Determination of Radiative Fluxes in an Absorbing, Emitting, and Scattering Vapor Formed by Laser Irradiation

Abstract

A two-dimensional computer model is developed to determine the radiative heat flux distributions within the vapor formed above a metal target irradiated by a laser beam. An axisymmetric cylindrical enclosure containing a radiatively participating medium is considered. Scattering is assumed to be isotropic and allowances are made for variation of the radiative properties of the medium and boundaries. The P-1 and P-3 spherical harmonics approximations are used to solve the integro-differential radiative transfer equation. The resulting equations are then solved for the radial and axial heat fluxes using a finite-difference algorithm. The most significant factors affecting the results obtained from both the P-1 and P-3 approximations were the optical thickness of the medium and the type of laser profile incident upon the medium. Using different wall reflectivities and scattering albedos had a smaller effect. Changing the medium temperature had an insignificant effect as long as medium temperatures were below 20,000 K.