validation of aerothermal chemistry models for re-entry...

Validation of Aerothermal Chemistry Models for Re-entry Applications: Theoretical and

Computational Synthesis

N. Joiner, J. Beck, M. Capitelli, M. Fertig, G. Herdrich, A. Laricchiuta, H. Liebhart, M. Lino da Silva,

L. Marraffa, P. Reynier, P. Tran

8th European Symposium on Aerothermodynamics for Space Vehicles Lisbon 2-6 March 2015

Fluid Gravity Engineering Ltd

Introduction

•  Synthesis of ESA TRP 2008-2012 •  Large multi-institutional team involved

–  FGE, ISA, IRS, ADS (then Astrium), LAEPT, MIPT, IST, IMIP, EM2C, IUSTI, CEA

•  Highlights of theoretical and numerical effort presented here –  Extensive numerical campaigns, multiple codes –  Not covered here: Material response codes also validated –  P. Reynier et al., Thursday morning in this symposium for

experimental synthesis


Introduction

•  Aim: to enhance operational software underlying European capability to design an atmospheric entry vehicle

–  Support high speed earth return –  Support potential high speed Titan entry

•  These mission scenarios can include substantial radiative heating

•  Multi-temperature CFD models used to anchor heating correlations in TPS design

–  Limitation: coupling of excited internal states and chemical non-equilibrium

•  State-of-the-art Collisional Radiative (CR) and State-to-State (STS) too computationally expensive for engineering level CFD

–  Underlying features of CR/STS must be captured to optimise TPS design –  Inputs to CR/STS typically ab initio rate coefficients, cross-sections, etc.

•  Potential to employ input data in reduced form to capture physics


Objectives •  High Speed Entry Vehicle Design Tool Requirements

–  Radiation capability •  Need N, N2 for Earth entry in VUV and UV-visible

–  Identified form earlier Radflight, FIRE II, aero-capture studies »  90% VUV, no significant contribution from other species

–  Focus on assimilation and development of data for N and N2

–  PARADE 11-species air QSS model developed

•  Need CN model for Titan entry –  Astrium QSS models available from Huygens studies –  General CR capability added to PARADE and CFD codes

–  Validation •  Require high speed data •  Literature ground tests •  New ground tests •  Existent flight data •  Extrapolation to new flight scenarios


Air model development •  Data assimilation

–  9 band N2 PARADE database (IRS) •  VUV bands (previously only Birge-Hopfield II)

–  Birge-Hopfield I , Birge-Hopfield II, Lyman-Birge-Hopfield, Worley, Worley-Jenkins, Carroll-Yoshino, e’X

•  Others –  First positive and second positive

–  Survey of electron impact excitation rates compiled for all molecules (IST)

–  Consolidated mapping of coalesced states of atomic nitrogen

•  Missing data development –  Ab initio computations of electron impact excitation data and

predissociation branching ratios (IMIP-CNR) Fluid Gravity Engineering Ltd

Air QSS Model Development •  Quasi-Steady-State (QSS)

–  Solution of detailed balance of electronic states, assuming that dominant excitation/relaxation rates are fast enough to establish local steady-state (Park)

–  Applied as post-process (attractive for rapid assessments)

•  PARADE is a NEQAIR85 descendant –  Decouple to allow other (new) data to be input –  Early PARADE version unstable, or Boltzmann populations

often recovered

•  QSS model improvements –  Greater stability

•  Hierarchical solution method –  Saha-Boltzmann equation incorporated into expansion of the

coalesced states –  Inclusion of new TRP data


N2 Model Improvements •  Large reduction in VUV contribution

–  Typical high speed simulations VUV accounts 20-30% of total


10−4

10−2

100

102

104

0 5000 10000 15000 20000 25000 30000 35000 40000

I h(W

/m2 /Å

)

h(Å)

Boltzmann (Original Data)Boltzmann (Improved N2 data)

QSS (Best available data)

10−210−1100101102103104105

800 1200 1600 2000

Air Validation

•  Validation of non-equilibrium radiation predictions against NASA EAST shock-tube –  At the time no reliable VUV data available –  TRP produced VUT-1 data looks CN contaminated –  Validate the QSS methodology with non VUV

bands and atomic lines •  Cross code verification against flight cases

–  Stardust and FIRE II


Air Validation


700-760nm 760-800nm

800-830nm 850-880nm

•  V=10.34km/s P= 40Pa •  Nitrogen and oxygen lines

•  EAST data: Johnston AIAA 2008-1245, Grinstead et al AIAA 2008-1244

Air Validation •  V=9.66km/s, P=13.3Pa •  290-480nm •  N2 and N2

+ important in this spectral range

•  Much improvement over Boltzmann predictions

Above figure taken from Johnston AIAA 2008-1245

Fire II (Equivalent sphere)


•  Super Catalytic convective fluxes agree with Johnston et. al JSR 45 pp.1185 (2008) (~300W/cm2 with out carbuncle)

•  Reduction of ~30% of radiative flux in agreement with Johnston et. al, although radiative fluxes are ~15% larger

•  Convective flux at stagnation often quoted by other authors is ~200W/cm2 (Non-catalytic result in Johnston et al, Hash et. al AIAA 2007-605, fully catalytic result in Greendyke and Hartung JSR 31 pp.986 (1994))

•  Total heat flux obtained from flight data is ~290W/cm2

!

!

Air Model Outlook

•  Significant improvement over Boltzmann model •  Number of recommendations for engineering models

–  Availability of non-equilibrium VUV validation data in short supply (very limited in Europe)

–  Implementation of new N2 data as a CR model •  parameterise QSS region of validity

–  Further investigation into chemical kinetics of oxygen ionisation

•  An early campaign of the ESTHER shock tube is planned to provide VUV validation data and develop the tools further –  New review of most up-to-date CR/STS models and data

required Fluid Gravity Engineering Ltd

Titan Model Development •  Astrium-ST developed Huygens QSS model for TPS

sizing –  Developed due to margin requirements for Huygens –  Implemented in operational codes as a CR model for the TRP –  Gockçen chemical kinetics (neglecting ionisation) baseline for TRP

•  CR model –  Pseudo-species representing excited states computed in CFD code –  CN(X),CN(A),CN(B) (data also available for three state N2 model) –  Arrhenius rates for production through chemistry and excitation

reactions –  Populations input directly to radiation database –  Quenching and resonant reaction species approximated by

Boltzmann population where not available in CR model

•  Validation and application at high speed –  EAST and TRP VUT-1 shock tube data


Huygens Validation •  EAST v= 5.15km/s P=13.3Pa

data (Bose et al JTHT 2006) •  Operational codes brought into

line with other codes •  Airbus DS (Astrium) results

top figure –  Low Sensitivity to kinetic models

(Chemical and CR) –  Review of ionisation reaction

kinetics required

•  Vibrationally specific models in literature shown to capture relaxation rate better

•  Possible EAST data discrepancy (next slide)

Fluid Gravity Engineering Ltd !

Distance (cm)

PWR(W/cm2.sr)

0 5 10 15

10-2

10-1

100

101

Experimental data EAST CASE 1 - P=13.3 PaCASE 1.1 : AST thermochem. model 1 + TRP CR modelCASE 1.2 : AST thermochem. model 2 + AST CR modelCASE 1.3 : AST thermochem. model 2 + TRP CR modelCASE 1.4 : AST thermochem. model 1 + AST CR modelCASE 1.5 : AST thermochem. model 1 + Boltzmann radiationCASE 1.6 : AST thermochem. model 1 + TRP CR model , activation TCASE 1.7 : AST thermochem. model 2 + AST CR model , activation T

EAST FACILITY - 2% CH4 98% N2 - P=13.3 PaSpec. Range 400 - 430 nm

EAST result 13.3 Pa- TRP Aerochemistry 12 Apr 2011 | | |

Huygens Validation


•  Brandis et al JTHT 2010 –  All conditions reproduced

except this one

•  Intensity scaled by 1/3 to fit X2 data

•  CR model now more conservative

•  Can bring the computation to scaled intensity –  Neglect resonant reactions

–  Include ionisation and

electron impact excitation in CR model

CN(X)+ N2 (X,v = 4)↔ CN(A)+ N2 (X,v = 0)CN(X)+ N2 (X,v = 11)↔ CN(B)+ N2 (X,v = 0)

!

Huygens Probe


•  C2, N2, N also included in radiation calculations with a Boltzmann distribution

•  Convective and radiative fluxes reduced by radiation coupling –  ~15% reduction in total heat flux at stagnation point

•  Coupled and uncoupled stagnation point fluxes in excellent agreement with Osawa et al. JTHT 22, 140 (2008)

Titan High Speed Validation


•  VUT-1 : V=8km/s P=25Pa •  Velocity consistent with

peak radiative fluxes on high speed entry

•  Intensity in reasonable agreement with experiment

•  Collision frequency of CN(X) estimated to be ~6x106s-1

•  CN(B) decay rate ~1.5x107s-1

•  Boltzmann-like distribution not unlikely

Titan High Speed Validation

•  Compare high speed case with EAST high pressure case

•  V=5.93km/s P=133Pa •  270-470nm •  Collision frequency of CN(X)

estimated to be ~3x107s-1

•  CN(B) decay rate ~1.5x107s-1 •  Absorption required in

detailed balance to obtain Boltzmann distribution


!

Titan High Speed Entry

•  Apply high speed condition to Huygens aeroshell

•  Boltzmann and CR models computed

•  Convective flux larger than radiative flux

•  Radiative fluxes lower than expected (~800W/cm2 from Huygens correlations)

•  There is still a non-equilbrium effect

–  To be confirmed with tighter radiation coupling


Titan Model Outlook

•  Evidence suggests some disparity in kinetics –  Gokçen kinetics for ionisation require review –  Vibrationally specific model required?

•  Recommended as priorities for ESTHER shock-tube investigation

•  Model appears to be conservative for Huygens –  But not as conservative as Boltzmann assumption

•  High speed Titan mission design –  Initial validation encouraging

•  Boltzmann or CR may be suitable

–  Higher post-shock densities è tighter radiation coupling in operational codes


Conclusions •  Non-equilibrium radiation models for CN (Collisional Radiative)

and 11-species air (QSS) have been developed for ESA operational engineering tools

•  The models have been validated against experimental shock tube data, and are found to provide more accurate assessment of radiative emission than a Boltzmann model.

•  The models have been applied to flight cases, with a loosely coupled scheme; the results generally compare well with cases found in the literature

•  The validation of the models and successful rebuilding of flight cases suggests that they are currently suitable for mission design and evaluation


validation of aerothermal chemistry models for re-entry...

Documents