Thermal analysis of hypersonic reactive flows on the SARA Brazilian satellite reentry trajectory

Numerical simulations of hypersonic flows are presented for the Brazilian satellite SARA undergoing atmospheric reentry. The Navier–Stokes equations are numerically solved by the finite volume method with the inclusion of chemical source terms to model the effects of dissociation and ionization. The two-temperature model proposed by Park is employed to analyze the translational–rotational and vibrational–electronic temperature modes. Despite the low density conditions, which lead to high mean free paths, a comparison of the present results against those obtained by DSMC shows that the present calculations are sufficiently accurate even at the highest altitude considered. Moreover, estimates of the Knudsen numbers for the present test cases indicate that they are sufficiently low to justify the continuum model. A mesh refinement study is carried out in order to evaluate the influence of near-wall mesh spacing and the number of volumes in the normal and longitudinal directions of the flow on the calculation of the heat flux over the satellite surface. Analysis of the results shows that thermodynamic non-equilibrium occurs along the entire reentry trajectory of the satellite. While for high altitudes the flow density is extremely low, at lower altitudes supersonic conditions are achieved and, in both cases, chemical reactions are not relevant. On the other hand, for some intermediate altitudes of the reentry trajectory, thermodynamic non-equilibrium is severely affected by the chemical reactions. In these cases, a weak ionization occurs besides dissociation of the gas species and the accurate prediction of the surface heat flux requires a reactive gas model.