The severe thermal environments under which hypersonic aircraft such as the National Aerospace Plane (NASP) will operate require cooling of the engine walls, especially in the combustor. A preliminary assessment is made of some candidate materials based on structural analyses for a number of convective cooling configurations. Three materials were studied: graphite/copper and tungsten/copper composite alloys with 50 percent fiber volume fractions and a wrought cobalt-base superalloy, Haynes 188. Anisotropic mechanical and thermal properties for the composites were obtained from a computer code, ICAN, which determines the composite material properties from the individual properties of the fiber and matrix materials. The structural analyses were performed by using the MARC nonlinear finite element code. Heat transfer analyses were conducted to calculate the metal temperature distributions

Kaufman, Albert

English

NASA Technical Reports Server

N88-22405
STRUCTURAL ANALYSES OF ENGINE WALL COOLING
CONCEPTS AND MATERIALS
Albert Kaufman*
Sverdrup Technology, Inc.
(Lewis Research Center Group)
NASA Lewis Research Center
ABSTRACT
The severe thermal environments under which hypersonic aircraft such as the
National AeroSpace Plane (NASP) will operate require cooling of the engine
walls, especially in the combustor. The NASA Lewis Research Center is under-
taking an extensive in-house effort to investigate composite materials and
cooling concepts for their applicability to NASP engine walls. In this study
a preliminary assessment is made of some candidate materials based on struc-
tural analyses for a number of convective cooling configurations. Three
materials are currently under consideration; graphite/copper (Gr/Cu) and
tungsten/copper (W/Cu) composite alloys with 50 percent fiber volume fractions
and a wrought cobalt-base superalloy, Haynes 188. Anisotropic mechanical and
thermal properties for the composites were obtained from a computer code devel-
oped at NASA Lewis. The code, called ICAN, determines the composite material
properties from the individual properties of the fiber and matrix materials.
TN_ R_vneR 188 material properties were obtained from an International Nickel
Company brochure. The structural analyses were performed by u_i,s Lhe ["_RC
nonlinear finite-element code. The analyses were based on steady-state opera-
tion at an inlet ramp condition. Heat transfer analyses were conducted to
calculate the metal temperature distributions. Elastic- plastic analyses were
performed for the Haynes 188 and W/Cu materials. The Gr/Cu composite was
treated as an elastic material because of the lack of adequate material prop-
erty information. The analyses demonstrate the applicability of nonlinear
structural analysis technology to complex real-world problems.
*Work performed on-site at the Lewis Research Center for the Structural
Mechanics Branch; subcontract number, 5215-80; technical monitor, Robert L.
Thompson.
2-265
https://ntrs.nasa.gov/search.jsp?R=19880013021 2020-03-20T06:32:37+00:00Z
ANALYTICALINPUTCONDITIONS
A preliminary assessment is madeof somecandidate materials based on heat
transfer and structural analyses for several cooling configurations. Three
materials were considered: Gr/C and W/Cucomposite alloys with 50 percent
fiber volume fractions and a wrought cobalt-base superalloy, Haynes 188. Ani-
sotropic mechanical and thermal properties for the composites were obtained
from the ICANcomputer code developed at NASALewis. The heat transfer analy-
ses were based on the gas and coolant temperatures and pressures shownbelow.
The heat flux was 500 Btu/ft 2 sec, which would be characteristic of the engine
inlet region.
CONFIGURATIONS
• RECTANGULAR PASSAGES
• CURVED (D-SHAPED) PASSAGES
• CIRCULAR PASSAGES
MATERIALS
• HAYNES 188
• Gr/Cu
. W/Cu
CONDITIONS
• GAS TEMPERATURE, 4000 °F; GAS PRESSURE, 50 psi
COOLANT TEMPERATURE, 100 °F; COOLANT PRESSURE, 1200 psi
° HEAT FLUX, 500 Btulft2 sec
CD-88-3"_ 773
2-266
FINITE-ELEMENTMODELS
Finite-element models were created for cooling configurations involving rectan-
gular, curved (D-shaped), and circular passages. The configurations had wall
and fin thicknesses of 0.015 in. Passagespacings were 0.150 in. for the rec-
tangular and curved geometries and 0.075 in. for the circular geometry. The
models were constructed of II0 twenty-node, three-dimensional elements. The
three-dimensional elements were needed to impose the directional properties of
the composite materials. Five passageswere modeled for each configuration in
order to avoid temperature and stress distortions from the boundary conditions
applied at the end surfaces. The shape of the structures was maintained by
applying the boundary conditions so that all nodes on the end surfaces were
tied together and had the samedisplacements perpendicular to the initial posi-
tion of these faces. Only the central passageswere considered in evaluating
the analytical results. Elastic-plastic analyses were performed for the
Haynes188 and W/Cumaterials by using the MARCnonlinear finite-element
code. Only elastic analyses were performed for the Gr/Cu material because of
the lack of inelastic stress-strain properties.
RECTANGULARPASSAGES
CURVEDPASSAGES
I
CIRCULARPASSAGES
i I
CD-88-31774
2-267
VERIFICATION OF STRUCTURAL ANALYSIS ACCURACY
So that the accuracy of the structural analyses could be verified with finite-
element models, an isolated circular passage was analyzed as a flat plate with
a central hole. Internal pressure loading was applied around the rim of the
hole. Calculated stresses at the horizontal and vertical diametral points were
compared with photoelastically determined elastic stress concentration factors
from Peterson (1974). Agreement between the analytical and experimental
results was within 4 percent.
STRESS
CONCENTRATION,
Kt=emaxlP
20
16
12
rla
CD-88-31775
2-268
TEMPERATURE DISTRIBUTION IN HAYNES 188 CIRCULAR CONFIGURATION
The temperature distribution in a Haynes 188 circular configuration is shown.
The maximum metal temperature was above i000 °F, in contrast to about 900 and
1300 °F for the rectangular and curved configurations, respectively.
Y
t
L-- x
Z
TEMP.
OF
1095
1037
979
921
864
806
748
690
632
574
$I_ ,..:..;..,
458_
400 !
342 --
284 _B
226
CD-86-3" "'E
2-269
TEMPERATUREDISTRIBUTIONIN W/CuCIRCULARCONFIGURATION
The temperature distribution for a W/Cucircular configuration is shown. The
maximummetal temperatures were about 600 °F. The metal temperatures in the
composite material structures were lower than those for Haynes 188 structures
because their thermal conductivities were muchhigher. The maximumtempera-
tures for the composite structures were not significantly affected by the pas-
sage geometry. This figure illustrates the temperature nonuniformity due to
the end boundary conditions and shows why the analyses had to be conducted for
a number of passages.
Y
Z
TEMP.,
OF
566
554
542
530
519
507
495
483
471
459
448
436
424
412
4O0
389
CD-85-3" 7_7
2-270
PEAK STRAINS IN COOLING CONFIGURATIONS
The bar graph shows the peak tensile and compressive strains for each material
for the three passage geometries. The Haynes 188 alloy had the largest
strains because it has the highest temperatures and thermal gradients; the
W/Cu composite had the smallest strains because it has the lowest temperatures
and thermal gradients. Of the three cooling configurations the curved geome-
try was the worst and the circular geometry the best in terms of the maximum
strain levels.
STRAIN
IN X
DIRECTION,
in./in.
.012 --
.008 --
.004
0
- .004
-.008 --
- .012
fll_l
#il_t
II1_1
II1#1
IIIII
IIIJll
l-k
I
/ZA
RECTANGULAR CURVED CIRCULAR
HAYNES188
Gr/Cu
WlCu
CD-88-31778
2-271
INELASTICSTRAINSIN HAYNES188 CURVEDCONFIGURATION
The inelastic strain distributions in the central passage region for the
curved configuration are shown for the Haynes 188 alloy. Compressive plastic
strains of almost i percent occurred at the hot upper surface. Smaller ten-
sile plastic strains are evident adjacent to the passage corners and on the
cold bottom surface. The creep strain distribution after 2500 seconds of
dwell time is also shown. An equivalent creep strain (which is always posi-
tive) of 0.75 percent was reached at the hot upper surface.
STRAIN,
in./in.
1 = -0.876E-02
2 = - 0.767E-02
3 - - 0.639E-02
4 = -0.621E-02
5 = - 0.404E-02
6 = - 0.286E-02
7 = -0.168E-02
8 = - 0.602E-03
9 = 0.676E-03
10 = 0.186E-02
I • I I
PLASTICSTRAIN
STRAIN,
in.lin.
1 = -0.343E-03
2 = 0.629E-03
3 = 0.140E-02
4 = 0.227E-02
5 = 0.314E-02
6 = 0.402E-02
7 = 0.489E-02
8 = 0.676E-02
9 = 0.663E-02
10 = 0.760E-02
¥--4 '_-- -_
EQUIVALENTCREEPSTRAIN
12500 SEC)
CD-88-3177g
o 070
FINITE-ELEMENT MODEL OF SIMULATED FILM-C00LING CONFIGURATION
Film cooling was studied by modeling cooling holes in the upper surface of the
rectangular central passage region, as shown in the finite-element model
below. This increased the number of 20-node, three-dimensional elements to
118. The effects of film cooling on the upper surface were simulated by reduc-
ing the gas-side heat transfer coefficient by 10 percent. This decreased the
maximum temperatures by several hundred degrees. The simulated film cooling
reduced the maximum metal temperature in the central passage region from 900 °F
to about 300 °F.
Y
X
CD-B8-31780
2-273
STRAIN DISTRIBUTION IN HAYNES 188 FILM-COOLING CONFIGURATION
The strain distribution is shown for the Haynes 188 film-cooling configura-
tion. High local strains are evident near the end surfaces. In the central
passage region the highest strains occurred adjacent to the passage corners.
There was a significant reduction in the maximum compressive strain at the hot
upper surface, from 0.0050 in the rectangular geometry to 0.0025 in the film-
cooling geometry. Also, the plastic flow previously encountered at the upper
surface was eliminated because of the lower metal temperatures, improved mate-
rial properties, and decreased strain levels.
STRAIN X,
in.lin.
0.00400
.00350
.00300
.00250
.00200
.00150
.OO1OO
.000500
0
-.000500 _ !
-.00100
-,00150
-.00200
-.00250
-.00300
-.00350
CD-88-3,_ 7_-
2-274
STRESS DISTRIBUTION IN W/Cu CONFIGURATION - ALL FIBERS IN Z DIRECTION
The W/Cu structures were initially analyzed for fibers oriented parallel with
the direction of the fins (z direction). This orientation would be required
in the thin-fin region and would be most convenient for the whole structure
from a fabrication standpoint. However, it places the weak transverse proper-
ties in the x direction, where the stresses are the most severe. Small plastic
strains (under 0.i percent) were induced at the hot upper surface.
Y
T
Z
ALL FIBERS IN Z DIRECTION
STRESSX,
psi
50 000.
40 000.
30 000.
20 000.
10 000.
O.
-10 000.
-20 000.
-30 000.
-40 000. _
-50 000.
i
-60 000.
-70 000.
CD-88-3_ 782
C - _ 2-275
STRESSDISTRIBUTIONIN W/CuCONFIGURATION- FIBERSIN X ANDZ DIRECTIONS
The fiber orientation was changed analytically so that the fibers were in the
x direction, transverse to the fins, in the bottom or cold wall. The fibers
at the top wall remained in the z direction. In doing this, essentially two
different materials were being joined because of the significant differences
in material properties between the longitudinal and transverse directions in
the material. These differences are even greater in the Gr/Cu composite. From
a structural analysis standpoint the stress-free temperature is that at which
the structure is cured. The curing temperature of the W/Cu composite was
assumed to be 1800 °F. This assumption resulted in reversing the signs of the
stresses in the walls so that tensile stresses were induced in the hot upper
wall and compressive stresses in the cold bottom wall.
FIBERS IN Z DIRECTION
FIBERS IN X DIRECTION
STRESSX,
psi
60 000.
50 000o
40 000.
3O 000.
20 000.
10 000.
O.
-10 000.
-20 000.
-30 000.
-40 000.
-50 000.
-60 000.
I
CD-88-31783
2-276
STRESSDISTRIBUTIONIN W/CuCONFIGURATION- ALL FIBERSIN X DIRECTION
In this configuration the fibers were oriented in the x direction everywhere
except in the fin region. This gave the structure the strongest properties in
the most severe direction and temperature region. No plastic straining
occurred with this orientation.
Y
Z
-_X
FIBERS IN X DIRECTION
FIBERS IN X DIRECTION
STRESSX,
psi
80 000. t
70 000.
60 000.
50 000.
40 000.
30 000.
20 000.
10 000.
O.
-10 OUU.
-20 000.
-3 000.
-40 000.
-50 000o
-60 000.
-70 000.
CD-88-31784
2-277
EFFECT OF FIBER ORIENTATION ON STRAINS IN W/Cu CONFIGURATION
This bargraph summarizes the effects of fiber orientation on the strain lev-
els. For the Gr/Cu composite the effect of changing the fiber orientation to
the x direction was to reduce the tensile strain and increase the compressive
strain. The W/Cu configuration with both the fin and transverse fiber orienta-
tions exhibited the smallest strains of the three candidate materials.
STRAIN
IN X
DIRECTION,
in./in.
.012 --
.008
.004
0
- .004 --
-.008 --
-.012 --
-.016 --
- .020 --
I
I
I
f///.I/.11
//////J
I
Z-Z Z-X X-X
Gr/Cu
_WlCu
CD-88-31785
2-278
CONCLUSIONS
D
• HIGHEST STRESS COMPONENT WAS IN TRANSVERSE DIRECTION TO FINS
• CIRCULAR PASSAGES GAVE LOWEST AND CURVED PASSAGES HIGHEST STRAINS
• WICu WITH TRANSVERSE FIBERS GAVE LOW TEMPERATURES AND STRAINS
WITHOUT PLASTIC FLOW
• HAYNES 188 WAS ACCEPTABLE WITH CIRCULAR AND FILM-COOLED GEOMETRIES; HIGH
CREEP STRAIN IN CURVED GEOMETRY
CD-88-31786
2-279
REFERENCES
Peterson, R.E., 1974, "Stress Concentration Factors." John Wiley & Sons.
2-280


Structural analyses of engine wall cooling concepts and materials

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