SAMPE Journal - March/April 2024 - 20

FEATURE / SUPERSONIC NOZZLES
m[g/s] AoA[0
6
8
.
]
10
12
14
16
6
8
10
12
14
10
10
10
10
10
pres[hPa]
153.5
177.2
197.5
215.9
234.4
257.9
152.5
174.8
193.4
212.1
229.8
pch[hPa]
2.25
2.94
3.54
4.23
4.91
6.11
2.41
3.73
3.07
4.52
5.30
qw[kW/m2
171.5
156.8
152.0
143.8
109.6
86.3
394.9
415.8
357.3
283.1
321.9
Table 4. Chamber pressure, reservoir pressure, and calorimeter heat flux for semielliptic
nozzle tests.
4. SHOWCASE ACTIVITIES FOR SPACE
MATERIAL CHARACTERIZATION USING THE
SUPERSONIC NOZZLE CONFIGURATION
4.1 Conical Nozzle Tests of Composite
Overwrapped Pressure Vessel (COPV)
This project led by VKI and coordinated by the
European Space Agency was designed to investigate
the demise of COPV during reentry using the
conical nozzle. Those components are made of a
metallic liner wrapped by Carbon Fibre Reinforced
Polymer (CFRP), which often makes them
survive the reentry, and thus, being problematic
for demisability. We produced two distinct test
configurations: a stagnation point and a sideways
configuration (Figure 8). Both configurations
consist of a composite structure comprising a
graphite and titanium liner enveloped in CFRP.
The choice of materials includes graphite for
comparison purposes and grade-2 titanium
strategically positioned in the regions of interest:
the frontal hemisphere for the stagnation point
and the central cylindrical tubing for the sideways
configuration. This mimics the composition of
an actual COPV with a titanium liner plus carbon
fiber wrapping. The thickness of the titanium
liner respects the thickness of the full-scale tank
(i.e., 0.8 mm). The CFRP sub-scale tanks utilized
fibers identical to those employed in the full-scale
version. Each sample has been instrumented with
four type-K thermocouples on the inside of the
liner (inner side of the graphite/ titanium piece,
Figure 8).
Based on computational analysis for the reentry
flight in the different configurations (tumbling,
fixed attitude in each direction), the maximum heat
flux condition was chosen, and the stagnation and
sideways samples were tested at 3.5 MW/m2
and 3.1
MW/m2, respectively (Table 5). The test time was
adjusted such that the total heat load remained
constant. Test time was then increased to reach
the full demise of the wrapping on the graphite
samples (Test 2 and Test 5). For the last runs, the
heat flux was increased to 5.5 MW/m2
(Test 3 and
Test 6). A picture of a COPV test in the Plasmatron
chamber during a test is presented in Figure 9.
One test from each configuration was chosen for
comparison in this article (Test 3 and Test 6). Both
samples had a titanium liner and were subjected to
5.5 MW/m2
heat flux for ≈ 174 sec. Figure 10(a,c) show
pictures of before and after the experiment for the
tested samples. It was apparent that after 174 seconds
of testing, some of the frontal carbon wrapping had
been removed and the white color observed on the
sample was due to the titanium oxidation as it reacts
]
(a) SW-side view
(b) stagnation-top view
Figure 8. Thermocouple placement for both configurations: (a) Sideway configuration (side view), (b) Stagnation
configuration (top view).
20 | SAMPE JOURNAL | MARCH APRIL 2024
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