PhD Public Defense of James Scoggins
Date: Friday 29 September 2017 to Friday 29 September 2017
Location : CentraleSupélec in Paris, Amphi IV, Bâtiment Eiffel 8-10 rue Joliot-Curie 91, 190 Gif-sur-Yvette France
The thesis is entitled:
Development of numerical methods and study of coupled flow, radiation, and ablation phenomena for atmospheric entry
This thesis focuses on the coupling between flow, ablation, and radiation phenomena encountered in the stagnation region of atmospheric entry vehicles with carbon-phenolic thermal protection systems (TPS). The research is divided into three parts: 1) development of numerical methods and tools for the simulation of hypersonic, non-equilibrium flows over blunt bodies, 2) implementation of a new radiation transport model for calculating non-equilibrium radiative heat transfer in atmospheric entry flows, including ablation contaminated boundary layers, and 3) application of these tools to study real flight conditions.
A review of the thermochemical non-equilibrium models and governing equations for atmospheric entry flows is made, leading to a generalized framework, able to encompass most popular models in use today. From this, a new software library called MUlticomponent Thermodynamic And Transport properties for IONized gases, written in C++ (MUTATION++) is developed, providing thermodynamic, transport, chemistry, and energy transfer models, data, and algorithms, relevant to non-equilibrium flows. In addition, the library implements a novel method, developed in this work, for the robust calculation of linearly constrained, multiphase equilibria, which is guaranteed to converge for all well posed constraints, a crucial component of many TPS response codes.
The steady-state flow along the stagnation line of an atmospheric entry vehicle is computed using a one-dimensional, finite-volume tool, based on the dimensionally reduced Navier-Stokes equations. Coupling with ablation is achieved through a steady-state ablation boundary condition using finite-rate heterogeneous reactions at the surface and imposed equilibrium compositions of pyrolysis outgassing.
The High Temperature Gas Radiation (HTGR) database provides accurate line-by-line (LBL) spectral coefficients. From a review of the major mechanisms contributing to the radiative heat flux for atmospheric entry vehicles, several contributions are added to the HTGR database, including H lines, C3 Swings and UV electronic systems, and photoionization of H, H2, and CH. The Hybrid Statistical Narrow Band (HSNB) model is implemented to reduce the CPU time required to compute accurate radiative heating calculations when many species are present. New SNB parameters are computed for the H2 Lyman and Werner systems, by adjusting the Doppler and Lorentz overlap parameters to fit curves of growth for each narrow band. Comparisons with band-averaged LBL transmissivities show excellent agreement with the SNB parameters. It’s shown that the HSNB method provides a speedup of two orders of magnitude and can accurately predict wall radiative fluxes to within 5 % of LBL results. A novel spectral grid adaptation is developed for atomic lines and is shown to provide nearly identical results compared to the high-resolution HSNB method with a 20-fold decrease in CPU time. The HSNB model yields greater accuracy compared to the Smeared-Rotational-Band model in the case of Titan entry, dominated by optically thick CN radiation.