AEDC-TR ABLATION TESTING IN HOT AND COLD COAXIAL JETS - PHASE I, COLD FLOW FEASIBILITY TESTS. April 1970

Transcription

1 ^ ABLATION TESTING IN HOT AND COLD COAXIAL JETS - PHASE I, COLD FLOW FEASIBILITY TESTS R. D. Herrn ARO, Inc. April 1970 This dcument has been apprved fr public release and sale; its distributin is unlimited. PROPULSION WIND TUNNEL FACILITY ARNOLD ENGINEERING DEVELOPMENT CENTER AIR FORCE SYSTEMS COMMAND ARNOLD AIR FORCE STATION, TENNESSEE

2 mms When U. S. Gvernment drawings specificatins, r ther data arc used fr any purpse ther than a definitely related Gvernment prcurement peratin, the Gvernment thereby incurs n respnsibility nr any bligatin whatsever, and the fact that the Gvernment may have frmulated, furnished, r in any way supplied the said drawings, specificatins, r ther data, is nt t be regarded by implicatin r therwise, r in any manner licensing the hlder r any ther persn r crpratin, r cnveying any rights r permissin t manufacture, use, r sell any patented inventin that may in any way be related theret. Qualified users may btain cpies f this reprt frm the Defense Dcumentatin Center. References t named cmmercial prducts in this reprt are nt t be cnsidered in any sense as an endrsement f the prduct by the United States Air Frce r the Gvernment.

3 A E DC-TR ABLATION TESTING IN HOT AND COLD COAXIAL JETS - PHASE I, COLD FLOW FEASIBILITY TESTS R. D. Herrn ARO, Inc. This dcument has been apprved fr public release and sale; its distributin is unlimited.

4 FOREWORD The research reprted herein was spnsred by the Arnld Engineering Develpment Center (AEDC), Air Frce Systems Cmmand (AFSC), under Prgram Element 62201F, Prject 8950, Task 12. The results f research presented in this reprt were btained by ARO, Inc. (a subsidiary f Sverdrup & Parcel and Assciates, Inc.), cntract peratr f the AEDC, AFSC, Arnld Air Frce Statin, Tennessee, under.cntract F C The wrk was perfrmed frm July 1968 t Nvember 1969 under ARO Prjects PW5903 and PW5003, and the manuscript was submitted fr publicatin n February 2, This technical reprt has been reviewed and is apprved. David C. Reynlds Harry L. Maynard 1st Lt, USAF Clnel, USAF Research Divisin Directr f Plans Directrate f Plans and Technlgy and Technlgy li

5 ABSTRACT An investigatin was cnducted t determine the feasibility f extending the capability f ablatin test facilities by surrunding the high enthalpy flw with a caxial cld air jet. The investigatin included bth analytical and cld flw experimental studies. It was determined that the caxial flw technique is extremely prmising, ffering the ptential f easily dubling the facility mdel size capability. Results f the cld flw experimental tests and criteria fr applicatin f the technique t high enthalpy facilities are presented. 111

6 CONTENTS Page ABSTRACT iii NOMENCLATURE vii I. INTRODUCTION 1 II. PROBLEM AREAS AND ANALYTICAL CONSIDERATIONS 2. 1 Aerdynamic Interactins Hardware Cnsideratins Viscus Mixing alng the Dividing Streamline 5 IE. COLD FLOW TEST APPARATUS 6 IV. EXPERIMENTAL RESULTS AND DISCUSSION 4. 1 Caxial Flw Fields Reentry-Type Mdel Tests Cne Mdel Tests 10 V. CONCLUDING REMARKS 11 REFERENCES 12 APPENDIX ILLUSTRATIONS Figure 1. Applicatin f the Caxial Flw Technique t Ablatin Testing a. Present Testing Technique 15 b. Caxial Flw Testing Technique Caxial Flw Nzzle Assembly Designed fr Arc-Heater Applicatins Effect f Caxial Flw (Cld Air) n the Spreading f the Velcity Mixing Regin fr Typical High Enthalpy Applicatins Cmparisn f Experimental Data with Theretical Calculatins fr the Spread f the Velcity Mixing Regin Caxial Flw Nzzle Assembly and Reentry Bdy Mdel fr the Cld Flw Tests Caxial Flw Nzzle and Reentry Bdy Installatin Caxial Flw Nzzle Assembly Dimensins and Cnturs a. Nzzle Assembly 21 b. Nzzle Crdinates 22

7 Figure Page 8. Pitt Pressure Distributin f the Caxial Flw Fields, PH/P,,, = 1 a. M c = b. M c = Stagnatin Temperature Distributin f the Caxial Flw Field, M c = 2. 0 and Pjj/p^ = Schlieren Phtgraphs f the Caxial Flw Fields, a. M c = b. M c = Cmpilatin f Mdel and Pitt Prbe Data n the Nzzle Centerline Cmparisn f Thery and Wind-Tunnel Data fr a Sphere-9-deg Cne Bdy Mdel Pressure Distributin withut the Caxial Air Jet, Pfj/p^ = Schlieren Phtgraphs f the Flw Fields Crrespnding t Fig Mdel Pressure Distributins withut the Caxial Air Jet, Pfj/p^ = Mdel Pressure Distributins with the Caxial Air Jet, M c = 2.0 andppj/p^. = Mdel Pressure Distributin with the Caxial Air Jet, M c = 2.5, PH/P^ = Schlieren Phtgraph f the Flw Field Crrespnding t Fig. 17, M c = 2.5, Pfj/p,,, = Mdel Pressure Distributins with the Caxial Air Jet Simulating Tests in a Pressurized Tank, M c = 2. 5, PH/P i Schlieren Phtgraphs f the Flw Fields Crrespnding t Fig. 19, M c = 2.5, Pfj/p^ = Effect f Axial Lcatin n the Mdel Pressure Distributin with the Caxial Air Jet, M c = 2. 5 and PH/P = 6 37 OD VI

8 Figure Page 22. Schlieren Phtgraphs f the Flw Fields Crrespnding t Fig. 21, M c = 2.5, Pjj/Pj,, = Effect f the Caxial Air Jet n the Pressure Distributins n a Sharp 10-deg Cne, Pj^/P = 6 and x/r e = 0 a. M c = b. M c = Effect f the Caxial Air Jet n the Pressure Distributins n a Sharp 10-deg Cne, Pjj/P = 1» x/r e = 0, and M c = 2. 5? 42 NOMENCLATURE C n Pressure cefficient, [ -E- - 1 ) /-J M P 2 2 \PH / / P t 2 \ y 2 Cp Stagnatin pint pressure cefficient, I 1 J /-r- M M Mach number p Flw static pressure r prbe r mdel pressure p t Ttal pressure p t Pitt pressure p Ambient r test cell pressure CD r Radial distance nrmal t jet centerline r e Nminal central nzzle exit radius, 0. 5 in. r n Reentry mdel nse radius, in. s Distance measured frm the nse alng the reentry mdel surface T{ Stagnatin temperature measured by the traversing prbe T - Central stream ttal temperature U Flw velcity x Distance frm the central nzzle exit measured alng the nzzle axis, psitive dwnstream vu

9 ^n T 6 6 Distance frm the tip f the 10-deg cne mdel measured alng the mdel axis, psitive dwnstream frm the tip Rati f specific heats Flw deflectin angle, see Eq. (1) Angle between the flw axis and a line nrmal t the mdel surface SUBSCRIPTS c H Cld air r annular flw cnditins High enthalpy r central flw cnditins Vlll

10 SECTION I INTRODUCTION The requirement fr studying ablatin and ther phenmena assciated with very high-speed flight has led t the develpment f a variety f small, high enthalpy, high pressure test facilities. The very large pwer requirements as well as prblems encuntered in develping large r multiple-arc heaters have limited the size f these facilities. Since the facility is perated at high stagnatin pressures and exhausts t atmspheric pressure, a nnunifrm expanding flw field exists ver much f the mdel nse, beginning with the intersectin f the nzzle Mach wave with the mdel, as shwn in Fig. la, Appendix. Therefre, fr nse cne ablatin tests f the types recently cnducted, nly a limited regin f unifrm flw is btained. One methd f eliminating the expansin wuld be t place the facility and the mdel in a pressurized tank. Hwever, this presents many serius peratinal and hardware prblems. Anther methd, as discussed herein, is t surrund the high enthalpy flw with a caxial cld air jet with static pressures matched at the interface. The caxial jet will eliminate the expansin at the high enthalpy nzzle exit, thereby prviding the crrect flw field ver a much larger regin f the mdel. This is typically shwn in Fig. lb. Als fr ablatin testing f blunt bdies, a prper matching f the cld airflw wuld impse the crrect flw field ver a bdy very large relative t the high enthalpy flw nzzle. Valid ablatin data culd then be btained until the mixing f the flws finally reduces the enthalpy f the mdel bundary layer. This caxial flw technique wuld therefre imprve the quality f the flw field, permit the testing f larger mdels, r reduce the facility pwer requirements. The bjective f the investigatin reprted herein was t determine the feasibility f the cncept and t develp the required criteria fr applying the technique t high enthalpy test facilities. The investigatin included bth analytical and cld flw experimental studies. SECTION II PROBLEM AREAS AND ANALYTICAL CONSIDERATIONS In the develpment f the caxial flw cncept, three majr prblem areas arise. They are (1) the aerdynamic interactin f the tw flws with the mdel, <2) the very real hardware prblems arising in applying

11 the technique t a high enthalpy facility, and (3) the viscus mixing between the flws. The prblems will be discussed further in this sectin. 2.1 AERODYNAMIC INTERACTIONS Prblems with the aerdynamic interactin f the tw flws arise.nt nly in develping and bringing the tw flws tgether withut majr disturbances, but als in determining criteria fr "tailring" the flws t btain a satisfactry aerdynamic flw field n the test mdel. T eliminate a shck and expansin at the junctin f the flws will require the flws t have equal static pressures at the nzzle exits. But even if equal pressure, inviscid, unifrm flw frm each f the nzzles and a zer-thickness nzzle wall culd be btained, the caxial flw interactin with the mdel flw field must still be cnsidered since the tw flws will have different gas specific heat ratis Slender Bdies Fr slender bdies, the primary benefit t be btained frm the caxial cld air jet is t mve the flw expansin t atmspheric pressure frm the high enthalpy nzzle exit t the uter cld air nzzle exit. Therefre, depending upn the relative size f the jets, a significantly larger regin f the mdel may be tested. Hwever, a prblem arises in that at the intersectin f the mdel shck and the high enthalpy jet bundary, a reflected shck r expansin must ccur unless the pressure change and the angle change fr the tw flws are exactly matched behind the mdel shck. This is shwn belw in the sketch f an idealized flw field. Cld Air Slip Line High Enthalpy Flw / Shck r Expansin Mdel

12 Fr tw-dimensinal expansins r cmpressins (which must als be valid lcally at the slip line-shck intersectin) 1 thrugh small angles the fllwing relatin hlds: ^ - ±-gla6 * r»* (r+1)m * I 4( f-» (*6) a P -/M^-l 4(M 2-1) ± higher rder terms Therefrej fr small slender bdies a matching f the linearized relatin fr Zip/A6 will apprximate the desired matching near the slip lineshck intersectin. This requires a "tailring" f the tw flws suchthat (i) T/M 2 -I /. VM 3 -IL.. (2) 'cld 'high air enthalpy jet jet in additin t the requirement fr equal static pressure at the nzzle exits Large Blunt Bdies The criteria f. Eq. (2) wuld nt be expected t give satisfactry results fr large blunt bdies where large flw deflectins are required. Hwever, if the crrect mdel pressure distributin can be btained, and the dividing streamline between the cld and the high enthalpy gas still be lcated utside the mdel bundary layer, the crrect test cn- ditins at the mdel surface will result. The exceptin, wuld be cases where gas radiatin cntributes a significant heat lad t the aft regins f the mdel. As will be shwn later, the mdified Newtnian thery gives a gd representatin f the pressure distributin ver the nse regin f blunt bdies. This relatin is C p C " cs 6 (3) p max Applying this relatin n each side f the dividing streamline between the tw flws as the flws apprach the mdel shck (cincident with the bdy fr Newtnian thery) establishes the requirement C P \ = S_ \ (4) ^max 'cld p max ' high air enthalpy jet jet

13 but since the static pressures f the tw flws are equal and the bdy surface pressure must be equal n each side f the dividing streamline, the criterin is established that the pitt pressure f the tw jets be equal. The required Mach number relatin fr the flws may be btained frm the Rayleigh pitt frmula: -[**?*] [ p *2 r ^im 2 l y- 1 r r+i P L * J I2r M - (y-l),2 ^ (5) Hwever, in practice, the desired relatinship may be readily btained frm flw tables crrespnding t the specific heat ratis f the tw jets. Restating, the criteria fr caxial flws ver large blunt bdies are and Pt L p) cld = P high air enthalpy jet jet 'cld -) p 'high air enthalpy jet jet (6) (7) It shuld be nted that the different criteria given fr slender and fr blunt bdies frtunately d nt result in drastically different Mach numbers fr the cld.airflws, at least fr high enthalpy flws with Mach numbers f interest fr ablatin testing. Als, bth sets f criteria result in a lwer Mach number fr the cld airflw than fr the high enthalpy flw. This requires a lwer ttal pressure and a lwer mass flw fr the cld air than wuld be required if the Mach number f the tw flws was equal. 2.2 HARDWARE CONSIDERATIONS During this investigatin studies were made f the prblems arising in designing, fabricating, and perating the caxial flw hardware. In these studies, tw majr prblems becme bvius. These are the very small size f the high enthalpy flw nzzle and the necessity fr cling the surfaces expsed t the high enthalpy flw. Ideally, the hardware shuld develp caxial unifrm flws with n disturbances generated by bringing the flws tgether. Obviusly, this

14 AEDC TR cannt be accmplished. The finite thickness at the nzzle exit causes a flw expansin and cmpressin analgus t the flw ver a backward facing step. This step becmes physically mre significant as the size f the hardware is decreased. The design f the nzzles shuld bring the flws tgether at as small and as near equal angles as pssible. Hwever, in rder t water cl as much f this nzzle lip as pssible, the nzzle must have a large wall angle. Als, the high enthalpy flw nzzle shuld be shrt t minimize the heat transferred t the nzzle. Frtunately, fr the testing f blunt bdies, even large flw disturbances at the nzzle exit are weak when cmpared with the blunt-bdy shck. f Figure 2 shws a preliminary design fr an arc-heater applicatin. The lack f space between the nzzles fr water cling is evident. Water cling fr all f the lip between the nzzles is nt pssible. Hwever, sme backside cling is btained frm the cld airflw and sme axial cling t the water passage will be btained. These cnsideratins place sme lwer limit n the Mach number and n the physical size f the high enthalpy flw. The design studies d shw that hardware can be fabricated fr an arc heater with a nzzle thrat as small as 3/8 in. in diameter and an exit Mach number f Nearly all f the prblems discussed becme mre tractable as the size f the hardware is increased. In particular, increasing the size f the nzzle fr the high enthalpy flw and a careful design ptimizatin shuld permit a larger annular aiflw and/r a lwer Mach number fr the high enthalpy flw. A lwer Mach number fr the high enthalpy flw wuld be desirable where a very high mdel stagnatin pressure is required. 2.3 VISCOUS MIXING ALONG THE DIVIDING STREAMLINE Even if the crrect aerdj'namic matching is btained, viscus mixing f the tw flws will invalidate the flw field at sme pint dwnstream n the mdel. Much effrt has been directed by many investigatrs t the prblem f tw-stream mixing. Hwever, the present prblem is that f the mixing f cmpressible, nnisenergetic, threedimensinal streams f different gases with initially disturbed flw prfiles, and therefre a mst difficult prblem t handle analytically. In additin, the influence f the mdel shck system n the mixing prcess is nt knwn. Current analytical techniques have been studied and an estimate made f the mixing prcess fr high enthalpy, caxial flw applicatins. The methd used was an integral technique develped by Krst (Ref. 1) fr cmpressible tw-stream mixing with a Prandtl number f ne. Estimates by Lamb (Ref. 2) were used fr the effects f nnisenergetic

15 mixing n the required similarity parameter. Results f a sample calculatin are shwn in Fig. 3 fr different values f the velcity rati between the tw streams. It shuld be nted that {1) the spread f the velcity mixing regin in the high enthalpy flw is nt large, and (2) the cld airflw des reduce the spread f the mixing regin int the high enthalpy flw. This relatively small rate f grwth f the mixing regin makes the caxial technique appear feasible; hwever, it lacks experimentally verified values fr the similarity parameter which gverns the spread rate. Therefre, unpublished experimental pitt pressure surveys btained in an arc heater were analyzed. These surveys were cmpared with the theretical calculatins fr the case f single-stream mixing and the results are shwn in Fig. 4. The quite gd agreement between thery and experiment gives sme cnfidence in the theretical calculatins and in the values chsen fr the similarity parameter. In general, it des nt appear that the viscus mixing will invalidate mdel ablatin data until well back n the test mdel. SECTION III COLD FLOW TEST APPARATUS T verify the caxial flw cncept and t prvide further insight int prblems t be encuntered in applying the cncept, cld flw experimental tests were cnducted. Cld flw tests were chsen partially because f the relatively high csts f high enthalpy flw experiments, but especially because f the extreme difficulty in btaining significant measurements in a high enthalpy flw. These tests were cnducted in the Prpulsin Wind Tunnel (PWT) 1-ft Aerdynamic Wind Tunnel (IS) mdified t be used as an evacuated test chamber. The cnfiguratins f the caxial flw nzzle assembly and the reentry-type mdel used in these cld flw tests are shwn in Fig. 5 and the installatin is shwn in Fig. 6. The central stream is carbn dixide gas heated t apprximately 800 R and with a nminal exit Mach number f Carbn dixide gas (CO2) was chsen t simulate the high enthalpy flw because its specific heat rati is representative f such flws. All calculatins fr the carbn dixide flw assumed a perfect gas with a specific heat rati f The annular air jet was unheated air at a stagnatin temperature f apprximately 480 C R. Tw different annular nzzles were used t give the air jet a nminal exit Mach number f either 2.0 r The carbn dixide ttal pressure was nminally 50 psia with the air stagnatin pressure usually set t

16 give equal static pressure at the nzzle exits. The test chamber culd be evacuated t permit peratin at an ambient pressure as lw as 70 psfa, thereby simulating the expanding flw field f a high pressurehigh enthalpy facility exhausting t atmsphere. The ambient pressure culd als be set equal t the nzzle exit static pressure, thereby simulating the prpsed peratin f high enthalpy facilities in a pressurized tank. Prir t designing the cld flw nzzle assembly, a preliminary design (Fig. 2) was made fr applicatin f the caxial flw cncept t a Linde 5-MW, N-4000 arc heater with a 3/8-in. thrat diameter nzzle. The nzzles fr the cld flw tests were then designed t be cnsistent with space and cnfiguratin limitatins f the high enthalpy applicatin. The size f the air jet relative t the high enthalpy jet is nt the maximum that culd be btained, but was selected t be cmpatible with the different air jet nzzles required by the different flw matching criteria. Once criteria fr the tw flws have been established, a careful design ptimizatin fr a particular facility shuld permit sme increase in the air jet size. The nzzles fr the cld flw tests are shrter than wuld be desired t develp unifrm, parallel flw but are typical f a high enthalpy facility applicatin. Bth the central CO2 and the annular air nzzles were designed by cmputer prgrams utilizing the methd f characteristics. N crrectins were made fr the nzzle bundary layer. The cnfiguratin and the design crdinates fr the nzzles are shwn in Fig. 7. Because f a fabricatin errr, the dimensins f the CO2 nzzle differ substantially frm the design values and therefre a set f "as built" crdinates are als presented. Tw pressure-instrumented mdels were used in the cld flw tests. One was a sharp 10-deg cne mdel and the ther a large hemisphere 10-deg cne, reentry shape mdel. Bth mdels have a 2-in. base diameter. The reentry shape mdel has a nse radius f in., which is the equivalent f a 1/2-in. nse radius mdel when the cld flw nzzle assembly is scaled t that typical f the 3/8-in. thrat diameter, 5-MW arc heater. Nrmally mdels n larger than l/4-in. radius are tested in these arc heaters. Bth mdels were tested at varying axial psitins as well as bth with and withut the annular cld airflw. Mdel pressures were measured n a mercury manmeter and recrded phtgraphically. An errr analysis based n a 95-percent cnfidence level shws the pressure data presented t be accurate t p/pt9 = ±^. 006 fr the reentry bdy data and t p/p^. = ± fr the 10-deg cne data.

17 In additin t the pressure mdels, pitt pressure and ttal temperature surveys were made f the nzzle flw field withut the mdels present. Als, schlieren phtgraphs f the flw field were taken bth with and withut mdels present. SECTION IV EXPERIMENTAL RESULTS AND DISCUSSION 4.1 COAXIAL FLOW FIELDS Prir t the mdel tests, pitt pressure and stagnatin temperature surveys were made thrugh the caxial flw fields. The results f these surveys are shwn in Figs. 8 and 9 fr cnditins where the ambient r cell pressure is equal t the nzzle exit static pressure. Schlieren phtgraphs f the crrespnding flws are shwn in Fig. 10. These data shw the tw streams t be f a generally gd quality with nminally the design Mach numbers. Bth the pitt pressure and the stagnatin temperature distributins shw very sharp bundaries between the ht CO2 and the cld airflw. There is very little mmentum r energy mixing between the tw flws, which is in agreement with predictins fr flws with nearly equal velcities. Althugh the stagnatin temperature distributins are very unifrm, the pitt pressure unifrmity is prer than hped fr. The nzzles were f an arc-heater-type design, being shrt t minimize nzzle heat transfer. The shrt design and the manufacturing inaccuracies previusly discussed resulted in the CO2 stream having a nnunifrm flw, particularly alng the nzzle axis. The axisymmetric design may prvide a "fcusing' 1 f wall disturbances n the nzzle centerline. This centerline nnunifrmity als becmes evident in the mdel stagnatin pint pressure data. Shwn in Fig. 11 is a cmpilatin f pitt prbe and reentry mdel stagnatin pressure data which emphasizes the axial variatin. The mdel stagnatin pressure data shwn have been shifted upstream by r e, which is the theretical mdel shck stand-ff distance. Mdel data are shwn bth with and withut the caxial airflw. Als shwn is the pressure near the nzzle exit as calculated by a methd-f-characteristics slutin fr the "as built" nzzle cntur. These data shw the centerline disturbance t be caused by the central nzzle and nt by the caxial airflw. Althugh the centerline flw is nt as unifrm as desired, it is generally as gd as that btained in archeated flws frm cntured nzzles, particularly after nzzle ersin has ccurred. 8

18 4.2 REENTRY-TYPE MODEL TESTS T evaluate the results f the mdel tests, an experimental r theretical basis f cmparisn is needed. Several wind tunnel studies f reentry bdies have shwn the mdified Newtnian thery t give very gd results frm the nse t near the junctin f the sphere and the cne. Figure 12 shws a cmparisn f this thery with wind tunnel data frm Ref. 3 fr cnditins very near thse f the current tests. Als shwn are the theretical values frm Refs. 4 and 5 fr 10-deg cnes, which the experimental data shuld apprach asympttically. The subsequent figures presenting the caxial flw data will shw the thery (crrected fr y = 1. 28) as a basis fr cmparisn. Because f the nnunifrm flw n the nzzle centerline, the caxial flw data are ratied t the pitt pressure fr unifrm flw with a specific heat rati f and a Mach number f 2. 5 instead f the measured stagnatin pint pressure. The results f tests withut the annular air jet are shwn in Fig. 13. Fr such a large mdel, the pressure rapidly falls ff t the ambient pressure, prviding a very limited regin f useful data. Schlieren phtgraphs crrespnding t these data are shwn in Fig. 14. One prpsal fr increasing the flw quality and the mdel size capability f present arc heaters has been t place the arc heater and the mdel in a pressurized tank. As shwn in Fig. 15, such a technique wuld prvide nly a small imprvement fr such a large mdel. The previus theretical analysis based n the mdified Newtnian thery (Sectin ) has shwn that the matching f the static and the pitt pressures wuld be required fr large blunt bdies, therefre requiring an airflw Mach number f fr the cld flw tests. Results f the tests with the annular airflw having the "incrrect" Mach number f 2. 0 are shwn in Fig. 16. A significant imprvement is seen ver the data previusly presented withut the air jet. Hwever, as expected frm the thery, the pressures are t lw ver the regin f the mdel that is influenced by the annular air jet. When the air jet Mach number is changed t 2.5, clse t the required 2.42, a remarkable imprvement is fund. The results f tests at an axial psitin typical f ablatin testing are shwn in Figs. 17 and 18. The annular air jet prvides the desired flw past the spherecne junctin f a mdel that is twice the size that can nrmally be tested. The technique therefre ffers the ptential f at least dubling the mdel size capability f high enthalpy facilities. Althugh it was nt evaluated in these tests, the caxial technique shuld give valid data even further aft n relatively smaller mdels. The decrease in pressure

19 aft f the junctin is caused by the expanding flw field riginating at the air nzzle uter lip, which wuld be eliminated in a pressurized tank. The results f tests simulating the tank, given in Figs. 19 and 20, shw that the desired flw field can be btained even further back n this large mdel. The results f the reentry mdel tests therefre shw that the flw matching criteria based n the mdified Newtnian thery (Sectin ) t be crrect fr large blunt bdies. The results f tests t determine.the effect f mdel psitin are shwn in Figs. 21 and 22. Tw effects are nted: (1) As expected, with the mdel very far dwnstream (x/r e = 5) the expansin frm the uter lip f the air nzzle strikes mst f the mdel causing the mdel pressures t be t lw. (2) When the mdel is very clse (x/r e < 1/2) the rise in pressure frm the mdel shck prpagates thrugh the mixing regin and causes a separatin f the flw fields. This is nted in the pressure dip at s/r n = 0. 8 fr the data at x/r e = 1/2. Hwever, neither f the phenmena is cnsidered t be a prblem in the actual applicatin f the technique. 4.3 CONE MODEL TESTS Tests were als cnducted with a 10-deg cne mdel t establish criteria fr the testing f small, slender bdies in caxial flws. As discussed in Sectin , the primary benefit expected frm the caxial jet is t mve the flw expansin dwnstream n the mdel and thereby prvide a significantly larger test regin n the mdel. That this result is in fact achieved is shwn in Fig. 23. These results shw the annular air jet t increase the valid test regin axially n the mdel frm apprximately ne nzzle exit radii t frm three t fur radii. Als, larger increases wuld be-btained by relatively larger annular air nzzles. The theretical pressure rati shwn is frm Refs. 4 and 5, crrected fr a specific heat rati f The deviatins abut the theretical value are believed t be caused primarily by the nnunifrm central nzzle flw and perhaps t a lesser extent by the incrrect Mach numbers f the annular air jets. An air jet Mach number f wuld be required t match the slender bdy criteria given in Sectin Hwever, as shwn by Fig. 23a, a facility designed by the blunt-bdy criteria culd well be used t test slender bdies als. The effect f the caxial air jet fr simulated tests in a pressurized tank is shwn in Fig. 24. The caxial jet prvides an imprvement in the mdel flw field by reducing the mdel shck-jet bundary interactin, but the imprvements are nt as prnunced as shwn fr the tests simulating an atmspheric exhaust. 10

20 SECTION V CONCLUDING REMARKS The analytical and cld flw experimental investigatin f ablatin testing in the flw field f caxial ht and cld jets indicates the fllwing cnclusins: 1. The caxial flw technique will prvide the crrect flw field ver the nse regin f relatively very large, reentry-type mdels and the technique can substantially increase the facility mdel size capability. 2. Fr very slender bdies, the caxial technique can increase the mdel length fr which valid data can be btained by a factr f at least tw t fur. This is achieved primarily by mving the flw expansin t atmspheric pressure frm, the high enthalpy nzzle t the cld air nzzle exit. 3. The flw matching criteria based n the mdified Newtnian thery is valid fr large reentry-type mdels. A facility designed fr the reentry bdy criteria can well be used fr slender bdies als. 4. Althugh the small physical size and the requirement fr cling the high enthalpy nzzle present significant design prblems, the studies shw that hardware can be fabricated fr a 5-MW arc heater with a nzzle thrat as small as 3/8-in. in diameter and an exit Mach number f It des nt appear that viscus mixing between the flws will invalidate the data fr currently envisined tests until well back n the test mdels. Hwever, experimentally verified data fr this type f mixing prcess is needed. 6. The cncept f testing in a pressurized tank (ht flw nly) will nt prvide a significant imprvement in capability fr large, blunt mdels as used in this investigatin. The pressurized tank des prvide an imprvement in capability when used with the caxial flw technique. 11

21 REFERENCES 1. Krst, H. H. and Chw, W. L. "Nn-Isenergetic Turbulent <Pr t = 1) Jet Mixing between Tw Cmpressible Streams at Cnstant Pressure. " NASA CR-419, April Lamb, J. P. "An Apprximate Thery fr Develping Turbulent Free Shear Layers.'' Jurnal f Basic Engineering, September 1967, p Sawyer, Wallace C. and Smith, Rudeen S. "Experimental Surface- Pressure Distributins n a 9 Spherically Blunted Cne at Mach Numbers frm t " NASA TM X-1730, January Staff f the Cmputing Sectin. Tables f Supersnic Flw arund Cnes. Massachusetts Institute f Technlgy, Department f Electrical Engineering, Sims, Jseph L. "Tables fr Supersnic Flw arund Right Circular Cnes at Zer Angle f Attack.'' NASA SP-3004,

22 APPENDIX ILLUSTRATIONS 13

23 ATMOSPHERE EXPANSION WAVES en ATMOSPHERE JET BOUNDARY COAXIAL - COLD AIR J I J I J J J Jl < i IT HIGH ENTHALPY AIR HIGH ENTHALPY AIR a. Present Testing Technique b. Caxial Flw Testing Technique Fig. 1 Applicatin f the Caxial Flw Technique t Ablatin Testing > m O

24 COOLING WATER COLD AIR ARC-HEATED Fig. 2 Caxial Flw Nzzle Assembly Designed fr Arc-Heater Applicatins 16

25 1 AEOC-TR j AMBIENT AIR, U C /UH =0 1 ug/«n - \j.c 0.1 " Uc/U H =0.4 " < Ul Ü COLD FLOW OR ^^"^ AMBIENT AIR ^^^s,^ Ck < Q < -0.1 \- NOZZLE EXIT HIGH ENTHALPY FLOW -0.2 i i i i VELOCITY RATIO, U/U H Fig. 3 Effect f Caxial Flw (Cld Air) n the Spreading f the Velcity Mixing Regin fr Typical High Enthalpy Applicatins 17

26 D O O EXPERIMENTAL THEORETICAL VELOCITY RATIO U/U H = 0.95 U/U H =0.05 AMBIENT AIR ". 2.0 u 00 ivv^^i M = 3.8 ARC HEATED AIR ~ CO _1 < < cc 4 6 AXIAL DISTANCE, x/r e Fig. 4 Cmparisn f Experimental Data with Theretical Calculatins fr the Spread f the Velcity Mixing Regin

27 ^^^^^^^ \SSWS\W4 ^^ mmm s^s^a AIR ^^^^^^^^ ALL DIMENSIONS IN INCHES Fig. 5 Caxial Flw Nzzle Assembly and Reentry Bdy Mdel fr the Cld Flw Tests 19

28 CO Fig. 6 Caxial Flw Nzzle and Reentry Bdy Installatin

29 M c 2.0 Nzzle Shwn ^t^k\\\\\\s^^ ALL DIMENSIONS IN INCHES. Nzzle Assembly Fig. 7 Caxial Flw Nzzle Assembly Dimensins and Cnturs 21

30 Air Nzzle Design lift 2.0 "A" "B" Air Nzzle Design M c 2.5 'B* CO2 Nzzle Design "C" "D" C0 2 Nzzle "As Built" "C" "D" H t t All dimensins in inches. b. Nzzle Crdinates Fig. 7 Cncluded

31 " < a. nice CO CO IU ( Q. t- O < RADIAL DISTANCE, r/r Q a. M c = 2.0 Fig. 8 Pitt Pressure Distributin f the Caxial Flw Fields, PH/PC = 1 23

32 0.6 X Q. 'S. O. < IU c 3 m hi DC a. t RADIAL DISTANCE, r/r e b. M e = 2.5 Fig. 8 Cncluded 24

33 1.0 x/r e = r- < DC Id < UJ Q. UJ r L x/r e = 0.3 y RADIAL DISTANCE, r/r e Fig. 9 Stagnatin Temperature Distributin f the Caxial Flw Field, M e = 2.0 and Pn/p«, = 1 / 25

34 a. M r = 2.5 b. M c = 2.0 Fig. 10 Schlieren Phtgraphs f the Caxial Flw Fields, p^/p = 1 26

35 1.5 CM.0 - t r- < iii c CO CO UJ ( Q. CALCULATED MODEL STAGNATION PRESSURE, M c = 2.0 and MODEL STAGNATION PRESSURE, M c = 0 PITOT PROBE RADIAL TRAVERSE, M c = 2.5 \ PITOT PROBE RADIAL TRAVERSE, M c = 2.0 A PITOT PROBE AXIAL TRAVERSE, M c = 2.5 -L _L AXIAL DISTANCE, X/r e Fig. 11 Cmpilatin f Mdel and Pitt Prbe Data n the Nzzle Centerline a

36 1.2 > m n CM. 0.8 < a: (0 CO UJ 0.6 ~ MODIFIED NEWTONIAN THEORY REF 3 M 2.30 M = 2.96 O 2.30 M D 2.96 Q O ~ _Q O 13 FT CONE THEORY O TT _L J. J DISTANCE ALONG BODY, S/r n 3.0 F.ig. 12 Cmparisn f Thery and Wind-Tunnel Data fr a Sphere-9-deg Cne Bdy

37 1.6 { 1 i 1 1 x/r e D O 1 O 1/2 x \. CM \ 1 -. t CD PRESSURE RATIO, O 0) 0 a \ y THEORY - u 0.4 z 0.2 O 0,0 8 n " i DISTANCE ALONG BODY, s/r n Fig. 13 Mdel Pressure Distributin withut the Caxial Air Jet, Pn/p«> = > m -4 O)

38 a en 00 2 x/r e = 1 x/r e = 1/2 Fig. 14 Schlieren Phtgraphs f the Flw Fields Crrespnding t Fig. 13

39 GO DISTANCE ALONG BODY, s/r n 3.0 Fig. 15 Mdel Pressure Distributins withut the Caxial Air Jet, PH/P«~ 1 > m O

40 1. t- 1 1 ' 1 i x/r e D O I X m < ] Q\ ^THEORY _ GO DO MODEL PRESSURE p p * en S D 5 \ D \ - D, D P P3i Q i Ü DISTANCE ALONG BODY, s/r n Fig. 16 Mdel Pressure Distributins with the Caxial Air Jet, M c and Pn/p«, = 6

41 CM < r UJ K 00 GO CO CO UJ cc a. a DISTANCE ALONG BODY, s/r n Fig. 17 Mdel Pressure Distributin with the Caxial Air Jet, M c = 2.5, PH/P«> a n H 31 a»

42 Fig. 18 Schlieren Phtgraph f the Flw Field Crrespnding t Fig. 17, M c = 2.5, pu/p^ 6 34

43 1.2 6 ' i 1 1 T ' x/r e A 5 x CM X \ j THEORY - G 2 O l i - r- < cc UJ cc V) - GO Ol CO CO 111 ce a. -i UJ 0.4 " D \ a v v * 6 1 Ö 6 i I > m n DISTANCE ALONG BODY, s/r n Fig. 19 Mdel Pressure Distributins with the Caxial Air Jet Simulating Tests in a Pressurized Tank, M c = 2.5, p H /p M - 1

44 D O x/r e = 5 GO x/r e = 2 x/r e = 1 Fig. 20 Schlieren Phtgraphs f the Flw Fields Crrespnding t Fig. 19, M = 2.5, PH/POO = 1

45 X CM GO -0 < cc Ul cc tn en UJ CC a. a > rn DISTANCE ALONG BODY, s/r a n n Fig. 21 Effect f Axial Lcatin n the Mdel Pressure Distributin with the Caxial Air Jet, M c = 2.5 and PH/POO = 6

46 6> 00 CO x/r e = 5 xae = 2 Fig. 22 Schlieren Phtgraphs f the Flw Fields Crrespnding t Fig. 21, M c = 2.5, PH/P 0-6

47 CO CD t/r. = 1 x/r e = 1/2 Fig. 22 Cncluded > m O

48 n H COAXIAL FLOW D ON OFF CONE THEORY CO 0) UJ er a UJ MODEL AXIAL STATION, X m /r e a. M e Fig. 23 EHect f the Caxial Air Jet n the Pressure Distributins n a Sharp 10-deg Cne,

49 x as CO CO 0.04 a ^ CONE THEORY COAXIAL O D FLOW ON OFF Q O ' > MODEL AXIAL STATION, X m /r e b. M e = 2.0 Fig. 23 Cncluded > m n H

50 t 0.12 O 0.08 K U : CO u 0.04 K a. lü Q O CONE THEORY I L COAXIAL FLOW O ON D OFF MODEL AXIAL STATION, X m /r e Fig. 24 Effect f the Caxial Air Jet n the Pressure Distributins n a Sharp 10-deg Cne, PH/POO = 1. */'e = < and M c " 2-5

51 UNCLASSIFIED Security Classificatin DOCUMENT CONTROL DATA -R&D (Security classificatin f title, bdy f abstract and indexing anntatin must be entered when the verall reprt is classified) 1. ORIGINATING ACTIVITY (Crprate authr) Arnld Engineering Develpment Center ARO, Inc., Operating Cntractr Arnld Air Frce Statin, Tennessee REPORT TITLE ABLATION TESTING IN HOT AND COLD COAXIAL JETS - PHASE I, COLD FLOW FEASIBILITY TESTS 4. DESCRIPTIVE NOTES (Type t reprt and Inclusive dates) Final Reprt July 1968 t Nvember AUTHOR(S) (F irst name, middle Initial, last name) R. D. Herrn, ARO, Inc. 2a. REPORT SECURITY CLASSIFICATION UNCLASSIFIED 2b. GROUP N/A e- REPORT DATE April 1970 Sa. CONTRACT OR GRANT NO. AF C PROJECT NO Task 12 d. Prgram Element 62201F 10. DISTRIBUTION STATEMENT 7a. TOTAL NO. OF PAGES 50 9a. ORIGINATOR'S REPORT NUMBERISi 7b. NO. OF REFS Bb. OTHER REPORT NOIS) (Any ther numbers that may be assigned this reprt) N/A This dcument has been apprved fr public release and sale; its distributin is unlimited. 11. SUPPLEMENTARY NOTES Available in DDC, 2. SPONSORING MILITARY ACTIVITY Arnld Engineering Develpment Center, Air Frce Systems Cmmand, Arnld AF Statin, Tenn ABSTRACT An investigatin was cnducted t determine the feasibility f extending the capability f ablatin test facilities by surrunding the high enthalpy flw with a caxial cld air jet. The investigatin included bth analytical and cld flw experimental studies. It was determined that the caxial flw technique is extremely prmising, ffering the ptential f easily dubling the facility mdel size capability. Results f the cld flw experimental tests and criteria fr applicatin f the technique t high enthalpy facilities are presented. DD FORM 1 NOV UNCLASSIFIED Security Classificatin

52 UNCLASSIFIED Security Classificatin 14. KEY WORDS LINK A ROLE WT LINK B LINK C ablatin test facilities electric arc furnaces jet flw supersnic nzzles UNCLASSIFIED Security Classificatin