Review of unsteady aerodynamics of supersonic parachutes

To date, in all the Mars landing missions, a supersonic parachute has been used to decelerate the capsule's entry into Mars' thin atmosphere from supersonic to subsonic speeds, because of its low mass and high aerodynamic drag. However, when the flexible porous parachute is placed in a supersonic flow, complex interdependent phenomena are observed around the two-body configuration system. These include aerodynamic interactions between the turbulent wake with shocks and coupled interactions between the compressible flows with the flexible porous structures undergoing large deformations. The flow instability around the parachute originates from these aerodynamic interactions between the canopy shock and the capsule wake, which depend on the Mach number, Reynolds number, proximity and size ratio of the canopy to the capsule, angles of attack of the canopy and capsule, and the material properties of the canopy. The effects of these parameters on the performances of the supersonic parachutes have been studied experimentally since the late 1950s. Computational fluid dynamics (CFD) and fluid-structure interaction (FSI) approaches have been used to understand the flow physics and the driving mechanisms of the aerodynamic interactions around the parachute system. However, the underlying mechanisms of these fully coupled interactions are not clearly understood. This review presents the recent developments in the study of supersonic parachutes based on the use of CFD and FSI simulations to predict their aerodynamic performances, summarizes the progress in experimental and numerical research aiming to investigate the unsteady aerodynamics in such a FSI problem, and concludes with discussions on the future challenges in the design and application of supersonic parachutes for Mars exploration missions.