Gas Surface Interaction Study of Low Density Ablators in ... · 6/26/2014 · Gas/Surface Interaction Study of Low-Density Ablators in Sub- and Supersonic Plasmas! ... 1.2-MW Inductively

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Gas/Surface Interaction Study of Low-Density Ablators in

Sub- and Supersonic Plasmas

!B. Helber

1,2, A. Turchi

1, O. Chazot

1, A. Hubin

2, T. E. Magin

1

!1Aeronautics and Aerospace Department, von Karman Institute for Fluid Dynamics, Belgium

2Research Group Electrochemical and Surface Engineering, Vrije Universiteit Brussel

1

NASA Applied Modeling & Simulation (AMS) Seminar Series June 26, 2014

!based on AIAA 2014-2122

11thAIAA/ASME Joint Thermophysics and Heat Transfer Conference

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TPM for Atmospheric Reentry

NASA Stardust probe, reentry: Jan. 15, 2006 (12.9 km/s) (AIAA 2008-1202)

2

Future Missions: Ablative TPM Sample return, ISS serving (Dragon, ARV,…), MPCV Atm. reentry speeds > 10km/s Mass loss and surface recession Prediction of material response required High margins decrease payload

New materials (1990’s) Phenolic impregnated carbon fiber preform Very porous low density ablators

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TPM for Atmospheric Reentry

Gas-Surface Interaction

Complex Multiphysics - Multiscale Problem

3

C248

NH (A−X)

OH (A−X)

CN violet (B−X)

CH (A−X)

C2 Swan

Na

Hβ

Hα

NO777 N lines

Air plasmaNitrogen plasma

Material

Radiation

/ 30

We aim at improvement of

Experimental Methods (VKI)

4

TPS Design / Material (VUB, Airbus DS, ESA)

Material Response Modeling & Validation (VKI, collaborations)

/ 30

In the following

5

GAS - PHASE

MATERIAL

chem. active surface

/ 30

Reactive Surface • surface temperature & emissivity • centerline recession rate • post-ablation topology (SEM)

In the following

5

GAS - PHASE

MATERIAL


/ 30

(2) Surface ➪ Temperatures / Recession

In the following

5

GAS - PHASE

MATERIAL


/ 30

(2) Surface ➪ Temperatures / RecessionGas-phase • Ablation species injection • Strong radiators and boundary

layer absorption

In the following

5

GAS - PHASE

MATERIAL


/ 30

(2) Surface ➪ Temperatures / Recession(3) Gas-phase ➪ BL emission & temp

In the following

5

GAS - PHASE

MATERIAL


/ 30

(2) Surface ➪ Temperatures / Recession(3) Gas-phase ➪ BL emission & temp(4) Material ➪ Pyrolysis outgassing

In the following

5

GAS - PHASE

MATERIAL


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(2) Surface ➪ Temperatures / Recession(3) Gas-phase ➪ BL emission & temp(4) Material ➪ Pyrolysis outgassing

In the following

5

GAS - PHASE

MATERIAL


(1) Materials and Methods for Ablation Characterization

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Materials of Investigation

6

Carbon fiber preform (Mersen Scotland Holytown Ltd.) • chopped carbon fibers, fully carbonised • density: 180-210 kg/m3, porosity: 90%

AQ61 (Airbus DS) • low density carbon-phenolic • made of short carbon fibers impregnated → compacted & pyrolyzed • low resin content

Asterm (Airbus DS) • low density carbon-phenolic • rigid graphite felt impregnated → polymerization • precursor similar to carbon fiber reform

no phenol

with phenol

with phenol

/ 23

Carbon fiber preform, non-pyrolyzing (Mersen Scotland Holytown Ltd.)

Materials of Investigation

7

AQ61, carbon-phenolic (AIRBUS DS)

650μm

13μm

/ 30 8

M">>"1"

Shock"

Relaxa/on"zone"

Aerospace"vehicle"nose"

M << 1

Real%flight%situa-on%

Ground%test%

y"Body"

x"

δ"

Ve"

(dU/dx)e"

M"<<"1"

plasma"jet"

TPS"sample"

Stagnation point similarity:!! Hf = Hexp!! pf = pexp!! βf = βexp, β = dU/dx|e

1.2-MW Inductively Coupled Plasmatron: Methodology

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1.2-MW Inductively Coupled Plasmatron

Gas: Power:

Heat Flux: Pressure:

9

water&cooled+calorimeter+

test+sample+

pitot+probe+

spectrometer+op1cs+

sample+condi1on+

control+system

+

High+speed+camera+

op1cal+access+pyrometer+

op1cal+access+radiometer+

Air, N2, CO2, Ar 1.2-MW > 12 MW/m2

10 mbar - 1 atm

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1.2-MW Inductively Coupled Plasmatron

Gas: Power:

Heat Flux: Pressure:

9

water&cooled+calorimeter+

test+sample+

pitot+probe+

spectrometer+op1cs+

sample+condi1on+

control+system

+

High+speed+camera+

op1cal+access+pyrometer+

op1cal+access+radiometer+

Air, N2, CO2, Ar 1.2-MW > 12 MW/m2

10 mbar - 1 atm

/ 30

Our interest !

Surface temperature Emissivity Internal Temperature In-situ recession analysis Volumetric recession Chemical composition Temperature estimation

(AIAA 2013-2770)

10

!test!sample!

plasma!torch!

light!collec/on!system!(lens!&!mirrors)!!

exhaust!&!!!!!heat!exchanger!!

reac/ve!boundary!!!!!layer!

op/cal!fibre!ends!

High!speed!camera!

test!chamber!

HR=4000!spectrometer!

Func/on!generator!

2=color!pyrometer!

Techniques for In-Situ Ablation Characterization

/ 30 10

1 2 3

Our interest !

Surface temperature Emissivity Internal Temperature In-situ recession analysis Volumetric recession Chemical composition Temperature estimation

(AIAA 2013-2770)

Techniques for In-Situ Ablation Characterization

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Three Dedicated Test Campaigns

11

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1. General ablation tests: • air and nitrogen • heat fluxes: 1 - 3 MW/m2, ptot = 15 - 200 hPa


11

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2. Grain study: • only air • 0.3 - 1 MW/m2, p = 15hPa


11

with-grain through-grain cylindricaltc 5mmtc 10mm

/ 30


2. Grain study: • only air • 0.3 - 1 MW/m2, p = 15hPa

3. High-heat flux tests (supersonic)


110 5 10 15 200

2

4

6

8

10

Time, s

Hea

t flu

x, M

W/m

2

with-grain through-grain cylindricaltc 5mmtc 10mm

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Volumetric Ablation (shape change)Non-pyrolyzing carbon-preform

−30 −20 −10 0 10 20 300

10

20

30

40

50

original shape

ablated shape

recession

Radius, mm

Hei

ght,

mm

Subsonic, 0.3MW/m2, 15hPa

−30 −20 −10 0 10 20 30

original shape

ablated shape

recession

Radius, mm


−30 −20 −10 0 10 20 30

original shape

ablated shape

recession

Radius, mm

Supersonic, 9MW/m2, 80hPa

• linear (axial) recession up to r = 20mm

• small shape change ➟ constant boundary conditions

• edge ablation (shoulder) due to peak heating

• shape change ➟ increase of surface temperature

• high centreline ablation • iso-q shape

➟ caused by shock or nozzle (35mm)

1212

/ 30

Surface Temperature Distribution by IR-imaging

13

1000

1400

1800

2200

1000

1400

1800

2200

1000

1400

1800

2200

1000

1400

1800

2200

Test start Test end

cylindrical

hemispherical

Tstag increase

qcw = 1MW/m2, ps = 15hPa

/ 30

Test Sample Shape Affects Temperatures

14

0 20 40 60 80 1000

500

1000

1500

2000

2500

Time from injection, sTe

mpe

ratu

re, K

0 20 40 60 80 1000

500

1000

1500

2000

2500

Time from injection, s

Tem

pera

ture

, K

qcw = 0.3MW/m2 qcw = 1.0MW/m2

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Test Sample Shape Affects Temperatures

14

hemispherical: quasi-steady

cylindrical: increasing

0 20 40 60 80 1000

500

1000

1500

2000

2500


mpe

ratu

re, K

0 20 40 60 80 1000

500

1000

1500

2000

2500


Tem

pera

ture

, K

cylindrical: lower internal heating

qcw = 0.3MW/m2 qcw = 1.0MW/m2

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Fiber Direction Slightly Affects Temperatures

15

0 20 40 60 80 1000

500

1000

1500

2000

2500


mpe

ratu

re, K

0 20 40 60 80 1000

500

1000

1500

2000

2500


Tem

pera

ture

, K

w-g t-g

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Fiber Direction Slightly Affects Temperatures

15

0 20 40 60 80 1000

500

1000

1500

2000

2500


mpe

ratu

re, K

0 20 40 60 80 1000

500

1000

1500

2000

2500


Tem

pera

ture

, K

through-grain: lower Tswith-grain: higher Ts w-g t-g

with-grain: higher internal temperature • unexpected (lower conduction in axis direction) • but: higher conduction in radial direction ⇨ stronger sidewall heating

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Emissivity: 0.86 - 0.97

16

1600 1800 2000 2200 24000.75

0.8

0.85

0.9

0.95

1

Temperature, K

Emis

sivi

ty, −

PG1

PG2

PG3

PG4

PG5

PG6

Gray body emissivity (8� 9µm, T):

"8�9µm,T =

B(IR)

B

bb(Pyrometer)

Planck’s law (spectral radiance):

B�(T ) =2hc2

�5

1

ehc

�kBT � 1[

Wm2.sr.nm

]

400 500 600 700 8000

2

4

6

8

10

12

Wavelength, nm

Inte

nsity

, W/(m

2 .sr.n

m)

Measured: T = 1724K, ps = 15mbar

Experimental data95% Conf. boundPlanck 1724K, ε = 0.90Planck 1744K, ε = 0.90

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Emissivity: 0.86 - 0.97

16

1600 1800 2000 2200 24000.75

0.8

0.85

0.9

0.95

1

Temperature, K

Emis

sivi

ty, −

PG1

PG2

PG3

PG4

PG5

PG6

Gray body emissivity (8� 9µm, T):

"8�9µm,T =

B(IR)

B

bb(Pyrometer)

Planck’s law (spectral radiance):

B�(T ) =2hc2

�5

1

ehc

�kBT � 1[

Wm2.sr.nm

]

400 500 600 700 8000

2

4

6

8

10

12

Wavelength, nm

Inte

nsity

, W/(m

2 .sr.n

m)

Measured: T = 1724K, ps = 15mbar

Experimental data95% Conf. boundPlanck 1724K, ε = 0.90Planck 1744K, ε = 0.90

w-g

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In-situ Recession Analysis (HSC)

17

0 20 40 60 800

2

4

6

8

Time, s

Rec

essi

on, m

m

Preform

2180K

2848K1724K

>3100K

(15mbar)

0 20 40 60 800

2

4

6

8

Time, s

Rec

essi

on, m

m

AQ61

2884K

2167K>3100K

(15mbar)

➟ diffusion limited at 15mbar between 2000K and 3000K

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17

0 20 40 60 800

2

4

6

8

Time, s

Rec

essi

on, m

m

Preform

2180K

2848K1724K

>3100K

(15mbar)

0 20 40 60 800

2

4

6

8

Time, s

Rec

essi

on, m

m

AQ61

2884K

2167K>3100K

(15mbar)


high T: carbon-phenolic

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17

2347K1686K

2307K

1724K

0 20 40 60 800

2

4

6

8

Time, s

Rec

essi

on, m

m

Preform

2180K

2848K1724K

>3100K

(15mbar)

0 20 40 60 800

2

4

6

8

Time, s

Rec

essi

on, m

m

AQ61

2884K

2167K>3100K

(15mbar)

(15mbar)

w-g

t-g


Tsurface


0 20 40 60 8002468

Time, s

Rec

essi

on, m

m

Preform

/ 30


17

2347K1686K

2307K

1724K

0 20 40 60 800

2

4

6

8

Time, s

Rec

essi

on, m

m

Preform

2180K

2848K1724K

>3100K

(15mbar)

0 20 40 60 800

2

4

6

8

Time, s

Rec

essi

on, m

m

AQ61

2884K

2167K>3100K

(15mbar)

(15mbar)

w-g

t-g

higher recession


Tsurface


0 20 40 60 8002468

Time, s

Rec

essi

on, m

m

Preform

/ 30

Ablation Regimes of Preform and AQ61

18

2000 2500 3000 35000

50

100

150

200

250

Temperature, K

Rec

essi

on ra

te, µ

m/s

Preform 15hPaPreform 80hPaPreform 200hPaAQ61 15hPaAQ61 80hPaAQ61 200hPa

/ 30


➟ diffusion limited ablation and sublimation regime➟ recession not much influenced by pressure! (AIAA 2012-2876)

18

2000 2500 3000 35000

50

100

150

200

250

Temperature, K

Rec

essi

on ra

te, µ

m/s

Preform 15hPaPreform 80hPaPreform 200hPaAQ61 15hPaAQ61 80hPaAQ61 200hPa

/ 30


➟ diffusion limited ablation and sublimation regime➟ recession not much influenced by pressure! (AIAA 2012-2876)➟ strong recession in N2 for T>3000K ➟ sublimation

comparison num. model: talk A. Turchi 18

2000 2500 3000 35000

50

100

150

200

250

Temperature, K

Rec

essi

on ra

te, µ

m/s

Preform 15hPaPreform 80hPaPreform 200hPaAQ61 15hPaAQ61 80hPaAQ61 200hPaPreform N2AQ61 N2

/ 30

Post-Oxidation Micrographs

Carbon preform oxidation

19

AQ61 oxidation

/ 30

Ablation / Pyrolysis Product Contaminated BL

Detection of contamination products originating from phenol 1. pyrolysis ➟ C2, CH, H, NH, OH 2. ablation ➟ C, CN

20

200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950

100

101

102

103

wavelength, nm

inte

nsity

, cou

nts/

s

Emission spectra of carbon−phenolic ablation in air and nitrogen plasma

C248

NH (A−X)

OH (A−X)

CN violet (B−X)

CH (A−X)

C2 Swan

Na

Hβ

Hα

NO777 N lines

Air plasmaNitrogen plasma

/ 30

Boundary Layer Radiation Profiles

CN Production: • gas phase: CO + N ⇌ CN + O • wall: Cw + Nw ⟶ CN

Experimental: Spatial CN violet emission (AIAA 2013-2770)

21

01

23

360 380400 420

20

40

60

80

dist. surf., mmλ, nm

I, W

/(m2 .s

r.nm

)

/ 30




21

01

23

360 380400 420

20

40

60

80


I, W

/(m2 .s

r.nm

)

0 1 2 3 4 5 6 70

200

400

600

800

1000

1200

Distance from surface, mm

I λ1λ2 [W

/(m2 .s

r)]

T = 2180K, ps = 15mbar

Spectrometer 1

Spectrometer 2Spectrometer 3

/ 30




21

01

23

360 380400 420

20

40

60

80


I, W

/(m2 .s

r.nm

)

0 1 2 3 4 5 6 70

200

400

600

800

1000

1200

T = 2180K, ps = 15mbar


I λ1λ2 [W

/(m2 .s

r)]

Exp. dataPolynomial fit95% Conf. bnd

/ 30

VKI: 1D Stagnation line description w/ surface ablation (A. Turchi AIAA 2014-2125)

22

species diffusionmass blowing HOT GAS

MATERIAL

CONTROL VOLUME


Surface Mass Balance (SMB)

[1] Kendall et al., NASA CR 1060 (1968)![2] A. Munafò, PhD Thesis, Ecole Central Paris, 2014

Approach for ablation modelling (Kendall et al.[1])

/ 30


22


MATERIAL

CONTROL VOLUME


convectedenthalpy

convective flux

HOT GAS

MATERIAL

enthalpy by diffusion radiation re-radiation

material conductionenthalpy char mass loss

Surface Mass Balance (SMB)Surface Energy Balance (SEB)



/ 30

Boundary condition from experiments & plasma free-stream Experimental data for validation

GOAL: Coupling 1-D SL-code & material code (PhD Candidate P. Schrooyen)


22


MATERIAL

CONTROL VOLUME


convectedenthalpy

convective flux

HOT GAS

MATERIAL

enthalpy by diffusion radiation re-radiation

material conductionenthalpy char mass loss

Surface Mass Balance (SMB)Surface Energy Balance (SEB)



/ 30


Simulate line-of-sight measurement

Numerical: Simplified approach using Specair slab

23

boundary layer

slab width Δyi at xi

stagn. line solution χi, Ti, pi,

SPECAIR

locations xi

ablating surface

x

y

Ii(λ)

/ 30




23

boundary layer



SPECAIR

locations xi

ablating surface

x

y

Ii(λ)

/ 30




23

boundary layer



SPECAIR

locations xi

ablating surface

x

y

Ii(λ) Perspective: Radiation Coupling (PhD Candidate J.B. Scoggins)

/ 30

Comparison of Boundary Layer Radiation ProfilesExperimental - Numerical

24

0 1 2 3 4 5 6 70

200

400

600

800

1000

1200

T = 2020K, ps = 200mbar


I λ1λ2 [W

/(m2 .s

r)]

Exp. dataPolynomial fit95% Conf. bndNum. data

/ 30


24

0 1 2 3 4 5 6 70

200

400

600

800

1000

1200

T = 2020K, ps = 200mbar


I λ1λ2 [W

/(m2 .s

r)]


0 1 2 3 4 5 6 70

2000

4000

6000

8000

10000

12000

T = 2783K, ps = 200mbar


I λ1λ2 [W

/(m2 .s

r)]


/ 30


24

0 1 2 3 4 5 6 70

200

400

600

800

1000

1200

T = 2020K, ps = 200mbar


I λ1λ2 [W

/(m2 .s

r)]


0 1 2 3 4 5 6 70

2000

4000

6000

8000

10000

12000

T = 2783K, ps = 200mbar


I λ1λ2 [W

/(m2 .s

r)]


/ 30

Comparison of Boundary Layer Radiation Profiles

Locations of maxima BL thickness Order of magnitude

Experimental - Numerical

24

0 1 2 3 4 5 6 70

200

400

600

800

1000

1200

T = 2020K, ps = 200mbar


I λ1λ2 [W

/(m2 .s

r)]


0 1 2 3 4 5 6 70

2000

4000

6000

8000

10000

12000

T = 2783K, ps = 200mbar


I λ1λ2 [W

/(m2 .s

r)]


- no nitridation in model - strong assumption of constant

properties over slab

/ 30

Pyrolysis-Gas Blowing Rate Determination

mpg + mc = (ρV)w

!

mpg = mtot -

25

−30 −20 −10 0 10 20 300

10

20

30

40

50

original shape

ablated shape

recession

Radius, mm

Hei

ght,

mm


(Vabl ˙ ρc)

Carbon Preform (non-pyrol.): ➟ mc = mtot = Vabl ˙ ρc

Non-pyrolyzing carbon-preform

/ 30

Mass Loss Carbon Preform: Weighed vs HSC

26

1 2 3 4 5 6 7 8 9 10 110

2

4

6

8

10

Uncertainty HSC

Test case, #

Tota

l mas

s lo

ss, g

weighedestim. HSC

discrepancy: - water - initial density - damage by

deinstallation

/ 30

AQ61 Pyrolysis-Gas Blowing Rates

27

−30 −20 −10 0 10 20 300

10

20

30

40

50

original shape

ablated shape

recession

Radius, mm

Hei

ght,

mm


Main challenges: Side-wall outgassing, non-1D effects, too-long test times

T p m %AQ1 2167 15 1.12 23AQ6 2884 15 1.77 44

AQ7 2906 200 2.26 60

STA (Simultaneous Thermal Analysis, VKI): charred AQ61: ρc = 80-85% ρv

➟ compare to num. model

/ 30

Conclusions

28

(1) Materials and Methods • hemispherical samples • HSC imaging ➞ volume recession ➞ (4) • IR-camera: emissivity

(2) Char blowing rates • higher recession for fibers through-grain • diffusion limited ablation & sublimation (P+AQ61) • Nitrogen: sublimation and nitridation of surface (SEM)

(3) BL emission • steady ablation process • num. estimation: order of magn., location of maxima, BL thickness

(4) Pyrolysis outgassing • Vol. ablation + TGA ➞ ṁpg

/ 30

Future Work

29

Material: • simultaneous TGA/DSC at VKI of resin, AQ61, Asterm (ongoing) • additional SEM (fiber direction study)

!Modeling:

• rebuild experiments with thermal response model (e.g. SAMCEF Amaryllis, or PATO)

• rebuild boundary layer emission with updated model (nitridation, recombination ➞ talk A. Turchi)

• compare experimental pyrolysis outgassing rates to model

/ 30

AcknowledgementsFunding and materials supply:

30

In particular: N.N. Mansour (NASA ARC),

J. Lachaud (UC Santa Cruz), F. Panerai (University of Kentucky) for informative support !

Jean-Marc Bouilly & Gregory Pinaud (Airbus Defence & Space) !VKI Plasmatron & Ablation Team !VUB SURF research team

/ 30

Oxidation of Preform & AQ61 in air

Carbon preform oxidation

Oxidation of Preform and AQ61

31

AQ61 oxidation

/ 30 32

Preform & AQ61 in nitrogenNitridation Preform

/ 30 32

Preform & AQ61 in nitrogenNitridation Preform

/ 30 33

AQ61 nitrogenAQ61 nitrogen

Preform & AQ61 in nitrogenNitridation AQ61

/ 30 33

AQ61 nitrogenAQ61 nitrogen

Preform & AQ61 in nitrogenNitridation AQ61

/ 30

APPENDIX: Combined Rebuilding Procedure

• Input: Boundary layer parameter (LTE CFD computation) & measurements from experiments

• Procedure: Iteration on boundary layer edge temperature Te: ⇒ qw

n = qwexp = qw(γ, Tw, pe, he, β)

• Output: Edge enthalpy He, boundary layer chemistry, (catalycity) 34

M"<<"1"TPS"sample"

Ground'test'measurements'Navier0Stokes0domain'EM0field'

domain'

Coupled'domain' Boundary'layer'parameter'

VKI'ICP'code'(LTE'assumpCon)'

qw,'Tw,'ps,'pd'

Boundary Layer Solver

/ 30

Complex Multiphysics - Multiscale problem

Gas-phase • Ablation species injection • Strong radiators and boundary

layer absorption !Gas-surface interaction • Surface reactions & recombination • Recession rate !Material • Pyrolysis gases production and

outgassing

chemical(species((diffusion(

surface(recession(

virgin(material(

pyrolysis((zone(

porous(char(

hot(radia7ng(gas(

boundary(layer(

convec7ve((heat(flux(

radia7on(flux((

shock(heated(gas((T(~(10,000K)(

heat(transfer(

mechanical(erosion(

pyrolysis(gases(

reac7on(products(

OH( OH(

35

Coupled phenomena

/ 30

CN Radiation Simulation for Temperature EstimationNon-equilibrium?

36

370 380 390 400 410 420 4300

0.2

0.4

0.6

0.8

1

wavelength [nm]

norm

aliz

ed in

tens

ity [−

]

ASTERM, ps = 15mbar, TS = 2130K

ν′=0→ν′′=0

ν′=3→ν′′=3

Experimental spectrum

370 380 390 400 410 420 4300

0.2

0.4

0.6

0.8

1

wavelength [nm]no

rmal

ized

inte

nsity

[−]


ν′=0→ν′′=0

ν′=3→ν′′=3

Experimental spectrum

/ 30

CN Radiation Simulation for Temperature EstimationNon-equilibrium?

36

370 380 390 400 410 420 4300

0.2

0.4

0.6

0.8

1

wavelength [nm]

norm

aliz

ed in

tens

ity [−

]


Trot = 9281K ± 640K

Tvib = 14912K ± 1100K

Experimental spectrumSPECAIR simulation

370 380 390 400 410 420 4300

0.2

0.4

0.6

0.8

1

wavelength [nm]no

rmal

ized

inte

nsity

[−]


Trot = 6311K ± 350K

Tvib = 7878K ± 320K

Experimental spectrumSPECAIR simulation

Non-thermal vibrational level distribution at low pressure (AIAA 2013-2770) ➟ Thermal non-equilibrium? ➟ Deviation from Boltzmann distribution?

/ 30

Boundary Layer Temperature ProfileNon-equilibrium at the wall?

37

0 1 2 3 4 5 2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

distance from surface [mm]

tem

pera

ture

[K]

ps = 15mbar, TS = 2130K

TrotTvib

0 1 2 3 4 5 2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

distance from surface [mm]te

mpe

ratu

re [K

]

ps = 100mbar, TS = 2097K

TrotTvib

Documents

Gas Surface Interaction Study of Low Density Ablators in ... · 6/26/2014 · Gas/Surface Interaction Study of Low-Density Ablators in Sub- and Supersonic Plasmas! ... 1.2-MW Inductively