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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