Computational Modeling of Hypersonic Nonequilibrium Gas and Surface Interactions

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1 Computational Modeling of Hypersonic Nonequilibrium Gas and Surface Interactions Iain D. Boyd, Jae Gang Kim, Abhilasha Anna Nonequilibrium Gas & Plasma Dynamics Laboratory Department of Aerospace Engineering University of Michigan Ann Arbor, Michigan Grant FA

2 Hypersonic Vehicle Analysis Gas Phase - strong shocks, thermochemical nonequilibrium, boundary layer, etc. - CFD, relaxation times, Arrhenius rate coefficients with twotemperature model Surface Processes - accommodation, ablation (oxidation, sublimation), catalysis, melting, etc. - coefficients, surface chemistry mechanism and rates Material Response - heat conduction, radiative emission, internal chemical reactions (pyrolysis), gas flow through porous media, etc. - thermal response model, physical properties of complex materials (conductivity, emissivity ) 2

3 Project Goals Nonequilibrium gas-phase processes: use computational chemistry and Master Equation analysis to perform detailed studies of: thermal relaxation processes (T-R-V) chemical processes (dissociation, exchange) develop reduced order models for use in CFD Nonequilibrium gas-surface processes: use coupled CFD-surface chemistry-material response tools to study gas-surface interactions (e.g., catalysis, ablation) assess models using experimental data (flow and surface) generated in high-enthalpy facility (Fletcher, Univ. Vermont) 3

4 Gas Phase Studies: Technical Approach State-to-state transition cross sections and rate coefficients: compute data for all ro vibrational states, e.g. using QCT reduce the number of state-to-state transition rates evaluated using a response surface design technique (Kriging) Master Equation (ME) analysis of thermochemical relaxation: constructed using complete sets of state-resolved transition rates for bound-bound and bound-free processes compare results with existing measurements use results to develop reduced-order thermochemistry models that can be implemented in CFD 4

5 Results: Bound-Bound H 2 Transitions State-to-state cross sections obtained using response surface design method 5

6 Results: Bound-Bound H 2 Transitions State-to-state cross sections obtained using response surface design method calibrated using a small number of QCT evaluations (1,800 instead of 60,000!) 6

7 Results: H 2 Thermal Relaxation Global relaxation parameters of the rotational and vibrational modes for H 2 +H 2 Rotational and vibrational relaxation times become similar at high temperature Technical details: Kim & Boyd, AIAA , Jan

8 Analysis of N 2 -N: Heat Bath Studies State-to-state transition cross sections and rate coefficients: use database of cross sections computed by Jaffe et al, NASA ARC ME analysis involves solution of 9,390 equations technical details: Kim & Boyd, AIAA , June 2012 Relaxation, Log(p!), atm-sec N+N 2 rotation, present N+N 2 vibration, present N+N 2 vibration, Park (1993) N+N 2 vibration, " v =3.0e-17cm Temperature, T -1/3 Log(K f ), cm 3 mol -1 sec Master, present QSS, present One-way, present Cary (1965) Byron (1966) Appleton et al. (1968) Hanson and Baganoff (1972) Temperature, K Normalized energy loss Rotational energy loss Vibrational energy loss Temperature, K Thermal Relaxation Parameters Chemical Reaction Rates Energy Removal Due to Chemistry 8

9 Analysis of N 2 -N: Shock Tube Studies One-dimensional flow equations combined with Master Equation: N 2 -N 2 included macroscopically using standard models applied to experiment of AVCO / Sharma technical details: Kim & Boyd, AIAA , June 2012 Temperature, K 25 T, present T r, present T v, present T, 2-T model 20 T v, 2-T model T r, AVCO RR 186 (1964) T r, Sharma and Gillespie (1991) T v, Sharma and Gillespie (1991) x1000 Species mole-fraction N, present N 2, present N, 2-T model N 2, 2-T model X, cm Temperature Profiles X, cm Species Profiles 9

10 Gas-Surface Interactions: Assessment of Computations Collaboration with Prof. Doug Fletcher (UVM): 30 kw Inductively Coupled Plasma (ICP) Torch Facility Samples exposed to high enthalpy gas flows Flow quantities measured using two-photon LIF: N-atom number density translational temperature Surface temperature and sample ablation also quantified Graphite sample in nitrogen flow (section in box is the portion simulated) Source: Prof. D.G. Fletcher 10

11 Free Stream: Mass flow rate [kg/s] Gas-Surface Interactions: Conditions Investigated Temperature T [K] Pressure [kpa] Wall temperature T w [K] Progress: subsonic inlet/outlet BCs added to LeMANS sensitivity to various thermochemistry models Mach number Translational temperature 11

12 Gas-Surface Interactions: Comparisons with Experiment Comparisons along the stagnation streamline Temperature [K] Experiment TE! N TNE! N TNE! N = 1 = 1.11 Relative N-atom density Experiment TE! N TNE! N TNE! N = 1 = T wall = 1590 K Distance from the surface [m] Distance from the surface [m] Translational temperature Relative N-atom density 12

13 Future Plans Nonequilibrium gas-phase processes: develop T-R-V relaxation models for CFD from ME results high fidelity CFD chemical reaction models including rotational mode will also be developed from ME analysis continue analysis for other important air interactions evaluation using existing experimental data sets Nonequilibrium gas-surface processes: compare surface chemistry models (catalytic recombination, finite rate chemistry module of MacLean & Marschall) model surface recession (material response code: MOPAR) study sensitivity to gas-thermochemistry rates and models assess modeling using Univ. Vermont experimental measurements of flow field properties and sample mass loss 13

14 Technical Challenges Nonequilibrium gas-phase processes: large number of different air species interactions (N 2 -M, O 2 - M, NO-M, etc.) fidelity required from computational chemistry? Master Equation analysis becoming expensive lack of modern, validation quality, experimental data Nonequilibrium gas-surface processes: isolating contributions of competing mechanisms to effects observed (e.g. flow processes, catalysis, ablation) uncertainties in facility operation (e.g. ICP exit conditions) 14

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16 Technical Approach: Computational Tools LeMANS (Scalabrin and Boyd: AIAA ) Navier-Stokes CFD code finite volume FVS implicit time integration (point/line) 2D/3D unstructured mesh parallel, domain decomposition finite rate thermo-chemical nonequilibrium effects validated for hypersonic flow using experiments, codes MOPAR (Martin and Boyd: AIAA ) material response code control volume finite element (CVFEM) quasi-1d pyrolyzing/non-pyrolyzing ablators momentum conservation through Darcy s Law (or Forcheimer s Law) moving boundaries has been coupled to LeMANS 16

17 Results: Surface Properties Total Heat flux = (Translational + Vibrational) convective heat flux + Diffusive heat flux 2.4E E+06 2E E E+06 TE! N TNE! N TNE! N = 1 = 1.11 Beginning of shoulder End of shoulder 1.4E E+06 1E+06 TE! N TNE! N TNE! N = 1 = 1.11 Beginning of shoulder End of shoulder q total [W/m 2 ] 1.4E E+06 1E+06 q diff [W/m 2 ] Distance from stagnation point [m] Distance from stagnation point [m] Total heat flux Diffusive heat flux 17