Low order reconstruction and modeling of supersonic parachute unsteady aerodynamics

This thesis is written to evaluate the results obtained by the Proper Orthogonal Decomposition (POD) reconstruction around a supersonic parachute during the reentry of a capsule in Martian atmosphere, based on the ExoMars mission. In particular, this drawn wants to validate the reconstruction by comparing it with the results gained by the Large Eddy Simulation (LES), with the in-house code STREAmS, which is a Navier-Stokes equations solver. The results of the thesis were calculated only after evaluating and validating the uniformity of the grid: this was done by comparing the area of the grid cells, in order that it was not too wide. The most important goal is to obtain a high percentage of energy in a few energy modes, at the last modes, so that the reconstruction can be fast and accurate: 10 modes are already enough to achieve this target. Results are examined in terms of instantaneous and mean fields. The reconstruction of instantaneous fields reveals the presence of canonical flow regions around the parachute, like normal shock and turbulent wake. In particular, specific attention is given to the aerodynamic interaction between the capsule wake and the bow shock ahead of the parachute because the fluctuations of the wake are amplified as it crosses the shock, leading to strong flow oscillations and potential system instability, due to the parachute breathing cycle. The comparing between POD and LES was done along the X-axis, with a constant Z-coordinate, and along the Z-axis too, keeping a constant X-coordinate (for different values of it). It was also evaluated for three different non-dimensional times, in order to gain a more complete description of the reconstruction. The last point that this thesis addresses is the Root Mean Square (RMS): it was done a comparison between POD-RMS and LES-RMS, so that it is possible to evaluate the POD field variations with the expected oscillations of the LES filed. This kind of examination was done to obtain more information about the accuracy of the reconstruction and to be more complete and stricter in defining the phenomenon by proper orthogonal decomposition.