NACA ACR 5120

57 Pages·2005·3.23 MB·English

.. -
~ - ACR No. 5120
c --- - --I I
NUV 1 53 945
1
NATIQNAL ADVISORY COMMITTEE
8 &>.
-3.F OR AERONAUTICS
M
dmes Aeronautical Laboratory
Moffett Field, Calif,
I
Washington
October 1945
c
AX ZXkS3fkZXTAL INVHSTIGATION OF BACA
. . ..
I
.~ SUBEtL3 GE3-DU CT E3T 3A9CZS
! 3~ ,Charles ,it. Trick, Wallace F. Davis,
L ~ U I O Ek , Randsll, and Emmet A, N,fossman
r-
sx:.lL!
3SY
. .
The rssults of preliKins.ry investigation of submerged-
;I
duct 'entrances presented. It is shown thEt an ontrsnco
mi,
of this typo possossas dosirable c r i t i c a l spord and prossuro-
rocovory ct3racterlstics when uses on n fuselage or nacr.l.le
i n region of low itcrsmentnl v'elocity aad thin boundary
3
l-.yer. The dzta o,'otsined indfc?,te tkzt snbmer-ged entrcnces
3re R O S ~s jliitihle f o r use with 'internal-flow syr(tems whfch'
diffuqe the cir only a small'hmount: for exaaple, those used
with j e t mc,';ors whjcfi have ax*ia.lLflow conpressdrs. Where C o w
plete diffusion of the air is required, fusslege-nose or wing-
leadin'f-edgz in1"dtz may pro%e :'to' Dc, supericr.
The results of the investig3tion have been prepared i n
such n .form 2,s t o perait their use by a designer and %he
ayplfcF.-tioa of these data t o a sp2cific design is discussed,
_- IBTRODUCT IOX
~
' a!
The use of the jet-pro?ulsion motor has greatly inten-
s i f i e d the need for efficient air-induction systems for
._
high-speed aircrnft. Although the a i r quantities used by
I
such motors are not g ~ e p t l yi n excess of the over-all air
'
requirenents of conventionnl air cra ft eagines of eouivqfent
kigh-speed tLr*Jst, thc perfornsnce of e .jet motor is
affected t o a much groster extent by pressure losses it
the'air-inductiqn system resulting from poGr design. A t
high speed, a loss ir; t o t - 1 pressure of 1G percent of tke
free-strean dynamic pressure for the air sup~l'iedt o the
j e t motor of a typic31 fight-ey aircr-i.ft may re sult in a
.
.
i
'.
1 2
rl
1P ss in thrust equivzlent t o about one-tenth of the 2ir-
i ,? p anc dr;lg. %hen it is realized th3t very few of the
s5r-iicduction systems of existing jet-propelled sircrafs
i
hive t o t a l pressure recoveries of more than 65 percent of
the freL+-strr::r= djazmic pressure, i t brcozes apparent that
there is :: great need for.inproved designs.
The E.ttional Advisory Committee f o r beronsutics, work-
ing closely with the ArEy and x~qvy, has been conducting
extensive rese:-rc@ on the problems of jet-motor 3ir-
induction syatms at its vericus l ~ i o r s t o r i e s Results
a
bk eoncerndd tiit?, fuseisgt+-cose inlets an8
=f +vL%.L--ui n -r%cs.c.;n3A.. ..-
external scoops have been published in references 1 and 2.
As a part of tkis research program, the Ames heronauticp
Laborat?ry, has undertaken the investigation of air inlets
subherged Dblow: th'e surface of the body irito which. the
enti'knce is placed.' "Phis type of. eir tnlet is not.~iiew;-
h--ving been tested f i r s t during the du'ct-entry reskarch of,
reference.3. 'Scbmerged aLd semisubierk&d'inlC%sh at$ dl80
t receiverf considerable attention frorn varidus iiirerKft
mahufacturera. It is the purpose of'fhe invkstigntion
' -
reportsd herein' to grovide more' complet.e'.inforEE.tion on - " .
?j ',entrances r>f this type sb as t o Befice their.'rols.tive ':'
.. h. e. r.f. ts c. o. n pfc'rcd with other tgpeis o.;.f f. : inlbts. . . . .a, . . .i.
'
X stLdp of* the. geometric' ch%,rbctBr-ist3cs of subme?ged
air iolete indicated the following pos-si?le advantages:
. . . . . . . ,.; J. - * ..-- . - ..
1: 3.kdu.ctior. of the length: of:'t ke 'Internal ducticg abd.
the el.iAinz-tion of tu.kting bents' ?::it:? a sp.viig in.weipht:.anc
redaction in pressure losses compared t o a wing-1ea.ding-edge
fuselage-nose inlets
0-
2. Zeduction in external drsg when compared with ex-
ternal fuselage SCOO-,~
. , .
1
'8. Sasier nt't'riinment oT high crit'icsl speed'at high-
* *
speed atttt\;de- thnn for external fxselaee scoops snd,a wid-er
rangr: of nirpl:Ans attitude for high cri+,ical speed than for
a b i ~ , gle ading edge or' fuselrLge-nose entrytnce
c
it WES belidvei! t h s t these advar.tages would favor the **
1' use' of such entrsnccs for. certsin 2,ir-inriuction sysC.ms, pro
7v idec!'tl;at design mdthods could be established t o elimina.te-
the ciisrscteristic low pr'_essnre recovery,
! i * . . . ,. , - - .
-
3
.3 80. 5120 NhCh ACX NO. 5120
* XODSL AI3 hPPA,PbTUS
. ir- 4
t -
2;*.-
The.Eenern1 investigption of the silbaerged entrances was
m d c i:i the i -3c 1.- by 1.5-foot wind channel shown in
figure 1. This wind char;nel is of the ogen-return type
2nd is powered with a high-cp,pacity centrifuga-1 blower
work- c.t$Pble of producing a masimlun.sirspeed of 180 rciles per
hour in the t e s t section. The air stream itse lf is very
ng
ssooth srd probsbly of low tur’bulenee ‘vec~riise sf the COG-
ts trrtction r a t i o of 13.0 t o 1.0.
md
Xeasurexents of the tunnel air stream indicated an
nd 2.
appreciably tkick boundary on t h e wells of t h e t e s t section.
In order t o o3tsin the thinnest boundzry layey possible, a
Il3Ut i c s l
le ts f s l s e w s l l W ~ Sbu ilt i n t o the wind-tunnel test section so
t n - t toe tanaef-wzll boundary layer passed bstween the
e
, fslse and true walls of the tunnel. The node1 submerged
1g . *’.
ch of, duct was placed in this f8,lse w a l l P_S shown in figure 1.
ala A i r flow i n t o the model duct entrance was controlled. through
0
the use of a small c e n t r i f u s d blower.
n
The model of the subnergetl-duct entrance was so designed
on
’0 * that the contours of the l i p , the sngle of the entrance
.. rznp (fie. I) 2nd the divergence of the rPmp could be chmged
.
without removing the other duct psrts. The o2eninEs tested
were of 4-sau.ire-inch area, one of 4- by 1-inch and the
reed
other 2- by ?-inch dinensioB. Tor a l l teats, t h e air drawn
53:
i n t o the entrnzice wes expanded t o n very low velocity in an
eo conical di?‘fuser of 13.0 t o 1.0 area. ratio.. Figure 2
E dna’
shovs a view of one of the entrances tested.
ght snd
,
ng-edge
A specific a;~iic3.tion of the re sults of .the general
inrestigaiioa was teste.8 on 0.25-scale rio.ds1 of a fighter-
rj
PX- :-=-e_ L2:_ -r-v,L..-‘--a-,- *L :E t’ne-trks 7-337 10-foot wind tunnel 30. 1. Views
of the subnsrged duct for this model ere shown in figures
3 (a> and (b).
.
-the .. Heasurenents of the >,ress.ire losses of ‘the a i r flowing
‘9, pro- i n t o the subqerge5 duct f o r the .teste ir! thekips 1- 5y 1.5-foot
-ina.te- wind chsnnel w4re m-.d,e both at t h e eiitrqnce 2nd. :It the end
of the d i f f u s w . The placinr of the tot.1-pressure tubes
f . and the stntic-Freasure tubes if; the entrance is shown
-
4 x;.XC9 AC% :io,:
4
1i
in fisure 4. PressGre losses at the end of the diffuser
* &ere neLA8ured with total-prrrrwr ~ t l t r 5 , %; sf.c-414 be
g ~ t e dtn it .rll measurements of the pressure rscovery at
v
.the end of the diffuser were made while the pressure-
i
zezcnricg rakes were locptad tn the duct inlet. The
pressure losses resulting frord t h e drag of these rakes are
of c ~ n s 5 d ~ r a bml ea gnitude And the data obtained f o r the
diffuser Ere of comparative ralue ocly. This i n no way
detr.-.cts from the valne of these neasurements since they
are ilsed f o r comparing t h e effects of vsrions changes t o
91
1 the eatrmce. Data useful to t h e designer were obtained
ti .W.:I cI ,i~ L ~ iU - Zra kes at the duct eslirance by pio%tfzlg conto-ars of
pyeeaure loss i n the entra.nce from the measured values
-o>t?.ined with the pressure-messuring tabes of figure 4 and
iztsgr2ting these pressure losses t o obtain the average.
loss. Losses measured with these rakes represent the value
obt2i3td K i t h 13O-percent diffuser efficiency. D a t a for
other diffuser efficiencies may be com~utedf rom these
XensureciFnts. For all t e s t s , the inlet-yelocity ratios arc
xezn v*?laes determined from .rir--auant itg mezsur enents msde
w i t h a cnlibrnted venturi meter located in the ai=. duct
’ 1e.rdinq t o t h e centrifugal blowe:.
t
Pressure-distribut ion testa were made over the li? and
the ranp of t h e entrance to permit an estimation of the
critic.xl spced. Pressure datal obtained with flush orifices
were usti with reftrence 4 t o obtain values of t h e c r i t i c a l
I
biacli numbers for various operntSng conditiJns.
The effects of rernoviE<? the boundzry-larer of the
surfqcc ahezti of the submerged duct we76 determined by
testing suction slots nt various iocations ahead of the
duct entrsnce. A s n s l l centrifugal blower ’used t o
WPS
zrovide su:r;ion. A i r quentrtios wcre mt;.zswed with a ePli-
br:ted.v epturt. A,sketcn of the boundnry-laycr-co~trol
t e s t &act i s shor~ni n figuFs 5.
B e a r l y 82.1 tests were made by holdicg the tucnel air-
speed constznt and varying the air quantity flowing in the
dxct t o v?.r; t-tle ialet-velccitp rtitio. A few t e s t s were
mEde -2t vs~3-h ish inlst-velocity rqtios by reaucirg the
tannel sirspeed.
Tcste of sui~mergee?--duct eatr*lr,ces f o r the 0.25-scale
ncdel cf tiie fig?-ter ~ i r c r n f tw cre made by inducing air
flow iEto tne inlets kit% ar- a i r pun? connocted t o a channf
i n the sper of the tig-su?portad model. The inlet-vr?~ocitj.
r
1-0.5120 NACA ACB 30. 5120 5
r a t i o wzs held constant while the model zngle of att..ck
was vsrIpd.4 Fressure losses were me-sured at the simulated
entrance tc&the Ealford J e t motor uith LL rake of 17 total-
pressure--measuring tubes in each duct.
BESULTS ASD DISCUSSIOB
Gener a1 Inv cs t i gat i on
d
5 of mIl-l t: isvestigntion of the subzcrged-duct ectr?nces in the
sroall wind chanriel was divided into phases, each concerned
with one p?rticular des-fgn variuble. These vsrizbles were
as foflows:
slues
1. R m p design
I-
2. Lir, design I
ar e 3. cib ntrnnce sha.pe and nsFect r a t i o
.de 4. Bo~ndnrj~--lzyert h i c h e s s
i
1 1
The discussib2 deals with each of these variables separ-
-tely. Portions of the discussion yr'e also devoted t o t h e
t
and f e w teste of boundary-lp-yer control and t o the external-dr%g
characteristics. Fiyure 2 defines t h e vnrfous elements of
fces t h e submerge6 entrar;ce.
? cal
&an designn,- During the prelibiinnry t e s t s of the sub-
m ergc:d ent7r.nces thc pressure rucctvzrics obtnincd 30th st tho
#
i rid of tiic diffuser ard at the duct entrzxce were disappDint-
ingly low. A maximum valua of pressure recovery of about 57
percerit WLS me.t,sured after con2let e diffuston :it inlet-
velocity rr.tio of 0.5. T?e pressure recovery dccressed t o
zero vhen the izlet--velocit3- r-ztio wgs incre-ised t o tl value
of 1.3. Tile critrtmco tested coxsisteG of n. 1- by &inch
opeuirg st the ecd of s 70 ramp boun2ed by straight parqllel
walls. Since at inlet-velocity ratios of less than 1.0, aore
?i: enters t n e - ~ p s t r e me od or' the rar;p thrn flows into the
r-
e3trCz.ce with resultznt s:jifl.ige ovcr +,ha sides pnd, since
the
the strenafinEs of the flow diverge ?s the opening is
El sppro~~chedi,t WPS suggested thct soxe ixgrovexent night be
obtaisei by di-rergizlg the walls of t h e rznir; t o fit the
stresnline? nore closely. Tests of the first aiverecnt w n l l s
~
showed a surprising incre-se i n the pressure recovery of 8
e
- t o 10 percc.nt ~ t ti nltt--veiocit;- rstios of less than 1.0.
12 order t o izvtstiF7te tilis further, tests of rcrious
m ne l
strstght divergent w p l l s nnd onc cbrved divergent wzll 9s
city
shown i n figarc. 6 and tsble Inwtre mn8e. The results
..
.
of thgse t e s t s are shown i n figure 7. The best pressure.
-. . redbveries were obtained with the curved divergeuce 4 which
' g a . ,~&~,r n~m xiaum pressure' rccov.ery ctf 73 percent at an inlet-
vclbcity rat i o of 0.40:- Inproveaent was also found at iflet-
~ e l o c i t yra 3ies grea+,er thm unity. It s h ~ i l l db e explained
tii2t the nezsure of divergence used i n this investigation is
the rztio of the width of the cntramce of the rEmp t o t h e
width of thc submerged entrRnce. An axminxtion of the
pressure-loss data o f figure 8(a) obtained i n the duct
cfitrnrice silo~stl 13.t t h e ezfect of the C i . i e ~ Lg ~.w-~-a7L ,-AI 5 ?a t o
rcaucc 3gprecisbly the losses suffered by the air entering
t.hF_ dact., T'he j,-?%rgyenent of f l n y lnsscs folznn Et, iclet-
I
velocity ratios of 1.0 or grezter indic2tes th5-t f i t t i n g the
costour of the r-?.mp wn.1l.s t o t h s stri.irn1inc.s .,does not give
a full explzriztion of the reduction of prcssure losses. It
is surEised tii3.t the divergect wxlls of the rasp a.ct t o
reduce t h c nsouiit of boundzlry-layer a i r which flows down
the rsm9, theruby increasing the pressure recovery at a l l
in1e t-vclo c it y ratios.
It was notioed, however, that while tile pressure losses
wcre nuch iupr ovd over t h e entrpnca as 3 whole, higher
losses thn2 those obtn5ned with no diverge1:ce were found
\ i n a sn:i11 region closs t o the sides in the upger half of
\ :
tke opcniqg just below tile lip. This effect is shown by
the dats cf ficure 8(3) t9k-c.n for t?ie pressure rake mounted
ore-half ir,ch f r o n the ctpccning, Flow studies iadicqted that
thest prrsrurc loeses wcr-t! o'rigicatixg i n 7 short stzlled
regior? tilo~igt ile a ~ l l so f thr. rrmp. A t t p.ts nade t o i
impyovc this cocditioL by rouiding'the c CP of the vr~lls
resulted i n even gre:iter logses. It F?-S found tkpt by
p1-cing s n ~ l rli r?ges or dcflec+,ors of a z~sxin;aoh eight of
one-h~-lf inch %long the toy of the divergcxLt w a l l s 9s shown
i n figurs 9, apprcciable grin cou!.a be obtaincd at Inlet-
velocity rztios grenter tiinn 0.6. cL7 kese data %re shovm Bn-
figare 10. The conbinatioc of the curved divergence and r'
?
dcfl.ectors iacre-ses the m?xinum pre sswe recovery after.
diffusion fro3 57 Fercezt (fig. 7 ) t o 78 percent. (fig. 10)
st an inlet-vel'ocity r a t i o of 0.4 and fron? 2G t o 36 percent
c?t ::.E inlet-velocity r a t i o of ucity. Tha effect of these
deflectors on the losses at the sides of the entrance is
shown i n figure 11,
The foregoipg results WGTC obtsincd wlth n ramp angle of
7'. , It WLLS iiectss=,r~-,t hcrefoTe, t o (?eter:ifne the effect of
chsngirzg the r:m.p sngle 01, t11e pressure losses and t o find
out vfietiier tLe use cf dSvCrc:t'zce wns a s cfficacious w i t h
grpnter r m p angles as for ij6. fie results of figure 12
show th:it, with parallel side ~:slls,e n sppreciable
: o . 5120
BACA .A23 ..No.. 5 I20 7
c ' - inproveZen4 in tho pressure recovery is experienced with
ich
;- incre.zs+icg*r asp angle espccislly a t the fnlet-velocity ratios
1e ,t-
greater t&+n unity. The results of tests-of various ramp
infet-
angl3s with divergent ,walls presented i n figure 13 show that,
?ne6
,for ram,p angles up to,10*, the use of divergent walls ,
cn is
results ir, E I reductio3 qf the pressure losses. For 15',;
a lzrgc IGSSi n pressure recovery was experiecced. The
.. f:'.
i e i u l t s of these test's indicate that, as a rwcp angle '1 *
t o increases the divergence used shauld decrease. Figure
;
14(a) shows the effect of ramp azgle Sn the pressure
ing
- distribution alosg the rmrp. Figure 14(b) shows the pressure
- distributic3 %long the ramp as it varies with inlet-velccity
tbe
rztio.
;v e
It . .
,I i D4 dts-*i- - 1x1 desigiing 3, satisfsctory l i p for the : ' '
submer_s.e d duct two reauirenents must 'be setisf ied. .FiGst,
z
the l i p nust have a shape thst w i l l give a high c r 5 t i c i 1 , .
11
speed at the l o w inlet-velocity ratios used ic high-speed '
flight; 2nd szcond, t h e lip shape mnst be such tnst -no
st?.lfir,g of the interns$,flow w i l l occur nt high inlet-
:sei
velocity r a t i o s or even e,i infinite inlet-velocity r R t i o
corresp3nding t o the sti'tic ground operation oE tine j e t
?
motor. With these crlteriE izi mind, seven l i p shapes
3f
were tested.' Lir;e 'draQ€r,eso f these shzpes are given in
figtlr'e 15, and t3bles :?(a) md IIC5) give their ordinates.
: t e a
The results of tests 'of these l i g sft~pec!e re'given in table
that
1x1. The first 'lip tested was poor 11: sll respects,
d ,
especielly insofar as the stalling of tine internsl'flow
wzs concerned. Addixiz curvature t o tile fnrier surfp-ce ( l i p
IS 2) improved these stalling tenCencies, but the c r i t i c a l speed
w?s still very poar. . Adding curvature t o t h e outer surfoce
)f
( l i p 3) did not inprove 'the critic31 speed and made the
iown
Snter2al-flow losses nuch greRter. Adding curvature t o 30th
..let-
the inside znc? outside surfeces c l f p 4).'inore8se the c r f t t c a l
in
speed and elislinatcd s t s l l i n g of the l i p except at infinite
:-
inlet-YelsCiEg ratio. Changing the nos4 -radius ( l i p 5 ) did
rol not iaprcrvg this condition, but"5n'incresse in camber and an
-
increase i*n nose ridius resuLted in 'Bn'e-ntirely sa,tisfactory
ent
l i p (Ifp 6). A further attenpt to' iaprovs t h i s kip by
e . ,
increqsink the l i p rti.dius resulted i n n - s t i l l furfher de- .
c cre?se fn critic gl speeds. It is' ccncluded tktat; for th'e
- duct teated, i i p 6 WRS entirely sstisfsctorg. ..I- - *
e* of 1 , .I.
-t of It WRS sntieippted t h a t chenging the ramp Qf tke"s'db--'
-2 d merg&d entr?nces night have Rn appreciable effect tn 'the angle
of flow at tHe l i p and thereby oristire critical'speed. 'Tes€e
r 11 . r '
of l i y 6 with 9 rmrp ncgle of 7 3 6howed a decreqse i n Ohe':'

-
EACA ACR Eo. 5120 9
i
512 0
--
a
inlets des gnfd for a specific nirplsnc 2iscu'ssed lstt?r
' indicate that the r a t i o of l i p size t o duct depth may be
lace 4 reduced tokt3bout two-thirds of that used for the lipa of
th&t t s b l c s ' I I ( s ) mid IIib).
was
-
Ee of -E--n.ntcr.e -?sg, ~ c rtat in. A few t e s t s wpre mpdb t 6 cleter-
. fact mfnc the effect Q-f enItran-ce -mpe-ct r-atio on t h e presbure-
lrfaces recovery characteristics. CoFparative results m e shown fn
o c i t r figure 21 for the 1- by $-inch opening (for which nost of the
Deed researcii W ~ Scc tniuctedj nnti a. 2- by 3-iach openinE. 'ilirs
&lla- effectiveness cf diverging the walls f o r the 2- by 2-inch
spening is of Cnmp?rnbl_e ?r.P,g2ltude t ? th?t fnund for the
1- by +inch cntry. The 5ax~.n~pmr essure racovcrv which
the ansg be reslizrd f o r the 2- 157 %inch opcning is slightly
*,
less than f o r the rec tmgulsr opcnlng. The C;its of figure
'fect
#npari - 22 indicate ths-t t h e lcss i n pressure rec-ver-y*r esulting
17 from n thick boundary l ~ y e ris sonewhst lcss f o r the sonere
dence open ing o
la the
-
a . iif fec t cf boununr v-1 Q Y er thi&nes.a. All the tests Cis-
,cilssed abrJve wCre rizi,e witn the normal boundc.ry layer of the
O B
felso w n l l of the wind cfimmel noted as bound-ry lnyer 1 i n
95.
figure 23. In ordcr t o aaccrtsin the effect of boundvy-
r
lager thickness .mc? t o Srovide data appllcablc> t o subaerced-
ngl e
3 duct installations far :rft'o ~?'t he fuselqgc of an zir-plcne,
:umber
t e s t s were also x.ide with the two cithcr bGun?.ary-layer
d for
thicknesses si~owni x: figure 23. Brsults of these tests
*bZe.
%re showo i n figure 24. As expecte?, tliese thicker bQundary
)n
lsyrrs npprtcisbly re2uced the ?ppar.?nt pressure recovery
nee
1 at thc end 3f the diffuser.
is ;is
l i p .
a 13 clrder t c ascertain the effect of the deflectors 3n
p- &a$
the pressure reCo7er$-, t o e t s Yere made with bctn normnl and'
)w- at-:
extenicci e.sflectms. (See fig. 10.) Thc re sults of thrse
tests 2rc shcvn 2 3 figure 25. It cay be seen thr,t, f o r tho
- thinxest 3our.dary layer, the nornnsl dcflecthrs showed an
.: r*
8,pprcciable Impru-.-ement while th? rxtcntlc.? firflectors fm-
-facer
prove2 the pPosaure recovery cnly f o r B smsll.rnnge of low
er
) ' . i l I inlot-vclocity rstios. With boundRry laysr 2, the usc of
exte;?!cd duflcctors very epprecisbly increvsed the pressure
I t . '--
rc-covtrg. ;tit:? bnun45ry layer 3 , tht? izprovrment resulting
1.._
. f r o m tile USL- of LcflPctcrs.wns less. This dccre-se In the
.
1- effectiTenc:ss of t h e dcflect3rs is believe!! Cue t o thr f%Ct
1. that tiit? br3undcy lsyer wqs verg, thick.
n
-2 f
-~ As w i l l be E ~ G W Ul s t c r i n this+ repcrt, t e s t s of a speci-
f i c n7oRei wlth a boundzry layer thinnGr tiim any of these
C .
ncationed i n the prccec?icn paragraph showo?, n decrcnso in
m
I