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D EVE L O P MEN ' rS I N A ll { C I( A I 0 'T J E T NOlS E TE(' I IN ¢ ) I/p( ; Y ( ) r l , , mdo A. ( ; u t l v rrez a nd ,l a mes I _ . S lon o N A S A L e wis IL e se a reh C e n t e r St MMAi{ Y T h i s pap er br i ef ly descr i bes s lg l_ t l'i c : m t d e v elopm e nts in t wo a r t, a s of je t no i se t e v lt - nolo g y : t h e dev e lop men t of le t n oise I c t 'h n olog 5 ' rel at i v e t o t ' o aml tl l_|l ' nozzle,q of a ll typ es , a n d a rec e n t ap pr oa cll t o t he anal y . ', is of fl igh t effec t s t ha t ap pe a rs t o allo w simu- lated fli gh t effects r esul t s t o be t rmm t 'or m ed t o at. t ea l fligh t c o n di t ions w it h a high degr t, e of c onf i dence . The eo,L rL n u lar nozzle sec t ion pre:_en t s resul t s appli c a ble t o high - b_ p .t ._- r at io tu rbofan engin e s , as w e ll as curren t w ork on in v er t ed-profile c oannular nozz l es a pp li ca bl e t o low - by pa ss- ra t io turbofan engines sui ta ble f or use in [ u t u r e sup e rsoni t' c rui se air c r aft.
I N ' l 'l i t ) l )l' C TI ( _ ) N Th i s pap e r r e vi ews s om e of the progl_css made i n jet nois e t eeimolo_ , _ sim' t , t im A i r- cr a ft Engine No i s e Redu c tion C onferen c e held at the N ASA I_ewis Resear c h ( ' en t er 4 ye a rs a g o and reported in refer e n c e 1. l ) uring t his time sp : m. 1 .ewis in - house 'rod contracted technology programs have been conc e rned wi t h no i se problems ty p i cal of a variety of a i rcraft, as illustrated in figure 1. These a i rcr a ft ira.lade c.onvention a l a i r- c raft (C TOL ) a n d power e d - lift airer : ff t using eng i nes lo c ated over t he wing (( r r\v_ mid u n der the wing ( UTW), all o f wh i ch use medium - t o h i gll-b y p a ss-ra i io t ul 4 _o f an en gl ne_.
as w e ll as superso n i c cl x t ise ai rc r af t , which use l o w - b y pass- ra t i o t urbof : m e n gines.
Co m mon i x : , ,11 these aircr , 'fft is the u se of some ty pe of turbofan engine. This h a s been re fl ected in th e emphasis pla ce d o n the study of e o'mnul a r lo t noise. , : s is describ e d in thi s paper. In addit i on , a re c ent approac i l t o t he unders t mld i ng of t he ef f ec t s of fli g h t _m } e t e n g in e e x h a u s t n o ise is di scussed .
O t her significa n t jet noise work being e a rrledou t a t Le_ v is in ._ut.h fmh l s a s i e t aot.,, c • suppressor technology and jet-s u r t 'ace interac t ion noise h a ve no t been covered i n t hi,_ paper because of time limitations.
('() A NN t' I . A !1 ,! I-;T N( ) I Si': Becaus e t urb o fan e n g in es a re t he p r i m a r y c a nd i da t es for all t hese t ._pe._ o! a i r c r ' d' t th e stu d y of c o annular Je t n oi se h a s been of t ,ar t l i n a l Impor t :rac e . l.' igtt r e 2 i x : t ge n er- iI I I r al i_.t,_l ._kt, l t,h t_l ;i t 'tHI D llll|tll' |j oz _h, _hrJwJn g lhe J l lllJ'_,l', 0 1' r 'Ol't,, II O Z X ] t , ;- a l vr o und c ,d b y lh_' t_i_It, i , _ i ' l'ill l, n c Jz / . l c , Th t ,l_ t Jr x h a u r d'-_ll' l 'illlh_ ftll'lll lh t ' t , t , v e g h m :__ d ' | lll ' lHll tqi _'t' lh a l a r_,lU q _cJvhlnl Inlhr R ¢ 0 nt, r atJo l l o I' j riJ1_l,_e' the regl o nwhe r t , lhr _,nr_, l'l . w a nd l '_ ,n llu_mi.xqn,l,.iun II . lh t , r t , g l o u who,n,lhe l' m l flo w ml. x t_,_ wllh lh t , a l i lhh, n l a ir I v _, R lo n lll l a ml lh,, rt' v , i_u_ _ v herrlhr m_ . 0vg_ . ,d _ t 'i,_ n11xwl t h lhe ;i ml_ h ,llI a lril'e g l_ m lll_.l,l a eh _I ' liH,,_t, l ' tl ,, i_ll,, , _ tq lt ' l ' i li t ', '_ l } t _ i , _ t ' , i l n¢l l l )t , J l ' | ' t ' l / llIVt ' Jnlj )O l ' Inn t , t _ I o ih t , _;V t , l_ i] | _t,i n o i _ t , _ , il , ,iHlu v _ , _d ' _ pa r llrul a v t,_; m mu| t _ v n ozzl e dt , l}_ , tld , , ; _ m lh_, rel a llv c , _I z _ ,, _ an d vr]orlt h, s _d' lh_ ' lw_ h l I'¢'_IlllS, , ,, , Co n ven ti o nal( ' o a m m l . ' _r N o zzl es _ ) _ . er t he pa st f e w yca 1 " _ a h11 " g e a nloulH o f l ' e_c a 1 " eh h a _ | )ee n d o ne o n the _et n oi s e ¢.h a r a rl t ,1"i , _tit' , _ o f "t. o nvcn ti ona l " (, o an nul a r n o zz h . , s re . g, , rc f s.'2trod : I t.l ,' ig ure ' 3 :, ] I t) X S _ t h t ' ¢' ]lill ' ll t' t _' lJ , " [j CS 0 | " the t't)ll V Cll[io ni| l t'O i Lll nu l al ' n oz z l es . The s e n o zz l e s have h t | ' I L' e fa ll H I' / _ ' H t O c o re " lr e tl ra ti osan tll', m veloc i t y t o co r e ve l oc ityr , tt i o _ s le ss / h a rt 1.0 .
h_ lh i, _ t, V l_e of c o m m u l ar noz zle the t .o r c- fl o w / f m_- l ' lo w : m d mer g cd - le t /' a n fl_l ent- a [ r mix- m l_ vet_' i _ ,n. _ a r t. , t h e s ig 3d fi c: mt no i, _ , . ,- pt_ , _ducin g pa r t so f the let . '[' h e s u nozzl es ar e ap -- } ) |ir a hle It_ h i l_h - b yp as , , _ - ra ti o turho fanc nl_ ine s , '_u i tab l c f o r c o nvc nti ona ! a n d S T( H , a i r - _'r:d ' t al q _li_ , atio ns, a , _wel l a , _ to su_'hrcse a rch fa cil ities as fr e e j e ts .
l . : x p er i menlal work has been eon (l u t't ed ( refs . 1 , : } . t rod 4) on sc a l e -mo d e l noz zles _J f t hi,_ t vl ) e, cover ing s uff i cient wlrl : itio n s in area r atio , velocit y r a tio, a n d exlt - p lan e t di:_e t _ to p ermi t p redi c t ion cu r ves Io be ge n era t ed for th l _ t y pe of e o mm u l ar nozzl e .
Th e r c ._ulls a r e shown in fi g u r e ,I a s a c han g e in n o ise f rom a referen c e leve l a s a f u nc- tion o f xctot ' it y ratio for a series o f ar e a ratios , Th e ref e r e n ce le v e l , ref e r red to a s _nU_e , _is. is t h e anti l og ar it hmic s u m of the n oise l e v els exp ec t e d f lx_m ea ch st ream con , _tdered as a e on ve : ' g e nt nozz le a cti ng alone and t h u s r ep r e s ent s the no is e leve l th at wou l d he ob , _ erved i n t he a bsence o f in t er a c t io n effe ct s . _ ' l ' h i s re f e r e n ce l eve l al s o e o r - : respon H :¢ to t he r es ul ts o f e ar ly le t n oise l ) r cdicti on meth o ds s u ch a s re f . 5.) T h e m a x l- i nure noise r ed uction obt a in e d for f ire -to-core velocities r a tios l e ss tl u m 1 incr e as e s w i lh t m ira.tease in a re a ratio from _m ix_i g _fl fi e t mt a mo u nt a t m_ a rea ra tio of 0,5 to I ! dl_ a t a n arcJa r at io o f I0. The ve l orlt y r a tio a t whi c h th e m ax im u m r e d u ctio n occurs , : \ a rie._ l , t .t w ee n 0.5 a n d O. . I. dependln_ oi-_th t. a w , a rat i o. As a p ract ica l app llc a tlon the v c , lo¢ .l l) r a t i os u sed In eon v c nt lo n al _md S T{ ) I , hl g h - b ypa ss -: ' a t io en g ines a r c a bove a x a ]ue o I' " q }p1_ x lma l e ly 0.7 fo r perform t m c e reaso n s, which limits t he eo a n nula r red u c- t i_ m s for l}r a _'t l ral u,_c to behvec n 3 _md , I dll. The red u c t ions in noise s u ch as shown in , lh i . _ li g ure _deve lo ped fro m t il t , d at a o1' ref. :h h a v e bee n inc o r po r a ted in t o desi gn pt _ - t't'_lur t '. _ ,_t lt ' h a , _ t i l t ' NA , _ A A ircraf t N oise Pred i c t i o n l ' t x_ g r a m _ A N¢ H) Ih ( ref . (; _ a nd the r_l're n I pl_lX ) sed S o t ' i ct y of A utomotive I , : n R lneers ISAI , :) p red i e tion p rored u l ' es. ' l l_ese " -i I _ h, _-* i l,,n T , r_ ,v t ,,i . v , ,: -: _0 ,' a, n , _t :lt Jp li c : l h [ o to _ , c)minu| t lr n o zz| o ,_ wi t h f_m-to_c_ , oro v v | o v it.% , r'a_ '. IbJ : -; _.'l'_' : Itt'l' lli : on I.II.
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lay , , rl v _l-_ Vt, lol.,liy - I' rol'llt, ('olmmflzl v Nozzl o _ {', rm n o } : _ r li , P / . / . l _, :. _ lh o l I w - _l m 't' in v e r t e d _ v l o v lty p r o l'll o _ _l'_m vo l o v l t y h i g h e r th lm _ I , .,it_ ,'_r4'_ h',ix_, I wv - m , , hl h ,rc, s ttn_ _,Imcllda t os for applica t ion to Low-bypass-r at io t _ H.fl m _ v n_.im, , _ : ' l'l w ,_ t , v n_il w s arc, I J u ln_ vonsl(I v r L .(I for use I n l'tltul' o supt , rs or li(, i' ( 'rlli:,l ' : li r¢'l ' _l l l ' r } li,_ 13lie o[ ilozzl t, , s hown s c h c m : tt l(, t dly In fig u re 5. Is characte r ized I ) \ ; i ; _lh;lil I' ; _ll -(()- t '( _r ( ' l il' t q} I ' ;lI[O IO[ lil t ' ()i ' ( t t 'l' u i " | . 0) a ll tl a fan-Co .. c u r t 2 veloci ty l'a t l o i l l i t_ o r : mt ,, , o t I. i_ t o 2 Ii . \ %i t h I b i s t _pc of nozzlt,, tl w l' , 'm- fiow / alnb i e nt- air and n lt, v _ ' o(I - it,t ,' a l n ldol l t - al r l n i x i n _ I ' ( , _lons a l' U t il e deta i n . ro t s oLI r ( 'es o f l e t n oi se . There- fort, , t ilt, pr o , lit,Lion mol l }otis h: ,. _t,d ,) n t,onvol_ttonal coan_ul t lr tel data. where t he c o r e- flow / f:m- i ] ow :!ml m y v _od - I t.t / t lmhiont - air mixh}g regi on s are d o mina .rt t , d o n ot apply .
:. To fill this _a p il l lot nois y tocl t n ology , l, v wis has b een sp on s o r in g ex'p e ri lT len t al studies ov vv t im l: l_t :} v v a v ._ w it h Pra t t & \_lfl in o, Air c r;fft and ( ,e n e ra l E le c t ric t o de te rm i n e " t ht. l l Oi . '_t' ch:i r act u 1'i , _tJ t '._ el' i nv er t ed- v e l oc i ty -p rof il e eoan n u l ar n ozzle s.
The I ) a._it , n l O dt'l,< t(, ._t o d i n t l_(_,sot . on t ra c tor s t udi es are shown in figu.re 6 , A eo- tuulular n uz / l_, wi t hou t plu t 4 :rod wi t h " m are a ratio of 0 . 7 5 and a fan-s t ream radius ra t io ' of t g . 71 ; i _ _howr_ in [lgul't, ti tIi }. ( l'his radius rat i o is defined a s t h e ra t io of fl_e fan- , s t r e am till e r rmlius t o tilt. f:m - _ t ream o uter radius . ) The model sh o wn in figure 6 ( b) is ;i (. o: t mlular nozzlt, with : _ ct , n t ral plu_ and wi t h an area ratio o f 0 . 67 t rod a fan stream radiu,_ r ' t tio of o. 90 , 'rht * ,_e L os t models had equival e nt to t al diame t ers of 13 . and 15 ten- ,!
- , ., tinlo t V l'S , rt,_po( ' t iv v ly .
_ , ; '1ypit' ai rt ,s ul t_. - Il o sul t s f_v o m the experimental programs are plotte d in figure 7 .:_ : l , _ pt.ak pt, v t't,ix'e(I noi._o level mormalized for i e l d e nsity e ffects) 1 as a function o f fan ; ie t veloci t y 1'O l . (, as( . ,s where th e fan j o t ve l o o tty was at least l. 5 ti m es the c ore i c t eel- ' oci t y. 'i'ho iot n o i , _o h,vols [ ' of the co'lnnular nozzles are 6 to 10 p erc e ived n oi se deci- ,, I)t , l . _ (l'Ntll}) low t _. t ' th : l n i f lie favo r able interaction occurr e d b e twe e n the two nets (bo t h l,.t_ t':: } :a L c - : tinl4 thxv}ugh ._t.lmt ': l t o conical n ozzl e s }, Bthv c o n the tx_o eoannular nozzles , t h ( _' con[Lgu r ation with thc central plug , which had a higher fan - stream radius ratio " showt , d :t 2 -1 'Ndl_ - _4 1' t, : | t t , r l_t)i m _ , rcduc t lon . Th e thrus t l o sses ar e about 1 . 5 t o 2 . 0 per - t'i'llt ( l ' tq't_ 'l'l' t ' , l IL l *el i t l t ' al lloZ z lol .
In :l ( hlt t ion I o the , h.lst, ( 'ommttl;tr t ,onfigura l |ons sho_ql , configurations wi t h m e t. ha rt- ic:ll st|[ ) p r t , ssol ' s wo r e i'|.'_ t) t,'s lt' (I l)y adding t , htlt ( ,s , convolutions, or tubes t o the fan s t ream . 0_ t{. ill , _olnt. t ' aSc'S , il l t ' ludin[L e jectors. These suppressed confi g urat i ons [Ti l t. exigent'n | _l t I])t' I'_ln i_' t dt'nsi t y is I m st, d on t'ozlit'al no z zle z'ostll t s . "m( t fo r t he : . lqLll_'t' O[ vt'lot ' i|.x she\el l i_ t ' t ' t ' \' : _l ' i( ' s i'ron l 1 . () : it :{7 : } m /' St ' c to 2. q) Ill % ' ( ' lo t'i t i os t l l) o\ ' t , 5 1 0 l_a , _t ' t' .
_ . 499 / I re d uced the noi se an a d ditional 3 to 7 PNdB, but at the expense of relatively large thrust l o s s e s (a s m u c h a _ 8 p ercent great e r than wit h the u ns u ppressed coannular no z z l es).
M i s sion an aly s e s (e. g ., ref. 7 _ have s h own that the noise reductions observed for t h e u ns u pp r e ss ed con fi guration s relative to early predictions, which did not account for J et inte r action effects, coupled with the low thrust losses involved (~1.5 to 2 percent) are sufficient to meet present FAIr-36 noise standards. As a consequence, the tech- nology studies have been concentrated on unsuppressed in verted-velocity-profile co- ann u la r no zz les in preference to s u ppr e ss e d configurations and extended to study th e el- . ,.
fccts on nois e and thr us t c h aracteris t ics of geo m etric variables s uch as radius ratio and ar e a ratio.
Parametri c trends. - Th e effects of velocit y ratio on the noise red u ction for two different - area - ratio c oa m mlar plug nozzles with constant fan radius ratio are shown in fig u re 8. Th e noise level r e lat i ve t o the synthesized level p redicted f or noninteraet i ng jets is plotted as a f u nction of core-to - f an velocity ratio for cons t ant fan operating con- ditions. (The core velocity was changed by vary in g both temperat u re and press u re.)
It c an be seen that , over this range, the fan - to - core area ratio has very little effect on the noise. M axi mum noise reduction occ u rs b etw een core-to - f an velocity ratios of 0.3 and 0.5. As the c o r e fl ow is reduc e d to very low values, less noise reduction is o b - tained, which coul d be attributed to the lack of suff i cient inner fl ow to pro m ote rapid velocity decay in the energetic f an stream. When the cor e fl ow is in c reas ed above a velocity ratio of 0.5, less noise r ed uction is again obtained, in this case because th e core stream affects the j et noi s e g enerate d in the m erged- l et / a m bient- ai r m ixing region.
Th e effect s of r adi us ratio on ae _ oa co ustic peffo l_an ee for t w o velocity ratios are sho wn in fig u re 9. Th e noise red u ctio n is s hown in fig u re 9(a) as a f u nction of f an - stream radi us ratio. A s the radi u s ratio is incr e ased, the noise red u ction is also in - c r eased, indicating t h e d e sirability, fro m an aco u stic point of view, of designing engine nozzles with a high f. _m radius ratio. The noise red u ction obta in ed wi th a core-to - fan velocity r atio o f 0.5 w a s la r ge r t han for th e no-.corc _ .flow ca s e, a s was previou z ly dis- c u s sed .
T h e e f fe ct of v el ocit y r atio and fan radi u s rat i o on t he t h ru s t characteristics bot h statically and wh e n exposed to an e x te r na l flow Mach n um ber of 0.3 6 (takeo ff conditions ) is s h o w n in fi g u r e 9(b). It i s obvio u s that the thrust losses obtained with no core flow • are q u ite sev er e (up to 10 p e rcent r e lative to a conve r gent nozzl e ). For a velocity ratio of 0.5, losses ar e much low e r (bet n veen 1 and 2 per c e nt additional loss e s r e lativ e to a converg e nt nozzle ) . An in cr ea se in th e r adiu s r atio c au ses an in c reas e in thr u st losses, indi c ating t h e ne e d . fro m a des i gm e r ' s p oint of vi ew. to tra de o ff t h e th r u s t los s es with t h e _.m ou n t o f noi se re d uct ion in o il i er to sel e c t t he o p ti mum nozzl e radius ratio f or an engine exha us t s y stem .
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Simulated flight effects. - The acou s tic information presented in the preceding sec- tions on the inverted-veloc i ty-profil e coannu l ar nozzles has been static data. ltow e ver, a most i m portant con s ideration is whether these noise r edu ctions relative to a conver- gent nozzle are m aintained under flight conditions. Conseq u ently, the acoustic progra m has also included experi m ental investigations of the s e m odel s under si m ulated flight conditions in an a co u s tic wind tunne l . Typical results obtained wi th a co annular nozzle without a plug with subsonic velocities in both streams ( fan -to-core velocity ratio, ~ 1.5) are shown in figure 10. The d ata are present ed in t e rms of overall sound p r essure level(OASPL) a s a function of the radiation angl e fro m the nozzle inlet. The wind tunnel results have been corrected for th e shear layer an d sound convection effect s of the tun- nel stream and converted to a flight frame of reference by th e methods of reference 8 .
Th e highest curve rep re sents the stati c condi ti on s , an d th e lower two curves show di- rectivitie s at f ree-- s trea m Mach nu m bers of 0.18 an d 0.30, respectively. Reductions in J et noise were obta in ed throughout the measured arc, f rom 60° to 150° fro m the inlet axi s . Peak noise reduction varied f ro m 5 to 7 dB be l ow the static case. The most sig- nificant re s ult wa s that the noise reduction due to forward velocity was th e same a s for a convergent nozzle, indicat in g that the noise reduction benefit evident un der static con- ditions is m a in tained in flight.
Si m ilar re sul ts are s ho wn in figure 11 for a case where the fan strea m wa s super- sonic (pressure ratio, 2.5). The subsonic core co nditions are the same as for fig- ure 10, p ro duc in g a 1.9 f an-to-core v elocity ratio here. The results are very similar except that th e peak reductions are somewhat s m al l er in m agnitude (by about 1 _ dB) and that in the fo rw ard q u adr an t th ere is an actual increase in noise level. The s e changes f rom th e subsonic case are caused by shock-generated noise. H owever, th is forward- _ quadrant e ff ect does not ch an ge the reduction in flight relative to a convergent nozzle, as the convergent nozzle is similarly affected.
DETERMINATION OF JET NOISE IN FLIGHT The presentation of th e preced in g simulated flight directtvity data for the coannula r nozzles int ro duces an other area of study where an alytical an d e xp eri m en ta l efforts ha w, been concentrated: the effects o f flight on l et noise an d the correlation of jet engine ex- haust noise flight data with si m ulat ed flight model test in for m ation. It is imperative to • be able to p re dict flight let noise characteristics hx _m an alytical models an d / or scale- model data becaus e actual flight testing for research an d development purposes is p l_ - hibi U ve in cost. Flight noise data f ro m l et engine s do not appear to agree with pred i c- tions based on classic a l J e t noise theories, such as discussed in reference 9. llow- _ ever, these differences seem to bc reconciled i f the flight effects are applied to the l et : m ixing noise an d to the interna l noise of the engines a s well, a s suggested in re f er- 5 01 J.
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" : ' ence 10. These effects of flight on j et en g i ne exhaust noise d i rectiv i ty are illu s trated !'
i n f i gure 1 2. In f i gure 12 ( a ) , flight effects on the j et m ix i ng noise are presented for a , t_ ic al t u r b o l et eng i ne. ' l_e so l id c u r ve r epresents t h e je t no i se prod u ce d st a ti call y i n term s o f n ois e lev e l as a funct i on o f radiat ion a n gle. The d i fference between the sol i d :::i a n d the dash e d l i n e s re p res e n ts th e re duc tion i n )e t noise du e to t he sou rce s tr ength re- i_ duc ti on in t roduc e d b y th e re duc ti on of the re l a t ive ve loc it y be tw ee n the j et a n d th e s u r - ' : rou n ding med iu m during fl i ght. Th i s effect i s c on stant at all a n gles. The dash - dot !., i: curve rep re sents the pre d i c t ed flight noise d irecti vi ty , in c o rp ora t ing th e dy na m i c e ef ect : !i o n nois _ as wel l . Th is d y n am ic effe c t te nd s to d e c reas e th e n o i se in th e af t quad r ar_t :, a n d incr e ase it in th e fo rw ar d q ua d r an t.
:i ; Th e fl igh t eff ect s on in te r n al n oi s e so u rce s a r e shown in fig u re 1 2 ( b ). B e ca us e _. th ese sour c es a re not s u bj ected to t he re la ti ve flow fie ld, th ere is no so urce str e ngth :_ red uc tion, b u t o nl y motion or dyn a mic effects. Th ese so u r c es h a ve n o re la tiv e m o t i o n _!_ ,:,. wit h respect to th e nozzle _ t h e refor e , the ve l o c i t y c han ge h as a gre a ter e ff e ct w h en a p- :' ° ' : p li e d to th e int e rnally g e ne rat ed n o i se, r e s ul t ing i n la rger i n creases o f n oi s e in th e f o r- _.!: wa rd q uad r an t than t h at sho wn in f igu r e 1 2( a) f or j et noise. As wi th j et noise, a re duc - _; t ion in noise occurs in the af t qu adr a n t .
, , , Th e ap p l i c ation o f th e pr ec e ding pr inc ip l es to the p redi cti on o f J e t eng in e e x ha ust ,i_.
: ,_ noise d ire c tivity for a h ypotheti c a l t u r b o jet en g ine a re s h own in fig u re 1 3 . Th e s tati c i°_, ' case is i ll ustrat ed in fi gu r e 13( a ). Th e sh o c k- fre e J et nois e, sho wn by the da sh ed ; ) _: curve, is g rea t er tha n t h e internally g ener a te d noise (das h -do t c urve). T he t o ta l ex- :i:: haust no i se (sol id cu rv e) is th e a nti l og a ri thmi c s um of t he }e t nois e an d i n ter n al noise _! levels an d is domin a te d by th e ] et m ix ing noise f or all angl es. Wh en th e fli gh t eff ec ts _?: are in clu d e d , a s s h o wn in figu re 13(b) , th e red uc t i on o f )e t noise at al l a ngl e s : : c o un - " te ract e d by th e i n c rease d con t rib uti on c i th e in te rnal nois e in the f orw ard q u a dr ant .
°_ Th e to t al e xha us t noise i s now do m inat ed by in t e rnal noise in t h e f o rw a rd q u adr ant: } e t .... no i s e c on tinue s t o d o m i nate in the aft quadrant. T o tal n oise s tatically a n d in fl i g ht is _: c ompare d in figur e 1 3( c ) . F o r th i s ca s e t h e fl ig h t ef f ect ha s in creased the }et exhau s t _, : ' total n oise in t h e forw ar d q u ad r a nt a n d re d c ced it in th e rear quadr ant .
_ ' App l ication o f this m et ho d o f fli g h t anal ysis o f j e t m ix in g a nd int er n al nois e t o t h e _, exha ust noise o f. tw o a ctua l en gin e s " is sho wn in fi gu re 14 . Th e en g in es s e l ec t ed h ad d is- _ : _, simi l ar levels of inte rn al noise , and i n the fi gure t h e actu al flight dat a arc c omp ared _ .'; w ith ca lcula t ed v a lu es . Th e res ults for a " h i gh' t -in t erna l -noise en g ine, th e Vip e r 610 : _ ' in an HS - 125 ai rpla n e ar e s h o wn i n fi gu re 14 (a). Bot h th e c al c ul ate d OA SPL va l ues _: . ( s h ow n by the cu r ves) a n d the d ata (sho wn b y t h e sy mb o l s (re f . 11)) sh o w t he in c re ase ' _i:: of noise l eve l in fli gh t in the f o rwa r d q u ac mt dis c ussed previous l y (figs. 1 2 an d 13).
_ .
, _ A l so sho w n, both ca lcul ated an d me a s u red, are t h e noise r educ tions in th e a ft q u adr an t.
, tt tt i ' The results f rom a similar evaluation for a l o w - in ternal -n oi se e n gine, the N ASA _i Lew i s - sponsor e d re fa n n e d JT 8D e ngi ne on a DC- 9 a i rp la ne, are sho wn in f i gur e 14 ( b ).
, 502 . ........ .....
' i
i
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In this case, both data and calculations In dicate a red u ction of exha u st noise in flight throu gh o u t all an gles. A very signific an t conclusion to be drawn f rom these results is that engine exhaust noise in flight can be predicted ff the internal noise of th e en gines is properly accoun te d for.
CON CL U DI N G REM A RKS This paper has very briefly described signtt, _ .tdevelopments in two areas of jet noise technology th at have g re at impact: Jet noise reduction an d th e prediction of flight effects. Coann ul ar nozzles including those with In vert ed velocity profiles, have been sho wn to offer signific an t noise reductions wi th little th rust loss. These resul ts are particularly applicable to supe r sonic cruise aircraft. It was also sho wn that flight effects on Jet engine exhaust noise c an be predic te d if th e in te rnal en gine n oi se is properly acco un ted for.
5 O 3 A P P ENDIX- SYMBOLS A C ORE c ore j et ar e a, m 2 AF A N f an jet area . m 2 A j ] e t (s i n g le ' _tre a m) a re a . m 2 CV th r u st eoe ff i c .ie n t, d i mens ion l ess c a am bi e n t s o nic v eloc it y , re s e e L si d e l ine d i stance, m M0 free - s t e a rn M a eh n um ber, d i m ensionless ' O A SP L ov erall so und p r essu r e le vel , dB re 20 / _N / m 2 O A S P Lc o A N N OAS P L for c o annular n ozzl e , dB re 2 0 b tN / m 2 . ?
• O ASPLc oRE +F AN O A SP L fo r synthes ize d coannula r no z zl e (ant t l og a ri thm tc su m o f •[i , f cor e }e t and fan } et OA SP L's). dB re 20 # N / m 2 ;:: P NLp k pe ak p er ce i ved noi s e leve l. PNdB :" Ri inne r ra d i us of fan st re am, m ; . Ro ou te r r adius of fan stream, m . : TCORE c o re jet t o tal temperature. K T FA N fa n ]et total temperat ur e, g ! / VC O R E c or e j e t vel o c i ty , m / see -' V F A N fan l et vel o city, m / s ee V } j e t (si ng le ,_tre a m) v e l o city , m / see • 0 angle f ro m n o zzle inlet , a xi s . deg P FAN fan jet d e ns i ty, k g / m 3 :, , i Pis a a m bie nt d e ns i ty at s t an d a r d c o nclitl o ns, kg/m 3 _ - • w den s i ty co rrec ti on exponent '¶ ., p .
) .
'i ,f 4" " RE F ERENC ES "i 1. A ircra f t Engine N oise Reduction. N ASA SP- 311, 1972.
!_ 2. Willia ms , T . J . ; Alt, M . R . M . H. ; a nd And ers on , J . S.: , o i s e an d Flow Char- _" _ , _t cteristics of Coaxial Jets. J. Mech• E n g. Sci., vol. 11, no. 2, April 1969, _ .' pp. 133 - 142.
3 . O lsen, W. ; and Fried man , R . : Jet Noise from C o -axial N ozzles o v er a Wide Range _ "' " of Geometric and Flow Para m eters. NASA TM X-71503, 1974.
.:._ 4. O lsen, W. A . ; Gut i errez, O . A. ; and D o rsch, R . G .: T he Effect of N ozzle Inlet _"il Sha p e, Lip Thickness, an d Ex i t Shap e and S i ze on S u bso ni c Jet N o i se. A I AA " : : Paper 7 3-1 87, Jan . 1973.
,_. 5. Jet N oise P rediction. Aerospace Infor m ation R eport 876, SAE, 1965.
, :_ 6. Stone, James R. : Interi m P rediction Method for Jet Noise . NAS A T M X - 71618, _' 1 974.
:ii" 7. Wh i tlow, John B. Jr. : Effect of Airpl an e Characteristics an d T ak eo ff Noise and o:_ Field Le n gth Constra in ts on"Engine Cycle Selection for a Mach 2.32 Cruise Appli- _i_ , _ , cation. NAS A TM X-7 1 865, 1976.
o * : 8. Am tet, Roy g. : Correction o f Open Jet W i n d T unnel Measurements for Shear Layer , , Refractions. A IAA Paper 75-532, M ar. ! 975.
_"_i. 9. Ff o wcs Willia m s, J . E. : Th e Noise fr o m T u rb u le n ce C onv ec t e d at H i gh Sp ee d .
..i_ Phil o s. Tr ans . R• S o c. Lo n d on , S er. A, vol. 255, n o . 10 61 , A pr. 1963, 'ii I pp . 469=503.
--_ 10. Stone, James R . : On the Eff ec t o u' . _.'_ight on Jet Engine Exh a ust Nois e . NASA TM "_ X -7 1 819, 1975.
;. : ' 11. B roo ks, J. R. _ an d W c_lro w, R . J . : Th e Ef f ects o f Fo rwa rd S p eed on a Nu mber of "_!i_ Turbojet E xh aust Sile n cer s . AI AA P aper 75-5 0 6, M ar. 19 7 5.
i : -_-._; • _:_ _' "I'# ?I i 505 ' 'Xl }, .................... : (CTOL) HIGH - B Y PAS S TURBOF AN
CO N V _O O N , _ _ C _
OVER THEWING (OTW ) _ HIGH-BYPASS TURBOFAN PO WERED UFT UNDER TH E W ING (UIW) VER Y HIGH- BYP A S S TURBOFAN
_ "
TURBOJET CRUISE AIRCRAFT _-- - , _ . - LOW-BYPASS TURBOFAN SUPERSONIC .__ Figur e 1 .- Types of aircr a f t a nd eng i nes a ffec t ed by devel o pmen t s i n J e t n o ise r educ t i o n t e chn olo gy.
f AFAN / AC O RE VFAN -/ i. THREE NOISE - PRODUCING REGIONS: • I. CORE-FAN MIXING If. FAN - AMBIENT MIXING III . MERGED-JETS - AMBIENT MIXING Fi gure 2.- No i se - pr o duc i ng reg i ons i n c o a n n ula r je ts .
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. i . % ' - - ;- Fig ur e 3 - Conve n tio na l coa nnu la r nozz l e s typic a l o f h igh- ir • , ; !, bypa ss- r a t i o turbof a n s a pp licable to C TOL and S T OL aircr a ft.
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V F AN i ',_ VEL O CI T Y RAT I O,Vr_E ,:, Figu re 4.- C o annular n o ise reduc t i o n f o r ; con ve n tional c o annular n o zzles.
: ': 507 / _ VFAN __corE -.
-- V_AN >Vcore
AFAN SMALL ~l I ACORE Figure 5.- Invert e d - veloclty-profile coannu]ar nozzles t ypical of l o w-bypass-ratio turbofans applicable to supersonic cruise aircraft.
" i " ; AFA-----N- : O,75 i ACORE FAN RADIUS RATIO: 0. 1 6 (a) Without plug.
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Fig u re 6.-Typlcal test models oi- inv_,rtrd.--\',,|,_,' i 1'."l,_,,i i lr co a nnular nozz ]t"_.
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i ' 1 500 2000 2500 3000 ! _, F AN J E T VELO C ITY , VFAN , F T I S EC ,/ , Figure 7 . - Peak noiseas fun c tion of jet velocity fo r ty p ical ;_ _" inv e r ted-veloc ity-pro f t ie coanuu iar noz zle s !
W :i " _ o ;z_ oo From ,NL_, ; " _ 6[-- TFAN " 95 8 K ( 17250R )
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' . VELOC I TYRATIO, VCORE / VI.AN ' _ Figure 8.- Effect o f vel_,clt, :' rdtl, , on uoise reducti o n r of inverted-velocity-profi l e co, annular nozzles.
i :, ; ' R a tio of inn e r t . o outer ldrl--:;t lt_illli rad i us, Ri / Ro_ ': :: O.90.
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(a) A c oustic. (b) A e rodynamic.
Figure 9.- Effect of radius r a tio on aero a coustic performance oi : inverted-velo c ity-profile c oannular nozzles.
, O, ' "O""C > , ,,... M ACH NO .
FT B FR EE-STREAM
_ = LI ,p" _" o 0
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_ 3 0
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6 0 90 120 150
AN G LE F ROM NOZZLE I NLET AX IS , deg
Figu r e 1 0.- St a t ic a nd simul a ted flig h t di re ctivities fo r i n v e rt ed-velo city -pro fil e c o annula r n o zz l e s wit h sub - soni c f an s tre am ( fa n p re ss ure r at i o, 1.8).
51 0 _ B FREE - S TREA M MAC HN O.
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6O 9O 12 0 150 ANG LE FROM N OZZ LE I N LET AXIS, d e cj Fi g u re Ii.- S t a ti c and simulat ed fli gh t d ir ec tlviti e s for in ve rt ed - ve lo cl t y - p r ofil e c o a nnul a rnozzl e s w ith su pe r- s oni c fa n str ea m (f a n pre ssur e ratio , 2 .S ) .
STATIC .... STATIC PROJTOFLIGHT, SOURCE STRONG A_ REDUCTIO N , m 20 - , _ .- , .,,.-- PRED FLI GH T , I_ DYNAMIC EFF, A D I0 A S _ _ D - 1 0 ( a) S ho c k-fr ee , J e t - mixin g nois e .
. 20 I { { I I
0 3 0 60 90 120 1 50 1 80 AN GLE FROM ENGIN E I N LET AXIS, O , de9 (b ) Int e rnallyg e n era t e dnois e .
Fi g ur e 1 2. - Typl ca l e ff ec tsof flight on j e t e n gi n e e x ha ustnois e.
........................... _ i = _ - _ -' _ ! t r
I
m m m IN _RN^ [ [ Y GE N ERATE_ N Q I _ [ | 7 0 F ..... J _ N O I SE ( _HO_ K. FRFE I -- , , , ,,0,, t_ or- _ _.. _ . _ ....
160 (a) Static, H0 = O, 13 o - / r , ; , ...... i, (b ) In - flight, M0 = 0.35.
1 6 5 ---- STAT I C o o° ' °°' _ 155-- "---, N -FUGHT. M 0 " 0. 35 o . O - °°° _ 1 45 y 13 5 1 2 S I I ..... I 1 1 I 0 _0 6 0 90 1 20 1 50 1 80 ANGLE FROM EN GI NE INLET A X I S ,e, d _ (e) Flight e ff e ct on total nois e .
._ F i gur e 13.- Synth e sis of jet engine exhaust noise dir e ctivity ",. for hypothetical Jet engine wi th rat i o of jet veloc i ty t o :_ ambient son i c velocity Vj / c a of 1.80.
i
• , _ T 1
: _ . t OdB . . . _ . 0,0 1 0 d° ,._:_ o _ , EXP CA L C ev .
__Z 0 "'- S T A T IC >. ; { q _ FLIGHT "- _ J __ _L _ I _ I l I _L_I_ I I l I 30 60 9 0 1 20 1 5 0 180 0 30 60 qO 120 1 5 0 1 80 ANGLE FRO M EN G IN E IN LET AX IS ,d _ . . ( a ) High _ n ternal noise (b ) Low internal n o i se : ( Vip er 610 e ng i n e i n (r efann e d J TGD e n gine L HS-1 2 5 alrplane), on DC - 9 ai r pl a ne ) .
Figur e 14.- Comparison of calculated and measured static and fllght dlrectlvities [ or e n gines with different ' levels of internal no i se r e lativE, to jet no i se.
, 512