proceedings of 24th european workshop on thermal … properties enhanced through material...

85

Appendix F

Development of numerical tools for design and verification ofablative thermal protection systems

Marco Giardino Elena Campagnoli(Politecnico of Turin, Italy)

Gianni Pippia(Sofiter System Engineering, Italy)

Massimo Antonacci(Thales Alenia Space, Italy)

24th European Workshop on Thermal and ECLS Software 1617 November 2010

86Development of numerical tools for design and verification of ablative thermal protection

systems

Abstract

In recent years there has been a great collaborative work between Thales Alenia Space Italia and theEnergetic Department of Politecnico of Turin devoted to the study of ablative heat shields. Two differentnumerical tools for the analysis of the behaviour of charring ablative materials have been developedwithin the frame of a co-founded internal research program.The first of these tools, called Ablatherm, is a Matlab R-based code that can be used during the initialdesign phase: it implements a simple model (that uses a very reduced set of material properties), it hasa short case settings time and execution time and it is very flexible (it can be used both through a scriptfile or a Graphical User Interface). This tool was tested using analytical benchmarks and real test casesand is now used by TAS-I for heat shield design.The second tool, still under development, uses the state of the art both for the model and for the toolimplementation, in order to perform rapid, full 3D simulations. This tool, developed on OpenFoamplatform, implementing a more complex model and requiring higher test case setup time and a hugeamount of material data that must be provided for a full run, is mainly intended for final verification ofthe full system configuration. For an intermediate design phase, it is also possible to use this second toolwith a reduced set of parameters.


24th European Workshop on Thermal and ECLS Software ESTEC, 16-17 November 2010

DEVELOPMENTOFNUMERICALTOOLSFORDESIGN ANDVERIFICATION

OFABLATIVETHERMALPROTECTIONSYSTEMS

MarcoGiardino

(Politecnico

ofTurin,Italy)ElenaCampagnoli

(Politecnico

ofTurin,Italy)

GianniPippia

(Sofiter

SystemEngineering,Italy)MassimoAntonacci

(ThalesAlenia

Space,Italy)


Index

Ablativeheatshields

Characteristicoftheusedmodels

1Dmodel

AblaTherm

Specifications

Necessarydata

Implementation

Validationvs.CMA

Validation

vs.SAMCEFAmaryllis

3Dmodel

Specifications

Necessarydata

Implementation

Testcasedefinition

Testcaseresults

Validation

vs.AblaTherm

Futureworks

Development of numerical tools for design and verification of ablative thermal protectionsystems 87



Ablativeheatshields

Notreusable.

Lightweight.

Adaptabletomissionconstraints.

Heatinsulationpropertiesenhanced throughmaterialdegradation.

SuitableforentryvehicleandSRCs.


Characteristicoftheusedmodels

1DMODELABLATHERM

Local1Dassumption.

Simplemodel.

Reducedsetofparameters.

Multilayercapability.

Extremelylowsetuptimeand executiontime.

Idealduringinitialdesignphase.

3DMODEL

Full3DCartesiansolver.

Stateoftheartmodel.

Highnumberofparameters (possibleuseofareducedset).

Multiplematerialwithin

thedomain

Isnottoomuchuserfriendly.

Relativelylongsetupandruntime.

Tobeusedforfinal,fullbody simulation.


systems



1DModel

Analyticalmodel

Oneequationmodel(energyconservation)+BC:

Charringmaterial(Arrheniusequation).

Internalheatfluxqc

(t):adiabatic,convectiveand/orradiative

heatflux.

Surfaceheatfluxboundarycondition:

)(),(

)(,0

0

0),(),(

0

tqttsxxT

tqtxxT

xTtTt

THxTT

xtTTc

w

c

p

heatRecession

fluxheat radiative

Surface

flux External

Blowingfluxheat

Net wall00

sQqqqq carbreceradradconvw


1DModel

Necessarydata

Materialproperties:

Virginandcharreddensities.

Arrheniuscoefficients.

Pyrolysis

reactionandsurfacerecessionenthalpy.

Temperaturedependenceofspecificheat,thermalconductivity, surfaceemissivity,bothforvirginandcharredmaterial.

Heatfluxdata(asfunctionofsurfacetemperature,coldwallevaluation, netvalues).




1DModel

Implementation

FiniteElementMethod(FEM)discretisation.

NonlinearNewtonRaphson

methodforfastandaccuratenonlinearity resolution(surfaceradiation).

Automaticgridgeneration,withlinearpluslogarithmicspacing;

formulti layercases,thenumberofelementsperlayercalculatedthrough

mean

conductivity.

Blowing

evaluation

atrun

time.

Initialsteadystatetemperaturedistributionevaluation.

ImplementedusingMatlab

environment.

Usable

as

command

line

function

orthrough

aGraphical

User

Interface (GUI).


Performedbymeansofcomparisonwithcommercial1Dsoftware(CMA):

Testcases sizingofasiliconbasedablatorondifferentareasofthe externalsurfaceofareentryvehicle.

Availablethermalablativepropertieshavebeenimplementedin bothcodes.

Thermalsimulationextendedinthe1Dsimplifiedcodetothe reproductionoftheconvectiveandradiative

heatexchangeinside

thevehicle.

Thepyrolysis

heatbehaviourasfunctionofmaterialtemperaturehas

beenintroducedinAblaTherm.

W.r.t.CMA,AblaTherm

doesnotaccountfor:

Surfacetransportofchemicalenergy.

Convectivetransferbypyrolysis

gases:

Differenceinsizingresultslowerthan


CMA simulation

AblaTherm

simulation

Caseonvehiclereentry.

Differentmodellingofsurfacethermo chemistry.

Sizingresults(i.e.shieldthickness)differfor lessthan10%.

1DModel

Validationvs.CMA


-200

0

200

400

600

800

1000

1200

1400

1600

0 50 100 150 200 250

1)2)3)4)5)

-120

-100

-80

-60

-40

-20

0

20

40

60

80

0 50 100 150 200 250

2)3)4)5)

ComparisonwithsimulationresultsofaMarsentryvehiclefrontshield:

SHIELDSURFACE

1) Amaryllis simulation results2) Empty3) AblaTherm

results, with prescribed heat fluxes correction4) AblaTherm, with ABLAT heat fluxes correction5) AblaTherm, with foam conductivity as function of atmospheric pressure

T [

C]

time

[s]

T

[C

]

time

[s]

1DModel

Validationvs.SAMCEFAmaryllis




-50

0

50

100

150

200

0 50 100 150 200 250

1)2)3)4)5)

T [

C]

time

[s]

-120

-100

-80

-60

-40

-20

0

20

40

60

80

0 50 100 150 200 250

2)3)4)5)

T

[C

]

time

[s]




ABLATIVE/COLDSTRUCTUREINTERFACE

1DModel



-50

0

50

100

150

200

0 50 100 150 200 250

1)2)3)4)5)

T [

C]

time

[s]

-4

-2

0

2

4

6

8

10

12

0 50 100 150 200 250

2)3)4)5)

T [

C]

time

[s]




COLDSTRUCTURE/INTERNALFOAMINTERFACE

1DModel



systems



3DModel Analitical model

3equationmodel(energy,solidmassandgasmassconservationequations)+ closureequations(Idealgaslaw,Darcylaw)+BC(Amar,A.J.Modelingof

OneDimensionalAblationwithPorousFlowUsingFiniteControlVolume Procedure,NorthCarolinaStateUniversity,2006

).

Pyrolysis

gasinlocalthermalequilibrium.

Pyrolysis

energyabsorptionthroughmixtureinternalenergyevaluation.

Charring

material(Arrheniusequation).

Surface

BCunderdevelopment.

gg

g

V Vgmeshg

Vgg

Vg

Vi

Vmesh

Vi

Vmesh

VVggg

V

MTp

pKv

dVmdSnvdSnvdVdtd

nidVmdSnvdVdtd

dSnvhdSnTkdSnvhedVdtd

,..,1for

0


3DModel

Necessarydata

Materialandgasproperties:

VirginandcharredsubdensitiesandArrheniuscoefficientsforeach decompositionreaction,materialcompositioncoefficients.

Solid:temperaturedependenceofspecificheat,thermalconductivity, surfaceemissivity,bothforvirginandcharredmaterial.Extent

of

reactionsdependenceofporosityandgaspermeability.

Gas:temperaturedependenceofspecificheat,gasmolecularmass andviscosity.

Formationenthalpyandreferencetemperatureforvirgin,charand gas.

BC:differentstandardconditions,somespecificunderdevelopment.




3DModel

Implementation

FiniteVolumeMethod(FVM)discretization.

ImplementedusingtheopensourceOpenFOAM

suite.Advantages:

parallelruninbothsharedanddistributedmemorymachines(MPI protocol,onworkstationorclusters).

Basedonopensourceplatform(Linux)andopensourcesuite.

Useunstructuredgrid(complexgeometricshapes,differentcellshapes).

Gridimportationcapabilities.

Simplifiedmodelwich

canrunneglectingthegaseffects(nongasdata needed)


3DModel

testcase

Geometry

andgrid:10x10cm,100x400cells.

Boundary

conditions:

Northside:time

variable,uniform

external

heat

flux

:

with

surface

reradiation;time

variable

uniform

pressure:

SouthandEastside:adiabatic

andimpermeable.

Westside:impermeable,time

variable

uniform

temperature:

Materialdata:PICA15

NASATM110440(1997).

22 1000100100sin611100 mWttettq

Patetp 200

52

KttT 3001000

sin25002


systems



3DModel

Results

1

Performances:solution

time

ona8coreworkstation

1400s.

Following

moviedescription:

Backgroundcolor:materialdensity(red

max,blue

min).

Colored

lines:isotemperaturelines,colored

with

temperaturescale; lines

at[(300:20:400)(600:200:3800)]K.

Vectors:oriented

using

pyrolysis

gasvelocity

andcolored

using pyrolysis

gasvelocity

magnitude.





systems

Slow Normal Fast Play/Pause Stop


3DModelValidationvs.AblaTherm

Thesolutionsobtainedusingthetwocodesarecompared.Toperformthe comparison,thefollowingstepswereperformed:

Ablatherm

runwasperformedneglectingsurfacerecessionand applyingthesameprofilefortheheatflux(withouttheblowing correction).

3Dcoderun:temperaturesolutionextractedontheEastsideofthe domain(negligible2Deffects).


video2d.swfMedia File (application/x-shockwave-flash)



3DModel

Validation

vs.AblaTherm

Slow Normal Fast Play/Pause Stop


videocomparison.swfMedia File (application/x-shockwave-flash)


3DModel

Validation

vs.AblaTherm


Futureworks

Finalization

of

the3Dcode:

surface

recession

models

implementation.

Different

surface

heat

flux

Boundary

Conditions

implementation.

Studies

for

integration

with

ESATAN.


systems



ANYQUESTIONS?

THANKSFORYOURATTENTION.



100


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