1、RESEARCH MEMORANDUM INVESTIGATION OF TWO SHORT ANNULAR DIFFUSER CORTFIGUFUiTLONS U?LUZLNG SUCTION AND IrJJECTION AS A MEANS OF SOUNDARY-LAYEZ, CONTROL By Stafford IN. Wilbur and Jam-es T. Higginbotham I a Lmgley Aeronautical Laboratory Y. . .- Langley Field, Va. ._ “ - . I 5.d- G I P Provided by IHS
2、Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-lXVZXiIGP“PION OF TWO SHORT AiWiiULAR DIFFUSER By Stafford W . Wiiiour and James T. Higginboth The performances of two annular difzuser designs zpplicable to turbojet afterburner instalhtioas xere investigated to dete
3、rnine the effectiveness 02 injection and suction boundary-hyer controls. The outer shell was cylindrical ir each case. The basic ceater-body design was en sbrupt dw type which produced an equivalent conical diffuser angle of approximately 1000. The addition of 2 corical center-body fair5ng to the ba
4、sic design produced a secon6 configuration corresponding to an eqLziva1en-t cor-ical diffuser -le of 32O. Both designs had increase in the measured static-pressure rise, ad a 50-percent reduction in the measured loss coefficient. Punping power corrections reduced the 33-percent increase in static-pr
5、essure rise to about 21percent and eliminated the reduction ia loss coefficient. Suctio?. control in the looo diffuser wically s-hped center body previ- ously tested with vortex-generator controls. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2 m
6、c INTBODUCTION Le performnce characteristics of subsoni .c - -annular-diffuser designs applictely 0.18 to 0.45 with e resulting ?naxhm Reynolds nmber (based on the hlet hydrau- lic dismeter) of approximtely 1.6 x lo6. D diffuser outer diameter d hydraulic dimeter, 4 x cross-sectional =ea of duct Per
7、imeter 02 two dovnstrem stations (stations 2 and 3) in order to iridicate the developzent of flow downstrem from the diffuser as it proceeded through the tailpipe. The surveys at station 2 gave an indication of Yce veloc- ity distribution at that point, although tne accuracy was low because of the r
8、adial velocity componexrlx, flow asymmetries, and high turbulence level. The surveys at station 3 gave more accurate velocity distributions and loss coefficients than those et station 2; therefore, the relative perfor-ance of the various configuretions is presented for this station, which was 1-09 o
9、uter body diameters from the start of the geometric expans ion. “ - Basis of Comparison The description of the flow at station 1 is presented in terns of the velocity ratio u/U in order to indicate the quality a_?a character of the inlet bounkry-layer distribution. The flow development in the diffus
10、er is presented in terns of the outer Tall longitudinal distribu- tion of static-pressure coefficient 4-h. The coefficient is refer- enced to the static presswe at stction la, which was sufficiently upstrean to be insensitive to flow or configmation changes between statiocs 1 and 3. The radial distr
11、ibution of relative velocity u/c1 describes the flow at stations 2 and 3 and, in addition, indicates the local redxction in velocity due to dlffusion. The overall diffuser performance is presented in term of the nean coefficients - bc, 43-la % Measu-red Provided by IHSNot for ResaleNo reproduction o
12、r networking permitted without license from IHS-,-,-NACA R4 5W-8 7 - Previous investigatioos hzve reported that in regions of turbulent Plow, the pressure aeasurements as recorded by a pitot-static tube iEdi- cate vdues that are higher tlzn is consistent with flov continuity. (See refs. 5 and 8.) Th
13、is error can be evzluated in terms of mss f lou if the hlet conditions zse assumed to be correct. The msasured mss flow at z do-mstrean station, as obtabed fron an integratian of the survey profiles, is greater than the corresgocding measured rmss flow at the ird.et, whereas for contiouity the flow
14、must be constaEt through a a closed-flow system. The ratio of tbis mass-flov discrepan-cy to the inlet riss flow . ks been cslculated Tor skkion 3 a thils, the awiliary sir sys-iem vas coE-+Lned to the diffuser proper an6 any variables which would be impossible to Essess in apglying Vne results vere
15、 el-;micAted. It was asswed tat the auxilfary air-flow pump operated at .m efficiency of 100 percent. In the case of injection, it was assumed that a pump would have to supply a pressure rise equel to the difference . between the inlet stgtic pressure and the zeasured total pressure in tne c chber u
16、pstream frm the injectloll gz:. For suction, it -as sssuned Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-that the pump would supply a pressure rise equal to the difference between the inlet mean total pressure and the chamber total pressure. The t
17、otal-pressure loss of the diffuser, including the pumping- power comideration, is then evaluated as (?) + P. The Measured 43 -1 Gl diffuser effectiveness 7 is evaluated as , where +P Ideal is the theoTetica1, one-dimensional, isentropic static- Ideal pressure coefficient corresponding to the mean in
18、let static and total pressures and the diffuser area ratio. RESULTS AND DISCUSSION Inlet Measurenents In order to define the inlet-flow conditions, total- and static- pressure surveys were made at station 1 for four equally spaced circumferential positions. Ultimately, the weighted aean values of th
19、ese measurements were used in determining the overall performance coefficients. Velocity profiles detemined by using the survey data are presented in figure 3 .in terms of the ratio of local velocity to the mmcinum velocity as a function of radiai position in the annulus. Inasaucn as no significant
20、circumferential variations were measured, the average of the four sets of data is presented. Figure 3 indicates that only small differences existed between the data for the inner and outer vsll with respect to velocity profiles end the significant botu-ikry-layer parmeters. The boundary layer filled
21、 the entire annulus, sh5lar to fully developed pipe flow, and the use of boundmy-hyer controls did not alter the inlet conditions for the r.=nge of varia3les tested. The inlet boundary layer of the investigatioc reported herein is essentially the same as thet of references 2 to 6. Provided by IHSNot
22、 for ResaleNo reproduction or networking permitted without license from IHS-,-,-9 . Flov Dbservations Observations of smll woolen tufts installed along the diffuser L walls indiczted t-mt two definite and distinct Tlow patterns occurred duri3g the hvestigation. The nore stable flov psttern was estab
23、lished when the flow separated from the cowl a short distance -*stream from the poict at which the auxiliary flow was irrtrcxiuced to the diffuser. The other flow pattern was established when the flow rermed attached to the cowl until its abrupt tednation zt the point where awclliary flaw -as encoun
24、tered. The attac3ed flow -was fomd to exist 0d.y for h jec- tion through gap settings of 0.062 a6 0.121 hch without the fairtag installed. At a gap setting of 0.062 inch, it was possible to obtain both flow patterns. The attached-flov case vas normally obtained when the flow was initiated. After eer
25、ating a period of time, the flow occasiomlly changed abruptly to the separated state. When segaration becme established, it was generally necessary to stop all air flow through the diffuser and then restart tle blowers before attached flow could be reestablished. It was noted during the tests that a
26、ttenqts to fnject the higher qwtities OT zuxiliary flow were a frequect cause of the precipitztion of separaked flaw. The tuft observations regsrding the two states of flow were substatiated by downstream pressure s-urveys. tuft fluctmtions, was present on the outer wall downstream of the inner body
27、, whereas for separated flow the tuTts Fn-diczted violent turbulence. - When the flow was attached, moderate turbulence, as evidenced by the - As discussed previously, additional infomation may be obtained with respect to the relative turbulence of the flow uncer various conditions by coaparing the
28、mss-flov EeasureEents at a do-mstream station with the neasurenellts at the 5d“t station. Smh a comparison is preseEted in figure k as a function of the percentage auxiliary flow. The data indi- cate kh% suction control. produced higher mass-flov errors, and, therefore, higher twbulence levels, than
29、 injection. The higher vzlues with suction are grobably a-ltributable i-n part to the inability of suction control to prevect flow separation fro= the cowl. The errors obtained with this diffuser are typical in nagnitude of those obtained in the in-vestigEtions o? references 5 sad 8. The data for st
30、ation 2 are not presented because of the data scatter and inaccuracies; however, the trevds observed are the sane as those observed at station 3 but of greater mgnitude. S-kAic-Pressure Distributions Longitudinal stetic-pressure distributions. - A convenient index to the flow development for a given
31、 diffuser is the longitcdinal static- pressure distribution, since the change in static pressure ger unit length is indicative of the char-ge of the mean *act pressure. Plots vall static-presswe orifices are giver, in figures 5 to 8 as a function * of the stztic-pressure-rise coefficient as detemed
32、from the outer- Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-10 NACA FN 5418 of diffuser iength for control and no control. The values given are slightly higher thar? mean values is the region imediately do-mstream fro= thc center body because of
33、raclial pressure gradients such as those described in reference 4. In addition, the data hve not been corrected f9r injectior, and suction pumping poxers. The data of the subject diffusers are coqared with those of the l25 diffuser of reference 6 and the 31 diffuser of reference 5 in figure 5 for th
34、e cases corresponding to no-flow controls. An increase in the radius at the break fron the 11 inches of the I25O diffuser to 2 the 3- 5 inches of the LOOo diffuser improved the static-pressure-rise coefficient - approximately 100 percent at station 2 and 20 percent a 4 Gl at station 3 in spite of se
35、paration from some position on the cowl. The addition of the fairing to form a 32O diffuser produced no signifi- cant hprovement, probably because the flow was separated from the cowliag cpstrean frox the fairing. The 31 diffuser, sMlar in length btlC of different geonetq from the cowl and fairing,
36、produced the best performance. This result is probably due to the lower initial rate of expansion produced by the l2.55-hch radius johing the ellipsoid of the 31 diffuser to the cylindrical center body. The larger radius undoubt- edly delayed separEtion to a larger area ratio. From the performance o
37、f these difrusers with no ccntrol and from flow observatio?-s, it is to be concluded that the cowl shoxld be designed with a nore gradual rate of area emansion (larger radius) ; thus, flow sepmation upstream from the auxiliary flow openings is prevented. The inproverrent achieved in the longitudinal
38、 static-pressure dis- tributions for the 100 diffuser through the use of injection or suction for bomhry-layer control is shown in figures 6(a) to 6(d). The n;aximum hprovements were achieved xith injection cmtrol ir- a region corre- spoMing to approximately Z/D = 1/2, (station 2) . This location co
39、rre- sponds to the point on the center line where the vertex of the cone of injection air occurs. Injection of auxiliary air was effective in increasing the static-pressure rise with either attached or separated flow on the cowl surface; however, with separated flow, nore injection air was required
40、to achieve a given perfomce. This condition is readily apparent in figure 6(b), vhere both separated- and attached-flow cases are presented for an injection flcw rate of 2.15 percent. The basic 100 diffuser, when utilizicg suctior, as a flow control, was responsible for some Improvement in the longi
41、tudinal static-pressure distribution, although it was largely ineffective when compared with injection. Figure 7 shows that the additfon of the fairing to the basic Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-. design to prohce a 32O diTfuser inc
42、reased the effectiveness 03 the suctior control and indicated that suction could not control the back- Plow region in the 100 diffuser. Both configurations sdfered from flow separation frolo the cowl with suction control. Figme 7 also shovs that injection control with the fairing in place vas very e
43、ffective wheG the auxiliery flow (6.13 percent) was sufficient to el7hica%e separation. , A cozqzrison of tjne longitucii-ml static-pressure rise for the U5O diffuser (ref. 61, the 100 dilfuser, and the looo difiuser with tne fairing (equivalent to a 32O diffuser) is shown in figure 8 for injection
44、quantities of R = 5.0 percent and suction quantities of R = 3.7 per- cent. These auxiliary-flow- quantities were chosen because these condi- tions produced the most unifom velocity distributions at station 3 for one or more of the configmatior-s, as will be discussed subsequently. The 31 dizfuser wi
45、th vortex generators (ref. 5) was also inclu3ed in this figure in order to assess the relative merits of vortex generators an0 auxiliary flow. With injection OP 5 . 1 percent, the 100 diffuser produced higher stEtic pressures throughout more of the diffusing region tha? any other configuration. The
46、remainins injection configurations produced less * because of poorer bssic design in the c8se of the 125 diffuser or . - % beczuse of separation on the cowl in the case of the 100 diffuser and fairing. The loOo and l25O diffusers produced higher rates of diffusion than the 31 diffuser with vortex ge
47、nerators in spite of the poorer basic design of the center bodies. Except for the case where the fairhg was used to elininate the extensive backflow regions, the corfigurations utilizing suction for flov control produced low values of -. 4 % Static-pressure-rise coefficients, stations 2 and 3.- The
48、static- pressure-rise coefficients at station J are presentid Zn figure 9 for the range of inlet Mach numbers. A smll, unfavorable Mach number effect is ev-lder-t for the no-control condition. For compareble auxiliary-flow rate, at-lsched flow gives a wall static-pressure rise grestly exceeding the
49、equivalent vdues obtainatjle with flow separation occurring 03 the inner body. The effect of the auxiliary-flow quantity R on the static-pressure- rise coeificient at stations 2 and 3 is shown in figure 10 for a mean irlet Mach number of zpproxinately 0.26. Station 2 is presented since it is in a region of mxhum improvement due to coatroi, whereas
