High-Fidelity Modeling of Supersonic Decelerators for Planetary Descent

Planetary exploration missions critically depend on the ability to achieve safe and reliable entry, descent, and landing (EDL). Among the technologies employed, parachutes remain indispensable for decelerating spacecraft from supersonic to subsonic velocities within the rarefied Martian atmosphere. Despite their extensive heritage, parachutes are still subject to complex dynamic instabilities, the most prominent of which is the so-called "breathing" instability. This phenomenon arises from the interaction between turbulence in the wake of the descent module and the bow shock of the trailing canopy. A comprehensive, physics-based characterisation of these processes is still lacking, limiting predictive accuracy and constraining design practices to conservative, empirically driven approaches. \noindent This dissertation addresses this gap through the use of high-fidelity flow simulations based on Large-Eddy Simulation (LES), complemented, where appropriate, by modelling strategies and experimental validation. The computational framework is provided by the in-house compressible flow solver STREAmS, which has been extended with immersed boundary methods and subgrid-scale LES modelling, and accelerated through GPU parallelisation. The research is organised around four main contributions. First, the turbulent wake of a Mars-class descent module at Mach 2 is characterised across a range of angles of attack, providing new insight into the large-scale structures responsible for aerodynamic instabilities. Second, the behaviour of a rigid hemispherical parachute trailing the capsule is examined to isolate the fluid-dynamic origin of the "breathing" instability, and a simplified model is developed to reproduce the associated drag oscillations. Third, the study is extended to the disk-gap-band parachute, demonstrating how its geometry exerts a stabilising influence on the instability by modifying recirculation patterns and shock dynamics. Finally, attention is directed towards the subsonic regime, where the wake of a rigid inflated canopy is resolved and validated against experimental data, emphasising the role of canopy geometry in modulating vortex shedding and local pressure fluctuations. Collectively, these studies represent the most extensive application of LES to parachute aerodynamics in the context of Mars exploration, with particular emphasis on elucidating the underlying fluid-dynamic mechanisms. The findings provide new physical explanations for long-observed instabilities, clarify the stabilising influence of established geometries, and demonstrate the central role of turbulence in driving unsteady responses across flight regimes. Overall, the work establishes a physics-based framework that complements empirical design practices, with the aim of informing future parachute qualification and reducing uncertainties in planetary descent.