Variable Geometry Gas Turbine Radial Compressors

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1 68-GT-63 $.50 PER COPY 75 TO ASME MEMBER f)lf"' THS MATERA[ MAY BE PROfCTED ill C0YRGHT LAW (TTLE 7 UoS. CODE). The Sociey shall no be esponsible fo saemens o opinions advanced in papes o in discussion a meeings of he Sociey o of is Divisions o Secions, o pined in is publicaions. Discussion is pined only if he pape is published in an ASME iounal o Poceedings. Released fo geneal publicaion upon pesenaion Copyigh 968 by ASME Vaiable Geomey Gas Tubine Radial Compessos C. RODGERS Sola Division of nenaional Havese Company, San Diego, Calif. An examinaion of he vaious mechanical and aeodynamic mehods of flow and pessue egulaion hough high-speed, single-sage adial compessos is pesened. Pefomance esing of a small gas ubine adial compesso wih a vaiable vaned diffuse sysem is descibed. Mehods of combined geomey vaiaion o obain minimum educion of efficiency wih flow vaiaion ae suggesed based upon heoeical maching sudies. Conibued by he Gas Tubine Division of The Ameican Sociey of Mechanical Enginees fo pesenaion a he Gas Tubine Confeence & Poducs Show, Washingon, D. C., Mach 7-2, 968. Manuscip eceived a ASME Headquaes, Januay 26, 968. Copies will be available unil Januay, 969. AMERCAN SOCETY OF MECHANCAL ENGNEERS, UNTED ENGNEERNG CENTER. 345 EAST 47h STREET, NEW YORK, N.Y. 007 Downloaded Fom: hp://poceedings.asmedigialcollecion.asme.og/pdfaccess.ashx?ul=/daa/confeences/asmep/84065/ on 08/9/208 Tems of Use: hp://

2 Downloaded Fom: hp://poceedings.asmedigialcollecion.asme.og/pdfaccess.ashx?ul=/daa/confeences/asmep/84065/ on 08/9/208 Tems of Use: hp:// Vaiable Geomey Gas Tubine Radial Compessos C. RODGERS NTRODUCTON Duing he pas seveal yeas he auho s company has been concened wih he impovemen of gas ubine adial-compesso peak efficiencies and sable opeaing anges. n paicula, effos have been dieced owad he impoved pefomance of small gas ubine auxiliay powe unis wih adial compessos, supplying boh high-pessue ai and shaf powe in combinaion, o sepaaely. Addiionally, occasion has aisen fom ime o ime o conside ohe applicaions, such as gas ubine diven compesso ses and complex gas ubine cycles demanding high compesso efficiencies and flow anges. The inenion of he pape is o: Discuss he vaious mechanical and aeodynamic mehods of flow and pessue egulaion hough high-speed, single-sage adial compessos. g GV J p q ms T u w 6 'fj = e p = NOMENCLATURE flow aea, sq in. absolue velociy, fps specific hea a consan pessue, Bu/lb deg F gaviaional consan, f/sec 2 inle guide vane Joules equivalen pessue, psia wok faco oo mean squae empeaue deg R ip speed, fps aiflow, pps diffeence diamee aio efficiency pewhil angle, deg flow coefficien Subscips c compesso ubine inle 2 dischage 3 ubine inle D diffuse Pesen he esuls of pefomanqe esing, a he auhols flim, on an expeimenal in. dia, single-sage adial compesso equipped wih a vaiable-vaned diffuse. To indicae specific compesso blading geomeies which povide opimum oveall pefomance ove exended opeaing anges, choosing he expeimenal es compesso as a one-dimensional model wih which o conduc heoeical opimizaion sudies. NECESSTY FOR VARABLE COMPRESSOR GEOMETRY The coninued developmen of he gas ubine powe plan o obain impoved pefomance and opeae ove inceased opeaing anges poves moe demanding o he compesso aeodynamicis. The aeodynamicis is faced wih he poblem of no only aaining a elaively high componen efficiency, bu also mainaining -his efficiency ove lage flow anges. Since he maximum efficiency of aeodynamic blading nomally occus wih a sligh -degee of flow sepaaion, he sable opeaing limi (suge) ofen lies adjacen o he islands of peak compesso efficiency. The poximiy of suge o maximum efficiency is, howeve, influenced by: e Relaive impelle and diffuse maching e mpelle eacion and flow disibuion e Mach and Reynolds numbe effecs Wih esablished design echniques, suppoed by componen esing, i is possible o develop high-speed, single-sage adial compessos capable of sable opeaion a peak efficiency. Consan-speed sable opeaing ange can be defined in seveal ways. n his pape i is eleced o define he flow ange as he aio of maximum flow (choke) o minimum flow (suge). Typical flow anges lie beween. and.25 a impelle ip Mach numbes of appoximaely uniy, wih anges of.25 applying o moe fully developed compesso ypes ha have a sligh degee of impelle ip backsweep. Single-sage flow anges of his magniude ae accepable fo wo-shaf and single-shaf, simple-cycle gas ubine engines. Lage compes-. so flow anges may be desied in he followj_ng cases:

3 Downloaded Fom: hp://poceedings.asmedigialcollecion.asme.og/pdfaccess.ashx?ul=/daa/confeences/asmep/84065/ on 08/9/208 Tems of Use: hp:// '7c COMPRESSOR EFFCENCY '7 TURBNE EFFCENCY T/T MAX CYCLE TEMPERATURE RATO ----_J4.0 PRESSURE RATO P 2 /P Fig.l Simple-cycle bleed/shp gas ubinecompesso aiflow aios Combinaion aibleed-shafpowe gas ubines Single-shaf gas ubines diving adial compessos Muli-sage compessos Ula-high-sage pessue aios Subsanial inceases in compesso flow ange o sui hese cases can be obained by mechanically o aeodynamically changing he compesso geomey. Befoe discussing he vaious vaiable geomey mehods, fis conside he paicula cases whee vaiable geomey may be desious in moe deail. Combinaion Aibleed-Shafpowe Gas Tubines Gas ubines supplying high-pessue bleed ai and/o mechanical shafpowe, and opeaing a consan speed, ae commonly used as aicaf auxiliay powe unis. Cycle calculaions a consan pessue aio show ha he useful enegy oupu and equied compesso flow ange ae popoional o he poduc of he componen efficiencies and cycle maximum empeaue aio ('Y\ c") T/T ). Fig.l shows he aio beween compesso aiflows a he pue bleed and pue shafpowe opeaing condiions fo a fixed ubine geomey. Compesso flow aio is ploed vesus pessue aio wih (") c. 'Y).T 3 /T ) as a paamee. Since maximum oupu is obained a. maximum values of (l'\c Y\ T 3 /T }, lage compesso flow aios ae indicaed. Fo example, conside a hypoheical combined bleed-shp APU wih a compesso pessue aio P 2 /P = 4.o, a compesso efficiency '/c = 0.80, ubine efficiency lf = 0.85, and maximum cycle empeaue aio T 3 /T = 4.0. A flow ange of.8 is equied beween he pue bleed and pue shafpowe opeaing condiions. Since such lage anges canno be aained wih fixed geomey com- ponens, i is nomal o opeae a a lowe compesso efficiency unde bleed condiions, and o cuail pue shafpowe oupu o povide a oleabl.e opea ing suge magin. Significan pefomance inceases can be obained in such gas ubine applicaions by using vaiable geomey eihe in he compesso o ubine componens. A vaiable ubine aangemen is, of couse, opimum fom engine pefomance consideaions in ha he compesso can be consained o opeae wihin is peak efficiency egimes, and no educion of aiflow occus when ansfeing fom he bleed o he shafpowe mode, Vaiable ubine geomey is a moe difficul developmen poblem han vaiable compesso geomey, especially wih he coninuing end owads highe maximum cycle empeaues; heefoe, i is mechanically pefeable o modulae he "cold end" hadwae. Muli-Sage Compessos The aangemen of wo adial compessos, o a single axial and single adial compesso, in seies, ae common feaues of seveal gas ubine powe plans. Wih high-sage pessue aios, some pefomance compomises may be necessay o povide a suge-fee acceleaion unde all envionmenal opeaing condiions. The lowand high-speed suge chaaceisics ae essenially deemined by he fis- and second-sage suge lines, especively. ncopoaion of vaiable geomey could impove he oveall suge chaaceisic of muli-sage compessos, heeby avoiding he necessiy o compomise engine pefomance. Gas Tubine Diven Radial Compessos Boh single- and wo-shaf gas ubines ae in use diving adial compessos eihe diecly, o hough inemediae gea ains. The woshaf aangemen simplifies he engine saing poblem because i is no necessay o unload he diven compesso duing he sa cycle. Unloading mehods seleced fo single-shaf aangemen may compise: inle holing vaiable inle guide vanes flow eciculaion vaiable diffuse nle flow egulaion is pevalen whee he compesso is equied o opeae agains a fixed downseam esicion, o ove a elaively small flow ange. f a lage flow ange is desied, hen a vaiable diffuse sysem can seve o boh egulae he diven compesso suge line (fo eihe a single- o wo-shaf gas ubine}, and o ac as an unloading device fo he single-shaf gas ubine duing sa.,, \! 2

4 Ula-High-Sage Pessue Raios The U.S. Amy Aviaion Maeiel Laboaoy is cuenly sponsoing developmen conacs fo single-sage adial compessos wih pessue aios up o en. Such ula-high-sage pessue aios cause conflicing demands beween he impelle and diffuse if boh ae o opeae in hei especive egimes of minimum loss ove he complee compesso opeaing ange. The econciliaion of hese demands can be achieved by vaiable geomey, eihe in he impelle o diffuse. Fig.2 shows he elaive posiions of he impelle and diffuse minimum loss egimes in ems of compesso flow and pessue aio fo a high-pessue-aio, single-sage compesso. A pessue aios ohe han design, he minimum loss egimes of he impelle and diffuse depa, he depaue inceasing wih change in pessue aio fom he design value. Thus, he highe he design pessue aio, he geae he depaue a pa-load condiions. The elaive displacemen of he minimum loss egimes esuls in educed oveall efficiency and, moeove, iegula suge lines. A fixed geomey ubine opeaing line lies almos paallel wih he diffuse minimum-loss egime. Selecion of opimum impelle and diffuse maching a he design pessue aio can, heefoe, esul in salled impelle opeaion a pa load. Fig.2 9 TURBNE OPERA TNG LNE 7 DFFUSER MN LOSS REGME 4 2 ARFLOW % DESGN MPELLER MN LOSS REGNE Relaive componen maching hypoheical ula-high-pessue-aio compesso The use of GV's on a ypical gas ubine adial compesso essenially simulaes an effec simila o ha of change in compesso speed, povided he GV's ae opeaing unsalled wihou a holing effec. This saemen is suppoed by examinaion of es esuls, and is based upon VARABLE GEOMETRY METHODS he following agumen. f suge and choke ae The following vaiable geomey mehods have been employed on adial compessos: e Mechanical Mehods Vaiable inle guide vanes. Vaiable impelle blades. Vaiable diffuse. e Aeodynamic Mehods Je e-eny. Mechanical Mehods Vaiable nle Guide Vanes. The use of vaiable inle guide vanes (GV) on a gas ubine incopoaing a adial compesso is adequaely descibed by Andeson and Shouman. Tes esuls ae pesened ove an inle pewhil ange of O o 50 deg wih oaion. Tes esuls wih gossly salled GV's se a 65 deg wih oaion ae pesened by Ecke 2 and indicae an appeciable educion in oveall compesso efficiency. J. R. Andeson and A. R. Shouman, "The Use of Compesso nle Pewhil fo he Conol of Small Gas Tubines," ASME 63-AHGT "Axial Kompessoen and Radial Kompessoen," Spinge, Belin, 953, p. 43. dicaed by he diffuse (as is he case ove he nomal opeaing ange), egulaion of GV s will meely educe he pessue level ino he diffuse; hus boh he suge and choke flows will essenially follow a simila vaiaion o ha poduced by speed changes. A vey low speeds and speeds geae han design, he impelle influences he suge and choke flows; heefoe, significan changes in he suge and choke flows ae possible a he exeme speed anges wih GV egulaion. A adial compesso wih a vaneless diffuse may show significan changes in he suge chaaceisic wih GV egulaion, povided he vaneless diffuse is no opeaing close o is salling limi. Radial and axial GV.ypes ae illusaed by Andeson and Shouman. Boh ypes ae in common gas ubine use. n addiion o flow egulaion, GV's may be used o minimize he elaive Mach numbe a he impelle eye ip a he expense of a sligh educion in pessue aio. Fig.3 shows he'effecs of inle pewhil on compesso efficiency aio, maximum flow aio, and wok faco q = g J Cp (L\T/T)/(U 2 / l/tl) 2, fo a ypical gas ubine adial compesso a a consan nondimensional ip speed u 2 /ffi = 65. The 3

5 Downloaded Fom: hp://poceedings.asmedigialcollecion.asme.og/pdfaccess.ashx?ul=/daa/confeences/asmep/84065/ on 08/9/208 Tems of Use: hp:// u 2 ffi = 65 FPS! R i PEAK EFFCENCY PEAK EFFCENCY AT e MAX FLOW MAX FLOW AT e = 0 gjcp LT/Tl q - - u 2 /J'/ Fig.4 Sola Tian gas ubine engine incopoaing vaiable vaned diffuse sysem e PREWHRL ANGLE DEG Fig.3 Typical effecs of GV s on adial compesso pefomance elaively lage efficiency educion a pewhil angles geae han 40 deg wih oaion aises fom GV salling losses. Only small amouns of negaive pewhil can nomally be oleaed due o he onse of impelle choking wih inceased inle elaive Mach numbe. GV s can impove he fuel economy of a gas ubine being used as a souce of consan powe and aed o a ho-day condiion. GV egulaion in he diecion of oaion could be employed duing cold-day condiions o boos maximum cycle empeaue and hus impove cold-day cycle efficiency; howeve, he poenial gains in fuel economy wih such a mode of opeaion may be offse o some degee by ubine maching consideaions. Vaiable mpelle Blades. Flow egulaion by aleing he impelle blade sagge is cuenly impacical a he elaively high oaional speeds equied fo gas ubines; howeve, his mehod of vaiable geomey is faily common in hydaulic ubomachiney, whee boh speed and size pesen mino esicions o he equisie impelle-blade linkage sysem. Vaiable Diffuse. The impelle seves o impa enegy in he fom of pessue and velociy o he woking gas, dependen upon he choice of eacion degee. f he impelle could achieve his funcion wihou he salling and choking esicions, a vaiable diffuse downseam of he impelle could povide almos consan pessue aio wih flow vaiaion fom zeo o design flow. n pacice, flow limis occu wih vaiable diffuse sysems due o oveheaing a low flow semming fom inenal flow eciculaion, and eff::ciency educion a high flow pio o impelle choking. Fo efficiency easons mos gas ubine adial compessos ae of he vaned-ype flow egulaion being obained by vane esagge. The same effec can be obained wih a vaneless diffuse by educing he widh beween fon and ea shouds in applicaions whee efficiency is no of pimay impoance. Fig.4 shows a vaiable vaned diffuse sysem insalled on a gas ubine manufacued by he auho s company. Pefomance es esuls fo an expeimenal vaiable vaned diffuse sysem ae descibed in a lae secion. Aeodynamic Mehods Complex vaiable geomey mechanisms could be dispensed wih if flow egulaion could be accomplished by aeodynamic mehods. The majoiy of aeodlfnamic egulaion mehods devised o dae involve some fom of seamwise mixing. Je Re-Eny. The mos effecive manne of aeodynamically changing he ciical hoa aeas is by diecing a je pependicula o he main seam pio o he impelle and diffuse hoa secions. f dischage ai is used fo je eeny a he impelle inle, a elaively highvelociy je is possible, and hus a lage momenum can be ealized wih only a small eciculaion flow. nle e-eny does' esul in an ininsic educion in pessue aio, apa fom mixing losses, due o inceased inle empeaue. Efficien e-eny mixing is he key o aeodynam- f. s i i i b d s c c b f. l a m( s c R 4

6 ( f f ;( {.. 80 b'< :" :>< u z 60 f:j Sl.....'l p.'"" '-.. P< "' g E-< gj p "'.'l P:: P< SURGE LNES RECRCULATED ARFLOW 0% U2 FPS 72.5 /OR o W ffi PPS./'R NLET FLOW FUNCTON Pl Al PSA. SQ N Fig.5 Radial compesso pefomance wih inle je e-eny Fig.6 Radial compesso es impelle ic mehods of flow vaiaion. Unfounaely, mixing losses incease as he impingemen angle inceases elaive o he main-seam flow diecion; hus mixing loss and je e-eny effeciveness ends ae opposed. Laskin and Kofskey 3 descibe he esuls of ess wih a je e-eny sysem a he impelle inle. n his paicula insance he je was dieced o aeodynamically impa 20-deg pewhil in he diecion of oaion fo he pupose of so-called "suge inhibiion." The es esuls ae shown in Fig.5 and indicae an appeciable displacemen of he suge line a he expense of a educion in pessue aio and efficiency o a degee which would no be accepable in a gas ubine cycle. The vaned diffuse discussed by Laskin and Kofskey was sized such ha maximum flow was limied by impelle choking, hus, as menioned peviously, significan changes in suge chaaceisics wee possible wih simulaed GV egulaion. Je e-eny a he impelle ip, using diffuse dischage ai, has been esed a he auho is fim wih he basic inenion of simulaing a eciculaoy leakage condiion ahe han a means of flow conol. Wih impingemen nomal o 3 E. B. Laskin and M. G. Kofskey, "ncease in Sable Ai Flow Opeaing Range of a Mixed Flow Compesso by Means of a Suge nhibio," NACA RM E7C05, 947. Fig.7 Radial compesso es diffuse he seam, maximum choked flow a a given i speed deceases wih eciculaion flow ae {he je effecively simulaing a smalle diffuse). Some displacemen of he suge line owads lowe flows also occus, bu mixing losses esul in lowe efficiency and pessue aio. Diffuse je e-eny along he sucion suface paallel o he main flow migh pove successful in boh egulaing flow and enegizing he bounday laye o peven sepaaion. Channel-ype diffuses of elaively hick secion would pemi appopiae low-pessue loss flow galleies, wih final je meeing a he vane suface. EXPERMENTAL PERFORMANCE OF A VARABLE VANED DFFUSER An expeimenal pefomance evaluaion of a 5.25-in. ip diamee adial compesso wih fou diffuse hoa seings ove a ange of non- 5 Downloaded Fom: hp://poceedings.asmedigialcollecion.asme.og/pdfaccess.ashx?ul=/daa/confeences/asmep/84065/ on 08/9/208 Tems of Use: hp://

7 ""',,.u :>< {.) 90 z 80 f:l 8 f. f. f.<, AD 00% DESGN. T ' l W;T; =- NLET FLOW FUNCTON p Al l l PPS.v R PSA.SQ N Fig.8 Effec of diffuse hoa aea on es compesso pefomance... p. "' 0 E:: ;;'i f.< 4 n 2 n f.< P:: p % % END GAP/HEGHT RATO o o PEAK EFFCENCY PEAK EFFCENCY AT DESGN AD MAX FLOW MAX FLOW AT DESGN AD gjcp 'T/T l ----q - (U2/ffil DFFUSER THROAT AREA DESGN DFFUSER THROAT AREA Fig.0 w NLET FLOW FUNCTON -- PlAl PPS.! R PSA.SQ N Effec of diffuse vane end gap on es compesso pefomance 56.3, 63.5, a he fou hoa seings, wih a diffuse vane gap-o-heigh aio of 0.9 pecen each side. is obseved ha aiflow is almos popoional o diffuse hoa aea. Pessue Fig.9 Vaiaion of wok faco q wih inle flow aio fo a given speed emains appoximaely consan wih flow vaiaion -- excep a he lowes coefficien p, es compesso diffuse seing, whee efficiency deceased appeciably. Suggesions fo educing he efficiency decay wih flow educion will be discussed dimensional ip speeds was made a he auho s company. Figs.6 and 7 show he es impelle and lae. Analysis evealed ha he impelle ip diffuse. The impelle had 6 blades wih alenae long and sho induce configuaion. The ing was appoximaely consan along he suge absolue ai angle fo a given diffuse hoa se diffuse had 5 vaiable vanes, each pivoed abou line, indicaing ha diffuse sall was pobably he esimaed design cene of pessue. Caliba- iggeing suge ove he es ange of flows and ions wee conduced wih hoa aea seings of 00, 72, 5. and 6 pecen of he design diffuse hoa seing. Gaps exised beween he vane ends and saionay shouds o peven binding. niial esing was compleed wih a gap-o-vane heigh ai? of 0.9 pecen each side followed by a epea calibaion wih he gap aio inceased o 3.6 pecen each side, a he design hoa seing only. Compesso efficiency was evaluaed fom measued empeaue ise and inle oal o dischage pipe saic pessue$. Tes Resuls Fig.8 shows he compesso es esuls a nondimensional ip speeds u 2 /\l'tl of 37,9, o.6, pessue aios. The effec of diffuse hoa aea on peak efficiency aio, flow aio, and wok faco q, fo he es compesso is shown in Fig.9. Fig.0 shows he effec of end gaps on compesso pefomance wih design hoa aea seing. When inceasing he end gap aio fom 0.9 o 3.6 pecen, a u 2 /ffi = 63,5, he p.eak efficiency deceased fom 78 o 72 pecen, bu he flow ange inceased subsanially due o a lage choked flow and a lowe suge flow. An appoximae ule fo he effec of diffuse vane end gap on efficiency migh hen be.\'\ pecen = pecen gap-o-heigh aio. The inceased end gap allows he flow o leak ove he diffuse vane end and effecively povides a lage hoa aea and, 6 Downloaded Fom: hp://poceedings.asmedigialcollecion.asme.og/pdfaccess.ashx?ul=/daa/confeences/asmep/84065/ on 08/9/208 Tems of Use: hp://

8 Downloaded Fom: hp://poceedings.asmedigialcollecion.asme.og/pdfaccess.ashx?ul=/daa/confeences/asmep/84065/ on 08/9/208 Tems of Use: hp:// \! i { ) l 'f heefoe, a lage choked flow. The displacemen of he suge line owads lowe flows wih inceased end gap could aise fom sepaae flow egimes beween he gap and vane flows. The cenal flow field is subjec o he vane choking and salling limis, while he gap flow, uninfluenced by he flow field aound he vane, may be analogous o ha along he shouds in a vaneless diffuse. n effec, lage end gaps appea o simulae he pefomance chaaceisics expeced of a combined vaned-vaneless diffuse, possessing he advanages and disadvanages of boh ypes of diffusion sysems. The envelope of he vaiaion in wok faco q vesus inle flow coefficien p = c /Uz fo he _!'-< " c u 'cl, 2 "'. 0 c' ll:i 0!'-< 5;l 0.8 i cl NLET FLOW COEFFCENT </> = ū2 complee es daa is shown in Fig.. The incease Fig. Effec of diffuse hoa vaiaion on of q wih deceasing flow coefficien es compesso pefomance aises fom: disk ficion losses eciculaion losses his findings) ha slippage phenomena is associaed incease in slip faco wih he concep of flow deviaion angle pas Wihou complee knowledge of boh he impelle blade ows. A consan deviaion a he impelle inle and oule flow disibuions, i is exi would hen esul in q inceasing as flow co impossible o sepaae hose individual effecs. efficien p deceases. A flows appoaching he design condiion he disibuions ae compaaively unifom, and unde hese condiions boh he disk ficion and eciculaion Reieaing -- slippage, disk ficion, and eciculaion effecs can be deemined only fom he diffeence of he inegaed momenum change losses ae small. A he lowe flows he acoss he impelle and he enegy inpu. This impelle is opeaing in a deep sall condiion, and eciculaion of boh he diffuse flow ino he impelle and he impelle flow back o he inwould be a demanding ask, equiing inicae flow suveys unde a balanced enhalpy condiion, jusified by pue eseach moives ahe han le is occuing. Alhough impelle inle aves- compesso developmen. ing was no conduced, definie evidence of flow evesal back o he inle when calibaing wih OPTMUM VARABLE GEOMETRY CONFGURATONS he smallep diffuse hoa aea was indicaed by: ncease in impelle eye ip saic pessue The exension of useful opeaing ange of above amospheic. ubomachiney hough he use of vaiable geome ncease and insabiliy of he measued y is ofen an.impovisaion of an exising design. inle empeaue. f vaiable geomey is sipulaed as a de is known ha inle eciculaion occus sign equiemen, i is necessay o specifically on adial compessos as he flow is deceased design he machine blading o povide opimum pefomance owads shuoff and ha pewhil wih oaion is ove he anicipaed opeaing ange. induced. The degee of pewhil is influenced by This may equie some pefomance compomises in he inle design. n his insance a saionay he nomal opeaing flow egimes a he expense impelle hub cone, suppoed by hee vanes, was of impoved oveall pefomance. This could be fied upseam of he impelle. These vanes esiced geneaion of a song inle voex acion. f he slip faco is assumed consan and he pewhil effec was negligible, hen he summaed disk ficion and eciculaion losses ae appoximaely popoional o he invese of he flow coefficien p. Sahle 4 has shown (and hee is an accumulaion of evidence o suppo 4 A. F. Sahle, The Slip Fae o of a Radial Bladed Cenifugal Compesso, ASME 64-GTP-. bes illusaed in ems of a specific example. Fo insance, he vaiable diffuse es compesso peviously descibed was no specifically designed o opeae wih a vaiable geomey sysem. This compesso configuaion can hen be examined o illusae how is pefomance migh be impoved a paial flow condiions. The blading opimizaion echnique adoped was o examine he heoeical chaaceisics of s evea l alenae vaiable diffuse compesso designs capable of coveing he same flow ange as he es compesso. These chaaceisics wee machine compued 7

9 . 0 0 < = u ><... z"' "' >< -u f:l z µ.. "' µ "' f:l < =. 5 "' "' deg "< <!! "' deg "< Fig.2 Vaiable diffuse FLOW FLOW AT PEAK EFFCENCY o = 0 esimaed efficiency vaiaion wih flow a u 2 /v'tl = 63.5 using a developed vesion of he mehod descibed by Rodges.5 This mehod is based upon he assumpion ha nondimensional flow and pessue chaaceisics will coespond o hose of a onedimensional geomeic model. Thee impelle diamee aios of e =.5,.96, and 2.5, wih pewhil angles of O and 30 deg,6 wee examined; all of hese heoeically capable of aaining idenical design-poin pefomances. The es compesso diamee aio e (defined as ip diamee/inle ms diamee) was.96. Fig.2 shows he esimaed vaiaion of efficiency wih flow fo hese geomeic configuaions fo a consan nondimensional ip speed of Minimum decay of efficiency wih u 2 /\l'tl = 63,5, flow is obained wih E = 2.5 and e = 30 deg. 6 Uncambeed GV s appoach hei salling limis when he pewhil angle exceeds appoximaely 30 deg. a diminishing change of incidence wih flow vaiaion. e Opimum impelle i_ncidence can be mainained ove lage flow vaiaions as he impelle inle blad.e angle is educed fo consan speed and inceasing pewhil. Lage diamee aios, of couse, ae geneally associaed wih low specific speeds, and hus low oveall efficiency; heefoe, compomise beween peak efficiency and desied efficiency vaiaion wih flow mus be made sepaae fom he componen maching consideaions. Some facos, ohe han maching effecs and mechanical design cieia, ha influence he level of efficiency a flows lowe han design ae: e mpelle blade numbe. Flow educion a consan speed inceases he impelle blade loading; hus impelles wih inceased solidiy should be seleced. e Choice of diffuse-vane incidence and loading disibuion, wih flow educion, o obain maximum flow ange and minimum end gap leakage losses. e mpelle and shoud configuaions associaed wih low disk ficion. e nle design o minimize impelle inle flow maldisibuion a educed flows. Consequenly, he selecion of ue opimum vaiable geomey design is difficul because hee ae many ineelaed influence facos. Exension of he opimum geomey selecions fo vaiable flow o include vaiable impelle configuaions eihe mechanical o aeodynamic was consideed oo pemaue. CONCLUDNG REMARKS Maximum decay of efficiency wih flow is obained wih E =.5 and e = 30 deg. Fig.2 also indicaes Possible vaiable geomey mehods fo single-sage ha flow educions of appoximaely 40 pecen appea possible wih opimum selecion of adial compessos have been examined and hei effecs (boh esed and esimaed) on he impelle geomey, vaiable diffuse, and GV compesso pefomance discussed. Ohe han he seings, povided ha efficiency educions of 3 pecen ae oleable. Minimum efficiency decay wih flow fo e = 2.5 and e = 30 deg can be also deduced o some necessiy o povide finie cleaance gaps beween mechanically vaiable blading, no consideaion has been given o he manne in which hese geomeies can be successfully incopoaed and conolled exen by agumen in ha: on a gas ubine engine. Mos gas u- As eo, he impelle eye will expeience bines vaiable geomey sysems ae no in fac fully vaiable, bu ae simple, wo-posiion de- 5 c. Rodges, "Typical Pefomance Chaaceisics vices. Some possible mehods of conolling vaia of Gas Tubine Radial Compessos, ASME 63- ble diffuses o povide suge-fee opeaion ae: AHGT-4. e Modulaion of vane posiion as a funcion of oule dynamic head. As menioned peviously, suge fo he es compesso was associaed wih nealy consan impelle ip angle, which appoximaes consan impelle oule dynamic head. Ex- (,, ' f ( i' a c w C. l. l c d\ d e f b m e. c p 8 Downloaded Fom: hp://poceedings.asmedigialcollecion.asme.og/pdfaccess.ashx?ul=/daa/confeences/asmep/84065/ on 08/9/208 Tems of Use: hp://

10 peimenal deeminaion of oule dynamic head a suge fo each vane posiion could hen povide a meeing elaionship fo a pneumaic conol sysem. e The diffuse vane sucion suface pessue gadien inceases as flow is educed owad suge, and finally becomes excessive esuling in flow sepaaion. The absol'ue pessue and pessue diffeence beween wo suiably posiioned saic aps on he diffuse vane sucion suface migh seve o indicae he poximiy of suge. As menioned peviously, he desiabiliy fo vaiable geomey will no doub incease as sage pessue aios incease in he ensuing yeas. To indicae he advanages of vaiable diffuses fo ula-high-pessue aio single-sage adial compessos, pefomance esimaes wee compleed fo he es compesso a ip speeds up o u 2 / v'tj = 85. Fig.3 shows he esuls of hese esimaes fo hoa aeas of 00, 72, and 45 pecen of he design value, pesuming a educion in peak impelle efficiency of hee pecenage poins beween u 2 / v'tl = and 85. is obseved ha he esimaed ovespeed pefomance wih AD = 00 pecen would esul in impelle inle choking, and hus nea veical pessue flow chaaceisics, causing boh an inflexed suge line and low efficiency. Reducing he diffuse hoa aea o 72 pecen would impove he suge line and efficiency, bu migh sill povide gas ubine maching poblems. Fuhe hoa aea educion o 45 pecen of he design value would povide suge-fee opeaion a he expense of educed oveall efficiency wih salled impelle op- 8 '"' i:i. "' 0 :: Q!l P<l 4 0:: :::> P<l "' 0:: i:i. o. 5 o o. 35 NLET FLOW W PSA SQ N Fig.3 Esimaed ovespeed chaaceisics of es compesso 85 FPS FR o , PPS! R condiions ae esimaed and should no be assessed as hose epesenaive of an opimized ula-high-pessue aio design. n addiion, i is emphasized ha he es compesso size was only 5,25 in., wih diffuse end gaps pesen, and ha ovespeed efficiency fall-off was based upon convenional blading pefomance chaaceisics. CONCLUSON Flow egulaion hough single-sage adial compessos is mos effec ively achieved by he use of vaiable GV s and/o vaiable diffuses. Combined vaiable GV s and. diffuse vanes povide minimum efficiency penaly wih flow educion. eaion. A a pessue aio of 7.5 and peak ef- The scheduling of inle pewhil wih diffuseficiency he inle flow funcion W v'tl/ P A would vane posiion should be opimized duing boh inibe 0.425, which is close o he opimum value fo ial design and componen esing. minimum impelle inle elaive Mach numbe. The The nex phase in he developmen of vaiexample is faily epesenaive of he inle flow able geomey sysems is o successfully incopocondiion ha would be seleced fo an ula-high- ae hese sysems on gas ubines o boh impove pessue aio design. hei vesailiy and pefomance. This phase has The efficiency levels shown a he ovespeed commenced a he auho s company.