Hopho, Russell N

Purser, Paul E

English

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NACA 
RESEARCH MEMORANDUM 
EXPLORA TORY MATERIALS AND lVIISSILE - NOSE -SHAPE 
TESTS IN A 4,0000 F SUPERSONIC AIR JET 
By Paul E . Pur ser and Russell N. Hopko 
Langley Aeronautical Laboratory 
Langley Field, Va. 
NATIONAL ADVISORY COMMITTEE 
FOR AERONAUTICS 
WASHINGTON 
1959 
https://ntrs.nasa.gov/search.jsp?R=19930089474 2020-06-17T05:51:33+00:00Z

c NACA RM L56J09 
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 
RESEARCH MEMORANDUM 
EXPLORATORY MATERIALS AND MISSILE-NOSE-SHAPE 
TESTS IN A 4,0000 F SUPERSONIC AIR JET 
By Paul E. Purser and Russell N. Hopko 
STh1MARY 
Some exploratory materials and nose-shape tests have been made in 
a small supersonic air jet having a stagnation temperature of approxi-
mately 4,0000 F at the Langley Aeronautical Laboratory. The materials 
considered included graphite, copper, carbon steel, and stainless steel; 
the nose shapes included 900 total-angle cones, hemispherical-face cyl-
inders, and flat-face cylinders. 
The tests indicated that graphite holds more promise as a heat-sink 
material than it had previously been considered to have. The tests also 
indicated that flat-face cylinders appear to be subject to approximately 
one-half the aerodynamic heat input as are hemispherical-face cylinders. 
INTRODUCTION 
Early analyses such as reference 1 indicated that one solution to 
the problem of survival of a long-range ballistic missile during atmos-
pheric entry lay in using high-drag shapes and thick skins which would 
absorb the extreme aerodynamic heat input. Since the publication of 
reference 1, the National Advisory Committee for Aeronautics has expended 
considerable effort, both analytical and experimental, in an attempt to 
determine the best external shape for the high-drag nose and the best 
material for the thick heat-sink nose skin and in the development of 
research equipment with which to attack these two problems. 
In the course of this general program, the Langley Laboratory has 
designed and built, on a laboratory scale, a ceramic pebble-bed heat 
exchanger which supplies air at stagnation temperatures up to slightly 
over 4,0000 F to a small Mach number 2 nozzle. Some recent exploratory 
materials and nose-shape tests in this hot air jet have provided some 
qualitative data considered to be of sufficient interest to warrant 
immediate publication. 
2 NACA RM L56J09 
DESCRI PTI ON OF 4,0000 F AIR JET 
The l aboratory- scale ceramic heat exchanger consists of a vertically 
mounted steel shell 2 feet in diameter and 11 feet high . The shell is 
lined with zirconium- oxide refractory blocks . A core of zirconium- oxide 
pebbles approximately 3/ 8 inch in diameter forms a bed 6 feet in depth 
and 8 inches in diameter . A water - cooled, 3/ 4- inch- diameter , supersonic 
nozzle is mounted at the top . A piston- actuated model-support system is 
mounted above the heat exchanger . This system effects a rapid entry of 
the model into the test jet . Figure 1 is a photograph of the ceramic 
heat exchanger and its allied equipment . 
Fuel oil is burned with air and oxygen to give the desired flame 
temperature . The hot combustion products are forced down through the 
bed during the pebble - heating cycle . During the "blowdown" cycle, air 
flows through the pebble bed in a path the reverSe of the heating cycle 
and exits through the nozzle . The stagnation temperature of the air 
equals the pebble temperature at the top of the bed, and during a blow-
down the temperature of the bed drops approximately 100 to 150 F per 
second depending on the thoroughness with which the bed is heated . 
The maximum bed temperature to which the heat exchanger may be 
utilized is limited by softening and "slumping" of the pebbles . The 
present equipment, therefore, can provide air stagnation temperatures up 
to slightly over 4,0000 F which corresponds to sea- level flight at Mach 
numbers up to about 7. The air for the jet is supplied by the 100-pound-
per - square - inch service system which limits the Mach number to 2 when a 
free jet is used at atmospheric exit pressure ; the jet velocity, however, 
is approximately 5,200 feet per second when the stagnation temperature 
is 4,0000 F . The Reynolds number based on stream conditions behind a 
normal shock is about 2 million per foot . 
RESULTS AND DISCUSSION 
Materials Tests 
Background.- Many investigators have considered the use of graphite 
as a possible heat - sink material, but nearly all of them dismissed the 
use of graphite because of fears about its oxidation characteristics . 
A recent investigation conducted by Maxime A. Faget at the Langley 
Laboratory, however , indicates that the use of graphite holds considerable 
promise for the following reasons : There must be a balance between the 
heat inputs or sources (aerodynanic heating and oxidation) and the heat 
outputs or sinks (heat capacity, radiation, and, for graphite, the heat 
of sublimation) . For many materials the rate of heat released by oxida-
tion is of the same order of magnitude as the rate of heat absorbed by 
the sublimation or fUSion ; whereas, for graphite the amount of heat 
NACA RM L56J09 3 
released by oxidation may be far smaller than the amount absorbed by 
sublimation so that the favorable effects of sublimation should outweigh 
the unfavorable oxidation effects . Also, because of its refractory nature, 
graphite may be allowed to reach higher temperatures which will decrease 
the aerodynamic heat input and increase both the radiative heat output 
and the usable heat capacity of the material. 
Test results. - In order to obtain a better understanding of this 
problem, models 1 to 3 (see fig. 2) were tested in the air jet at a 
stagnation temperature of 4,0000 F. The models were 900 total- angle 
cones made of AGR graphite, 347 stainless steel, and SAE 1018-1025 carbon 
steel. As shown in figure 3, the graphite model suffered far less damage 
in 17 seconds than did the steel models in about 10 seconds . It might 
be noted that the annular depression seen in the steel models in figure 3 
is probably caused by the heating being more intense in the region where 
the nozzle-exit shock intersects the model surface than in other regions 
on the surface . 
Further research .- Attempts are being made to improve graphite by 
impregnating it with compounds that either sublime or break down endo-
thermically . In the first phase of this experiment, a flat - face graphite 
model was impregnated with ammonium chloride, which sublimes at about 
1,0000 F, and tested in the hot air jet at a stagnation temperature of 
4,0000 F. When the model was put into the jet, it began heating and the 
ammonium chloride started to sublime and leave the carbon . Because of 
the heat absorbed by the sublimation process and the action of the sub-
IDned material as a transpired coolant, the impregnated mode l required 
5.9 seconds to reach a visible glow, whereas an identical unprotected 
model glowed in 3 . 7 seconds . Continuation of this type of research with 
other materials will be desirable before the results Can effectively be 
evaluated . 
Nose -Shape Tests 
Background .- For several years experience with heat - transfer measure -
ments on hemispherical noses has indicated r ather low Reynolds numbers 
for transition from laminar to turbulent flow and, thus, from low to high 
heat - transfer rates on the hemispherical surface. Maximum noted local 
values of the transition Reynolds number have been of the order of 1 mil-
lion, and the region from 300 to 500 around the nose from the stagnation 
point appears most susceptible to transition (see, for example, ref. 2) . 
In some unpublished studies by P . R. Hill of the Langley Laboratory, 
causes of early transition were sought which might be fundamentally asso -
ciated with geometry. Among the factors considered were the local Reynolds 
numbers on the body , rotational flow behind the bow shock and disturbances 
in the local flow where it reached transonic speeds in expanding around 
the nose, since the trouble seemed to begin at about the transonic region . 
The idea of the flat face to reduce the local Reynolds numbers, to flatten 
4 NACA RM L56J09 
the bow shock to reduce vorticity, and to reduce the physical extent of 
the transonic region was arrived at by Hill in 1955. It seemed that the 
naturally lower Reynolds number per foot of the flow on the flat face 
would permit a longer physical run of laminar flow; in addition, the more 
rapid growth of area with distance from the stagnation point on the flat 
face as compared with that on the hemisphere would tend to thin and sta-
bilize the laminar layer. The flat face would serve to reduce the extent 
of the transonic flow region also, since the flow would traverse the com-
plete face before reaching the sonic line. Regardless of any stabilizing 
effects on the boundary layer, the flat face would have a lower value of 
the velocity gradient along the surface near the stagnation region than 
would the hemisphere because of its larger radius of curvature, and this 
decrease in velocity gradient would result in lower heat transfer on the 
flat face for either laminar or turbulent boundary layers (see ref. 3). 
A preliminary test in a jet produced by an acid-ammonia rocket motor 
with a flat-face model verified the superiority of this shape . The 
remaining ~uestion was simply that of determining the optimum corner 
shape, and research programs were initiated for this purpose. 
Test results.- In order to obtain a direct qualitative comparison of 
the heat transfer to hemispherical- face and flat-face cylinders, models 4 
to 8 were tested in the 4,0000 F air jet. The temperatures noted in fig-
ure 3(a) are the stagnation temperatures at the time of model entrance 
into the jet. A decrease occurs in stagnation temperature with "blow-
down" time of 100 to 150 F per second as mentioned previously in the 
description of the ceramic heat exchanger . Models 4 to 6 were made of 
stainless steel and consisted of a hemisphere, a flat face with rounded 
corners, and a flat face with sharp corners. The hemisphere model started 
to burn and to melt in about 12 seconds ; the flat -face models were rela-
tively undamaged after about 21 times that period of time in the jet. 
2 
Similar hemisphere and rounded-corner flat-face models were made of cop-
per· (models 7 and 8). For these models the hemisphere started to melt 
in 11.3 seconds and the flat face started in 20.8 seconds. Again the 
flat-face model suffered less damage than the hemisphere after a longer 
time in the jet. Figures 3(a), (c), and (d) show the appearance of 
models 4 to 8 after the test; the relative heat transfer as indicated by 
the relative damage to the models is quite evident. Even after more than 
30 seconds in the jet the corners on model 6 appear to have suffered no 
damage. The comparative times to melt for the copper models indicate 
that the general level of the aerodynamic heating on the flat face is 
about one-half that on the hemisphere; this difference in aerodynamic 
heating is in qualitative agreement with the trends noted in some recent 
theoretical work by Van Driest (ref. 3)· 
General observations.- The lack of damage to the sharp corners of 
model 6 may not continue at angles of attack other than zero. In the 
NACA RM L56J09 5 
preliminary tests of a flat -face cylinder in a 3,9000 F jet produced by 
an acid-ammonia rocket motor, some damage occurred to the sharp corners 
when the support strut loosened and the model assumed an angle of attack 
of about 50. This is one of the particular points of concern which 
requires more research . Unpublished data at the Ames Aeronautical 
Laboratory (following the investigation reported in ref. 4) indicate that 
the flat-face models may have less dynamic stability than hemispherical-
face models and, thus, may be more susceptible to increased heating due 
to angle of attack . 
CONCLUDING REMARKS 
From some exploratory tests in a 4,0000 F supersonic air jet it 
appears that graphite offers considerable promise as a heat-sink material; 
the effectiveness of the graphite can apparently be increased by impregna-
tion with other materials . Similar tests indicate that the aerodynamic 
heat transfer to flat -face cylinders is appreciably less than to 
hemispherical-face cylinders. These results are qualitative in nature 
and continuation. of research to provide more quantitative data on both 
the materials and nose-shape problems is desirable. 
Langley Aeronautical Laboratory, 
National Advisory Committee for Aeronautics, 
Langley Field, Va., September 17, 1956. 
REFERENCES 
1. Allen, H. Julian, and Eggers, A. J., Jr.: A Study of the Motion and 
Aerodynamic Heating of Missiles Entering the Earth's Atmosphere at 
High Supersonic Speeds . NACA RM A53D28, 1953· 
2. Chauvin, Leo T., and Maloney, Joseph P.: Experimental Convective 
Heat Transfer to a 4-Inch and 6-Inch Hemisphere at Mach Numbers 
From 1.62 to 3.04 . NACA RM L53L08a, 1954 . 
3 . Van Driest, E. R.: The Problem of Aerodynamic Heating. Rep. 
No. AL-2303, North American Aviation, Inc., May 1, 1956 . 
4. Allen, H. Julian: Motion of a Ballistic Missile Angularly Misaligned 
With the Flight Path Upon Entering the Atmosphere and Its Effect 
Upon Aerodynamic Heating, Aerodynamic Loads, and Miss Distance. 
NACA RM A56F15, 1956 . 
6 NAeA RM L56Jo9 
L-93426.1 
Figure 1 .- General arrangement of laboratory-s cale ceramic heat exchanger. 
NAeA RM L56J09 
I . T6 Radius 
1------.. -r t 
---+-.6 - I 
I------I-L 
Models 1,2 EX 3 
Model 6 
----++-(Q)++----
-1 + ~]-----(Q)­
~~ +~~ 
Models 5 EX 8 
~ Radius 
--(gc-
Models 4 a 7 
Figure 2. - Sketch of models. (All dimensions are in inches.) 
7 
8 
Original Shape 
Tstag = 4,0000 F 
Material 
Time to melt 
'rime in jet 
Original Shape 
Tstag = 3, 8000 
Material 
Time to melt 
Time in jet 
Original Shape 
Tstag = 3,8000 F 
Material 
Time to melt 
Time in jet 
F 
Materials and Nose-Shape Models 
Model 1 
1018-1025 steel 
3 sec 
7 . 3 sec 
( 0 
Model 4 
347 stainless 
11.6 sec 
13 .6 sec 
C~D 
Model 7 
Copper 
11.3 sec 
13.8 sec 
Model 2 
347 stainless 
8. 5 sec 
11.5 sec 
( 0 
Model 5 
347 stainless 
25.7 sec 
(ran out of film) 
NACA RM L56J09 
Model 3 
AGR graphite 
17 .0 sec 
0 
Model 6 
347 stainless 
33 · 1 sec 
f,--------,O 
Model 8 
Copper 
20 . 8 sec 
21. 5 sec 
(a) Models 1 to 8. L-95279 
Figure 3.- Models tested . 
Model 1 Model 2 Model "Z. 
(b ) Models 1, 2, illld 3. L-95278.1 
Figure 3.- Continued . 
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Figure 3 .- Continued . 
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Exploratory Materials and Missile-nose-shape Tests in a 4,000 Degree F Supersonic Air Jet

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