Barnhardt, Michael

Candler, Graham

Nompelis, Ioannis

Schwartzentruber, Tom

Stern, Eric

English

University of Kentucky

NASA Space Technology Research FellowshipMicroscale	  Modeling	  of	  Abla1ve	  Thermal	  Protec1on	  System	  MaterialsEric	  Stern,	  Graham	  Candler,	  Tom	  Schwartzentruber,Ioannis	  Nompelis,	  Michael	  Barnhardt11NASA Space Technology Research FellowshipAbla1on	  Modeling• Engineering	  material	  response	  codes	  in	  use	  today	  take	  a	  macroscopic	  view	  of	  the	  TPS.• Typically	  involve	  heavy	  empiricism,	  and	  many	  assump1ons22NASA Space Technology Research FellowshipTPS	  Modeling• The	  goal	  of	  this	  work	  is	  to	  beGer	  model	  processes	  at	  the	  micro-­‐scale	  to	  inform	  macro-­‐scale	  models.– Volume	  averaging.– Model	  reduc4on!• This	  will	  aGempt	  to	  build	  and	  expand	  on	  previous	  efforts	  in	  micro-­‐scale	  modeling	  by	  enabling	  more	  physics	  3 Lachaud, et al., JSR, 20103NASA Space Technology Research FellowshipTPS	  Modeling• The	  goal	  of	  this	  work	  is	  to	  beGer	  model	  processes	  at	  the	  micro-­‐scale	  to	  inform	  macro-­‐scale	  models.• ...as	  well	  as	  build	  a	  framework	  where	  higher	  fidelity	  models	  can	  be	  incorporated	  from	  the	  nanoscale4Poovathingal, et al., J. Phys. Chem., 201312 Lachaud, et al., JSR, 20104NASA Space Technology Research FellowshipOutline• Methodology– DSMC– Surface	  Genera4on	  and	  Movement– Coupled	  Abla4on• Preliminary	  Valida1on	  and	  Applica1ons– Simplified	  Darcy	  Flow– Flow-­‐tube	  Permeability	  Experiments• Future	  Work55NASA Space Technology Research FellowshipWhy	  DSMC?• First:	  what	  is	  DSMC?• Knudsen	  numbers	  in	  the	  porous	  medium	  range	  from	  high-­‐slip	  to	  rarefied	  regimes.• DSMC	  can	  (in	  principle)	  simulate	  all	  of	  the	  relevant	  physics.	  – Convec4on– Mul4component	  Diffusion– Gas-­‐phase	  Kine4cs	  – Sophis4cated	  GSI	  Models– Non-­‐equilibrium	  handled	  inherently• DSMC	  can	  simulate	  arbitrarily	  complex	  geometries6 Lachaud, et al., JSR, 20106NASA Space Technology Research FellowshipMGDS2• Parallel	  implementa1on	  of	  the	  DSMC	  method	  developed	  at	  the	  University	  of	  Minnesota.– 3-­‐Level	  Cartesian	  Mesh– Automated	  Mesh	  Refinement– Models	  for	  dissocia4on,	  vibra4onal/rota4onal	  relaxa4on.7 1. Zhang and Schwartzentruber., Comp. and Fluids, 20122. Nompelis and Schwartzentruber, AIAA Paper, 20147NASA Space Technology Research FellowshipMGDS2• Parallel	  implementa1on	  of	  the	  DSMC	  method	  developed	  at	  the	  University	  of	  Minnesota.– 3-­‐Level	  Cartesian	  Mesh– Automated	  Mesh	  Refinement– Models	  for	  dissocia4on,	  vibra4onal/rota4onal	  relaxa4on.8 1. Zhang and Schwartzentruber., Comp. and Fluids, 20122. Nompelis and Schwartzentruber, AIAA Paper, 20148NASA Space Technology Research FellowshipMGDS2• Parallel	  implementa1on	  of	  the	  DSMC	  method	  developed	  at	  the	  University	  of	  Minnesota.– 3-­‐Level	  Cartesian	  Mesh– Automated	  Mesh	  Refinement– Models	  for	  dissocia4on,	  vibra4onal/rota4onal	  relaxa4on.9 1. Zhang and Schwartzentruber., Comp. and Fluids, 20122. Nompelis and Schwartzentruber, AIAA Paper, 20149NASA Space Technology Research FellowshipMGDS2• Parallel	  implementa1on	  of	  the	  DSMC	  method	  developed	  at	  the	  University	  of	  Minnesota.– 3-­‐Level	  Cartesian	  Mesh– Automated	  Mesh	  Refinement– Models	  for	  dissocia4on,	  vibra4onal/rota4onal	  relaxa4on.10 1. Zhang and Schwartzentruber., Comp. and Fluids, 20122. Nompelis and Schwartzentruber, AIAA Paper, 201410NASA Space Technology Research FellowshipMGDS2• Parallel	  implementa1on	  of	  the	  DSMC	  method	  developed	  at	  the	  University	  of	  Minnesota.– 3-­‐Level	  Cartesian	  Mesh– Automated	  Mesh	  Refinement– Models	  for	  dissocia4on,	  vibra4onal/rota4onal	  relaxa4on.11 1. Zhang and Schwartzentruber., Comp. and Fluids, 20122. Nompelis and Schwartzentruber, AIAA Paper, 201411NASA Space Technology Research FellowshipMGDS2• Parallel	  implementa1on	  of	  the	  DSMC	  method	  developed	  at	  the	  University	  of	  Minnesota.– 3-­‐Level	  Cartesian	  Mesh– Automated	  Mesh	  Refinement– Models	  for	  dissocia4on,	  vibra4onal/rota4onal	  relaxa4on.12 1. Zhang and Schwartzentruber., Comp. and Fluids, 20122. Nompelis and Schwartzentruber, AIAA Paper, 201412NASA Space Technology Research FellowshipMGDS2• Some	  addi1onal	  features	  have	  been	  added	  to	  the	  code	  specifically	  for	  this	  work.– Ini4aliza4on	  of	  simula4on	  to	  CFD	  (using	  US3D).– Subsonic	  Boundary	  Condi4ons– Simple	  gas-­‐surface	  interac4on	  model– Abla4on	  modules1313NASA Space Technology Research FellowshipMGDS2• Some	  addi1onal	  features	  have	  been	  added	  to	  the	  code	  specifically	  for	  this	  work.– Ini4aliza4on	  of	  simula4on	  to	  CFD	  (using	  US3D).– Subsonic	  Boundary	  Condi4ons– Simple	  gas-­‐surface	  interac4on	  model1414NASA Space Technology Research FellowshipMGDS2• Some	  addi1onal	  features	  have	  been	  added	  to	  the	  code	  specifically	  for	  this	  work.– Ini4aliza4on	  of	  simula4on	  to	  CFD	  (using	  US3D).– Subsonic	  Boundary	  Condi4ons– Simple	  gas-­‐surface	  interac4on	  model– Abla4on	  modules1515NASA Space Technology Research FellowshipMGDS2• Some	  addi1onal	  features	  have	  been	  added	  to	  the	  code	  specifically	  for	  this	  work.– Ini4aliza4on	  of	  simula4on	  to	  CFD	  (using	  US3D).– Subsonic	  Boundary	  Condi4ons– Simple	  gas-­‐surface	  interac4on	  model– Abla4on	  modules1616NASA Space Technology Research FellowshipMGDS2• Some	  addi1onal	  features	  have	  been	  added	  to	  the	  code	  specifically	  for	  this	  work.– Ini4aliza4on	  of	  simula4on	  to	  CFD	  (using	  US3D).– Subsonic	  Boundary	  Condi4ons– Simple	  gas-­‐surface	  interac4on	  model– Abla4on	  modules1717NASA Space Technology Research FellowshipOutline• Methodology– DSMC– Surface	  Genera4on	  and	  Movement– Coupled	  Abla4on• Preliminary	  Valida1on	  and	  Applica1ons– Simplified	  Darcy	  Flow– Flow-­‐tube	  Permeability	  Experiments• Future	  Work1818NASA Space Technology Research FellowshipFiberGen• The	  objec1ve	  is	  to	  develop	  a	  tool	  that	  is	  able	  to	  generate	  triangulated	  surface	  meshes	  of	  random	  arrays	  of	  “fibers”	  to	  use	  in	  microscale	  simula1ons.• We	  have	  developed	  FiberGen	  with	  the	  following	  features:– It	  can	  generate	  2D	  and	  3D,	  random	  and	  non-­‐random	  arrays	  of	  cylindrical	  fibers.– The	  user	  specifies	  a	  box	  size	  to	  fill	  with	  fibers,	  and	  a	  target	  porosity.– The	  user	  can	  prescribe	  proper4es	  such	  as	  nominal	  fiber	  diameter,	  fiber	  length,	  angular	  biases	  (i.e.	  orthotropy),	  as	  well	  as	  variance	  and	  distribu4on	  in	  each.– Triangulated	  surface	  is	  output	  in	  STL	  format.– It	  also	  includes	  a	  post-­‐processor	  for	  analyzing	  the	  geometry.1919NASA Space Technology Research FellowshipFiberGen• Addi1onally,	  the	  code	  creates	  data	  structures	  for	  the	  mesh	  which	  are	  used	  for	  evolving	  the	  surface.• Fiber	  data	  structures	  are	  wriGen	  to	  HDF5	  format	  for	  efficient	  I/O	  in	  massively	  parallel	  applica1ons.20Example geometry having porosity of 0.85, and nominal fiber radius of 6 micron. The figure on the right is of the same geometry after having undergone a prescribed “ablation.”20NASA Space Technology Research FellowshipSurface	  Data	  Structure21– The	  surface	  is	  composed	  of	  many	  fibers– Each	  fiber	  is	  composed	  of	  discrete	  elements	  along	  the	  axis.– Each	  element	  contains	  many	  triangles	  on	  their	  surfaceSURFACEFIBERSELEMENTSTRIANGLES21NASA Space Technology Research FellowshipSurface	  Movement22V1 V2 V3 V4 V5– Now	  we	  would	  like	  to	  leverage	  this	  framework	  do	  develop	  an	  efficient	  method	  for	  evolving	  the	  surface	  under	  the	  influence	  of	  surface	  reac4ons	  (abla-on)– We	  begin	  by	  compu4ng	  and	  storing	  the	  volume	  of	  each	  element	  for	  each	  fiber.22NASA Space Technology Research FellowshipSurface	  Movement23V1 V2 V3 V4 V5V1 V2 V3 V4 V5– We	  then	  update	  the	  element	  volumes	  as	  the	  simula4on	  progresses,	  and	  reac4ons	  on	  the	  triangles	  remove	  material	  from	  the	  fibers.– An	  effec4ve	  radius	  that	  yields	  a	  straight	  cylinder	  of	  the	  same	  volume	  is	  computed	  for	  each	  element.23NASA Space Technology Research FellowshipSurface	  Movement24V1 V2 V3 V4 V5– The	  radius	  on	  each	  side	  of	  each	  element	  is	  then	  defined	  as	  the	  average	  between	  it	  and	  it’s	  neighbor.	  – The	  surface	  is	  then	  reconstructed	  from	  conical	  frustum	  segments.V1 V2 V3 V4 V524NASA Space Technology Research FellowshipSurface	  Movement25V1 V2 V3 V4 V5– Note:	  there	  is	  error	  in	  the	  volume	  of	  the	  reconstruc4on,	  however	  we	  always	  track	  and	  operate	  on	  the	  actual	  volume,	  so	  mass	  is	  conserved.	  – The	  surface	  is	  then	  reconstructed	  from	  conical	  frustum	  segments.V1* V2* V3* V4* V5*25NASA Space Technology Research FellowshipSurface	  Movement26This	  treatment	  is	  able	  to	  replicate	  some	  of	  the	  dominant	  morphologies	  we	  observe	  at	  the	  micro-­‐scale.– non-­‐uniform	  thinning– “needling”26NASA Space Technology Research FellowshipSurface	  Movement• This	  reconstruc1on	  method	  could	  be	  thought	  of	  as	  a	  Axisymmetric	  Volume	  of	  Fluid	  (VoF)	  approach.• Benefits:– Rela4vely	  easy	  to	  implement– Error	  in	  volume	  is	  small	  and	  bounded	  for	  our	  work	  (<1%)– Extending	  code	  to	  modeling	  fiber	  material	  response	  would	  be	  (fairly)	  straighjorward	  (i.e.	  solving	  the	  heat	  conduc4on	  equa4on	  is	  quasi-­‐1D).– Surface	  reconstruc4on	  is	  very	  fast• Limita1ons:– Limited	  to	  axisymmetric	  shapes– Not	  easily	  extensible	  to	  tomography-­‐generated	  surfaces2727NASA Space Technology Research FellowshipOutline• Methodology– DSMC– Surface	  Genera4on	  and	  Movement– Coupled	  Abla4on• Preliminary	  Valida1on	  and	  Applica1ons– Simplified	  Darcy	  Flow– Flow-­‐tube	  Permeability	  Experiments• Future	  Work• Conclusions2828NASA Space Technology Research FellowshipGas-­‐Surface	  Interac1on	  Modeling• In	  DSMC,	  the	  gas	  surface	  interac1on	  is	  modeled	  by	  determining	  the	  probability	  that	  a	  gas	  par1cle	  will	  react	  if	  it	  strikes	  a	  surface• For	  our	  current	  analysis,	  we	  use	  a	  temperature	  dependent	  probability	  for	  carbon	  oxida1on	  given	  by	  Park.• Devising	  more	  sophis1cated	  treatments	  for	  the	  GSI	  is	  an	  ac1ve	  area	  of	  research.29Park, Nonequilibrium Hypersonic Aerothermodynamics, 199129NASA Space Technology Research FellowshipCoupled	  Abla1on• We	  have	  found	  (so	  far)	  that	  the	  surface	  update	  is	  generally	  very	  fast,	  therefore	  we	  update	  fairly	  frequently	  since	  there	  is	  liGle	  to	  no	  penalty30Generate virgin fiber geometry using FiberGen“Cut” surface out of gridUpdate element volumes based on gas-surfacereactions.SignificantAblation? NOYESCall FiberGen to reconstruct surfaceRun DSMC Solver30NASA Space Technology Research FellowshipMovies31Ablation of a porous geometryAblation of a single fiber31NASA Space Technology Research FellowshipOutline• Methodology– DSMC– Surface	  Genera4on	  and	  Movement– Coupled	  Abla4on• Preliminary	  Valida1on	  and	  Applica1ons– Simplified	  Darcy	  Flow– Flow-­‐tube	  Permeability	  Experiments• Future	  Work3232NASA Space Technology Research FellowshipSimple	  Darcy	  Flow• To	  begin,	  we	  seek	  to	  validate	  the	  approach	  for	  simple	  Stoke’s	  flow	  through	  idealized	  porous	  medium.-­‐ We	  compare	  to	  both	  CFD,	  and	  models	  (analy4cal	  and	  empirical)	  in	  the	  literature-­‐ CFD	  augmented	  with	  Maxwell	  slip	  model33DSMCCFD33NASA Space Technology Research FellowshipSimple	  Darcy	  Flow• Results	  show	  good	  agreement	  with	  literature.• ...as	  well	  as	  intui1ve	  departures	  due	  to	  Knudsen	  number	  effects,	  as	  well	  as	  microstructure	  changes34Regular Array of Cylinders Random Array of CylindersLee and Yang, JHMT, 199734NASA Space Technology Research FellowshipFiberForm	  Permeability• Now	  we	  want	  to	  look	  at	  more	  relevant	  geometries	  and	  condi1ons.• Flow-­‐tube	  experiments	  performed	  at	  NASA	  Ames.• Experimental	  data	  well-­‐fit	  by	  Klinkenberg	  form	  of	  Darcy	  equa1on.• Material	  permeability	  tested	  at	  various	  pressures	  and	  temperatures• Significant	  varia1on	  in	  permeability	  observed	  due	  to	  rarefied	  effects.35Marschall and Milos, JTHT, 199835NASA Space Technology Research FellowshipPreliminary	  Results• Simula1ons	  were	  performed	  near	  the	  low	  end	  of	  the	  pressure	  range	  (~	  1kPa)	  of	  the	  experiments.• Gas	  used	  was	  N2	  at	  room	  temperature.• Size	  of	  volume	  was	  200x50x50	  microns	  with	  a	  porosity	  of	  ~0.85• Two	  nominal	  fiber	  radii	  were	  used– 6	  micron	  (single	  fiber)– 10	  micron	  (fiber	  bundle)• Several	  fiber	  orienta1ons	  were	  simulated3636NASA Space Technology Research FellowshipPreliminary	  Results• Fiber	  orienta1on	  is	  defined	  as	  the	  angle	  of	  the	  fiber	  with	  “pressing”	  plane.• Error	  bars	  are	  those	  reported	  in	  the	  paper	  for	  all	  runs.37Df = 6µm Df = 10µm37NASA Space Technology Research FellowshipPermeability	  Results• Takeaways:– Microstructure	  is	  important– We’re	  in	  the	  ballpark!38• Caveats:– Seems	  to	  be	  large	  scaker	  in	  the	  experimental	  data– Simulated	  geometry	  likely	  doesn’t	  cons4tute	  a	  “representa4ve	  volume	  element”– Experiment	  gas	  was	  air38NASA Space Technology Research FellowshipFuture	  Work39Gas-Surface Modeling• Develop new gas-surface interaction model that takes better advantage of the improved fidelity of DSMC- “Active site” based approach• Incorporate probabilities from Molecular Dynamics simulationsExperimental Validation• Interested in performing targeted validation experiments in the NASA Flow-tube facility on “simple(r)” microstructureSimulate Stuff!...(cool stuff)FiberGen• Add analysis toolbox for computing geometric properties and statistics.• Woven geometriesPoovathingal, et al., J. Phys. Chem., 2013 Stern et. al., Gordon Research Conf, 201339NASA Space Technology Research FellowshipAcknowledgements• The	  author	  would	  like	  to	  thank	  the	  NASA	  Office	  of	  the	  Chief	  Technologist	  for	  suppor1ng	  this	  work	  through	  the	  NASA	  Space	  Technology	  Research	  Fellowship.• Addi1onally,	  the	  author	  would	  like	  to	  thank	  the	  many	  researchers	  at	  NASA	  Ames	  and	  the	  U	  of	  M	  who	  were	  generous	  enough	  to	  lend	  their	  support,	  and	  tremendous	  exper1se	  on	  this	  and	  other	  topics:40Questions?Mike WrightDavid HashMike BarnhardtRaj VenkatapathyDinesh PrabhuNagi MansourFrancesco PaneraiSteve SepkaJim Arnoldet al....Pramod SubbareddyJoe BrockIoannis NompelisU of M NASA40

Microscale Modeling of Ablative Thermal Protection System Materials

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Microscale Modeling of Ablative Thermal Protection System Materials

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