1、-V- copy 25 . ,RM E51F26au.t:u.RESEARCH MEMORANDUM- EINVESTiGAN AT MACH NUMBER 1.91 OF SIDE AND BASE PRESSUREJDISTRIBUTIONS OVER CONICAL BOAT TAILS WITHOUT AND WITHJET FLOW ISSUING FROM BASEBy Edgar M. Cortright, Jr.,and Albert H. SchroederLewis Flight Propulsion LaboratoryCleveland, OhioNATIONAL AD
2、VISORY COMMITTEEFOR AERONAUTICSWASHINGTONSeptember 12, 1951 W-Provided by IHS Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-1a71NACA RM E51J?26NltlXONALADVISORY cowm FORRESEARCH MEMORANDUM.INVESTIGATION AT MACH NUMBER 1.91 OF SIDE AND BASE PRE%URE - *.DISI!RIBUTI
3、ONSOVER CONICAL BOATTAXLS WITHOUT AND WITH : i a71J731!FLOW ISSUING FROM BASE .,BY Edgar M. Cortright, Jr.; and Albert H. Schroeder hbwMMARY -the experimental pressure distributions at zero angle Of attack fe .parallel to, but slightly less negative than the predicted values. “-”Linearized theory ga
4、ve somewhat poorer agreement. A s-qirical:,.theory is presented which enables the prediction of a base pressure coefficient referenced to conditions just upstream of the base for anarbitrarily boattailed body of revolution in a supersonic stream at . .“zero angle of attack, provided the flow is unse
5、parated upstream of the .base. ;“,The effect of the et on the external aerodynamics of the boattqils:,was greatly Uependent on the boattail geometry. When the boattail 1,etiended to a sharp edge at the nozzle exit (completelyboattailed), the,-.Gjet increased the pressures ahead of the base. As much-
6、as a 25-percent :decrease in the boattail pressure drag resulted at a jet pressure ratio of 15. At low ales of attack, the pressure increases were asymmetrical . ;on the boattail, which tended to shift the body center of pressure . “Tforeward. when an annular base was present, the jet affected pr-il
7、y the base pressure. me net effect of the jet for a cylindrical afterbody -was approximately todouble the annular base drag at a jet pressure ratio .of 4; the drag was unaffected at a jet pressure ratio of 15. Irithe caseWUWMIENT1:iwdla ,.Provided by IHSNot for ResaleNo reproduction or networking pe
8、rmitted without license from IHS-,-,-2 NACA RM E5U?26of incompletelyboattailed bodies with annular base, total boattail(side plus annular base) pressure drag increases of 25 to 40 percentwere encountered at jet pressure ratios of approximately 3; dragdecreases of 35 to 60 percent were obtained at a
9、jet pressure ratio of 15Small smounts of Jet air (basebleed) correspondingto values ofjet pressure ratio of 1 or less decreased the base pressure drag. Inthe case of the cylindrical afterbody, increases of approximately30 percent in base pressure coefficientwere obtained at zero ahgle ofattack. Incr
10、eases of approximately 60 percent-in base pressure coeffi-cient were obtained for the boattailed bodies.INTRODUCTIONSupersonicmissile and aircraft designs frequently utilize axiallysymmetricbodies or nacelles in which a propulsive jet dischargesfromthe base. In many cases,.the jet exit area is less
11、than the maximumbody cross-sectionalarea and scme degree of boattailing is required.In some configurationsthe pressure drag of the boattail and annularbase, if present, may far exceed the forebody pressure drag.The choice of boattail geometry is complicatedby the fact that notheoretical method for c
12、alculation of the external pressure distributionsat supersonicvelocities is currently available which considerstheinterference effects of an exiting jet. DesTite this fact relativelylittle experimentalwork has been done to evaluate the phenomena. Pre-liminary studies of the jet effects on the extern
13、al flow over the A-4missile are presented in reference 1. A more recent aerodynamicinvestigation (reference2) includes some effects of an annular Jetexhausting from the base of a psrabolic bo of revolution at Machnumber 1.92. Convergent-divergentnozzles with various exit velocitiesand pressure ratio
14、s were utilized and the body was fully boattailed toa sharp edge at the nozzle exit.In the present investigationthe pressure distributions over alimited but systematic series of conicallyboattailedbodies ofrevolution were obtained without and with a jet dischargingfrom thecenter of the base. The jet
15、 exit nozzlewas of the simple convergenttype operating at various degrees of overpressure. The pressure dis-tributions=with no jet are comparedwith linearizedtheory and themethod of characteristics. A semi-empiricaltheory is developedwhichenables the prediction of a base pressure coefficientreferenc
16、ed toconditions just upstream of the base for an arbitrarilyboattailed bodyof revolution in a supersonic stream of zero angle of attack, providedthe flow is unseparated upstream of the base. The effects of the jeton both the boat%ail side and annulsr base pressure distributionsareexperimentallydeter
17、mined. Integratedb9attail pressure drag coeffi-cients are presented and tieboattail geometry.a71a.-. .compared from the standpoint of-optim.mProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA FM E51J?26a71SYM60LS%The followlng symbols are used in t
18、his rert:.CPcp)b%?3c!p,a%DmDnMjMljPPPaquuvVx%2drag coefficient, drsg/ P-P()pressure coefficient,-%base pressure coefficient referenced to condition justPb-Pupstream of base, qlincrment of pressure coefficient due to set air flowincrement of pressure coefficientdue to angle of attackbase diameter of
19、body, (in.)msximum body diameter; (in.)nozzle exit diameter, (in.)Mach number $ifyjtheoretical jet Mach nuniber,Mj =local Mach number measured in jet mixing regiontotal pressure of jet airpressure measuredly a pitot tube in jet wakestatic Tressureambient pressure for ha-jet spreading testsdynsmic pr
20、essurevelocity of air at outerlocal velocity of air infree-steam velocityaxial perturbationedge of boundaryboundsry layervelocity.layer.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4 c NACA RM E51J?26x axial distance from model tip, body diameters
21、Y normal distance from model surfacea71a angle of”attack, (deg)b thickness of boundsry layer at u . 0.99 c angle between boattail surface and body axis, (deg)g.CDe cylindrical coordinatemeasured in plane normal to bodySxis, e=o on windward side of model+ free streamlinebody axisSubscripts:b base of
22、modelangle at base measured with respect to the-.-0. free-stream station1 station on model just upstream o$_baseAPPARATUS AND PROCEDURESupport SystemIn an investigationof jet effects on the extern aerommics ofbod3.es,one of the foremost eerimental difficulties lies in introduc-ing relatively large q
23、uantities of high pressure air into the modelwithout influencing the external flow in the region of measurement.A hollow side strut supportwas utilized in reference 1. In order toavoid strut interference of the type resulting from such a support,reference 2 utilized a hollow sting and thus required
24、an annuler exitnozzle. In”the present investigationan adaptation of a half-bodysupport systemwas employed. A sketch of the model attached to thesupport is shown in figure 1 and a photograph of the model assemblyin the tunnel is shown in figure 2. The model configurationswerebodies of revolution comp
25、osed of a single nose s,ectionwith inter-changeablebases that provided boattail variation. High pressureair was throttled and then ducted into the model”through a Qollowstinga71 In the model the air was turned (fig. 1) and passed through a-straightening screenbefore discharge from a convergentnozzle
26、. Supportinterferencephenomena we Wnitedby the presence of a.splitterplateto those associated with plate boundary layer and small disturbances.a-.from the”plate leading e these discrepanciesbetweenthe half jet and the full jet are believed to have had no appreciableeffect on the results of these exp
27、eriments.Models and InstrumentationThe assembled body of revolution had a length of 18 inches and afineness ratio of 12. The first half of the body was contoured accord-ing to equation (14) of reference 1, while the remainder was cylindricalexcept as modified by the presence of conical boattails. Pa
28、rticular%oattail geometries included in the investigation,along with the pres-sure instrumentation,are shown in figure 6. The parameters variedincluded boattail angle C, Oo, 5.63,7.03,and 9.330; and base tobody diameter ratio / of 0.506 (completelyboattailed), 0.704(incompletel.yboattailed), andl.O
29、(cylindricalafterbody). l?henozzle- exit to body diameter ratio was constant at 0.5. The nozzle profilewas contoured for a constantMach number gradient based on one-dimensionalconsiderateions.Jet total pressures were normally determined at the nozzle entrance(fig. 1) by apitot tube reke which was co
30、nnectedto a mercury manometerboard. Low jet pressures and all static pressures were measured with adibutylphthalatemanometer board (referened to vacuum), which was readProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-6 nqmEm!L. NACA RM E51J?26.visuall
31、y to _ hence, no changeswere made in the original extrapolations. They do indicate, however,possible inaccuraciesin the curves as presented in that the reductionin boattail pressure drag due to the jet effect is slightlyunder-estimated for jet pressuxe ratios below 15. Th point will be dis- .=cussed
32、 in a later section in which the integratedpressure drags sxeconsidered.The flow mechanism whereby the jet interferencetakes place isillustratedby schllerenphotographs and a qualitativesketch of theflow over the CS 9.33 fully boattailed configuration (fig. 14). As .the jet pressure ratio is increase
33、d, the exiting set eands and deflectsthe external flow with a resulting shock wave and pressure rise. This tincreasedpressure propagates upstream through the subsonicportion ofthe boundary layer on the bodyj an increased rate of boundary layergrowth and thus compressiontoward the resr of the body re
34、sult withpossibly a regiou of separatedflow ahead of the base. Schlierenphotographs of the three fully boattailed configurationsoperating at ajet pressure ratio,of 15 are shown in figure 15 to.inticate thesimilarityof flow fields. Ih figure 16 the 7.03boattail is shownwith artificially induced bound
35、ary-layer transition at the tip of themodel. The thickenedboundary layer was no longer distinct in thiscondition and.the trailing shock wave with the jet in operation appearedto stand farther upstream than with the thinner boundary layer. .-Inasmuch as the interferenceproblem is largely one of shock
36、 “boundary-layer interaction,the quantitativeresults of figures 11 to 13would be expected to be sensitiveto the boundary-layer thickness andprofile at the base and hence to Reynolds mimber and surface condition a71of the body. The investigationswith artificialboundary-layer transitionto turbulence a
37、t the model tip were qade to determine this sensitivity.In general, the data (figs. U and 13) indicated an appreciably increased “Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-5 TfACARM E51J?26.9CQNNNpressure rise at the base of the body due to the
38、 jet but no markedkextension of the interference effect farther upstream as a result ofthickening the boundary layer. As an appsrent result of this sensitivitycombined with probable slight variations of the body boundsry layerduring the course of the investigation, some difficulty with reproduc-ibil
39、ity of pressure distributionswith jet was experienced. It can beconcluded that the jet interference the body centerof pressure thus tended to shift forward. At e = 50 where theboundary layer had thinned considerably,the jet interaction effect wasnegligible except for the 9.33 boattail. At an angle o
40、f attack of 60we jet interactionwas fairly uniform =ound the body for most pressureratios.The data for the c = 5.63 boattail at an angle of attack of 6appear unusual inasmuch as little jet effect is indicated. Actuallythis indicatesthat the region affectedly the pressure feedback has*ed dcmstieam of
41、 the last orifice. With forced boundary-layertransition, a set effect similar to the a= 30 conditionwas observed.Also when the pressure orifice was added just u+pstreemof the base ate = 90, values of CP3 of 0.14 were indicated at a jet pressureratio of 15.Boundary-LayerMeasurements at Angle of Attac
42、kIn order to aid in visualizing the effect of the set at angle ofattaak, figure 23 presents pitot pressure contours at the plane of thebase for the boatteil of cm 7.03 and /Dm= 0.506. Pitot contoursat zero angle of attack are included for reference (figs. 23(a) and23(b) and indicate only a slightly
43、nonuniform jet effect around thebody. In figure 23(c) the thickening of the boundary layer on the lee-ward surface of the boattatl at 60 angle of attack with no jet isevident. At a jet pressure ratio of 10 (fig. 23(d)the boundary layahas thickened about the entire body although the degree of uniform
44、ityis difficult to determine from these data. cBase Pressure MeasurementsOnly tie pressures acting over the sides of the various boattailconfigurations“havethus far been considered. Of equal interest is theproblem of base pressures. The base pressure data are most convenientlydiscussed in two parts:
45、 the first part is concernedwith base pressureswith no jet flow, and the second part considersthe pressures acting onthe annular bases with jet flow.No jet. - F1OW fields have been hypothesizedwhi lead to the .fairly successful prediction f base pressure characteristicsforhodles of revolution with c
46、ylindricaltiterbodies in a supersonicstream. (See references 7 to 9.) I addition, considerableexperimental -base pressure data have been collectedfor such bodies (references7, lo,Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA RMand 11,able inE5
47、U?26 13for exsmple). No theoretical treatment and few data s.reavail-the literature, however, which consider the effect of anarbitrary boattail geometry on base pressure.A semi-agpiricalthedy is presented herein to predict a basepressure Codficbnt Cp,b referenced to conditions just upstresm ofthe ba
48、se for an arbitrarily boattailed body of revolution at zero angleof attack in a,supersonic stream, provided the flow is unseparated tieadof the base. The essential assuion of the method is that the freestreamline angle $ (measuredwith respect to the body axis) at thebase of an arbitrary body of revolution is a function only of the localstream Mach number ahead of the base Ml and of the boundsry-layerthickness and profile ahead of the base. (Approximatelythe same resultscan be obtained by assuming dependence of on rather than Ml.This assumption yields the correct result that base pressure i
