Impact of Non-Tangent-Slab Radiative Transport on Flowfield–Radiation Coupling

Abstract

For coupled flowfield–radiation simulations, required for Earth entry at velocities greater than $10\mathrm{km}/\mathrm{s}$ , tangent-slab radiative transport is shown to sufficiently model the divergence of the radiative flux (this term couples the radiative energy to the flowfield energy equations). However, as shown in previous studies, the tangent-slab approximation does not sufficiently model the radiative flux reaching the surface (i.e., the radiative heating). These conclusions are reached through the development of a detailed ray-tracing approach capable of computing both the divergence of the radiative flux and the radiative heating. This approach is orders of magnitude more computationally expensive than the tangent-slab approximation. The ability of the tangent-slab approach to accurately model the divergence of the radiative flux, but not the radiative heating, is shown to be the result of a cancellation of errors during the angular integration. The current work shows that combining the tangent-slab approximation for the divergence of the radiative flux with the ray-tracing approach for the radiative heating (as a final step) provides sufficiently accurate results (radiative heating values within 1%), in an efficient manner, for coupled flowfield–radiation problems.