Clearance Effects on RIT's

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NASA TT F-10,441

A STUDY OF THE RADIAL-AXIAL-FLOW TURBINE W I T H LOW BLADE HEIGHTSAND LARGE CLEARANCES

L . N. Odivanov, A. P. Tunakov

ABSTRACTThe rad ia l - ax ia l - f low tu rb in e wi th b lades of vary ing

h e i g h t s i s t e s t e d . I t i s f ound t ha t e f f i c i ency r i ses upt o a c e r t a i n b l ad e h e ig h t ( i l = 0.075) and ef f i c ie nc y de-c r e a s e s s l i g h t l y w it h a f u r t h e r i n c r e a s e i n b l a d e h e i g h t.

I n recent y e a r s a cons ider able number of s tu di es have appeared /133*on t h e e f f e c t o f d i f f e r e n t f a c t o r s on t he o p e r a t i o n of r a d ia l -a x i a l- f lo w( c e n t r i p e t a l ) t u r b i n e s , bu t t h e i r f i n d i n g s are r a th er incomple te, and i n somecases even con t r ad i c t o r y .s t a n t i a l l y on t h e n a t u r e of t h e ex p er im e nt a l t u r b i n e .

The r e s u l t s of t h e s t ud i e s o f t en depend s ub -

I n c o n s t r u c t i n g o u r e xp e ri m en t al t u r b i n e , t h e b a s i s u s ed w a s t h e t u r b i n efrom t h e pr ev io us ly s tu d ie d TKR-14 turboco mpressor (Ref. 5 ) . I t s a c t u a le f f i c i e n c y d ur in g t e s t s i n a i r d i d n o t e xc ee d 0.65.our previous work recommended the following:

To ra i se i t s e f f i c i e n c y ,

(1) I n c r e a s i n g t h e o v e r - a l l d i a m e t r i c a l d im en si on s of t h e c o l l e c t i o nchamber;

(2 ) Displac ing t he ba f f l e between t h e two ha lves o f th e nozz le boxi n t h e d i r e c t i o n of r o t a t i o n ;(3) E l i m i na t ing s t agnan t w akes i n t he co l l e c t i o n chamber;(4) Using modern aerodynamic shapes f o r th e nozz le blad es which havelow s e n s i t i v i t y t o a change i n ang l e of a t t a ck ;(5 ) D ecreasi ng t he ang l e of a t t a ck a t r o t o r - w hee l i n l e t ; t h i s may bedone by decrea s ing a ngle a1 and a t t h e same t i m e r a i s i n g t h e h e ig h t of t h e

nozz l e b l ad es t o keep t u r b i ne d i s cha r ge capa c i t y unchanged ;

( 6 ) Reducing degree of r ea c t io n by en l arg ing ro t or d i scharge area;( 7 ) I n s t a l l i n g a shaped sh ie ld ( coque) t o e l im ina te sudden expans iona t e x i t f rom t he r o t o r w hee l;

~~ ~* Numbers i n t h e m ar gi n i n d i c a t e p a g in a t io n i n t h e o r i g i n a l f o r e i g n t e x t .

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(8 ) I n c r e a s i n g e x i t a n g l e a2 of flow from t h e t ur bi ne and makingt h e o u t l e t c l o s e r t o a n a x i a l one, p a r t i c u l a r l y i n t h e p e r i p he r a l p a r t ;(9) Imp ro vin g d e b ur r i ng of t h e ro t o r w he el s a f t e r c a s t i n g , p a r t i c u l a r l ya round the ex i t edges ;(10) En la rg ing ra d ia l c l ea rance between th e nozz le box and th e r o t o rwheel;(11) In s t a l l i ng the rmal i n s u l a t i on be tween the tu r b in e and bea r ing bodyt o d e cr e as e h e a t l o s s e s t o t h e water coolant ; and(12) Using a shaped end w a l l i n t h e nozz le box .

Condi t ion ing the TurbineSome of th e s e recommendations were exp er im en ta ll y v e r i f i e d when oper-a t i n g t h e t u r b i n e i n c ol d a i r wi th a pressu re d rop o f p /p 5 1.52.

t he f i r s t ser ies of experiments , t he ef fe c t iv e torqu e developed by thet u r b i n e w a s measured from deflec t ion of t h e body of an e l e c t r i c b rake wi th

I n /1340

Figure 1Diagram of Expe rime ntal Tu rb ine

1 - Bearing; 2 - Fl e x i b l e t u b e ; 3 - Lever; 4 - 18-kw generator;5 - Reducer; 6 - F l o a t i n g c o l l a r ; 7 - Support ; 8 - Bearing; 9 - R e-c e i v e r : 10 - Nozzle blade cascade; 11 - Air-p ressu re me te r ; 1 2 - Rotorwheel ; 13 - Exhaust duct ; 1 4 - St a t i o n a ry s h i e l d i n g ; 15 - r p m pickup.

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Figure 2Diagram of Turb ine Blading a t Various Blade Heights

a r e d uc i ng g e a r . I n t e r n a l t u rb i n e t o rqu e w a s a s c e r t a i n e d as t h e sum of thee f f e c t i v e t o rq u e an d f r i c t i o n a l moment i n t h e b e a r i n g s .by measu ring f r i c t i on a l moment wh i l e s pe c i a l ly c rank ing the sh a f t w i th a weightThe l a t t e r

w a s foundi n s t e a d o f t h e t u rb i n e ro t o r w he el .

At low b l a d e h e i g h t s , t e s t s of which w e were t o conduct l a t e r , t h etu rb in e ' s in te r n al power had t o be appreci ab ly reduced and had t o be commen-s u r a b l e w i t h f r i c t i o n fo r c e i n t h e be a r in g s ; o t h e rw is e m ea su re me nt al e r r o rwould have r i sen .

There fo re , t h e ru n ni ng p a r t of t h e t u rb i n e w a s r e c o n s t ru c t e d fo r i n -d i r ec t l y measu ring t he in t e rn a l moment.

A s k e t c h of t h i s v e r s i o n o f t h e e xp e r im e n ta l t u rb i n e w i t h t h e b r ak i nga p p a ra t u s i s shown i n F igur e 1.The s l i d i n g b e a r i ng s of t h e t u r b i ne w i t h t h e i r f l o a t i n g c o l l a r s 6 are

mounted i n t h e s e p a ra t e s u p p o r t 7, which may move back and f o r t h s l i g h t l yr e l a t i v e t o t h e axis of r o t a t i o n on r o l l e r b e a r in g 8.r i g i d l y conn ected by means of reduc er housing 5 t o g e n e ra t o r h o us in g 4 , t h erear se c t io n o f which i s mounted on r o l l e r bear in g 1.suppor t and th e housings of reduc er and gene ra tor may th us swing on two r o l l e rb e a r i n g s ; th is permi t ted measurement of t h e r e a c t i v e t o rq u e on them, t h i s t o r -que bei ng equal t o in te rn al moment of the tur b in e .w a s measured on d i a l sca les by means of l e v e r 3 .

Thrus t bea r ing 7 i sThe tu rb ine bea r ing

The pul l f rom the torque

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Figure 3

0.4570.278

0.2780.257

0.257

0.257

ad

27.215

151 3

13.5

14.5

t

C h a r a c t e r i s t i c of Turbine with Shaped End Wall i n Nozzle BoxThe t a b l e g i v e s r e s u l t s of cond i t i on i ng t he t u r b i ne .

Number i no r d e r

A l t e r a t i o n s t ot u r b i n e

O r i g i n a l t u r b i n eNew nozz le boxT or o i da l r ece i ve r

a / t reducedHeight of nozzle

blades reducedShaped nozzle boxw a l l

and sh ie ld

5at 1 (roughly)16.516.5

16.516.5

10.5

10.5

0.650.72

0.76------

1 /135

0.710 .79

0.840.813

0.83

0.87

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Figure 4Dependence of In te rn al Eff ici ency of Turbine on ul / c a tadDifferent Blade Heights

( A - & t p l = i # , O - - d : p a == 1,s.0 Pp;/P,= 1,w.._.-=Tu?

T he t u r b i ne of a TKR-14 turbo-compressor with a ro to r wheel diameter ofd l = 140 mm w i t h n o a l t e r a t i o n s w a s used as t h e i n i t i a l v e r s i o n (1).Angle a1 i n t he t u r b i n e w i t h t he new nozzl e box (2) w a s apprec iab ly r educed , s ot h a t a t t h e i npu t t o t he r o t o r w heel , unde r peak e f f i c i e ncy cond i t i ons , t h e r ew e r e s m a l l p o s i t i v e an g l es of a t t a c k .unchanged.f low- ra te th rough th e tu rb i ne , and l ikewise en larged angle a2 .

Height of ro to r wheel blades remainedT hi s l e d t o a s u b s t a n t i a l d e c r ea s e i n d e g re e of r e a c t i o n and a i rFigure 2 shows

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th e con tour used f o r th e nozz le b lades .ang le ; t he re fo re , h a l f o f them operated a t l a r g e a t t a c k a n gl e s (up t o 60O).N ev er th el es s, t h i s a l t e r a t i o n in c re a se d i n t e r n a l e f f i c i e n c y of t h e t u r b i n e by8%.

A l l t he b l ade s had t h e s a m e e n t r y

I n t h e n ex t t u r b i n e a l t e r a t i o n ( 3 ) , t h e co l l e c t i on chamber w a s re-placed by a t o r o i d a l r ec e i v e r of i nc r eas ed d i ame t e r. I n s t ea d o f a s h i e l d , as t a t i ona r y cow l i ng w a s i n s t a l l e d a t the ro to r wheel d i scharge , making i t pos-s i b l e t o e l i m i na t e s udden expans ion of t h e f low.i n t e r n a l e f f i c i e n c y o f t h e t u r b i n e by 5%.

These improvements raised

I t w a s deci ded t o r educe ang l e a1 a b i t more by changing t h e an- /136This ang leg l e a t which th e nozz le b lades were s e t , b u t t h i s prov ed t o b e a mis takeand l ed t o an app r ox i ma te l y 2.5% r educ t i on i n t u r b i ne e f f i c i enc y .w a s subsequent ly aga in increased ( i n experiments w i t h lower b lade he ig h t and

shaped w a l l ) .The nex t a l t e r a t i o n of t h e t u r b i n e ( 5 ) , r educed t he he i gh t o f nozz l eb l ade s and moving b l ades , w h i le r e t a i n i ng t he r a t i o o f t he areas which were

normal t o t he f l ow a t the r o t o r wheel inpu t and ou tpu t .h e i g h t r e s u l t e d i n re d uc i ng t h e c u r v at u re o f t h e e nd w a l l , th e mean d iamet er a tt h e ou t pu t o f t h e w heel , and i n i nc r eas i n g t he ave rage B2 angle.

Decreas ing th e b l a d e

T h i s r a i s e d t u r b i n e e f f i c i en cy by 1 .5% .I n t h e l a s t a l t e r a t i o n ( 6 ) , t h e t u r b i n e w h ee l w a s l e f t unchanged,

bu t one of th e end w a l l s i n t h e n o z zl e box w a s r ep laced by a shaped w a l l i ncon formit y with th e recommendations of ME1 (Moscow Power-Engineering I n s t i t u t e )(Ref. 2 ) . I ts contour i s shown i n Figure 2b. The f in d i ng s of t h e Moscow Pow-e r- En gi ne er in g I n s t i t u t e i n d i c a t e t h a t t h e sh ap ed w a l l reduces l os se s i n t h eno zz le box from 5.1% t o 2.5%. The e f f e c t o f t h e shaped w a l l i s obvious ly no tr e s t r i c t e d t o t h i s . I t a l s o must improve uni for mit y of f low a t t h e i n p u t o ft h e r o t o r w h ee l, e s p e c i a l l y a ro un d t h e e nd w a l l s , and, cons eque ntly, must re-d uc e l o s s e s i n t h e r o t o r w he el . T h er e fo re , t u r b i n e e f f i c i e n c y must b e r a i s e dt o a gr ea t e r deg r ee t ha n s im pl y reduc i ng l o s s e s i n t h e nozz l e box.t u r b i n e the re w a s a 4% r i s e i n e f fi c ie n c y. I n o ur

F i g u r e 3 g i v e s t h e c h a r a c t e r i s t i c s o f a t u r b i n e w i t h a shaped wa11./137F or pu rpos es o f com pari son, t h e b roken l i ne s deno t e t h e ch a r ac t e r i s t i c s o fa f l a t -w a l l e d t u r b i n e w i t h t h e same blade he i gh t . With a s l i g h t c ha ng e i np r e s s u r e r a t i o , t h e e f f i c i e n c y a nd de gr ee o f r e a c t i o n ha r d ly v a r i e d .w a l l r e s u l t e d i n a p e r c e p t i b l e i n c r e a s e i n d e l i v e r e d f l ow th ro ug h t h e t u r b i n e ,which may be expla ined by an i nc re ase i n ang le a1 and f low co e f f i c i en t of t h enozz l e box . The deg ree of r e ac t i on a l s o i nc r eas ed s l i g h t l y .

The shaped

The r e s u l t p roduced by condi t ion ing t h e tu rb in e w a s t o s uc ce ed i n r a i s i n ge f f i c i en cy by 16% and b r i ng i ng i t t o 87%, d e s p i t e t h e s m a l l s i z e of t h e t u r b i n e .I t s hou l d , how ever , b e bo r ne i n mind t h a t t h e s e r e s u l t s were obtained on anexper imental machine, whose receiver shape and exhaust duct are l i t t l e s u i t e d

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Figure 5Diagrams of Turbine Losses

(l)- dl tout; ( 2 ) -


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- c.Figure 6T u r b i n e C h a r a c t e r i s t i c as a Function of Blade Height

(l)- c o u t p u t ; (2) - cd j , , k ; (3) - ul/cadw a s reduced by tr imming. Turbine blad ing a t maximum blade height i s showni n F i g u r e 2 a by t h e s o l i d l i n e s .h a u s t d u c t a re r endered by th e broken l i ne s .r o to r wheel b lades and th e hous ing w a s approximately 0.5 mm i n a l l t e s t s .

A t t he l ow er he i gh t s , t h e w a l l s of t he ex-The ra d ia l c l ear anc e between t he

The t e s t s were made a t th re e pre ssur e r a t i o s , pg/p ,, o f 1 .48, 1 .35 , and1.24.F i g u r e 4 g iv e s t h e r e l a t i o n s h i p s of t u r b i n e i n t e r n a l e f f i c i e n c y P t oia t t h e d i f f e r e n t b l a d e h e i g h t s. E f f i c ie n c y was pr ac t i ca l l y i ndependen tu1 "adof p r e s su r e r a t i o a t a l l f o u r r e l a t ive b l a d e h e i g h t s .

r a t i o w a s 0.62-0.7. A l l curves had th e appearance which i s cus tomary i n r ad i a l -ax i a l - f l ow t u r b i nes .

The optimum ul/cad

M a x i m u m e f f i c i e n c y i n t h e s e t e s t s va r ie d f rom 0.83 t o 0 .71.F i g u r e 5 shows t h e d epend ence o f l o s s d i s t r i b u t i o n i n t h e t u r b i n e a tthe d i f f e r e n t b l ad e he i g h t s on ul /cad .I t f o l l ow s fr om t h e g raphs t h a t t he pe rcen tage o f l o s s i n t he nozz l e

boxes dropped as u l / cn o z z l e s b e ca u se of t h e t u r b i n e ' s i n c re a s ed d e gr e e o f r e a c t i o n . A s b l a d e h e i g h t

r o s e ; t h i s w a s r e l a t e d t o reduced h e a t t r a n s f e r i n t h ead

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went down, t h e l o s s e s i n t h e nozz l e box wen t up because o f t h e r i s e i np e rc e nt a ge o f t i p l o s s e s . The p r op o rt io n o f d i s k f r i c t i o n l o s s e s grew f o rtwo reasons as b l ade he i gh t decr eas ed. F i r s t , because o f dec r eas ed a i r /138f low through th e tu r b i ne , and, secondly , because of e nl ar ge d f r i c t i o n s u r-f a ce on t h e d i s cha r ge w a l l .

A s i s ev iden t f rom th e graphs , the l os se s i n t h e r o t o r w he el , t a k i n gi n t o a cc ou nt t h e l o s s e s t h ro ug h t h e r a d i a l c l e a r a n c e be tw ee n t h e r o t o r whe eland t h e hous ing a t a l l b l a d e h e i g h t s were minimum a t u l / c % 0.65-0.7.ad

R ot or w he el v e l o c i t y c o e f f i c i e n t J, w a s f i g u r e d f o r r e l a t i v e b l a d e h e i g h tR1 = 0.075. The m a x i m u m r o t o r w heel v e l o c i t y c o e f f i c i e n t of 0.78 w a s ob t a i neda t t h e p o s i t i v e a t t a c k a ng le i % 30".f a c t ( R e f . 7 ) t h a t v e l o c i t y c o e f f i c i e n t J, us ua l l y r eaches i t s maximum a tp o s i t i v e a t t a c k angles .w e r e ob t a i ned a t R 1 % 0.05, and compri sed about 5% of th e t o t a l he a t d rop .f i r s t g lan ce , i t seems t h a t a t g r e a t b la de h e ig h t t h e l o s s e s i n t h e r o t o rwheel should be the l e a s t , s i n c e -- as b l a d e h e i g h t r i ses -- th e p or t io n com-p r i s e d by t i p l o s s e s w i t h i n t h e t o t a l l o s s e s grows smaller . The e x i s t enc e o fan optimum may be a t t r i b u t ed t o t he oppos i t e e f f ec t exe r t ed on t o t a l r o t o rw he el l o s s e s by t i p l o s s e s , on t h e on e h an d, and by l o s s e s i n fl ow d e f l e c t i o n ,on t h e o t he r hand ( f low de f l e c t i o n occu rs bo t h i n t h e m er id i an p l ane and i nt h e c i r c u m f e r e n t i a l d i r e c t i o n ) . L osse s i n f l o w d e f l e c t i o n are known t o de-crease as s moot hnes s o f de f l e c t i o n i nc r e as es , i . e . , a s t h e r a t i o of h y d r a u l i cd i am et e r t o ave r age de f l ec t i on r ad i u s becomes smaller .h e i g h t s t h e l o s s e s i n f lo w d e f l e c t i o n a r e r ed uc ed .t h i s h av e a c e r t a i n m i m i m u m i n t h e g iv en case when x l % 0.05.

This corro bora tes t h e prev ious l y knownMinimum l o s s e s i n t h e w heel as b l a d e h e i g h t changedA t

Therefore , a t low bladeT o t a l l o s s e s r e s u l t i n g f rom

Figure 6 shows how lo s s d i s t r i bu t i on , r e ac t io n degree p , and r a t i o o fd e l i v e r e d f l o w t o r e l a t i v e blade height depend on r e l a t i v e bla de h e ig h t whenU1/cad = 0.65.

R a t i o of d e l i v e r e d a i r f lo w t o r e l a t i v e b l a d e h e i g h t ,Gw 1140P$ ii ,

d e c r e a s e s a t low b l ad e he i gh t s ; t h e e x pl a na ti o n f o r t h i s i s t he i nc r eas eddeg r ee of r e a c t i o n .

Ef fe c t o f Radia l C learance on Turb ine Ef f ic ien cyA number of s t u d i e s have been devot ed t o t h e e f f e c t o f t h e r ad i a l clear-

ante -- i . e . , th e c l ea ran ce between t he r o to r wheel b lades and th e hous ing --on t h e ope r a t i on o f t h e r ad ia l - ax i a l- f low t u r b i n e .

The e f f e c t o f t h e r a d i a l c l ea r an c e w a s f i r s t s t ud ie d i n a paper byThe research w a s conducted on an a i r t u r b i n e by. Y e . Kovalevskaya (Ref. 4 ) .a method of t r imming th e ro t o r blading.r a d i a l ( e lG < 90").a n c e w i t h i n w id e l i m i t s (wi thout changing th e r a d i a l d i scharge c learance) had

I n p ut i n t o t h e r o t o r wh ee l w a s non-The t e s t r e s u l t s showed t ha t va r yi ng t h e ax ia l i n p u t clear-

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49

Figure 8Dependence of T urbine E ff ici enc y on Average Relative RadialClearance

p r a c t i c a l l y no e f f e c t on t u r b i n e e f f i c i e n c y .t h e wh ol e r a d i a l c l e a ra n c e by 1%e d t o a n e f f i c i e n c y d ro p o f 1 t o 1 . 5 % .

Simultaneous enlargement of

Rozenberg e t a l . (Ref. 7 ) c a l c u l a t e d t h e e f f i c i e n c y l o s s when i n c r e a s i n gt h e r a d i a l c l e a r a n c e by u s i n g t h e e m p i r i ca l f ormu la

where 6 i s average ra d ia l c l ea rance , and

-- average b l a de he igh t .av'Valdenazz i ' s a r t i c l e (Ref. 8) makes a n a t t e mp t t h e o r e t i c a l l y t o d e t e r -A number of rough assumptions were made

For example, i t was assumed that a l lm i n e l o s s e s i n t h e r a d i a l c l e a r a n c e .when de r i v i ng t he formula he proposes ,t h e e n er gy o f t h e f l u i d f l ow in g th ro ug h t h e r a d i a l c l e a r a n c e i n t o t h e a d j a c e n tchanne l i s l o s t .

d e s i g n o n d e gre e of c l e a r a n c e l o s s e s .

The formula w a s n o t e x p e r im e nt a ll y v e r i f i e d .A c e r t a i n c o n t r a d i c t i o n i n r e s u l t s i n d i c a te s t h e e f f e c t o f r o t o r wheel

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, T ur bi nes w i t h va r i ou s r ad i a l c l ea r ances were t e s t ed i n o r de r t o amassexpe ri m en ta l da t a . The c l ea r anc e e f f e c t w a s examined a t a r e l a t i v e b l a d eheigh t o f i l = 0.075.

T h e r a d i a l c l e a r a n c e was changed by tr imming th e r o t o r wheel bla ding .Tests were f i r s t c a r r i e d o ut by chang ing t h e i n p u t r a d i a l c l ea r ance 6 1 ( F i gu r e7 ) . The ro t o r wheel w a s t rimmed i n accordance wi th t h e same pat te rn used whent h e wh eel w a s f ab r i c a t e d t o g i ve t h e minimum c l ea r a nce w i t h t h e housi ng. Hered i sc h ar g e r a d i a l c l e a r a n c e 6 2 remained constant. I t s r e l a t i v e va l ue w a s

The second group of t e s t s w a s conducted with a cons t an t m a x i m u m clear-ance 6 1 and with a v a r i a b l e c l e a r a n c e 6 2 . H e r e t h e r e l a t i v e v a lu e = 6 121

w a s 0.39. Measurements showed t h a t with t h e minimum cle ara nc es t h e pr es su red i s t r i b u t i o n a lo ng t h e p i t c h of the nozz le box w a s cus tomary on both s ides( i . e . , t h e r e w a s a pr es su re minimum i n t he wake of t h e noz zl e blade edge andm a x i m u m i n t h e c e n t e r of t h e n o z z le c h a nn el ). A s c le ara nce became la rg er ,t h e n a t u r e o f p r e s s u re d i s t r i b u t i o n on t h e d i s c ha rg e w a l l changed: Pressurebecame equa l i zed because o f vo r t i c i t y i n t h e c l ea r anc e r eg i on .s u r e on bo t h w a l l s w a s p r a c t i c a l l y t h e same.

/142Average pres-

The t raverse n a t u r e of t h e f lo w a t t h e t u r b i n e o u t l e t showed t h a t f lo wo u t l e t a n gl e a2 and d e l i v e r e d o u t l e t v e l o c i t y A2 r o s e s h a r p l y i n t h e r e gi on oft h e c l e a r a n c e as t h e c l ea r ance grew l a r ge r . The exp l ana t i on f o r t h i s l i e s i nt h e f a c t t h a t -- as t h e c l e ar a n ce g e t s l a r g e r -- t h e a i r on t he pe r i phe r yd e l i v e r s less of i t s ene rgy t o t h e r o t o r w heel b l ad i ng .

F i g u r e 7 shows t h e t u r b i n e c h a r a c t e r i s t i c s a t d i f f e r e n t r a d i a l clear-A 33% i n c r e a s e i n r e l a t i v e c l e a r a n c e 81 r e s u l t e d i n aances .p ro ve d t o b e l i n e a r .r e l a t i v e e f f i c i e n c y d ro p,

ro se f rom 0 .045 t o 0 .07 (wi th u l / cap r a c t i c a l l y no c ha ng e i n d i s c ha r g e P os se s a t low va lu es of ul /c ad (around 0 . 4 )as t h e c l e a r a n c e i nc r e a se d .

The dependence of m a x i m u m e f f i c i e n c y o n v a r i a t i o n i n c l e a ra n ce 6 1i , of 12 .7%. Discharge-loss co ef f i c i en t 5d i s

A s th e g raph shows, th er e w a si = 0.65) .

A s c l e a r a n c e 62 g r e w l a r g e r , e f f i c i e n c y ni f e l l i n a c u r v i l i n e a r d e -pendence. A t t h e same t i m e , th e d i scharge lo s s es became gr ea te r . Therefore ,t h e c u rv e s s howing t h e v a r i a t i o n i n i n t e r n a l e f f i c i e n c y rl*pa r am e t e r s p roved t o be more gen t l y s l op i ng t ha n t h e same cu r ves f o r

i n t h e r et a rd e dii

/143ependence of i n t e r n a l e f f i c i e n c y o n a ve ra ge r e l a t i v e c l ea r ance -61 + 6 2E 1 + E 36 =good approximation of a s t r a i g h t l i n e . E xp ra po la ti on of t h i s l i n e t o 3 = 0g i v e s a nominal e f f i c ie nc y va lu e of 0 .876 when th er e i s no c l ea r ance , i . e . ,

is shown i n F ig ur e 8. When 3 < 0 .2 , t h e d a t a p o i n t s g i v e a

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= 0.876."i (6 = 01 The dependence of rl on b obeys the equat ioni I'I 1 z- ,876 - 1,Og: '

o r -'1 - = ?1 /T l , , aco t == 1 - ,24%).

The dependence of 6 on b i s p l o t t ed i n F i gu r e 8. Here t h e b ro ke n l i n ein d i ca te s th e ana logous re l a t i on sh ip accord ing to Rozenberg (Ref. 6 ) .

A s th e graph makes evi den t , th e curves a re i d e n t i c a l i n n a t ur e , b u t t h el e n g t h of t h e i r r e c t i l i n e a r segment i s d i f f e r e n t :ou r f i nd i ngs t ake t h i s s egm en t t o b < 0.2. Rozenberg's goes t o \< 0 . 0 4 ;

The exp lana t i on f o r t h i s i nc on gr ue nc e i n t h e r e s u l t s l i e s i n t h e f a c tt h a t o u r t u r b i n e w a s more ef f i c ien t .l a r g e r , t u r b in e e f fi c i e n cy f a l l s o ff t o a certain minimum value, a f t e r whicht h e r e i s no more change . The re w a s i n a d d i t i o n , of c o u r s e, t h e e f f e c t e x e r te dby d i f f e r e n c e i n t u r b i n e d e s i gn .

Obviously, as r ad i a l c l ea r ance g r ow s

ConclusionsT es t i ng a r ad i a l -ax i a l - fl ow t u r b i ne w i t h b l ades of va r y i ng he i gh t s

d em on st ra te d t h e f a c t t h a t e f f i c i e n c y rises up t o a c e r t a i n l i m i t i n g b l a d eh e i g h t ( i n o u r t u r b i n e i , = 0.075).t u r e , w hich caus es i nc r eas ed l o s s e s i n f low de f l ec t i on , a s l i g h t d rop i n e f f i -ciency may s e t i n when b lad e h e igh t i s f u r t h e r i nc r eas ed . The e f f i c i e ncy d ropa t low b la de he ig h t s r es u l t s fundamenta l ly f rom increa sed d i s k los se s and lo sse si n t h e n o z z le s. As f e l l f rom 0 .118 t o 0.0286 , d i s k lo s s es rose f rom 2 t o9%, and l os se s i n th e nozz le box f rom 2 . 2 t o 5%. L os ses i n t he r o t o r w hee l areminimum a t x, 9 0.05.increment of 4%.

Because of th e in cre ase i n end w a l l curva-

Shaping the end w a l l of th e nozz le of th e nozz le box gave an e f f i c ien cy

Improvement o f th e tu rb ine b lad ing thu s r a i se d e f f i c ie nc y f rom 0.71 t o0.87.

I n r ad i a l -ax i a l - fl ow t u r b i n es t h e l o s s e s due t o t h e r a d i a l c l e ar a n ce be-tween ro to r wheel b lad in g and t he housing are 1-1.5% p e r each perce nt of in -crease i n r e l a t i v e c learance . This i s s u b s t a n t i a l l y less t h a n t h e same l o s s e si n ax ia l - f low turb ine s wi th unshrouded moving b lades (1 .4 t o 2 .8% of los ses p e re a ch p e r c e n t of r a d i a l c l e a r a n c e) . I n c re a s e i n r a d i a l c l e a ra n c e l e a d s t o i n -c r eas ed d i s cha r ge l o s s e s , bu t w i t h low u l / cad va l ues t h e r e i s a smaller i n -crease i n d i s c ha r ge l o s s e s . As r a d i a l c l e a r a n c e i n c r e a s e s , f lo w d i s c o n t i n u i t ya t r o t o r whee l d i s cha r ge a l s o i nc r eas es .r a d i a l c l e a r a n c e , t h e f e a s i b i l i t y of i n c re a s in g a n g le a2 must be considered.

I

I n des i gn i ng a t u r b i n e w i th a l a r g e

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NASA TT F-10,441

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References I144

Deych, M. Ye., Zaryankin, A. Ye., Sherstyuk, A.N., Dineyev, Yu. N.Issledovaniye napravlyayushikh apparatov radial'nykh turbin (A Studyof Return-Circuit Rigs in Radial-flow Turbines).Vysshey Shkoly, No. 4, 1958.povysheniya ekonomichnosti radial'no-osevykh turbin (Some Ways toImprove Fuel Economy of Radial-axial-flow Turbines).No. 5, 1962.Zaryankin, A. Ye.turbin (Tip Losses in Nozzle Boxes of Radial-flow Turbines). IzvestiyaAkademii Nauk SSSR, Otdeleniya Tekhnicheskikh Nauk, "Energetika iAvtomatika", No. 2, 1960.stenkoy korpusa na effektivnost' raboty radial'nor tsentrostremitel'noyturbiny (The Effect of the Clearance Between the Turbine Rotor-Wheeland the Front Wall of the Housing on Operating Efficiency of theCentripetal Turbine).aviatsionnym lopatochnym mashinam (Proceedings of the First Inter-university Conference on Bladed Aviation Machines). Oborongiz, 1958.turbokompressora ripa TKP-14 (Some Results from Investigating the TKR-14Turbocompressor). Trudy Kazanskogo Aviatsionnogo Instituta, No. 76,1963.Rozenberg, G. SH., Kostyrkin, V. F. , Kastal'skiy, S. A. Rezul'tatyissledovaniy radial'nykh turbin s lopatochnym i bezlopatochnymnapravlyayushchim apparatom (Results of Research on Radial-flow Turbineswith Bladed and Bladeless Return-Circuit Rigs). Sudovyye GazovyyeTurbiny (Marine Gas Turbines). "Morskoy Transport", Izdatel'stvo , 1961.Tunakov, A. P. 0 poteryakh v protochnoy chasti tsentrostremitel'noyturbiny (Losses in the Blading of the Centripetal Turbine). TrudyKazanskogo Aviatsionnogo Instituta, No. 63, 1961.Valdenazzi, L. G. Loss Due to Leakage in Unshrouded Radial Impellers.IRAS, 11, No. 542, 1956.

Nauchnyye DokladyZaryankin, A. Ye., Sherstyuk, A. N., Zatsepin, M. F. Nektoryye puti

Teploenergetika,Kontsevyye poteri v soplovykh apparatakh radial'nykh

Kovalevskaya, A. Ye. 0 vliyanii zazora mezhdu kolesom' turbiny i peredney

Trudy pervoy mezhvuzovskoy kmferentsii PO

Odivanov, L. N., Tunakov, A. P. Nekotoryye rezul'taty issledovaniya

Received April 23, 1963.

Scientific Translation Sewice4849 TocaZoma Lane. La Canada, California

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Clearance Effects on RIT's

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