Supersonic Parachutes and Descelerators

Parachutes

Supersonic parachutes have been used as aerodynamic decelerators during entry and decent into low-density atmospheres, e.g., for Mars space exploration missions. Owing to their low mass and high packaging efficiency, they provide a highly efficient means of deceleration from supersonic to subsonic speeds. The behavior of these parachutes, at supersonic speeds, encompasses complex interdependent phenomena in fluid structure interaction (FSI) research. It involves bluff and porous body aerodynamics, nonlinear structural dynamics and fully coupled interaction between the compressible fluid flow, with shocks, and the membrane structure undergoing   large deformations. As observed in some flight regimes, the inflated parachute undergoes rapid oscillatory deformations which  greatly affects the parachutes’ structural integrity and drag characteristics. This results from inevitable tight coupling between the parachute structure and the surrounding flow. The complex dynamics observed is related to the oscillatory axial movement of the bow shock upstream of the parachute canopy due to over/under pressurization, the  disparity between the tensile and compressive stiffnesses of the  suspension lines connecting the parachute with the capsule (entry vehicle),  inflation instabilities due to the imbalance of fluid forces with structural forces, which are aggravated by the very low inertia of the parachute, and contact forces due to the folding of the canopy. The performance of the parachute is a function of Mach number, shape and size of the capsule, distance between the capsule and the parachute, the shape and size of the canopy, the material properties of the canopy and the cables, and the angle of attack of the capsule. These complex systems have been studied experimentally, mostly in the 60s, sponsored by the US Air Force, and later by NASA during the qualification of the Viking mission to Mars. The modified cross, disk-gap-band and modified ring-sail parachutes are a legacy of this era.

We perform FSI simulation using our three-dimensional compressible solvers. Some example results are show below.

 Simulation of experimental flexible geometry used in validations.

Side view of parachute and prominent flow structures: bow shocks, expansion fans and wakes.

 

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Aeroshells

The design of light supersonic parachutes, inflatable decelerators and propulsion systems used in the entry-decent-landing (EDL) sequence of planetary exploration missions has advanced research into the development of sophisticated hybrid computational fluid dynamics (CFD) and finite element analysis (FEA) models. These computational models describe the fluid-structure interaction of systems with complex geometrie. In our group, we investigate a family of concepts called aeroshells. These are inflatable structures that can create large blunt areas with low weight deployment. We use large-eddy simulation (LES) together with finite-element modeling of the structure using a thin shell model.

Example of supersonic aeroshell. Shown is Mach number at the centerplane.

 

Different instants of inflated and deflated tension-cone concept geometry from fully coupled 3D simulation.

Hydrodynamic details of the flow structure around the aeroshell.