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Copy No. . i!'~

RM No. A7130

"I V

RESEARCH MEMORANDUM AN EXPERIMENTAL l"NVESTIGATION OF T"rlE DESIGN VARlABLES

FOR NACA SUBMERGED DUCT ENTRANCES

By Emmet A. Mossman and LalU'os M. Randall

Ames Aeronautical Laboratory Moffett Field, Calif.

,MS J"""Itt",~r:t e"rJ.&tm: ~~fl,..f >/If _r~'\l_" ~ff-'II"" II ... tlatl

NACA :m lio. A 7130

MTIONAL ADVISORY CCf!MI1'l!EE FOB AEROMUTICS

AN EXl'ERIMENTAL lllV1!STIGATION OF 'mE DESIGN VAllIAllLES

FOR 'NAC! stmME:imD !llJCT ~ES

By EmMt A. Mossman and Lauroa '(. Randall

Informatia~ concerning the ~tere aud design var1abl~s affect1Ilg IUl MCA submerged duct design is presented. !I!1e pr1n-cipal var1ablds investigated include entrance width-to-depth ratio, ramp-vall divergence, ramp lIlISle, and deflector size. TGstll were also Il!ade to show the e1'fect -:If v~.ation of bound!U7-~i!)r thick-nsss and ramp-floor contour.

Pl'essure recov&ry at the duct tJlltrance and atter slisht diff'uaion, pressure distribution OTel' the lip and ramp. and dl:'ag are given as funct10ns of the inlet Teloc1ty ratio 01 the entrance. An evaluation of the MCA submcl'ged entries 1nd1cates that latis-factory duct characteristics may be found tor a 1'IUl8" of' the test variables. It tLp;peara that an opt1lxum. NACA su'bllle~ :ll2l.et design should employ curTed divergtns ramp walls, a 50 to ~ ramp angle. and a width-to-depth ratio of trail 3 to 5. The boundary-layer thicknese 01' the surface into which the inlet ill placed VaG found to have e. large effect on the pressure recovery.

Possible applicatione of this type of' inlet an~ their particular adTalltagss are discuslled.

lllTROmCTIOIl

For the development of a satisfactory air-induction system of an aircraft, several aerodynamic criteria must be evaluated '.n con-junction with those involving structural design and installation. Aer~cally. the 13;rBtl!lll should not reduce ths available anergy of the entering sir, the dl:'ag of the bod,y into which it is placed should not be increaaed, and the high-speed characteristics of' the b~ or aircraft should not deterioratel. Although. in prac'!;1co, an air-induction systl!lll poseibly doss not meet all these requirements, the lII!Ir1ts of a syst6ll1 can be determined by the degree to which its characteristics approach the timnm •

. , ,'.;j--"""-'d_-..-,

__ ~J

2 HACA mHo. A7I30

A :previous investigation of an air intake submergod belov the bo~ surface (reference 1) vas exploratory in nature and vas meant to indicate the trend for future research of this type inlet. ~is present report gives the results of more extensive investigations of HACA submerged duct entrances oonducted at the Ames Aeronautical Laboratory. 'nle work includes further developnent of certain con-figurations found to be desirable from preliminary tests and the investigation of other design ~tera not previously considered.

SYMBOIS

A duct-Bntrance area, equare feet

B distance ramp floor :l.s submerged below reference contour at station Where entrance lU"l3a is lJISasured

CD]) duct drag coefficient( fti: ) D drag. pounds

d duct depth

H total pressure, pounds per eq~ foot

t:iIl loss in total pros sure, pounds per square foot

M mach nUIolber

MeR critical Mach number

P I pressure coef'f'ic1ent ( p ~ Po ) p static pressure, pounds per square foot

q dynmnic :pressure (iPT), pounds per square foot

U velOCity outsid!) bounda.r;y lBier, feet per second

u local velocity in boundar,f layer, feet per second

V velocity, feet per eecond

w duct width

p air denSity, slugs llOr cubic foot

•

RAOA mHo. A 7130

(1 + 11)

dUf'uBer efficiency ( ~ - lh) .l.-Pl.

M.'2 H" MS MS 1+-+-+--4 40 1600 80,000'"

x 100, perqent

Ii-p q(l + TI), ram. pressure, pounds per squar/l! foot

R - Po

lio - Po r.ooa recovllr.1 ratio

inlet-velocity ratio

Subscripts

o t~e etrealll

l. duct-entrance station

.'2 station attIJr diffusion

3

Various models of submerged-duct entrances were teB~ed in the Ames 8- by 36-inch wind tunnel of the 7- by la-foot v:1nd~·tunnel section, which is shown schematically cn figure 1. Each entrance to be investigated vas placed in a removable portion of one of the 36-inch valls of the test section, this wall thus simulating the fuselage skin for a typical submerged-inlet application. Air was draliJl through the inlet by a constant-llpeed centrifugal pumP. the quantity flov being measured by a calibrated venturi and regul.ated by a motor-controlled Plus-type valve located at the pump exit. ~e tests vere made at tunnel epeede ransing frOJll 180 to 260 feet per second.

All :parts or the entrances for ths greater portion of the investigation vere flush with or belov the surf'ace of tho tunnel vall. ~e area of the various entrancos was held constant at 16 square inches end the width-to-depth' ratio varied from 1 (4- by 4-inch) to 6 (9.81- by 1.64-inch). A separate modol vaa required to teat each of the six width-to-dspth ratios. (Soe fig. 2.)

For oach modol four =p plan foms vere invl!stigated (fig. 3). Ramp angle could bel 'i8r1ed frOll 50 to 150 • Figure 4 shows the geometric chang~ of the l'I!lIlP with ramp angle for one entrance con-figuration. Erov1s1onvas also made for testing a c'Xl'Ved r.ooap floor shape, nth the vld = 4 entrance for r.ooap lengths which corresponded

COII!'H! I!JllJiit' I

4 co~ lJACA EM Ho. JI. 7130

to the 50, "(0, 90, and 11.50 straight rallIP floors. 'l!hi8 oUl'Ved ramp floor, shown on figure 5, repres~ted the upper-eurfe.oe profile shape of the aft :portion of a 65-eer1es 10lt-draS a1rtoiJ .•

Deflectors, or small ridges along the top edg6 of the ramp wall with heights of 0.25, 0.50, 0.15, and 1.00 inch and lengtha of 25, 50, 75, and 100 percent of the ramp length vere tested (fig. 6).

The basic lip shape (fig. "() was the same for all models, but the dimensions of the lip varied directly as the depth of the duct entrance. In every cooe the lip incidence could bs varied through an angle range of ± 50.

The models included a transition section vhicn simulated an internal duct system with gradual diffusion. This section stal~ed 8 inches aft of the lip leading edge and for each model transformed from the rectangular cross section of the submerged duct inlet to a circu·.ar cross section 5.25 inches in diameter. ~e transition ssction was 36 inches long with a 1.35 expansion in area, constant for all models.

Rakes of pressure tubes for measuring ram recovery were locatsd at wo stations (fig. 2), one at the duct entrance and the other after diffusion in the 5.25-inch-diameter circular section. ~e rakes located at the entrance contained 64 evenly spaced total-pressure tubss and 4 static-pressure tubes. These rakes were mounted slightly behind the leading edge of the lip in each case Gt a station where the lip inner contour faired into a constant area ssction. The rake aft of the diffusar ssction had 33 total pressure tubes and 4 static-p!'eaaur8 tubas. '!he wind;"tunnal air dO'llDBtream of the inlet was surveysd by a series of individual rakes, locatsd 8 inches aft of tha lip station, which completely bracketed the wake caused by the entrance. Each of the individual rakes containsd 15 tubes and were located at 8 spanwise stations.

Pressure distributions were obtained from small flush static-pressure orifices built into the submerged duct entrances along the center lines of the lip and ramp and also along a section of the lip 1 inch from the side wall of the entrance.

To aid in the analysis of the data it was necess~ to evaluate the sxisting testing conditions. The boundar'".f layer of the test section tunnel wall, measured at the duct-entrance station, is given on figure 3. It Should be noted that this boundary layer is consider-ably thlcker than would be normally experienced if a submerged

c~

•

NACA EM No. A 7I30 5

entrance vere located at or forYard of the ving on a similarly scaled fuselage. Efforts to reduce thie mturaJ. bOUIlda.ry-la;rer thickness did not prove successful, due l!le1nJ;y to the Wind-tUDIlel geometry. !!!he ratio of total bOUIlda.ry-~er thickness to duct depth (wid = 4) is 0.80 for thesa tests as comr.ered to 0.31 for a typical fighter installation (station O. reference 2). From this it is evident that the pressure recoveries ~sentsd in this re~ nmst not be considered as the mx:Jw1lll 'Values obtaimble vi th lfACA sub-mersed duct entries. !1!l1e lips or all lItcdels of the Bubmerged entrance vere located at the same position along tha test section vall.

'1'0 detel'll1ine tha diffusor or internal duct efficiencies. bench tests of the 'aix diffusers vere made. A cone vas attached to the entrance in place of the ramp and lip to assure satisfactory flow oonditions. !!!he presaurs losses vere measured aft of the diffusers in the circular portion of tha diffuser at the same location and vith the SBlII9 raka that 'Was UIIed to determine the preS!lurs recovery aft of the diffusere in the vind-tUDIlel tests. Results of these tests (fig. 9) show the efficiencies (I1D) of all ~ix diffusers to be about 91 percent.

The principal ~ters investigated in the wind tUDIlel 'Were ramp plan tom, vidth-to-depth ratio, =p angle, and defle.:3tora. A limited number ot teats 'Was made to ehow the effect of variation of ramp-floor contour and bounde.ry-~er thickness at the loc~tion of the duot en'!;ranoe. For evaluation of the relatiTe merits of the various oonfigurations measurements vere taken to deter.mine the prsssu.~ reoovery aft of the diffuser seotion and at the entrance. pressure distribution on the lip and ramp, and drag of the oonfig-urations, through a range of inlet velocity ratios from 0 to 1.5.

Tables I and II are indices showing the range of modifications to the submersed duot entry.

llESUL'lS Al'ID DISCUSSION

!!!his investigation to obta:l.n data for the developnent and apPlioation of NACA submerged-duct entries was ooncerned ."ith the effeot of various oonfiguration ohanges upon the degree of fulfill-ment of the cI'iteria set forth. The measuremente neoessary for evaluation, ae mentioned previously, vere pressure rscovery aft&r diffusion and at the entrance, pressure distribution, and drag. Under these oategorise the following parameters are disoussed:

1. !lamp plan form.

6 CO~ .-, .. NACA EM No.A7130 2. Width-to-depth ratio

3. Bamp angle

4. Ralnp floor shape

5. Boundary-layer thickness

Because of the nature of the investigation. the results and discussion of deflectors are presented se~tely from the other divisions at the conclusion of this section.

A figure guide is given in table III. Only the more pertinent drag and prBSsure-distl'ibution .results are presented, the greater portion of the data being given in terms of pressure recovery.

Pressure Recovery

On this type inlet the velocity distribution is not uniform over the entrance area, and determining the entrance losses (Appendix A) becomes a difficult process. Consequently, a large portion of the data is evaluated from consideration of the pressure recovery after diffusion. Since the diffuser efficiencies from bench tests are equal, a comparison, for two inlet cont'igurationG. of the results after diffusion is a direct measur.e of their relative merits with respect to pressure recovery. This comparison, of course, includes the effect of the inlet on the diffuser efficiency. Entrance pressure recovery was obtained only for the most important values of the deSign parameters.

Pressure Recovery after Diffusion.-

~mp plan form.- The results of previous investigations (refer-ences 1 and 2) showed that the ram pressure recovery of the submerged duct entrance could be ~ppreciably increased by diverging the walle of the ramp. The effect of ramp plan form 1s shown in figure 10, which gives the pressure recovery measured after the diffuser section for two width-to-depth ratios. In all cases the curved diverging ramp which was previously developed (refElI'enCe 1) gave the highest ram pressure recovery for the low inlet-velocity-ratio range (Vl/Vo ::;0.6). However, the effect of ramp plan form 1s also a funcGion of w1dth-to-depth ratio;> and ramp angle and Will be discUE/sed in later sections.

In the instances were the pressure recovery is increassd by diverging the ramp plan form, the process is apparently one ,-

CONtfJ""":fIfC ,-;~

mCA m No. A7I30 7

•

of diverting the boundery layer outside the ramp around the entrance. Experimental data show this posaibly to be due to two causes. The firet is indicated from a canJ;nrison of the ramp pressure d1stl'ibution with that on the sur.f'ace in the :Ilrmediate prox:1lJl1ty of the entrance. These pres.sures indicate that at velocity ratios belov 1.0 the boundery layer outside the ramp would have a tendency to flaw away, fran the inlet. Second, it has been found that if the top edge of the divers-iIlg ramp walls vere rounded, the effsct of divergence vould be greatly reduced. It was surmised that some of the ill1provement vas caused by the resietance of the external boundery-layer air to flow over the rather sharp edge of the ramp walls.

Width-to-depth ratio.- The effect of varying the width-to-depth ratio of a submerged entrance is given in figure II for a con-stant ramp angle of ~. Figure 11 shows that for the J;tU'allel wall, nondiverging :t:'8lllp changing fralt a vld ratio of 6 to a wid ratio of 1 increases the lD8x1mlD! pressure recovery atter diffUSion fi:om 70 to 80 percent. This trend vas expected since most of the boundary-la;rer ai;r in front of a nondiTorg1ng ramp flaws into this typa of entrance. Conaequen~. for the deeper and narrovor entrances this 10N'-ent'rgy air is a smaller percent-age of the total qusntity adlIIitted. Increasing the divergence of the ramp valls diJdnished this ~ffect. ~is 11'8.8 entici1;lated Since, 88 mentioned previously, With a diverging rtI.1!I.p lilUch of the boundery-la;rer air i8 diverted around the entrcnce. thus decreasing the beneficial effect of reduciIlg the width-to-depth ratio found with a nondiverging ramp.

The vidth-to-depth ratio necessary tor mev!l!t1l!! pressure recovery also increased as the divergence increased. This lIII!IJ" be better visualized by the f'olloviIlg table:

Maximum Fressure wid for V3./Vo tor Recovery (af'ter HaxiIllUlll Max:lmula

Dif'fUIJion) Recovery Recovery

Parallel valls 0.80 1 0.70

Straight diver-ge..1ce Xo. 2 .845 2 .55

Straight diver-gence lio. 3 .860 3 .43

Curv-ed diver-gence .865 3 .40

3 CONF~ RACA EM No. A7I30

RACA EM No. A 7I30 cob:rw I"A'f:c=e 9

walls increases the tendsncy toward seIaration. Second, in-creasing this angle increases the obliquity between the ramp walls and the free-stream flow. This makes it more dltticult for the air tlowing along the outside ee.ge to follow the dive~gent contour of the side walls. Consequently, air spills over the sdge of the ramp walle, admitting much of ths bOUAdary layer and causing a cross flow betwesn this ai.t' and the air flowing down the ramp. A combination of tb~~~ two adverse conditions causes large pl.'0ssure lossss to OCCil!' 1..0. the corners of the submerged en'trance When the ramp angle is increased. '!his is shown in figure 13, which gives the distribution of preBB~e loss across ·the submerged entrance for several config-urations. From figure 12 it appeare that for the larger ramp anglee (above 100 ) the optimum ramp plan form should have some-what less divergence than that employed for the lower ramp angles.

From the results of the investigation of ramp angle. a better comparison of the Jlll!rits ot Tarious width-tO=depth ratios can be obtained. In most cases the use ot a given ramp angle is dic-tated by the length available ahead of' the duct entrance. Fora constant-area duct entrance and a oonstant ~E angle, the requir0d ramp length is much larger tor the deep and narrow entrances. '!hUB tor a 70 ramp angle, the ramp leD8i1h for a wid ratio ot 1 :1s 2.45 times the l'alllP length of a wid ratio of 6 entrance. Since ramp length usually cor£titutes a deSign limitation, a more usable com:pariBon of' the entrances of varioUB width-tO=depth ratios can be obtained by com:paring the pressure recoveries at a constant ramp length. To obtain this com:parison, pressure-recovery data after dif'fusion were plotted against a ramp-length term. This term was lIIade nond1Jlll!naional by squaring the ramp lens~ and dividing by the duct entrance area. '!he

2 cross plots of' pressure recovery as a function of (romP length)

entrance area are giTen in figure 14. A comparison ot these curves indicates that for many design conditions width-tO=depth ratios of 4 to 6 will give the highest pressure recovery.

Ramp-floor shaps.-A com:parison of the Pl~ssure recoveries for the straight and curved l'IUIlp floore is given in figure 15. The straight floor is seen to be superior for the configurations tested, but the difterence in pressure recoTery is small, usually lese than 2 percent for the more optimum configurations. '!he presont exper1mental results indicate this ~ter to be of secol;ldary :l.mportance in obta:\ning high-pressure recovery. Therefore, small changes in the contour of the floor that lIIaY be required to obtain a smooth junction between the ramp floor and fuselage skin ahould not noticeably affect the pl.'0ssure

10 CO~ MCA EM No. A7I30

recove~ of the installation.

meet of' b2BPdl'mr-llmW tlrlelm'U.- A eCQll.~:t'ison of the natural and thickened bounda~ layers is siven in figure 16. Figure 17 shows that, as eXI>!!cted. increeeing the bountJ.er,y-layer thickn&ee decreased the ram recove~. This decrease wee practicall1 the same for all configurations tested and wee approximatel1 equal to 0.12 ram recove~ ratio. These tests clearl1indicate that diverging the ramp walls kseps only a portion of the bound.e.lT-layer air frCQll. entering the duct. and aonsequentJ;,r stresses the tmpo~~ce of locating the entrance in a region of thin boundar,r layer for =:I.mum recovs~.

An att8lllpt 'liaS made to cOl'1'elate the change in ram recovel'1 with the change in bountJ.er,y layer. Varioue bo~-layer pam-maters were considered (bountJ.er,y layer. displacement. and lIlOIIIentum thicknesses. etc.) and the factor h wee selected as being mos·t I>!!l"tinent in estimating the pressure recovery for this tYI>!! of submerged inlet. The term h is defined all a height which contains an amount of free-stre!llll ram pressure equivalent to the total pressure lost within the bountJ.er,y layer. and may be emluated from the f'ollwing equation:

h - [O.::sa: dy - 0 Ho-Po

. Where

8 total bountJ.er,y-layer thickness

As a firet approximation. the change in ram due to thicken-ing the bountJ.er,y layer or changing the duct depth and holding wid constant. may be est:!llla.ted from the f'ellOll'ing equation:

(H -p) (H-P A 13 _ 13 He- Po He- Po

where the subscripts I!I. and b refer te different config-urations. Obviouely, this is not a rigeroue relation, but it sheuld give an indication of' the change in ram which would be expected if' the bountJ.er,y-layer conditions ef a given entrance were altered, or the size of the inlet changed (all dimen-sions remaining geometrically similar). The values of h fer the natural bountJ.er,y layer end the thickened bountJ.er,r layer .

NACA 1M No. A7I30 II

are 0.227 and 0.530 inch, respactively. A cOll1llEU'1son of' the estimated chango in ;p1.'6ssure recovery calculated by this equation with the measured change for the tao bottnds.ry-laYElr conditions of thoie tests is given in the follow1ns table. ~ie table ie for Z'Illllpa v1th curved divorsenco and a ~ rrunp angle.

Calculated Values , Measured Values

ot.6(H -Po) Bo - Po (n - Po) of t:. Ho - Po .

!l Vo i . 2.0 !'. • 4.0 d if .. 6.0 ~. 2.0 ;r. 4.0 ~ .. 6.0 -0.4 0.071 0.101 0.123 0.095 0.120 0.ll2 0.8 .071 .101 .123 .105 .llO .ll3 1.2 .071 .101 .123 .095 .095 .105

The use ot the h factor resulted in a much closor aPl'lt'o:d.-motion than any 01' the other bound!u7-la,yor ~ters considered.

,.Entrance Pressure Recover,z.- or llr1lilary interest in the design ot &. duct1ng system 1s the entrtmclt prllssure recovory. frOll! which tho 108S0S chargeable to the d1fi'usOl· ~ !"goluded. !!he l!!!Ithod of com-putation used :In detem1n1ng this entrance prllBSure recovol;1 1s given in Appendix A.

The effects of ramp plen fom,ramp angle and 'Width-to-depth ratio. are shOlln in figures 18(a). (11). end (c). Compsr:!.son of these curves of entrance pressure recovery with corresponding curves for recovery after diffusion (figs. 10. 11. 12) shov that the resulte follow the same trends. In gensral, the prav:l.ous analysis accounting for the differencee between various configurations is applic~bleo ~e sl1sbt discrepancies found :In the analysis bc)'tveen dat!l. for entrance pressure reccvery and prES8ure recovery after diffusion (f1Se. II and 12) can probably be attributed to changes in diffuse:!." efficiency with changing entrance conditions. !!!he losses at the entrance together 'With the losses after diffUSion enable en eval-uation to be made of' the change in diffuser efficiency for lIllY con-figuration. (See reference 2.) Using these losses. diffuser effiCiencies tor two entrance configurations have been calculated

12 CONF~ NAOA EM No. A'1I30

and are com;pared :!.n figure 19 with those obtained from bench tests. The difference between the two sets of curves represents the effect of the inlet on the diffuser efficiencies.

rresoure Distribution 8nd Critical Mach Number

In thie part of the investigation esttmations of the critical-speed characteristics of the submorgod duct sntr8nces yere made from an analySis of the pressure distributions over the lip and ramp. The critical Mach numbers were estimatsd t:t'CD the peak lov-spoed PNSS1U'8 coefficients by the nfl'llllfn-'l'sien method (reference 3). 'DIiB method doss not apply to three-d1l:ccnsionel flov (reference 4). Just what corrections Should be used for the flO1l around a BublllBrged inlet is not known. but it is believed the results given by the method of reference 3 will be conservative.

L!J!.- The critical-speed charecteriotics of the lip are depend-ent upon the inclination of the flov approaching the lip. A decrease in the inclination of the flov is defined as an angular change of the flO1l which causes the stagnation point to move toward the outside surface of the lip. '.!!hue, adecrease in the flow inclination decreases the incremental velOCity OTer the outside surface of the lip. and vice versa fQr the inside surface.

'DIe pressure distribution over the lip is given in figure 20. Here is ehown the change in the stagnation point With inlet velocity ratio and the effect of this change on the peak negative pressure (oeff1ciente. Increasing the inlet velocity ratio always decreases the inclination of the flow.

The effecte of ramp plan fom on the cri tical-speed character-istics of the lip are given in figure 21(a). With a nond:Lvergent remp there is no appreciable change in the flow inclination across the entrance. For the lip section, 1 inch from the edge of the entrance. diverging the ramp also caused practically no variation from the data obtained with nondiverging walls. For the center-line section of the liP. however. diverging the ramp caused the stagnation point to mOT$ toward the outside and consequllntly in-creased the critical Mach number for the flow over the outSide surface (fig. 21(a)). This cca:parison shOli's that with a divergent ramp there is a disti~ct ~~ation across the entrance of the angle of flow approaching the lip. 'DIe flow near the edge of the entrance has a more positive inclination and produces the largest incremental velocities ove~ t~e outside surface.

The effect of ramp aLgle on the critical Mach number for the lip is shown in figure 2l(b). As v.ould be antiCipated. increasing

~ CON.F:afP ' /'

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NACA EM No. A 7I30 13

the l"Blllp angle decreased the flO'll inclination. T'.

14 cor NAOA :m No. A 7I30 lower peak incremental velocities over the ramp than the curved ramp floor when divergent walla are used. 'l'he studies of ramp floor con-tour in the present investigation were 11llited in scope. A more ftUld!lmental study of the effect of ths ramp pressure gradient on critical speed and pressure racove.-y should ba made. 'l'he =p floor should probabl;r be designed so that the pressure gradient will have the least slope at the design inlet velocity ratio.

Drag

Drag of the submerged entrances was ll.eteMined by surveying the Flrtion of the air st:ream containing the wake d:ue to the inlet. and is equal to the difference in mcmentum of the air stream. vi th and Without thG duct :tnstalled. 'Rio method of cal.culat:tns the drag is given in Ap:pendiX B. 'l'he drag coeffic,"ents based Oll duct-entrence area are lll'esented in figure 25 for the various conf'lgurations. while figure 26 shaws th!& ,"stribution of the momentum loss, aft of the entrance. .

In al.l cases, the drag decreases as the inlet "f'elocity ratio is increased. Figul"e 25(8.) shcr.rs that the drag increases as the diver-sence ill increased. 'l'his was expected. since a nondivergillg rem.p permits a larger portion of the boundary-layer air to flaw into the inlet. In general., it appears that configurations which result in higher ram recovery haTe larger attendant drags. 'l'he negative vaJ.ues of drag result from the fact that the lOBS in IIIOIIImtum dcnmstream of the entrance was less than the loss due to the boundary ltver that previously existed. 'l'his can be Bean on figure 26.

For thG curved divergent ramp, the drag for most usable config-urations should be quite lcr.r for the high-epeed and climb flight range. Assuming a wing-iU'8a-to-duct-entrsnce-area ratio of 150. a typical. CD due to a subl!llerged duc'!; in the high-speed attitude would be approx:tms.tely from 0.0003 to 0.0006. It should be remembered that the effect of the duct wake along the fuselage aft of the entrance is not included.

Deflectors

Deflectors, or ridgea along the divergent contour of the entrance, have been shown to increase the ram recovery when used with certain inlet configurations and conditions. '!his series of tests was performed to find the effect of deflector size. and to evaluate the use of deflectors for various inlet configurations. 'l'he criteria used for evaJ.uation were the same as those for '!;he principal investigation.

OO~

• lIACA II( Ifo. A,7I30 15

It vas found that increasing the deflector l~ f~ 25 to 50 percent oZ the :t'eJIIp length cauaed the :.cst pronounced increases :in pressure :reCOTOr;}' (fig. 27(a}). except for the 0.25-1nch-high

liAOA l'H lio. A7I30

derlector~ are not equally beneficial for all ramps. The inc~nt of :t'I!lll recovery due to deflectors increased vith increasing divergence. With nondivergent (pmUlel) valls the ilnprovement'llas negl1g1ble.

The results of tests to find the effect of deflectore on ramp angle are shown in figure 29(b). When these data are cOll!:pued with those for s1ln1lar configuratiOllS vithout deflectors (fig. 12) it can be seen that deflectors a.re beneficial. fI'Olll the standpoint of l'!UII recovery. tor all installa\tions. A mors comprehensive comparison ot tha thl."ae wid ratios t!!steLt can be obtained frOll! the cross plots of these data. given in figure 30. Here is shown the preSSUl'8 recovery as a function.of the ramp-length te~ previously derived.

Pressure recovery at the duct entrance is given in tigure 31 for several deflector-5ntrance configurations. The trends shown by these data are in good agreement vi tIl the ~ais alre~ discussed.

Deflectors apparently increase the pressure reco~ery by assisil-ins the air flmrine; outside the ramp to follOW the diverging contour of' the side valls. This prevents much. of the CroSB flaw of air OTor the top edge of' the ramp valls and also helps ·to divert lIOre of' the boundar,y layer around the entrance. With regard to the selection of a deflector to glve best recovery, it should be noted that results of other investigations (ref'erenco 2) clearly indicated that the require-ments for deflectors are dependent upon the location of tho entr.ance. It'llas found that when the entrance was ple!.ced in a region of' thin boundary layer, increasing the defloctor length f'rolil 50- to 100-percent ramp length caused a definite d!mroose of' preooure recoTery. It i9 probable that deflectors which extend the full longth of the ramll should be used only for thick boundary-'~r conditions.

Althoush the use of def'lectors results in h1glter prelilsure recovery. it 'lIae found that their effect was sOlll!mhat deteriorating to drag characteristics of the entrance. Figure 32 giTes the drag for several inlet configurations vith deflectors. Ca.~ theBe data vith drag for s1lll1lar configurations vithout deflectol:'lll (fig. 25) shows that deflectors increv.sed tho drag for all confi@U"fl.tions tested when tho air enters thl!l inlet at a velOCity ratio abOTe 0.6. This cOlllparison also indicates the deflectors caused tho largest drag for shallow entrances (v/d = 4.0 ana 6.0) and steep l'I!Iillll angles where the gain in pressura rsco-e-ery vas the greatest. All woul.d be expected. figure 32(c) also shows the.t increasing the deflector size. both length EUld heigltt. increased the drag.

The preasura distribution over the ramp when deflectors are used is given in figure 33. COlIIpl.rison of these data with figure 23 indicates that deflectors cause s~ addition to the incremen~ velocities over the ~p. The critical-speed characteristics of the lip for the curved diverging ramp. with and without deflectors,

..... CONFIDi:.NfIAL .-- .-

•

mCA EM lfo. A 7:£30 17

are given in figure 34. ~is can~son Shows that detlecto~ increase the critical Mach n~er tor the flow OTer the outside surface at the center section of the entrance while decreasing thet MeR for this tlow near the edge of the entrance. A larger flow-ang!et Tariation acroos the entrance is therefore indicated lihen deflectors are used.

ro3SIBLE APEICATIOll.'S FOR NACA S'IlBMEOOED J:liLmS

It should not be llle.intainsd that the Elubl!lerged entrance is applicable as an inlet for all ducting installations. but it does have certain characteristics in addition to th080 presented which make it pe.rticular~ suited tor sp3citic ducting applications. The use of MeA Bu'bl1lerged inlets could, in SOIII$ cElses. result in greater aer~Cal cleamleee by effecting more favorable fuselage contour lines and perha;pa reduc:l.ns the fuselage' frontal area. ~e structural canplex1ty of the duct1ng sya"teln should be dilIIin1Shod and larger space proTided for internal components. ~1B type at duct should also reduce considerebl;r the ingestion of foreign material b;r in-ertia se~~tion.

A possible Jet-enslne installation utilizing MCA subl!lerge:!. ducts is ehown in figure 35. In this illustration the sUbl!Iergod-duct design 1s centered around a single Jet engine located in the fuselage a:t't of the pilot's enclosure. l'lacement at the twin entries ahead of the wina III1IW!1zed the influence ot the Wings pressure field and situated. the entry in a region of thin bouncl.ary layer (reference 2). A wid ratio of about 4 seemed advisable fram internal space liln1tations. and a ramp using curTed divergence together with a ramp angle between 50 or 70 was selected. ~is installation should give opt:llltum pressure recovery. low ov"r-all drag and an efficient internal-flow systen. since the necessity for sharp bends and rapid ex:pansions have been elim:ina.ted. Reference 2 discusses a duct-flow instability that could occur With this type of installation.

For airplanes employing two Jet engines the necessity of using Wing nacelles could often be elim:ina.ted by housing the engines Side by side in the fusolage. ~e HACA submerged inlet appears to be very adaptable to such an installation. '!he use of single ducts leading to each jet engine would be similar in desia;n and location to that shown in the previous illustration. With a single duct leadina to one Jet enginEt. the flow instability prenoualy mentioned could not occur. '!hI!! ehort internal ductina of such an inata;Uation should result in minimum lossee, especially for engines with exie.l-type compressors.

Certain types of missiles. which are ])OI'sred by Jet enginas in

C9J&~

18 liACA EM No. A'iI30

the f'uselage and haYe no pt'OT1aion for landing gear~ are ideally adaptable tor an XACA au'blllerged-duct system. ~e single inlet could be placed. on the underside of the fUlleJ.age and the :l.natallation would have the design and aerodynamic adTantage :mentioned :pl'OVi.:lUSly.

Other applications could include same ducting systems :l.nvolving cooling and carburetor air. If' this type of entrance oould be sub-stituted for the protruding scoop-t;ype of inlet, the aerodynlllllic neatnElss of the a:lrcrart would be greatly enhanced.

From investigations tIl.'t'.t have been made of the configuration changes and pa1'alII9tere afi'ecting the deB1gn of NACA sublllElrged-duct installations it Was concluded that:

1. ~e boundar.1 layer at the location of the submerged entrance will influence the ram recoTery. Due to the relatively thick tuzmel boUll!l.ary layer into which the entrance vas placed, it is believed that the pressure recoTeries ,pr')Bented in this report are 10W'er than could be expected. for moat airplane installations but that the com-pu'ison between configurations is 'Y8lid.

2. Significant sains 1n pressure recovery for a vide range of coDf'igurations resulted. freat the UIIe ot the curved divergent rem:p. 1'h1s is es;pac'.a1ly true in the 10"1f inlet-veloci ty-mtio ranse, :;; =: 0.9, vhere hish pressure recoTery is lIIOst necessary.

3. ':rho effect of v:!.dth-to-depth mtio VM greatest tor the nondivergent (p!Irallol) =p valle. ~e best recoTery for this configumtion ocoUl"%'Od for a v/d ratio. 1 (square) entrance. As the ~~all divergence increaees vld reti0 has lOSR effect, 8lk1 the BqUlU"O Wt..7 is inferior to moat rectaDgular entries. With curved diTergence the ~ recoTery inc~nt due to change in vld ratio i8 about hal:f that nth ~lel valls.

4. RelIIp 8ll81e or, in Bam cnses, ramp length, had an ouw+and-:tng efi'ect an rall1 recOTery. ~e detr1ll1ental eff'ect of increasing =p angle beQ8lIlO sreeter as the diTergenoe VM increased.

5. In genoml,it ".ppeare that an inlet v:!.th curYed divergence. ". 50 or ~ ramp 8IJSl.e, and e. wId ratio or f'X'OllI 3and 5 o!f'ere opt:lJluJl characterist1cs.

6. Good. cr1t1cal-speed characteristics can be obta1ned. v:!.th proper lip design. ~el'e 1e e. spanviae change in angle ot ".ttack of the lip when a d1versinB mJIll i8 UIIod, and it !eJ' be neceasar,r to

C01!]'+~lAL

•

NAOA :ElM No. A 7I30

tll':tst the lip, de;pend:tns on the pJ;'eSSUl'e fiold into which the entrance is ][aced.

19

7. Fo!' :most desisn conditioll8 the drag 'WBJJ found to be emall. ROIi'ever, in the selection of an ollt:lJlnun configuration, the drag and = recoTery Mould be weighed. In thie respect, the use of deflectore may not always prove advantageous.

ALes Aeronautical Laboratory. National Advisory Committee for AeroDautics,

Moffett Field, Calif.

APE!:!lDIX A

MEmOD OF OBTADiIlD DUCT LOOSES AT mE ElmlAliCE

AlID AFT OF TIm DLFOB'tJSER SECTION

~, as in ths most general case, the straam fil.aments for a steady flaw a:rt/ not Ill!Isumed to have the llaIiB nOli' energy, then the total pressure for a given weight of fluid ~s:tns a given section is (reference 5)

CAl)

Usually, it is not necessary .to a;pply thil! exact method, but it DI!3 be requisite if the total pressure distribution at the :measur1Dg station has local regioIll!- of high loss. Such WaB th!'l cllse at the submerged--duct entrance for inlet Telocity ratios between 0 and 0.8. In cOlllllUt:tns the losses for this range, equation (1) wes modified to reduce the ctmptttational yon:

(A2)

where

20 liAOA liM No. A 7I30

h locel total head

p local. density

a local area

V local velocity

1 number of equal areas (equals number of tubes)

assuming

A = a xl

Then

H=f •••

For this application subscripts 1., 2, frio ... , denote local areas considered.

(A3)

~e difference between tho losses cos]Uted in the preceding manner and those ollta1ned trOll an 1ntergrating *UlOlll8ter yere found to be negligible at the entrance for the reMinder of the inlet-velocity-ratio range. V1./Vo·s frail 0.8 to 1.4. Such'11"a8 the cas., also for the entire inlet-olelocity-mtio range at the measuring station after diffueio~.

NACA EM No. A 7I30 ~EmAL 21 APEllHDII J3

METHOD OJ' OB!l'AllIIlG DBAG OJ' THE SUBMEmED EN'nlAltCES

If' the 1Il000000tuIIl change betwoen two atatiOJlll alalg a .trallll1 tubo is lII!Iaaured. the reaulting drag foree lIIa7 be coaputed:

D .. f {U - u) dill or

D .. p f u(Uo - u) dA where one station is :In the free streBll.

Ass1l'11l1n8 the dene1tiea at Uo I!.lld. u are equal,

(J31)

(J32)

(B3)

!few. aSlIUlling that tree-stream static pressure ex1.te :In the Yake (p '" Po)

Then

or

2 JJ tf1.f. dydx + - - dydx A qo (B5)

22 OOllFI~ RAeA !iN No. A7I30

Exxend1ng the first ~ of this eqtlation in a binomial expansion aI!d ccabin1ng with the remainder giTes

2

°IlD "i ff ': d:sdx - irK ff ( 'f) ~dx. • • (:a6)

It vas tound thl!.t there Yere su1':l'1c1ent tubes in the measuring rake

so that a value at ~ obta1~, 'nth the aid of an integrating qo

manOll!lter and iSubst1tut&d 1n place 01' the integrals in equation (:a6) gaTe Ter.1 eatietactor,r correlat1onvlth the poin~1-po1nt lntegration at equatlon (:a4).

To indicate hCllf the 8ubll!Orged-duct-dr.cg deterlllination vas made, it III1ght be best to consider a cOllJ)a1'ieoo between the drag of a nose inlet ant! of a subJlClrged inlet'l; as detel'lll:!.nad by ~ntum surveys. ~s oom~lBon ahould inolude the alI' flow thro~ the entrance to OOl'l'l5opond1ng stations at the .1et-engine cca:p1;'8ssor. What happens after this ~ection i8 a tunctlon ot the 3~t-eng1ne characteristics and does no't enter this diecussion. To a:1lllulate the :p1;'eced1ng oondition. oonsider that the air atte~ entering ths duct is relllOTsd at right angles to the air stream eo that there i8 no IIOIIIOntull of the exit air in the drag direction. Then

Loss in 1IOIIIOn-tUll of ths

Drag ot inlet .. entering air at the duct entrance

, For the nose inlet

D = o +

For the submerged inlet

MOIIIIntlUl ot + entering air +

(I'm drag)

L08S in 1!I00000ntUlll bDhind the duct

(:p1;'ofUe drag)

D .. J ment(Vo- Vent) dAent + J ment Vent dAenfft J ~t(Vo- Vatt)dAatt where iD1 is the maaa flClVing thro~ each unit area.

OONIfr

NACA liM No. A7I30 CONF~mu. 23

111ually, f'or the nose-tyllO :!:nlet, tho :tIIalIentUll1 of the entering air is taken into account as xart of' the internal drag and subtracted out. To lII8ke a fair cOlllI&'isCll between tho nose and sublll.orged inlets, for a given quantity of' flow, the same r«tIl drag should bo accounted f'or in each case. HoweTer, fol.· this oond:1tionl the :t'tIll1 drag of the aub~ed entrance i8 leaa than that f'or the nose inlet since air i9 inducted which has already received a 108S of' momentUlll, this losa boiDS equal to the second tem of the preTious equation. It' it i8 assUlI!ed that the :tIIalIentUII 01' the entering air is (llIentV 0) for both ill8taliatioll8 and i8 su'btl'l:!.cted f'rom each caoe, the drag becanes:

For the nose inlet

~ the submerged inlet

D = J lI'aft(Vo-Va:rt) dAa:rt In an actual duct application, tho ait' now OTer the body with the duct entrance removed JIlU8t bit considered, so that another term is necessary. ~e final f'orm of: the equation used to evaluate the drag then becomes:

24 KAOA l'H Xo. A 7I30

1. l!'r1ck~ Charles W •• Dl\.v1s, Wallace l!' o. Be"" .. " ~ LaUl.'OB M •.• and MO!laman~ x.et A.: .An Expel'blental Invest1gatlon of KACA Subwtrged~ct 1:ntrances. l!'.ACA ACE lfo. 5120, 1945.

2. MOBsmen, Emmet A., and Ge.Ult~ Donald E.: DeTelopaent of KACA SubJr.&rged li1J.eta and a CaI1puoison wlth Lead1~dBe Inleta tor a. l/4-SCalS Model of a. Flghter Alrplane. KACA Cm! Xo. A7A3l, 1947.

3. von~, Th.: CCCIl:pl'eBslbll1ty Efi'ecta ln Aero~CB. Jour. Aero. Scl., Tol. 8, no. 9. July 1941, pp. 337-356.

4. Lees, Lester: A DlscUllslon of tb.e Appllcatlon of the PlUdtl-Glauert Method to Subsonic Ccm:pl'ess1ble Flaw over a. Slende!:' llo~ of Revolutlon. ~>li.aA TN No. 1127, 1946.

5. Rouse, Hunter: Fluid Mech8n:Lcs tor HydzaUl10 Engineers. McGral1-R1U, 1938, pp. 47-54.

•

•

'~,

.,;IC·

5' f J ';.-;

~ ~ S' ~i

...,

TABLE J:

Index: of tho Su'IlIMrged-Duc~tl';J IIod1tlcatioI13

Eamp floor Bo1llldar;y vld Deflectors RalIIp plan tom Bamp 8Jl8l e Bhape thicmesl!

Parallel valJ.8 E1mp Straight divergence !io. 2 4, 6 .,0 Straight lratural lI'ono plan 1'om Straight divergence No. 3

Curved divergence

. ParallelvallB

wid I Straight divergence lIo. 2 l~ 2, 3. 70 Stra:lght lratural ?lone Straight divergence No. 3 4, 5~ 6 Curved divergenco

Parallel 'Walls a50, 70, Ramp angle Straight divergence No. 2 2. 4, 6 t. 11.5°, Stra1ght lratul'tlJ. "one Curved divergence 10;0 llamp floor. Parallel walls 4 c5° i' 9° Curved lratural. :rem. Bhape Curved divergence ~ 0' ~ ll.5 Boundary Curved divergence 2, 4, 6 ~ S'Gra1;;ht I !.I.'h1cklMd :rOM thickness

Parallel valls 5°, .,0, 9° 1 Deflectomd Straiglit divergence Xo. 2 2,4. 6

11.5°. 15° Strrt1~t I &-urved diTergence 1

a. ~ 1dth wid", 4 lUld 6. b. Only 1dth .,jIll = 2. c. Angle dcfmad by Co stmght 11ne connectillg beginn1Dg and end of' z:ap. d. See table II for cClllbimttions tested.

Height • 1/4 tn.. lratural 1/2 m •• 3/4 :In.,l m. ~ .. 25%,50%. /15%. 200%

N~TIOHAL AtlVJ5:0RY coIu< I TTEE rot WOIIl.UT1C5

~ :z>

!i! i5= •

~ ~

~

Heisht Lensth 1/4 inch

wId 4 25%

Ramp angle T' wid 4

50% Ramp ansle T'

wid 4 15%

1° Raap angle

wid 2, 4, 6

100% Ramp angle 1°

1/2 inch

----4

1°

4

1°

4

T'

NAOA m No. A7I30

3/4 inch 1 inch I. ,--,

, , I

4 --1° --4 4

T' 'f 4 4

T' T'

2, 4, 6 4

5°. T'.9°, T' 11.5°. 15°

NATIONAL ADVISORY COHHlnEE FOR AERONAUTICS

... _-_ .•. _--------------

NAOA m 10. A 7130

Modifioation

Bamp plan form

wId

Bamp anglo

Bamp floor shape

Boundary-layer thickness

Deflectors

TABI\E III

FIGtmE GUIDE TO RESULTS

Pressure ?.z:oessure Drag recoTo17 distribution

FiSS. 10. 18 F~.gs. 21, 23 FiSS. 25. 26

FiSS. ll. 18 ll'igs. 22. 23 FiSS. 25. 26

FiSS. 12. 14.

13. 18

Figs. 21. 23 Figs. 25. 26

Fig. 15 Fig. 24 lione

Fig. 17 lione None

Figs. 27. 28. Figs. 33. 34 Fig. 32 29. 30. 31

NATIONAL ADVISORY COMMITT£E rOi AERONAUTICS

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a U CJ/STRNaE FROM REFERENCE LINE TO R~MP Q -6.54 % L. STAr/ON- (PDINr AT WHICH DUCT ENTFU1NCE FIRER 1$ MEfl~uR£,DI

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STA-~L Y-l'.S I

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HATIONAl. ADVISORY COUUITTEE fOR AEr.:c+lAUTICS

FIGURE: S. - THE CURVED RIlMP FLOOR TESTED IN THIS INVESTlGI'ITION OF THE: SUBMERGED DUCr

ENTRI'INCES. CON'JOi'filN.TW. &'

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HA71OH.lLAQVlSOftY COMM(TTE£ FQft AEPlQHAUTICS

Fig. 6

HGURE: 6. - THE: 1JE:FZ.E:CTOFIS TESTE:D IN THIS INVESTI&9T1ON OF THE: SUBM"F!Gm

DUCT "NTR/INC£' •

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•

~- / • / /;

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HATI~AL ADVISCfI,Y CDWWlTTU FOft AEftDHAUTlCS

F,GURF: 7. - THe LIP PROFILF: USED IN THIS INVESTIGIITION OF THE SUBM€RGED £NTRI'INC£

CONFiDEN i IAL

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NACA RM No. A7130

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FiGURE e. - THE: NIITlJRFlL BOUNtMRY Ll9YER OF THE WIND nwNEL WIILL MeflSuRED ~r THE l..OCRTION OF THE DUCT ENTRnNCE.

-, r I I ~I

--I - -I/o' ['!l:t;}tOO -'" I ~ ~. . .. 1_

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Fig. 8,9

""TKlHAL ADVISORY C

Fla. 10 NACA RM No. A7130

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INI.ET VEI.OCITV RATIO, VyV.

INI.ET VE1.0C/7V RATIO, VVV. NATIONAl. ADVISORY

COMMITTEE FD!I AERONAUTICS

F'GIJRElo.- VI9R/~TION OF RAM RECOvERY RRTIO, MEASUReD I9FTER THE DIFFUSER SEt:.TIONJ WITH INl.ET VELOCITY R19TIO FOR FOUR Pi..t'lN FORMS OF THE RRMP. 7- RAMP ANGLE.

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