View-Factor Based Radiation Transport in a Hypersonic Shock Layer

Abstract

Introduction A TOMS and molecules in the hot shock layer formed in front of a hypersonic vehicle often release some of their internal energy by spontaneous emission of electromagnetic radiation. The isotropically emitted radiative energy propagates through the shock layer, sometimes undergoing absorption, until a portion of the remaining energy eventually reaches the body surface and heats the vehicle. In cases of high-speed entries of large vehicles, the radiative heating can be larger than the convective heating from the hot gas. It is therefore crucial to the design of the protective heat shield that this radiative-transport process be modeled accurately. In practice radiative transport is typically reduced to a onedimensional line-of-sight problem by assuming small body curvature and small tangential flow gradients. This approach is known as the tangent slab model. In this Note, we present a three-dimensional transport model based on geometric view factors between the emitting volumes and surface elements, which significantly improves the accuracy of radiative heat-flux estimates for an optically thin shock layer. This method can also be applied to absorbing gases, but the cost can be significantly more than the tangent slab model if fine spectral resolution is required.