Numerical Modeling of Earth Reentry Flow with Surface Ablation

Abstract

Vehicles entering planetary atmospheres at high speed require an ablative heat shield to withstand the high thermal energy flux to the body. The interaction between the ablative products and the flowfield is not well characterized. In this study, numerical simulations were conducted to investigate the influence of carbon ablation on shock-layer radiation. Data collected from experiments performed in the X-2 expansion tunnel at the University of Queensland were used to compare to the simulations. The model was a short half-cylinder made of isomolded graphite and was tested in Earth entry flow. The graphite model was heated within a temperature range of 1770–2410 K over the course of the experimental campaign. The radiation emitted from the CN violet bands was measured by ultraviolet spectrometry in a spectral range from 353 to 391 nm. The simulations used the Park as well as Zhluktov and Abe finite-rate surface kinetic models for determining the chemical state of the ablating boundary layer. The Park model consistently overpredicted the radiative heat fluxes, but better comparison was achieved when a modified nitridation rate was used. The Zhluktov and Abe predictions displayed good agreement with the measured radiative heat fluxes at 1770 K but remained well below the measured values at the higher wall temperatures. The lack of a nitridation mechanism in the Zhluktov and Abe model is suggested as the reason for these underpredictions.