CONFERENCE PRESENTATION - Investigation of GSI and Modeling of Catalycity for TPM testing in PWT

INVESTIGATION OF GAS-SURFACE INTERACTIONS AND MODELLING OF THE REFERENCE CATALYCITY FOR THERMAL PROTECTION MATERIAL TESTING IN PLASMA WIND TUNNELS Guerric de Crombrugghe von Karman Institute for Fluid Dynamics

October 4, 2012

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PART I: SCOPE PART II: TEST CAMPAIGNS PART III: GAS-SURFACE INTERACTIONS PART IV: CONCLUSION

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PART I: SCOPE

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Super-orbital atmospheric re-entry Facts:

Challenges:

• Performed from hyperbolic orbits

• Stringent requirement on TPS

for energy considerations • Entry velocities for Mars sample return 11.6 ¨ ¨ ¨ 14.5 km{s vs. 8.2 km{s for the Space Shuttle

• Increasing radiative heat flux

• Corresponding enthalpy scales as v 2

• Non-equilibrium processes • Flight duplication in ground

facilities not possible Ñ models are even more important

Apollo Command Module Credits: NASA

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Catalycity modeling Catalycity model today Probability of dissociated species recombination at the wall.

Recombination being an exothermeric reaction, it adds to the already important heat transfer.

Issue A probability hides the very physical nature of catalycity: a balance between diffusion of dissociated species to the wall, and reaction rate at the wall.

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PART II: TEST CAMPAIGNS

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Heat flux measurement in the Plasmatron (1/2) Local Heat Transfer Simulation (LHTS) method: The flow is duplicated in the boundary layer around the stagnation line as long as the outer edge enthalpy He , static pressure ps , and velocity gradient βe are reproduced

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Heat flux measurement in the Plasmatron (2/2) Probe in the plasma flow and corresponding measured heat flux

For a given measurement of heat flux and pressure, the output of the numerical re-building is a correlation between outer edge enthalpy He and material catalycity γ

Outer edge enthalpy [MJ/kg]

50

1100

Heat flux [kW/m2]

900 700

40

30

20

500 300

−5

10 100 −100 0

25

50 Time [s]

75

−4

10

−3

−2

10 10 Catalycity (log) [−]

−1

10

0

10

100

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Minimax • Draw 3 S-curves for probes having the same geometry but different

calorimeter materials • Interval defined for outer edge enthalpy He • Corresponding interval for the reference probe’s catalycity γref

Outer edge enthalpy [MJ/kg]

60

50

40

30

20

10 −5 10

Quartz calorimeter Copper calorimeter Silver calorimeter

−4

10

−3

−2

10 10 Catalycity (log) [−]

−1

10

0

10

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Damk¨ohler probes (1/2)

• The reference catalycity being fixed, the heat flux is recorded varying

the LHTS parameters: outer edge enthalpy He , static pressure ps , and velocity gradient βe • Different velocity gradient βe are obtained with different probe radius

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Damk¨ohler probes (2/2): results low pressure

3500 3000

Experiment Qw(frozen) = 1.6876*Qw(reference) H−W. Krass. (2006) F. Panerai (2012)

2000 Heat flux Equilibrium probe [kW/m2]

Heat flux Frozen probe [kW/m2]

4000

2500 2000 1500 1000 500 0 0

500 1000 1500 Heat flux Reference probe [kW/m2]

2000

1500

H−W. Krass. (2006) Experiment F. Panerai (2012) Qw(equilibrium) = 0.8061*Qw(reference)

1000

500

0 0

500 1000 1500 Heat flux Reference probe [kW/m2]

2000

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PART III: GAS-SURFACE INTERACTION ANALYSIS

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1. Wall Damk¨ohler number 2. Gas-phase Damk¨ohler number 3. Catalycity

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Wall Damk¨ohler number (1/3) Wall Damk¨ohler Daw : state of the flow close to the wall Daw “

kw τdiff “ τhete vdiff

with

kw “ f pTw q “ cst

and

vdiff “

De δ

• Daw Ñ 0: reaction-controlled wall • Daw Ñ 8: diffusion-controlled wall 0.8

0.7 O diffusion coefficient [m2/s]

N diffusion coefficient [m2/s]

0.7

0.8 Fully recombined mixture Mixture for H = 36.24 MJ/kg

0.6 0.5

1500 Pa

0.4 0.3 5000 Pa

0.2 0.1 0 0

Fully recombined mixture Mixture for H = 36.24 MJ/kg

1500 Pa

0.6 0.5 0.4 0.3

5000 Pa

0.2 0.1

10000 Pa 1000

2000

3000 4000 5000 Gas temperature [K]

6000

7000

0 0

1000

2000

3000 4000 5000 Gas temperature [K]

10000 Pa 6000 7000

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Wall Damk¨ohler number (2/3): diffusion velocity

vdiff “

De δ

ps “ 1, 500 Pa

ps “ 10, 000 Pa

12

1.6 1.4

8

Diffusion velocity [m/s]

Diffusion velocity [m/s]

10

Frozen Equilibrium nitrogen oxygen

6 4 2 0 15

1.2 1 0.8 0.6

Frozen Equilibrium nitrogen oxygen

0.4 0.2

20

25 30 Outer edge enthalpy [MJ/kg]

35

40

0 15.5

16

16.5 17 17.5 Outer edge enthalpy [MJ/kg]

18

18.5

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Wall Damk¨ohler number (3/3): conclusion

kw vdiff Daw

He Ò ´ Ò Ó

βe Ò ´ Ò Ó

ps Ò ´ Ó Ò

N vs. O ? ă ?

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Catalycity ps “ 1, 500 Pa

ps “ 10, 000 Pa

0

0

10

10

Frozen Equilibrium

−1

Catalycity (log) [−]

Catalycity (log) [−]

Frozen Equilibrium 10

−2

10

−3

10

15

−1

10

−2

10

−3

20

25 30 Outer edge enthalpy [MJ/kg]

γ

35

40

He Ò Ò

βe Ò Ò

10 15.5

ps Ò Ó

16

16.5 17 17.5 Outer edge enthalpy [MJ/kg]

18

18.5

N vs. O “

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PART IV: CONCLUSION

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Conclusion

kw vdiff Daw γ

He Ò ´ Ò Ó Ò

βe Ò ´ Ò Ó Ò

ps Ò ´ Ó Ò Ó

N vs. O ? ă ? “

• The variations of γ are linked to that of the parameters of Daw , as

both describe the chemistry at the wall • As kw is not varied, one can only conclude that γ varies as vdiff • If kw was to be varied, one would most probably conclude that γ

also varies as kw • Therefore γ is not described by the inverse of Daw but by another

function γ “ f pvdiff , kw q

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ANY QUESTIONS?

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