Document
Source of Acquisition NASA Wa shington, D. C.
TECHNICAL MEUORANDUliS HAllONAL ADVl SOrtY OO:I1i.,IITTEE FOR ]I.EROKAUTlOS No . 651 OF TgE BUCHAREST POLY~ECH~lC l~STITUTE W as :li ng ton Dece r:lb er , 1931 I~ATI O NAL ADYISORY COMMIT'.VEE FOR AliJR O :i. I TAUTICS TECHNICAL MEMORANDUM N O. 65 1 WINJ) TUFNEL OF THE J3UCnAJ{EST POLYTECHNI C IHST ITUTE* The new wi nd tunne l of t h e Bu c ha rest Po l ytechnic I nsti - tute , d esi g ne d by Mes s rs. C ~ r & fo l i and stroesco , is of t he c l o sed - c ircu i t t yp e , the retllrn being sym r.1G tric c:, l with re- spect t o the lon g i tud i n a l axis of the tu nn el . Th e tun ~ el is of t i.l e horizonta l tY 'p e (fi g s . 1 , 2 , 3 c.. nd 4) , with a d i ame t e r of 3 . 2 m (10 . 5-ft.) a t the b e g i nn i ng o f t ~e en- t r an c e c 0 ::' 1 e ( 3 ) , an d 1 . 5 m ( 4 • 92 ft .) at t h e en t r an c e t 0 t ~1 e t es t C 11. amb e r (4 ). Th e I at t e r , 2 m ( 6 • 56 ft . ) Ion g , m ay be eith e r of t h e op en - jet type (shown in p icture) or enclo s ed in a c y l indrica l housin g as shown by the dotte d 1 ine s i n ?i g ure I cm d in secti on in Figure 3 .
The tunnel section is c i rcular from the en tr a nce cone to t~e p ro p eller an d ann ular in the return passage . A honeyc o mb is mount e d in the beg i nni ng of th e en tr ance c o ne .
T he c ross sectio n of t~le exit cone ( 5 ), wrlic:C is circ'.ll L'. r t hr o ughou t its len g th , increases f ro m 1 . 5 n ( 4 . 92 ft . ) to 2 . 5 ill ( 8 . 2 ft . ) at the p ro p eller . At t h is po int t~e sec - tion bec o me s annular and the circuit n ako s a be nd of 1 80° , the return bein g pe r fe ctly sy m8 etric a l wit h respect to the tun n el axis . Honeycombs a re installed in the ann ulus (7 and 8) to keep the current pa r al lel. T he cr o ss section o f th e annu lar retur n p a ssaGe increases g ra dua lly f ro m t~e be~d t o the entrance co ne . T he variati on in areas is shown i n Fi g ure 5 .
T~8 tu nn el is h o used in a bu il ding wn lcn has , e x ter- n a ll y , t h e uhap e of all octa .g on a l p rism . (}) ' i r; s . 6 , 7 and 8.) I n si d e there is a c y lin d er of 5 . 72 m (1 8 . 77 ft . ) ma x - imu m (lia m ster . T he return circuit is 10c8.te d between t J.-,j. s c y lin d er a nd the outsi d e wa lls of the t unn el .
Access to the test cil am ber (1 3 ) is had thro ugh tl e r e - turn passag e, in t he form of a st re a~ li ned p assa g e . (1i R s .
9 and 10 . ) In order to p revent t h is obst ac le from disturb - i ng the retu r n f low , the tunnel section was wi d e ned at tbis p oi nt . H enc e , the section of t h e re tu rn p assa g e g_adually i ncreases t oward the entrance c o n G, althou gh its symmetry i s distu rb e d by t~1.e test ch a n, tJe r .
*Data received f ro m Paris O ffi ce.
N. A. e . A. Te c~n ica l Memorandum No . 651 T he fact t ha t an obstac l e , a l thou gh str e am li ned , is p l aced in the retu r n fl o w, 'f ou l d or r linarily le ad t o sepa - r at ion of t h e flow behind the obst ac l e , which , in the pre~ ent c as e , i s of symmet ri c a l biconvex section. This di ff i- cu l ty is obv i ated by suckin g o f f t~c f lo w beh in d the ob - st ac le . (F i g . 4 .)
The me th o d by which this resu l t is achieved is one of th e outstand i n g features of the tu~ne l. It g re a t l y re - duces tho turbu l ence and increase s the eff i ciency of t he t unne l . The su c ti o n is p r o du c ed aut o matica ll y by connect - i ng t he b urb l in g area with t h e l ow- pressure region at t~e po in t of max i mum a ir- f lo w voloc i ty in tho entrance cone .
T nc c onnection is est a blished by an annu l a r meta l collec - t or (1 6 ) a round the junction with the ex i t cone a nd a sys - tem of p ip e s ( 1 8) which lead through the test chamber to slots in t~e re'r of t h e b i convex o b stacl e ( 20 ).
In ad dition to the a bove - ment i oned ad v an t age s , t h is s ystem a ls o i mp ro ves the flow i n t: l e test chambe r , inc-s - L lUC r. as t21 e p ower f u l jet of air which ente rs the circa12. r o peni~G ( 1 5 ) carries off t h e air la ye r in the imme d i ato n e i g n~ orhood of the wa ll (boun da ry l ayer) . T his ~es~~ts i n un i l orm vel o c i ty a l on g the diameter of t~e teR~ c~am ber and thr o ughou t its l ength .
Po w er is s up~9 1i ed by an electric mot or (9) ( f i g . 1) d e velop ing 50 hp at 14 60 r . l) . m. T ile ;J ro pe1 l o r ( 6 ) is mounted d irectly on the m otor sh Bf t, t~e who l e be i ng c ar - ried by a ca n ti l ever meta l framew o rk (1 7) su ~p or ted by a concrete structure which is entir el y in d ep en d ent o f the body of tile tunne 1 (12) .
A speed of 41 . 7 m/s ( 1 36 . 8 ft . /s ec.) has be en re a c hed with only 32 hp , which corres p on d s to t he e xt re hl ely good
eff i ci ency fa cto r P = 3 . 35 . At s pee ds of less than 30
m/s ( 98 . 4 ft . /sec . ) , the tunne l has p r o ved very s a ti s f act o - ry as to uni f ormit y of fl ow in the test c hambe r. Prel Lli - nary tests at h i ghe r v e locities a re b ein G made .
The b a l anc e now in us e is of t he standard wire ty p o .
Th e tunne l p r ope r is built of wo od and p l ywood , cov- ered with waterproof tabric .
Tra ns lation by W . L. K op orind~ , Nationa l Advisory Co mu i tte e for A eron au tics .
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School Wind Tunnel with enclosed experiment chamber .
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~-2 _ 5 m -; i' : Length of different port io n s of circuit on median line b;j 1-'- ()'q Fig. 5 Vari a tion in cross-s e ction of tUllnel t hrou g hout closed circuit. ~~el of the Bucharest
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Po1ytec~~ic Sch ool.
CJl _ .. .. --~ Figs. 7,8 N.A.C.A. Technical Memorandum No. 651 • Fig. 8 Outside view of tunnel (Exit cone end and motor cabin) Figs. 9,10 N.A.C.A. Technical Memorandum No. 651 Fig. 10 Test charaber. Open jet arrangement. Mo