A study on heat flux predictions for re-entry flight analysis

Abstract

The analysis of the risk from re-entry objects has become an important topic. Concerning the uncertainties and different flow regimes, the object-oriented tools have been developed and used for various re-entry mission scenarios because of the simplified computation process and low calculation burden, which allow a probabilistic analysis. In this study, the heat flux correlations that are used in the object-oriented tools are investigated and compared to better understand the heat flux predictions with respect to re-entry survivability. Often these tools calculate the continuum stagnation-point heat flux using the correlation formulae of Lees and Fay-Riddell, which usually assume local thermo-chemical equilibrium with a fully-catalytic wall condition in the shock layer. Based on this observation, heat flux measurements were conducted in a hypersonic wind tunnel, and validated with the theory of Fay-Riddell considering the equivalent velocity gradient. For the comparison, in total, 11 different heat flux correlations were examined. It is shown that, based on the formula of Fay-Riddell, the differences in the final integrated heat flux were less than 16% which led to a large discrepancy in the survivability estimations for the cases of small spheres made of aluminum. This shows the importance of considering the heat flux correlation as well as the velocity gradient effect for such re-entry analysis.