There are three material properties that must be defined in the Material details view for radiation simulations: absorption coefficient, scattering coefficient and refractive index. For details, see Material Details View: Pure Substance in the CFX-Pre User's Guide. For multicomponent flows, set the properties in the Mixture Properties section of the Material details view because this can save substantial CPU time. For details, see Mixture Properties Tab in the CFX-Pre User's Guide and Radiation Properties.

Absorption coefficient, scattering coefficient and refractive index may be a function of intensive thermodynamic variables such temperature and pressure, as well as composition. In some applications, the radiative properties are not uniform in the whole spectrum (that is, non-gray media). In this situation, you may specify these properties as a function of the CEL spectral variables: frequency, wavelength in vacuum, or wavenumber in vacuum. The spectral variable is evaluated at the midpoint of the spectral band in frequency space.