Sonderforschungsbereich/Transregio 40 – Annual Report 2016
73
GH2/GO2 Supply Facility for Hot Plume Testing
in the Vertical Test Section Cologne (VMK)
By D. Kirchheck A N D A. Gülhan
German Aerospace Center (DLR), Institute of Aerodynamics and Flow Technology,
Supersonic and Hypersonic Technologies Department, Linder Höhe, 51147 Cologne, Germany
The paper at hand belongs to a series of investigations of hot plume interaction phenomena in the field of space transportation. Scientific motivation of these investigations
is the understanding of the physical mechanisms in base flows that are for example
present at rocket launchers. The paper shortly summarizes the technical challenges
that are resulting from base flow interaction phenomena and develops a motivation for
an enhancement of the experimental testing capabilities in that field. In the second part,
an effort of the German Aerospace Center (DLR) to achieve that goal by expanding the
vertical wind tunnel facility in Cologne by a gaseous hydrogen oxygen supply unit to enable hot plume interaction testing with GH2/GO2 combustion is presented. The design
of the facility is summarized and an outlook on the gain for future investigations in that
field is given in the conclusions.
1. Introduction
While the requirements on the development of space transportation systems changed
over the last decades and factors like reusability, cost-efficiency, and environmental sustainability are gaining impact, reliability and safety are still the driving aspects for the
course of development today, and for the future. Therefore, many attempts are taken
to decrease uncertainties in the design process by using wind tunnel and numerical
simulations.
One of the aspects, which is of great interest with respect to the aforementioned is the
base flow region of launchers, where hot gases from the rockets plume and the wake
of the rockets main body interact to generate massive mechanical and thermal loads
on base components like the nozzle structure. To preliminary determine these loads,
sophisticated numerical methods and complex test setups are necessary. In the Collaborative Research Center SFB-TRR40, funded by the German Research Foundation
(DFG), numerous works have been published on this issue. Next to numerical investigations on generic rocket configurations, experimental effort was made on transonic,
supersonic and hypersonic configurations with different types of plume to simulate the
interaction phenomena, causing the challenges of realistic flight.
One of the main tasks in this context is, to create similarity conditions for the base
flow region, which includes the velocity regime, type of incoming boundary layers, and
especially the behaviour of shear regions between the external and internal flow. Driving
parameters for the shear flow similarity are the momentum density and the ratio of absolute velocities, which means that extensively high velocities have to be generated in the
model plume to exceed the absolute velocity of the incoming external flow. A common
74
D. Kirchheck & A. Gülhan
silencer
test chamber
control valve
pressurized
air
entrance to
test chamber
free stream
wind tunnel
nozzle + model
heat storage
2m
F IGURE 1. Vertical test section cologne (VMK)
way to cope with that is to increase the plume temperature at constant nozzle geometry and thus, constant exit Mach number. In cooperation with our project partners, till
now, different plume temperatures have been realised with different media between cold
air plume (280 K), cold and heated helium plume (280 K, 470 K, 600 K), and in addition
tests were carried out with solid propellant combustion to generate realistic stagnation
temperature.
An attempt to combine the advantages of all previous test campaigns, which are the
constance of stagnation properties for a continuously fed nozzle, the realistically high
temperatures of a combustion process and the simplicity of the numerical tools necessary for simulation of quasi static conditions in the plume is the use of a gaseous
hydrogen/gaseous oxygen (GH2/GO2) supply system for an internal combustion inside
the wind tunnel model for the generation of a high temperature plume. This topic is dealt
with at DLR cologne since late 2013, thus, the actual paper will summarize our state of
the art and the facility which will be available by early 2017.
2. Equipment
The GH2/GO2 facility is being built as an extension to our vertical wind tunnel test
section, the VMK. It is, therefore, one of the main boundary conditions for the conception
of the new supply system and will be presented in the following paragraph.
2.1. The Vertical Test Section Cologne (VMK)
The VMK is a blow down type wind tunnel with an open test section, capable of generating either subsonic or supersonic conditions in a vertical free stream (Fig. 1). It is
connected to a 1000 m3 pressure reservoir, enabling typical test durations of 60 s. After
the pressurized air at a maximum total pressure (pt ) of 35 bar passes the control valve,
it can be heated by the heat storage to a maximum total temperature (Tt ) of 750 K. The
GH2/GO2 Supply Facility for Hot Plume Testing
4
pt = 35 bar
Tt = 288 K
3.5
Max. supersonic Mach number
pt = 35 bar
Tt = 750 K
ÅisÅ
Mach number
3
2.5
ps = 1,0132 bar
Tt = 750 K
ÅairÅ
s
Å
1.5
0.5
ÅwithÅtwo
level cond.:
ÅSea
inÅ
orderÅ
to
p = 1,0132 bar
ÅtemperatureÅ
T = 288 K
Åof
s
2
1
75
Min. supersonic Mach number
Max. subsonic Mach number
ps = 1,0132 bar
Tt = 288 K
Åthree
Min. subsonic Mach number
0
10
20
50
100
200 300
6
Unit Reynolds number [10 / 1m]
F IGURE 2. Operational range of the VMK facility
test section can be equipped with different nozzles for different Mach numbers. Subsonic testing is typically done with a 340 mm nozzle. The test section has four optical
entries which are aligned on the specimen to allow optical measurements from a save
position. Additionally, measurement systems can be set up directly in the test chamber,
which makes the VMK an immensely flexible wind tunnel with regard to measurement
techniques.
2.2. Operational Range of the VMK Facility
The operational range of VMK is depicted in Fig. 2. In the subsonic range, Mach numbers between 0.5 and 0.95 are possible and in the supersonic range, Mach numbers are
possible between 1.5 and 3.25. The facility is capable of simulating ground conditions
up to a Mach number of 2.8.
2.3. Suitability of the Test Section
In the early days, the VMK test section was designed to withstand tests with combustive
and explosive media for testing of propulsion units. Therefore, it is constructed of heavy
reinforced concrete walls with a thickness of about 70 to 80 cm. Together with its corresponding steal doors, optical windows and a pressure relief flap it is highly suitable for
GH2/GO2 combustion testing. In addition, safety devices were updated, to guarantee
state of the art security standards.
3. Design Requirements
With respect to nozzle exit velocity, the design is mainly driven by the requirements of
the collaborative research centre, where different test cases are specified with varying
stagnation temperatures for the internal flow, as seen in Fig. 3. Temperatures vary between 925 K as a low temperature condition where instrumentation of the combustion
76
D. Kirchheck & A. Gülhan
6000
2,0
u max
m/s
OFR = 0,7
5,0
4,0
3,0
1,0
6,0
H2/O2
(pcc = 115 bar)
4000
2000
1 : Tcc ≈ 280 K
2 : Tcc ≈ 470 K
3 : Tcc ≈ 600 K
1
2 3
4 : Tcc ≈ 925 K
5 : Tcc ≈ 3600 K
4
5
0
0
1000
2000
3000
4000
T cc / K
F IGURE 3. Operating conditions of future model combustion chambers
Description
Symbol
Reference condition
RC0 RC1
RC2
Unit
IG
Controlled quantities
Mass flow oxygen
Mass flow hydrogen
ṁO2
ṁH2
36.7 239.5 397.4 0.6 . . . 20.0 g/s
52.4 39.9 66.2 0.3 . . . 10.0 g/s
ṁ
OFR
P
89.1 279.4 463.6 0.9 . . . 30.0 g/s
0.7
6.0
6.0
1.0 . . . 8.0 −
0.5
4.8
7.9 0.036 . . . 1.2 MW
U ncontrolled quantities
Total mass flow
Oxidizer − fuel − ratio
Chamber performance
M odel dependant quantities
Combustion chamber pressure
pcc
Combustion chamber temperature Tcc
20.7 68.9 115.0
925 3550 3620
TBD
TBD
bar
K
TABLE 1. Reference conditions (RC) for GH2/GO2 hot gas tests
Description
Symbol
Test bench
Total mass flow
Mass flow oxygen
Mass flow hydrogen
Maximum chamber pressure
ṁ
−
ṁO2
450 (G/L)
ṁH2
113 (G)
pcc,max
96
CCL
Unit
DLR M3.1
Mascotte
400 (L)
−
−
40
−
40 . . . 400 (L)
5 . . . 75 (G)
100
g/s
g/s
g/s
bar
TABLE 2. Operational parameters of exemplary test benches. Abbreviations (L), (G) specify the
state of fuel/oxidizer as liquid or gaseous, respectively. [1]
GH2/GO2 Supply Facility for Hot Plume Testing
77
chamber is made possible and 3600 K as most realistic test case in terms of nozzle
exit velocity. Temperatures are set by adjusting the oxidizer fuel ratio (OFR) between
0.7 (hydrogen rich combustion) to 6.0 (nearly stoichiometric combustion). These operating points are composed in the figure with the conditions for cold and warm plumes of
air or helium, by the other project partners in SFB-TRR40. The diagram clearly shows,
what will be the gain of this newly facility, increasing the range of possible nozzle exit
velocities from approx. 2500 to 5000 m/s.
The requirement for chamber pressure is taken from typical rocket engine configurations like the Vulcain II engine and set to 115 bar. This way, combustion pressures and,
thus, nozzle pressure ratios in low altitude simulations can be set to reach high similarity. A more detailed, recent investigation of the similarity configuration of rocket base
flow is reviewed in [1]. The paper compares different approaches from literature and
provides a reasonable differentiation, which then leads to the baseline of our reference
configurations.
With a given geometry for the combustion chamber and the nozzle throat, different reference conditions can be deduced from temperature and pressure requirements. These
reference conditions are listed in Table 1 with RC0, the low temperature condition, RC2
the high temperature condition as mentioned before and RC1, a medium pressure condition in between. What can be seen here, is also the range of ignition mass flow that
will be possible with the facility. A comparison of the performance data with similar facilities is given in Table 2. In this context the described performance data gives a medium
sized test bench with the additional advantage of high quality external flow, which is
what makes the facility unique within the European countries as to the knowledge of the
authors.
4. Facility Design
4.1. General Integration into the Wind Tunnel Facility
The GH2/GO2 facility is designed as a self-sufficient system and can be operated either
with or without external flow from the wind tunnel nozzle. The interface between these
two parts is therefore singular and mono-directional as shown in Fig. 4 and will not limit
the original performance range of VMK itself. The GH2/GO2 supply will contain a gas
storage, connected to the instrument panel and the piping into the VMK test chamber.
The components will be presented shortly in the following paragraphs.
4.2. Gas Storage
The gas storage is located outside in a secured area. It contains hydrogen and oxygen
for the combustion process as well as nitrogen for inertization and purging of the test
chamber in an emergency situation. The storage is made of standard bundles with 12
bottles each in 300 bar version. They are connected in parallel to realize the high flow
requirements. The size of the storage can be taken from Table 3. It is sized, to give a
minimum count of 18 tests in maximum flow condition (RC2).
4.3. Instrument Panel and Piping
The instrument panel (Fig. 5) is located half way to the test section. From there, piping
length and number of bends is minimized to reduce disturbances and to allow for good
controllability of the mass flow and reliable ignition timing. Deviation from the set point
value in the flow control loop is specified as less then 1 %.
78
D. Kirchheck & A. Gülhan
silencer
300bar
15°C
120bar
15°C
air / hot gas
1atm
15 - 3000°C
VMK
Testkammer
test chamber
N2
storage
specimen with
comb. chamber
H2
storage
N2
H2/O2
instrument panel
H2
wind tunnel
nozzle
O2
O2
storage
purge air
pressurized air
60bar
15 - 450°C
heater
pressurized air
60bar
15°C
pressure
reservoir
H2/O2 supply facility
VMK
F IGURE 4. Integration of the GH2/GO2 supply into the VMK environment
Description
Symbol
Packaging
Storage pressure
Storage volume
Storage mass
n
ps
Vs
ms
Gastype
GH2
GO2
Unit
GN2
4 × 12 4 × 12 2 × 12
300
300
300
2.4
2.4
1.2
50
1100
400
bottles
bar
m3
kg
TABLE 3. Storage capabilities for the GH2/GO2 supply system
4.4. Model Interface
After reaching the test chamber (Fig. 6), the piping system is connected to the model
support via flexible tubes. The model support is a center body, which is held inside the
wind tunnel nozzle by the tubing for GH2 and GO2 supply. As an upgrade to the center
support the generic rocket model is placed directly on top of it.
The design of an exemplary specimen with an implemented combustion chamber and
a modular injector design is discussed in detail in [2], but the main components are also
shown in Fig. 7. Depicted is the subsonic wind tunnel nozzle (1), which is mounted on
top of the center support adapter (2), which holds the supply tubes for hydrogen (3) and
for oxygen (4). The center body (5) is connected to the combustion chamber (6) and
the single head coaxial injector (7). After burning the gases, they are expelled through
the model nozzle (8) into the surrounding wind tunnel flow. The detailled design of the
combustion chamber and the injector is done in cooperation with our project partners
in [2].
GH2/GO2 Supply Facility for Hot Plume Testing
79
pressure indicators H2 vent
potentially explosive atmospheres
filter
coriolis flow meter
frame rack
terminal box
H2 control valve
H2
N2
main feeding
O2
SRS
MPG 03 NC
O2 control valve
coriolis flow meter
filter
manual isolation valves
ignition feeding
cabling
O2 vent
F IGURE 5. Instrument panel of the GH2/GO2 supply facility
H2
O2
N2
4.5m
installation
room A
VMK
installation
room B
4m
control room
manual
isolation valves
purge air
system
wind tunnel
nozzle/model
explosion proof
concrete wall
F IGURE 6. Vertical test section cologne (VMK) - crosssectional view
5. Conclusion and Outlook
As described before, the discussed GH2/GO2 supply unit, which will be an upgrade
to the Vertical Test Section at the German Aerospace Center (DLR) Cologne paves the
way to more sophisticated experimental investigations in the field of hot plume interaction that are unreached by European institutions at the time being. It will expand the
experimental capabilities of creating high velocity, high temperature plumes in model
scale to enhance the similarity of interaction phenomena in the base flow region of
rocket launchers. The application of readily developed measurement techniques for the
environment of solid propellant hot plume testing promises a reliable evaluation process
with high quality data due to constant combustion conditions, longer test durations and
less interference signals due to clean plumes with minimum particle loading. In com-
80
D. Kirchheck & A. Gülhan
340 mm
8
1
6
7
9
3
4
2
5
F IGURE 7. Wind tunnel nozzle with integrated model
bination, this will enable statistical evaluation of PIV data sets and more sophisticated
optical methods like OH-LIF in the vicinity of the recirculation and the shear region. Altogether, the effort will give more insights into small-scale phenomena and will improve
validation processes for numerical methods in that field. Finally, that will lead to a valuable contribution to the the Collaborative Research Centre SFB-TRR40.
Acknowledgments
Financial support has been provided by the German Research Foundation (Deutsche
Forschungsgemeinschaft – DFG) in the framework of the Sonderforschungsbereich
Transregio 40. The support of the technical staff during the work at the Supersonic
and Hypersonic Technologies Department in Cologne is highly appreciated.
References
[1] S AILE , D., K IRCHHECK , D., G ÜLHAN , A. AND B ANUTI , D. (2015). Design of a Hot
Plume Interaction Facility at DLR Cologne. Proceedings of the 8th European Symposium on Aerothermodynamics for Space Vehicles. Lisbon, Portugal, 2–6 March.
[2] S AILE , D., K IRCHHECK , D., G ÜLHAN , S ERHAN , C. AND H ANNEMANN , V. (2015).
Design of a GH2/GOX Combustion Chamber for the Hot Plume Interaction Experiments at DLR Cologne. Proceedings of the 8th European Symposium on Aerothermodynamics for Space Vehicles. Lisbon, Portugal, 2–6 March.