A trajectory-based analysis for obtaining aerodynamic heating environment for the Huygens probe is carried out using the thermochemical nonequilibrium computational fluid dynamics code. Radiative heat transfer is accounted for in computational fluid dynamics calculations where a modern multiband radiation model is employed. In this study, we first compare the radiative heat flux obtained by the ray-tracing approach in three-dimensional space with that given by the tangent-slab approximation, to determine how the difference in obtaining radiative heat flux can alter the overall aerodynamic heating environment We then explore the radiative cooling effect on surface heat flux through radiation coupled computational fluid dynamics calculations. It is shown that the radiative heat flux value at the stagnation point obtained by the ray-tracing approach becomes about 17-19% smaller than that given by the tangent-slab approximation due to body curvature at all the chosen trajectory points. Furthermore, it is also shown that the radiative cooling effect can reduce the surface radiative heat flux by almost the same amount at the stagnation point when computational fluid dynamics calculation coupled with radiation is conducted. It is therefore confirmed that, even for the relatively lower radiative heating rate such as for the Huygens entry flight, we need to employ the ray-tracing approach instead of the tangent-slab approximation, and also need to account for radiative cooling effect through radiation coupled computational fluid dynamics calculation, to evaluate the surface heating condition accurately.
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