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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