Venus atmospheric entry flow duplication in theX2 superorbital expansion tube
Guerric de Crombrugghe
Centre for Hypersonics& The University of Queensland
01/10/2013
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PART I:THE CENTRE FOR HYPERSONICSadapted from various presentations of Pr. R. Morgan
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Australia is a very large country
This country is scaringly huge.
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The University of Queensland
• Founded in 1909;
• > 5,000 teaching staff;
• > 32,400 undergraduate student;
• > 12,200 postgraduate student.
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The Centre for Hypersonics
• ∼ 60 people, including 5 VKI alumni;
• Active in:• Development of hypervelocity test facilities;• Scramjet propulsion (experiment, analysis and design);• Rocket flight testing;• Aerothermodynamic experimentation and analysis;• Advanced instrumentation for aerodynamic measurements;• Computational fluid dynamic analysis of hypervelocity flows;• Optical diagnostics for hypervelocity superorbital flows.
• Four facilities:• T4 shock tunnel (scramjet);• X2 expansion tube (super-orbital entry);• X3 expansion tube (scramjet & super-orbital entry);• Drummond tube (education).
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Schematic operation of tubes
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The X2 expansion tube
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The X2 expansion tube
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High enthalpy scaling, ρL approach
Binary dissociation rate behind a normal shock RD = ρT ne−EdkT (1− α)
T >> Ed/k, and kT ≃ v2/2Ed → duplication parameter: v2/2Ed
If recombination can be neglected, Damkholer number Da = lDL
lD ∼ 1/ρ → duplication parameter: ρL
Reynolds number for viscous effect Re = ρvLµ
→ proper scaling requires using same fluid, same v , and duplication of ρL
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High enthalpy scaling, ρL approach
Binary recombination length scale lD ∼ 1/ρ2
→ recombination and equilibrium are not properly modelled
Only accounts for binary reactions→ complex combustions are not properly modelled
Radiation not scaled properly→ issue if Goulard number Γ = 2qrad
1/2ρv3 > 0.01
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High enthalpy scaling, ρL approach
Centreline profile Titan for Titan entry at 5.7 km/s and 1/100 scale(Gnoffo, 2005)
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Pros of expansion tubes
• High total enthalpy simulation of aerodynamic flows possible;
• Equivalent flight speeds up to 15 km/s demonstrated;
• Large range of conditions / test gases available;
• Nonequilibrium radiant and chemical phenomena can be created;
• Continuum and rarefied flows;
• Heat transfer / force / pressure measurement / laser diagnostics;
• High total pressure and ρL simulation capability;
• Can operate with nozzles for enlarged core flow area;
• Cheap.
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Cons of expansion tubes
• Short run times (15 µs to 1 ms);
• Complex chemistry and fluid dynamics involved in determining testconditions;
• Diaphragm inertia influences flow;
• Restricted core flow at high Mach numbers;
• Unusable flow quality if incorrectly operated;
• Low density at very high speeds;
• Long tube lengths sometimes required;
• Diaphragm debris;
• Turbulent boundary layers at high Reynolds numbers.
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PART II:PLUMBING THE ATMOSPHERE OF VENUS
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Rationales for Venus exploration
1. How did Venus originate and evolve? Whatare the implications for the characteristiclifetime and conditions of habitableenvironments on Venus and similar extrasolarsystems?
2. What are the processes that have shaped andstill shape the planet?
3. What does Venus tell us about the fate ofEarths environment?
S. Limay and S. Smrekar. Pathways for VenusExploration. Technical report, Venus ExplorationAnalysis Group, 2009.
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Challenges of Venus exploration
P. Gnoffo, K. Wailmuenster and H. Hamilton. Computational
Aerothermodynamics Design Issues for Hypersonic Vehicles Journal of
Spacecraft and Rockets, 36(1):2143, 1999.16 / 32
Venus entry vs. Mars entry
0 2 4 6 8 10 12
10−4
10−3
10−2
10−1
Flight velocity [km/s]
Fre
e−
str
eam
density [kg/m
3]
Mars direct ballistic entryPioneer Venus Day probe, 1978
Slowest Venus entryVega 1, 1984
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Challenges of Venus exploration
• 11 · · · 12 km/s entry velocity;
• 15 · · · 50 gs peak deceleration;
• 3 · · · 40 MW/m2 peak heat flux;
• sulphuric acid cloud layer;
• up to 100 m/s high altitude winds;
• > 725 K surface temperature;
• 9,200 kPa surface pressure.
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Venus atmospheric entry probes
Venera first generation(1967-1972)
Venera second generation(1975-1984)
Pioneer Venus(1978)
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Pioneer Venus multiprobe
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Aeroheating rebuilding
Day probe
7075808590951001051101151200
2
4
6
8
10
12
14
16
Altitude (km)
Heat flux (
MW
/m2)
Convective
Radiative
Total
North probe
7075808590951001051101151200
2
4
6
8
10
12
14
16
Altitude (km)H
eat flux (
MW
/m2)
Convective
Radiative
Total
C. Park and H.-K. Ahn. Stagnation-point heat transfer rates for Pioneer-Venus
probes. Journal of Thermophysics and Heat Transfer, 13(1):3341, 1999.
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Shock layer radiation
B.A. Cruden. Absolute radiation measurement during planetary entry in the
Nasa Ames electric arc shock tube facility. In 27th International Symposium on
Rarefied Gas Dynamics, 2011.22 / 32
Post-shock conditions
7 7.5 8 8.5 9 9.5 10 10.5 11 11.56000
7000
8000
9000
10000
11000
12000
Po
st−
sh
ock t
em
pe
ratu
re [
K]
7 7.5 8 8.5 9 9.5 10 10.5 11 11.50
100
200
300
400
500
600
Shock velocity [km/s]
Po
st−
sh
ock p
ressu
re [
kP
a]
Temperature
Pressure
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Post-shock conditions
7 7.5 8 8.5 9 9.5 10 10.5 11 11.510
−6
10−5
10−4
10−3
10−2
10−1
100
Shock velocity [km/s]
Mo
lar
fra
ctio
n [
mo
l/m
ol]
CCONN2NOOCNCO2C2C2OO2
7 7.5 8 8.5 9 9.5 10 10.5 11 11.510
−6
10−5
10−4
10−3
10−2
10−1
100
Shock velocity [km/s]
Mo
lar
fra
ctio
n [
mo
l/m
ol]
C+N+O+e−C−CO+C2+NO+O−O2+
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Research objective
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Same test condition but different model size...
0 2 4 6 8 10 12
10−4
10−3
10−2
10−1
100
Flight equivalent velocity [km/s]
Fre
e−
str
ea
m d
en
sity [
kg
/m3
]
1/16 model
Flight
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...to study different points of the trajectory& the scaling law
0 2 4 6 8 10 12
10−4
10−3
10−2
10−1
Flight equivalent velocity [km/s]
Fre
e−
str
ea
m d
en
sity [
kg
/m3
]
Flight
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Post-processing: along the tunnel
4 5 6 7 8 9 10 11 12 13 144
6
8
10
12
14
16
Distance from the reservoir−driver interface [m]
Sh
ock v
elo
city [
km
/s]
L1dPitot ’shock−speed’Pitot ’flow−behind−shock’x2s2189x2s2194x2s2195
ACCELERATION TUBE
SHOCK TUBE
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Post-processing: in the test section
0 2 4 6 8 10 12 1410
−4
10−3
10−2
10−1
Equivalent flight velocity [km/s]
Fre
e−
str
eam
density [kg/m
3]
Day probeNorth probeNight probePeak radiative heatingPeak total heatingx2s2189x2s2194x2s2195
1/10 model
Flight
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Next steps
• Second Pitot survey to achieve somewhat slower flows for similardensity;
• Numerical rebuilding of the experiments to perform (in-house code:Eilmer);
• Test campaign (IR and UV spectrometry, possibly also VUV).
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Possible campaign in shock tube mode
6 7 8 9 10 11 12
101
102
103
Shock velocity [km/s]
Sta
tic p
ressure
[P
a]
Day probe
Without secondary driver
With secondary driver (optimum)
EAST data points
Radiative heating starts
Radiative heating stops
Peak radiative heating
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THANK YOUAny questions?
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