DSMC Computation of Radiative Heat Flux During Huygens Entry into the Titan Atmosphere

Abstract

Designers of thermal protection systems (TPS) for planetary hypersonic entry vehicles must rely on computational methods to predict the total heat flux generated within the shock layer. Methods for predicting the convective heat flux are readily available, however, predicting the radiative heat flux, in particular the nonequilibrium part, is non-trivial. We demonstrate the suitability of the direct simulation Monte Carlo (DSMC) method for calculating radiative heat flux. We use the Cassini/Huygens Probe entry into the Titan atmosphere as a demonstration case. The shock layer radiation is driven predominantly by chemically generated CN. Unfortunately, measured cross-sections for the excitation of CN are not available; however, by using shock tube measurements of electronic transition moments coupled with synthetic emission spectrum calcu¬lations, we are able to indirectly estimate this cross-section. Our results, using this cross-section, indicate that at the trajectory point of maximum heating the radiative heat flux is approximately 20% of the convective one.