AD-779 087

ELECTRON BEAM ANALYSIS OF mFHE PROPEl-TIES OF MOLECULAR NITROCEN AND NITRICOXIDE IN THE AFFDL 2-FOOT ELECTROGAS-DYNAMICS FACILITY

S. L. Petrie, et al

Ohio State University

S I• I.[ II

I Prepared for:Air Force Flight Dynamics Laboratory IFebruary 1974

H

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O PREPORT DOCUMENTATION PAGE READ INSTRUCTIONS]REPOT DCUMNTATON AGEBEFORE COMPLETING F0RM-I REPORT NUMUEI11 Z. GOVT ACCESSION NO. ItECI•iENT'S CATALOG NUkI3ERn A

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ELECTRON BEAM ANALYSIS OF TILE PRCVERTIES OF Final

MOLECULAR NITROGEN AND NITRIC OXIDL IN TilE AFFDL 1 Dec 71 - 22 Aug 73

2-FOOT ELECTROGASDYNAMTCq FACILITY 6. PERFORMING ORn. REPORT NUhoDEr

7. AUTtIORta) A CONTRACT OR GRANT NuMSERI(a`)

S. L. PetrieJ. J. Komar F33615-72-C-1023 R/

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AREA & WORK UNIT NUMBERS

The Ohio State University Research Foundation131.4 Kinnear RoadColumbus., Ohio 43212 Project Number 1426

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Air Force Flight Dynamics Laboratory (AFSC) February 1974United States Air Force I1. NUMER OF PAGES

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19. KEY WORDS (Cont~inue on reverse aide it nocoafcry said Idontify by 1 ¢10C- Iulmboe)

Electron beam instrumentation; Arc-heated wind tunnel; ElectrogasdynamicFaility; "V Molecular nitrogen; Nitric oxide; Vibrational temperature measure-iiment; Number density measurement; Inviscid flow analysis

20. ABSTRACT (Collnue cm ravtivs a•, do It noceaea'y and Identify by block number)

The electron beam fluorescence technique was used to measure the vibra-

Lional temperature and nuaber density of molecular nitrogen and nitric oxide

at the exit of the 7-inch conical nozzle of the Air Force Flight DynamicsLaboratory 2-Foot Electrogasdynalnlcs Facility. In addition, the vibrational

temperature and species concentration of nitric oxide were measured at theexit of the 19-inch conical nozzle. Tests were conducted at reservoir pres-

sures of 250. 350, and 500 psia, with reservoir euthalpies varyiLug from 2127to 5931 BTU!b. Theotc results assuming flaite-rate chemlcalIJAN 73 1473 EDITION OF I NOV 65 IS OBSOLFTE L_

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notiequilibrium were compared with the experimental data. For the 7-inch nozzletests, poor agreement between the measured and predicted nitrogen concentra-tions was obtained. The excitation-emission mechanisms for elcctron beamexcitation -If the NO# system in NO-air and NO-nitrogen mixtures were investi-gated and it is shown that the excltation is dominated by secondary electronsresulting from beari-induced ionization of molecular nitrogen. Application ofthe electron beam technique to the measurement of nitric oxid- r,-mb-r cntitiesshowed that the nonequill'Uium theory over-predicts the amount of nitric oxidepregent in the expansion process. Reasons for the discrepancies between thetheoretical and experimental results were examined.

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vrU.S.Governmont Prinlno offlco; 1974 - 758-433/533

AFFDL-TR-74-8

ELECTRON BEAM ANALYSIS OF THE PROPERTIES OF MOLECULAR NITROGEN A

AND NITRIC OXIDE IN TILE AFFDL 2-FOOT ELECTROGASDYNAMICS FACILITY

9I

S. L. Petrie

J. J. Komar

Approved for public release; distribution unlbif~ted,

JI (II

FOREWORD

This technical report was prepared by S. L. Petrie atid J. J. Komarof the Aer-nautical and Astronautical Research Laboratory of The Ohio M

State University Research Foundation on Contract F33615-72-C-1023(OF 3361-Ak). The rese•rch reportud here was prformad on Task 142601.H. Lee of the Air Force Flight Dynamics Laboratory, Wright-PattersonAir 'orce Base, Ohio war the project engineer for the e¢ntract and forthe facility tests.

This report covers work conducted from 1 December 1971 to22 August 1973.

The manuscript was released by the authors in August, 1973, forpublication as a technical report.

This technical report has been reviewed and is approved.

Chie , Flight Mechanics Division

Air Force Flight Dynamics Laboratory

lii

ABSTRACT

: Tihe electron beam fluorescence technique wras usied to mnouear theS~vibrational temperature and 'utudber densiLy of molecular nitrogent and

nitric oxide at the exit of the 7-inch conical nozzle of the Air ForceFlight Dynamics Laboratory 2-Foot Electrogasdy-namics Facility. Inaddition, the vibrational temperature and specites concentration of

S~nitric oxide were measured at tha exit of the 19-rinch conical nozzle.Tests wer-e conducted at reservoir pressures of 250. 350, and 500-.•ola,

S~with reservoir enthalpies varying from 2127 to 5931 Btu/ib. Theoreti-S~cal results assuming finite-rate cem~eical nonequi1ibrium were compared

with the experimental data. For the 7-rinch nozzle tests, poor agree-ment between the measured and predicted nitrogen concentrations wail ob-tained. The excitation-emission mechanisms for electron beam excitationof the NU y syutew in NO-alir and NO-hitrogsen mixtures were investigatedand it is shown that the excitation is dominated by secondary electronsresulting from beam-induced ionization of molecular nitrogen. Applica-tion of the electron beam technique to the measurement of nitric oxidenumber densities showed that th~e nonequilibrium theory over-predictsthe amount of nitric oxide present in the expansion process. Reasonsfor the discrepancies between the theoretical and experimental resultswere examined.

il!i

I

TAELE OF CONTIJT9 -

S ction

I INT130DUCTION 1

11 EL1CTRON BEAM MEORY 2

A. (OEIIEAL CONSIDERATIONS 2

13. VIrPRTIONAL T4MPERATITRE M=UR W-ri 3

C. NUMIER DENSITY MEASURM T 4

III CALIBRATION UFElIMENTS 10

A. GENERAL A-PPROACH 10

B. ELECTRON BEAM GENERWATOR 10

C. INST•UMENTATION 10

D. CALIBRATION RF-3ULTS iii

IV APPARATUS AND PROCE)URES 21

B13 ELECTRON BEAM SYSTEM 22

C. TES3T PROCE)URES 24

D. DATA REDUCTION TDMHNIQUES 24

V R0I9ULTS AND DISCUSSIONS 29

A. Tii)ORE!LICAL ANALYSES 29

D. NOMINAL RUN C0ONDITIONS 29

C. PROBE DATA 29•

). VIBRATION11L TEMFERATUREb 35

E. NUMBER DENSITIES ?i3

VT CONCLUSIONS 52

A. ELECTRON BEAM ¶E"11NIQUES 52

B. TIHEORIU ICAL-FIXPERIMENTAL COMPARISONS 52

REI' ,-t'ER cN C i;3

v1

I3I

T alble

IPROBE LOCATIONS DI TNCORE DOWNSTRFAM Or, NOZZ LE Xr 21

1.1 QUENCHING, CONSTJWNS 27

MI N {AJ M A RESERVOIR CONDITIIN SUINVART 30

LIST OF ILLUSTRATIONS

3. 1atio of Intensitics for the (1,5) and (0,2) Dands ofthe NO ý and (0,I) Mnd (1,2) Swids of h Nte Systems 5

2 8(TV)/S(300 Kt) f~or (O,v") anid (1,v") Bwikdb of the N&,-and NO y Systee 9

3 Electron Beam Genertor-Gap Lena Schematic 111

It Elactrin Beam Gener•'(Aor Scheiau*.lio 1.2

5 Calibration Inatrume ,ttiou Schematic 13

6 n1tena:1ty of NO 7 (0,2) Rime in Va'iouo Gan Mictuarea 15

7 ImensLy of NO y (1,5) Pxnd In t•.ioug Ga6 Mixtures 168 Spectrca Sean of NO 7 Systmu in 670 NO, 3D% Air 18

9 ,1/I for NO y (0,2) and (1,5) Bands 20

10 Inst- rumet ta tion S clwwa•a Ic 23

11 Typical Riun Record of Spectral SCarT p=

12 Test Chamber Pistollation in the 2--Foot EGF 27

1.3 Pitut Presoure Sauveya at Run Condition 2; 19fInchNozled Po 0 350 pala 30

14 Pitot Preseýxre Surveys at Man Conditlo' 3; 19-InchNozzle; po = 500 pola 1

V1

aa

LTST OF ITaISTRAlTIONS - (Contniucd)

15 Pitot 1ressure Surveyi at uin Condrition 1; 7-Inch

A

No-zln; p- 0 250 pisi 3

16 Pitot•'ressur-e Suiwveys Rt- Run Condition 2, 7-nm ahuNozle; N =- 350 pain 33

17 Pitot Pressure Surveys at Run Condition 3; 7-InchNozzle; Po = 500 pala 34

18 Pitot Pres.ure Surveys at VWaous WAxa1 Stations -Run Condition 1., 7-Inch Nozzle 36

19 Pitot Pressure Surveys at Various Axial Stations -ffim condltIon 2- 7-1nch Nozzle 37

120 Pitot Pressure St•ukway at Various AxalJ Stations -Run Condition 3, 7-Inch Nozzle 38

21 Axial Centerline Pitot Pressures; 7-Inch Nozzle 39

-L rncbr.rs 7-fnch Nozzle 1,

O2 NO Vtbratloail Temperatures; 7-inch Nozle1It4 NO Vibrational Temperaitues; !9t]Thch Nozzle 42P-5 N, Nu•ber Densities at Rxin Condition 1; 7-Tnch Nozzle 44

26 N2 NMmber Denitles at Ru, Condition 3; 7--Inch Nozzle 45

27 NO Number Densities at Run Cunittion 2; po ) 350 psia;7-Inch Nozz?1.e 47

28 NO Number Densities at han CoudItion 3; • = 500 psia;7-inch Nozzle 148

29 NOD Number Densities at Run ConL•ition 2; Po w 350 psia;19-.Inch Nozzle )49

30 NO Number Densities at Rua Condtiocnj 3; po - 500 pl.a;19-Inch Nozzle 50

vii

U

U

fj frt'.ction of photons a ~~b~o'h, by i#peclcn J i• &rotud

G~o)vibr~tcnn1 te~rm value in j•roumnd elmctrxonic enurgy utata

h) LagnatLon wnthalpv

! ph~om].t tJ •S'r ourr StFII

pho toio0ulrtplier current with no oaccltct'ton by uocondnryI

p~rt~fŽffim .1ort.i Wel" ý,haissvUn

N to~a1 numbe r d1,l, It:y

Nk nusbper doi~aty of lpight ~ 1Sfraction oquefcphono deneliy of sipi k

! ~NN2,[N2 ] N2 latiblr density

NNOC O NO numib1lCr densiity

p statrtc pressAure Ip' quenching prmvalue i

Pooatnit.plon (reservoir) ccrur

Q (vi) cro~s iptoct ltn ipior cxcatt. h noion by pc Ltatn b elcL:oo

vARM

alactan bem crren

QkO (v,) crotai r.csion for "~Citrtonti Of idr~cien k by u&ccondariFeiect roan.

Qv•T (VC) total cross aatinn for lnnixatl.n *t Oper-le-a k by pi trza-r;

Shlat trailpfer rite

q(v' v ) Franck-Condon foartor for v' ! v" trgnstt)nn

S(TV) vibrationl tCamparature correction to dansity

T taiitftlational temporature

Tv vibrational tempera~t re

t time

V, v ,vo vibration~l quanLum numbers

v g'.primary electron velocity

vs Aoaoiddry 0"•Lr".. t Vret locitvy

Zkj collision fraquency for collitaor.n betwean specl.es k aind j

%,. vj %vatwivuumbar for j r arsivion

meAn frov pWth r*-lnctloii for secondary etectronn

Mans dtengity

c for pro-run calibration conditions

o for reservoir conditione

SC for condltlonin ii i t t. - tit chaimb)r

I for Chnnnel I

I1 for Channel II

*' for prIfrte-., tXC Ic ed elect ronic OtiO-gy SLatc

Ix

Lo

I. 1N1TRODUCTION

Arc-heated wind tunnels are generally characterized by a highdegree of thermodynaric and chemical nonequilibrium wit'hln the expansionprocess. To predict test-section gas pro !rtiags end properly interpretmodel data obtained with such facilities, an accurate theoretical analy-

sis of the flow process employing finite-rate chemical and thermodynamicreactions is required.. The accuracy of the analysis depends directly onthe applicability of the kinetic model (i.e., the set of reactionsemployed) and the availability of the appropriate rate constants.

While certain wind tunnel calibratiou data (i.e., pitot pressure,flow velocity, stagnation point heat transfer rate) are relativelyineependent of the detail.ed ther.mochemical processes, other calibrat. onf, ctors such as the static temperature, Yach number, Reynolds number,etc., are not. Since many of the quantities which cannot be directlymeasured must be Imown to relate the wind tunnel data to equivalentflight conditions, an accirate theoretical model must be available.The accuracy of such a model can be determined iV appropriate measure-ments can be made which will allow comparison of the theoretical resultswith experimental data.

The chemical species of interest for much of the operating rangesof typical arc-heated wind tunnels consist of: N2 , N, O, 0, NO, NO+,and e-- White N__ 0. and o0 mrkeP up at. least 95% of the gas mixlture.nitric oxide can be extremely important in drtermining the gas composi-tion. The nitric oxide shuffle reactions, N2 + 0-- NO + N,N + 02 -• NO + 0, and N2 2 02 - NO + NO, are binolecular and hence, areextremely rapid. In certain operating ranges, these shuffle reactionscontrol the rate of oxygen recombination in the nozzle expansion pro-cess, and thereby heavily influence the resulting gas properties at thenozzle exit. Hence, measurement of the properties of nitric oxide canbe extremely useful in determining the accuracy of the shuffle reactionrates and their :elative effects on the resiulLs o0 the theoretical pre-dictions.

A series of expertrients hi s been performed in the AFFDL 2-FootElectrogasdynwa iFccility (EGF) in which the electron beam diagnostictechnique has been applied for the measurement of certain gas properties.In Ref. 1, the technique was applied for the measurement of the vibra-tional temperature, rotational temperature, and number density ofmolecular nitrogen. In Ref. 2, the species concentrations of molecularand atomic oxygen, and the vibrational temperature of molecular oxygenwere determined. Application of the electron beam Uiagnostic techniqueto tht determination of the properties of nitric oxide were investigntedby Petrie and Komar. 3 The calibration experiments.of Ref. 3 have beenextended and the diagnostic techniques have been applied for measuringthe properties of nitric ox'de in the 2-foot EGF operating at ncminalflow Mach nunbers of 8 and 1.0. In addition, the vibrational temiperatureand number density of molecular nitrogen have been measured at a flowMach number of 8 to extend -the lowter density measurements of Ref. 1.

I-

As in Refs. 1 and 2, the electron beam data are compared with

usual facility operating parameters and nozzle exit pitot pressures toletermine the properties of the test gas at the measuring station. Theseexperimentai results are compared with those from the theoretical analy-sis to provide additional information useful for assessing the applica-bility of the theoretical model.

The general theory for electron-induced radiation in nitric Oxideis summarized in Section II. Section III describes the experimentaltechniques used, and the results of certain calibration experiments.

The remaining sections describe the application of the diagnostic tech-niques in the 2-foot EGF.

II. ELECTRON BEAM THEORY

A. G2MERAL CONSIDERATIONS

Radiation intensities sufficient for accurate determination of gaspropeaties in an arc-heated wind tunnel can be obtained with electronbeam currents near 20 mA at beam voltages fram 5 to 75 kV. The beam isprojected across the flow, and the interaction of electrons with gasparticles produces a column of radiation which is nearly coincident withthe beam of electrons. Profiles of gas properties are obtained byex•inLing va:rious points along the length of the beam. High-beam volt-ages are required to obtain good spatial resolution in the measurements;at low-beam voltages and high gas densities elastic scattering of thebeam electrons is severe.

When an electron beam is passed through the flow at the nozzleexit, radiation is observed due to bombardment oa most species knowva toexist in the flow field. The radiation resulting froa excitation ofmolecular nitrogen and nitric oxide is of particular interest.

The predoainant radiation due to excitation of molecular nitrogenis the first negative system of the ionized nitrogen molecule (N21')."The most intense band is the (0,0) band at 3914 A. Much experimentalwork (summarized in Ref. 4) has been done with the first negative systemin nitrogen and air to verify the applicability of the diagnostic tech-nigue. Deteails of the meho.ds can be found in R~efs. i' and 1-79

Electron beam excitation of nitric oxide results in observation ofradiation in the y, Ogawm, asd Feast syste•n,.3 In air flows, the vsystem 'is useful for vibrational temperature and number density measure-ments at wavelengths below approximately 3044 L. At higher wavelengths,the y bands are o~rerlapped by bands from the N2+ systems. The Feast andOgawa systems appeaa1 only weakly at wavelengths between 5800 and 6100and relatively little is known of their strueture. The uncertaintiesassociated with these systems and their low radiation intensities makesthem unsuitable now for electron beam diagnostics.

ITe electronic transition comprising the NO y system is denoted byNO(A 2 Z+) -> NO(X 211). Emission is excited by collisions between electronsana nitric oxide molecules in the ground electronic energy state NOU(X2 ).oADetailed considerations of the excitation-emission process in pure nitricoxide are given by Petrie and Komar-: and will not be repeated here. Itshould be noted, however, that the transitions are resoneant. That is, Uthe excitation and emission processes connect the same electronic statesso that self-absorption of the radiation is possible. The analysis ofRef. 3 indicates that self-absorption can be neglected for nitric oxidenumber density-path length products at least up to 10s m 29 for tran-sitions which do not involve the ground vibrational energy level. Inthe studies reported here, only those bands not involving the greou•n)advibrational energy state were used so that self-absorption effects canbe neglected.

For both molecular nitrogen and nitric oxide, it is assu3med thatexcitation occurs with no perturbation in the rotational and vibrationalpopulation distributions in the ground electronic energy s.-ta-te. Sincethe Born approximation is assumed to apply, onLy those tran-sitions whichare allowed by optical selection rules are considered. Hence. both theexcitaLAon and emission transitions are assumed to be governed by theFranck-Condon princip -.

The rotational stractu-, of the NO y bands is quite complicatedsince the emission is a 2 it'--I transition. Separation of the individualrotaioa lnes requi.res both hlitg- spectr... l. r-so lVery intensae"radiation so that an acceptable tign,•,o-oise rato e.n be obt(ain.ed6As discussed in Ref. 2, for rotational tewmeraýture ,ca."u.eaIen there islittle need to resolve the rotational & Uixre of bnds other thenthose in the Nf+ first negative systa ho rafpid equilibration of therotational. energy modes -f all& heavy tes with the. tnrns ation',&ener&y mode allows the rotati.ona2 t", atvxe of each species toassumed equal to the translational ;1ým. ature of the gaws, •exnce, themeasurement of the rotational i peratou: of- molecula:r nitrogen will.suffice to describe the rotation, aislational temperatures ofall heavy species.

D. VIBIATIONAL TEMPERATUMhL FXSURE.M-TWT

The ratios of intensities of two vibra)tional be,)nds in both tle Nflfirst negative and NO 7 systems ,\rno determined by assuming that thepopLlations of the vibr'ational energy levels of both N2 and NO can bedescribed by Boltzmenn distributions witn vibrational tekperatureswhich need not be equal to -the translational temperature nor equal toeach other. The ratio of intensities of two vibrational bands is givenby

7%q2(vj.',vo) eGvhev 7 v2j3q(vp',v 211 )(V2) eV "

VO V"

3 JIM

where 0 a and q2 are the Fr anck-Condon factors for the emission transi-dions, q(v 't,vo) is the Frauck-Condon factor for the excitation transi- Ution from the vo vibrational energy level in the ground electronic statejto the v.1 -vibrational level in the excited electronic energy state,and G(vo) is the vibrational term value in the ground electronic energystate.

From Eq (.), the ratio of intensities of two bands in the emissionis a function only of the vilbrational temperature of the molecules inthe ground electronic energy state. The ratios of intensities of variousband combinations for both molecular nitrogen and nitric oxide are shownas fu•nctions of vibrational temperature in Figure 1. The Franok-Condonfactors employed to construct Figure I are given in Refs. I and 3.

With the assumption of direct excitation, the vibrational tempera-tures are determined by measuring the relative intensities of the vibra-tional bands and consulting the curves of Figure 1. It is notable thatmuch greater sensitivity to vibrational temperature is obtained withmolecular nitrogen than it is with nitric oxide. The relativelv smallvariation in intensity ratio with vibrational temper•ature for nitricoxide places severe requirements on the elactro-optical system employedto make the band intensity measurements.

C. NUMBER DENSITY MEASIRDET

It is a comnion practice to determine the number density by measuringthe intensity of one or more vibrational bands which appear in the beam-excited emission. In order to interpret the band intensity in terms ofnumber density, the excitation-emission mechanisms which lead to theradiation must be known. It is well known that for molecular nitrogen,the N_2 + first negative system is excited primarily by beam electronsand that secondary electrons have a negligible effect. However, becauseof the low excitation energy of the NO 7 upper state (5.2 eV comparedto 18 eV for the N2+(B 2 Z) state), secondary excitation mechanisms maybe important in p.roducing the NO y system.

As described in Ref. 8, the rate of excitation of gas molecules toexcited electronic energy states due to excitation by primary andsecondary electrons can be given by

NeveNQjis(vs) r, NkQkT(re)

NeveNjQo(ve) + k N it + (2)

k

where the first term accounts for excitation by primary electrons andthe second term allows for excitation by secondary electrons. Ndenotes the number density of excited species, No is the electron

4000- f

ujjS.j3000- -]!

2000--zI

NO `5_)00:2

> 1000

00 2 3INTENSITY RATIO

Figure 1. Rltio of Tntensities for the (1,-5) and (0,2) Bands ofthe NO 7 and (0ý,I) and (1,,2) Bands of the N2 + Systems

5

number density within the beam, ve is the velocity of the primaryelectrons, Nj is the number density of the species in the groundelectronic energy state, and \s is related to the diffusion coefficientof the secondary electrons. The quantities Qo(ve) and Qj1 (v&) are thecross sections for excitation of species j by primarr electrons andsecondary electrons and, QkT(ve) and Qks(vs) ar\. the total cross sectionsfor ionization of species k and excitetion of species k by secondaryelectrons.

Sin6e the NO y system is resonant, population of the upper electronicenergy state as a result of absorption of resonant photons should beincluded in the analysis. In addition, excitation cauved by the colli-sion of ground state molecules with electroniccally excited particlescan be included. The rate of excitation due to these two nxehtanismsis given by

d-" A + f ZjtjNk* (3)k

where f1 is the fraction of the resonant photons absorbed, Aji is thetransition probability for spontaneous emission, and ZkI is the frequencyof collisions between grou..nd state molecules and excited p crticles ofspecies k. Note that induced emission is ignored in Eq (3).

The collision frequency Zkjt is given in the same form as that forusual binary encounters except that the cross section for excitationis employed instead of the simple kinetic cross section. Hence,

[k 4Nj Qkj &V/-fri (4)To allow explic.it appearance of the number densities, the collisionfrequency is rewritten as

Zkj - ZkJ/Nj (5)

De•o-pilatIon of the excited state is assumed to occur due to

spontaneous radiative transitions and collision quenching. Hence,

Nj*kAii + E Aj+ + Z NkQJc (6)

6

where Qkc is a "tquenlching speed" with iunts of cross section times speed.8

In the steady stbate, Eq, (2)-(6) give the concentration of excitedparticles as

xI.x. i + 101tl/iN j - F.. . . . ... ..

Ajji + A k

NeVeNjQs(vs) 1 NytQT(Ve)it + • ZicjNicNj (7) -

NeveNQ(ve) Qs(V) + XS2 kt INItkSvsItk

where Nkc (Aji + A)/Qitc is considered a quenching nwumber density8

and A = 2 Ajk,It 7 j

The intensity of the radiation is given by

I= Njx'hcvjiAji (8)

where h is Planck's constant, c is the speed of light and vjL is thewavenumber of the j -> i transition, The output of a photomtultiplierviewing the radiation is related to the intensity by various sensitivityfactors which arise because of absorption by optical components, theinstrument function of the device used for spectral resolution, thephotomultiplier gain, etc. These factors are combined into a singlecalibration constant, ci, which also includes the multiplicative con-stant which relates Ne, 7e, and the electron beam cross-sectional area-to the beam current, J. Hence, the ratio of photomultiplier signal-to-beam current is given by

Aji + A Nk/Ni

)NkQks(vs) + is t k

7

The constant Cj must be determined by calibrating the entireelectro-optical system. This is usually done under room-temperatureconditions. lot-ever, the intensity of at vibrational band depends uponthe various factory of Eq (9) and the vibrational temperature. Toaccount for the vibrational temperature effects, the photomultipliercurrent can be given byl'o

[a i (c1S(Tc$~;AJ 1 - _ + r+d A •k/Nk -j

Qs ( "s) NkQkT(ve)

Qo(ve) + k ( 0 )k1NkQk"(v)+ Nk+ I O

WhlereJ

q v) q(v°'v') -G(v0 )hc/kT1S(Tv) Q-(Ti )q(v ' ,v") ao

S(TV - -I v•'V •v "11 "• v CV V )F)and S(Tc) i.o S(Tv - 300 K). The functions S(Tv)/S(T0 ) for the v' 0and I progressions for the N2+ first negative and NO y systems aregiven in Figure 2.

In a strict sense, the correction for vibrational temperatureeffects applies only to that portion of the excitation due to primaryelectrons (a similar form can be written for the resonant absorptionterm). Collisional excitation by secondary electrons and excited parti-cles may be accompanied by perturbation in the vibrational populationdistribution so that Eq (11) no longer applies to the entire excitationprocess. In addition, preferential collision quenching of variousexcited vibrat-ional energy levels may occur. These effects must beevaluated in specific applications before the excitation-emissionanalysis can be applied with confidence.

47

8 4

I

0 -o 1

I__ . . I '4.I•e e . .. . IId d

( I~)$(± mu0±9 !9 JINI

z I.9

II

III. CALIBIXWION EXPERIMNiTr IA. GENERAL APPROACH

A series of calibration experiments was conducted to evaluate therelative importmnce or the various excitation mechanisms accc4ýpaflyingelectron excitation of nitric axide. The variations of the radiativeintensities of the (0,2) eand (1,5) bands of the O y system were IiW.nveaItigated over a range or gas density in pure nitlic o~ctde, nitric oxide-air, end nitric oxide-nitrogen mixtures. The experiments extend thoseof Ref. 3 which were conducted only in pure nitric oxide. The resfltsare inteapreted in terms of the excitation-emission analysis of Ref. 3and Section 11,

B, UEECTRON DFAM GENERATOR

The electron beam generator used for the calibration experimentbsis shown schematically in Figure 3. The system differs from thatdescribed in Refs. 2 and 3 end nsed in the previous EGF experimentsI.The present electron beam generator allows accelerating potentials up -•to 75 kV, while the older version was limited to voltages up to about20 kV.

The electron beam generator cone'ist's of a duopl.asmeýtron electronsoCuree, a gap Lenas IoM b rc g and la eadn b teer"L,•gand focusing systems. The lens elements are mounted Inside a 6-inchstandao-d steel Ueo which is connected to a 6-inch oil diffusion pvumpA baffle is used betwee the dlffusion pump aund the be•a chamber toreduce bacastreamuing of0 diffusion pump oil. The electrons exit frcuthe bean chlmtber through a O,03-inohldiameter, 0.30-inch-long exit Achannel. A"

The maximum acceleration potential is 75,000 V with a maximum boomcurrent or 60 mA. To minimize defocusing of the beam as it traversesthe drift tube and passes through the exit orlflce, the electrons areaccelerated from high potentials toward ground potential. An electricalschematic of the beam generator system is given Jn Figure h.

The main oplatiei instinmentb-ation system employed in the ealibrtationstudies is shown schematically in Fig1ure 5 and is deseribed "in detail inRef, 3. Spectral resolution was accomplished( with a Jarrell-Ash 0.5-MrEbert s•cmaing spectrometer. The grating was rtled with 30,000 lines/il.yielding a dispersion of i6 A/mm and a maxn:Dilm resolution of' 0.2 A. AnEMil 62568 photonnultiplier was used with -the spectrometer. The photo-currents were measuried and amplified with a Keithley Model 10-.7 ptcoeamueter.The beam current won mo.It-ored by measutrif ng the voltage d(rop ao•rO•s t.he

30

F771

III

vvIf•I III a1 I4 ... . I•

4'r

r 7

tYI:=c IT---- IL•44 !-L .,

11! L] " : .• •,•' 1W _ >

12

I .- 6 I-•o--•At••L' ... "']tilt•°..\Q -a. " ....

• " _I') _

,1.2

_I-

'F

0 °O"n t°

[Iii

.OD

9-

tAwl

11-: ES reni I

li UI TV

13

beam current nmnettr. The outputs from Lhe picoanne-tor and beam currentawnineter entered on on-line angiog rcamuter whero the ratios of the photo-mnuitplier and beam current signals were ronnad, and the results weredisplayed on X-Y p•uLLerv. Since the photcz!ailxli"ar outputL vD.rltsI I Aaery 1; with hoeCurent,, tlie r atloc of a ±giwd o JIn n tUne reasaaurea ol'the relative intensity of the region of the spectrIn uindetr investigationwith the epectraneter1

For the calibration e2pairmenta, the lleotron beam wee projectedinto mi l8-inch-dimtetr, l8-inch-iong cadimiumr-plated steel test chamber.The eloctron beaw Senerator wva.. electrical.ly laotated fiN= the testchamber so that the antire chamber nerved an a Varadey cage for themiatsu,,ment of boom current. The electron beami wan captured in a water-cooled 9qG elbow to eliminato baok-eoattering of tow energy electrons.Previou teats have damanstrated that this configur'ation virtuallyelilinatea radiation due to excitation by aecondary eleaetrons resultingfrom baaburdmont of the chamber waJ.is by bemr. electrons.

Mixtures of nitric oxide-nitrogan emd nitric oxide-air were suppliedthrcigh two separate flow metering systeas. Nitric oxide was suppliedby one metering ayetnm, while either air or nitrogien was supplied bythe other.l The grases were uixerd yn-n-ndt-iertl-y in the teat chaember.Dynamic mixing was chosen over the simpler procedtre of using pre-mixedgasoe to roduoe the n•hmical reactions which occur beLween niýric oxideand molacular oxygen i No-alr mixtures.

'Clie teote were conducted by voc•ctwbig thu Ldt. eliooer •vo a Prom-sure less th, - I =1 Hg and pumping on the system for at least 30 minutes.The doa1red flow rates of nitric oxide mid tie aecond gao were theneatablilhed it-lh the flow maters. At that time the valve between thevacuum pump and the toet chamber was cloved and the output of the photo-mulItiplier d.vl.dod by bamun current was plotted versus the chambor pros-su•re on eu X-Y plotter, izaw phcd;oi•m.ftiplAer ad beam current signalswere also plotted versul. proeu~ro. The rate of pressure rise was lowenough to asure that all electrical components responded to the changein signals acccmpanying the pressure increases.

The presoure in the teot chamber wun measured with a varlablereluctance presaure transducer.. The electrical output of the trmasducerNqao sent to the tuilog computer wh-er veaious ua.Lbr-•tLon consttnta wereapplied 'o obtain correocted pressure. The result:i4i pressure was are-cor'ded on X-Y mtotters.

D. CALIBRATION RESZULTS

The inteisllties of the NO y (0,2) tnd r,) hands are pklotitedversus NO partial pressure in Figvrea 6 and 7. It is clear that theband biten ities do not correlrte with the NO pirtial pressire, W1.h0chwuniLd indicate the presnoce of excitaltion nctchwaiiams in &adition, todni'ect excitation b bgane clectro1s.

14

1 soI is i - i7S _____0 1

'I0

020

(0 •.r 0 i2 0

rC)3

- II II II II II

-D 0 0 0 0 0.% I1CL Z Z Z Z Z 4ws .Mi

Sb Iv P

--

-- " 0

! . 0

o. q • o q o

SiLINnl AdW dlIBdV -iN2-1flt9 PV'A9/ I.LISN•J.NI

0o1 I I T Fo ,.'

oZ 0: 1') 0

-" 1-0 I--C 0 0. 0W -00000

0 0 0

z or: o

n 0 0 0 0

00K>0

LiU

Q.

-> 0 6)01 0

00

K>0 N

S0 0 F4

L __ .!L 1L J. J___

31V3S QJIVlI9.•V-lN8jnolL'8/AAISN-31NI

.16

To determine if the variations of band intensities versus pressurein NO-air and NO-N 2 mixtures resilt from. overlap of some other electronictransition, every known transition listed by Peerse F.nd Gaydon9 in N2 ý,N2+, O_, and Oa+ was investigated. The following bands of nitrogencould, overlap the NO r, (0,2) band: the (14,25) band of the Lyman-Birge-Hopfield system, at 2481.7 Aý, and the (O0-' 1 band of -the Herman-Kaplansystem at 2471.4 L. The NO y (1ý5) band , y be overlapped by the (1,7)band of the nitrogen Fifth Positive system at 2681.2 A, and the (0,4)band of Gaydon's T system at 2678.7 A.

A spectral scan of the (0,2) band obtained vith electron beamexcitation of a gas mixture with an NO-air number density ratio ofapproximately 2 is shoin in Figure 8. The band profile is the sameas that observed in pure NO (Ref. 3).

No evidence of b&L.d overlap can be detected in ayv of the NO 7band profiles. In addition, the systems 1.sted above have never beenre'oorted in excitation of N2 by an electron beam. It is concluded thatband overlap is not a likely cause for the oiserved intensities of theNO Y bands in NO-air and NO-N 0 mixtures.

It is particularly noteworthy that the intensity variations withpressure in NO-air and NO-N 2 mixtures are nearly identical when thedata are examined at equal N2 partial pressures. It is thus concluded -

intensities.

The intensity variations can be explained in terms of the excitation-emission analysis of Section II. The intensity divided by beem currentfor room-temperature mixtures is given by Eq (9), repeated below forconvenience.

I~ci

1- '-

A-jL +A I

jQo(Ye)Nj +k _-----+Nrj

As previously discussed, the influences of absorption can beneglected for the vibrational bands of interest here; hence, fj is setequal to zero.

If collisions between ground state NO molecules and excited speci escontribute significantly to the obqerved radiation, then the intensitiesshould very quadratically with the gas pressure, especially at low

17

4-ý1bUJ)

0>

0

NN

I:-•

° ,*i-.I

pressures where collision quenching can be ignored. Such a quadraticvariation is not observed (Figures 6 and "7); henes, excitation byexcited molecular and atomic species is ignored.

It is known that N2 has a large total cross section for ionization4

so that it can be assumed that N2 dominates the production of secondaryelectrons. In addition, because of the low excitation energy of theNO(A 2 Z) state, it is assumed that secondary electrons are lost primarilybecause of their collisions with ground state NO molecules. It is con-sistent with the latter assumption to assume that the range of secondaryelectrons is short in mixtures contabning NO so that the secondaryelectron diffusion term in the denominator of the second term in Eq (9)can be neglected. Hence, Eq (9) becomes

It

or

I QN T1 e) NN (s

where. ••o VA Iit IntensitY which would be observed if there were nocontribution due to excitation by secondary electrons. Note that thisanalysis ignores all effects of collisions of particles with the con-tainer walls.

To test the validity of Eq (13), the data of Figures 6 and 7 arepresented in Figure 9 as I/Iý versus NNq_2/NNO for several total pressures.

Good agreement with Eq (13) is noted; the slope of the variation ofI/Io yields a ratio of cross sections, QNk,T/QO, of 3.28. The two datapoints obtained with air at a NN,/NNp ratio of 1.67 do not correlatewith the other data. This may be due to the presence of quenchingmechanisms involving molecular oxygen which would not be present in aflowing system. For example, the reaction NO + 0.4 N02 + hv may occurwith sufficient frequency to reduce the number of NO molecules availablefor excitation by the primary electrons.

The calibration results are significant since they indicate thatsecondary electrons provide the predominant excitation of NO in mixturescontaining N2 . This is not observed in pure NO because the yield ofsecondary electrons is much greater in collisions between beam electronsand N2 molecules than it is in collisions between electrons and NOmolecules. However, since the intensities of both the (0,2) and (1,5)bands vary in the same manner with NN2 /NNo (Figure 9), there is nonoticeable influence of the secondary excitation on the band intensityratio. Hence, valid vibrational temperature data should be obtained byreducing the band intensity data with Eq (1).

19

•o°z z=

-C\j

Ii'

zz

0 00 i -i .LL -- J-jj 0- 0

•I/L.Lo 0

c'j

\--j--0

02

IIV. APPARATUS AND PROCEDURES

A, WIND TUNNEL SYSTEM AND INSTRUMENTATION

The experimental studies were conducted in the 2-foot Electrogas-dynamics Facility of the Air Force Flight Dynamics Laboratory. Thefacility consists of a direct current arc heater, a conical eonver~ent-divergent nozzle exhausting to a free-jet cabin, and a pressure recoverysystem. For the experiments discussed here, nozzles with exit diametersof 7.0 and 19.4 inches were used. Further details of the facility maybe found in Ref. 10. The typical tunnel run time in these studies wasfive minutes,

A pitot pressure-mass flow probe and a stagnation point calorimeter

were eamployed in these tests. The pitot pressure-mass flow probe wasmounted on a survey strut which allowed the probe to traverse the flowin a plane through the nozzle centerline. Pitot pressures were measuredin 2-inch increments at three points below the centerline, on the center-line, and at four points above the centerline. Mass flow per unit area(00) was measured only on the centerline.

IThe stagnation point calorimeter was a water-cooled Gardon-type

cvlindrical probe with a hem~sph~rrn nose Another arAdo-_•yp.calorimeter permanently installed on the tunnel centerline was used toobtain a continuous record of stagnation heating rate during the electronbeam experiments.

The location of the various probes used with the 19-inch and7-inch nozzles are summarized in Table I.

TABLE I. PROBE LOCATIONS IN INCITES DOWNSTREiAM OF NOZZLE EXIT

ProbeNozzle Electron Pitot

Dia. (in.) Beam Pressure19 4,06 6.06 1.75 23.81

7 3.06 1.56 0.69 6.06

A portion of the tests included radial pitot pressure surveys at variousaxial stations in the 7-inch nozzle.

In addition to the flow field instrumentation , facility operatingparameters were recorded during each run. These parameters includedarc voltages, arc current, mass flow rate, water flow rates, andtemperature rises.

21

V

The facility data were recordeb through the on-line analog-digitaldata processor. Analog data signals from t'le tunnel instlruentationwere entered through signal conditioning equi-pulent, fed into the pro-cessor and computed, alid the results stored ift digital foTh on magnetictape. Run identification and time reference data also were recordedwith each data scan. At a specific test point, the data chamels wererecorded at a rate of 16 samples per second f'•r a time interval of about10 seconds, I•mediately after the conclusion of a run, the Individualscans for each dUta point were time averaged to give the final data ata test point.

B. ELECTRON BEAM SYST•M

The electron beam system employed in the 2'-oot EGF is" identicalto that described. in Section II (Figure 3). The entire assembly ismouited inside the wind tunnel test cabin so that the electron beam wasprojected downward throough the nozzle centerline at distances downstreamof the nozzle exits as given in Table I. The electron beam power sup-plies and vacuum control console are located in a control panel adjacentto the turnnel. The beam generator is electrically isolated from thetest cabin so that no special beam collecting device is required; thatis, the tunnel test cabin serves &s the beam receiver.

!Lectron beau wiith C-urrento of approxijateay 20 mA ab voltagesnear 40 IV were used for the tests. The beam currents were determined.by measuring the voltage drop across a 570-$2 resistor in series with -the beam current wmmeter. The beam currents were monitored continuouslyduring the wind tunnel run by displaying the voltage drop across theresistor on a X-Y plotter, 4,

The optical system for collection of the vibrational, terperatureand number density data is shown schematically in Figure 10 and isdescribed in detail in Ref. 2. Spectral resolution was accomplishedwith two 0.25-m Jarrell-Ash scanning spectrometers. The spectrowetergratings were ruled with 1180 lines/mn yielding a linear dispersion of33 A/mm and a maximum resolution near 1 A.

The spectrometers and imaging optics were mounted on a traversingtable which was attached to the tunnel test cabin. The table was movedin the vertical plane by a variable speed motor with a total traversingcapability of 12 inches. A precision potentiometer was attached to thetraversing table to provide an electrical signal proportional to thelocation of the field of view in the electron beam. -

Both channel I and channel II intensities were measured with WM{. t6256S photomultipliers. Various load resistors were employed in thetnode circuitry of the photomultipliers and the resulting voltages were

measured with PAR Model 324 lock-in amplifiers. The chopping frequencywas 167 11z. The signals fran the lock-in amplifiers were dispJlayeddirectly on two X-Y plotters.

22.j

w a

i-. 1 4 I. 4 *.

L..L• F.l •LWCL

,... . _, 4, .4,

0

i.61

23 IiK

C. TEST PROCEDUMES

Prior to a wind tunnel toot, the spectral locations of the spectrom-eters Wtre sot, ta 1011ow±-cOthdQdŽ disOchArge lamp which yield5 radiationin thO NO y bands wOo turned on, alnd the chopping wheel w46 starv•edThe lock-in amplifiers were phase locked to the incoming signal and thelight intensity wAs adjusted to provide photomultiplier outputs approxi-mately %qual to those cxpeoted durinog the run, Thn phVtcvultlpilarWere allowed to fatigue under this condition for at leaut 30 minuLesprior to the start of the wind tunnel run. This prdoedure was nueessaryto stabilize the gains of the photomultipliers and lock-in avaplifierr,thus eliminating drifts ill the relative sensitivities of the tuochannels during the course of the run.

Immedlately before the start of a run, the tunnel v•auum systemwas started and a pressure of approximately 0.2 Torr was maintained inthe tesot cabin region by leaking room air into the vacuum pumps. Theelectron beam was turned on and was scanned over the entire travel ofthe optical system. The signals from both channels were recorded onX-Y plotters to provide the calibration of the relative sensitivitiesof the two channels. During this scan, the test cabin pressure andelectron beam current also were recorded. The beam was extinguishedand the tunnel was started. The time lapse between the calibrationexposure and the start of the run typically was less than one mioute.

pitot pressure survey was taken and the centerline heat transfer ratewas measured. At the conclusion .of the probing, the electron beam wasscanned in one direction. The spectrometers were then reset: to measurethe zero-reference signals and the beam was scanned in the oppositedirection.

Run records typical of those obtainod with the NO y bands areshown in Figure 11.

D. DATA REDUCTION TECHNIQUES

To convert data such as that of Figure 11 to temperature anddensity, the sensitivities of both channels at each point along thebeam must be obtained. Points at one inch intervals along the beam inthe test flows were arbitrarily seiectad for data reduction.

To calibrtt:eý the seustt.vlt;;tes of the two data channels for nitricoxide measurements, a small test chamber was attached to the end of thledrift tube of the electron beam generator. The chamber was evacuatodwith a mechanical vacuum pump and nitric oxide was continuously suppliedto the chamber through e precision needle valve. The pressure in thechamber was measured with a variable reluctance pressure transducer.The electron beam was projected through the test chamber and capturodin a water-cooled 90 ' elbow, The entire chamber was isolated

24

OD1-0-,

iid

•) C)

- IL : LL

V K(CT-VOS \kJVE•.IMiV),.LtSN3,.NI

25

olecteically from tlhe drift Lube so that it servoll as the beam currentmeaouring device. The electro-optical system used for the calibrationopeorl'Ponts duplicated that uafwd in the wind tunnel runs. A photog.raphof the teot chamber installation in the EGF Is shown in riguru 12.

'She Intenoitles of the NO y (0,2) and (l,$) banda at 2478 A and2680 A waro measured with channels I and 11, reopoctively. The calibra-tion constants, el, of Eq (12) wore determined from the measured inten-aites 9 beau currenot, and pressure as

k(1/+3) 2 (1NO (1K/4)NNO 1i?~ NN2 NN 34

The ratio of nitrogen and nitric oxido number densities wasdetermined by closing the valve whiclh connected the vacuum pump to thetest chamber and measuring the rate of increase of the chamber prasstur eboth with NO flowing at the rate used during the calibrations and withno NO flow. The latter data were used to establish the rate of airleakage into the chatmbor.

To allow the calibration results to be properly applied to thewind tunnel experimenta and to provide a continual check of the aensi-tivitios of the two channels, the ýnvensicy of the (1,3) band of theN2+ first negative system at 4652 A was measured with both charnnelsduring all pro-runm aid, otatic tes ch1a mber call"brnvionn. This hanid wasC1hosen since its intensity under static conditions was nearly equal totho•. obtained from the (0,2) and (1,1) bands of nitric oxide.

The NO number desilties were obtained from the Intensitios of the(0,2) and (1,5) bands with Eq (12) written in the following form-

1 +YýNk /Nt4 N2k((15)

tS( /,S -c i+(i+ 3.28 N27N' ) -N2 (J(I/PJ)C

where (I/fJ)N and (l/pJ)N2 denote the invter.tties of the (1,3) band ofthe N2+ first negative system obtained during the static chamber andpre-run calibrations, r(Sct ...... .. The qe,,hig ,-i-denitv hor NAý I _f-N0O,was obtained from Ref. 11 and those for N2 and 02 were 0rom Ref. 4,The quenching densities are summarized In Table II. The quenchingfactor was calculated employing spacies number densities resulting fromthe nonequillbrium calculations. Since the quenching factor was nearlyunity for both the 19-inch and 7-inch nozzle tests, no iteration on thespecies concentrations was necessary. The vibrational temperaturefactor, S(Tv)/S(Tc) was determined from Che measur'ed vibrational tewper-atures and Figure 2.

26

Figure 12, Tent Chnamber Inst,,LJ.ttionLil tho 2-Foot BaF

TABLE, 11. QU4CIM.(NG CONS'•NTS

Specie• [i'.'Sp)NOLOp' rr W' (cn-' ) p' (Torr) N' (c;') p' (torr) N' (oWn '")

NO 2.35 7.56 x. 1-01 3-1.30 3.61, X 1OI 0,85 2,73 x 10'

N- - 1.90 6,1L x .101 1.77 5a70 :C a.0--

N•Averelalfe val uec for' v' 0: O id v' !levels or NO(A2F•)

I"P

27

Tho nitric OXr.io vibrationnl temapraturoes wore dotemmined from theratio of' mnasfxod (1,5) tnd (0A•) band intensition. To cecount for therelative seneitivitita of the lio ohann•els, the measuroed ratios werescaled according to the ratio mo•suied i•n the static teak chamber.Hence, the intensity ratio wan dtoermhied as

L~~L~47650 t~ (16)aI

where the subscripts I and II denote the intensities a-f ahannels I andII, rospectively, mid 0.765 is the room-temperature vibrational beandintensity ratio for channels with equal sensitivities (Figure 1).

T!ho number densities of molaoitlar nitrogen. were determlIned from

the measured intensitios of the (0,1) and (1,2) bhande of the N?+ firstnegative system at 4278 A mnd 4236 A, respoctively. The (0,1) bandintensity wan measured with channel I, while that for the (1,2) bandwas measui'ed with channel. 11. Since a pre-rmn calibration for eachchannel was easily possible by passing the elactron beam tin ough thetunnel teat eabin tinder static pwIp-dm conditions, the data .adklctio-nprocedures for the Nl measurements were simpler than those for the NO

-till.. 14vnban err .4m ofi obtainead t'rom the measurd b.AdisxeaUJtieu with the procedur• describ,,d in Re•. 1; that is,

NN NJ(17)NN• WjW~7TI(1~7r

whore (NN2) is the N_2 n•u.ber donsity of the pro-ru)n calibratlons. The

quenching factor was determIxed fProm the species ooneentrmaiona obtalnedd-,rome the nonequilibrium cai'oulation with no iteration on the individualspecies couientralions. The quencrhing densities, •ý, for N. were

obtained frc•i Ref, 4 wad axe summarized in Table I.,

ph o 1, vibret tonal. te-po:.atnrreti were dete-;rhied fran the mentasuredband intensities with the formula

LA. (Izl)h ,y.8•2 T)n 11 Y i (.8)

where 7.85 is the band intensity ratio for channels having equl.sensiti.vities (Figure .).

28

To minimize the influences of run-to-run variations in the datacorrelations, the measured number densities were nondimensionalized bythe corresponding reservoir number densities. The reservoir values[NOlo and [AN2o were determined from the reservoir ccmposition obtainedfrom the average reservoir enthalpy during the scan of the electronbeam.

V. RESULTS AND DISCUSSIONS

A. THEORETICAL ANALYSES

For comparison with the experimental results, the inviscid flowIroi-erties at various stations in the EGF nozzles were obtained with anozzle-flow computer program which is described in Ref. 2. The programcomputes the numerical expansion of a reacting gas mixture startingfrom an equilibrium reservoir through a 'streamtube of arbitrary geometry.The rotational and trmislational degrees of freedom are assumed to beequilibrated throughout the expansion. The vibrational energy mode canbe assumed to be either in equilibrium with the translational energymode or frozen at the reservoir condition. The electronic energy modeis assumed to be equilibrated with the vibrational energy mode. Thec hemir yKr ,a ... .tz b ue " e reaecjoir state, remain inequilibrium, or to proceed in a nonequilibrium fashion through theexpansion. Corrections for the growth of the nozzle boundary layer areincluded in the analysis.

B. NOMINAL RUN CONDITIONS

Wind tunnel data were obtained at three nominal run conditions.The nozzle throat diameter was 0.4375 inch. For conditions 2 and 3,the heater was operated at reservoir pressures of 350 and 500 psiaand nominal enthalpies of 3500 and 2500 Btu/lb, respectively. Forcondition 1, another arc heater was employed which supplied a nominalenthalpy of 6000 Btu/lb with a reservoir pressure of 250 psia.

The nominal reservoir conditions are summarized in Table III. Therange of enthalpies (in Btu/lb) employed were 5599 to 5931 for condition1, 2885 to 348o for condition 2, and two enthalpy ranges for condition 3,2127-2301 and 3694-3936.

C. PROBE DATA

The pitot' pressure data are summarized in Figures 13.-17. It shouldbe noted that little run-to-run variation in the pitot pressure wasobtained.

29

TABLE III. NOMINAL REWERVOIR ACONDITION $UNMAMRYI

Run PO HO To

Condition (psia) (Btu/lb) (K)

1 2pO 6000 6564

2 350 3500 471A

3 500 2500 3973

2.0

OPEN SYMBOLS -ABOVE h1.6 SOLID SYMBOLS -BELOW ¢,.

RUN Ho(Btu/Ib)

0 46 28851.2 47 30

00 I 0 0

00S0.8U

00.4 O 0

0 _ _

0 2. 4 6 8 10

INCHES FROM TUNNEL _Figure 13. Pitot Pressure Surveys at Run Condition 2;

19-Inch Nozzle; Po 350 psi&

30

OPEN SYMBOLS -ABOVE ..-

SOLiD SYMBOLS-BELOW _

i16 RUN Ho(Btu/Ib)0 49 2127

0 50 23050x 1.2-1

i0 F ) Re Do'•. .[]

00S0.8 -0H

00

0.4

0 I lI ...

0 2 4 6 8 10

INCHES FROM TUNNEL (.Figure 14. Pitot Pressure Surveys at Rmu. Condition 3;

1.9-Inch Nozzle; Po 500 psia

31

0

> wwZ "-% t

w 0

•c t'- \

nr" > 0 cu ?"

O~~Oc

ooo W0 I I I I I 4-

a- o.1 1> 0 .r74

___ I I -o 'd

1 32

8.0

7.0 C i

AAV

6.0 V

05.0-

0 RUN Ho(Btu/Ib)0o 58 3,480).4.0 60 3420"le k "1.0961

a.OPEN SYMBOLS-ABOVE TUNNEL CL

3.0-- SOLID SYMBOLS- BELOW TUNNEL _

2~0

1.0-I.O_

O0 L__ 0I 2 302

INCHES FROM TUNNEL CL

FigLure 16. Pitot Pressture Surveys at Run Condition 2;7-Inch Nozzle; po = 350 psia

33

| | | | | i i | !

8.0

Zoo&OV6.00

5.0

o 4.O RUN Ho(Btu/Ib)

0 63 21570 64 2129

3.0 0 65 3909L• 66 3936v 67 3694

2.0 OPEN SYMBOLS -ABOVE TUNNEL C

SOLID SYMBOLS- BELOW TUNNEL (L'

1.0

0. 0 1 2 3

INCHES FROM TUNNEL 6.

SFigure 17. Pitot Pressure Surveys at Run Condition 3;L• 7-Inch Nozzle; Po = 500 psia

34

Axial surveys of the pitot pressures were taken to determine thepitot pressure gradients throughout the region of measurement in the7-inch nozzle. The data are summarized in Figures 3.8-21. The axialvariations of pitot pressure shown in Figare 21 were used to determinethe pitot pressures at the electron beam location to allow accuratecomparisons of the experimental data with the restifts of the theoreticalpredictions.

Similar axial surveys of pitot pressure in the 19-inch nozzle arereported in Ref. 1, where it is showvan that the axial variations arenegligible for all run conditions in the 19-inch nozzle.

D. VIBRATIONAL TEMPERATUDES

The measured vibrational temperatures of molecular nitrogen non-dimensionalized by the reservoir temperature are summarized for the7-inch nozzle in Figure 22. Excellent run-to-run repeatability wasobtained and little data scatter was observed.

The vibrational temperature ratio of approximately 0.A obtained atrun conditions 1 and 3 is in agreement with vibrational temperaturedata obtained in the 19-inch nozzle as reported in Ref. 1.

The- behavior of' the nitrogen vba~nltmeauedsrbtonear the boundary layer edge is expected and indicates the tendency fora greater degree of vibrational relaxation to occur ii the low-speedportions of the flow field. Stiuiar effects were observed in the19-inch nozzle., Note, howewer, at all run conditions there i-s asizable degree of vibratiaial nonequilibrium.

The measured vl orational tempurat'n'es cf nitric oxide nondimen-sionalized by the reservoir t ermttues ere siumuarized for the 7-inchand 19.4ncb nozzles 5n Figures Ž3 and 24.

Vibratioial temperetare data could not be obtained for nitric oxideat run -ondition 1, fox either nozzle, because of the combination of anextrem(7y 1ow nitric oxide concentration and a sizable background signal.Thit result is e:cpected, however;, since estimates of 'the nitric oxideconcentrations at 'these -rn conditions show that the nitric oxide partialpressure is leps than 0.0001 Torr. Since the low density limit for themeasurement technique is near 0.001 Torr, the nitric oxide concentra-tions at these run conditions are more than an order of magnitude belowthe detectable limit. The measurement problem at rum condition I iscourpounded by the background radiation which is approximately twice asintense as those at rim conditions 2 and 3.

The sensitivities of the ratios of band intensities in the NO ysystem place extreme requirements on the accuracy of 'the intensitymeasurement system (Figure 1). For exaMple, for the (i•5)/(O,Ž) bandcombination, an error in the measured ratio of ±1i% will yield an error

35

0.8

. x=0.69 in.LO 0.6-

06

02 3

x-2,52 in.

x

Lo 0.6 VA!....

04

S0,46-0 2

o ! 2 3 :-

0.8

0.

R0. 6

INI

0 2 3INCHES FROM TUNNEL .

RUN Ho(Btu/ib) Po(psia)0 76 6055 251O 77 5416 252

OPEN SYMBOLS-ABOVE TUNNEL ,SOLID SYMBOLS--BELOW TUNNEL

Figure 18. Pitot Pressure Surveys at Various AxialStations - Rn Condlition 1, 7-Inch Nozzle

361

x x=0.69 in.S0.6-

CL 0

0.4 Oj2 3

00xwX? 0.6 4,•, • ~x=2,52 in. •

o~,,)- IS S

0.4 .J!00 x4.34 in.

RUN__%o 78 3078 351F0 79 3755 354

OPEN SYMBOLS-ABOVE TUNNEL L-SOLID SYMBOLS-BELOW TUNNEL

Fi6're 19. Pitot Pressure Surveys at Various Axia.Stati-ons - l,•u Condition 2, 7-Inch NozzleJ

237

0.84 x069 ir.

00• x= 2,58 in.

0. -0 I al

0.

0.4 ._ I

RUN Ho(Btu/Ib) Po(PSfo )0 80 2769 502(3 81 .3566 503

OPEN SYMBOLS -ABOVE TUNNEL •SOLID SYMBOLS -BELOW TUNNEL

F~i.g-e 20., Pitot 1-"•e~su're S~urveys at Varilous Axialdttons - Run Condition 3,tt 7-Inchi No•,mz~l

38

C'A

pPPROBE ELECTRON

x 7 -

0 I 3 4

x, AA4A

0 I 2 13 4 6I!I I I

o I 2 3 4 5INCHES DOWNSTREAM OF NOZZLE EXIT

RUN Ho(Btu/Ib) Po(psio)o 76 6055 251o 77 5416 252'A 78 3078 351A79 3755 3540 80 2769 502

8 81 3566 503i,.ture 21. Axial CenterXine Mtot Pressures;

7-11ieh Nozzle

39

0.6

RUN CONDITION I

0I-

0.2-EQUILIBRIUM VIBRATION

0 2 3 40.6 ------- T .__

RUN CONDITION 3•o 0.4 - . . _.:,•,

------ EQUILIBRIUM VIBRATION

:0I0 ! 2 3 ,4

INCHES FROM TUNNEL

RUN COND RUN H (Btu/Ib) T0 ('1)10A I 74 5931 65290 i 75 5599 6346 40 ,3 64 21 29 3672o 3 65 3909 5131FLAGGED SYMBOLS- BELOW -UNFLAGGED SYMBOLS --ABOVE t

Pigure 22. Np Vibrational Tenperatures;

74Inch Nozzle

40€ ., iN

00,8

0.6-

RUN CONDITION 20 •__W__.______L !0 1 2 3 4

0. . .... -r ...----i- -

RUN CONDITION 3

06 TQA *20%

0.2-

0 4 3INCHES FROM TUNNEL .

RUN COND RUN Ho(Stu/Ib) T0(0K)2 60 A, 4651

11 2 62 304,3 43603 66 3936 51553 67 3694 4944

FLAGGED SYMBOLS "BELOW (UNFLAGGED SYMBOLS-ABOVE 4.

Fiintule '23. -NOVi T rt e ;7-Inch Novzz~e

"h, i

I

O, -1RNCODTO 1.0.-RUN CONDITION a

0 2 4 6 8 I0O,

oAim

INCESFROM TUNNEL CLRUN COND RUN HO(BTu/Ib) T(J¶

o 2 46 288$ 42.5 1o 2 47 3029 43460 3 49 212" 4625

FLAGGED SYMBOLS- BELOW 9,UNFLAGGED SYMBOLS-ABOVE 9 A

Figxrue 21t. NO Vibractional Temperatur'es;19-Ilnel No?0,z3.e

42

in vibrational temperature of ±25%. Hence, the accuracy of the NO Ivibrational temperatures is estimated to be i±20%.

The scatter in the data of Figures 23 and 24 is generally withinthe ±201/% accuracy expected for these measurements. The averages of thenitric oxide vibrational temperatures fall into two general categories:a vibrational temperature ratio near 0.4, and a ratio near 0.25. Aclose coupling between the vibrational energy modes of the variousspecies is expected due to the extremely rapid vibration-vibrationenergy exchanges which occur. However, an interesting trend in thehigner vibrational temperature data obtained in the 19-inch nozzle isevident in Figure 24. These higher temperature data show a definitetendency for the vibrational temperatures to decrease near the edge ofthe boundary layer. These variations may be related to the mechanismswhich lead to chemiltuninescence caused by the reaction NO + 0 -- NO2 + hv.Relatively strong radiation due to chemiluminescence has been observedat various r~un conditions, 1 2 and it is likely that the associatedchemical reaction will perturb 'the nitric oxide vibrational populationdistribution.

The behavior of the ni'vric oxide vibrational temperature near theboundary layer edge is in agreement with that obtained for the molecularoxygen vibrational temperature variations. 2 However, the changes inboth the molecular oxygen and nitric oxide vibrational temperaturesnear the boundary layer edge are opposite to those changes obtained forthe N2 vibrAtio•n' teýp + .... t iT s exected that a greater degreeof vibrational relaxation will occur within the lower-speed portionsof the boundary layer. Although the amount of relaxation in the boundarylayer is small, decreases in the vibrational tempera'tres are expectedrather than increases noted in Figures 23 and 24. As discussed in Ref.2, these vibrational temperature variations might result from a couplingbetween the vibrational relaxation and the fast nitric oxide shufflereactions.

E, NUMBER DENSITIES

The measured molecular nitrogen concentration profiles for the7-inch nozzle are given in Figares 25 and 26. The theoretically pre-dicted concentrations are also included.

The run-to-run repeatability and scatter within a given run arewithin the ±10%1o accuracy expected for these measurements.

The nitrogen number density data obtained at run condition 1 withthe 7-,inch nozzle are in good agreement with the results of the theo-retical pred Xtions.

The n- • .,en number density data obtained ab run condition 3 is inpoor agreement, with the results of the theoretical predictions. Itshould be noted that there is little scatter in the run-to-run variations

43

10 0

103

RUN Ho(Btu/Ib) [N2]o (crf•-3

0

Z -4 A 74 5931 1.068X10 9 l"10 0 75 5599 1.130 x loll

"FLAGGED SYMBOLS-BELOW '• -- IJIl M¼•-- L"•,2k LI/ ' i ,vvt.jj., , -,.. '-... -

-THEORETICAL RESULTS FOR_ Ho= 5700 Btu/1b Po=250 psia-FROZEN

-" NONEQUILIBRIUM

- -- EQUILIBRIUM

L0 _____L_____0 I 2 3 4 5INCHES FROM TUNNEL Q_

Figure 25. NK Number Densities at Run Condition 1;7-Inch Nozzle

-2210

0 RUN Ho(Btu/Ib [N2] 0 (cr-3 )

-- C 64 2129 4.99x10' 9-Z -4 .0 6 5 3908 3.II x I0'9

FLAGGED SYMBOLS - BELOW •.z UN"LA..ED SYMBOLS- ABOVE -

T THEORY AT Ho =3000 Btu/Ih, po=5 0 0 psia

FROZEN10 - -NONEQUILIBRIUM

EQUILIBRIUM

-0I J

0 I 2 4 5

INCHES FROM TUNNEL .

Figure 26. Na Number Densities at Run Condition 3;7-Inch Nozzle

451

rP

and that the differences between the theoretical and experimental re-sults are well outside the ±10% error band expected for the data.

The experimental techniques give redundancy in the number densitymeasurements. The number densities can be obtained either from theintensities of the (o,i) or the (1,2) vibrational bands. The numberdensities obtained from these two bands are coupled only through thedensity correction factor, s(Tv), which must be obtained from the vibra-tional temperature measurement. As seen in Figure 2, -this coupling isrelatively weak. In all cases, the nitrogen number densities obtainedfrom the two vibrational bands agreed with an error less than ±2%.Hence, it is concluded that the differences between the theoretical andexperimental predictions of the nitrogen number densities are not aresult of systematic errors in the measurement of the nitrogen concen-tration.

Many factors enter into the comparisons of the theoretical andexperimental results. The data are nondimensionalized by the reservoirnitrogen number densities, which are determined from thermochemicalcalculations assuming complete equilibrium in the reservoir. In addi-tion, the theoretical predictions are based on the centerline pitotpressure values, while both axial and radial pitot pressure variationsexist. The dLifferences between the theoretical and experimental nitro-gen number densities may result from cumulative errors in these factors.Note that there is little variation in the predicted nitrogen nu.mberdensities due to changes in the assumed chemical model, since molecularnitrogen behaves almost as an inert chemical species in the temperaturerange of these tests.

The measured nitric oxide species concentrations are compared withthe results of the theoretical predictions in Figures 27-30. Exceptfor the data obtained with the 19-inch nozzle at run condition

(Figure 30), the measured number densities are consistently below thepredicted values, indicating a greater degree of chemical recombinationthan predicted by theory. Nitric oxide concentrations resulting fromassuming chemically frozen and chemical nonequilibrium only are includedin Figures 27-30. The theoretical results assuming chemical equilibriumin the nozzle expansion give nitric oxide concentrations less than2 X 10"5 Vol %

Generally, good run-to-run repeatability and little data scatterwithin a given run were experienced with the nitric oxide number densitymeasurements. The number densities shown in Figures 27-30 are those

obtained from the intensity of the NO y (0,2) band. The number densitiesobtained from the NO y (1,5) band generally agreed with those from the(0,2) band to within 8%.

The factors which affect the comparisons of the theoretical andexperimental nitrogen densities also influence the comparisons for thenitric oxide number densities. However, the consistency of the differ-ences between the measured and predicted nitric oxide concentrations

46

- I.

- - I

S~Ef

16-4

RUN H0 (Btti/Ib) [INOo] (cm 1)

-0 60 3420 3.00xIO 80 62 3049 3.36X 108FLAGGED SYMBOLS- BELOW

10"5 --" UNFLAGGED SYMBOLS- ABOVE CLTHEORY AT Ho=30OOBtu/Ib, po=350psia- -FROZEN

NONEQUILIBRIUM

()I2 3 4 5A

INCHES FROM TUNNEL ?

Figure 27. NO Number Densities at Run Condition 2;ib= 350 psia; 7-Inch Nozzle

47

Ilk-44

I --4_0 10 --

RUN Ho(Btu/Ib). [N 0o (cm"')

"0 66 3936 3.40x10'6

0 67 3694 3.90x1018_.Z FLAGGED SYMBOLS -BELOW (L

IV UNFLAGGED SYMBOLS-ABOVE -THEORY AT Ho=3800 Btu/Ib, po=500 psia

FROZENNONEQUILIBRIUM

I0"-s I I I I ... -

0 I 2 3 4 5

INCHES FROM TUNNEL C

Figure 28. NO Number Densities at Run Condition 3;Po = 500 psia; 7-Inch Nozzle

48

S-.

S." RUN H0(Btu/Ib)[N ocm3

3 47 3029 3.42 x10'

I0 FLAGGED SYMBOLS - BELOW CUNFLAGGED SYMBOLS - ABOVE CL

FROZENNONEQUILIBRIUM

-6IIi1. . .-'10

2 4 6 8 10

INCHES FROM TUNNEL CLFigure 29. NO Number Densities at Run Condition 2;

Po = 350 psia; 19-Inch Nozzle

".9

-0 I0 .Ii I_=

0--4 RUN Ho(Btu/lb) [NO]o(cm"3) ---

o 0 49 2127 5.08x10-0 -FLAGGED SYMBOLS BELOW CLZ - UNFLAGGED SYMBOLS ABOVE _L-

-THEORYAT Ho2t29 Btu/Ib, Po500 psi a

Z 10 -FROZENNONEQUILIBRIUM

0 2 4 6 8 i0

INCHES FROM TUNNEL (t

Figure 30. NO Nurber Densities at Run Condition 3;Po= 500 paia; 19-Irseh Nozzle

50

suggests that the reaction rates of one or more of the nitrio oxideshuffle reactions should be changed to give an incroase In the rate ofdisappearance of nitric oxide. Numerical experimentation with the non-equilibrium flow computer program is required to establish the apprc')ri-ate shuffle reaction rates. As discussed in Section I, changes in theshuffle reaction rate onstants may have important influences on 'thetheoretical predictions of the overall properties of the test gas atthe nozzle exit.

Both the molecular nitrogen and nitric oxide species concentrationsmeasured with the electron beam are influenced by the rate of collisionquenching. The quenching densities xpplied in these studies to relateband intensities to number densities were obtained twn room-temperatureexperiments and no translational and/or vibrational influences wereincluded. The collision quenching of the N2 + first negative system at -*the run conditions for the 7-inch nozzle result in quenching factors,1 + ZNJI/Nj., near 1.5. Hence, collision quenohing is an importantde-excitation mechanism for the N2 + first negative system, and errorsin the quenching cross sections could be responsible, in part, for thediscrepancies between the theoretical and experimental number densities.

Quenching of the NO y7 system is much less severe than it is forthe N2 + first negative system. For the conditions of the 7-inch nozzletests, the quenching factor was less than 1.17. Hence, collisionquenching of the NO y radiation was not a particularly important factorin oonverting bead intensities -to iim-ber density. However, the accuracyof the nitric oxide number density measurements depends directly on theapplicability of the excitation model proposed here. The relativeimportance of excitation by secondary and primary electrons must bedetermined to obtain accutrate nitric oxide number density data. Theintensities of the NO y radiation, as a result of excitation by second-ary and primary electrons, were determined from room-temperature experi-ments, and it is possible that dtfferent excitation cross sections existat elevated translational and vibrational temperatures.

511

!IV1. CONCLUSIONS

A. ELBOTION BEAM TIXAhftIIQUES

These studios have substantiated the applicability of the highvoltage version of the electron beam generator for the 2-Foot Flectro.geadynamios Facility, In addition, the applicability of the diagnostictechniques for the measurement of the vibrational t% erature and speciesconcentrations of nitric oxide have been demonstrated. Operation of thebeam generator at high voltages (40 kV) leads to an increase win thespatial resolution in the measurements becanue of the associated de-crease in elastic scattering of beam electrons. The performance of thebeam generator during these tests indicates that it could easily beused at. flow densities greater than that corresponding to pressure of10 Torr at a temperature of 300 X.

The utcertainties associated with the exoitation-eanission processesfor N2,0, 0, 0a* and NO at high gas densities should be investigated indetail. The relative influences of excitation by secondary mid primaryelectrons should be examined under controlled conditions of elevatedtranslational and vibrational temperatures. The appropriate quenchingcross sections for these species must also be known as functions oftranslational temperature, vibrational temperature, and number densitybefore accurate electron beam data can be obtained at high densities.

Determination of the upper density liuait for applicatiou of theelectron beam technique is required before the fUll potential of thetechnique can be realized. From a mechanical point of view, no particu-lar difficulties in generating electron beams suitable for higher densityflows are anticipated with the present beam generator configuration.

B. TI•MOREICAL-E(PERIMFITAL COMPARISONS

The discrepancies between the theoretical, and experimental nitrogennumber densities experienced in these studies were not expected. It isunlikely that they result from deficiencies in the nonequilibrium theorysince the chemical activity of molecular nitrogen in these studies isquite low. The discrepancies probably result fixon a combination offacility-related effects sad unknown errors in the collision quenchingcross sections needed to convert band intensities to nwmber density.

Comparisous between the theoretical and experimental nitric oxidenumber densities indicate that the theory under-predicts the rate ofdisappearance of nitric oxide within the nozzle expansion process.Numericel experiments with the nonequilibrium flow ocauputer program arerequired to establish shuffle reaction rates which lead to better agree-ment between the theoretical and experimental results.

52

---------

Additional experimental studies should be conducted to obtain -temperatu-re and concentration data at enthalpy levels intenediate be-tween those of rmu condition I wnd run conditionrs e. and 3ý The resuli'sof these studies could then be employed effectively with those fProm thenumerical experitents to isolate the apparent recombination rates appli-cable to the expansion process. In addition, the concentration andvibrational temperatture of molecular oxygen and the concentration of.atcatc oxygen should be determined at high densities to allow a morecomplete ecompaison of the theoretical and exerimental results, Inal cases, these studies should be performed with the Intent, of. develop-ing a theoretical model for the expansion process which is usetu, for

predicting tunnel calibration data that cannot be measured directly.

53

-•!

1. Petrie, 8, L., Boia'ski, A. A. and Lee, H, F., "Electron Beam 1F'lowField Arwayaes in the AFtDL Two-Foot Eloatrogasdyrnwiii Faaftkity)"AFFDL-TR-71-161. (1971).

2. Pebrie) S. L. •nd KoMOa' J J 4 . "Eleoctron Beam Analysis of thePr'ope1•tieo of boleo•cx wnd Atomio O>,Wgen in the AFIFL 2-FootElecyro6,ýasdynlmioio Facility," AFFDL-TR-73-10 (3.973),

3. Petrie, S. L. and Koem&r, J. J., "Applicabion of the Electron Be=niFluorescence Technique to the Measurement of the Properties ofNitric Oidae in Nonequilibrilm Flows," AFFDL-TR-72-lhh (1972).

4, Mwitz, E. P., "The Electron Beam Fluorescenne Teclhique," AGAM)-graph 132, (Dec. 1968).

5. Petrie) S. T-,ý Pieree, G. A. &nd Fishburne, B. S., "mialysis ofthe Therniochehica.1 State ot mi Expanded Ail, Plarac," U. S. AirForce Flight Dynamics Laboratory Rept. AFFDL-TR-64-191 (1965).

6, Petrie, S. L., "Flow Field Analyses in a Low Density Axc-Heated oWind Tnnel.," Poo lngof the 65 Heat Trkf.uisfor and Fluid"Mech"aAnics e'ttlot, Stanford Unmiv. 7( of

7. Sobaciehr, D. 1. a nd Duckett' ]I. J . "A Spectrographic Pan I•ito ofa 1-Foot Hypersonic-Arc-Tiniona., krstream Using an rleotron BeamProbe " NASA TR R- (3.94).

8. Petrie) S. L., et al., "Electron Benm Studies of the PropertieA ofMolecular and Atomic Oxygen," AFFDL-TR-71-30 (.971).

9. Pearse, R. W. B., and Gaydon, A. G., The Edentific&tion of Molecular'SEcta, Chalvmann told Hall Ltd., Iondond•T •S}

10. Parobek, D. M., "Performance of Freestrean Flow 3istrutuentaticon for9-Inch Contoured Nozzle Tests in the 1aD 11-Mcgawatt Elctrog dynamicFacility," U, S. Air Force Fl:ight Dynan0d.cs Labor&m•ovx Rept. IAFtIL-TR-65-2.79 (1965).

11. Melton, L. A. and Klemperer, W., PELa.et. Space Sod, 20, 157 (1972),

12. Maitrup, P. N. and Herrett, 1R. 11., "Opt-ical Scattering Diagnos-ticTechniques for llyl)ersonic A•c Flows," AF1DL-TR-T71I4. (1971).).

[~514