An extensive program to improve the operation of the Ames 16 Inch Shock Tunnel was carried out. This included reduction of driver slosh wave amplitudes and detonation risk by the use of premixed He/O2 gas, longer wait times between the last gas load and driver gas ignition, an improved gas loading sequence, the use of four instead of one ignition wire, and the use of lower ignition wire voltages. Successful operation of the tunnel at pressures of 2000-6000 psi and enthalpies up to 12,000 J/gm was achieved. A new diaphragm breaking technique, self break on the driver combustion pressure rise, was tested and found to produce clean breaks over the full pressure range of the tunnel. Improvements were made to the driver gas loading manifold and a preliminary design was made of a gas mixing system which mixes all three gases on the fly just before injection into the driver. Other improvements as well as tests are discussed

Bogdanoff, David W.

English

NASA Technical Reports Server

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2-/c,
EXPERIMENTAL INVESTIGATION
OF NOZZLE/PLUME AERODYNAMICS
AT HYPERSONIC SPEEDS
Periodic Progress Research Report
for
Cooperative Agreement NCC2-487
for the period
April 1, 1991 - January 31, 1992
Submitted to
National Aeronautics and Space Administration
Ames Research Center
Moffett Field, California 94035
Dr.
Thermosciences Division
Dr. Jim Arnold, Chief
George S. Deiwert, Technical Monitor
Prepared by
ELORET INSTITUTE
1178 Maraschino Drive
Sunnyvale, CA 94087
Phone: (408) 730-8422 and (415) 493-4710
Telefax: (408) 730-1441
Dr. K. Heinemann, President and Grant Administrator
Dr. David W. Bogdanoff, Principal Investigator
16 March, 1992
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rI. SUMMARY
An extensive program to improve the operation of the
Ames 16 Inch Shock Tunnel was carried out. This included re-
duction of driver slosh wave amplitudes and detonation risk
by the use of premixed He/02 gas, longer wait times between
the last gas load and driver gas ignition, an improved gas
loading sequence, the use of four instead of one ignition
wires and the use of lower ignition wire voltages. Success-
ful operation of the tunnel at pressures of 2000-6000 psi
and enthalpies up to 12,000 J/gm was achieved. A new di-
aphragm breaking technique, self break on the driver com-
bustion pressure rise, was tested and found to produce clean
breaks over the full pressure range of the tunnel. Improve-
ments were made to the driver gas loading manifold and a pre-
liminary design was made of a gas mixing system which mixes
all three gases on the fly just before injection into the
driver.
The driver gas free test time was estimated by various
methods to be _5 msec for I0,000 J/gm enthalpies. A spark
1
spectroscopy system to allow more precise measurements of
the test time has been designed and constructed. Fifty-
five instrumentation amplifiers with a gain of iO0 and a 3
db roll-off frequency of 70 kHz have been constructed and
have proven very satisfactory.
Tests have been performed on a wedge model with hydrogen
injection. The model is instrumented with surface pressure
and heat flux gauges, pitot probes, accelerometers and pres-
sure transducers to monitor the hydrogen fuel flow. Also,
holographic interferograms were taken in the spanwise di-
rection. Test were made at driven tube reservoir pressures
of 4000 and 6000 psi and reservoir enthalpies of I0,000 and
12,000 J/gm. Tare runs (air flow, no injection), mixing runs
(nitrogen flow, H2 injection) and combustion runs (air flow,
H2 injection) were made. The data has been only partially
reduced and analyzed to date.
A new test section has been installed and a new rake to
calibrate the test section is being constructed. Calibra-
tion will take take place in 4-55/92. A scramjet combustor
model is being constructed at GASL and combustor tests will
begin in 6/92. D. W. Bogdanoff is the chief designer of the
2
hydrogen fuel injection system for the combustor model.
II. DETAILED DISCUSSION
A. Improvement in operation of facility
In this contract period an extensive program for im-
provement of the operation of the Ames 16 Inch Shock Tunnel
has been carried out. The main goals have been the follow-
ing:
• 0peratlon of the tunnel at higher pressures and enthalpies
• Reductlon of the amplitude of driver slosh waves
• Reductlon of detonation risk
• Reductlon of test gas contamination
• Reductlon in the time required to turn the tunnel around
• Reductlon of damage to components during tunnel operation
The after burn driver slosh waves are believed to be due to
poorly mixed driver gas and the voltage asymmetry of the
wire ignition system. The conditions that produce large
amplitude slosh waves are also very likely to produce det-
onations under unfavorable conditions. Several steps have
been taken to improve the gas mixing. First, premixed He/02
and HB are now used, instead of three separate gases. The
3
composition of the mixed gas is continually monitored dur-
ing the loading process with a thermal conductivity gauge.
This ensures that two of the three gases are properly mixed
and avoids the introduction of heavy, slowly diffusing pure
oxygen into the tube. Earlier in the test program, the wait
time from the loading of the last gas until driver gas igni-
tion was only 15-20 min. Thus, relatively little time was
available for gravitational equilibration and diffusion
mixing of the driver gas in the vertical direction. Longer
wait times, up to 24 hr, were tested and shown to produce
significant reductions in the driver slosh waves. Such long
times are not acceptable for fast tunnel turn around. How-
ever, the wait times were increased to 90-150 min, which
had been shown to still produce significant reduction in
the driver slosh wave amplitudes. These were the maximum
wait times which could be used without adversely effecting
the tunnel turn around time. Also, an improved gas loading
order, H2 followed by the He/02 gas mixture, has been in-
stituted. This also produced significant reduction in the
slosh wave amplitude.
The use of three and four, rather than one ignition
4
wires was tested. The use of more ignition wires reduces
the burn time substantially, thus reducing the time avail-
able for slosh waves and detonations to build up. We now are
using four wires regularly. Reduction in the wire voltage,
while maintaining the wire final temperature has been tested
and found to reduce the slosh wave amplitude. (Such reduc-
tions can be accomplished by increasing the capacitance of
the capacitor bank used to heat the wire(s) or by using thin-
ner wires.) The capacitor bank voltage has been reduced from
18.5 kV to 14.0 kV. Several techniques were tried which were
found not to improve matters or to make things worse. These
were:
• Thermal stirring of driver gas before ignition
• Reversal of wire polarity
• Use of Dannenberg and Stewart's highly diluted gas
mixture.
Accordingly, these techniques were abandoned.
Controlled, successful operation of the tunnel at pres-
sures of 2000-6000 psi was achieved. By operating the tunnel
in the non-tailored, equilibrium interface mode reservoir
enthalpies up to 12,000 J/gm have been achieved. This corre-
5
sponds to flight in the stratosphere at Mach 16.
Breaking of the diaphragm using the lance is limited to
I000 psi operation. High explosive jet cord can be used to
break the diaphragm over the full pressure range of the tun-
nel, but severely contaminates the flow. A variant of the
double diaphragm technique was tested but failed due to det-
onation in the interdiaphragm space followed by detonation
in the driver. Self-break of the diaphragm on driver pres-
sure rise was tested and found to produce clean breaks over
the full pressure range of the tunnel. This is now the di-
aphragm break method being used. The variation of the di-
aphragm break pressure using this technique was found to be
17.57..
The orifices of the early driver gas injection mani-
folds burned out fairly easily. New manifolds with amuch
more robust hole design have been constructed. In addition,
short sections of manifold with screw-in, replacable ori-
fices will be tested in the 1992 tunnel entry. A more robust
manifold restraint system has been constructed and will also
be tested in the 1992 tunnel entry. A preliminary design has
been made of a gas mixing system which mixes all three gases
6
on the fly before injection into the driver. Such a system
would likely produce large reductions in slosh wave ampli-
tude and detonation risk and would eliminate the manifold
and all work and expense associated with it and would elimi-
nate the wait time between loading the driver gas and igni-
tion. This system may be implemented in the fall or winter
of 1992.
B. Driver gas free test time
Test section static pressure measurements suggest a
test time of 8 or 9 millseconds before heavy (greater than
15_) driver gas contamination under "hot" (10,500 J/gin) op-
erating conditions. Correlations from the literature sug-
gest driver gas free test times of 5.5 and 13 milliseconds
for hot and "medium" (4,700 J/gm) operating conditions, re-
spectively. For the "hot" conditions, laser based OH tem-
perature measurements suggest a driver gas free test time of
_5 msec. A spark gap has been constructed so that spectro-
scopic measurements of driver gas helium arrival time can be
made. The 584.7 nm line of helium will most likely be used
for these measurements. It is planned to implement this sys-
tem in the fall or winter of 1992.
?
C. Instrumentation amplifiers
We have developed an in-house amplifier based on single
inexpensive chip. Fifty-five of these amplifiers have been
built. Most of the amplifiers have a gain of I00. The 3 db
roll-off frequency of these amplifiers is 70 kHz. The ampli-
fiers have given excellent service in the wedge model tests
(see Sees. D-F).
D. Wedge model - description
The chord and span of the wedge model are 38 cm and 46
cm, respectively. The model has five 30 ° 0.305 cm diameter
hydrogen injection ports arranged in a spanwise row at about
mid chord. The model can be pitched over a angle of attack
range of 0 ° to 22 °. The model instrumentation includes 12
static pressure transducers (Kulites) and 14 heat trans-
fer ganges (I0 coaxial thermocouples, 2 platinum thin film
gauges and 2 thin skin slug calorimeters) on the model sur-
face. Seventy precent of the surface gauges are downstream
of the injectors. Two pitot probes are located at the model
leading edge and a seven head pitot rake is located at the
trailing edge. Four accelerometers measure accelerations in
S
the x, y and z directions. Laser holographic interferograms
can be taken in the spanwise direction.
The hydrogen fuel system can inject room temperature
hydrogen at plenum pressures up to 2Y arm. Two pressure
transducers measure the hydrogen plenum pressure and the
mass flow is measured using a venturi. The venturi upstream
pressure and pressure difference are measured with pressure
transducers. The venturi was calibrated with a sonic ori-
fice using nitrogen and helium flows.
E. Wedge model - tests run
Three types of tests were run. Tare runs used air as the
driven tube gas with no hydrogen injection. Mixing runs used
nitrogen driven tube gas with hydrogen injection. Finally,
combustion runs used air driven tube gas with hydrogen in-
jection. Eleven tests were made in the series, including one
test with detonation in the driver, leaving ten good test
runs. One preliminary tare run was made at 136 arm driver
pressure and Math 14 driven tube reservoir enthalpy. Seven
runs were made at 272 atm driver pressure. Six of the runs
were at Mach 14 enthalpy, comprising one tare run, two mix-
ing runs and three combustion runs. One of the three combus-
9
tion runs was made at twice the hydrogen mass flow rate of
the other two runs. (We will refer to this run as the "high-
q" run.) The last 272 atm driver pressure run was made at
Mach 16+ enthalpy. Two runs, amixing and a combustion run,
were made at 408 atm driver pressure and Mach 16 enthalpy.
F. Wedge model - preliminary results
The data has only been partially reduced at this time;
hence the following results are preliminary. Very little
of the 408 atm driver data has been reduced. Hence, the dis-
cussion below deals with 272 arm driver pressure data only.
Overall, data acquistion was very good; about 90_ of the
data which should have been collected was, in fact, col-
lected. The in-house built amplifiers performed very well,
as discussed above.
The platinum thin film heat transfer gauges proved very
fragile in our environment. After the first two tests, both
gauges had been destroyed, showing infinite resistance. One
slug calorimeter failed on the next to last test; the re-
maining calorimeter remained operational for the full test
series. For each run typically up to two coaxial thermo-
couples would initially give good data and then open up to
I0
infinite resistance. However, the coaxial thermocouples
could be restored to service by abrasion and burnishing. At
the end of the wedge test program, all coaxial thermocouples
were still operational.
For the tare runs the static pressures were nearly iden-
tical over the whole wedge surface, as expected. With hy-
drogen injection, pressure increases due to the hydrogen
plume shocks could be seen. These pressure increases were
larger for the high-q run. The aft pitot rake showed the
wedge shock location and the reduction in dynamic pressure
due to the hydrogen injection plume. The reduced dynamic
pressure area was larger for the high-q run. The wedge shock
moved further away from the wedge surface with injection,
presumably since the plume shock merged with the wedge shock
and strengthened it.
The heat flux data for the tare run showed greatly in-
creased heat flux just aft of the injection holes, presum-
ably as result of the holes tripping the boundary layer.
For the gauges just aft of the injectors, no effect could
be seen midway between the injectors, However, gauges mid-
way between the injectors and just upstream of the trailing
II
also showed this increse, indicating that the tripped re-
gion was spreading laterally. With injection, gauges on the
injector centerlines showed an increase of heat flux (com-
pared to that with tare runs) just upstream of the injec-
tors, likely a result of plume shock compression and a re-
duction of heat transfer downstream of the injectors, likely
a result of hydrogen film cooling. The increase upstream
of the injectors was larger for the high-q run. With injec-
tion, for the gauges midway between the injectors, the heat
flux increased downstream of the injectors, likely a result
of plume shock compression, except at the most downstream
station, where the heat flux decreased, likely a result of
progressive spanwise spreading of the hydrogen film cooling
effect.
The laser holographic interferograms showed the wedge
shock, the plumes of hydrogen up to the pitot rake and the
plume shock merging with the wedge shock near the trail-
ing edge of the model. The reduction of the data is con-
tinuing and a paper giving the results will be presented at
the 28th AIAA/SAE/ASME/ASEE Joint Propulsion Conference in
Nashville, TN, July 6-8, 1992.
12
G. New test section
A new test section, built by Fluidyne, has been in-
stalled. This test section will allow greatly improved
physical and optical access to the model. Critical input for
the test section design was provided by D. W. Bogdanoff in
the following aresa: expected model loads, model mounting
system, instrumentation feedthroughs and window design.
H. Rake to calibrate new test section
A new rake is being constructed at Fluidyne to allow
calibration of the new test section. The rake will have _36
heads to measure pitot and static pressure and stagnation
point heat flux. This rake will be much more versatile than
the earlier fixed rake. It will be able to traverse in the
the x and z directions and to rotate. It also has 3 times as
many heads as the earlier rake and can measure heat flux,
which the earlier rake could not. Considerable input was
provided by D. W. Bogdanoff in the design of the rake. This
included calculation of forces on the rake, designs for all
three types of heads, shield designs for the pitot pressure
heads and recommendations for instrumentation feedthroughs
13
and wiring and amplifier configurations. Calibration of the
new test section using this rake will take place in 4-5/92.
I. Combustor model
A scramjet combustor model is being fabricated for Pratt
and Whitney and Rocketdyne by GASL. Considerable design in-
put for this model was provided by D. W. Bogdanoff. This in-
cluded calculation of forces on the model and recommenda-
tions regarding selection of transducers, location of pitot
rakes and configurations of instrumentation feedthroughs,
wiring and amplifiers.
J. Hydrogen fuel system for combustor model
D. W. Bogdanoff is the chief designer of the hydrogen
fuel system for the combustor model. Input has been received
from Ames, Pratt and Whitney, Rocketdyne and GASL person-
nel. Two systems are required, one for the cowl side and one
for the body side of the model. Very high hydrogen mass flow
rates, up to I+ kg/sec (total) must be delivered. The sys-
tem will initially be based on a i0 msec, 750 psi valve made
by Marotta. (At a later time, a considerably more expen-
sive i0 msec, 3000 psi valve made by Flodyne may be used.)
14
An initial system configuration was made based on two 90 ft
long Ludweig tubes. The final selected configuration is
based on two spherical reservoir vessels with volumes of
_i ft 3. Provisions have been made in the design for evac-
uation, loading and flushing with He or No. The necessary
safety systems, including burst discs, adequate venting op-
tions and fail-safe valve arrangements, have been included.
Another safety requirement is that the total amount of hy-
drogen in the system is limited to 400 scf. Remote pressure
measuring transmitters have been provided in the initial
hydrogen storage reservoirs and the two spheres. Special
feedthroughs for the tunnel vacuum wall and special fittings
for use with the Marotta valves have been designed. The de-
sign is about 90°/_complete and procurement and fabrication
of components will start in 3/92.
15


Experimental investigation of nozzle/plume aerodynamics at hypersonic speeds

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