DESIGN, MANUFACTURING AND TEST OF A PLUG NOZZLE ROCKET ENGINE

AIAA-02-4038 DESIGN, MANUFACTURING AND TEST OF A PLUG NOZZLE ROCKET ENGINE Eric Bsnard *, Hsun Hu Chn, Tom Mullr Mchanical and Arospac Enginring Dparmn California Sa Univrsiy, Long Bach John Garvy Garvy Spaccraf Corporaion Huningon Bach, CA Absrac Th papr prsns h dsign, manufacur and s of a small 1000 lbf ablaiv annular plug nozzl rock ngin. Th ngin was dvlopd by sudns wih h hlp from faculy and indusry profssionals as par of h California Launch Vhicl Educaion Iniiaiv (CALVEIN). Th dsign mhodology is prsnd for h ovrall ngin and is subsysms (injcor, combusion chambr and plug nozzl). Th flow ovr h plug nozzl is analyzd in mor dail using Compuaional Fluid Dynamics (CFD) in condiions corrsponding o a saic fir s. Basd on his analysis, h approxima dsign mhod usd for drmining h plug nozzl shap is shown o yild a highly fficin nozzl. Th analysis also shows h imporanc of modling flow propry variaions wih mpraur. Th ngin characrisics ar discussd along wih is manufacuring. Th ngin was sd and oprad succssfully for 200 ms afr which h graphi plug faild. A diffrn approach for scuring h plug nozzl is undr invsigaion and should lad o a nw ngin in h nx fw monhs. Finally, bnfis of doing chnology dvlopmn and validaion a such scals ar prsnd. Th xampl of CFD mhod validaion for powr-on in-fligh flow condiions in subsonic, ransonic and suprsonic rgims is discussd. 1. Inroducion Th concp of plug nozzls is no nw. Rsarch on h opic acivly sard in h 1950 s and lad o svral saic fir ss in h 1960 s [.g. 1-6]. Thir us was invsigad for h Spac Shul Main Engin (SSME) bu h chnology was dmd oo risky a h im. Mor rcnly, during h 1990 s, NASA invsd in h dvlopmn of arospik chnology for Singl-Sag-To-Orbi (SSTO) Rusabl Launch Vhicls (RLV) as par of h now-dfunc X-33 program. This program ld o h dvlopmn of svral linar arospik ngins, RS 2200, which wr sd rpadly. To da, howvr, no arospik ngin is known o hav powrd a rock in fligh. Unlik convnional bll-shapd nozzls, which opra opimally a on paricular aliud, plug nozzls allow h flow xpansion o slf-adjus, hus improving hrus cofficins. This improvmn ovr convnional bll-shapd nozzls occurs a aliuds lowr han h dsign aliud. This is paricularly criical for SSTO vhicls, which opra boh in h amosphr and in vacuum. A aliuds highr han h dsign aliud, plug nozzls ssnially opra similarly o bll nozzls. For mor dails abou h bhavior of h flow abou plug nozzls, s for xampl Rf. 7. Whil h rms plug and spik nozzls ar inrchangabl, som auhors associa arospik nozzls wih runcad spik nozzls wih bas bld. In his papr, all hr rms shall b usd inrchangably. * Lcurr, AIAA Mmbr Profssor, AIAA Associa Fllow Indpndn Conracor, AIAA Mmbr Prsidn & CEO, AIAA Mmbr Copyrigh 2002 by h Inc. All righs rsrvd.

Th arospik ngin discussd hr was dvlopd as par of h California Launch Vhicl Educaion Iniiaiv (CALVEIN), a collaboraiv program sablishd a California Sa Univrsiy, Long Bach (CSULB) in parnrship wih Garvy Spaccraf Corporaion (GSC). On of h componns of h program was h dvlopmn of an arospac sysm dsign curriculum. This curriculum aks h sudns hrough h produc dvlopmn cycl, from rquirmn dfiniion o h acual manufacuring and s of an arospac produc, using a Sysms Enginring approach in an ingrad produc am nvironmn [8]. For h 2001-02 acadmic yar, sudns ook on h challng of dsigning a small-scal annular ablaiv arospik ngin. Sc. 2 prsns h mhodology usd by h sudns o dsign h ngin and focuss on h flow characrisics ovr h plug nozzl. Sc. 3 oulins h ngin manufacuring procss and ss conducd. Anohr objciv of CALVEIN is o conribu o h dvlopmn of chnologis for low cos RLV s. This can b accomplishd in svral forms, ihr by dvloping h chnologis hmslvs, or by dvloping s plaforms, which would b usd or asily modifid o prform low cos chnology dvlopmn and validaion. On xampl would b o insrumn such ngin on board a low cos rock, such as on of CSULB s Prospcor rocks [8], and launch i o xprimnally characriz h ffcs of vhicl arodynamics on arospik ngin prformanc. Ths ar discussd a h nd of h papr. 2. Dsign mhodology and ngin flow characrisics 2.1. From rquirmns o Prliminary Dsign Rquirmns Wihin h framwork of CALVEIN, sudns wr rquird o dsign a 1000 lbf hrus annular ablaiv arospik ngin o b ingrad o on of CSULB s rocks, Prospcor-2 or 3. Th basic vhicl uss LOX and hanol as propllans. Th sysm is prssur-fd, wih ank prssur s a 390 psi. Typically, h injcor is dsignd for a prssur drop of around 90 psi in ordr o g a chambr prssur of 300 psi. Also, in ordr for h roughly 200 lb vhicl o clar h launch pad and gain an aliud of a las 4000 f bfor parachu dploymn, a burn im of a las 6 sc. was imposd. This projc was buil on h xprinc 2 gaind by sudns in dvloping 1000 lbf hrus ablaiv ngins using convnional bll-shapd nozzls [8]. Concp and ovrall ngin sizing Svral ngin concps wr considrd. Dsigns wih fins o hold h plug in plac wr rjcd bcaus of h high mpraurs ha h fins would b subjc o. Th dsign volvd oward h concp of Fig. 1, in which h plug is hld in plac by a cnr rod mound on h fac of h injcor. Also, bcaus of h small scal of h ngin, a singl annular combusion chambr was chosn. No shown is h igniion por which was a singl small solid rock moor providing a 3 scond burn im. Fig. 1. Solid modl of h arospik ngin From h rquirmns sad abov and h slcion of h dsign aliud (12,000 f), h spcific impuls, oal mass flow ra, chambr volum, hroa and xi aras ar compud. For an idal xpansion a 12,000 f, h ara raio is 5.12. For hs calculaions, a characrisics vlociy (C*) fficincy of 90% and a chambr characrisic lngh (L*) of 50 can b assumd [9,10] so ha h spcific impuls (ISP) is approximaly 235 s and h hrus cofficin would b C F = 1.495 (compud wih TDK). Basd on hs gnral characrisics of h ngin, h nx subscions addrss h dsign of h hr main subsysms, injcor, combusion chambr, and plug nozzl. Th las subscion focuss on h flow prdicions abou h plug nozzl.

2.2. Injcor and combusion chambr dsign Having drmind h main ngin characrisics, Fig. 2 shows h injcor dsign procss. Afr svral rad sudis, a sris of 16 spli ripls was slcd bcaus hy allow posiioning h liquid oxygn hols away from h chambr walls. Also, h hroa gap is only a fw millimrs. Basd on h daa obaind from prviously dvlopd ablaiv ngins wih graphi nozzls wihou film cooling, i is ncssary o add film cooling in ordr mainain his gap wihin rasonabl limis (h dsign hroa gap is approximaly 4.5 mm). A film-cooling ra of 30% (alcohol) is providd by igh our and igh innr hols. Th numbr of hols and hir siz was drmind as a compromis bwn prformanc and manufacurabiliy in a ypical univrsiy machin shop. Fig. 3 shows cross-scions of h injcor. Th hanol manifolds ar shown in rd and h LOX manifolds ar shown in blu. Wigh Flow Ras Ful hols Discharg Cofficin Injcor Typ Injcor Layou Tank Prss. (psi) Orific Sizs Ovrall Injcor Dsign Mixur Raio Fig. 2. Injcor dsign procss Film Cooling LOX Hols Film Cooling Fig. 3. Main injcor pla cross-scion Momnum Ra Raio Th combusion chambr was sizd o nsur propr burning of LOX and hanol. Lik on prvious ngins, an ablaiv chambr was mad (silica fibrs and phnolic rsin) wih a sl our shll. 2.3. Plug nozzl dsign Th conour of an arospik nozzl can b dsignd by using ihr a simpl approxima mhod [3,4] or Rao s mhod basd on calculus of variaions [1]. Th simpl approxima mhod assums a sris of cnrd, isnropic xpansion wavs occur a h cowl lip of h arospik nozzl. Using his mhod, h plug nozzl conour for a givn xpansion raio, ε, and raio of spcific has, γ, can b drmind. A brif dscripion of his mhod is givn blow. Sinc h flow is assumd o b paralll o h nozzl axis a h xi, h hrusr angl is givn by (Fig. 4a) θ = ν M ) ( whr M is h Mach numbr a h xi and h Prandl-Myr funcion, ν, is givn by ν = γ + an γ 1 1 1 2 1 2 γ 1 ( M γ + 1 1) an Th hroa ara is 2 2 F A = π( r r )/ cos θ = p C and h xi ara of h arospik is 2 2 A = π( r r ) b c F M 1 whr r dnos h radius of h cowl lip, rb dnos h bas radius of h arospik nozzl, p c h chambr prssur, F h hrus and C F h hrus cofficin. Onc h xpansion raio ε = A A is givn, r and r can b drmind for a fixd A. Th radial coordina of h arospik nozzl is givn by 2 2 2 2 A sin( µ + θ) r = r ( r r ) A sin µ cos θ and h axial coordina of h arospik nozzl is givn by r r x = an( µ + θ) whr θ = θ ν and h Mach angl µ = sin 1 (1/ M). Th rlaionship bwn h Mach numbr and h ara raio is givn by A A γ+ 1 1 2 γ 1 (1+ 2 2( γ 1) ) = M γ + 1 2 M For h prsn ngin, basd on an idal xpansion a 12,000 f and h hroa ara drmind in Sc. 2.1, r = 47. 7 mm. Fig. 4b shows h compud idal plug nozzl. For srucural 3

rasons, a non-zro bas radius, r b, was slcd (13.5% of r, i.. 6.44 mm). γ was assumd o b consan a 1.21. Th corrsponding runcad plug nozzl is also shown in Fig. 4. For h currn flow condiions, hy diffr vry lil. Also, h calculad plug lngh (approximaly 2.3 r ) is h sam as h on which can b drmind from Rao s mhod [1]. (a) 1.2 1 0.8 0.6 0.4 0.2 0 r r θ M µ M -1.5-1 -0.5 0 0.5 1 1.5 2 2.5 3 Idal x/r (0 @ ip of housing) Idal - Truncad Insid chambr r b aack. Thn, h rock could b flown wih som insrumnaion o gahr xprimnal daa and compar wih compuaions. Th Navir-Soks solvr slcd for h prsn applicaion is OVERFLOW [15] for i has h capabiliy of compuing flows wih variabl γ. Th axisymmric msh was gnrad using ICEM-CFD [16], ovrlappd and hn pr-procssd wih Pgasus [17]. Th Spalar-Allmaras urbulnc modl was usd in h compuaions. Th inl flow condiion was spcifid insid h chambr by imposing oal prssur and mpraur, and xrapolaing h mass flow ra for saisfying h sonic flow condiion a h hroa. This approach is ncssiad by h fac ha h sonic lin a h hroa is no sraigh and a-priori unknown du o h wo-dimnsional naur of h flow fild. Fig. 5 shows a comparison bwn compud dnsiy gradins mploying h cnral diffrnc and Ro schms a dsign prssur/aliud, i.. a prssur raio (PR) of 32 for a consan γ (γ = 1.21). As xpcd, h lar is abl o capur shocks whn h formr may no, paricularly if hs shocks ar wak. Fig. 6 shows h bas flow as compud wih h Ro schm. (b) Fig. 4. (a) Noaions for plug shap dsign mhod and (b) compud plug shaps. Barrl Shock Rflcd Barrl Shock 2.4. Plug nozzl flow characrisics On of h main issus associad wih h us of plug nozzls in launch vhicls is h lack of validaion of compuaional mhods for prdicing ngin prformanc undr a wid rang of powrd fligh condiions, including spd and angl of aack. To h auhors knowldg, publishd xprimnal daa and corrsponding Compuaional Fluid Dynamics (CFD) analyss ar limid o saic fir ss or o cold flow ss in wind unnls and h lik [11-13]. Th problm is furhr complicad by h inrs in blding propllans a h plug bas in ordr o incras hrus [14]. For his cas, vry accura soluions ar rquird in ordr o drmin opimum configuraions wih confidnc. As a firs sp oward powr-on CFD validaion, his scion addrsss h compuaion of h flow ovr h runcad plug nozzl dsignd in h prvious scion in saic fir s condiions. Th nx sp would b o prform similar compuaions a various flow condiions by varying aliud (or ambin prssur), Mach numbr and angl of Expansion Fan 4 Mach Disc Fig. 5. Schlirn-yp plo a dsign prssur (PR=32) for h Ro schm (op) and cnral diffrnc schm (boom) Dividing Sramlin Sagnaion Poins Sramlin Isolin M=1 Fig. 6. Mach numbr and flow parns nar h plug bas a dsign prssur

Th hrus can b calculad by ingraing h forcs along h bas and plug ara, and by adding h momnum across h hroa. Th rsul is a hrus of 982 lbf or 4372 N, and a hrus cofficin of 1.472. Wih h dfiniion of fficincy as CFi CF η = 1 C whr C Fi is h idal hrus cofficin and nglcing h losss du o fini ra kinics (no modld in h CFD), h viscous and divrgnc losss can b compud. Thy ar shown in Tabl 1 along wih ypical valus for bll shapd nozzls rprsnaiv of SSME prformanc [6]. As xpcd, a dsign prssur/aliud, hr ar virually no divrgnc losss for h arospik ngin. Also, viscous losss ar lss for h annular arospik ngin bcaus h nozzl ara is lss han for an quivaln bll shapd nozzl. Fi Fig. 7. Mach numbr disribuion for variabl g (op) and consan g (boom) a dsign prssur (PR=32) Efficincy Bll nozzl [6] Arospik nozzl Divrgnc 0.992 0.9995 Viscous 0.986 0.9947 Global 0.978 0.9942 Tabl 1. Comparison of bll and arospik nozzl fficincis OVERFLOW has wo opions for including variaions in γ. I can ihr accoun for γ variaions as a funcion of mpraur, or acually solv for mulipl spcis. Figs. 7 and 8 show a comparison of Mach numbr and prssur disribuions a dsign prssur for boh consan (boom) and variabl (op) γ using h formr approach. Whil h flow in boh cass xhibi similariis, hr ar som small diffrncs in shock and xpansion fans srngh and locaion, paricularly in h plum. In h xpansion fans, h prssur is narly h sam whil h Mach numbr is lowr in h cas of variabl γ compuaion. Also, shock locaions appar slighly downsram for variabl γ and h shocks ar srongr in h plum. Tabl 2 shows h hrus conribuions for boh cass. Lil diffrnc is obsrvd. Th diffrnc, howvr, is largr han h losss du o drag. Thrfor, i migh b infrrd ha in ordr o accuraly compu h flow abou such configuraions, having a capabiliy for varying flow propris is criical for powr-on flow prdicions. Fig. 8. Prssur disribuion for variabl g (op) and consan g (boom) a dsign prssur (PR=32) Variabl Gamma Consan Gamma Prssur 3436 N 3364 N Momnum 1022 N 1031 N Viscous -24 N -23 N Toal [N] 4435 N 4372 N Toal [lbf] 996 lbf 982 lbf Tabl 2. Effc of variabl g on hrus conribuions 3. Manufacuring and ss 3.1. Manufacuring procss Th injcor was machind ou of aluminum. Th drilling of h film cooling hols was paricularly challnging bcaus of hir small siz (0.022 for h insid and 0.016 for h ousid, s Fig. 9). Also, h many groovs and manifolds addd o h im ndd o machin h injcor. Th our combusion chambr was mad ou of sl and h ablaiv linr was mad ou of silica fibrs and phnolic rsin. Th linr was laid-up on a pic of machind polypropyln. Th hroa insr and h spik rod and nozzl wr machind ou of a singl pic of graphi (Fig. 10). Th spik was hld o h injcor fac hrough a rod approximaly 3 long. Th hroa our insr was bondd do h ablaiv linr a im of linr lay-up. Th innr combusion chambr is shown in Fig. 11 afr 5

machining and bfor insrion ino h sl our chambr. Fig. 12 shows h fully ingrad ngin. Two pors ar visibl on h lf, on for chambr prssur masurmn and h largr on in h back for housing h solid moor usd for ngin igniion. Fig. 9. Tripl injcor wih film cooling hols Fig. 12. Fully ingrad ngin 3.2. Injcor war-flow s A war flow s was conducd o vrify propr impingmn of h various flows (Fig. 13), drmin h acual prssur drop across h fac of h injcor, and rim h fd-lins if ndd. Th prssur drop was largr han anicipad (150 psi insad of 90 psi) on h ful sid bcaus of h complx groov parn insid h injcor (h ful nrs h injcor from h cnr and mus also rach h our rim of h injcor). Trim orifics wr addd on h LOX sid o obain h propr mixur raio. Fig. 10. Machind graphi plug and hroa insr Fig. 13. War flow s of h injcor 3.3. Saic fir s and dvlopmn saus Fig. 11. Compld ablaiv linr and hroa insr Th ngin was ingrad ino h GSCdvlopd saic fir s (SFT) sand, which includs a propulsion sysm and load clls for hrus 6

masurmns. Fig. 14 shows h SFT sand fid o VTS-2 a h Mojav Ts Ara (MTA), si ownd and oprad by h Racion Rsarch Sociy (RRS). Thr load clls ar locad bwn wo half-inch aluminum plas. Also, chambr prssur is masurd by a prssur ransducr mound on h sid of h chambr. Engin igniion is prformd by lighing a small solid moor also mound on h sid of h chambr which provids approximaly 3 sconds of burn. Fig. 15 shows h ngin 200 ms afr igniion in which a sabl combusion is obsrvd. Unforunaly, h spik faild srucurally righ afr ha, chockd h hroa and lad o an xplosion in h injcor (Fig. 16). Th faild boom porion of h spik can b sn in h middl of Fig. 16 as i is bing jcd away from h ngin. Th lf ovr from h spik rod and whr i faild ar shown in Figs. 17 and 18, rspcivly. Unforunaly, bcaus of oo low a sampling ra, no usful daa was rcordd during h s. Fig. 15. Arospik ngin 200 ms afr igniion Fig. 14. Arospik ngin on saic fir s sand Inrsingly, h graphi did no brak nar h bas of h injcor whr bnding momns would hav bn largr nor nar h nd of h rod supporing h spik suggsing ha bnding was probably no h caus of failur. Insad, having usd a vry bril marial in nsion snsiiv o microcracks, wihou addiional suppor hrough h nir lngh of h spik, was probably h caus of h failur. Analyss ar currnly bing conducd o gain mor informaion as o wha changs o mak in h nx vrsion of h ngin. Various mans of scuring h plug nozzl for a svral scond burn ar bing invsigad. Th s, howvr, validad h igniion squnc and, for a fw ms, h soundnss of h dsign. Sudns ar alrady a work machining h nx injcor and prparing h nx rvisd ngin. A saic fir s is plannd for h Fall 02 and, if succssful, will b followd by a launch of h prviously-flown Prospcor-2 vhicl. 7

Fig. 16. Explosion in injcor righ afr spik failur Fig. 17. Main injcor pla and faild cnr rod diffrncs in hrus and plum characrisics. Also, h nozzl is shown o b highly fficin. Th ngin was manufacurd and sd. Th saic fir s was succssful for 200 ms afr which h ngin spik nozzl srucurally faild, rsuling in an xplosion of h ngin. Sudns ar now improving h baslin dsign o b abl o s a nw ngin in a fw monhs. Th ngin will hn b saic-fir sd and, if succssful, h s will lad o h rus of P-2 for h firs fligh of an arospik ngin in h hisory of rock propulsion. From an R&D prspciv, byond such milson, h ru bnfi of dvloping h ngin lis in h abiliy o insrumn h fligh vhicl o hlp characriz h arospik prformanc and flow physics ovr spik nozzls ovr various fligh rgims (spd and angls of incidnc). In paricular, if succssfully dvlopd, such plaform could b modifid o sui any dsird arodynamic shap and usd o valida in-fligh powr-on CFD prdicions. Such invsigaions could b prformd a low cos and many scald configuraions could b sd a subsonic as wll as suprsonic spds. As a sp in his dircion, rsarch is bing conducd o us CFD o characriz h slipsram ffcs on h annular arospik ngin prformanc whn oufid o h Prospcor-2 rock. Ths rsuls could hn b vrifid in fligh wih som snsors and, hus, conribu o paving h way oward h us of arospik ngins in omorrow s rusabl launch vhicls. Plug failur locaion Fig. 18. Locaion of spik failur 4. Conclusions Th papr prsns h dsign, manufacur and s of a sudn-dvlopd 1000 lbf hrus ablaiv annular arospik ngin. Th ovrall ngin dsign procss is oulind. Th dsign of ngin subsysms is also prsnd. Ths includ h injcor, h combusion chambr and h plug nozzl. In ordr o assss h capabiliy of xising CFD ools o compu h flow ovr arospik nozzls undr opraing condiions, h flow ovr h plug nozzl is compud using h NASA-dvlopd OVERFLOW cod. Rsuls show ha variaions in γ wih mpraur lad o small, albi no null, 8 Acknowldgmns Th auhors would lik o acknowldg h California Tchnology Trad & Commrc Agncy for parially funding CALVEIN. In addiion, hy would lik o rcogniz h arospik ngin dsign sudn am, paricularly Sh Quioriano, Jffry Lang, Collin Cory and Brandy Irish. Rfrncs 1. G. V.R. Rao, Spik Nozzl Conour for Opimum Thrus, Ballisic Missil and Spac Tchnology, Vol. 2, C.W. Morrow (Ed.), Prgamon Prss, 1961. 2. K. Brman and F.W. Crimp Jr., Prformanc of Plug-Typ Rock Exhaus Nozzls, ARS J., Jan. 1961. 3. G. Anglino, Approxima Mhod for Plug Nozzl Dsign, AIAA J., Vol. 2, No. 10, 1964. 4. H. Grr, Rapid Mhod for Plug Nozzl Dsign ARS Journal, April 1961.

5. R.P. Humphry, H.D. Thompson and J.D. Hoffmann, Dsign of Maximum Thrus Plug Nozzls for Fixd Inl Gomry, AIAA J., Vol. 9, No. 8, Aug. 1971. 6. R.A. O Lary and J.E. Bck, Nozzl Dsign, Boing Thrshold Journal, Spring 1992. 7. J.H. Ruf and P.K. McConnaughy, Th Plum Physics Bhind Arospik Nozzl Aliud Compnsaion and Slipsram Effc, AIAA Papr No. 97-3217, 1997. 8. E. Bsnard, J. Garvy, T. Hollman, T. Mullr, H.H. Chn and H.P. Chn, Sudn Dvlopmn and Ts of a Gimbald Annular Arospik Engin, AIAA Papr No. 2002-4184, July 2002. 9. O. Biblarz and G. Suon, Rock Propulsion Elmns, Wily-Inrscinc, 7 h Ed., Dc. 2000. 10. D. K. Huzl and D. H. Huang (Ediors), Modrn Enginring for Dsign of Liquid-Propllan Rock Engins, Progrss in Asronauics and Aronauics, Vol. 147, AIAA, 1992. 11. E. Kousavdis and G. Suckr, A Numrical Invsigaion of h Flow Characrisics of Plug Nozzls Using Flun, AIAA Papr No. 02-0511, Jan. 2002. 12. M. Onofri al., Plug Nozzls: Summary of Flow Faurs and Engin Prformanc, AIAA Papr No. 02-0584, Jan. 2002. 13. R. Schwan, G. Hagmann and P. Rijass, Plug Nozzls: Assssmn of Prdicion Mhods for Flow Faurs and Engin Prformanc, AIAA Papr No. 02-0585, Jan. 2002. 14. T. Io and K. Fuji, Numrical Analysis of h Bas Bld Effc on h Arospik Nozzls, AIAA Papr No. 02-0512, Jan. 2002. 15. D. Jsprsn, T. Pulliam and P. Buning, Rcn Enhancmns o OVERFLOW, AIAA Papr No. 97-0644, 1997. 16. ICEM-CFD Hxa, hp://www.icmcfd.com, 2002 17. N. Suhs, S. Rogrs and W. Diz, Pgasus 5: An Auomad Pr-Procssor for Ovrs-Grid CFD, AIAA Papr No. 02-3186, Jun 2002. 9