Assessment of flow-induced stability in the ExoMars disc-gap-band parachute for Mars supersonic descent

We present high-fidelity, time-resolved simulations of a rigid disc-gap-band (DGB) parachute trailing a descent module in a supersonic regime. The study employs large eddy simulation combined with an immersed boundary method and GPU parallelisation to reproduce the 'Rosalind Franklin' ExoMars flight geometry at Ma infinity=2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Ma_\infty = 2$$\end{document} in a rarefied Martian atmosphere. The parachute is treated as a rigid surface to isolate fluid dynamics and minimise modelling assumptions. We analyse the flow field surrounding the DGB and its unsteady statistics to identify mechanisms that promote flow stabilisation. Results show that the DGB yields noticeably lower axial and tangential force fluctuations compared to non-slotted counterparts. This effect originates from a persistent annular outflow through the gap, which confines the main toroidal vortex within the canopy cavity. By limiting backflow, the gap reduces turbulence-shock interaction ahead of the parachute. In this manner, the frontal bow shock sits closer to the canopy, appearing flatter. Amplitude in the stand-off oscillations is also reduced. Spectra of drag and shock position signals show matching dominant frequencies with a hemispherical parachute, suggesting that the fundamental oscillation patterns are similar. High-frequency components associated with the lateral bow shock modes appear strongly dampened given the more effective stabilisation off-axis. Overall, the simulations indicate that the DGB geometry reduces the intensity of the 'breathing' instability by altering the extent of the wake-shock interaction through its annular gap outflow.