TY - JOUR
T1 - Generalized Chapman-Enskog continuum breakdown parameters for chemically reacting flows
AU - Swaminathan-Gopalan, Krishnan
AU - Subramaniam, Sharanya
AU - Stephani, Kelly A.
N1 - Funding Information:
This work was supported by an Early Career Faculty grant from NASA's Space Technology Research Grants Program (Grant No. NNX15AW46G). The authors gratefully acknowledge Dr. Peter Gnoffo and Dr. Alireza Mazaheri of NASA Langley Research Center for providing the LAURA solutions presented in the analysis.
Publisher Copyright:
© 2016 American Physical Society.
PY - 2016/12
Y1 - 2016/12
N2 - The generalized Chapman-Enskog (GCE) method for rapid and slow thermochemical processes is employed to formulate a set of continuum breakdown parameters for chemically reacting flows. These GCE breakdown parameters are derived for one-temperature, two-temperature, and three-temperature models, through classification of the relevant thermochemical time scales relative to fast elastic collisional processes and slow flow processes associated with changes in macroscopic observables. Continuum breakdown mechanisms owing to multicomponent diffusion, thermal diffusion, normal and shear stresses, Fourier-type heat fluxes based on translational, rotational, and vibrational temperatures, bulk viscosity, and relaxation pressure are presented for chemically reacting flows. The GCE breakdown parameters, derived from rigorous kinetic theory, capture the proper physical mechanism leading to continuum breakdown. These breakdown parameters are used to analyze continuum breakdown in a Mach 24 reacting air flow over a sphere and continuum breakdown is observed in the shock and close to the sphere surface. The flow field near the sphere surface is found to be characterized by sharp species concentration gradients due to gas-phase and surface reactions. Chemical reactions thus lead indirectly to the distortion of the velocity distribution function (VDF), providing a pathway to continuum breakdown that is captured by the GCE specieswise diffusion breakdown parameter.
AB - The generalized Chapman-Enskog (GCE) method for rapid and slow thermochemical processes is employed to formulate a set of continuum breakdown parameters for chemically reacting flows. These GCE breakdown parameters are derived for one-temperature, two-temperature, and three-temperature models, through classification of the relevant thermochemical time scales relative to fast elastic collisional processes and slow flow processes associated with changes in macroscopic observables. Continuum breakdown mechanisms owing to multicomponent diffusion, thermal diffusion, normal and shear stresses, Fourier-type heat fluxes based on translational, rotational, and vibrational temperatures, bulk viscosity, and relaxation pressure are presented for chemically reacting flows. The GCE breakdown parameters, derived from rigorous kinetic theory, capture the proper physical mechanism leading to continuum breakdown. These breakdown parameters are used to analyze continuum breakdown in a Mach 24 reacting air flow over a sphere and continuum breakdown is observed in the shock and close to the sphere surface. The flow field near the sphere surface is found to be characterized by sharp species concentration gradients due to gas-phase and surface reactions. Chemical reactions thus lead indirectly to the distortion of the velocity distribution function (VDF), providing a pathway to continuum breakdown that is captured by the GCE specieswise diffusion breakdown parameter.
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U2 - 10.1103/PhysRevFluids.1.083402
DO - 10.1103/PhysRevFluids.1.083402
M3 - Article
AN - SCOPUS:85017250933
VL - 1
JO - Physical Review Fluids
JF - Physical Review Fluids
SN - 2469-990X
IS - 8
M1 - 083402
ER -