The primary basis for heat transfer analysis of turbine airfoils is experimental data obtained in linear cascades. A detailed set of heat transfer coefficients was obtained along the midspan of a stator and a rotor in a rotating turbine stage. The data are to be compared to standard analyses of blade boundary layer heat transfer. A detailed set of heat transfer coefficients was obtained along the midspan of a stator located in the wake of a full upstream turbine stage. Two levels of inlet turbulence (1 and 10 percent) were used. The analytical capability will be examined to improve prediction of the experimental data

Blair, M. F.

Dring, R. P.

English

NASA Technical Reports Server

N87-11221
MEASUREMENT OF AIRFOIL HEAT TRANSFER
COEFFICIENTS ON A TURBINE STAGE
Robert P. Dring
Michael F. Blair
United Technologies Research Center
INTRODUCTION
The primary basis for heat transfer analysis of turbine airfoils is
experimental data obtained in linear cascades. These data have been very
valuable in identifying the major heat transfer and fluid flow features of
a turbine airfoil. The question of major interest is how well all of these
data translate to the rotating turbine stage. It is known from the work of
Lokay and Trushin (ref. i) that average heat transfer coefficients on the
rotor may be as much as 40 percent above the values measured on the same
blades non-rotating. Recent work by Dunn and Holt (ref. 2) supports the
conclusion of ref. 1. What is lacking is a set of data from a rotating
system which is of sufficient detail as to make careful local comparisons
between static cascade and rotor blade heat transfer. In addition, data is
needed in a rotating system in which there is sufficient documentation of
the flow field to support the computer analyses being developed today.
Other important questions include the impact of both random and periodic
unsteadiness on both the rotor and stator airfoil heat transfer. The
random unsteadiness arises from stage inlet turbulence and wake generated
turbulence and the periodic unsteadiness arises from blade passing effects.
A final question is the influence, if any, of the first stator row and
first stator inlet turbulence on the heat transfer of the second stator
row after the flow has been passed through the rotor.
OBJECTIVES
The first program objective is to obtain a detailed set of heat
transfer coefficients along the midspan of a stator and a rotor in a
rotating turbine stage (Fig i.) These data are to be such that the rotor
data can be compared directly with data taken in a static cascade. The
data are to be compared to some standard analysis of blade boundary layer
heat transfer which is in use today. In addition to providing this
all-important comparison between rotating and stationary data, this
experiment should provide important insight to the more elaborate full
three-dimensional programs being proposed for future research. A second
program objective is to obtain a detailed set of heat transfer coefficients
along the midspan of a stator located in the wake of a full upstream
turbine stage. Particular focus here is on the relative circumferential
location of the first and second stators. Both program objectives will be
carried out at two levels of inlet turbulence. The low level will be on
the order of 1 percent, and the high level on the order of I0 percent,
which is more typical of combustor exit turbulence intensity. The final
program objective is to improve the analytical capability to predict the
experimental data.
373
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PROGRESS
Heat transfer measurements will be obtained in this study using low
conductivity rigid foam castings of the test airfoils. A uniform heat flux
will be generated on the surface of the foam test airfoils using
electrically heated metal foil strips attached to the model surface. Local
heat transfer coefficients around the airfoils will be determined using
thermocouples to measure the temperature difference between the heated
metal skin and the free stream.
Photographs of the First Stage Rotor Model at various steps of
fabrication are presented in Fig. 2. The first stage of the fabrication
process consisted of developing a metal 'baster airfoil". An aluminum
rotor blade, chosen at random from the Large Scale Rotating Rig (LSRR)
rotor, was carefully inspected to determine locations with surface
waviness. These slight deviations from a perfectly "developable" surface
(a surface with no compound curvature) are an inherent characteristic of
the "multiple radial station contour tracing" machining process used to
manufacture the aluminum airfoils. Despite the fact that this surface
waviness only consists of depressions a few thousandths of an inch deep at
their maximum, they do present a problem unique to this method of
instrumentation. The metal foil which will be glued to the exterior
surface of the airfoil is extremely intolerant of surface waviness. Even
miniscule depressions on the airfoil translate to "wrinkles" or "lumps" on
the finished, assembled foil surface. For this reason it was necessary
that any depressions be filled to produce as nearly a "developable" surface
as possible. This filling procedure consisted of a
trial-and-error/inspection iteration towards the finished airfoil. An
airfoil was accepted as a "master" only after a completely wrinkle-free
"test" metal foil could be glued to its entire surface. An inviscid flow
computation of the velocity distribution around the finished "master"
airfoil indicated that the maximum change in local velocity produced by the
surface filling (measured maximum filling thickness) was only 1/4 percent.
A photograph of the completed '_etal master airfoil" is presented in Fig.
2.
The next step in the model fabrication process (not shown in Fig. 2)
consisted of casting a concrete mold of the master airfoil. Special low
shrinkage gypsum cement (USG Hydrocal) was used to produce a smooth airfoil
surface and a precise geometrical reproduction.
A steel skeleton (Fig. 2.) was fabricated for each of the test
airfoils to ensure adequate strength to endure both the aerodynamic and
centrifugal forces of the test environment. The skeleton provided a secure
location to attach the foam airfoil to either the rotor hub or the stator
case. The photograph of the first stage rotor skeleton presented in Fig.
2. shows the attachment "button" for fastening the blade to the hub.
The rotor airfoil was cast in rigid foam with the steel skeleton
mounted in the concrete mold. A special fixture ensures that the mounting
button on the skeleton was precisely located at the same position relative
to the concrete mold as was the botton on the original '_etal master
374
airfoil". Photographs of the suction and pressure surfaces of the cast
foam rotor blade are shown in Fig. 2. For this particular model the
suction surface was instrumented and the pressure surface was the
"backside" through which the instrumentation was routed. The suction
surface view shows the pattern of holes to be used for installation of
themocouples. The holes in the suction surface were evenly spaced at one
inch increments at the midspan location for the demonstration test. The
pressure surface view shows the trenches cut into that surface for routing
of thermocouple leads, the copper buss bars for connecting to the foil skin
and the electric power leads. The copper buss bars ensure that the voltage
along each end of the foil strip is uniform, producing a uniform current
over the entire foil surface.
The rate of heat transfer varies strongly with location near the
leading edge of an airfoil. Measurement of these extreme gradients in heat
transfer requires a dense grid of thermocouples in this region. In an
attempt to obtain accurate measurements in the leading edge region for the
present test airfoils, a new high density thermocouple installation
technique has been assessed. Shown in Fig. 3. is a photograph of the
leading edge array installed in this particular rotor model. The
photograph shows the backside of the leading edge region of the foil before
it was installed on the airfoil. Also shown are a specially fabricated
template for accurately locating thermcouple beads and a thin "transfer
template" which is shown attached directly to the backside of the foil.
This "transfer template" was removed following the completion of the
thermocouple installation. Shown in the photograph are 20 thermocouples
located at 0.050 in. apart within an estimated accuracy of Z 0.005 in.
The next photograph of Fig. 3. shows the rotor model with the heater
foil installed on the suction surface only. In this photograph the
thermocouples have been welded to the backside of the heater foil and
routed through the trenches to the support botton. The third photograph of
Fig. 3. shows the model with the foil attached to the pressure surface and
connected to the buss bars. At this stage the instrumentation cavity was
refilled with urethane foam to conform to the original pressure surface
contour. The final photograph of Fig. 3. shows the completed test model
coated with flat black paint. This paint coating ensures a uniform, known
emissivity so that a slight (%3 percent) but accurate radiation correction
can be incorporated into the data reduction routine.
A demonstation of the rotor heat transfer measurement technique has
been successfully carried out. This test showed: (I) that the instrumented
Urethane foam heat transfer models could survive the centrifugal loading in
the rotating frame of reference, (2) that the instrumenation within the
heat transfer model, and specifically the dense array of thermocouples
around the leading edge, could survive the centrifugal loading, and finally
(3) that the slip-ring unit provides a reliable and effectively noise-free
method of acquiring thermocouple data in the rotating frame of reference.
The actual test airfoils (first stator, rotor, and second stator) each have
typically 95 thermocouple sites with 60 at midspan and 20 concentrated near
the leading edge of each airfoil. The instrumentation diagram for the
first stage rotor is shown in Figure 4 as an example.
375
••
REFERENCES
Lokay, V.I., and Trushin, V.A.: Heat Transfer from the Gas and
Flow-Passage Elements of a Rotating Gas Turbine. Heat Transfer -
Soviet Research, Vol. 2., No. 4, July 1970•
Dunn, M.G., and Holt, J.L.: The Turbine Stage Heat Flux Measurements.
Paper No. 82-1289, AIAA/ASME 18th Joint Propulsion Conference, 21-23,
June 1982, Cleveland, Ohio.
OBJECTIVES
• Turbine first stator and rotor
heat transfer data
• Rotor-stator interaction (AX)
• Free stream turbulence
• Comparison with cascade data
• Second stator heat transfer data
• Stator-stator interaction (ACirc}
• Quasi-steady and/or unsteady
boundary layer analysis
376
TURBINE STAGE AT 15% AXIAL GAP
Stator
Rotation
1
Rotor
FIG. 1
377
STAGES 0 F 
; I  I ,  ' I l l  : i i l l  
c m 1  2 3 4 5 ' 6 ' :  8 Q 1 0  
METAL MASTER AIRFOIL 
SUCTION SURFACE OF CAST AIRFOIL 
i l ~ ' i l l , l , , l l l l i i , : l '  
c m 1  2 3 4 5 6 7 8 Q i O  
STEEL SKELETON 
PRESSURE SURFACE OF CAST AIRFOIL 
FIG .2 
378 
84-2-25-2 
ORIGINAL PAGE IS 
OF POQR QUK'lTY 
STAGES OF FABRICATION FOR THE FIRST STAGE ROTOR 
* .^ I  , 0 
LEADING EDGE THERMOCOUPLE GRID AIRFOIL WITH FOIL PARTIALLY INSTALLED 
AIRFOIL WITH INSTRUMENTATION CAVITY CLOSED COMPLETED TEST AIRFOIL 
FIG. 3 
379 
84-2-25-1 
ORIGINAL PAGE IS
OF POOR QUALITY
INSTRUMENTATION DIAGRAM FOR THE FIRST STAGE ROTOR
u_
t--
t--
.m
I
>-
B x = 6341 in. TOTAL ARC LENGTH = 18.753 in.
°I. I I l T I
28 2 26
32 * 25
5_ __ _*
37 16
4 _5
14
3 - 72 73 13
2 - 77* 81 8*
4
9191 2\\
o -l l I I I I 92,_-_
0 1 2 3 4 5 6
X -- inches
NOTE -- ORIGIN OF ARC LENGTH (S)IS THE AXIAL TRAILING EDGE
(MAXIMUM X), S INCREASES MOVING COUNTERCLOCKWISE
SUCTION SURFACE AIRFOIL TCs 1-58
PRESSURE SURFACE AIRFOIL TCs 38-93
T C # XlB x S/B_
1 0 975 0 069
2 0945 0 148
3 0 912 0227
4 0 878 0 306
8* 0845 0385
12 0 611 0 463
13 0773 0 542
14 0 735 0 621
15 0692 0 700
16 0 643 0 779
20* 0588 0858
24 0 525 0 936
25 0456 1 015
26 0382 1 094
27 0303 1 173
28 0.226 1 252
32* 0155 1 331
3_ 00_5 1 410
37 0044 1 488
38 0.003 1 567
T C # XJ8 x S/B
39 0001 1 575
40 0 00G 1 583
41 0 000 1 591
42 0 002 1 599
43 0 0(04 1 607
4.4 0 007 1 615
45 0 012 1 622
46 0 017 1 630
47 0 023 1 638
48 0 030 1 646
49 0 037 1 654
50 0 044 1 662
51 0 052 1 670
52 0 061 1 678
53 0068 1 686
54 0 076 1 693
65 0 083 1 701
56 0 O90 1 7O9
57 00_ I 717
58 0 103 1 725
3" C # XJBx S/B_
59 0 139 ! 764
60 0 172 1804
61 0211 1 843
62 0 251 1 8_3
63 0 290 1 922
67* 0 371 2000
71 0 445 2 060
72 0 513 2 159
73 0 574 2 237
77* 0 629 2 316
61 0 680 2 395
82 0 730 2 47,d
83 0 774 2 553
67" 0 820 2 632
91 0 8_8 2 711
92 0 899 2 789
93 0940 211(_
* AT THESE AXIAL STATIONS TCs LOCATED
AT 50% SPAN AND _-8.3, 16.6AND25%
AWAY FROM MIDSPAN
FIG. 4
38O


Measurement of airfoil heat transfer coefficients on a turbine stage

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