AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN I- I I- I I II n I I/ RESULTS OF RAM-JET BTLTEERFLY MODEL TESTS WTM-148 Prepared by: -—' J. A. Parchem Il ~~ru~~~~c_01 Approved by: W. C. Nelson - - May 22, 1950

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN'TABZ OF CONiTETS I II'IV V VI VII.VIII Sumary Introduction Description of Model and Associated Equipment Test Cnditione Caamntary on Test Results Data PBduction Graphs and Photographs of Significant Data References Appendix A - Na al Frequency Computations Appendix B - Screen Choking Ccputations Page 1 2 4 12 13 15 35 46 47 49 ii --- - --

AERONAUTICAL RESEARCH CENTER- UNIVERSITY OF MICHIGAN......' WT-148 -. LIST OF FIUES AD TABLE Figure Bo. Page 1 Exploded Tiew of Ram-Jet Butterfly Model with Massa Pressure Microphone and Butterflies 7 2 Cut-Away View of Massa Pressure Microphoe and Butterfly Mounted within Model 8 3 Exploded View of raa-Jet Butterfly Model with Massa Pressure Microphone and Flow Choking Screens 9 4 Cut-Away View of Flow Choking Screens Mounted within Model 10 5 Ram-Jet Butterfly Model Associated Equipment 11 6 Effect of Butterfly Excitig Frequency on Bow Shock Pulsation Frequency 36 7 Effect of Butterfly Exciting Frequency on Pressure Wave Frequency 37 7A Effect of Butterfly Exciting Frequency on Pressure Wave Differential with Butterfly Accelerating from Rest to 900 cps 38 7B Approximate Butterfly Acceleration Characteristics during BuNo. 49 —10-14-10 38 8 Selected Fastax of Flow with Comon Model Configuration ai Variable Butterfly Exciting Frequency 39 Butterfly Diameter, 1.25 inches Nozzle Outlet Diameter, 0. 7 inches 9 Selected Oscillo4cope Film of Presutre Wave Patterns with CcaMn Model Coafiguration and Variable Butterfl.y xiting Frequency 40 Butterfly Diaeter, 1.25 inches Nozzle Otlt Diameter, 0.75 inches iil - -- 1 ---- -~

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN WM-148 I LIST 0p FIQUS AP) TABIS (CON3nTI D) Figure No. Page 10 Selected Oscilloscope Film of Pressure Wave Patterns with Conmon Model Configuration and Variable Butterfly Exciting Frequency 41 Butterfly Diameter, 0.75 inches Nozzle Outlet Diameter, 0.75 inches 11 Oscilloscope Film of Pressure Wave Pattern with Butterfly Accelerating from Rest to 900 cps 42 12 Effect of Butterfly Size upon Bow Shock Pulsation and Pressure Wave Pattern with Butterfly Exciting Frequency Held Constant 43 13 Selected Oscilloscope Film of Pressure Wave Patterns with Flow Choking Screens of Varlous Solidity Ratios 44 14 Selected Oscilloscope Film Shoving Intervals where Pressure Wave Pattern is Periodic between 700-750 cpa 45 Table No. 1 SummSry of TIest Data-Ram-Jet Butterfly Model 16 r - -- -- iv - -- -- --

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN WTM-148 -- I. SUTIARY At the UMERI Supersonic Wind Tunnel during August and. October, 1949, a series of tests at Mach 1.9 was conducted on a 12" ram-jet butterfly model. This non-burning rane-Jet vas used for the purpose of investigating the effect on flow in and about the model by periodic disturbances Internally generated by a spinning butterfly. The min sources of data were high speed Fastax Schlieren and a Massa sound pressure microphone. With butterfly exciting frequency varied from 0 to 940 cp8, the restlting bow shock pulsation and internal static pressure variation frequencies proved to be a direct function of the exciting frequency. The one exception occurred at an excitin frequency of 50 cps where no shock pulsation vas observed. sEperimentally^ the natural frequency of the idel vas seen to, be approxi ately 270 cpse hich was 8g% of theoretical closed tube natural frequency. Agreement between the theoretical and experimntal third haronic was poor, An attempt to induce bow shock pulsation by choking the internal model flow with high density screens met without success. Several tests with diverse model configurations and operating conditions produced data that showed a tendency of the internal pressure to oscillate at approximately 725 cps. 1 1

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN II. INTRODUCTION Early in 1949 a program was initiated at the UMERI Supersonic Wind Tunnel to investigate the effect of internal flow disturbances upon the flow in and about a ram-Jet. In May, 199, the first-phase testing was carried out at Mach 1.9 using a 12-inch cold. mdel ram-jet with a 1.5-inch diameter constant area duct siamlating the burner and a 1:2 subsonic diffuser. The specific test purpose was to block the internal flow by a series of plugs with sharpedged orifices of various- dia ters mounted at or near the model outlet. The w1oel bec chobWkd only when a solid plug was used, in which case the bow shock pulsated with a frequency approximaately 85% of the theoretical natural frequency. No shock pulsations ooourred without model in choked condition. The report of these tests is contained in Reference 1. October, 1949, found the second phase of the test program coMpleted. The particular test objective was twofold. Primarily, the flow was made subject to periodic disturbances generated internal to the 1Dmel by means of a spinning butterfly valve. The gnitude of the disturbances was controlled by different size butterflies. Exit conditions were regulated by a series of nozzles with divere-area ratios. Secodarlly, an effort wa made to produce bown shock pulsation by blockg internal flow with high deneity. screens speclffially 6aesgn1ed to o=Dhok the xdel. The uaoel used. in the first-phase tests was msrely adaified to acco-iodate butterflies, nozzles, and creens. The test section Mach Number throughout was 1.9, All external flow phenamnon was recorded on high speed Schlieren notion pictures. Also, a sound pressure nicrophoe was placed just downstream of the diffuser in order to Basure the frequency an magnitude of any internal static pressure variations. N6 other data source was provided. This mrorandum's purpose is to report the results of the second-phase tests with little attempt to explain or draw conclusions frco the data gathered. In June of this year the third-phase tests are expected to take place. The present ran-jet oxdel has been fitted vith two cone-type central body diffuers. The cone angle for each is identical. Howeerr, downstream of the cone one central body will'displce a larger vol3u of the siulated burner th the other.'This mification will perait study of flow under shock wallwing conitions s ell as any effects which internal volum I cha s ight produce. Operation of the butterfly will not be affected I 2

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN WTM-148 by this installation. Without the central body, the ol reerte to its present configuration so that repetition of previous tests can be conducted. This is the intnt. It is hoped that this will. lead direotly to the fourth phase - viA tunnel testing of a burning ram-jet. 3

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN. -----—' — \~wm- 148 -- II. DESCRITION' MIODIL AUD ASSOCIATED E&UXPHT Rama-et Butterfly Model: The reader is referred to Figures 1, 2, 5, 4, and 5 contained in this section for all details of the wdel configuration, installation andt accessory parts, such as butterflies, nozzles, screens, etc. Approxinate diaensions can be scaled directly from the photographs. Western Electric Fastax 16 m. High Speed Caera: Made by Western Electric (Bell Telephone Laboratories, Inc.), N.Y. Model D-163269 Serial No. 16269 Speed Range 0-8000 frame/sec. Film spooled in 100 ft. rolls especially for Fastax by Kodak. Installation of camra is shown in Figure 5 of this section. Massa Soudu Pressure Microphone System Model GA-107:T Made by Massa Laboratories, Inc., Cleveland Microphone Model M-1258 Serial No. 2 Eploys ADP crystals Microphone dia. = 3/16 in. Pressure sensitivity 4 microvolts/dyne/cm2 Frequency response range 50 cyo - 250 ke. Microphone linear to pressure agnitudes of several million dynes/cm2 Preamplifier Model M-114B Power Supply Model M-116D Special Calibration Unit built by UMERI Controls Group Rang 0.0001, 0.001, 0.01, 1.0-5 psi Ballantine Amplifier provided by Controls Group Installation of microphone is shown in Figures 1, 2, 3, and. Duont Dual-Beam Cathode-Ray Oscilloscope: Made by Dumont Laboratories, Ino., Passiac, N.J. Type 297 Serial No. 159 115/230 V Single Phase 50 - 60 cycles 300 atte This oscilloscope is shon in Figure 5.. -- -- ---

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN WTM-148 ---- Fairchlld 35 mm. Camra: ade for Dmont Laboratories by Fairchild Type 314 Serial No. 113 Two Speeds 60 in/min and 60 in/sec Ultra Speed Anaco Film in 100 ft. rolls This camera is shown in Figure 5. 120 Cycle Pulser Unit: This unit was designed and built by the UMERI Controls Group. It is used in conjunction with the Fastax camera and Duont osoilloscope. In the Fastax camra is an argon timing light. The unit supplies voltage pulses of 120 cps (derived from the 60 cycle power line fequency) causing the argon light to pulse and in turn produce a short pip On the somnd track of the film. Simultaneously, the pulse was sent to the oscilloscope on one of the beams to be recorded as& a pip on the oscilloscope film. The width of the pulses is 1/11 of distance between pulses. Thus, a time reference is established. See Reference 2. Butterfly Tachometer and Shaft Pulser: This unit was also designed and built by the UMERI Controls Group. In operation it is similar to the 120 Cycle Pulser Unit. In this case, the voltage pulses from the butterfly shaft comautator (Figure 1) cause the sam argon light to produce a pip on the Fastax film sound track simnltaneous with a pip on the oscilloscope film. These pulses or pipe have a ratio of width to distance between pulses of 1/20. The butterfly position was carefully coordinated with the coamntator so that appearance of a pip indicates that the butterfly was fully closed (face of butterfly normal to the flow). Thus, there are two pips per revolution. In relation to the 120 cps pipe the position and speed of rotation of the butterfly mre known from two sources. See Figures 8 and 12 for reproduction of timing pips. The pulser contains an electronic tachometer which is used for indicating nominal butterfly speeds. It proved quite inaccurate. Figure 5 shows these pulser units. Reference 2 carries a complete description of the units as well as operation instructions an. wiring diagram. -.. -- 5 ---

AERONAUTICAL RESEARCH CENTER -UNIVERSITY OF MICHIGAN Xutterfly Itetr: |ba1 by (Genwra IlanAtrea CGo.,, iyra, 0. MHoae 61400 D.C, (tivwreaw) eries 24 V 7 am 1 /8 p 8o0 ra (1m lt.) bie -or wa driven ftr.4 d. o utrren. It can be ien ia Figure 1. Powlreut (Var)ao): Mad by Superior lotrio Co., Bristol, Conn. Tipe 116 Pria, Y 115 50 - 60 oyc 7.5 zs. output Two vere seed, one to oontrol butterfly wtor spee a the other to eontol Fastax bmera speed. Their relation to the other eqOilnt 1a to be aen n nFiure 5. 6. —` — —. ---

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/ tERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN -- -- --- - --- WTM-l3A8 XI. T..' COIa: OTI: S A total of 26 res vn made on Augst 12, October 12, 13, and 14, 199. The program as Int.rrrpt In j tut because of ohanical difficulties encountered in op rating the butterfly shaft. As has al dy been pointed ot all run were ad at a test section Mach Number of 1.9. TB9 dew point rang fro -8 to -23~. The reservoir temperature always fell betwe 553 an 60~1. exc t the runs in August which wre at 79~r., Tb. S e rwer or bartrie prssure vas consistently betwi 29n 29. 33" ad 29. g. Tw tanlk ainr i iiately preceAing a run neer fell belvIr' g nor above 2 g' B. m, gth of test runs was gearally about 7 sehon, altog one was as long as 1 sooonds and one w-as. f- 6:eea lngth. Tb ie3 was orientated at zero angle of attack and yav. The Fastax Schlieren yieled data rearding the relation between bov shoo pulsatn freqency, other fl pbamon and the butterfly exciting frequcy. The M sa irophone by way of the oscilloN pe film, indicated magnitudes and frequencies of internal statie presure variatlons in con-a parison with butterfly excitiag frequences. Thse were the important variables outside of butterfly site and nozzle area ratio. The accuracy of all frequency Ueaurenta, except were noted, is not ore than + 1.5i. With the Massa calibration unit used, the pressure differentials are subject to as woh as + 20% error. Ioproveant of the calibration muit, shotly to be undrtaksn, will allow considerable reduction in this presr differential error. Since the Massa microphone was being used for the first ti in this organization it vas to be expected that certain difficltiee voul be encountered. As a result there was an insufficient number of pressre differential points to provide a firm foundation for plotting curves. Figure 7A is an exoeption but Cn this is not quantitative. On the oscilloscope film, tia correlation between the tiaiag trace aM pressure vare trace is subject to error since it was not possible to Iaintain at the Eae* level the nutral position of'beth bea.imaGes on the eoilla cope aoreen. It is estimated th this level variation might be as hih as ~0.04 inches on the screen. This level variation represents a possible time correlation error of ~ 1/400 seconds between the two traces on the oscilloscope film at film speeds of 50 to 60 in./sec. I -— 5 --- -- -- -- -

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN i - - ----— Wi r-148 V. CONwNrsTAa ON T8T RSULMTS Butterfly Tets: Inspection of Figure 6 shows that bow shock pulsation frequency varies directly with butterfly exciting frequencies from 0 to 940 cps - except for twe points at butterfly frequency of approximately 50 cps. Wheneter the axplitu&e of the shook pulsation gt sotl, as in the aes:Vlt 0-.7- ln. butterfly, the frequency vas impossible to masure. Tberefore it is possible that the shook pulsation aplitude for these two points was too slall to detect. The Figures 8 and 12 show typical Fastax from which these data aere obtained.. Also refer to Table 1. Figure 7 of pressure wvae frequency variation vith butterfly exciting frequency duplicates the results obtained from the Fastax. In this aase, the 50 cps points were obtained. from oscilloscope flrl whereupon there was considerable noise. Again it is possible that the oscillation defied a*tection. Hovsoer, these 50 cps points were aompcanied by another pheoMa - enon to be pointed. out later. Examples of oscilloscope flmL yielding thsee data can be seen on Figures 9, 10, 11,ad 12 (especially Figre 10, Run Nos. 49-10-14-14 and 49-10-14-12). Very interesting information was acquired from lR Jo. 49-10-14-10. In this instance the butterfly accelerated from rest to 9X epa. Zvon thbogh this id& not represent steady state conitions there seed to be sufficient evidence that the natural frequency of the wdel is approximately 270 cps. This is about 85% of the theoretical closed tube natural frequency. The third harmPnic of the model appears to be about 700 cpa* which does not agree too wll with theory. These facts are to be noted on Figure 7A whvich ras obtained from fil reproduced as Figur 1. It is to be seen that tbe wam wmm pressure differential occurs at butterfly exciting frequency of 700 ops. LHfwer, Figure TB shows that the acceleration vas appreciably lover at the the 2700 op peak. This can easily acounmt for the distorted picture. Reducing the size of butterfly used from 1.25 inches to 0.75 inobes caused. a drop in pressure differential by approxinately 90% at simalar butterfly frequencies. In every run but oneusing an open tail pipe for a nozzle, the odel. was choked irrespective of butterfly speed. T is evidence that noz les with smaller area ratios shouU have been used.. I. I 13 - -- -

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN WTM-148 Flow Coktng Screen Teats: On the basis of cold model internal flow blocking tests by use of plugs (Reference 1) it was thought that bow shock pulsation oould be induced by using high density screen. Screens of 80Y, 87%, and 95% solidity ratio were used and Do shock pulsation was noticeable. In each case the odel vas choked. Increasing the solidity ratio resulted in oent of the bow shock upstream, Figure 13 has reproduced oscilloscope filJS; from runs with the different screens. During several runs there appeared on the oscilloscope film unsteady intervals which displayed a pressure wave frequency between 700 and. 750 cp. This occurrence accompanied each of the flow choking screen runs. It also shoved up during the runs where the butterfly frequency was 50 cps and one where the butterfly was known to be stationary. The model was choked in each case and the Fastax gave np evidence of bow shock pulsation. Table 1 and Figure 1h indicate the evidence. 14 - --

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN I -- ~ - *., * i tEl-148. — VI. DATA TBAE TI0N This section is divided into three main parts. The first, Table 1, consists of a complete somury of all important data recorded during the testse. The second part contains all Information, in detail, obtained from the Fastax Sbclieren otion Piot.re.. The method by which the butterfly and. bow shook pulsation frequencies vere calcuated is as follows. From the 120 ops titing pipe on the sound track (Figure 8) the film speed in frame per seoond for a certain length of film was determine. During this length, the nuber of fra pss pasing per cYole ( rolution from one butterfly pip to the next) of butterily operatton we read. Dividing the flm speed by the fr per butterfly oyc yielded the butterfly exciting frequency. Thie omaptat-om of the ahook pulsation frequency ra simadlrl carri. ot. Sinoe the utterfly otion Is rotary the speed in rpm for | ech frequew y Is g1Tn. Ih lat part prsent all data reduced from the osoillosaope Motion pictures. Tb detr inton of press rv adi butterfl frequencies w ietial wlth the mthod used in a nalying the astax. In most oanes, the frequencies e che by noting the n r of Ocyles ootrring luring on 1/120 eecd oyxle2 (1 gresz 9 11) and theln m tplying by 120, This WeliminatM the Sidlter<iate step of oaiting the film speed.. bre the film is aelerting this latter method. ars preferred. ObTiously the pressure dTifferWbtil m IAitX s war. aoeired w ely by ooqaring the ae in qgueston with the aUesolat"e eslibration c rre. The c-hronolgial orde. of pre]ntlng the Fastza and. oscilloscope data follow that uase In Tabl 1. 15

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN Fastax Schlir WTMD-148 Fastax Schlieren Data. Fastax No, 9 (Run No. 49-8-12-1): Bow Shock Film Speed Butterfly Exciting Freq. Pulsation Freq. frames/sec. frames/cyc. cps reI frames/cyc. cps 4560 8.0 570 17,100 8.0 570 4560 7.9 577 17,310 8.0 570 4560 7.85 581 17,430 7.85 581 4320 7.2 600 18,000 7.2 600 3960 6.5 610 18,300 6.5 610 3600 5.8 620 18,600 5.8 620 3120 5.0 624 18,720 5.0 624 2760 A 4 627 18,810 4.4 627 2520 630 18,900 4.0 630 Intermittently some of the butterfly pips seem to be missing. One of the shaft contacts must be faulty since the same Din is missing repeatedly. It was the intention to accelerate the butterfly during film exposure. Data shows the onoosite hapnened. The film was over-exposed so that the flow field could not be seen except for one bow shock reflection above and downstream of model. The oscillation of this reflection was used to determine shock frequency. An expansive exhaust from the nozzle was noted to oscillate at same frequency as butterfly. Fastax No. 10(Run No. 49-8-12-2): Butterfly was stationary. Model was not choked at any time during film exposure and no shock pulsations were detected. Film was over-exposed. 17 - --

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN....1 —---- WE-148 -8 Fastax No. 11 (Run No. 49-8-12-4) During exposure of the film the model was choked during three intervals. The Deriod between first and second interval was about 0.46 seconds and between second and third interval about 0.28 seconds. Except for these intervals the model was not choked. It seems certain that the butterfly was not rotating steadily. It was probably turning erratically or wobbling back and forth. A study of the sound track showed that the butterfly was in its most closed position during the three instances where the model was choked. This is evidence that the model can be choked with the combination of 1.25 in. butterfly and 1.5 in. nozzle. At the time of the test run considerable confusion was experienced regarding this run since the butterfly tachometer indicated the butterfly to be turning at annroximately 2500 rm,. It was later discovered that the tachometer would indicate 2500 rpm if the 120 cps pulser unit was on while the butterfly was stationary. The film was not sufficiently good in quality to print for this report. Fastax No. 18 (Run No. 49-10-14-1): The butterfly was not turning but was orientated in its most open position. No shock Pulsation was detectable. The model was choked throughout run. See Figure 8 for a selected strip of this film. 18

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAIN FaMstax o. 16 (n N. -1-48 Fastax No. 16 (Run No. 49-10-13-6): I Bow Shock Film Speed Butterfly Exciting Freq. Pulsation Frea. frames/sec. frames/cyc. cps rpm frames/cyc. cps 3000 13.7 219 6570 13.0 231 3340 15.3 218 6540 16.0 209 3660 16.7 219 6570 17.0 215 3840 17.5 219 6570 17.5 219 4030 18.3 220 6600 18.0 224 4220 19.0 222 6660 19.5 217 4500 20.2 223 6690 20.5 220 4710 21.2 222 6660 21.0 224 4840 21.8 222 6660 22.0 220 4990 22.5 222 6660 22.5 222 The bow shock pulsed quite violently while the model was in a choked condition. It appeared that the bow shock was in its most downstream position when the butterfly was anoroximately closed. Actually, the shock started moving upstream arnroximately 0.001 seconds before the butterfly fully closed. See Figures 8 and 12. J Fastax No. 17 (Run Film Speed frames/sec. 2980 3360 3720 3920 4120 4300 4500 4720 9-20 No. 49-10-13-7): Butterfly Exciting frames/cyc. cps 7.4 403 8.5 395 9.5 392 10.0 392 10.5 393 11.0 391 11.5 391 12.2 387 13.0 379 19 Freq. rm 12,090 11,850 11,760 11,760 11,790 11,730 11,730 11,610 11,370 Bow Shock Pulsation Frea. frames/cyc cps 7.0 426 8.5 395 9.5 392 10.0 392 10.5 393 11.0 391 11.5 391 12.0 393 13.0 379

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN "' B....... Fastax No, 17 (Run No. 49-13-7): Cnt'd Bow shock definitely pulsed but not so violently as in Run No. 49-10-13-6. The shock hesitates somewhat while it is in its downstream position. It appears that the shock is upstream when the butterfly is closed. This condition is opoosite from that for Run No. 49-10-136. See Figure 8. Fastax So. 14 (Run NO. 49-10413-4): Bow Shock Pil Speed Buttortly Exciting Freq. Pulsation Freq. frames/sec frasa/cya, epa rp frames/cyc cps:3000 4.7 638 19,140 4.7 638 3320 5.2 639 -19,170 5.25 632 3700 5.8 638 19,140 5.8 638 4020 6.3 638 19,140 6.3 638 4220 6.67 633 18,990 6.6 639 4500 7.1 634 19,020 7.1 634 4680 7.25 645 19,350 7.25 645 4890 7.6 644 19,320 7.67 638 4980 7.8 638 19,140 7.8 638 The bow shock is again definitely pulsing. The amplitude of the shock pulsation is decreasing as the butterfly exciting frequency decreases. The shock is in its ost downstream position about 0.0005 seconds before butterfly closes. See Figure 8. -- ---. - -—, --- - ------ - - -... -- 20 -

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN I IWEM-A8- 8 Fastax No. 25 (Run No. 49-10-1v49): L Bow Shock Film Speed Butterfly Exciting Freq. Pulsation Frea. frames/sec frames/eye. cps rpm frames/cy cps 3000 3.2 938 28,140 3.2 938 3300 3.2 943 28,290 3.5 943 3580 3. 942 28,260 3.8 942 3910 4.15 943 28,290 415 943 4200 4.33 9 29,100 44 33 970 4380 4.67 938 28,140 4.7 933 4500 4.8 938 28,140 4.8 938 4680 5.0 937 28,110 5.0 937 4800 5.1 942 28,260 5.1 942 4;920 5.2 947 28,410 5.3 930 The amplitude of the bow shock nulsation is quite small but still large enough to make frequency measurements. The bow shock is downstream Just before the butterfly close#, The butterfly shaft was seen to whip badly but its frequency was not measurable. See Figure 8. I Fastax No, 13 (Run Film Speed frames/sec. 3000 3290 3600 3960 4200 4440 4680 4860 No. 49-013-12): Butterfly Exciting frames/cyc cps Freq. rpm Bow Shock Pulsation Freq. frames/cyc cps 11.3 12.5 13.5 14.8 15*.7 16.5 17.3 18.0 266 263 266 265 268 269 270 270 7980 7890 7980 7950 8040 8070 8100 8100 11.0 13.0 13.5 15.0 16.0 16.5 17.5 18.0 273 253 266 262 262 269 268 270 -- --- - - - 21

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN w m.-1148 Fastax No. 13 (Run No. 49-10-13-2) Cont'd The bow shock frequency was difficult to determine since the compression areas were light on the film negative. Shock reflections near tail of model proved to be fairly successful in comnuting nulsation frequency. No accurate time correlation between shock and butterfly position because of the light compression areas. Fastax No. 12 (Run Film Speed frames/sec. 3120 3240 3360 3600 3700 3850 4060 4280 4440 4560 4680 4800 No. 49-10-13-1): Butterfly Exciting Freq. frames/cyc cps rpm 5.1 5.25 5.33 5.6 6.0 6.3 6.6 6.7 6.9 7.25 7.6 7.5 612 617 630 643 617 612 615 639 643 629 616 640 18,360 18, 510 18,900 19,290 18,510 18,360 18,450 19,170 19,290 18,870 18,480 19,200 The bow shock definitely pulsed. However, no accurate determination of shock frequency could be made for two reasons. First, the amplitude of shock pulsation was extremely small. Second, the compression areas on the negative were light. Nevertheless, comparison with Fastax #14, wherein butterfly frequency was 638 cps showed that shock frequencies for this run were about the same order of magnitude as the butterfly frequencies. - -- 22

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN WTM-148 Fastax No. 12 (Run No. 49-10-13-1) Cont's The butterfly frequency is seen to be unsteady. The butterfly shaft was known to be near a resonant condition. Review of film shows shaft is whipping. The average butterfly exciting frequency was taken to be 626 cps. Fastax No. 30 (Run No. 49-10-14-14): Film Speed Butterfly Exciting Freq. frames/sec frames/cyc cps rem 2580 47.5 54 1620 3120 62 50 1500 4010 89 45 1350 4500 106 42 1260 4920 120 41 1230 4960 120 41 1230 The model was choked throughout run -but the flow was steady with no apparent bow shock nulsation. There apneared to be some expansive exhaust issuing from the model outlet. This exhaust oscillated at same frequency as the butterfly. Fastax No. 28 (Run No. 49-10-14-12) Film Speed Butterfly Exciting Freq. frames/sec. frames/cyc cps rpm 4890 91 54 1620 4950 113 44 1320 4800 142 34 1020 4650 201 23 690 4320 - O 0 The model was choked throughout run but the flow was steady with i I - _ -- -- 23

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN W-K I - -.48 Fastax No. 28 (Rua No. 49-10-4-12) Cont-td no apparent bow shock pulsation. There apoeared to be some expansive exhaust issuing from the model outlet. This exhaust oscillated at same frequency as butterfly, Fastax No. 27 (Run No. 49-10-14-l) Film Speed Butterfly Exciting Freq. frames/sec frames/eye cps r 5040 47.0 107 3210 5040 47.0 107 3210 4900 45.5 108 3240 4680 44.5 105 3150 4380 41.7 105 3150 4080 38.2 107 3210 3840 36.1 106 3180 3240 30.8 105 3150 2640 25.1 105 3150 The model was choked and the bow shock pulsed. However, the amplitude was too suall to make any frequency calculations. However, it is estimated that shock frequency was the same order of magnitude as butterfly frequency. Fastax No. 29 (Run No. 49-10-14-13) Film Speed Butterfly Exciting Freq. frames/sec. frames/cye cps rpm 5040 22.7 222 6660 4920 22.0 224 6720 4800 21.5 223 6690 4560 20.3 224 6720 4320 19.25 224 6720! 1 24

AERONAUTICAL RESEARCH CENTER -UNIVERSITY OF MICHIGAN Fastax No. 29 (iun No. 49-10-14-13) Cont'd Film Speed Butterfly Exciting Freq. frames/sec, frames/eye cps rpm 3950 17.5 226 6780 3600 15.7 229 6870 3240 14*1 230 6900 2880 12.3 235 7050 The model was choked and bow shock pulsed. However, the amplitude was too small to make any frequency calculations. It is estimated that shock frequency was the same order of magnitude as butterfly frequency. Also, it appeared that bow shock pulsation amplitude was greater than that for Fastax No. 27. See Figure 12. Fastax No. 19 (Run No. 49-10-14-2): Film Speed Butterfly Exciting Freq. frames/sec frames/cyc cps rpm 5040 15.0 336 10,080 5040 15.1 334 10,020 4920 14.7 335 10,050 4800 14.4 333 9,990 4500 13.4 336 10,080 4260 12.6 338 10,140 3820 11.4 335 10,050 3360 10.0 336 10,080 3000 9.0 333 9,990 The model was choked and bow shock pulsed. However, the amplitude was too small to make any frequency computations. It is estimated that shock frequency was the same order of magnitude as butterfly frequency. -- -- ---- --- 25 -- -- --

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN'' -^~~ --- I W M4-148 - - Fastax No. 26 (Hun No. 49-10-14-10) Film Speed Butterfly Exciting Freq. frames/sec frames/cyc cps rpm 4920 4.9 1003 30,090 4920 4.9 1003 30,090 4740 4.8 987 29,610 4500 4.6 979 29,370 4320 4.45 971 29,130 3960 4.25 932 27,960 3720 4.1 908 27,240 3370 3.9 864 25,920 3000( 3.65 822 24,660 2520 3.4 741 22,230 1800 3.1 580 17,400 1560 3.0 520 15,600 The model was choked and bow shock nulsed. The amnlitude of pulsation was very minute. Therefore, no shock frequencies were calculated. It was estimated that shock frequencies were of same order of magnitude as butterfly frequencies. Fastax Nos. 15 and 24 (Run Nos. 49-10-13-5 and 49-10-14-7): In these runs the butterfly was stationary. The model was choked but no shock pulsation was evident. Fastax Nos. 20, 21, 22, 23 (Run Nos. 49-10-14-3, -4, -5, -6): In each instance the presence of the i.rta screens caused the model to be choked. However, there was no noticeable shock pulsation. It appeared that the bow shock was displaced upstream with increased solidity ratio of screens used. — ~ ~ ~ ~ ~~ - - - - -- P. - _- - - PV -- - - I - -- - -- 26

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN WTM-148 Data from Massa Microphone: Oscilloscope Film No. 49-10-14-1: Calibration curve (crest to trough): 0.1 psi = 0.13 in. The pressure trace shows no periodicity - only noise. The pressure differential is 0.1 osi. The butterfly was stationary in its most open position. See figure 9. Oscilloscope Film No. 49-10-13-6: Calibration curve: 1.0 nsi = 0.27 in. The butterfly exciting frequency was 237 cps. The pressure wave frecuency was 237 cps. The pressure wave differential was 2.7 rsi. The high Dressure side of the wave went slightly off the record. However, this was taken into account in measuring the differential. The maximum film speed was 59,40 in/sec. See Figures 9 Pnd 12. Oscilloscone Film No. 49-10-13-3: Calibration curve: 1.0 nsi = 0.17 in. The intensity of the 120 cps timing pips and butterfly frequency nips was too weak to nrovide a basis for any frequency measurements. Knowing the nominal film speed as 60 in./sec. the pressure wave frequency was estimated as 358 cps. It is certain that the butterfly was rotating. The pressure wave differential was 0.37 psi. See Figure 9. Oscilloscope Film No. 49-10-13-7: The exact calibration is doubtful. It was not recorded at the time of the run. Later questioning of the oscilloscope operator nroduced evidence that the calibration was 1.0 psi = 0.27 in. On this basis the pressure wave differential was 1,85 psi. The 120 cns timing pins and 27

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN --'"' WM, - butterfly were illegible. From the nominal film speed of 60 in./sec. a pressure wave frequency of 375 cps was estimated. It is certain that the butterfly was rotating. See Figure 9. Oscilloscope Film No. 49-10-14-9: Calibration curve: 0.1 nsi =09 in. The butterfly exciting frequency was 923 cps. The nressure wave is somewhat obscure but quite regular. The calibration should have been in 1.0 psi range obaerviag the maxima and minima of the trace. Nevertheless, it can be said that the pressure wave differential exceeds 0.85 psi. Even though the pressure trace is obscure it is certain by inspection that the pressure wave frequency is also 923 cps. See Figure 9. Near the end of the record the butterfly decelerated from 923 cns to 570 cps. It is quite interesting to watch the pressure wave change shape as the butterfly slows. The pressure wave differential decreases as the butterfly frequency decreases. At butterfly frequency of 630 cps the pressure wave differential is approximately 0.5 psi. This value agrees quite well with pressure wave differential of 0.57 osi at butterfly exciting frequency of 628 com obtained during Run No. 49-10-13-1. The butterfly diameter -was 1.25 inches in either case. During this region of butterfly deceleration it proved impossible to measure pressure wave frequency since the wave pattern changed so rapidly. Oscilltosope Film No. 49-1013-2: Record was void because, of operating difficulties. I Oscilloscope Film No. 49-10-13-1: Calibration curve: 1.0 nsi = 0.175 in. There were no 120 cps 1 r " 28

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN TWML48 timing pips or butterfly frequency pipe. Knowing that the nominal film speed was 60 in./sec. the oressure wave frequency was estimated as 628 cps. It is certain that the butterfly was rotating. The pressure wave differential was 0.57 psi. Oscilloscope Film No. 49-10-14-14: Calibration curve: 0.1 psi = 0.195 in. The butterfly exciting frequency was 50 cps. The oressure trace is mostly noise. There are intervals, however, which display wave periodicity of approximately 750 cps. During these intervals the maximum pressure wave differential is about 0.062 psi. It seems there is no correlation between butterfly position and the appearance of these 750 cps intervals. See Figures 10 and 14. Oscilloscope Film No. 49-10-14-12: Calibration curve: 0.1 osi = 0.13 in. The butterfly exciting frequency is 56 cps. The pressure trace is mostly noise. There are intervals, however, which display wave periodicity of annroximately 750 cps. i)uring these intervals the maximum pressure wave differential is about 0.075 psi. There seems to be no correlation between butterfly position and the appearance of these 750 cps. intervals. See Figure 10. Oscilloscope Film No. 49-10-14-11 Record was void because of operating difficulties. Oscilloscope Film No. 49-10-14-13: Calibration curve: 0.1 psi = 0.09 in. The butterfly exciting - -- -- 29 -

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN i — -- -' - W~frahe ---— T~1148 frequency was 218 cps. The pressure wave frequency was 218 cps. The pressure wave differential was 0.245 DSi. See Figures 10 and 12. Oscilloscope Film No. 49-10-14-2: Calibration curve: 0.1 nsi = 0.08 in. The butterfly exciting frequency was 336 cps. The pressure wave frequency was 336 cps. The pressure wave differential was 0,200 pal. See Figure 10. Oscilloscope Film No. 49-10-14-10: There was no calibration curve. During this run the butterfly was made to accelerate from 0 to 1050 cps (31,500 rpm) in annroximately 2.35 seconds. The velocity and acceleration characteristics of the butterfly as taken from the film are tabulated as follows: Velocity - time Acceleration - time Butterfly Exciting Butterfly Ex- Butterfly a/a10O Time Freq. Time citing Freq. Acceleration sec. sec. Xcp x120 cps x120 cps 7120 sec. % 0 0 1.0 100 51.9 100 1.0 100 4.3 200 36.7 71 4.3 200 6.8 275 23.6 46 8.0 300 10.3 365 28.6 55 11.7 400 11.7 400 22.8 44 14.0 450 16.3 475 12.4 24 18.0 500 20.7 550 22.6 44 20.7 550 25.3 635 14.3 28 23.0 600 30.3 693 9.1 18 26.6 650 37.8 740 4.2 8 31.0 700 40.3 755 8.1 16 39.7 750 42.8 780 15.2 29 43.9 800 45.3 810 5.4 10 51.7 850 51.7 850 4.8 9 65.7 900 65.7 900 2.4 5 30

AERONAUTICAL RESEARCH CENT:ER w — UNIVERSITY OF MICHIGAN -—;- ~wrTM-148Oscilloscope Film No. 49-10-14-1lt: Cont'd In the above table alo0 is the acceleration at butterfly frequency of 100 cps. The table carries to 900 cps only, because higher frequencies were accompanied by a complex pressure wave whose frequency was impossible to ascertain accurately. The pressure wave frequency clearly follows in magnitude the butterfly frequency ur to 900 cps. See Figures 7B and 11, Even though no quantitative measurement of the pressure differentials was possible, qualitatively there was considerable information. The pressure wave differential variation with butterfly exciting frequency is tabulated below. This information was not taken directly from the film but from a print of the film magnified 2.5 times. Butterfly Ex- Pressure..Wave A. Butterfly Ex- Pressure Wave Am citing Freq. Differential Ah3,citing Freq. Differential i^ cps inches % cps inehes % 0.10 5 600.55 27 100.12 6 625.75 37 150.27 13 650 1.33 66 200.36 18 675 1.86 92 250.48 24 700 2.02 100 270.56 28 710 1.82 90 300.43 21 720.61 30 340.35 17 730.68 34 380.44 22 760 1.07 53 400.40 20 800 1.07 53 450.35 17 850 1.18 58 500.35 17 900.90 45 550.46 23 The theoretical closed tube natural frequency of the model is 315 cps. On this basis the peak pressure should have occurred at apDroxi31

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN. —-A — -----.Wt38 mately the same butterfly exciting frequency. There is a peak at 270 cps. Doubtlessly, the magnitude of it has been greatly affected by the high acceleration of the butterfly at that frequency. Previous tests on this same model showed that the measured natural frequency was about 85% of theoretical. In this case 270 cps is also about 85% of 315 cps. The much higher pressure differential peak at 700 crs is probably the third harmonic showing up. At this frequency the butterfly acceleration is much lower. It is interesting to note that the oressure wave patterns at 220 and 340 cps agree quite well with the steady butterfly frequencies of 218 and 336 cps reported for Oscilloscope Film Nos. 49-10-14-13 and 49-10-14-2. The model configurations were identical in each instance. See Figures 7A, 7B and 11. Ocilloscope Film No. 49-10-13-5: This record consisted of noise only. The pressure wave differential was negligible. Oscilloscope Film No. 49-10-14-7: Calibration curve: 0.1 psi 0.11 in. Butterfly is stationary. The pressure trace is mostly noise. However, there are intervals which display periodicity of 700 - 750 cps. During these intervals, the maximum pressure differential was about 0.1 psi. Near the end of the record the butterfly closed with no apparent change in wave pattern. Oscilloscope Film No. 49-10-14-8: Calibration curve: 0.1 psi = 0.08 in. The useful oart of the record is very short. The rest is a pressure trace during the tunnel stopping ___

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN I —------------- WEM-148 ---- -— * ----- process. Before tunnel stopping, the pressure trace looked very much like that for Run No. 49-10-14-7. The nressure wave differential is 0.1 psi. Oscilloscope Film No. 49-10-12-1: Calibration curve: 1.0 Dsi = 0.19 in. In this run the Massa microphone was isolated from the airstream by a wax plug. This was done in order to check the noise level of all operating equipment. Butterfly frequency was nominally 270 cps. The pressure trace has no measurable noise. However, there are low amolitude peaks of anproximately 0.1 psi. These peaks are all troughs (low Dressure) with no crests when compared to the mean line. They show little periodicity. Oscilloscope Film No. 49-10-.1-2: Calibration curve: 1.0 psi = 0.19 in. The Massa microb*ione was isolated fromi the airstream by the same method and for the same purpose as in Run No. 49o0-12-1. The nominal butterfly frequency was 600 cp.s Again, the trace showed pressure troughs and no crests. The maximum differential of these troughs was 0.2 psi. There is a slight amount of noise pick-up. Oscilloscope Film No. 49-10-14-33 Calibration curve: 0.1 nsi = 0.27 in. butterfly assembly was not installed. The 95% solid flow choking screen was in, place. The pressure wave pattern showed considerable noise. During certain intervals there seems to be some pressure wave neriodicity but it is unsteady. During these intervals the pressure wave frequency is approximately 750 cps. The maximum pressure wave differential is 0.045 psi. See Figures 13 and 14. 33

AERONAUTICAL RESEARCH CENTER UNIVERSITY OF MICHIGAN WM-148 Oscilloscope Film No. 49-10-14-4: Calibration curve: 0.1 psi = 0.27 in. Butterfly assembly was not installed. The 87% solid flow choking screen was in place. The wave pattern showed high frequency noise. Quite frequently there occurred intervals during which the pressure wave was periodic. These intervals do not, appear to be periodic in their occurrence - the whole pattern is unsteady. During the intervals of periodicity the wave frequency is approximately 700 cps. The maximum pressure differential varies between 0.04 and 0.06 psi. See Figure 13. Oscilloscope Film No. 49-10-14-5: Calibration curve: 0.1 psi - 0.27 in. Butterfly assembly not installed. The 80% solid flow choking screen was in place. The record was identical with No, 49-10-14-4 except that the maximum pressure wave differential varied from 0.05 to 0.10 psi. Oscilloscope Film No. 49-10-14-6: The record was void because of operating difficulties. _ -- --- - ---- _-% - - __

AERONAUTICAL RESEARCH CENTER UNIVERSITY OF MICHIGAN WTM-148 VII. WRAPHS AMD PHOTO(GAPIS OF SIGIItJCAlNT DATA Outside of Figures 6, 7, 7A, and 7B, which are plotted data, the remaining figures In this section are photographic reproductions of portions of important Fastax and oscilloscope film. It is felt that this particular selection includes only those runs which were fruitful. The several processes involved in king these photographs doubtlessly produced much distortion in them. Thus, no effort should be expended to take accurate data from them. One will find in checking certain film strips that the frequency data cited in the label do not agree with the record, even allowing for film distortion. Thes data list avreae frequeny aginitudes. Therefore, the particular film strip chosen for best reproduction purposes is not guaranteed to agree Proper manner to read the film is from left to right. The pressure tracks on the oscilloscope film were situated in such a way that the waves approaching peaks correspond to increasing static pressure sand the waves approaching troughs correspond to decreasing static pressure. - -- 55 - ---- ---- -. --- ---

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0 BUTTERFLY;EXciT,' —-—'.%V, —-G — 1,50 C.=,,$ PRIESSUIRE WAVP FIRE UENCY D0 —. — B,,',P:RESSUl" —,R —'E WAVE....................................... DIFFERENTIAL.,062. I R;i ------- --- ----------.......... ------- ---------------------- ---......................................................................................................................................................................... I......................................................................................................... I...................................................................................................................................................................................................................................................................... -........................................................................................................................................................................................................................................................................................... RUN Na 49- 10- 11.4-12 SI TTERFI EX01"T'ING F.-IRECIL N 56 01FIS............:Ss.1, -E pRil- R.-Ill WAVE FREQUENCY DOUBT!"" PRESSUIR. E WAVE Itw..................................... D FFERR 71AL.- 5 IOSTI - - --------- - ------.................................................................................................. ----------------........................................................................................................................................................................................................................................................................................................................................................................................................................... -.................................................................................................................................................................................................................................................................................................................................................................... I...... I....................................................................................................................................................................................................................................... RUN NO. 49-10-14-15 BUTTERFLY EXCITIN FREC'U"EMENCY, 2`8 PIR-REESS'U"IRRE WAVE -Cli 218 CPS PIRIESSURE WAVE........................................... 0 -.F F E R. E 11.71, - All.2-45- iPS-1.................................................................................................................................................................................................................................................................................................................................................................................................................................................................... -----------------------..................... R N' NO. 49-10-14-2 BUTTEIRFILY. EXCITING --- - ----- - ---- FREQUEENNG Y.), 556:0F S PRESSUR S ^.Y,E 356 CPS PRI-ES-SU:.-IRE WAVE...............................................:E E ------ - - - ------- ------ 'FF R NT?,-.............. - -------------------- RE IGu S"w* OSC L-0-ir: SS RIS WAV AT:M,:N -BIU::LY 0: MON 0 N AT I 0 -N A VAR CT *r,:=-:RF!i V' Di 7ii." A,,- M` IE T I.-R. So NOIA: AL ZZt.:V: A........................................................................... I g........................ - - --------------.....~. CZ S.................!8.8..... 01 l I I m 1 I I m~~~~.................................... __,............................................................................................................................... - -----............. -07 - ItI E WT I1F:O 75 1 —i -NIH S.41

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AERONAUTICAL I AX RESEARCH CENTER - UNIVERSITY WB-148 OF PMCHIG (OAN I. - -:. n 1. Parchdy. Ask _.lm Univ rltty of Michi ronauical Reserch Cntr WTM109, WillW Rm, 149,9 2. Jacob, D M, KI, Bo o r T*10~e naa~~ ple } Uhteiersity of Miobin Aernautical ebearoh CQoter Mz-36, Willov Rim, 19)9. 3. a Sck, PAL l D. Van Nostrand Co., Nov York, 1935. 4. Adir, A. A Variation th Mach.r of Static A Total Pr,1exrrs t=ro$.; i..r._yo: s 8o~ _: N_,A.AC.A. Wart/i Report L-23, WasByngton, 19S6. I - -- -- -- 46 -- --- —

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN I. w ulm-148 -- -. APPENDII A KATIRAL. EBQO CMP7TATIO The natural frequenoy (Reference 3): epressiton for an air column in a rigid tube is f = ocps 2L where: n = 1,2,3,... identifying the harmonic for open tubes n = i, 3/2, 5/2,... idenifying the harnanic for closed tubes a = local speed of sounm, ft/sec L = effective length of tube, ft Assuing the ram-jet as a closed tube, the physical length of the tube will be equivalent to the distance from nodel inlet to axis of butterfly rotation. This distanoe is 10.062 inches. Reference 3 suggests adding 30% of the tube daiamter to the pbysical length in order to obtain effective length. Thus, L = (10.062) + (.3)(1.5) = 10.51 in. The speed of sound expression is a =..kTs- 49 F4T ft/sec where T is static temperature in R Assuming that the Mach Number of model internal flow is 0.3, then T- = 1 +. 1 + T 2 2 (,3)2 1.02 where To is reservoir temperature The average To for these tests was To = 58 + 460 = 5l8~R Therefore, T = = 507 R 1.02 Also, a = 49 5 = U03 ft/sec -- *7 -- - ----

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN The theoretical closed tube natural frequency of the model is, therefore, fc (2)( o110 ) 1 5 a (2)(10.51) 1 cp where n = i If it is wished to calculate the natural frequency of model as an open tube, then the physical length is 12 inches. The effective length turns out to be L = (12) + (.3)(1.5) = 12.45 inches Assuming all other conditions to remain unchanged except n = 1, the theoretical open tube natural frequency of model is, therefore, f (= )(110.)(12) _= 1 c_ o (2)(12.5) -5.. cs -- - 48

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN I'''' -- / I 1"WT2-148,, aPIRDI1 B SCIEE CHKING CCKPUTATIONS The ram-jet blockig model testa reported in reference 1 showed that the model obviously Va choked vhea a olid plug wa used (coadition of bow ashoock pulsation). SThe plug with the sallest orifice (13/16" dia.)which W!v ued did not choke the model nor did it cause the shoc pattern to pulsate. Tho solidity of this 13/16" di&. plus is Ao 8 1 --- At where: 8 = plug solidity, % Ao= orifice area, in.2 At= interl area of wodel,ia2 - (.121 In thes tests it wa estimated that the Mach Number upstream of the plug was between 0.2 amd 0.3. As a rough apprzximation it rvas aasumd that the choking characteristics of plugs with orifices were similar to high density or fine mesh screens. Reference 4 reports results indicating that choking Mach Number in a tube is a function of the acreen solidity. On this basis, it was thg that us in flcw choking screens with solidity ratios greater than the 71% solid plug would choke the mdel and induce pulsation of the bow shock. From reference 4 for screens s = (M + n) d - md2 = 1 - - where: S = a = d = Mc= (.579) LI+ (.2) MJ O Screen solidity ratio, % Mesh of shute, wires/inch Mesh of wvrp, wires/inch Diawter of wire, inches Mach Number before screen for choking at screen.'9 -- - -- --- --

AERONAUTICAL RESEARCH CENTER - UNIVERSITY OF MICHIGAN -.-. — I.. W. -148 - -.-. I The screens chosen for this test program were as follows: a. One-60 x 50 mesh, 0.010" dia. twilled Monel wire Sa = (60 + 50) (.01) - (50)(60)(.01)2 = (1.10) - (.5)' 80% b. One-60 x 55 mesh, 0.011" dia. twilled Monel wire Sb - (60 + 55) (.011) - (55)(60)(.011)2 = (1.265) - (.399) - 87% c. One-30 x 150 mesh, 0.0085" x 0.007" dia. Monel wire This solidity ratio could not be calculated but was estimated to be 95%. I 50