COPYsNO. 9

RM No. E&t21

I’I

RESEARCH MEMORANDUMSOME EFFECTS OF STATOR CONE ANGLE AND BLADE-TIP LEAKAGE

ON 40-PERCENT-REACTION TURBINE HAVING ROTOR-BLADE CAPS

By Robert E. English, Robert J. McCreadyand John S. McCarthy

Lewis Flight Propulsion Laboratory

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NATIONAL ADVISORY COMMITTEEFOR AERONAUTICS

WASHINGTONbMarch 23, 1949

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HAIIIONAL ADVISORY KMIl2EZ IK)R AERORAUTICS

SOME-OF-COI?EM=ABDBLADE-TIP-a

ON BO-PERCENT-REACTION TURKtHE HA?TNG ROTOR-BURR CAPS

By Robert E. &&ah, Robert J. MoCreadyand John 5. McCarthy

For an investigation of the effects of stator cone angle andtip lealcege on turbine perfonaanoe, a single-etage turbine having40-percent reaction wat3 operated with two etatore and two atation-ary shrouds: (1) a stator having a cone angle of 70° and a etator-blade height 0.92 of the rotor-blade height; (2) a stator havinga O" cone angle and a blade height equal to the rotor-blade height;(3) a labyrinth, no-leakage shroud; and (4) a cylindrical stationaryshroud ham a radial clearance 0.016 of the blade h&&t. In allcases, the rotor blades were equipped with caps that formed a con-tinuous, cylindrical rotating shroud.

Theturbinewas operated at an entranue temperature of 660°Rwith total-pressure ratios from 1.25 to 3.70 and equivalent meanblade epeeda from 166 to 655 feet per eeoond. For this range ofconditions, the over-all perfommnce of the turbine was determined.

With the O*-c-e-angle stator, the peak brake efficiency wasapproximately 0.04 higher than with the 70°-cone-angle stator. Withthe 70°-cone-angle stator, separation probably occurred at the tipsof the rotor blades; the separation was eliminated by changing thecone angle to O" and making the etator-blade height equal to therotor-blade height. Whenthe labyrinth shroud was replaced bythecylindrical shroud, the efficiency was not changed by a measurableamount.

As part of a pro~ramto develop techniques for designing tur-bines of high efficiency, an investigation is being conducted at

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2 4U.*.,-~dE WA IZM No. E8I21

the IfACA Lewis laboratory to determine the performance of asingle-stage, cold-air turbine in which the relative importance ofdesign variables is evaluated by incorporating systenreLtic changesin the blade design. This investigation should provide data forthe design of turbines and indicate where f’urther studies may mostprofitably be concentrated.

The first phase of this program is an investigation of theeffects of stator cone angle and tfp lea-e on turbine performance.In order to observe the effect of stator cone angle on over-allturbine performance, two stators were used.: a stator with a 70°co- angle and a stator-blade height 0.92 of the rotor-blade height;and a stator tith a 0' cone angle and a stator-blade height equalto the rotor-blade height. The effect of tip leakage on turbineperformance was Investigatedby operatingtheturbine with a laby-rinth no-leakage shroud and a cylindrical shroud.

Of the possible combinettions of these variables three con-figurations of the turbine were studied:stator and the labyrinth shroud; (2) the 06 '

1 the 70b-cone-angle-cone-angle stator and

the labyrinth shroud; and (3) the O"-cone-angle stator aad thecylindrical shroud. For the investigation of these three config-urations, the turbine w&a operated at total-pressure ratios of 1.25to 3.70 and equivalent mean blade speeds of 188 to 855 feet persecond using air at a temperature of 660° R.

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The following symbols are used in this report:

velocity of a&, (ft/sec)

turbine-&&t work, (Btu/lb)

standard acceleration due to gravity, 32.17 (ft/sec2)

specific enthalpy, (Btu/lb)

mechanical equivalent of heat, 778.3 (ft-Lbbtu)

absolute pressure, (lb/q ft)

absolute temperature, (?R)

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HACA RM No. E8I21

u‘V

W

u

al

B

3

mean rotor-blade speed, (ft/sec)

absolute VdoCity of gas, (ft/BeC)

gas velocity relative to rotor, (ft/sec)

Weight flow of air, (lb/sea)

angle of absolute velocity measured from direction of rotor-blade motion, (deg)

angle of relative velooity measured from direction of rotor-blade motion, (deg)

prefixdenotingchange

bra& efficiency

m&B8 density, (BlU&U ft)

0 NACA sea-level air; 2116 @b/q ft)and 518.4' R

1 stator entrance

2 rotor entrance

3 rotor exit

3 ideal Jet

8 ieentropic

U tangential component

X axial component

super0cr1pt:f total, or StagnatiOn, state

The aerodynamiccorilitionB :

design of the turbine is for the follaring

4 -9 IIAOA RM No. E8I21

Entrance absolute total temperature, Tl', oR................

1960Entrance absolute total pressure, pl', lb/sq ft 2829

in.Hg . . . . . . . 40Mean rotor-blade speed, U, ft/sec . . . . . . . . . . . . . . 1210Total-to-static press ........... 4.0Amount of reaction

uq gt:, Pl'/&q (hlt . . . . . . . . . . . . . ..0.4 0

Because the experimental investigation was condutited at a lowturbine-entrance temperature (660' R) as contrasted with the designconditions and because the performance data are expressed In termsof the entrance and exit total states, blade speed and pressure ratioare more conveniently stated in terms of equivalent mean blade speedat MACA sea-level air conditions and total-pressure ratio. Thedesign conditions correspond to an equivalent mean blade speed U s

( >of 645 feet per second and a total-pressure ratio pl'/p3' of 3.32.The velocity-vector diagram for the mean section is given in figure 1.The turbine was designed for a stator exit angle a2 of ZOO, a con-stant along the radius. Upstream of the stator, downstream of therotor, and In the axial clearance space between the stator and therotor, both the static pressure and the mass flow per unit of annulusarea were assumed to be constant along the radius. The expansion inthe turbine was assumed to be adiabatic, and the working fluid wasassumed to have a ratId of specific heats equal to 1.300 and aspecifio heat at constant pressure equal to 0.300.

The turbine wheel was composed of 150 blades that were 1.50 incheslong; the mean diameter midway between the rotor entrance and exitwas 13.25 inches and the outer wheel diameter, 14.75 inches. (Seefig. 2.) The blades were die-cast aluminum, each with an integralcap at the tip, so that with the blades clamped between two disksthe caps formed a continuous, rotating shroud. (See fig. 3.) Therotor-blade profile is shown in figure 4.

stators

A stator (fig. 5) was available from another turbine whose rotordiameters and blade height were the m as those of the experimentalturbine; in addition, the trailing-edge angle bf the stator bladeswas equal to 20°. If the assumptions used In designing the rcotorblades are applied to this stator and the effects of rotor-bladeoverlap sre neglected, the stator meets the design conditions at theentrance to the rotor. The stator had a cone angle of 70° and

WLCAEMI!Jo.E6I21 5

contained 28 et&or bladee. The atator-blade height wa8 about *l/8 inch lees than the blade height at the rotor entmnce, or 0.92of the rotor-blade height. This et&or was east in on8 piece.

A second stator (fig. 6), vhioh va8 of velded mnetrnotion,had. a O" eons angle, and oontained 36 etator blades. The stator-blade height was made equaltothe blade heightatthe rotorentrance.' Ifthesssmaptioneu~ledindesigningthe rotorbladeare applied to this stator, the atator meets the deeign oonditioneat the rotor entrance.

Four difference8 exi8ted inthe two etatore;mly, the methodof oonatruction, the number of etator bludee, the oonethe stator-blade height. -PJdThe internal8urfacee of the 70 goone-angle stator wers hand-finished 80 that the 8urfmea of both statorswere of approximatelyequalroughneee. Because the eolidity is highand separation istmlikelyto oofmr inetiher 8tator,the number ofetator blades should have little effect. The cone angle and thestator-blade height are the signifioant differencea. With eaohetator, the4 minimum axiul cle- b&men the stator blade8 andthe rotor blades ua8 between 0,120 anb 0.140 inoh.

The two shrouds ueed in thi8 investigation are 8hown in fig-ure 7. The lab&i&h, no-leakage, 8tationa;ry shroud (fig. 7(a))consiete of a circular ring with two dimumferential groove8 on theinner surface. Theradialolmranoebetweenthe labyrinthetation-a-y ehroud and the cylindrical rotating ehrou$ formed by the bladecaps is 0.025 inch. Leakagebetweenthe labyrinthehrozzdardtheblade capawsm prementedbyintroduc3ingsir intothe epaoe down-etream of the labyrinth 8hrond.. The amotmt of labyrinth-eealingairwas eoadjustedthatthe pressureeinthe tvo cizcmferentialgrooveswere qnalized;whenthepreesureewem equal, itwaea88tzmedthat no air leaked past the shroud.

The cylizx3rical etationary shroud (fig. 7(b)) is the 8ame widtha8 the blade ospe. The radisl olsaran~e between the b3ade capsand the ehrond wa8 0.025 izmh, or 0.016 of the blade height.

configQrations

Thethreetrrrbine oonfiguratione inveetigatedam showninfigure 8. Configuration1include8the 70°-oom-angle statorand

6 l!UCAEMNo. E8l21

the labyrinth stationary ehroud; configuration 2, the O"-cone-anglestator and the labyrinth stationary shroud; and configuration 3,the O"-oone+angle stator and the cylindriaal stationary shroud.

Experimental Rquipment

The arrangement of the experimental equipment is dia@ammati-tally shown in figure 9. Room air enters the electrostatic precip-itator where dust particles are removed and passes through a sub-merged flat-plate orifice, an automatically controlled steam-supplied air heater, a surge tank, and into a pair of ducts leadingto the plenum chamber immediately upstream of the turbine stator.The air-flov path from the plenum chamber through the turbine isshown in figure 10 with the labyrinth shroud and the 70°-cone-anglestator of oonfigaration 1 installed in the turbine. Air enteringthe plenum chamber passes through an l&mesh, 27-gage soreen, turns,and flows through a straightening grid. The airthenpassesthroughthe stator and the rotor and leaves the turbine through the annularpassage between the two exhaust-guide shells coaxially mounted inthe tail pipe. The space betueenthe outer guide shell-the tailpipe is provided to carry off the sealing air supplied to the laby-rinth.

Downstream of the turbine, the air flows through a large surgetank into a low-pressure exhaust system (fig. 9). The air pressuredrop 8crose the turbine is controlled by a butterfly valve doun-stream of the second surge tank. A3OO-horsepoverwaterbralre,cradle-mounted for torque measurements, was used for powerabsorption.

Pnstrumentation

The location of the turbine instrumentation is shown in fig-ure 10. Entrance total pressure pl' was indicated by a total-pressure tube 3/4 inch upstream of the stator blades; the entrancetotal temperature Tl' wasmeasuredwlththermocouplesatfour sta-tions within the pair of ducts leading to the plenum chamber. Theexit statio pressure p3 was measured-by six wall taps located inthe exhaust-guide shells downstream of the rotor. The exit totaltemperature T3' was measured by three total-temperature thermo-oouples at the downstream end of the two exhaust-guide shells.

l

NACA RM No. E8I21 7

Water-brake torque was indicated by an RAW4 balanced-diapIr?a.gmdynamometer-torque itiicator (referenoe 1). Air flow w was mesa-ured by the 7-inoh submerged flat-plate orifice upstream of the airheater (fig. 9). Turbine speed was Ml-ted by a calibrated elec-tric tachometer.

The accuracy inreadingthe datamaybe summarlzedas follows:

(1) Absolute pressure, f0.05 inch of mercury(2) Tempera~s,f1° R(3) Orifice pressure drop,&O.O5 inch in a range with a mini-

mum of15inches(4) Torque, f0.05 inoh in a range with a minimum of 17 inches(5) Rotative speed,&13 rpm in a range with 8 minim of

3700 rpa

An estimate of the reproducibility of the measurenmnts indicatesthat the probable variation in the bmke efficiency for 8 singledata point is less than 0.01 for total-pressure ratios q'/pg'greater than 2.00.

ExperimentalProoedure

mixwere takenatturbine speeds from 37OOto16,800 rpm(equivalent meanpesst.lre r8tiossure r8tios, thespeeds. For allbetween658'andthe air flow andof mercury.

blade speeds fro; 188 to 855 ft/sec) at total-Pl'/P3' from 1.25 to 3.70. At each of ten pres-turbine was opelgtedat sixto tendifferentruns the entrance total temperature was held662O R; the entrance total pressuq varied withthe barometric pressure between 2% and 28 l110he8

Allturbins perfOrmeanC e data were reduced to HACA sea-levelair oonditione at the turbine entrance. The perfo- was deter-mined In terms of the following variables:

(1) Brake efficiency, q(2) Total-pressure ratio, pl'/~'(3) Rquivalent turbine-shaft work,

(4) Equivalent mean rotor-blade speed,

8 HACAFMNo.EXC21

(5) Ratio of equivalent mean rotor-blade speed to equivalentml'

m8ss f1ms wpo- (This is the reciprocal of m&se flov

per unit blade speed.)(6) Ratio of mean rotor-blade speed to ideal Jet speed (blade-

to-Jet speed ratio), U/kJ

The brake effioiency of the turbine, which includes the mechan-ical efficiency of the turbine, is defined 88

rl E= A&$

The weight flow of air w was determined from the orifice mea--ments and the data of referenoe 2.

The ideal enthalpy drop A,hl,3' was computed using thechart of air properties in reference 3 and the values of entrancetotal pressure and temperature and exit total pressure,and P3’r

~1% Tl',respeotively. Deoause the exit total pressure ~3'

was not dtiotly measured, this value was computed. The exitst8tio pressure p3, the exit total temperature T3', the weightflow w, and the annular area between the exhaust-guide shellswere used to determine the exit total pressure p3' by adding tothe measured St&tic pressure 8 ~~TXUIC pressure computed from con-tinuity with the assumptions that the tangential velocity is zeroand the axial velocity is constant; these assumptions result inefficienay values t&bt are- always conservative.

The ideal Jet speed V.J is the Jet speed for an isentropioexpansion from the entrance total state to the exit static pras-sure, that is,

V3 = 4jZJ43 (hit - h3),

The isentropic enthalpy drop (hl' - h3)s was computed from refer-enqe 3usingthe entrancetotaltemperature andpree~ 8ndthSexit static pressure, pl', Tl', and p3, respectively.

RESULT8 AND DISCUSSlON

The performanc e characteristics over the ran@ of operationcovered in this investigation are shown for configurations 1, 2,and 3 in figures ll, 12, eand 13, respectively. For each of the

l NACA EM No. MI21 qlwslllo91Al 9

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three configurations, the curves of cmtant equivalent blade speed

U are vertical above 8 pressure ratio plt/p31 of approxi-mately 2.25 because the flow through the et&or blades was ohokingand the equivalent weight flow therefore remained oonstant. Theover-all performance &aracteristics are similar for the three con-figurations and each oonfiguration has an efficiency near the maxi-mum over the range of pressure ratio from 1.25 to 3.70.

Brake efficiency ?l plotted against the ratio of blade-to-Jetspeed ratio U/VJ (fig. 14) is nearly independent of total-pressureratio pl'/p3* for configuratim 2. Because this independenoe ofpressure ratio also exists for configurations 1 and 3, the bisonof the three configurations in figure 15 at a pressure ratio of 3.00is representative of the entire range of pressure ratios. In addi-tion to showing the same changes in brake efficiency as figures 11to 13, figures 14 and 15 indicate that the maximum brake efficiencywas obtained with a blade-to-jet speed ratio U/V.J between 0.50and 0.55. The maximum brake effioiency was 0.795 for oonfiguration 1and 0.833 for configur8tion 2, a differenoe of approxtitely 0.04.With the X%oone-angle stator, separation probably occurred at thetips of the rotor blades; the perfortnanoe was improved by chaugingthe cone angle to O" and making the stator-blade height equal to therotor-blade height, thereby eliminating the separation (figs. 8(a)ana 8(b)). If the efficiency were computed using the total-to-statiopressure ratio pl*/p3 instead of the total-pressure ratio pl*/p3',the relative adventage of configuration 2 over oonfiguration 1 wouldbe substantially unohanged.

For configuration 3 (fig. 8(c)), the maximum,brake effioienoywas 0.835, an increase of less than 0.005 over the maximum effioienoyof configuration 2. Although any tip leakage introduoed by replaoingthe labyrinth no-leakage shroud with the cylindrioal shroud wouldcause a reduotion in the working fluid passing through the rotorblades, the measured efficiency slightly increased. Within theprobable reproducibility of the data, the performance of coufigura-tion 2 is identical to the performance of configuration 3.

In order to determine the approximate magnitude of the leakageair flow between the blade oaps and the cylindrical stationary shroud,the wed&t flow through 8 thin-plate Orifice of equal area was OCmPUtedand multiplied by a factor of 0.7 (reference 4). The conditions for&mum leakage flow ocourred at the highest blade speed and pressureratio investigated; at these omditious the Computed leakage wasabout 1.7 percent of the air flow entering the turbine. Because the.

10 _.-4 NACA R-4 No. E8I21

leakage air flow is mainly from the boundary layer at the outerradius of the flow amulus, this air uontains only a -11 portionof the total energy passing through the turbine.

For configuration 3 (figs. 8(c) and 13), the brake effioienoywas 0.82 at the total-pressure ratio and equivalent mean bladespeed for which the blades were designed.

SUlMARYOFREsuyrS

An investigation of the effeCta of stator oone angle and blade-tip leakage on turbine performance was oauducted with 8 turbinehaving 4O-perOent re&CtioII and 8 design assumption Of Oolletantstatic pressure over the blade height. Caps at the tips of therotor bladee formed a oontinuous rotating shroud. The turbine wasoperated with a turbine-entrenoe temperature of approximately 660° Rat total-pressure ratios f?un 1.25 to 3.70 and equivalent meanrotor-blade speeds of 188 to 855 feet per second. The followingresults were obtained:

1. With the 0°-me-angle stator, the peak brake efficienoywas approximately 0.04 higher than with the 70°-cone-angle stator.With the 70°-oone-angle stator, separation probably occurred at thetips of the rotor blades; the performance was Improved by ohangingthe cone angle to 0' and making the stator-blade height equal to therotor-blade height, thereby eliminating the separatMn.

2. Replaoing the labyrinth, no-leakage shroud with a aylin-drical stationary shroud that had a radial olearance of 0.016 ofthe blade height from the oylindrical rotating shroud and using theO"-cone-angle stator produoed no measurable ohange in brake efficiency.

3. The maximum brake efficienoy was obtained with the blade-to-Jet speed ratio between 0.50 end 0.55.

Lewis Plight Propulsion Laboratory,National Advisory Committee for Aeronautics,

Cleveland, Ohio.

EACARMNo.E8I21 -- .* ll

1. Moore, Charles s., Biermanu, Arnold E., and Voss, Fred: The NACABalanced-Diaphragm Qymrnometer-Torque Indicator. EACA EBNo. 4C28, 1944.

2. Anon.: Fluid Meters, Their Theory and Application. A.S.M.E. Ees.Pub., pub. by Am. Sot. Mech. Eng. (Hew York), 4th ed., 1937.

3. NACA Subcommittee on Compmssors: Stand8rdProcedures forRatingand Testing Multistage Axial-Flow Compressors. NACATNITo. 1138,1946.

4. Stodolu, A.: Steam and Gas Turbines. Vol. I. McGmw-Hill Bookco., Inc.,1945. )

1927, p. 188. (Reprinted, Peter Smith (Rex Yorh),

Veloc i ty(ftlsec)

u 1210“2 2177v3 1281wq I I20w3 2081

Angle(deg)

a2 20 .0a3 106.482 41.783 145.5

F i g u r e 1. - Velocity-vector diagram for mean sect ion.

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NACA Rh4 No. E8121

Air flow

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Figure 2. - Sketch of rotor blade shawing turbine dbnensions,

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NACA RM No. E8f2t f 5

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Flgum 3. - Phot~@~@ Of aSWmblsd rotor Bhawing r0ta-b~ cyMnitrlcal hrcu& fcm.& byblade oaps.

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.NACA RM No. E8121 17

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NACA RM No. E8121I

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NACA RM No. E8t21 19

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Figure 7. - loatallrtlm of atatimary rhrwe shalng IaDyrint~llng air-fla path ona mdlal clearam.

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NACA RM No. E8121 21

Labyrinth Btationaryshroud

(a) ConfIguration 1.

rylindr~calatatlonary

a7@e stator

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Equivalmt mm blade spesd Ula(l/a~?, ftlsec

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Equivalent wan blade apeed/aqulvalabt weight fkm, ~c~)/wpo, ft/lb

Flgura I I . - Over-all psrfqrnsnca chart with 7p-cons-angle statar and labyrinth shroud IconfiguratIon I).

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Equivalent man b l a d e spWd U(ag/a(i, ft/asc

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Flpurs 12. - Owr-all prfomncd chart with CrJ-cons-an~la atator and labyrlnth shroud (co~flourstlon 2).

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Equivrlsnt n ssn blade smed Ul~o/a~), ft/WC

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Equivalent -ban blale spaa/cquivalsnt reipht flw. ti#woU, it/lb 0

Flours 13. - C=+usrall mrfarmsnca chart with Oq-mm-anpla stator rns cyllndrlcal shroud fcorflpuratlon 3). E!hl

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NACA RM No. E8121 27

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.30, I.I .2 -3 .4 . 5 .6 .7 .8

Blade-to-jet speed ratio, UIVj

Figure 14. -- Efficiency of configuration 2 at various pressure ratios.

NACA RM No. E8121I

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Blade-to-jet s p e e d r a t i o , U/Vj

F i g u r e IS. - Cofiptirison o f c o n f i g u r a t i o n s I, 2 , a n d 3 a t a total-p r e s s u r e r a t i o o f 3 . 0 0 .

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