Multi-fidelity evaluation of aerodynamic coefficients for re-entry objects of arbitrary shapes

In recent years, the problem of space debris has become relevant and is now being studied to reduce the impact that has on the population. For this purpose, at the von Karman Institute for Fluid Dynamics, the project DSMCFED aims to develop a toolset to analyze the re-entry phase of spacecraft during their disposal. The main objective is to simulate the spacecraft fragmentation during the de- scent into the atmosphere by coupling high-fidelity tools to analyze the aerothermo- dynamics, the trajectory, and the thermo-structural response. In this context, to compute the trajectory of the objects it is necessary to evaluate their aerodynamic coefficients at different altitudes, so a code to study the flow interaction with the body is needed. Direct Simulation Monte Carlo has been identified as the method to solve the problem in the rarefied/transitional regime, however when the altitude decreases and the regime approaches the continuum, the computational cost associated with the simulations drastically increases; different approaches are sought to reduce the weight of the simulations to evaluate the aerodynamic coefficients of the objects at different configurations to perform the trajectory propagation. This thesis aims to find alternative methods to complement DSMC analysis and reduce the time needed for the simulations while ensuring a good degree of accuracy. In the first part, the reader is introduced to the addressed problem and to the aerodynamic theories useful to understand the discussion. Subsequently, the numerical solvers and the relative methods applied in the simulations are shown. Finally, the different test cases are defined and the simulation results are exhibited. Based on these considerations, a tentative approach has been drafted to complement the DSMC simulations using lower-fidelity software to reduce the computational cost related to the evaluation of the aerodynamic coefficients at different attitudes during the re-entry.