1、RESEARCH MEMORANDUM JET EFFECTS ON THE DRAG OF CONICAL AFTERBODIES FOR MACH NUMBERS OF 0.6 TO 1.28 By James M. Cubbage, Jr. Langley Aeronautical Laboratory Langley Field, Va. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NklXONAI, ADVISORY COMMITTE
2、E FOR AERONAUTICS RESE2w.xMEMoRAmuM JEI EFFECTS ON TBB DRAG OF CONICAL AFTEKSODIES FOR MACH NUMBERS OF 0.6 To 1.28 By James M. Cubbage, Jr. S-Y - . ; An investigation has been conducted at Mach numbers from 0.6 to 1.28 to determine the drag characteristics of a series of conical sfter- bodies with a
3、 cold sonic jet issuing from the base. The models investi- gated had boattail sngles from 3O to 45 with ratios of the jet diameter to the base diameter of 0.65 and 0.73; values of the ratios of the base diameter to the msximum diameter were 0.55, 0.70, and 0.85. -jet total-pressure ratio rsnged from
4、 the no-jet-flow condition to approxi.- mately 8. The results show that the boattail angle for minimum afterbody drag at subsonic speeds was in the 5 2.50 and 5O at supersonic speeds. to 80 range and between approximately These values of boattail angle were not altered significantly over the range o
5、f jet pressure ratios investi- gated. The pressure ratio of the jet did, however, influence the level of the minimum drag coefficient. The afterbody drag coefficients of a 30 and 45 boattailed body were equal to or greater than that of a cylindrical afterbody for certain test conditions. In general,
6、 the afterbody drag coefficient increased as the ratio of the base diameter to the maxFmum diameter increased at both subsonic and supersonic speeds. INTRODUCTION Present-day jet-propelled aircraft capable of supersonic flight cruises at high subsonic speeds in order to achieve a significant oper- a
7、ting range. Since afterburner operation is not required for the cruise condition, the exit area of the nozzle must be reduced to maintain pro- pulsive efficiency. The reduction in nozzle exit area necessitates increased boattailing of the afterbody or a larger base annulus. These changes in the shap
8、e of the afterbody cm result in lower static pres- sures; thus, the drag of the afterbody increases and the range capabili- ties of the aircraft reduces. -L- - Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2 NASA RM L57B21 The investigation reporte
9、d herein is part of a study to determine the effects of a propulsive jet on the drag of the afterbody from which it issues through the speed range from subsonic to supersonic speeds. rl The initial part-of this study was concerned with jet effects on a cylindrical afterbody and is described in refer
10、ence 1. The work of reference 2 and the present investigation were conducted concurrently and the conical afterbody configurations of the former are geometrically similar to the configurations of this investigation. Studies by other researchers have been conducted at transonic speeds and some of the
11、se are reported in references 3 to 6. Reference 3 presents data on conical and contoured afterbodies obtained in a perforated tunnel in addition to results from a study of boundary-layer and tunnel-wall effects on the data. Reference 6 is one of several reported studies of jet effects on the afterbo
12、dy of rocket-launched free-flight models. The present investigation was conducted in the Langley internal aerodynamics laboratory over a Mach number range of 0.6 to 1.28 at corresponding Reynolds number of 3.b x lo6 to 4.8 x 10 6 per foot. The conical afterbodies investigated had boattail angles of
13、3O, 5.60, 8O, 16O, 3o”, and 45O with ratios of the jet diameter to the base diameter of 0.63 and 0.75. Values of the ratio of the base diameter to the maxi- mum diameter of these models were 0.55, 0.70, and 0.85. The jet total- pressure ratio was varied from no jet flow to approximately 8 and the st
14、agnation temperature of the issuing jet was approxtitely 70 F. A %B boattail drag coefficient, s 1 (rbrm2 _ Cp,B d(z) CD,b CD,a area base drag coefficient, -$,b % - Aj 4ll afterbody drag coefficient, cD,S f- +,b 8-l pressure coefficient, m g Ka2 . . . Provided by IHSNot for ResaleNo reproduction or
15、networking permitted without license from IHS-,-,-NACA RM L57B21 - d diameter v H total pressure M Mach number P static pressure U velocity of flow at distance y from model support tube and parallel to tunnel center line %I free-stream velocity r radius X distance along center line of model from jun
16、cture of sfter- body and model support tube Y perpenducular distance from model-support tube boundary-lsyer thickness boattail angle; angle between center line and a generatrix of model Y ratio of specific heats Subscripts: a sfterbody b base 3 m maximum j Jet B boattail co free stream x local 0 sta
17、gnation . Unless otherwise stated, “base diameter ratio“ and “jet diameter ratio“ will hereinsfter refer to the ratio of the base diameter to the - - Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4 NACARM 5721 maximum diameter and ratio of the jet
18、diameter to the-base diameter. In addition, “jet pressure ration will refer to the ratio of the jet total pressure to the stream static pressure. APPARA!rus AND ME-mom A drawing of the tunnel used in this investigation is presented as figure 1. This tunnel is the same facility employed in the invest
19、i- gation reported in reference 1 and is described in detail in that refer- ence. A minor modification at the rear of the test section (at the con- clusion of the tests of ref.- 1) increased the cross-sectional area of the test section at this point and, in turn, increased the maximum Mach number of
20、 the tunnel-by about-0.04. The stream stagnation temperature at the maximum Mach number was approximately 1800 F. The model support arrangement shown in figure 1 is also identical to the one described in reference- 1. The forward strut was used to duct high-pressure air to the model support tube and
21、 the two lower struts contained all pressure leads from the model. The jet air was supplied from three l,OOO-cubic-foot tanks which were pressurized to approximately 100 pounds per square inch. Pneumatically operated valves were used to maintain a constant pressure at the entrance of the jet nozzle.
22、 The temperature of the air supplied to the jet nozzle was approximately 70 F. A sketch of a typical model is presented in figure 2(a) and a photograph of ll of the 22 models tested is presented as figure 2(b). The boattail angle p was varied from 3O to 45; the base diameter ratios were 0.55, 0.70,
23、and 0.85. Static-pressure brifices 0.020 inch in diameter were installed along a meridian of the sfterbody. The shortest afterbody contained five boattail static orifices, whereas the longest model had Il. Two 0.020-inch-diameter base-pressure orifices were installed 0.09 inch from the edge of the b
24、ase on each model; one orifice was in line with the boattail orifices and the second was located 90 counterclockwise from the first (see fig. 2(a). A single 0.020-inch-diameter orifice was located 0.375 inch upstream from the cone-cylinder juncture on all models and was in line with the boattail ori
25、fices. The shape of the sonic nozzle was identical for all the models and consisted of a 100-included-angle convergence section followed by a constant-diameter portion 0.2 inch in length. Jet diameters of 1.3 and 1.5 inches were used in this investigation. All models were installed in the test secti
26、on with the line of boattail orifices in a vertical plane through the center line of the model and opposite the slotted top wall of the test section. t Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACARM 5721 5 A 0.0 this figure shows that the bou
27、ndary layer was fully turbulent at a point 5.5 inches upstresm of the base. The boundsry-layer thickness at this point was approximately 0.4 inch or 20 percent of the maximum model dismeter. RESULTS AND DISCUSSION . J . Afterbody Pressure Distributions A typical pressure distribution over a conical
28、afterbody at M, = 0.9 and at a jet pressure ratio of 4 is shown in figure 4. A schlieren photograph of the model at these test conditions is shown at the top of the figure. Although this distribution is for a particular model operating at specific test conditions, it is representative of those obtai
29、ned for other models at other test conditions. The rapid acceleration of the flow at the cone-cylinder juncture is noted as well as the extent to which this acceleration affects the pressures upstream of the juncture. The pressure coefficient corresponding to the static pressure necessary for sonic
30、flow along the model is indicated by an arrow on the ordinate at x = -0.4. a, As the flow proceeds along the afterbody it compresses rapidly and reaches above s the end point for all curves is the base pressure coefficient. SchlJeren photographs of the flow field about four afterbody configurations
31、at several values of jet pressure ratio and Mach number sre shown in figure 6. The distri- butions for the p = 45O model were essentially the same as those for the 30 model and are, therefore, not shown. For the latter, the dis- tributions shown in figures 5(b) and (c) and the schlieren photographs
32、in figure 6(d) show that the flow separates completely at the cone- cylinder juncture. It will also be noted that the base pressure coef- ficient is nearly the sameas the average boattail pressure coefficient. The value of this coefficient is approximately equal to the pressure measured at the base
33、of a cylindrical model with the same ratio of jet diameter to model diameter. (See ref. 1.) The effect of the relatively thick boundary layer on the results of this investigation has not been experimentally determined. However, work by other researchers (refs. 3 and 4) shows that vsriation in E/dm f
34、rom 0.05 to 0.184 did not significantly affect the base pressure or boattail drag coefficients. In reference 3, S/d, was vsried from 0.07 to 0.184 at transonic speeds and at M = 1.5 for a series of boattailed afterbodies. In reference 4, S/dm was varied from 0.05 to 0.18 at M= 2.0 for a cylindrical
35、afterbody. The tunnel-wall interference effects are also thought to be small with the possible exception of the range between I however, large base diameter ratios result in lerge base sreas which can cause large base drag penalties. Long afterbodies allow the external flow to compress to a higher p
36、ressure along the afterbody and, thus, help to increase the pressure acting on the base, but for some configurations the increased boattail drsg may offset any reduction in base drag. Comparison with other data.- Figure 13 presents a coqsrison of data from references 2 and 3 with results from the pr
37、esent investiga- tion. The data are for a 15O boattailed afterbody with a base diameter ratio and jet diameter ratio of 0.75. In neither reference 2 or the present investigation were models with j3 = 15O and db/dm = 0.75 tested so that the basic data were interpolated from several crossplots to obta
38、in afterbody drag coefficients for this coqarison. Model 1 of reference 3 had a tunnel blockage of 3.1 percent; reference 2 and the present investigation had blocked areas of 3.88 end 3.08 percent, respectively. Data for model 1 of reference 3 at a wall convergence angle of 0.5O were chosen since it
39、 was reported that the most uniform Mach number distribution of the empty tunnel was obtained at this wall setting. Some difference exists between the magnitude of $,a for the present work and that of reference 3 at the no-jet-flow condition. This is thought to be due largely to extending the data o
40、f reference 3 to the no-jet-flow condition by simply fairing the curves to Hj/p, = 1.0. It will be noted in the basic data curves of figures 7 and 8 that at sub- sonic speeds cD,a for j3 = 160 tends to increase abruptly between no jet flow and Hj/p, = 1.5. At a jet pressure ratio of 5, the present d
41、ata and that of reference 3 are in good agreement throughout the Mach number range of these tests. SUMMARYOFFGWIXS in experimental investigation at Mach numbers of 0.6 to 1.28 of jet effects on the drag of a series of conical afterbodies yielded the following results: 1. At high subsonic speeds, the
42、 boattail angle for minimum after- body drag coefficient was in the range between 50 and 8O. At supersonic Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-12 NACA RM L57B21 speeds, the optimum value of boattail angle was in the range from approxi- ma
43、tely 2.5O to 5O. 2. Opt- values of boattail angles were not altered significantly over the range of jet pressure ratios investigated. The pressure at which the jet operated did, however, influence the level of the minimum drag coefficient. 3. The presence of the jet was unfavorable on afterbody drag
44、, except at jet pressure ratios ofabout 6 or greater, and the variation of after- body drag with jet pressure ratio decreased as the ratio of the base diameter to the maximum diameter decreased. 4. For the 30 and 45O boattailed bodies, the pressures over the boattail were about constant and equal to
45、 the base pressure due to complete separation of-the flow from the model. The afterbody drag coefficient of these models was approximately equal to or greater than the base drag coefficient of a cylindrical afterbody. 5. At subsonic speeds, the effect of the ratio of the base diameter to the maximum
46、 diameter on afterbody drag coefficient was small; at supersonic speeds, the effect depended to a large-extent upon the jet- total-pressure ratio. In general, the base drag coefficient decreased as the ratio of the base diameter to the msxfmum diameter decreased. Langley Aeronautical Laboratory, Nat
47、ional Advisory Committee for Aeronautics, Langley Field, Va., February 8, 1937. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA RM L57B21 13 REFEBENCES 1. Cubbage, James M., Jr.: Jet Effects on Base and Afterbody Pressures of a Cylindrical After
48、body at Transonic Speeds. NACA RM L56G.9, 19%. 2. Silhan, Frank V., and Cubbage, James M., Jr.: Drag of Conical and Circular-Arc Boattail Afterbodies at Mach Numbers From 0.6 to 1.3. NACA RM 56122, 1957. 3. Pel, C., and Rustemeyer, A.: Investigation of Turbojet Ekhaust- Interference Drag. Rep. R-080
49、1-12, United Aircraft Corp. Res. Dept.9 Nov. 1955. 4. Cortright, Edgsr M., Jr., and Kochendorfer, Fred D.: Jet Effects on Flow Over Afterbodies in Supersonic Stream. NACA RM R53H25, 1953. 5. Henry, Beverly, Jr., and Cahn, Maurice S.: Preliminary Results of an Investigation at Transonic Speeds To Determine the Rffects of a Heated Propulsive Jet on the Drag Characteristi
