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Venus atmospheric entry flow duplication in the X2 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 HYPERSONICS adapted from various presentations of Pr. R. Morgan

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Australia is a very large country

This country is scaringly huge. 3 / 32


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

−Ed

Binary dissociation rate behind a normal shock RD = ρT n e kT (1 − α) T >> Ed /k, and kT ≃ v 2 /2Ed → duplication parameter: v 2 /2Ed If recombination can be neglected, Damkholer number Da = lD ∼ 1/ρ → duplication parameter: ρL Reynolds number for viscous effect Re =

lD L

ρvL µ

→ 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 =

2qr ad 1/2ρv 3

> 0.01

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High enthalpy scaling, Ď L approach

Centreline profile Titan for Titan entry at 5.7 km/s and 1/100 scale (Gnoffo, 2005) 11 / 32


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 test

conditions; • 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? What are the implications for the characteristic lifetime and conditions of habitable environments on Venus and similar extrasolar systems? 2. What are the processes that have shaped and still shape the planet? 3. What does Venus tell us about the fate of Earths environment? S. Limay and S. Smrekar. Pathways for Venus Exploration. Technical report, Venus Exploration Analysis 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 −1

10

Free−stream density [kg/m3]

Mars direct ballistic entry Pioneer Venus Day probe, 1978 −2

10

−3

10

−4

10

0

Slowest Venus entry Vega 1, 1984

2

4

6 8 Flight velocity [km/s]

10

12

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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

North probe

16

Heat flux (MW/m2)

12

16 14

Convective Radiative Total

12 Heat flux (MW/m2)

14

10 8 6

10 8 6

4

4

2

2

0 120

115

110

105

100

95 90 Altitude (km)

85

80

75

70

Convective Radiative Total

0 120

115

110

105

100

95 90 Altitude (km)

85

80

75

70

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


12000

600

11000

500

10000

400

9000

300

8000

200 Temperature Pressure

7000

6000 7

7.5

8

8.5

9 9.5 Shock velocity [km/s]

Post−shock pressure [kPa]

Post−shock temperature [K]

Post-shock conditions

100

10

10.5

11

0 11.5

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Post-shock conditions 0

10

−1

Molar fraction [mol/mol]

10

−2

10

C CO N N2 NO O CN CO2 C2 C2O O2

−3

10

−4

10

−5

10

−6

10

7

7.5

8

8.5

9 9.5 Shock velocity [km/s]

10

10.5

11

11.5

0

10

−1

Molar fraction [mol/mol]

10

−2

10

C+ N+ O+ e− C− CO+ C2+ NO+ O− O2+

−3

10

−4

10

−5

10

−6

10

7

7.5

8

8.5

9 9.5 Shock velocity [km/s]

10

10.5

11

11.5

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Research objective

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Same test condition but different model size...

0

10

1/16 model

Free−stream density [kg/m3]

−1

10

Flight −2

10

−3

10

−4

10

0

2

4 6 8 Flight equivalent velocity [km/s]

10

12

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...to study different points of the trajectory & the scaling law

−1

10

Free−stream density [kg/m3]

Flight −2

10

−3

10

−4

10

0

2

4 6 8 Flight equivalent velocity [km/s]

10

12

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Post-processing: along the tunnel 16

L1d Pitot ’shock−speed’ Pitot ’flow−behind−shock’ x2s2189 x2s2194 x2s2195

Shock velocity [km/s]

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12

ACCELERATION TUBE

10

8

6 SHOCK TUBE

4 4

5

6

7 8 9 10 11 Distance from the reservoir−driver interface [m]

12

13

14

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Post-processing: in the test section

1/10 model −1

Free−stream density [kg/m3]

10

Flight

−2

10

−3

10

Day probe North probe Night probe Peak radiative heating Peak total heating x2s2189 x2s2194 x2s2195

−4

10

0

2

4

6 8 10 Equivalent flight velocity [km/s]

12

14

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Next steps

• Second Pitot survey to achieve somewhat slower flows for similar

density; • 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

3

Static pressure [Pa]

10

2

10

1

10

6

Day probe Without secondary driver With secondary driver (optimum) EAST data points Radiative heating starts Radiative heating stops Peak radiative heating 7

8

9 10 Shock velocity [km/s]

11

12

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THANK YOU Any questions?

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SEMINAR - Venus Atmospheric Entry Flow Duplication in the X2 Superorbital Expansion Tube