CORRELATED-k METHOD FOR SOLVING ATOMIC RADIATION PROBLEM IN HYPERSONIC NONEQUILIBRIUM FLOWS

Open Access
Author:
Bansal, Ankit
Graduate Program:
Mechanical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Michael F Modest, Thesis Advisor/Co-Advisor
Keywords:
  • Hypersonic
  • shock-layer
  • nonequilibrium
  • radiation
  • k-distribution
  • spectral models
  • plasma
Abstract:
Radiative heat loads from nonequilibrium shock-layer are of great concern in the design of modern spacecrafts. Simulation of shock-layer radiation requires accurate modeling of spectral absorption and emission coefficients of high-temperature plasma, and solving the Radiative Transfer Equation (RTE) at thousands of wavelengths. Although the line-by-line solution of the RTE is very accurate, it is computationally very expensive to couple a line-by-line model with flow-solvers. This thesis discusses a full-spectrum k-distribution spectral model that allows efficient evaluation of radiative heat loads in a hot plasma dominated by radiation from the atomic species N and O. Application of the new spectral model to shock-layer plasma radiation is demonstrated by solving the radiation transfer equation along the Stardust stagnation-line flow-field. The full-spectrum k-distribution method is reasonably accurate compared to the line-by-line method. For more extreme gradients in species concentrations and temperature, k-distributions were found not to be correlated. Challenges posed by the extreme nonequilibrium gas conditions were overcome by sorting atomic lines into a number of nonoverlapping groups. The detailed methodology of the grouping scheme is presented. Although the full-spectrum k-distribution approach make it possible to evaluate radiative fluxes at a fraction of the cost needed for line-by-line calculations, it is not very efficient to construct them from raw line-by-line absorption coefficient data. An accurate and compact narrow-band k-distribution database is developed for the lines of N and O. It was observed that the overlap between the two atomic species N and O is almost insignificant. This is a very important observation as it allowed databasing k-distributions from the two species independently. The database allows users to calculate desired full-spectrum k-distributions through look-up and interpolation. The accuracy of the database was tested by comparing narrow-band mean absorption coefficients and narrow-band emissivities with those obtained from line-by-line calculations. Application of the database in constructing full-spectrum k-distributions accurately and efficiently is discussed. Results from a number of heat transfer calculations and cpu-time studies are presented.