Spray Characteristics of a Liquid-Liquid Coaxial Swirl Atomizer. at Different Mass Flux Ratios

Transcription

1 Spray Characterstcs f a Lqud-Lqud Caxal Swrl Atmzer at Dfferent Mass Flux Rats K. Ghrbanan 1, M.R. Sltan 2 Sharf Unversty f Technlgy, Tehran, Iran and M. Ashjaee 3 Unversty f Tehran, Tehran, Iran and M.R. Mrad 4 Sharf Unversty f Technlgy, Tehran, Iran Abstract An expermental nvestgatn s perfrmed t explre the characterstcs f sprays prduced by a lqud-lqud caxal swrl njectr n a nn-cmbustng envrnment. Phase Dppler anemmetry s used fr the measurement f velcty and Sauter mean dameter f drplets acrss and alng the njectn axs fr varus nner- and uter mass flw rates. sults f the cmbned spray are cmpared wth thse f nner- and/r uter spray alne. The results ndcate that the nner njectr has a larger nfluence n the flwfeld f the cmbned spray cmpared t the uter ne. Further, the maxmum velcty f the cmbned spray s clse t the center f the spray thckness and decreases as the dstance frm the nzzle ext s ncreased. Hwever, the maxmum Sauter mean dameter f drplets alng the njectn axs mves t the uter perphery and ncreases as the dstance frm the nzzle ext s ncreased. 1 Assstant Prfessr 2 Asscate Prfessr 3 Asscate Prfessr 4 Ph.D. Student 1

2 Furthermre, the cmbned spray flwfelds are flud dynamcally smlar n terms f the velcty and the average Sauter mean dameter f the drplets. Nmenclature A Area based n d A Area based n n d n A Area based n d C D, Inner rfce dscharge ceffcent C D, Outer rfce dscharge ceffcent d Inner dameter f nner njectr rfce d n Outer dameter f nner njectr rfce d s Inner Injectr dameter at nlet sectn d s Outer Injectr dameter at nlet sectn d Inner dameter f uter njectr 2

3 rfce L ch Characterstc Length m& Mass flw rate r Radal pstn ynlds number V Ttal velcty V ch Characterstc Velcty V, max Inner njectr maxmum velcty V, max Outer njectr maxmum velcty We Weber number z Axal pstn ρ a Ar densty P l Lqud pressure drp ρ l Lqud densty σ Lqud surface tensn µ l Lqud Vscsty 3

4 Intrductn Lqud fuel/xdzer atmzatn s used extensvely n rcket engnes t explt ther hgh mxng effcency wthn a gven length f cmbustn chamber. As knwn, atmzatn prcesses are nherently cmplex nvlvng the clse cuplng f bth the thermdynamc state f the flud as well as the njectr desgn. The state f fragmentatn f the njected lqud nt smaller flud elements and ts mxng, evapratn, and cmbnatn at the mlecular level wth ther speces n chemcal reactn s f crtcal mprtance. Therefre, the characterstcs f the resultng spray feld have a sgnfcant mpact n the cmbustn stablty as well as the prpulsn effcency. Over the past few decades, a seres f theretcal and expermental studes are launched n ndustry and academa twards a better fundamental understandng f the lqud atmzatn phenmena. Studes are carred ut t predct the spray characterstcs f caxal swrl atmzers, emphaszng the velcty as well as the drp sze dstrbutn and ts nfluence n the evapratn and mxng f fuel and xdzer spray. A theretcal study f the lqud flm flw n the nner wall f the center pst f a swrl njectr was perfrmed 1. The measured spray characterstcs exhbted behavrs smlar t thse f a cnventnal arblast atmzer. Burck 2 nvestgated cld flw characterstcs f gas/lqud caxal njectrs. Ht wax freezng methd was used t study a central lqud sheet surrunded by an annulus gas. It has been fund that bth the mass flux- and the mmentum flux rats may affect the drp sze, mxng, and vaprzatn effcences. Further, phtgraphy, patternatn, and phase Dppler partcle analyzer was emplyed by Hautman 3 t examne the spray structure f gas/lqud caxal njectrs where the center lqud was swrled. It was bserved that the spray structure was smlar t thse f a pressure swrl njectr where the smaller drplets were beng entraned nt the central regn f the spray. In addtn, t was reprted that the spray angle and the drplet sze change as the gas and lqud mass flw rate change. Furthermre, Erglu 4

5 et al 4 and Hardalupas et al 5 emplyed phase Dppler anemmeter (PDA) t lk nt the lcal spray characterstcs f sngle caxal njectrs. In the latter reprt, spray characterstcs were examned n the bass f the ext Weber number and the gas-t-lqud velcty rat. It was reprted that fr sprays wth the same gas-t-lqud velcty rat, a decrease f lqud tube dameter by 50% mprved the atmzatn by apprxmately 25% and an ncrease f the gas-t-lqud velcty rat enhanced the atmzatn prcess. In a dfferent attempt by Hardalupas et al 6, spray characterstcs f three dentcal caxal ar-blast atmzers, placed n a trangular arrangement, were nvestgated. It was fund that dwnstream mergng f the ndvdual sprays was strng n the regn between the nzzle axes. Ramamurth et al 7 nvestgated the dsntegratn characterstcs f swrled annular lqud sheets f caxal njectrs at dfferent njectn pressures. Swrl was generated by a helcal swrler and, n sme cases, ntrgen gas was njected caxally ver the uter surface f the lqud sheet. The results ndcate that caxal swrl njectrs shuld be desgned wth large annular clearances and hgh-centrfugal frces t ensure the frmatn f annular sheets n the regme f the dvergng cncal shape. In anther study, L and Shen 8 used PDA t nvestgate the spray parameters such as SMD and mean velcty at varus radal and axal lcatns fr dfferent gas-t-lqud velctes at the nzzle ext. It was fund that the drplet axal velcty had a jet-lke self-smlar spatal dstrbutn alng the radal and axal drectns. Svakumar et al 9 studed the nteractn between tw cncal sheets f lqud, frmed by caxal swrl njectrs. Phtgraphc technques were used t explre the swrlng mtn, generated by passng the lquds thrugh sngle start rectangular helcal passages. The results ndcated that after mergng f the tw cncal lqud sheets, the pnt f mergng mves upstream. In a dfferent attempt, Svakumar et al 10 nvestgated the spray characterstcs f lqud-lqud caxal njectrs. It was reprted that the mergng prcess f lqud sheets leaded t an ncrease f SMD by 40-50%. 5

6 As mentned abve, a seres f nvestgatns are cnducted n pressure-swrl njectrs due t the varety f ther applcatn. These studes have explred the effects f nzzle desgn, peratng cndtns, prpertes f lqud and ambent cndtns n the spray characterstcs such as mean drp sze, spray angle, dscharge ceffcent, and flm thckness theretcally and expermentally. Hwever, nly lmted expermental studes are reprted n lterature n the detaled spray structures and atmzatn characterstcs resultng frm lqud-lqud caxal swrl (LLCS) atmzers. In LLCS cnfguratn, the lqud fuel and xdzer are njected nt the cmbustn chamber thrugh the nner and uter rfce f the caxal swrl njectr, respectvely. The present wrk s mtvated by a better understandng n the nteractn prcesses between the lqud sheets f lqud-lqud caxal swrl atmzatn. An n-huse-desgned LLCS njectr s nvestgated n terms f velcty as well as drp sze dstrbutn at dfferent statns frm the njectn plane by means f PDA. Further, smltude features are nvestgated fr the spray flwfeld. Expermental Setup and Instrumentatn The present authrs have cnducted a seres f expermental studes n varus gvernng parameters f lqud spray pattern f swrl type njectrs 11,12,13,14. The spray frmatn f varus swrl njectrs at dfferent njectn pressures as well as dfferent gemetrcal arrangements are nvestgated. Spray cne angles, breakup lengths, and velcty cmpnents are btaned as a functn f pressure drp. At lw njectn pressures, a hgh-speed, hghreslutn CCD camera s used t vsualze the essental features f the lqud sheets and breakup prcesses whereas at hgher pressures, PDA s used fr the smultaneus measurement f velctes and drplet szes n regns f nterest. In the present paper, attentn s fcused n PDA results fr an n-huse-desgned LLCS njectr. Lqud s njected smultaneusly at dfferent mass flw rates and pressures thrugh the nner as well as 6

7 the uter rfce f the caxal swrl njectr, representng fuel and xdzer flw rates, respectvely. A schematc llustratn f the njectr and ts gemetrc cnfguratns are shwn n Fg.1 and Table 1. Table 1 Gemetrc cnfguratns 2.0 mm d d 5.8 mm d d n 2.15 mm d 6.0 mm s d 9.0 mm s Fg. 1 Schematc f the LLCS njectr It shuld be mentned that the swrlng mtn s generated by passng the lquds thrugh tangental nlet prts wth crcular crss sectn. the nner njectr has tw tangental nlet prts wth dameter f d p = 1. 2mm and the uter njectr has fur tangental nlet prts wth dameter f d p = 1. 5mm. The swrl ntensty, gven by the swrl number, S, used by Svakumar 10, s derved fr present caxal njectr fr bth nner and uter rfces ( S, S respectvely). 7

8 S = d d n d s 2 p S ( d = d n d n 2 p ) d s Where n, n are number f tangental nlets fr nner and uter parts, respectvely. Accrdng t the gemetrcal dmensns fr present caxal njectr, swrl number fr the nner njectr s S = and fr uter njectr s S = Expermental Setup The expermental setup, as schematcally llustrated n Fg.2, cnssts f tw lqud supply systems, an njectr muntng system, an ptcal table fr laser dagnstcs, and a data acqustn system. 8

9 Fg. 2 Schematc f the expermental setup Fr the present study, water s used as the test flud and s suppled t the nner- as well as the uter caxal swrl njectr frm dfferent pressurzed tanks. The water supply system ncludes tw water tanks, pressurzed ntrgen bttles, pressure regulatrs, flwmeters, and water flters. Further, bth water supply systems have a rated maxmum pressure f apprxmately 6.2 MPa (900 psa). The lqud-lqud caxal swrl njectr s munted n a three-axs traverse system fr precse pstnng n the hrzntal as well as vertcal planes wth the njectr rfce beng pnted dwnwards. In addtn, the water spray s njected nt a large cllectn vessel t the ambent cndtn. The cllectn vessel s lcated adequately dwnstream f the njectr ensurng nt t nterfere wth the flwfeld beng nvestgated. 9

10 Dagnstcs Phase Dppler anemmetry s used fr the smultaneus measurement f velctes and drplet szes. PDA s a pnt measurement technque based upn an extensn f the basc prncples f the cnventnal dual-beam laser Dppler velcmeter except that three phtdetectrs are used t reslve the ambguty n the phase angle f the measured ptcal sgnals fr the determnatn f drplet szes. A cherent multlane argn-n cntnuus wave laser s used as the lght surce. The laser beam s sent t the transmtter where the clrs are separated n green (514.5 nm), blue (488 nm), and vlet (476.5 nm) fr axal and dameter measurements, velcty determnatn, and laser lght extnctn measurements, respectvely. The laser beam s splt nt tw beams f equal ntensty by the transmttng ptcs, and fcused t an ntersectn t frm a prbe vlume at a pnt n the spray. The prbe vlume characterstcs are defned by the ptcal arrangement f the transmtter. A prtn f the prbe vlume s maged at the slt wthn the recever. When a drp crsses the frnge pattern f lght n the prbe vlume, scattered lght s receved smultaneusly by three pht-multpler tube detectrs. The Dppler sgnal analyzer electrncs, and asscated sftware, prcess the sgnals frm the detectrs t smultaneusly get drplet sze and velcty cmpnent perpendcular t the plane f the frnges. A secnd cmpnent f velcty may be btaned by emplyng an addtnal par f laser beams at a dfferent wavelength n a plane rthgnal t the frst par f beams. The addtnal beam par frms anther prbe vlume cllcated wth the frst ne s that the secnd velcty cmpnent s btaned fr the same partcle. Fnally, the sgnals are dwnladed nt a PC fr data strage. Detaled nfrmatn abut the ptcal characterstcs f the PDA system s prvded by Mrad 15. The PDA transmttng and recevng ptcs s munted n a hrzntal plane and the PDA laser beams ntersect wth the spray t frm a frnge pattern n the hrzntal plane. The 10

11 measurements fr the drplet sze and velctes are based n 3000 samples per pnt fr a maxmum duratn tme f 25 secnds resultng n uncertantes f less than 6 µ m and 0.5m / s fr SMD f drplets and drplet velctes n the man thckness f the spray cne, respectvely. Fnally, fr flw vsualzatn, spray mages are captured by a 640x480 pxel dgtal camera where a strbscpe s used as the lght surce. Transent Spray Frmatn As a startng pnt, the spray frmatn when dschargng thrugh the nner nzzle f the LLCS njectr s studed. In a pressure-swrl atmzer, angular mmentum s mpsed n the lqud t frm a swrlng mtn. Under the actn f the centrfugal frce, ntally, a swrlng lqud flm emerges axally frm the njectr ext and frms a swrlng hllw cne sheet wng t the azmuthally cmpnent f velcty. Small-scale structure s develped n the lqud surface at the ext; hwever, larger-scale structure quckly dmnates the flm alng the adjacent expandng sheet and the sheet starts t splt becmng a seres f dstrted lgamentlke elements. Further, addtnal breakup may ccur due t cllsn r aerdynamc frces defrmng the lqud partcles t the pnt f secndary atmzatn. The expermental range f ynlds numbers,, and Weber numbers, We, fr bth the nner and the uter nzzle sprays are calculated where and We are defned as: ρ V L ch µ 1 ch = and 1 2 ρavch Lch We = (1) σ Whle the characterstc length L fr the nner spray s set equal t the nner dameter f the ch nner rfce, fr the uter spray, t s defned as the dfference f the nner dameter f the uter rfce t the uter dameter f the nner rfce, d d, as llustrated n fgure 1. In n 11

12 addtn, the characterstc velcty V ch s set equal t the axal velctes at the crrespndng nzzle exts. Fnally, a cmparsn between the expermental range and the engne peratnal cndtn s made and gd smlarty s btaned. a) b) c) d) e) f) g) h) Fg. 3 Spray frmatn fr the nner nzzle f the LLCS njectr Fgure 3 shws the develpment f the spray passng thrugh several stages such as drbble, nn, tulp stages and fully develped spray as the lqud njectn pressure fr the nner 12

13 nzzle s ncreased frm zer. It can be seen by nspectn that fr very lw njectn pressures, ( P < 0.2 bar), a hllw bubble shape f lqud sheet, nn stage, s frmed at the nzzle rfce fllwed by cntnuus lqud sheet dsntegratn nt drps, Fg. 3a-b. Further, the length f the hllw bubble, whch may be cnsdered as the breakup length fr ths mde, ncreases wth njectn pressure. A further ncrease f the njectn pressure wll result n sheet nstablty and thus a sem-burst f the hllw bubble s fllwed by a transfrmatn nt a cncal smth lqud flm, tulp stage, Fg. 3c-e. Furthermre, as the dstance frm the nzzle rfce ncreases, perfratns are develped resultng n a decrease f the sheet thckness. At hgher dschargng pressure, Fg. 3f, annular waves appear and the lqud sheet experences wave dsturbances a state n whch external frces dmnate the surface tensn frces n the lqud. Ultmately, wave frequency ncreases wth njectn pressure resultng n develpment f shrt-length waves as well as shrter breakup lengths. A fully develped spray crrespndng t a flw ynlds number f s shwn n Fg. 3h. The mpact f the spray frmatn fr ncreasng the dschargng pressure fr the uter nzzle f the LLCS njectr whle mantanng the dschargng thrugh the nner nzzle at a fxed value s nvestgated. Fgure 4 shws the cndtns where the nner nzzle s mantaned at an nn stage wth a ynlds number equal t 5000 whle the mass flw rate fr the uter nzzle s ncreased frm ts tulp stage t wavy dsntegratn mde. It s apparent frm Fg. 4 that an ncrease f the dschargng pressure fr the uter nzzle wll frst nt affect the nn stage f the nner nzzle; hwever, at a ynlds number equal t 25244, t wll dsntegrate the nn stage f the nner nzzle abruptly t frm a cmbned fully develped spray. Fnally, t shuld be mentned that a further ncrease f the dschargng pressure fr the nner nzzle wll shft the ynlds number fr a fully cmbned spray pattern t lwer values fr the uter nzzle. 13

14 a) b) c) d) e) f) e) f) Fg. 4 Spray frmatn f the LLCS njectr f varable and cnstant dschargng pressures fr uter- and nner nzzle, respectvely. Fully Develped Test Cndtn A sectnal vew f the spray flwfeld s schematcally llustrated n fgure 5. The crdnate z has ts rgn lcated at the nzzle ext and s pnted t the dwnstream drectn f the spray. The crdnate r s nrmal t the z-crdnate and s n the radal drectn f the spray. 14

15 Hllw spray cne Inner Flw (Fuel) Outer Flw (Oxdzer) Data pnts r Man thckness f the spray cne z Fg. 5 Schematc f the spray flwfeld In the present paper, measurements are perfrmed alng the r-crdnate as well as z- crdnate. Further, the prbe vlume and the ttal number f measurement pnts are selected t ensure measurements acrss the man thckness f the merged spray sheets but als nsde the spray cne f the nner flw (fuel) as well as utsde the spray cne f the uter flw (xdzer) at any test cndtn presented n ths paper. Equally spaced measurement pnts by 5 mm are selected t capture data startng frm the nsde regn f the ar-cre t the utsde regn f the cmbned spray sheet. Infrmatn abut the peratng cndtns s summarzed n Table 2. Table 2 Operatng cndtns f LLCS njectr Operatng Parameters Present Study Mass flw rat (MFR) Velcty rat (VR) Inner rfce: Length-t-dameter rat Lqud densty, kg / m 998 Mass flw rate, lt / hr Weber number ynlds number

16 Outer rfce: Length-t-dameter rat Lqud densty, kg / m 998 Mass flw rate, lt / hr Weber number ynlds number Expermental sults and Dscussn Tw grups f measurements are presented n ths paper. Frst, a parametrc study n the mutual nfluence f the nner and uter spray patterns n each ther s perfrmed. In ther wrds, at a fxed z-pstn but varable r-pstns, velcty and SMD dstrbutns are btaned fr varus nner- and uter ynlds numbers. Secnd, the ynlds numbers f the uter and nner sprays are kept fxed and the velcty and SMD prfles f the cmbned spray are determned at varus z-pstns. The range f the ynlds number fr the test cndtn s smlar t the actual njectr cndtns f nterest. PDA valdatn rates are n the rder f 70-90% where hgher rate crrespnds t the spray man thckness regn and lwer rates fr the hllw regns. Fully Develped Cndtn f Indvdual Caxal Injectrs As a startng pnt, measurements are cnducted t cnfrm the precse algnment and centerng f the ntegrated caxal nzzles as well as the spray symmetry alng the z- crdnate. The detals f the valdatn prcedure and the measurements are gven by Mrad 15. Further, prelmnary experments are perfrmed t dentfy the ntatn pnt f the fully develped cndtn f the sngle njectrs ndependent f each ther. It shuld be mentned that prevus expermental nvestgatn has revealed that the smallest mass flw rate fr a stable, cnstant dscharge ceffcent calesces wth the ntatn f a fully 16

17 develped spray pattern 16. Hence, the effect f the flw rates n the varatn f the dscharge ceffcent f sngle caxal njectrs s nvestgated where the dscharge ceffcent s defned as C D = A m& 2 ρ P L L (2) It shuld be nted that the area, A, n the abve equatn fr the nner and uter sprays s set equal t A and A A n, respectvely. The results fr dschargng ether thrugh the nner nzzle nly r the uter nzzle nly are shwn n fgure 6. It can be seen by nspectn that the dscharge ceffcent fr the nner nzzle nly has a sharp drp and reaches an asymptte at C D, = fr a mass flw rate f 70ltr / hr whch s n gd agreement wth reprted data fr smplex njectrs 17. Hwever, the dscharge ceffcent fr the uter nzzle nly shws a farly smth drp and reaches an asymptte at C D, = fr a mass flw rate f 170 ltr / hr Dscharge ceffcent (C D ) Inner spray alne Outer spray alne Mass flux (lt/hr) Fg. 6 Varatn f the dscharge 17

18 ceffcent wth mass flux fr nner- and uter rfces It s apparent frm fgure 6, that the values fr the lwer mass flw rates f the nner- and uter njectrs, crrespndng t ltr / hr and ltr / hr as ndcated n Table 2, respectvely, are wthn the range f cnstant dscharge ceffcents. Further, t s evdent that the selected expermental range fr the mass flw rates s ndependent f ynlds number. In addtn, ne may calculate the hydraulc dscharge area, the axal velcty, and s the ynlds- and Weber numbers by knwng the dscharge ceffcent. Hence, fr the mass flw rates 70 ltr / hr and 250 ltr / hr, the ynlds numbers are equal t and Fnally, experments are als perfrmed t assure that under the fully develped cndtn the nner spray s always n the ar-cre f the uter spray. Nrmalzatn In general, n rder t enhance cmparsn, expermental data fr njectrs are made dmensnless by values at the uter dameter f the nzzle rfce. Hwever, n the present study fr lqud-lqud caxal njectrs, due t the exstence f tw uter dameters namely, ne fr the nner nzzle and ne fr the uter nzzle the z- and r-crdnates are made dmensnless wth respect t the dfference between the uter dameters f the nner- and uter nzzles as fllws: z zˆ = and d d r rˆ = (3) d d Further, the velcty dstrbutn s als made dmensnless as 18

19 V(r, z) Vˆ = (4) V ref where V ref s the average velcty f the maxmum velctes f each njectr at the nzzle ext (z=0). In ther wrds: V ref V, max + V,max = (5) 2 where V, max and, max V crrespnd t [; ] = [0;74376] and [; ] = [40390;0], and are equal t 56.1 and 41.3 m/s, respectvely. These maxmum velctes used fr nrmalzatn are btaned based n Bernull s equatn fr a pressure drp t ambent cndtn. Actual velctes at the nzzle ext have been estmated by usng dscharge ceffcents fr nner and uter rfces and the estmated actual velctes are btaned less than maxmum velctes used fr nrmalzatn. Spray Interactn Prcesses Velcty Plane The velcty prfles at a fxed z-pstn ( ẑ = 10.5), varable r-pstns 0 rˆ 16, and dfferent ynlds numbers are shwn n fgures 7a-e. Fgure 7a shws the velcty prfles fr the uter spray at dfferent ynlds numbers whle there s n flw thrugh the nner njectr, = 0. It can be seen by nspectn that as ne mves alng the rˆ -axs, the velcty Vˆ frst ncreases frm the nsde perphery and reaches a maxmum smewhere wthn the spray thckness and then decreases twards the utsde perphery f the spray cne. Further, an ncrease f prfle twards hgher maxmum velctes Vˆ max. wll result n a shft f the velcty 19

20 a) =0 (uter spray alne) z=10.5 V Hllw Cne gn f Outer Spray r b ) c) = (nner spray alne) z= = (nner spray alne) z=10.5 V 0.3 V Hllw gn f nner spray r r d ) e) = (nner spray alne) z= ( nner spray alne) = z=10.5 V 0.3 V Inner Part f Spray Cne Man Thckness f the Spray r r Fg. 7 Velcty dstrbutn fr varable 20

21 As a next step, the nner njectr s suppled wth a flw f ntal ynlds number = whch s slghtly less than the chsen maxmum ynlds number fr the uter njectr = In addtn, fr nterpretatn purpses, the velcty prfle fr whch the uter njectr s nt suppled (that s, the nner spray nly) s drawn as a sld lne. A cmparsn between fgures 7a and 7b reveals that the cmbned velcty prfles n fgure 7b reman unchanged cmpared t thse n fgure 7a. As a result, ne may cnclude that, under these cndtns, the nner ynlds number = s nt strng enugh t alter the cmbned spray pattern n fgure 7b. Thus, measurements are carred n fr cndtns n whch the nner ynlds numbers are ncreased up t = (fgure 7c-e). As shwn n fgure 7c, whle the cmbned velcty prfle f [ ; ] [51482; 40390] = remans almst unchanged, the cmbned velcty prfle crrespndng t [; ] = [51482; 25244] s altered and reaches a relatvely hgher maxmum velcty Vˆ. A further ncrease f the nner ynlds number = 62941, fgure 7d, wll result n max an ncrease f the maxmum velcty Vˆ max f the cmbned velcty prfles. Hwever, t s mprtant t nte that althugh the cmbned velcty prfle f [ ; ] [62941;25244] = s changed cmpared t thse n fgures 7a-c; nevertheless, the velcty prfle f the nner spray alne, [; ] = [62941;0], s s sgnfcant that ts values are larger than thse crrespndng t [; ] = [62941;25244] at any pnt n the spray thckness. Ths tendency gets strnger as the nner ynlds number becmes mre dmnant t the system. As shwn n fgure 7e, the velcty prfle f the nner spray alne, [; ] = [74376;0], s almst larger than any pnt f the cmbned spray patterns. Furthermre, fr the cmbned 21

22 velcty prfle, whle the nner spray cne angle s ncreased, the uter spray cne angle s slghtly decreased cmpared t the velcty prfle crrespndng t the nner spray alne [ = 0], fgures 7c-d. SMD Plane The SMD f drplets at a fxed z-pstn ( ẑ = 10.5), varable rˆ -pstns f 0 rˆ 16, and dfferent ynlds numbers crrespndng t fgures 7a-e are shwn n fgures 8a-e. Fgure 8a shws the SMD prfles fr the uter spray at dfferent ynlds numbers whle there s n flw thrugh the nner njectr, = 0. It can be seen by nspectn that as ne mves alng the rˆ -axs, SMD frst ncreases frm the nsde perphery and then flattens acrss the spray thckness. Further, an ncrease f wll result n a mnmal drp f SMD values. Hwever, ne may cnclude that the SMD prfles fr the uter spray alne fr varus reman unaffected. Cmparsn between fgures 8b-e reveals that the SMD fr drplets f cmbned sprays, except fr thse at the nner perphery, are very clse t each ther and ther values are sustaned relatvely cnstant fr varable nner ynlds number. On the ther hand, t s apparent that the SMD prfles fr the nner spray alne are shfted t lwer values fr hgher (sld lnes n fgures 8b-e). Cnsequently, ne may cnclude that, under current cndtns, the SMD f drplets fr the cmbned sprays reman relatvely unaffected by varable as well as. 22

23 a) = (uter spray alne) z= SMD( m) µ Hllw gn f Outer Spray SMD( µ m) Hllw gn Inner Spray = (nner spray alne) z= r b ) c) Man Thckness f the spray cne after mergng SMD( µ m) = (nner spray alne) z = SMD( m) µ r d ) e) = (nner spray alne) z= SMD( µ m) r = ( nner spray alne) z= r r Fg. 8 SMD dstrbutn 23

24 Crss-sectnal Perfrmance Map PDA Measurements f the cmbned sprays at a fxed z-pstn ( ẑ = 10.5) are summarzed n fgure 9a-b. Whle fgure 9a llustrates the maxmum velcty as a functn f and Vˆ max f the cmbned sprays, fgure 9b shws the crrespndng averaged SMD f drplets. Hence, ne may vew fgure 9a-b as a crss-sectn f the perfrmance map f the lqudlqud caxal swrl njectr. It can be seen that bth prpertes, Vˆ max and SMD avg, have ppste behavr. In ther wrds, SMD avg decreases wth ncreasng max Vˆ. The prpertes SMD avg and Vˆ max pssess ther lwest and hghest value at a pnt where the ynlds numbers and are the largest, respectvely. Hwever, n the present nvestgatn, t s apparent that has a strnger mpact n the atmzatn effcency than. Ths ccurrence may be due t the smaller rfce f the nner njectr and ts twn-nzzle gemetry that prvdes a hgher mmentum t the drplets. Maxmum Velcty (m/s) SMD( µ m) a ) b) Fg. 9 Perfrmance map fr LLCS njectr at ( ẑ = 10.5). a)velcty dstrbutn, b)smd dstrbutn 24

25 Spray Cne Prpagatn The dwnstream varatn f velcty dstrbutn and SMD f a cmbned spray s presented n fgures 10 and 11. Measurements are made at varus radal pstns at sx dfferent z- lcatns and at [ ; ] = [57218;30292] wth Vˆ max and SMD avg equal t 17.97m / s and 138.8µ m, respectvely. Ths cndtn s smlar t the actual peratng cndtn f the njectr = = z V r Fg. 10 Dwnstream varatn f the velcty dstrbutn SMD( m) µ = = r Fg. 11 Dwnstream varatn f SMD dstrbutn z 25

26 Fgure 10 llustrates the spatal dstrbutn f the dmensnless velcty Vˆ. It can be seen by nspectn that, at a fxed ẑ -pstn, the velcty reaches a maxmum value smewhere clse t the centerlne nsde the cmbned spray thckness and then decreases t the perphery f the spray. Further, alng the dwnstream ẑ -pstn, the spray thckness spreads ut and the maxmum velcty Vˆ max f the cmbned spray patterns decreases as the dstance frm the nzzle ext s ncreased. Frm fgure 10, t s apparent that the behavr f the drplet velctes Vˆ at the nner- and uter perphery f the merged spray s dfferent. Whle, alng the dwnstream z-axs, drplets at the nner perphery are decelerated at a strnger rate than that by Vˆ max, drplets at the uter perphery are almst mantaned at the same velcty. Hwever, t s evdent that the reductn f the drplet velctes Vˆ alng the nner- and uter perpheres and pstns crrespndng t Vˆ max are apprxmately a lnear functn. The crrespndng SMD dstrbutn s shwn n fgure 11. It s apparent that the behavr f the SMD dstrbutn at fxed ẑ -pstns s smlar t the crrespndng velcty prfle. In ther wrds, the SMD f the drplets reaches a maxmum value SMD max clse t the pstn f the maxmum velcty Vˆ max and then decreases t the perphery f the spray. Hwever, alng the dwnstream z-axs, the varatn f SMD max s ppste t max Vˆ. Near the center, SMD max f the cmbned spray patterns ncreases as the dstance frm the nzzle ext s ncreased. Further, whle SMD ncreases alng the uter perphery t values clse t SMD max, t decreases alng the nner perphery t smaller values. Fnally, a mntncally grwth f SMD max wth the z-axs s evdent. The fregng results suggest that alng the dwnstream z-axs the drplets clser t the njectr ext have hgher velctes than thse farther dwnstream n the spray thckness. Further, as the drplets are transprted alng the dwnstream z-axs, velcty prfle flattens 26

27 due t the lss f ts mmentum. The results are cnsstent wth Lagrangan analyss n sngle drplets 18. Furthermre, the decrease f the SMD alng the nner perphery s explaned by the ccurrence f the addtnal breakup and vaprzatn f the drplets n ne sde and the transprtatn f relatvely small drplets frm the central- and uter perphery regn f the spray thckness twards the nner perphery n the ther sde. As a result, larger drplets havng larger nerta are mgrated frm the nner perphery t the central regn f the spray descrbng the mntncally grwth f the SMD max. Self-Smlarty Smltude may be explted fr predctng an njectr s drp sze and velcty feld. The fregng results ffer evdence n favr f the smltude hyptheses assumng that the njectr s nternal flwfeld s ne where the nvscd thery apples and njectn ynlds number s n the turbulent range as n the present experments. Hence, the velctes and SMD f the drplets at each z-pstn are nrmalzed by the maxmum value f the velcty and the maxmum value f SMD n the same z-pstn, respectvely: ˆ V ( r, z) V z = and V max ( z) SMD(r,z) SMˆ Dz = (6) SMD (z) max Further, the nrmalzed crdnate s defned as fllws: r rˆ z = (7) z z 0 where z 0 s cnsdered as the center pnt f the nner njectr and s equal t zer. Fgures 12 and 13 shw the nrmalzatn f the velcty and SMD f the drplets fr dfferent r- and z-pstns, respectvely. It s apparent that whle the radal prfles f velcty and SMD are dfferent at varus nner- and uter ynlds numbers, as shwn n fgures 7 and 8, but the crrespndng nrmalzed results crrbrates the smltude hypthess. 27

28 Self-Smlar gn z V Z Hllw Cne gn Smlarty Desn't hld r Z Far Out f Spray Cne Smlarty Desn't hld Fg. 12 Nrmalzed velcty dstrbutn Self Smlarty gn z SMD Z r Z = R = Fg. 13 Nrmalzed SMD dstrbutn Addtnally, fgure 12 ndcates that the velcty prfle s self-smlar n the range f 0.67 rˆ z A clser examnatn reveals that ths range s apprxmately equal t the spray thckness at the crrespndng z-pstns. Therefre, pnts utsde the crcled regn replcate measurements ether alng the spray perphery r utsde the spray. A smlar bservatn s made fr S Mˆ D n fgure 13. As a result due t self-smlar behavr f bth z 28

29 the velctes and SMD f the drplets, ne may map the atmzatn flwfeld f a partcular lqud-lqud caxal swrl njectr desgn by smple scalng f avalable data, hence preventng a large prtn f experments that are needed fr ptmzng the njectr desgn. Cnclusns Cmbustn applcatns n bth rcket and gas turbne prpulsn systems requre cnjectn f fuel and xdzer n a frm that enhances mxng and mprves the chemcal reactn prcesses t be cmpleted n a mnmum cmbustr length. Hence, a systematc flud dynamc study f lqud-lqud caxal swrl njectr n a nn-cmbustng envrnment s cnducted t elucdate the features gvernng atmzatn. PDA s used fr a cmprehensve analyss f velcty and Sauter mean dameter f drplets. Measurements are perfrmed acrss and alng the njectn axs fr varus nner- and uter mass flw rates. sults f the cmbned spray are cmpared wth thse f nner- and/r uter spray alne. In the present paper, fur sgnfcant cnclusns are btaned frm the water spray studes. Frst, the measurements shw that smaller drps are mvng slwer than the larger nes. Secnd, t s fund that the nner njectr has a larger nfluence n the flwfeld f the cmbned spray cmpared t the uter njectr. Velcty and SMD measurements at a fxed z-pstn but dfferent nner- and uter mass flw rates ndcate that, fr the velcty dstrbutn, the varatn f the nner ynlds number has a strnger mpact n the cmbned spray than any varatn f the uter ynlds number. Further, the Sauter mean dameter f the drplets fr the cmbned spray at a fxed nner ynlds number reman relatvely unaffected by varable uter ynlds number,. Thrd, assessment f the dwnstream varatn f the flwfeld f a cmbned spray fr nner- and uter mass flw rates smlar t the real peratng cndtns revealed the ppste 29

30 behavr f the maxmum velcty t the maxmum Sauter mean dameter. It s fund that whle, Vˆ max f the cmbned spray, whch s clse t the center f the spray thckness, decreases as the dstance frm the nzzle ext s ncreased, SMD max mves t the uter perphery and ncreases as the dstance frm the nzzle ext s ncreased. Fnally, nrmalzatn f velcty and SMD measurements frm dfferent flwfelds that are prduced by the njectr at dfferent flw rates are fund t cllapse. The results reveal that the cmbned spray flwfelds are n fact flud dynamcally smlar bth n terms f the velcty as well as the Sauter mean dameter f the drplets that vary wth the radal pstn. In cnclusn, results cnfrm expectatns that althugh sheet breakup ccurs much clser t the njectr ext, ths des nt necessarly result n much smaller drps. It s well knwn that atmzatn s a result f the frces f nerta and surface tensn actng n the flud leavng the njectr. Therefre, the fneness f the spray depends upn whether the lqud stream mmentum s hgh enugh t cause sgnfcantly lqud/lqud shear nteractns. In addtn, t shuld be nted that there s mmentum exchange between the njectn lqud sheets and the ambent stagnant gas as well. Hence, the cmbned spray results frm a three-way nteractn between lqud/lqud and ambent gas. Fnally, t shuld be emphaszed that secnd rder effects such as the bundary layer thckness wthn the flm, the njectr wall rughness, the tube ext lp cndtn, and s frth, d exst and culd have a measurable effect n the resultng flwfeld. In the present paper, the secnd rder effects are nt nvestgated and assumed t be neglgble. Therefre, further nvestgatn s requred t explre these and whether the surface tensn r the aerdynamc frces are dmnant n the frce balance n rder t establsh the physcal mechansms gvernng atmzatn. 30

31 Acknwledgement The fnancal supprt f the Sharf Unversty f Technlgy s gratefully acknwledged. ferences 1 Inamura, T., Tamura, H., and Sakamt, H., Characterstcs f Lqud Flm and Spray Injected frm Swrl Caxal Injectr, Jurnal f prpulsn and Pwer, Vl. 19, N. 4, July- August 2003, pp Burck, R. J., Atmzatn and Mxng Characterstcs f Gas/Lqud Caxal Injectr Elements, Jurnal f Spacecraft and Rckets, Vl. 9, N. 5, 1972, pp Hautman, D. J., Spray Characterzatn f Lqud/Gas Caxal Injectrs wth the Center Lqud Swrled, Atmzatn and Sprays, Vl. 3, 1993, pp Erglu, H., and Chger, N. A., Intal Drp Sze and Velcty Dstrbutns fr Arblast Caxal Atmzers, Jurnal f Flud Engneerng, Vl. 113, 1991, pp Hardalupas, Y., and Whtelaw, J. H., Characterstcs f Sprays Prduced by Caxal Arblast Atmzers, Jurnal f Prpulsn and Pwer, Vl. 10, N. 4, 1994, pp Hardalupas, Y., and Whtelaw, J. H., Interactn Between Sprays Frm Multple Caxal Arblast Atmzers, Jurnal f Flud Engneerng, Vl. 118, 1996, pp Ramamurth, K., and Tharakan, T. J., Expermental Study f Lqud Sheets Frmed n Caxal Swrl Injectrs Jurnal f Prpulsn and Pwer, Vl. 11, N. 6, 1995, pp L, X., and Shen, J., Expermental Study f Sprays frm Annular Lqud Jet Breakup Jurnal f Prpulsn and Pwer, Vl. 15, N. 1, 1999, pp Svakumar, D., and Raghunandan, B. N., Jet Interactn n Lqud-Lqud Caxal Injectrs, Jurnal f Flud Engneerng, Vl. 118, 1996, pp Svakumar, D., and Raghunandan, B. N., Rle f Gemetrc Parameters n the Drp Sze Characterstcs f Lqud-Lqud Caxal Swrl Atmzers, Atmzatn and Sprays, Vl. 8, 1998, pp Ghrbanan, K., Ashjaee, M., Sltan, M. R., Mesbah, M. H., and Mrad, M. R., Expermental Study f the Spray f a Lqud-Lqud Caxal Swrl Injectr fr Dfferent Injectn Pressures, 9th Internatnal Cnference n Lqud Atmzatn and Spray Systems, ICLASS 2003, Srrent, Italy, Ghrbanan, K., Ashjaee, M., Sltan, M. R., Mesbah, M. H., and Mrad, M. R., PDA Drplet Sze and Velcty Measurement f a Swrl Atmzed Spray, 9th Asan Cngress f Flud Mechancs, Isfahan, Iran, Ashjaee, M., Sltan, M.R., Ghrbanan, K., and Mrad, M.R., PDA Study f Tw Phase Flw n a Spray Feld f a Jet- Swrl Type Injectr, 3rd Australan Cnference n Laser Dagnstcs n Flud Mechancs and Cmbustn, Australa,

32 14 Ashjaee, M., Ghrbanan, K., Sltan, M. R., Mesbah, M. H., and Mrad, M. R., PDA Measurements f Drplet Sze and Velcty In Mxng gn f Tw Sprays, 9 th Cnference f Iranan Scety f Mechancal Engneers, Tehran, Iran, Mrad, M. R., Determnatn f the Spray Characterstcs f a Lqud-Lqud Caxal Injectr Utlzng PDA and Neural Netwrk Analyss, Sharf Unversty f Technlgy, March Ghrbanan, K., Ashjaee, M., Sltan, M. R., Mesbah, M. H., and Mrad, M. R., Expermental Flw Vsualzatn f Sngle Swrl Spray Pattern at Varus Pressure Drps, AIAA 39 th Jnt Prpulsn Cnference and Exhbt, Huntsvlle, Alabama, USA, July AIAA Suyar, M. and Lefebvre, A. H., Flm Thckness Measurements n a Smplex Swrl Atmzer, Jurnal f Prpulsn, Vl. 2, N. 6, 1986, pp Mrad, M.R., Sltan, M.R., Ashjaee, M., and Ghrbanan, K., Expermental Study and a Lagrangan Mdelng f Drplet Velcty fr the Spray f A Swrl Atmzer, 4 th Iranan Aerspace Scety Cnference, Amrkabr Unversty f Technlgy, Tehran, Iran,