t h e flow field i n a two-test-section tunnel, This study (UWAL Rep, 7 7 3 ) was encouraging and its r e s u l t s were used to choose the experiments to be conducted i n the model tunne 1 .
Thus the c b j e c t i v e s of the experimental work ware devel- oped as f o l l w s : 1. To v e r i f y t h a t the model t u n n e l fluw is a t r u e reproduction of flow i n the f u l l scale tunnel.
2. To determine i f a high q u a l i t y flow environment can be produced i n the proposed new test section.
To find i f any changes occur in the 8 x 12 t e s t 3.
e e c t i o n as a result of adding the proposed new test s e c t i o n .
It is the purpose of this r e p o r t t o d e s c r i b e the design of t h e model tunnel and t o p r e s e n t the experimental work carried o u t t o answer the three questions stated above.
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80 1 8 11. D s s c r i p t i o n of Model Tunnel and Equipment 1. Model Tunnel The design and c o n s t r u c t i o n of a p i l o t m o d e l t u n n e l of t h e UWAL 8 x 1 2 foot wind t u n n e l was started i n June, 1963. I t was d e s i r e d t h a t t h e model tunnel be as large as possible in order t o obtain an a c c u r a t e f l o w survey and reasonable Reynolds N u m b e r . Space l i m i t a t i o n d i c t a t e d the scale of the model tunnel t o be as s m a l l as possible. The f i n a l scale was s e l e c t e d t o be 1’8, The power loss due t o Reynolds Number effects w a s predicted u s i n g the data obtained i n the Boeing Company’s 1/20 scale model tunnel. The scal- i n ? l a w used was to match the p r o p e l l e r advance r a t i o ( V / n D ) and t i p Mach N u m b e r which r e s u l t s i n speeds i d e n t i c a l t o those v a l u e s of t h e f u l l scale t u n n e l .
The model t u n n e l is e r e c t e d on i t s side i n t h e lobby of t h e full s c a l e t u n n e l f o r easy access t o major p a r t s of t h e tunnel. See Photo 1. For t h e sake of convenience and t o correspond w i t h the f u l l scale t u n n e l the upper r e t u r n d u c t is designated “ w e s t ” and t h e lower d u c t “ e a s t , ” and the panel closest t o t h e o p e r a t i n g console corresponds t o t h e c e i l i n g of the f u l l scale tunnel. A l l dimensions, s i g n conventions, and v e r t i c a l and h o r i z o n t a l d i r e c t i o n s used i n t h i s report are i n the sense of the f u l l scale t u n n e l , t .
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u n l e s s otherwise s p e c i f i e d . Photo 1 s h o w s the basic model t u n n e l w i t h its 8 x 13 test s e c t i o n c e i l i n g for a c c e s s t o the test s e c t i o n . One panel removed c e i l i n g panel down stream of each p r o p e l l e r is re- mov~ble far r e t u r n d a c t access, The ?x?1l,m,outh t1irEinq vanes, d i f f u s e r t u r n i n g vanes, and p r o p e l l e r a n t i - swirl vanes are a d j u s t a b l e i n t h e i r a n g l e s of i n c i - dence. The s e c t i o n s of t h e t u n n e l c o n t a i n i n g t h e p r o p e l l e r s and d r i v e motors can be r o l l e d o u t on a p a i r of c a b i n e t drawer slides for ease of maintenance and i n s p e c t i o n .
Each propeller, which h a s seven aluminum blades, is d r i v e 2 by a 403 c y c l e , 14 HP induction motqr throuch a set of s t r a i g h t bevel ( c o n i f l e x ) gears located w i t h i n t h e n a c e l l e . The gear r a t i o is a 23'35 r e d u c t i o n . These g e a r s a r e l u b r i c a t e d by a jet of q i l meeting t h e m i l i t a r y s p e c i f i c a t i o n MIL-L-1-017.
The two motors are n o t mechanically synchroniped w i t h each other, but t h e propellers a r e w e l l synchronived because of the torque c h a r a c t e r i s t i c of induction motors, s i n c e the motors a r e e l e c t r i c a l l y i n parallel from t h e same v a r i a b l e frequency power source The first modification t o be constructed was t h e l a r g e s t t h a t can p o s s i b l y be b u i l t w i t h i n t h e l i m i t s of t h e b u i l d i n g s i t e , a b u i l d i n g extension of 7 5 feet.
i 8 * l Both r e t u r n d u c t s , downstrean of the propellers, w e r e extended 7 5 feet full scale with an expansion m l y i n the v e r t i c a l d i r e c t i o n at the same c m s t a n t angle of expansion (3.9O half angle) as i n t h e full scale tunnel. The bellmouth end of the basic t u n n e l con- f f g c r a t i o n was designed and construct& t o match t h i s vertical expansion of t h e r e t u r n d u c t s which yielded a b e l l m o u t h of 7 9 . 5 x 7 9 . 7 5 feet high full scale. This end is a l s o made detachable frqm the rest of t h e t c n n e l , e n a b l i n g t h e bellm3uth end t o be extended lengthwise t o accommodate a l a r g e test s e c t i o n This large test s e c t i o n s i z e was chosen t p be 31 x 19 feet hish full scale. Figure 1 s h q w s t h e r e l a t i v e proportions. The l a r g e t e s t s e c t i o n then follows a c o n t r a c t i o n r a t i o cf 2 . 3 2 and t h e model 8 x 13 test s e c t i o n has a c o n t r a c t i o n r a t i o of 4 31.
The model '1 x 19 test s e c t i o n is 60 f e e t l o n c full scale, and cses 1 5 feet for its c o n t r a c t i o n . It ex- pands 2 . 0 I n . t o t a l i n 69 feet d i s t r i b u t e d on a l l four sides t o correct for the c a l c u l a t e d displacement thickness of a t u ' f i u l e n t boundary layer. Atmospheric s l a t s a r e prsvided i n two s i d e w a l l s of t h e 3 1 x 19 test s e c t i o n . The atmospheric s l o t s ir, t h e model 8 x 12 t e s t s e c t i o n ware closed when the large test s e c t i o n e x t e n s i o n was added. Photo 11 shows the model tunnel with i t s 2 1 x 19 test s e c t i o n added.
, A maximum dynamic p r e s s u r e obtained so f a r i n t h e model 8 x 12 t e s t s e c t i o n is 113 psf (a'bout 2 5 8 mphj speed of 7r)r)O rpm.
a t a propeller 3 . F l o w survey Probes A m a l l stiff pr&s was c c n s t r u c t e d t o measure f l o w a n c l e s i n the model 8 x 1 2 test s e c t i o n . The probe!
c o n s i s t s of four ( 4 ) hypodermic needles c u t a t 4 ' - O and one (1) a t 9q0 t o the c e n t e r l i n e , bundled tocether t o form a probe s i m i l a r t o a P r a n d t l tube.
This probe was c a l i b r a t e d i n t h e f u l l s c a l e t u n n e l hecause af i t s non-standard t i p shape. See Figure 1 for the probe c a l i b r a t i o n curve and a sketch of t h e probe The probe is i n s e r t e d i n t o the model 8 x 1 2 test s e c t i o n throuch a s l o t provided i n the c e i l i n c .
A "checkerboard" panel attached t o the model t u n n e l locates t h e probe i n t h e test s e c t i o n a t pre- determined l o c a t i o n s corresponding t o those surveyed i n the f u l l scale t u n n e l . See Photo 111.
Another probe, a standard P r a n d t l t u b e , w a s constructed t o survey f l o w angles i n the model 2 1 x 19 test s e c t i o n The stern of t h i s probe extends f r o m t h e c e i l i n g t o the f l o o r of the model test s e c t i o n . Since t h i s is a standard P r a n d t l tube, t h e c a l i b r a t i o n curve for t h e UWAL N o . 1 probe was used t o reduce the d a t a ob- t a i n e d by this probe. See Photo IV. Because the v e l o c i t y i n t h e 31 x 19 test s e c t i o n is low, t h e ~ 1 2 8 9 1 probe i s connected t o a manometer i n c l i n e d a t 1qo from the h o r i z o n t a l plane, 3 . Location of Survey P o i n t s The model 8 x 17 test s e c t i o n w a s surveyed for upflDw, crossflcv an6 d y ~ t ~ i i c presslire i n t h e vertical plane of the balance trunnion a t 7 d i f f e r e n t v e r t i c a l l e v e l s a t 11 d i f f e r e n t e a s t and w e s t d i r e c t i o n p o i n t s cover- i n g an a r e a of 75% of t h e h e i g h t and 7R4 of the width of t h e 8 x 17 test s e c t i o n , The m o d e l 31 x 19 test s e c t i o n is provided with f i v e ( 5 ) v e r t i c a l survey p l a n e s which are at 10 f o o t f u l l s c a l e i n t e r v a l s along t h e test s e c t i o n . The pro- can be l o c a t e d a t any v e r t i c a l s t a t i o n a t pre- determined east and w e s t l o c a t i o n s . Upf l o w , croas- flow and dynamic pressure were surveyed a t 7 d i f f e r e n t v e r t i c a l l e v e l s at 7 d i f f e r e n t east and w e s t p o i n t s at s t a t i o n s 1, 3, and 5 covering a volume of 88% of t h e h e i g h t , 6% of t h e l e n g t h and 803k of t h e width of the 91 x 19 - 6 0 foot lona f u l l scale test s e c t i o n .
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111, Testing Procedure The v a l i d i t y of the basic nodel t u n n e l w a s f i r s t v e r i - f i e d by confirming the c o r r e l a t i o n of upflow, crossflaw and dynamic p r e s s u r e d i s t r i b u t i o n between the m o d e l and full scale 8 x 13 test s e c t i o n s w i t h the tunnel i n its original unmodified c o n f i g u r a t f m . Tf;e repeatability of the flow p a t t e r n i n the model 8 x 12 test section was also confirmed, The second group of runs were made after i n s t a l l i n g the 60 foot long 2 1 x 19 test s e c t i o n , The first flow survey i n t h e 3 1 x 19 test s e c t i o n was conducted without any modification t o t h e basic p o r t i o n of the model wind tunnel. Upffow, crossflow and dynamic pressure were msasured by using the P r a n d t l tube described in t h e previous chapter and an inclined manometer. Develop- ment work was carried o u t as necessary to produce accepta- ble flow q a a l i t y i n the 31 x 19 t e s t s e c t i o n . A complete f l o w survey i n the V/STOL test s e c t i o n was conducted when t h e f i n a l improved f l o w p a t t e r n was established.
Upon completion of the flow survey i n the 2 1 x 19 test s e c t i o n , it w a s necessary to i n v e s t i g a t e any changes i n the flow pattern i n t h e 8 x l:! test s e c t i o n due t o the a d d i t i o n of the V/STOL test s e c t i o n , A survey of up- f l a w , crossflow and dynamic pressure i n the model 8 x 1 7 test section was again conducted and the r e s u l t s w e r e compared w i t h the d a t a p r e v i o u s l y obtained.
~ L * R e s u l t s and Discussion IV.
A measure of power required t o o p e r a t e t h e model t u n n e l w i t h and without the 2 1 x 19 test s e c t i o n is shown i n Figure 3. T h i s f i g u r e shows the o p e r a t i n g angle of a t t a c k of t h e propeller b l a d e s f o r a given c o n d i t i o n of the t u n n e l conffguration. With t h e a d d i t i o n of t h e l a r g e test s e c t i o n , t h e angle of a t t a c k was reduced i n d i c a t i n g a r e d u c t i o n i n t h e power required. This power reduction is a t t r i b u t a b l e t o the f a c t t h a t t h e v e l o c i t y a t t h e bellmouth t u r n i n g vanes i s l o w e r than t h e o r i g i n a l t u n n e l c o n f i g u r a t i o n by a f a c t o r of 0.65 which reduces t h e c o r n e r loss. It t h e r e f o r e can be concluded t h a t the aaount of reduction i n t h e corner l o s s due t o t h e lower v e l o c i t y is g r e a t e r than t h e a d d i t i o n a l f r i c t i o n loss due t o t h e 75 f o o t l e n g t h extension. Thus it can a l s o be concluded t h a t t h e maximum v e l o c i t y o b t a i n a b l e i n t h e 8 x 1 2 test s e c t i o n w i l l n o t be impaired w i t h t h e a d d i t i o n of t h e 75 f o o t extension.
R e s u l t s of upflow, crossflow and dynamic p r e s s u r e surveys i n t h e unmodified model 8 x 13 test s e c t i o n are compared w i t h those of the f u l l s c a l e t u n n e l t o e v a l u a t e t h e dsgree of flow s i m i l a r i t y between t h e two test s e c t i o n s .
R e s u l t s of upflow surveys are compared and presented i n Figure 4. The general p a t t e r n of upflow a n g u l a r i t i e s i n t h e f u l l scale 8 x 17 test s e c t i o n i s reproduced a m a ~ i n g l y w e l l i n the unmodified model t u n n e l * c 1 . - . . .
8 x 1 2 test s e c t i o n as shown i n the f i g u r e , R e s u l t s of crossflaw surveys w h i c h are presented i n F i g u r e 5 also shm a s u r p r i s i n g l y good c o r r e l a t i o n be- tween the unmodified model and f u l l scale 8 x 1 2 test sections. There are no sicpificmt d i s c r a p z x ~ c i e si n the crossflow a n g u l a r i t i e s bztween the two t e s t s e c t i o n s , Dynamic pressure d i s t r i b u t i o n was surveyed i n t h e same vertical plane where the u p f l w and c r o s s f l a w w e r e sur- veyed. T h e results of this survey are presented i n F i g u r e 6 which shows a comparison of the dynamic p r e s s u r e d i s t r i b u t i o n between the unmodified model and f u l l scale
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8 x 12 t e s t sections. The measured dynamic p r e s s u r e for ezch survey p o i n t was divided by the t u n n e l i n d i c a t e d dynamic pressure. The data presented i n Figure 6 shows a d i f f e r e n c e i n the absolute v a l u e s of the dynamic pres- s u r e r a t i o between the m o d e l and full scale 8 x 1 2 test s e c t i o n s , The discrepancy is due to t h e fact that the l o c a t i o n of the r e f e r e n c e dynamic p r e s s u r e source relative to the model t u n n e l is d i f f e r e n t f r o m that of the full Thus t h e measured r e f e r e n c e dynamic pres- scale tunnel.
s u r e i s n o t e x a c t l y t h e same as that of the full scale tun- n e l . It also should be noted t h a t no c o r r e c t i o n was made i n the model t u n n e l 8 x 12 t e s t s e c t i o n for t h e boundary l a y e r growth. The primary i n t e r e s t of the r e s u l t s shown * i n Figure 6 is t h e f l a t n e s s of each curve which i n d i c a t e s a balanced v e l o c i t y d i s t r i b u t i o n i n the plane w h e r e the survey was made i n the test s e c t i o n . R e s u l t s presented i n these Figures 48 5, and 6 , i n d i c a t e t h a t the flaw i n the model 8 x 1 2 test s e c t i o n is t r u l y a good reproduc- t i o n of the f i ~ in i 2 i e fil3.i scale 8 x 3 . 2 test section.
With the a d d i t i o n of the 21 x 19 test s e c t i o n t o t h e basic model tunnel, another complete survey of upflow, crossflaw and dynamic pressure i n t h e m o d e l 8 x 12 test s e c t i o n was conducted, and presented again i n Figures 4, 5 , and 6 , respectively. The changes i n crossflcrw a n g u l a r i t i e s are i n s i g n i f i c a n t , and v i r t u a l l y no change
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appears i n upflow a n g u l a r i t i e s and dynamic p r e s s u r e d i s t r i b u t i o n . Results of flow a n g u l a r i t y surveys i n the 2 1 x 19 test s e c t i o n without any m o d i f i c a t i o n t o the t u n n e l are shown i n Figures 7 , 8 , and 9. These flow p a t t e r n s for the o r i g i n a l c o n f i g u r a t i o n of the 21 x 19 t e s t s e c t i o n have q u i t e large local flow angles. Dynamic pressure d i s t r i b u t i o n shown i n Figures 10, 11, and 12 i n d i c a t e d that t h e v e l o c i t y is, g e n e r a l l y h i g h e r a t t h e east s i d e of the test s e c t i o n than the w e s t . The immediate object of the mode1 t u n n e l then w a s t o reduce t h e magnitude of t h e flow a n g u l a r i t y and t o o b t a i n an evenly d i s t r i b u t e d dynamic p r e s s u r e i n the 2 1 x 19 t e s t s e c t i o n .
A series of runs was made t o i n v e s t i g a t e t h e cause of the large flaw a n g u l a r i t y i n the V/STOL t e s t Prection, mese runs c o n s i s t e d of f i n d i n g t h e e f f e c t s of v o r t e x genera- tors i n the d i f f u s e r , p r o p e l l e r blade angle reduction, angle of incidence of the p r o p e l l e r a n t i - s w i r l vanes, am2 C M ? e adjustment of the bs1hout3 turning V ~ , F - B S ~ None of these nethods r e s u l t e d i n an appreciable improvement of the fluw p a t t e r n i n the 2 1 x 19 t e s t s e c t i o n , but it was discovered d u r i n g t h e i n v e s t i g a t i o n t h a t t h e w e s t r e t u r n passage had more drag than the east.
An e x t e n s i v e search for the e x t r a drag i n the w e s t r e t u r n d u c t was conducted b u t ended f r u i t l e s s , Therefore i n order t o expedite the a t t a i n m e n t of a high q u a l i t y flaw in the 2 1 x 19 test s e c t i o n , it was concluded t o add more d r a g i n the east r e t u r n d u c t thereby o b t a i n i n g somewhat better b a l l a n c e d d r a g between the t w o r e t u r n passages, This w a s accomplished by i n s t a l l i n g a l a y e r of an o r d i n a r y household i n s e c t screen a t the downstream end of the east r e t u r n d u c t , With t h e screen i n the r e t u r n duct, the adjustment of the bellmouth t u r n i n g vanes was found to be effective i n c o n t r o l l i n g t h e flaw p a t t e r n in the 21 x 19 test s e c t i o n , The final f l o w p a t t e r n i n the 21 x 19 test s e c t i o n w a s obtained by a d j u s t i n g t h e bellmouth t u r n i n g vanee, and presented i n the plastic overlay form i n Figure8 7, 8 ,
e
c .
* f 801 18 and 9. A considerable improvement of t h e flow a n g u l a r i - ties i n the V/STOL test s e c t i o n can Le c l e a r l y seen i n these f i g u r e s . Dynamic p r e s s u r e d i s t r i b u t i o n i n t h e test s e c t i o n was a180 s i g n i f i c a n t l y improved and shown i n Figures 13, ii, and 12.
During the aforementioned i n v e s t i g a t i o n of the l a r g e f l u - a n g u l a r i t y source, the angle of incidence of t h e p r o p e l l e r a n t i - s w i r l vanes proved t o have a s e n s i t i v e e f f e c t on t h e v e l o c i t y p r o f i l e i n t h e r e t u r n ducts. The t o t a l head p r o f i l e i n each r e t u r n d u c t was measured and t h e e f f e c t of t h e adjustment of the s w i r l vane angle of incidence i s shown i n Figures 13 and 14.
The e f f e c t of t h e 2 1 x 19 - 60 f o o t test s e c t i o n on the
flaw a n g u l a r i t y i n the 8 x 1 2 test s e c t i o n is v i r t u a l l y none as shown i n Figures 4 and 5. The dynamic p r e s s u r e d i s t r i b u t i o n i n t h e 8 x 12 t e s t s e c t i o n was also found t o be unchanged as presented i n Figure 6. This f u l f i l l s one of t h e b a s i c requirements t h a t t h e p r e s e n t e x c e l l e n t aerodynamic q u a l i t y i n t h e 8 x 12 test s e c t i o n s h a l l n o t be degraded.
V. Conclusions Wind t u n n e l t e s t i n g of V/STOL a i r c r a f t models w i t h a l a r g e dawnwash angles necessitates a large test s e c t i o n i .
. . . _ . .
i n order to obtain a s m a l l r a t i o of the model t o test s e c t i o n size t o minimize the t u n n e l w a l l i n t e r f e r e n c e .
F e a s i b i l i t y of adding such a l a r g e test s e c t i o n t o t h e p r e s e n t UWAL wind tunnel w a s experimentally i n v e s t i g a t e d by using a 1/8 s c a l e model of the p r e s e n t 8 x 12 wind t~rn91.
Evaluating the r e s u l t s obtained from the model tunnel, it is concluded t h a t :
1 . It is f e a s i b l e t o add A 2 1 x 19 - 60 f o o t long
test s e c t i o n without degrading the p r e s e n t e x c e l l e n t aerodynamic q u a l i t y of the 8 x 1 2 test section.
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2. Flow a n g u l a r i t y i n the 21 x 19 test s e c t i o n is c o n t r o l l a b l e by a d j u s t i n g the bellmouth t u r n i n g vanes .
3 . There w i l l be no a d d i t i o n a l power required t o o p e r a t e t h e above i n v e s t i g a t e d c o n f i g u r a t i o n of the two-test-section UWAL wind tunnel.
The p r e s e n t configuration of the model t u n n e l h a s a 75 f o o t f u l l scale length extension of which 15 f e e t is used f o r t h e contraction. T h e minimum length required to establish a good aerodynamic environment i n the V/STOL test section h a s n o t yet been determined, b u t work i s continuing w i t h t h i s objective.
1. R o b e r t G o Joppa, V/STOL Wind Tunnel Testinq and UWAL Facilities, UWAL Report No. 744, 1962, 2, Ro'Dert G o Joppa and V i c t o r H, Ganzer, An Aerod~namic F e n s i t i i i t y Study of IWo-Test Section Wind T u n n e l s for V/S19L Testinq, UWAL Report No. 773, 1964.
3, Ralph €3. McCormick, Wind T u n n e l S u m m a r v Report
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No, 301-12-1 Total Pressure Loss Survey in the B O 8 i n q Wind Tunnel, BWT-T6st N o . - 3 0 1 , 1 2 , 1954.
Page 21 Photo 1 Basic 8 x 1 2 Model Tunnel Without Extension
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