Influence of air permeability on inflation process and aerodynamic characteristics of disksail parachutes

The supersonic parachute is one of the key parts of successful soft landing of the Mars probe; however, the mainstream parachute type used in the landing mission of Mars exploration, the disk-gap-band parachute, has reached the size limit of the deceleration capacity of this type of parachute. Due to the requirement of the heavier payload of Mars exploration missions in the future, NASA has carried out special research on supersonic disksail parachutes. However, all the flying tests of disksail parachute have failed, and the reason is probably related to the air permeability of the parachute (fabric permeability and geometric porosity). In this paper, the fluid-structure interaction method is used to design different combination schemes of air permeability of the supersonic disksail parachute. The influence mechanism of different geometric porosity/fabric permeability distribution ratios on the flow field structure and aerodynamic characteristics in the process of parachute opening is analyzed under the premise of the same total porosity. In addition, a disk-gap-band parachute with the same porosity as that of the G5F5 and G7F3 disksail models are designed, and its opening characteristics are analyzed. The results show that for the supersonic disksail parachute with a total porosity of 12%, when the contribution ratio of geometric porosity/fabric permeability is 5∶5, the fluctuation amplitude of the bow shock ahead of the canopy is small, the stability performance of the parachute has obvious advantages over that of the parachute with the air permeability of other combinations, and the inflating time is the longest under the joint action of geometric porosity and fabric permeability; when the contribution ratio of geometric porosity/fabric permeability is 7∶3, the drag performance of the parachute is the best, and the drag performance of the disksail parachute shows a downward trend as the contribution of fabric permeability increases from 30% to 70%; when the contribution ratio of geometric porosity/fabric permeability is 6∶4, the parachute has the largest oscillation angle and the worst stability. By comparing the opening processes of the disksail and disk-gap-band parachutes, it is found that disk-gap-band parachutes exhibit a common “disk-style” inflation sequence, while disksail parachutes exhibit a “band style” inflation sequence, that is, the airflow first inflates from the canopy band and then gradually spreads to the entire canopy surface. The results of this study can provide a theoretical reference for the design of a new generation of Mars parachutes.