The objective of this 36-month experimental and analytical program is to develop a heat transfer and pressure drop database, computational fluid dynamic techniques, and correlations for multipass rotating coolant passages with and without flow turbulators. The experimental effort will be focused on the simulation of configurations and conditions expected in the blades of advanced aircraft high pressure turbines so that the effects of Coriolis and buoyancy forces on the coolant side flow can be rationally included in the design of turbine blades

Kopper, F. C.

English

NASA Technical Reports Server

N87-11225
A --
COOLANT PASSAGE HEAT TRANSFER WITH ROTATION
A PROGRESSREPORT
F. C. Kopper
Uni ted Technol ogi es Corporati on
Pratt & Whitney
INTRODUCTION
In current and advanced turbofan engines, increased cycle pressure and tempera-
ture are employed to achieve reduced specific fuel consumption and increased
thrust/weight ratios. As a result, turbine airfoils are subjected to increasingly
higher heat loads which escalate the cooling requirements in order to satisfy life
goals. If high turbine efficiency is to be achieved, cooling flow requirements must
be kept as low as as possible and the anticipated significant effect on the local
metal temperatures (and ultimately on airfoil life) must be evaluated. One way to
keep the quantity of cooling air bounded would be to develop more efficient internal
cooling schemes. Also, development of reliable methods for predicting the thermal
and aerodynamic performance of these schemes would eliminate the necessity of main-
taining a safety margin surplus of cooling air.
To predict local metal temperatures, and ultimately blade life, the turbine de-
signer faces the problem of accurately evaluating the local heat transfer from the
hot gas to the blades and from the blades to the coolant flowing within the internal
passages of the airfoil. Furthermore, for an acceptable design, the heat transfer
must be tailored to reduce gradients while at the same time maintaining an appro-
priate overall level of metal temperature. To accomplish these design goals, the de-
signer must be able to predict local boundary conditions both on the external hot
gas side and the internal coolant side of the airfoil walls. These boundary condi-
tions, which consist of the external gas driving temperature (Tg), external heat
transfer coefficient (hex), internal heat transfer coefficient (hc), and internal
coolant temperature (Tc), are input to computer prediction codes that solve the heat
conduction-structural aspect of the airfoil analysis, subsequently arriving at a
life prediction.
To predict local coolant side heat transfer coefficients and coolant temperature
rise in the cooling passages of current and advanced turbine blades is difficult be-
cause of the complex geometry of the passages and the turbulence-promoting devices
that are used to achieve high levels of airfoil cooling effectiveness. Currently the
design analysis of airfoil internal passage heat transfer and pressure drop relies
on correlations derived for the most part from testing models in a static
(non-rotating) environment. Executing tests with rotation is difficult and costly
and, as a consequence, there are almost no data in the literature that a turbine de-
signer can use with confidence to account for the effects of rotation on the in-
ternal heat transfer coefficients and pressure loss in typical turbine blade de-
signs. Some data are available for smooth tubes over a limited range of relevant pa-
rameters, but application of these data to the complicated flow passages of a tur-
bine airfoil would not be appropriate. As a consequence, adjustment factors are gen-
erally applied to the static test derived correlations to bring them into nominal
correspondence with engine experience. This, in theory, accounts for rotation ef-
fects. Design application of computer codes to predict 3D viscous passage flow has
been limited because the computer codes are in an early stage of evolution. These
codes, however, offer the potential for analyzing arbitrary geometries accounting
for all real-world effects.
'_ 401
https://ntrs.nasa.gov/search.jsp?R=19870001792 2020-03-23T15:05:40+00:00Z
OBJECTIVE
The objective of this 36-month experimental and analytical program is to develop
a heat transfer and pressure drop database, computational fluid dynamic techniques
and correlations for multi-pass rotating coolant passages with and without flow tur-
bulators. The experimental effort will be focused on the simulation of configura-
tions and conditions expected in the blades of advanced aircraft high pressure tur-
bines so that the effects of Coriolis and buoyancy forces on the coolant side flow
can be rationally included in the design of turbine blades.
EXPERIMENTAL MODEL
The coolant passage heat transfer model features a four-pass serpentine arrange-
ment designed to reflect the passages in a gas turbine blade. A photograph of the
partially assembled model is shown in figure I. The radial passages have a square
cross section with 12.7 by 12.7 mm (0.5 by 0.5 in.) dimensions. The model test sec-
tion surfaces consist of copper seoments, 10.7 by 49.3 mm (0.42 by 1.94 in.), which
are heated with thin film electrical heaters. The copper segments are separated from
each other with 1.5 mm (0.060 in.) strips of G-II composite material. The copper
segments are held in place with a frame constructed of G-IO composite material. G-IO
and G-II were chosen because of the low thermal conductivity and high strength.
The heat transfer coefficients on the test section surfaces are obtained from
(a) heat balances on the copper segments and (b) thin film heat flux gages mounted
on the segments. Pressure measurements are obtained along the straight sections and
in the turns. The model instrumentation with 64 heated segments and 16 pressure
measurement locations, is shown in figure 2. The 12 heat flux gages are positioned
to determine local heat transfer gradients in the inlet region and on the walls
downstream of the first two turns. The electrical leads from the heaters, thermo-
couples and heat flux gages are brought through hermetically-sealed connectors and
sliprings to a computer-based data acquisition system. The pneumatic leads are
brought through a leak-tight connector to 16 differential pressure transducers (ZOC
model by Scanivalve) and a reference pressure transducer. The electrical signals
from these pressure transducers are also routed through the sliprings to the data
acqui si ti on system.
DATA REDUCTION
Data acquisition/analysis consists of three general categories: equipment cali-
bration, model heat loss measurement, and heat transfer coefficient calculations.
The equipment calibration follows standard experimental procedures.
Next, model heat losses are determined experimentally. The model is brought up
to a constant wall temperature, steady-state operating condition with no coolant
flow. The energy needed to maintain constant wall temperatures then equals the
energy conducted through the model walls to the environment. These values are
normalized by the temperature difference between the heated copper walls and the
model exterior to account for slight variations in environmental conditions during
testing. This difference represents the driving gradient for conduction losses and
is measured for each test.
402
For each copper element the net energy convected to the fluid is calculated by
subtracting the electrical line losses and conducted heat losses from the total
energy supplied. Bulk fluid temperatures are then calculated based on an energy bal-
ance for each flow path section as follows:
qnet, 4 walls
Tb = _c + Tb.
out p In
where the model inlet bulk temperature is measured. Once bulk fluid temperatures are
determined, heat transfer coefficients are calculated from the equation
h
qnet, wall
A (Tw-T b)
where Tb is the average of the inlet and exit bulk temperatures. Thus heat trans-
fer coefficients are calculated for each individual copper wall element. This quan-
tifies local heat transfer processes and helps isolate local effects of rotation.
RESULTS
To date experimental heat transfer and pressure drop results have been obtained
for stationary conditions (no model rotation). This data will serve as the baseline
for assessing the impact of rotation and buoyancy effects. Figure 3 presents the
heat transfer results obtained for a Reynolds number of 25,000 which is a represen-
tative nominal value for airfoil cooling passages. This figure shows that the heat
transfer downstream of the entrance and turns decays monotonically to approximately
the level (marked by arrows) for fully developed flow in a square duct as estab-
lished by Lowdermilk, et al. (ref. l). The expected periodicity from pass-to-pass is
achieved.
Heat transfer in the turns is approximately 2 to 2 I/2 times that of fully de-
veloped flow levels. There is no heat transfer data in the literature with which to
directly compare the current results. Sahm and Metzger (ref. 2) have found heat
transfer levels around 2 to 2 I/2 times fully developed values for 180-degree square
cornered bends. This is in agreement with the current results. Figure 4 compares
the entry length behavior for the current data with results from the literature. For
the first outward straight passage the four data points (solid circles) include the
guard heater region and the following three straight segments. As the flow enters
the channel from the plenum it passes through a screen and begins boundary layer de-
velopment. Previous measurements just downstream of the screen showed the velocity
profile of the core flow to be similar to fully developed turbulent flow. Because
the near wall shear flow characteristics would be similar to those of developing
flow, it would be expected that the entry length heat transfer behavior be in rea-
sonable agreement with results for combined hydrodynamic and thermal boundary layer
development. This is supported by the comparisons of figure 4 (Boelter et al,
ref. 3, and Aladyev, ref. 4 for pipe flow; Yang and Liao, ref. 5, for square duct
flow). Heat transfer levels downstream of the first bend would be expected to be
lower than for the first passage. This, again, is in agreement with observation. A
creditable correlation for the effects of the bend secondary flows on the downstream
heat transfer is not available.
403
Pressure drop measurementsare shown in figure 5 for a non-heated stationary
test condition at the sameReynolds numberas for the heat transfer results but at a
lower pressure. The results indicate a negligible pressure drop in the straight
sections which is in agreement with predictions and about 0.8 dynamic heads pressure
drop through each turn. This agrees with a value of 0.71 dynamic heads determined
from reference 6 for connected 90-degree square elbows. The slightly higher loss
for the model is believed to result from the diffusions and accelerations the flow
experiences as it negotiates the area variations in the turns.
THREE-DIMENSIONALVISCOUSFLOWCOMPUTATIONS
Computation of heat transfer and pressure drop for the reported experimental
conditions employing a generalized aerothermal fluid dynamic solver for three-
dimensional elliptic, turbulent, steady flows has been started; results are
currently not available.
TESTINGWITHROTATION
Table I defines the planned test points for the first phase (smooth passage
investigation) of this program and reflects the domain of interest for turbine blade
coolant passages.
l •
.
.
.
.
.
REFERENCES
Lowdermilk, W.H.; Weiland, W.F.; and Living..d, I.N.: Measurement of
Heat-Transfer and Friction Coefficients For Flow of Air in Noncircular Ducts at
High Surface Temperatures• NACA Research Memorandum RME53J07, January 25, 1954.
Sahm, M.K.; and Metzger, D.E.: Effects of Turn Geometry Parameters on Heat
Transfer Around Smooth Wall 180° Turns in Rectangular Ducts of Aspect Ratio l.O
to 3.0. Technical Report ERC-R-83029, Mechanical and Aerospace Engineering,
Arizona State University, July 1983.
Boelter, L.M.K.; Young, 0.; and Iversen, H.W.: NACA TN1451, Washington,
July 1948.
Aladyev: I.T. Experimental Determination of Local and Mean Coefficients of Heat
Transfer For Turbulent Flow in Pipes. NACA Technical Memorandum 1356, 1954.
Yang, J.W.; and Liao, N.: An Experimental Study of Turbulent Heat Transfer in
Converging Rectangular Ducts. Paper No. 73-WA/HT-27. ASME Journal of Heat
Transfer. November 1973.
American Society of Heating Refrigeration and Air Conditioning Engineers:
Handbook of Fundamentals, 1972, p. 472.
404
TABLE I
Test Matrix
l
Test
_o.
I
2
3
4
5
6
7
8
9
I0
ii
12
13
Ba s ic
Dimensionless Parameters
AT H
R e Ro
Tin d
25,000 0
12,500 0
50,000 0
25,000 0.210
12,500 0.210
50,000 0.210
25,000 0.420
25,000 0.105
25,000 0.210
25,000 0.210
25,000 0.210
25,000 0.210
25,000 0.210
0.14 --
0.14 --
0.14 --
0.14 52
0.14 52
0.14 52
0.14 52
0.14 52
0.07 52
0.21 52
0.14 34
0.14 52
0.14 52
Secondary Dimension-
less Parameters
AP _H Gr Grmax
f, V Re-_ x 10 -8
0
0
0
1.53
i .53
I .53
3.06
0.76
I .53
1.53
I .00
1.53
1.53
0
0
0
0.32
0.32
0.32
1.28
0.08
0.16
0.48
0.21
0.32
0.32
0
0
0
2 o01
0.50
8.03
8.03
0.50
1.00
3.01
1.31
2.01
2.01
Comments
Nonrotating
Baseline
R e Varied
R o Varied
t AT/T Varied
H/d Varied
1 a Varied
q'
;
Dimensionl ess Parameters
Reynolds number, Re
Rotation number, Ro
Density or temperature
ratio
Radius ratio
Rotational Grashof
number, Gr
OVdH/_ = VdH/V = _dH/(A_)
RdH/V
AP/O, AT/T
H/d H
No 2 Re 2 (AT/T)(H/dH)
405
PHOTOGRAPH OF UNINSTRUMENTED COOLANT PASSAGE HEAT TRANSFER MODEL 
TRAILING EDGE (+n) PLANE TEST SECTIONS REMOVED 
ORIGINAL PAGE IS 
OF POQR QUALI'R 
Figure 1 
84-7-37-2 
406 
INSTRUMENTATION
ORIGINAL PAGE IS
OF POOR QUALITY
PLAN FOR COOLANT PASSAGE HEAT TRANSFER MODEL
TEST SECTION ELEMENT IDENTIFICATION:
SURFACES 1-32 ARE ON SIDE WALLS PERPENDICULAR TO VIEW SHOWN
SURFACES 33-48 ARE ON +9 LEADING PLANE
SURFACES (49)-(64) ARE ON "+.Q TRAILING PLANE
PRESSURE MEASUREMENT LOCATIONS r_ - [_}
NOTE: EACH TEST SECTION SURFACE IS INSTRUMENTED WITH TWOTHERMOCOUPLES
,
HEATED STRAIGHT
TEST SECTIONS
GUARD
HEATER
MEASURED INLET
BULK TEMPERATURE
FIRST TURN
6 7
34
, !
2
/
(50)
// (49
7
_1 THIRD TURN -_D \
(54)
39
(55)
4O
I
!
(56)
41
(57)
42
6 1_,
f
(63)
46
9 14.
(62)
45
lO _sl I
(69
44
11 12
(60)
43
6 /7
_.h I '
(64)
----._
32
/is
!
II
II
3O
o
29
27 28] I. _
SECOND
TURN
Fi gure 2
18
UNHEATED
SECTION
@
MEASURED OUTLET
_,_BULK TEMPERATURE
84--7--37--1
407
20O
tO0
5O
_F
II
-I
Z
2O
ILl
rn
Z
200
_.1
U_l
c,9
c,o
Z
100
5O
2O
G = GUARD
_:0.0 rpm
P = 146.9 psia
r_ = 0.0131 Ib/sec
HEAT TRANSFERRESULTS
Twall =618 °R
Tb' inlet = 538°R
&T/T=0.149
Ref,inle t = 25260
Ro=0.0
Hid h -
LEADING AND TRAILING TEST SECTION SURFACES
I I I I
[--]33-48
49 - 64
88
8
8 8
e 8 8
e 8
O
I I I I I I
0 1 -18
A19-32
O
A
SIDE WALL TEST SECTION SURFACES
I I I
e _ MEASURED HEAT FLUX GAGE DATA
I I O
O O O
A A
A A
0 0 A 0
0
A
0 A
°o #o o
0
0
t
G OUTWARD I FIRSTSTRAIGHT TURN
I I I I I
i NwARoISEOONOI UTWAROSTRAIGHT TURN STRAIGHT _TURN I
Figure 3
Nuf,
408
,,=,
m
m z
_z
Z u.
0 0
LU
U-
2 50
2.25
2.00
1.75
1 50
! .25
1DO
Ref, inlet = 25.260 J YANG & LIAO: SQUARE DUCT
MEASURED DATA Re 23,500
I Nuf _=O0174Ref 0"8 mm BOELTER, YOUNG&IVERSEN:
COMBINED HYDRODYNAMIC
D + THERMAL DEVELOPMENT
Re = 50.000
ALADYEV: CIRCULAR DUCT EXPERIMENT
WITH WATER, Re _, 20,000
• FIRST OU13NARD STRAIGHTI
SEGMENT -- 4 WALL AVERAGE
• INWARD STRAIGHTSEGMENT- 4WALLAVEeAGE
I RANGE OF DATA
o.75 I I I I I I I I
0 2 4 6 8 10 12 14 16
X/D h
Figure 4 Entry Length Heat Transfer Comparison
ORIGINAL PAGE IS
OF POgR QUALITY
¢:,- .E
-2
-3
-4
PRESSURE DROP RESULTS
It = 0 rpm
P = 36 2 ps_a 3T = 0 0=F
r_ = 0 0123 Ib/sec Re = 25045
.& _ & &
&
A
&
&
8 &
i I I
J OUTWARD J FIRST J INWARDG STR IGHT TU N STRAIGHT
G = GUARD
Vin = 39 3 Itlsec
O,n = 4 38 psf = 0 843 ,n H2O
I I I i I
J SECOND J OUTWARD J TH'RD J 'NWARD ITURN STR IGHT TU N STRAIGHT G
Figure 5
409


Coolant passage heat transfer with rotation, a progress report

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