Comparative analysis of reduced-order spectral models and grouping strategies for non-equilibrium radiation

Amal Sahai, Christopher O. Johnston, Bruno Lopez, Marco Panesi

Research output: Contribution to journalArticle

Abstract

Radiative transfer calculations in complex three-dimensional domains are plagued by computational bottlenecks due to the combined cost of resolving spectral, angular, and spatial dependence. The current work presents a systematic study into the efficacy of three commonly used reduced-order wide-band models, Planck-averaging, and statistics-based k-distribution and theory of homogenization, for modeling non-equilibrium radiation. A reinterpretation of Planck-averaging based on the maximum entropy principle combined with the commonly used multi-band opacity binning allows a direct equivalence to be drawn with the two statistics-based approaches. Additionally, the three seemingly distinct methods are shown to be strictly derived only for local thermodynamic equilibrium conditions which limits their accuracy when simulating non-equilibrium radiation. This shortcoming is addressed through the development of a novel grouping strategy for defining larger groups of individual frequencies from detailed radiation databases (based on line-by-line or narrow-band models) while accounting for variation in all radiative properties under non-equilibrium. Radiative transfer calculations for different Earth and Jupiter entry problems are performed using the different spectral models. Conventional reduced-order wide-band approaches converge slowly to the solution obtained using detailed spectral models. However, the new non-equilibrium grouping strategy allows both total quantities-of-interest and their detailed spectral variation to be predicted accurately while employing fewer reduced-order groups. The current model-reduction methodology provides nearly two orders-of-magnitude decrease in required spectral evaluations along a given line-of-sight with respect to narrow-band methods (and three to four orders with respect to original LBL databases) and is ideal for coupled flow-radiation calculations.

Original languageEnglish (US)
Article number106752
JournalJournal of Quantitative Spectroscopy and Radiative Transfer
Volume242
DOIs
StatePublished - Feb 2020

Fingerprint

nonequilibrium radiation
Radiation
Radiative transfer
radiative transfer
narrowband
Statistics
statistics
broadband
local thermodynamic equilibrium
Opacity
radiation
homogenizing
opacity
Jupiter (planet)
entry
line of sight
equivalence
Entropy
Earth (planet)
Thermodynamics

Keywords

  • Grouping strategy
  • Non-equilibrium
  • Reduced-order method
  • Spectral model

ASJC Scopus subject areas

  • Radiation
  • Atomic and Molecular Physics, and Optics
  • Spectroscopy

Cite this

Comparative analysis of reduced-order spectral models and grouping strategies for non-equilibrium radiation. / Sahai, Amal; Johnston, Christopher O.; Lopez, Bruno; Panesi, Marco.

In: Journal of Quantitative Spectroscopy and Radiative Transfer, Vol. 242, 106752, 02.2020.

Research output: Contribution to journalArticle

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