INVESTIGATION OF GAS-SURFACEINTERACTIONS AND MODELLING OF THEREFERENCE CATALYCITY FOR THERMALPROTECTION 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:

• Performed from hyperbolic orbitsfor energy considerations

• Entry velocities for Mars samplereturn 11.6 ¨ ¨ ¨ 14.5 km{svs. 8.2 km{s for the Space Shuttle

• Corresponding enthalpy scales as v2

Challenges:

• Stringent requirement on TPS

• Increasing radiative heat flux

• Non-equilibrium processes

• Flight duplication in groundfacilities not possibleÑ models are even more important

Apollo Command Module

Credits: NASA4 / 20

Catalycity modeling

Catalycity model todayProbability of dissociated species recombination at the wall.Recombination being an exothermeric reaction, it adds to the alreadyimportant heat transfer.

IssueA probability hides the very physical nature of catalycity: a balancebetween diffusion of dissociated species to the wall, and reaction rate atthe 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 aslong as the outer edge enthalpy He , static pressure ps , and velocitygradient βe are reproduced

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Heat flux measurement in the Plasmatron (2/2)

Probe in the plasma flow andcorresponding measured heat flux

0 25 50 75 100−100

100

300

500

700

900

1100

Time [s]

Heat flux [kW

/m2]

For a given measurement of heat flux andpressure, the output of the numericalre-building is a correlation between outeredge enthalpy He and material catalycity γ

10−5

10−4

10−3

10−2

10−1

100

20

30

40

50

Catalycity (log) [−]

Oute

r edge e

nth

alp

y [M

J/k

g]

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Minimax

• Draw 3 S-curves for probes having the same geometry but differentcalorimeter materials

• Interval defined for outer edge enthalpy He

• Corresponding interval for the reference probe’s catalycity γref

10−5

10−4

10−3

10−2

10−1

100

10

20

30

40

50

60

Catalycity (log) [−]

Oute

r edge e

nth

alp

y [M

J/k

g]

Quartz calorimeter

Copper calorimeter

Silver calorimeter

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Damkohler probes (1/2)

• The reference catalycity being fixed, the heat flux is recorded varyingthe 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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Damkohler probes (2/2): results low pressure

0 500 1000 1500 20000

500

1000

1500

2000

2500

3000

3500

4000

Heat flux Reference probe [kW/m2]

Heat flux F

rozen p

robe [kW

/m2]

Experiment

Qw(frozen) = 1.6876*Qw(reference)

H−W. Krass. (2006)

F. Panerai (2012)

0 500 1000 1500 20000

500

1000

1500

2000

Heat flux Reference probe [kW/m2]

Heat flux E

quili

brium

pro

be [kW

/m2]

H−W. Krass. (2006)

Experiment

F. Panerai (2012)

Qw(equilibrium) = 0.8061*Qw(reference)

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PART III: GAS-SURFACE INTERACTIONANALYSIS

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1. Wall Damkohler number

2. Gas-phase Damkohler number

3. Catalycity

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Wall Damkohler number (1/3)Wall Damkohler Daw : state of the flow close to the wall

Daw “τdiffτhete

“kwvdiff

with kw “ f pTw q “ cst and vdiff “De

δ

• Daw Ñ 0: reaction-controlled wall

• Daw Ñ 8: diffusion-controlled wall

0 1000 2000 3000 4000 5000 6000 70000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Gas temperature [K]

N d

iffu

sio

n c

oeffic

ient [m

2/s

]

Fully recombined mixture

Mixture for H = 36.24 MJ/kg

1500 Pa

5000 Pa

10000 Pa

0 1000 2000 3000 4000 5000 6000 70000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Gas temperature [K]

O d

iffu

sio

n c

oeffic

ient [m

2/s

]

Fully recombined mixture

Mixture for H = 36.24 MJ/kg 1500 Pa

5000 Pa

10000 Pa

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Wall Damkohler number (2/3): diffusion velocity

vdiff “De

δ

ps “ 1, 500 Pa

15 20 25 30 35 400

2

4

6

8

10

12

Outer edge enthalpy [MJ/kg]

Diffu

sio

n v

elo

city [m

/s]

Frozen

Equilibrium

nitrogen

oxygen

ps “ 10, 000 Pa

15.5 16 16.5 17 17.5 18 18.50

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Outer edge enthalpy [MJ/kg]

Diffu

sio

n v

elo

city [m

/s]

Frozen

Equilibrium

nitrogen

oxygen

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Wall Damkohler number (3/3): conclusion

He Ò βe Ò ps Ò N vs. O

kw ´ ´ ´ ?vdiff Ò Ò Ó ă

Daw Ó Ó Ò ?

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Catalycity

ps “ 1, 500 Pa

15 20 25 30 35 4010

−3

10−2

10−1

100

Outer edge enthalpy [MJ/kg]

Cata

lycity (

log)

[−]

Frozen

Equilibrium

ps “ 10, 000 Pa

15.5 16 16.5 17 17.5 18 18.510

−3

10−2

10−1

100

Outer edge enthalpy [MJ/kg]

Cata

lycity (

log)

[−]

Frozen

Equilibrium

He Ò βe Ò ps Ò N vs. O

γ Ò Ò Ó “

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PART IV: CONCLUSION

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Conclusion

He Ò βe Ò ps Ò N vs. O

kw ´ ´ ´ ?vdiff Ò Ò Ó ă

Daw Ó Ó Ò ?γ Ò Ò Ó “

• The variations of γ are linked to that of the parameters of Daw , asboth 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 γalso varies as kw

• Therefore γ is not described by the inverse of Daw but by anotherfunction γ “ f pvdiff, kw q

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ANY QUESTIONS?

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