Investigation of unsteady wake dynamics in subsonic flow over a rigid parachute

The present study investigates the flow separated from a rigid parachute canopy by characterising the nature of the turbulent structures constituting the shear layer and the near wake. The aim is to emphasise the role of the decelerator geometry in inducing the flow instabilities observed during descent. High-fidelity LES provides a full three-dimensional, time-evolving reconstruction of the flow field around the selected geometry in a subsonic turbulent flow. Wind tunnel experiments use planar PIV to characterise the wake flow field in a matching test case condition for validation purposes. Wake velocity profiles show good agreement between experiments and simulations. The focus is placed on the geometry details of the parachute, specifically on the alternated convex-concave features of the inflated canopy shape, and their role in affecting flow separation. Results show that the creased configuration promotes the formation of counter-rotating vortices in the valleys, locally delaying detachment by entraining flow into these regions. On the surface, the three-dimensional flow patterns reflect in pressure fluctuations that, in a flexible canopy, would lead to high-frequency oscillations at the canopy skirt, contributing to the onset of the so-called 'breathing' instability. The analysis isolates the effects of geometry from material response, highlighting the relevance of canopy shape in determining the wake structure.