1、215.d. .copyRM L56C21E_ r-l-1RESEARCH MEMORANDUMJET EFFECTS ON BASE AND AFTERBODY PRESSURES OF ACYUNDRICAL AF”TERBODY AT TRANSONIC SPEEDSBy James M. Cubbage, Jr.kngley Aeronautical IdxmatoryLangley Field, Va.HAD()TECHN?CF*L L:BnARYAFL 2811NATIONAL ADVISORY COMMITTEEFOR AERONAUTICSWASHINGTONhky 23, 1
2、9561I.t.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-.,- .NACA FM L56c2J-TECHLIBRARYKAFB,NMI;lllllll!llllllllllllllllllllllln144i5aNATIONAL A.DVISC)RYCOMMITTEETOR AERONAUTICSRESEARCH MEMORANDUMJET EFFECTS ON RASE AN13AFTEIW)IW PRESSURES OF ACYLIND
3、RICALAYTERBODY AT IRUSOI?IC SHIllSBy James M. Cubbage, Jr.An investigationhas beenhers to study the effects of acylindrical afterbdy upon theand supersonic conical nozzlesconducted at transonic stream Mach nun.cold jet issuing from the base of aafterbcilyand base pressures. Both sonicwere studied in
4、 thi6 investigationwithjet-to-base diameter ratios rsmging from 0.25to 0.85. Free-stream Machnumbers ranged from 0.6 to 1.25 md the jet total-pressure ratio fromthe no-jet flow condition to approximately 8.o. The effect onlasepressure of introducing small quantities of air into the region adjacentto
5、 the base annulus was also investigated.The results show that for the confirmation tested the effect ofthe issuing jet on base pressure was, in general, detrimental at jettotal-pressureratios less than about 5.0over the range of Mach nunbersinvestigated. Very low base pressures were obtained at soni
6、c free-stream velocities with a jet total-pressme ratio of about 2 to 3. Theeffect on base pressure of varying the jet-to-baee diameter ratio waspronounced. Base bleed waflbeneficial tireducing the base drag undercertain conditions and had little or n“oeffect under other conditions.INTRODUCTIONThe r
7、ange capabilities of supersonic aircraft may be substantiallyroved by cruising at the lower transonic speeds where less thrust isrequired. In order to realize maximan jet efficiency in this speedrange, the size of the jet nozzle must be reduced from that-requiredfor the msximm supersonic speed of th
8、e aircraft. If this requirementof vsriable nozzle mea is satisfiedwithout chemges in the afterbdycontour, then the area of the annulus between the afterbcdy smd nozzleexit must increase as the peed of the aircraft decreases. As a resultof the decrease in the static pressure over the enlarged base an
9、nulus,a bsse hag ofappreciable magnitude may be experienced.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2 NACAFM L56c21nAlthough a considerablevolume ofdata is available to show thevariations in magnitude of the base pressure as a function of noz
10、zle andafterbody contour, of nozzle dismeter relative to base diameter, and of .jet pressure ratio in the supersonicregion, relatively little has beendone at tronic speeds. A recent comprehensiveinvestigation of aseries of contoured afterbodies for a range of boattail angles and jet-to-base diameter
11、 ratios at tramsonicMach numbers up to 1.1 is reportedin reference 1. Reference 2 contains similar data at high subsonicspeeds. Data from other investigationsare availablebut for the mostpart are restricted to tests of specific configurationsin which thedetermination of base drag was a seconcbxy obj
12、ective.The investigationreported herein was conducted in the Langleyinternal aerodynamics laboratory to determine the effect of jet total-pressure ratio, jet-to-basediameter ratio,”and nozzle geometry on thebase and afterbody pressures of a cylindricalafterbody at transonicstream Mach numbers. The j
13、et-to-basediameter ratio was varied from0.25 to 0.75for the sonic nozzles and from O. to 0.85 for the super-sonic nozzles. Jet nozzle angles ranged frcm 0 to -25 for the conicalsonic nozzles and from 5 to 25 for the supersonic conically convergent- Adivergent nozzles. The supersonic nozzles had an a
14、rea expansion equiv-alent to a Mach number of 2.0. The effect on the base.pressure of intro-ducing small quantities of air into the dead airregion adjacent to the ,:Adbase annulus was also investigated.The -presentinvestigationcovered a Mach nwnber range from . 0.6to 1.25 with correspondingReynolds
15、numbers of 3.4 x 106 to 4.2 x 106 perfoota71 The jet total-pressureratio /Hj PW was varied from no jet flowtO Hj/Pm w 8. The jet stagnationtemperature for all tests reportedherein was approximately 70 F.S-xMEmSAb area of base annulus, (db2 - dJ2)*II 1 area of annular base bleed openingCp ressure coe
16、fficient, positive when diverging in the directionof flow from center line of nozzle7 ratio of specific heatsSubscripts:a afterbcdyb basec plenun chamber surrounding test sectionJ jeto stagnation conditionsm free streama-. ,.Provided by IHSNot for ResaleNo reproduction or networking permitted withou
17、t license from IHS-,-,-NACAm L56c21APPARATUSTunnelThe + -by L2.inch slottedtest section employed in this investi-gation is shown in the photograph of figure l(a) and in the drawing offigure l(b). Each of the top and bottom walls containedfour slots;the width of the slots was such that the open-to-cl
18、osedarea ratio ofthe slotted wall was 1/8. The individual slots were .pered in bothwidth and depth over the first 7 inches of their length; the widthincreased from O to 3/8 inch, while the depth decreased from 1 to1/8 inch. From x = 7 to the end of the slot, the slot cross sectionremained constant.T
19、he stream-tube expansionnecessary to accelerate the flow to super-sonic velocities was accompli-shedby removal of air through the slotsinto the interconnected chambers outside the slottedwalls. At low super-sonic velocities, this air was returned to the main stream at the down-stream end of the slot
20、ted section where the cross-sectionalarea of thepassage was approximately 16 percent lsrger than the geometric minimum.at the upstream end of the tunnel. Auxiliary suction was used to etiendthe Mach rnmnberrange of the tunnel from 1.18 tol.25 Wd to maintain a -.constsmtMach number in the test sectio
21、n as the jet total-pressurerati?was varied. Air for the tunnel main stresm was suppliedby two centrif-ugal blowers through a 40-inch4iameter supply duct. The maxinun t-nel stagnationpressure available for these tests was approximatelyl? atmospheres at a stagnationtemperature of lti” F.The model supp
22、ort consisted of a 2-inch-diametertube cantileveredfrom the tunnel entrance bell as shown in figures l(b) and 2. Theupstream support struts were hollow, the two lower struts containingallpressure leads wkcllethe top strut was used to duct blgh-pressureair tothe model support tube. The downstream str
23、uts were solid and of hexag-onal cross section. The Jet air was supplied from three l,OOO-cubic-foot tanks which were pressurized to approximately 100 pounds per squareinch. Pneumatically operated valves were used to maintain a constsmtpressure at the entrance of the jet nozzle.ModelsA total of 16 j
24、et nozzles were studied in this investigation.Drawings of these models end photographs of several mcdels are presentedas figure 3. The original four sonic-nozzlemodels had convergentangles 0 of 0, -5, -12) and -25 and a jet exit dismeter equal to65 percent of the base diemeter j,/db.= 0.65). I%e 0 a
25、nd -uoProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACiIRML56c21 5 nozzles were later mcdified to dj/ = 0.75. Limited data were also1taken for a 0 = -25 nozzle with djldb =0.25 and O.45. The initialthree supersonicnozzles had divergence singlesof
26、5, I-2,and 25 withdjdb =0.75. The diameter ratio for the 12 model was later increasedto 0.85. The convergenceangle and throat length as well.as the ratioof throat erea to jet exit area ( = 2.0) were identical for all ofthe supersonicmciielsinvestigated.Four base-bleed mdels (figs. 3(c) and 3(d) util
27、ized the jetsupply air as a source for the bleed flow. Reductions in the base-bleedflow rate at a particular jet pressure ratio were accomplishedby closingoff a nuniberof the bleed-flow throttling orifices. For the testsreported herein, data were teken with 16, 8, and 4 throttling orificesopen. The
28、exit srea for the bleed flow on the 0 nozzle was increasedby removing the thin flange at the end of the mmiel. A bsffle ring wasinstalled as shown in figure 3(c) to tbxottle the high-velocity flowissuing from the bleed-flow orifices. A boundary-layer smvey mcxiel,shewn in ace in the tunnel infigure
29、4, was used to estimate the thi.clmessof the boundary layer onthe support tube at a station inches upstream of the base of theafterbcdy. The two survey rakes were located on the vertical center lineof the tunnel and each was composed of five O.O-inch-diameter total-pressure tubes spaced 0.01, 0.025,
30、 0.04, 0.1, and 0.25 inch from thesurface of the mcdel eupport tube.InstrumentationThe stream stagnationpresswe smd temperature were measured in theupstream 40-inch-diameter supply duct while the test-section referencestatic pressure PC was measured in the tunnel plernznchsmber. Static-pressure orif
31、ices along the center line of one side wall were used toobtain tunnel Mach number distributions; for these tests, a metal platewith orifices spaced at l-inch intervals replaced one window.Along the mciielafterbody, static-pressureorifices wae installedon two meridians 180 apert; the tial locati,onof
32、 these orifices isshown in figure 3(a). Base pressure was measwed by a single orificelocated 0.055 inch from the outer edge of the base ,= shown in fig-ure 3(a). The O.O-inch-diameter total-pressureprobe shown in figure 4was used to obtain jet total-pressureprofiles across the vertical diam-.eter of
33、 the jet exit. The end of the probe passed within 1/64 inch ofthe base of the mcdel (except in the case of the boundary-layer surveymodel) and the pressure was continuouslyrecorded by two 2-variable-1 recording potentiometers.Provided by IHSNot for ResaleNo reproduction or networking permitted witho
34、ut license from IHS-,-,-6 -eoI?FIDmnw!Ii* NACAmf L56c21.All static pressures, with the exception of the two in the throatof the jet-flow metering venturi, were recorded photographicallyfrommultitube manometerbomds containingtetrabromoethane. The venturistatic pressures and the total pressure in the
35、entrance tube were irecorded visually from mercury-filledU-tube manometers at low pressmesand from Euurdon gages at the higher pressures. The tunnel stagnationpressure was read from a mercury-filledU-tube manometer.RESULTS MD DISCUSSIONTunnel Mach Number Distributions andWall InterferenceEffectsTime
36、-averagedMach number distributionsdetermined from the tunnelstagnationpressure Ho and static pressures along the center line ofone side wall of the tmel are presented in figure 5. The correspondingvalues of , as computed from the chamber static pressure pc and the .-tunnel stagnationpressure, are ho
37、wn on the left-hsmd side of the figure.The effect of the presece of the model and support tube on the Mach “number distributions is shown in figure 5(a) where distributions for theempty tunnel are comparedwith those obtainedwhen the model was in ace.Figure 5(II) compares distributionsfor the case of
38、 no jet flow with thosefor the case of a sonic nozzleoperating at a jet total-pressureratio ofabout 4.0. The expansion of the tunnel flow at the jet exit station atvalues of I hence, for the caseof no jet flow, some effect of wall-reflecteddisturbancemay be presentat the lower supersonic speeds. For
39、 the jet-on case, except when thereflected disturbsmce intersectsthe subsonic flow near the base betweenthe external and jet flow, no error would be expected since disturbancescould not be propagated upstream through the surrounding supersonicflow.The effect of the jet on the distributionscan be see
40、n in figure 5(b) as .a change in the distributionsdownstream of the jet exit station due tothe reduced expansion at the afterbodybase.w=Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA RM L56C21 a. !. 7At speeds less than sonic, the time-averaged
41、 ch number distribu-tions of figure 5 do not show any abrupt variations. This result wouldindicate that sny disturbance present is of a transient nature. Thegradual deviation of the distribution for lQ = 0.9 (fig. (a), isthought to be due in part to the boundsry layer on the mdel supporttube .md the
42、 increased sensitivity of the flow to small changes in sreanear sonic speeds smd to the acceleration of the flow as it turnstowsrds the center line of the tunnel to compensate for the increasedcross-sectionalsrea downstream of the model.Although the areas of probable interference effects are dat thi
43、s value, the base pressme coefficient reachesa minimum. From figure 13, it can be seen that the jet pressme ratiocorrespondingto minimw base pressure increases as the jet-to-base diam-eter ratio decreases. At = 0.9 (fig. 13(a) the mimimum value ofbase pressure decreases as 3/% ecreases d iCr=se” M1e
44、at . 1.1 (fig. 13(b) the minimum base pressure is nesrly independentof dj) and Hj/pm.Effect of base bleed.- In references 2, 6, and 7, a reduction inbase drag was obtained by intrmiucing small quantities of ah into the. region adjacent to the base snnulus. Similar tests were =de during thepresent in
45、vestigationwhere air directed from the primary jet flow aheadof the nozzle was intrduced into the base annulus through annulsrProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-12 NACA RM L56c21opening (fig. 3(c). The bleed mass-flow rate, therefore, in
46、creased asthe jet mass-flow rate increased. Calculationsbased won the base pres-sure and the pressure in the small chamber upstream of the base bleedopening of the basic bleed model indicatedthat the maximum bleed mass-flow rate obtained was of the order of 2 to 3 percent of the jet mass-flow rate.
47、Total-pressuresurveys across the base annulus showed thatthe bleed flow issuing from the small annular open-on the basic bleedmcdel with all throttling orifices open had considerablevelocity atJi% = 4. This conditionwas detrimentalto the base pressure in thatthe high.velocitybleed flow aided the jet
48、 flow in aspirating the base.By closing part of the throttling orifices,the mass-flow rate andvelocity of the bleed flow were reduced approximately 75 percent. Inorder to reduce further the velocity of the bleed flow without changingthe maximum bleed flow rate, the basic bleed model was modified toi
49、ncrease the exit area for the bleed flow from 0.06Ab to O.I how-ever, even with this drag reduction, the base pressure was still quitelow. In addition, the penalties incurred in obtainingthe bleed flowmay offset any drag reduction gained from increasedbase pressure. Dataobtained for the basic bleed model with e
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