Document
5 59326
TECHNICAL MEMORANDUM
X-85
CASCADE INVESTIGATION O F COOLING CHARAG TERISTICS O F A CORRUGATED -INSERT AIR-COOLED TURBINE B L A D E FOR USE IN A TURBOPROP ENGINE Cleveland, Ohio CLASSLFIED DWUMENT - TITLE UNCLASSIFIED This materlal contabs Information aiiectlng the natlonal defense of the UnIted States wlthln the meanlng of the esplonaga laws, Tltle 18, U.S.C.. Secs. 783 and 194, the transmlsslon or ravelatlon of whlch ln my manner to a n unauthorized person I s prohlblted by law.
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
March 1960
WASHINGTON
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CON FI DENTlAL
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0 0 . 0 0 0 CONFIDENTIAL NATIONAL AERONAUTICS AND SPACE ADMINISTRATION TECHNICAL MEMORANDUM X-85 CASCADE INVESTIGATION O F COOLING CHARACTERISTICS O F A CORRUGATED-INSERT
AIR-COOLED TURBIPJE BLADE FOR USE IN A TURBOPROP ENGINE+
By Hadley T. Richards S U M M A R Y The cooling effectiveness of a small air-cooled turbine blade f o r u s e i n a turboprop engine w a s experimentally investigated i n a s t a t i c cascade f a c i l i t y . Three t e s t blades of 1.4-inch span and 0.7-inch chord were subjected t o combustion-gas temperatures of about 1060°, 1360°, and 1 6 6 0 ' R. Tlie blade cooling-air temperatures ranged from about 560' t o 800° R. rl Gas Reynolds numbers varied from 85,000 t o 380,000.
I 4 - The cooling effectiveness of t h e corrugated-insert blade reported herein was found t o be almost i d e n t i c a l with that of a cast-finned blade investigated previously. A t t h e r o o t region, t h e corrugated-insert blade was from 18O t o 65' F cooler than t h e cast-finned blade. This range of temperatures corresponded t o about a 10-percent improvement i n the cooling effectiveness of t h e blade.
A nondimensional method of correlating t h e experimental heat-transfer data of t h e blades, which had been developed for a preceding blade de- sign (previously reported), was u t i l i z e d successfully with t h e data of t h i s investigation.
INTRODUCTION The b e n e f i t s obtained by increasing t h e t u r b i n e - i n l e t temperature of turboprop engines and t h e thermodynamic e f f e c t s on engine performance of cooling t h e turbines a r e reported i n reference 1. The problems of cooling blades f o r possible a p p l i c a t i o n i n t h e turbines of turboprop engines are discussed i n reference 2. A f u r t h e r discussion of t h e prob- A s p a r t of a lems of cooling small blades can be found i n reference 3.
program f o r investigating cooled turbine blades f o r turboprop engines, a blade with a n outer p r o f i l e t h e same as that reported i n reference 2, b u t of d i f f e r e n t construction and i n t e r n a l heat-transfer surface config- The uration, has been investigated a t t h e NASA Lewis Research Center.
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* T i t l e , Unc lass i f i ed .
E-535 CONFIDENTIAL 2 CONFIDENTIAI, blade configuration investigated was of t h e It corrugated-insert type.
w a s expected that t h e increased i n t e r n a l heat-transfer surface area, r e l a t i v e t o that of t h e design reported i n reference 2, would promote more e f f i c i e n t cooling. a The blade had span of 1.4 inches and a chord of 0.7 inch. The e n t i r e a i r f o i l portion of t h e blade was made from sheet-metal components brazed i n t o a cast-metal base.
The purpose of t h e present investigation w a s twofold. One objec- t i v e was t o determine t h e cooling c h a r a c t e r i s t i c s of t h e corrugated- M insert-type turbine blade and t o compare i t s cooling performance with I u t h a t of t h e cast-finned blade previously reported i n reference 2. A 0; (J second purpose w a s t o provide f u r t h e r corroboration of the c o r r e l a t i o n procedure o r i g i n a l l y evolved i n reference 2.
The cooling c h a r a c t e r i s t i c s of the corrugated-insert blade were determined i n a s t a t i c cascade t e s t f a c i l i t y that accommodated nine blades. Three blades i n t h e c e n t r a l p a r t of t h e cascade were instrumented w i t h t h e r m o c o u p l e s . The b l a d e s w e r e investigated a t combustion-gas R. Use of a n e x i s t i n g temperatures of about 1060°, 1360°, and 1660' f a c i l i t y (used i n r e f . 2 ) f o r t h e supply of combustion gas limited t h e maximum temperatures t o 1660' R, but s t i l l allowed f u r t h e r check of t h e c o r r e l a t i o n presented i n reference 2. The gas Reynolds number ranged 85,000 t o 380,000. Blade cooling-air temperatures ranged from about from 560' t o 800' R, and t h e cooling-air Reynolds number from about 2100 t o 20,000.
SYMBOLS coolant passage hydraulic diameter ( 4 x flow area)/wetted perim- dh,a eter, f t gas-side hydraulic diameter (average blade gas-side perimeter) / s r , g f t function f a c c e l e r a t i o n due t o gravity, f t / s e c 2 g Reynolds number, pVdh/pg Re T temperature, OR velocity, f t / s e c V 1.25 Z T (Rea, i CONFIDENTIAL CONFIDENTIAL viscosity, ( l b ) ( sec)/sq f t CI P density, lb/cu f t
temperature-difference r a t i o , (Tg,e - Tb)/(Tg,e - T a , i )
Subscripts: a cooling air m M b blade
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w e e f f e c t i v e g combustion gas o r combustion-gas side i i n l e t T turbulent flow Superscripts I average conditions a t p a r t i c u l a r span location
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- average conditions f o r e n t i r e blade
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APPARATUS Blades The turboprop turbine blade used i n t h i s i n v e s t i g a t i o n had a span of 1.4 inches and a chord of 0.7 inch, t h e same as t h a t used i n t h e Analysis of several i n t e r n a l designs in- first blade design ( r e f . 2 ) .
dicated t h a t one with t h i n sheet-metal corrugations might have some advantage from t h e standpoint of heat t r a n s f e r over t h e semistrut design used i n reference 2. A blade t h a t u t i l i z e d sheet-metal components of 0.005- and 0.010-inch thickness, furnace-brazed together, w a s b u i l t , as shown i n f i g u r e 1.
Cross-sectional v i e w s of t h e blade at t h r e e span- wise locations are shown i n f i g u r e 2.
The outer s h e l l , both pressure and suction surfaces, w a s separately formed of Haynes Alloy 25 by a stretch-forming process. The thickness was constant at 0.010 inch. The same material of 0.005- of t h e material inch thickness w a s formed i n t o corrugations with a n amplitude of 0.025 and a p i t c h of 0.050 inch. I n an i n i t i a l brazing operation, these cor- side of t h e pressure-surface and rugations were brazed t o t h e inner The suction-surface blade s h e l l s , as shown i n f i g u r e s l ( a ) and ( c ) .
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***. .** 4 CONFIDENTIAL e brazing was done i n an induction-heated, vacuum-atmosphere furnace with t h e use of a commercial brazing material. It should be noticed t h a t only on t h e suction surface do t h e corrugations extend from t h e base t o t h e t i p of t h e blade s h e l l ( f i g . l ( a ) ) . A t 50 percent of t h e span, t h e pressure-side corrugations a r e terminated because of the lack of space The smaller sheets of metal on within t h e blade c a v i t y ( f i g . l ( c ) ) .
t h e inner surface of t h e suction and pressure s h e l l s shown i n t h e photo- graph form a n inner i s l a n d a t blade assembly. This island i s necessary t o force cooling a i r t o follow t h e passages formed by the corrugations
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near t h e outer surface of t h e s h e l l .
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The base of t h e blade w a s c a s t of X-40 a l l o y and w a s joined t o t h e s h e l l i n a second brazing operation t h a t a l s o joined t h e two halves of was then ground t o t h e shape necessary t o accommo- t h e s h e l l . The base d a t e t h e blade i n t h e cascade t e s t The completed blade i s section.
shown i n f i g u r e l ( d ) .
Te s t Fac i li t y The cascade t e s t f a c i l i t y w a s t h e same as t h a t described i n d e t a i l i n reference 2 except f o r t h e method of mounting t h e t h r e e t e s t blades i n t h e c e n t r a l region of t h e cascade. I n order t o overcome t h e cooling- a i r leakage t h a t w a s encountered i n t h e apparatus of reference 2 and thus eliminate t h e necessity of leakage c a l i b r a t i o n t e s t s , t h e coolant supply t o each of t h e t h r e e t e s t blades investigated herein w a s provided by employing separate coolant supply tubes. These tubes were welded d i r e c t l y t o t h e bases of t h e individual t e s t blades and were connected t o a cooling- a i r plenum, as shown i n figure 3. The supply tube from t h i s chamber w a s attached t o t h e pipe from t h e cooling-air regulating and metering A i r from a 125-pound-per-square-inch source was f i l t e r e d equipment.
through a 25-micron f i l t e r and was reduced i n pressure t o t h e metering rotameters.
INSTRUMENTATION Blades Eighteen thermocouples, s i x i n each blade, were i n s t a l l e d i n t h e t h r e e t e s t blades a t t h e locations shown i n f i g u r e 2. The spanwise and t i p . The t h e root, midspan, locations correspond approximately t o of 36-gage thermocouples made blades were instrumented by cementing ( approximately i n shallow grooves (0.005-in. diam.) Chromel-Alumel w i r e electromotive surface of t h e blade. The output 0.008 i n . deep) i n t h e c a l i b r a t e d i n on a potentiometer f o r c e of these thermocouples w a s read degrees Fahrenheit.
CONFIDENTIAL CONFIDENTIAL 5 Cascade The instrumentation of t h e cascade w a s unchanged from t h a t described i n reference 2 with t h e exception of t h e instrumentation within t h e cooling-air supply chamber. The temperature and pressure of t h e blade- i n l e t cooling air were measured by probes i n s e r t e d within t h e tank t o a depth o f approximately 1/2 inch, opposite t h e entrance of t h e t h r e e tubes supplying air t o t h e cooled blades.
EXPERIMENTAL PROCEDURE The cooling c h a r a c t e r i s t i c s of t h e blades were obtained by measuring t h e temperatures of t h e blades over a range of cooling airflows, gas d e n s i t i e s , and gas temperatures. The gas conditions were set, and blade temperatures were measured a t i n t e r v a l s of varying cooling a i r f l o w from zero t o choked flow i n t h e blade passages, with s u i t a b l e time allowed f o r temperature s t a b i l i z a t i o n a t each point. The blade temperatures measured with zero cooling a i r f l o w were used as t h e e f f e c t i v e gas t e m - i n each s e r i e s . The gas-flow conditions were changed, p e r a t ure Tg, e and t h e procedure was repeated. The gas flows per u n i t flow a r e a ahead of t h e three t e s t blades ranged from 30 t o 52 pounds per second per square foot. This range of flows corrected t o sea-level conditions varied from 34 t o 36 pounds per second p e r square f o o t . The r a t i o of cooling-air t o combustion-gas flow ranged from 0 t o about 0.025. The t e s t s w e r e conducted a t t h r e e gas-temperature l e v e l s t 1060°, 1360°, and 1660' R.
CALCULATION PROCEDURE A s i n reference 2, t h e data of t h i s i n v e s t i g a t i o n a r e not presented on a n absolute basis, b u t r a t h e r are c o r r e l a t e d with dimensionless parameters t o permit more general use. The range of coolant Reynolds number a t t h e b b d e i n l e t varied from 2100 t o 20,000 with t h e majority The c o r r e l a t i o n equa- of t h e data i n o r near t h e turbulent-flow regime.
t i o n f o r turbulent flow derived i n reference 2, w a s used t o c o r r e l a t e t h e data of t h i s r e p o r t .
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CONFIDENTIAL RESULTS AND DISCUSSION Before heat-transfer investigation of t h e blades was begun, surveys i of t h e gas-flow conditions (dynamic pressure and airstream d i r e c t i o n ) upstream of t h e t e s t blades were conducted. These surveys indicated no change from t h e s a t i s f a c t o r y flow conditions obtained during t h e inves- t i g a t i o n conducted i n reference 2 .
The correlated data f o r t h e corrugated-insert blade a r e shown i n f i g u r e 4 f o r t h e root, midspan, and t i p regions of the blade. The data C c p o i n t s represent a c o r r e l a t i o n of t h e average blade metal temperatures C a t each spanwise location f o r a range o f gas temperatures and cooling- a i r flows. The maximum deviations for a value of (p with respect t o t h e mean l i n e s ( s o l i d l i n e s ) drawn through the data points were f 4 , ~11.5, and k13 percent f o r t h e root, midspan, and t i p positions, respectively.
This deviation of (p from t h e mean l i n e corresponds t o a maximum devia- t i o n i n blade temperatures ( a t the blade t i p ) of ~ 2 4 ~ R f o r an average t u r b i n e - i n l e t gas temperature of 1 6 6 0 ' R and a cooling-air temperature of 560' R.
Also shown i n f i g u r e 4 i s a s e r i e s of dash-dot l i n e s t h a t represent t h e c o r r e l a t i o n data f o r t h e average blade metal temperatures at t h e root, midspan, and t i p of the cast-finned blades investigated i n r e f e r - ence 2.
I n order t o d i r e c t l y compare these data with those of t h e a present corrugated i n s e r t blade, recalculation of t h e Z T values of t h e former blade was necessary. Since t h e cooling-air i n l e t a r e a and hy- d r a u l i c diameter were not t h e same f o r t h e two designs, t h e cooling-air Reynolds numbers could not be d i r e c t l y compared. Therefore, the Reynolds numbers f o r t h e cast-finned blade were recalculated with t h e dimensions of t h e corrugated-insert blade so t h a t values of cp could be d i r e c t l y Comparison of the correlation curves f o r t h e corrugated- compared.
i n s e r t blade with those of t h e cast-finned blade show no difference a t t h e t i p and midspan locations.
I n t h e r o o t region, however, t h e (p values for t h e corrugated-insert blade were s i g n i f i c a n t l y higher ( i n d i - c a t i n g lower average metal temperatures1 than f o r t h e cast-finned blade over most of t h e range of ZT. For a Tg,i of 1 6 6 0 ' R, T a , i of 560' R, and a value of Z T equal t o 3.0, t h e average root region temperature of t h e corrugated-insert blade would be about 948' R, while t h e cast- finned blade would be about 1018' R. Thus, f o r these conditions t h e corrugated-insert blade would be about 70' cooler a t the blade base than t h e cast-finned blade. For a zT value of 9.0, and ,i and Ta of 1 6 6 0 ' and 560' R, respectively, t h e corrugated-inserf blade would be only about 1 5 ' cooler than t h e cast-finned blade. The b e t t e r cooling performance of t h e corrugated-insert blade, as compared with that of t h e cast-finned blade i n t h e r o o t region, probably r e s u l t s from t h e additional i n t e r n a l heat-transfer surface area over t h e cast-finned design. Also, t h e thinner suction-surface w a l l of t h e corrugated-insert blade, when compared with the cast-finned blade, would contribute t o a lower metal temperature f o r a given s e t of gas and cooling-air conditions.
CONFIDENTIAL C0NFIDENTIA.L 7 Since, i n f i g u r e 4 , t h e data of each individual spanwise location correlated, a s i n g l e curve of o v e r a l l average (p against ZT could be calculated t o permit a p p l i c a t i o n of t h e experimental cascade data t o engine conditions, as i n reference 2.
Because t h e average blade temperatures at a s p e c i f i c spanwise loca- t i o n correlated very well, as discussed previously, a n attempt w a s a l s o made t o determine whether l o c a l blade metal temperatures would c o r r e l a t e D i n t h e same manner as i n reference 2.
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over 4 A s indicated i n reference 2, c o r r e l a t i o n of l o c a l value of $ a range of gas temperatures w a s obtained when t h e parameter ZT w a s constant. Examination of f i g u r e 4 discloses i n s u f f i c i e n t data points a t any given value of One reason f o r z + t o permit t h e correlation.
t h e lack of data a t a constant value of over a range of temperatures w a s the i m p r a c t i c a b i l i t y of controlling a1 "T t h e variables i n t h e param- eter. If t h e use of t h e data over a small range of ZT (from 5.25 t o 5.75) i s permitted, l o c a l cp data f o r t h r e e gas temperatures a r e a v a i l - able, and a n attempt a t correlationing local cp data can be made.
Figure 5 shows t h e value of cp based on l o c a l blade metal tempera- t u r e s p l o t t e d again& distance from t h e leading edge of t h e blade f o r t h e pressure and suction surfaces over t h e range of parameter zT given previously. Because t h e blade metal temperatures correlated very .) w e l l on both a n average and l o c a l basis, t h e data curves shown i n f i g - ures 4 and 5 can be used t o estimate t h e cooling performance of t h e blades a t operating conditions other than those employed i n t h e s e exper- iments. The d e t a i l s of t h e method f o r so doing are presented i n r e f e r - ence 2 and a r e not repeated here. Reference 2 shows a s p e c i f i c example of t h e use of t h e d a t a t o estimate t h e coolant-flow requirements and l o c a l blade metal temperature f o r an air-cooled turboprop engine operat- ing a t a t u r b i n e - i n l e t temperature of 2460' R, f l i g h t speed of 300 knots, and a n a l t i t u d e of 30,000 f e e t . Because t h e cooling performance of t h e corrugated-insert blade i s so s i m i l a r t o that of t h e cast-finned blade i n reference 2, t h e a i r f l o w requirements and temperature d i s t r i b u t i o n s reported i n t h e reference would a l s o be applicable t o t h e corrugated- i n s e r t design. Actually, t h e corrugated-insert blade would require s l i g h t l y less cooling air, would cool b e t t e r on t h e suction-surface p a r t t h e of t h e blade, and would cool somewhat b e t t e r i n t h e r o o t region of blade. I n a n engine application, f a c t o r s such as f a b r i c a t i o n procedures r a t h e r than t h e cooling and techniques required i n making t h e blades, performance, would probably d i c t a t e which of t h e two blade cooling con- f i g u r a t i o n s would be more desirable.
CONFIDENTIAL 8 CONFIDENTIAL * CONCLUDING RENARKS The cooled turboprop blade designs ( t h e corrugated-insert design reported here and t h e internally-finned design previously reported) a r e t h e r e s u l t of a n a l y t i c a l investigation of a number of possible designs.
Selection w a s based on a t t a i n i n g reasonably high cooling performance with designs that appear t o have p o t e n t i a l from a f a b r i c a t i o n standpoint.
A l l of t h e blades reported here and i n reference 2 were made a t the Lewis Research Center and a r e e s s e n t i a l l y "handmade" products. t ?
It i s u believed that the cooling performance of t h e corrugated-insert blade and c, t h e cast-finned blade a r e about as high as can be a t t a i n e d i n forced- u convection air-cooled turbine blades as small as those considered here and i n reference 2. Additional discussion of t h e e f f e c t of blade s i z e on t h e cooling performance of small blades can be found i n reference 3.
SUMMARY OF RFSULTS The r e s u l t s of an investigation i n a s t a t i c cascade t o determine t h e cooling effectiveness of a small air-cooled, corrugated-insert t u r - bine blade s u i t a b l e f o r u s e i n a turboprop engine a r e as follows: 1. The cooling effectiveness of t h e corrugated-insert blade was found t o be almost i d e n t i c a l with t h a t of a cast-finned blade previously c reported. A t t h e c r i t i c a l midspan section t h e r e w a s no p r a c t i c a l d i f - ference, while i n t h e r o o t region t h e a d d i t i o n a l metal f i n a r e a of the corrugated-insert blade and a thinner blade wall section r e s u l t e d i n b e t t e r cooling (about 1 8 ' t o 65' R) than with t h e cast-finned blade.
2. A nondimensional method of c o r r e l a t i n g t h e experimental heat- t r a n s f e r data of t h e blades, which had been developed f o r a preceding blade design (previously reported), w a s u t i l i z e d successfully f o r t h e data of t h i s investigation.
L e w i s Research Center National Aeronautics and Space Administration Cleveland, Ohio, September 4, 1959 REFERENCES 1. Esgar, Jack B I : Turbine Cooling. Trans. ASME, Jour. Eng. f o r Power, sec. A, vol. 81, no. 3, J u l y 1959, pp. 226-233.
r 2. Stepka, Francis S., Richards, Hadley T., and Hickel, Robert 0.1 Cas- cade Investigation of Cooling Characteristics of a Cast-Finned A i r - Cooled Turbine Blade for Use i n a Turboprop Xngine. NACA RM b E57D19, 1957.
CONFIDENTIAL 3. Esgar, Jack B., Schum, Eugene F., and Curren, Arthur N . !
Effect of Chord Size on Weight and Cooling C h a r a c t e r i s t i c s of Air-Cooled Turbine Blades. NACA Rep. 1354, 1958. (Supersedes NACA T N 3923.)
c CONFIDENTIAL • • • • . • · • • • • • • • • • • ~ • • • • • ... • • • • 0 • • ••• ••• • •• · • • • ••• • • • • • • • ••••• • • • • • • ••••• • ...
• ... • ••••• • • • 8 • • ••• •••• • • · ••••• ••••• •• • • t-' o (") H ~ t-i i § .
C- 49594 cascade blade S£S-3: .
Completed blade (d ) completed and parts pressure .
blade, Shell, surface ~ test ( c ) cascade .
metal Shell cast corrugat~ insert insert Sheet as turboprop Base, ~ insert - (b) center iSland Integral Corrugated j _ 4..'- 1 .
suction .
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COrnIDENTIAL ( a ) Tip.
( b ) Midspan.
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Figure 2. - Cross-sectional view of air-cooled corrugated-
i n s e r t turbine blade f o r turboprop engine, showing location of thermocouples.
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• ••• • •• •• • • • • •• • • • • • • • • • • • •••• • • • • • • • •• •••• • •• • ••• • •• • •• 0 • • • • •• • • • • •• 12 CONFIDENTIAL Thermocouple leads Cooling - air p le n um Temperature and pressure probe Figure 3. - Corrugated - insert turboprop bl ades showing cooling - air supply system to the t h ree instrumented bl ades.
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r e f . 2 f o r cast-finned . 5 . 4 .
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C o r r e l a t i o n parameter, zT = a .
(Re,, ) O - Ta, i Figure 4. - C o r r e l a t i o n of corrugated-insert blade meJal temperatures a t p a r t i c u l a r span l o c a t i o n s .
T ~ , i, 5 6 0 ' t o 7 9 8 O R; Reg,b, 0.85 t o 3 . 8 ~ 1 0 5 ; Re,,i, 0 . 2 1 t o 1.99~10~.
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c u r - r - c o r - 0 cooco 0 00 I NASA - Langley Field, Va. E-535 C ONF IDENT IAL