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In current study, for a special fabric that is used for parachute canopies; the permeability of the canopy has been estimated empirically and numerically. Moreover, the coefficients of Darcy's equation resulted from experiment, used in 2D numerical simulation of a single parachute-like body. Assuming permeability for the fabric, the drag coefficient was showed a 39 percent decrease rather than solid canopy. Comparison between solid canopy and permeable one, showed significant differences in the results, especially in streamlines and pressure distribution. In order to diminish the numerical effort, the canopies were taken as 2D hemi-spherical porous cups. So-called two dimensional numerical simulations using FLUENT® software was conducted on a group of paired permeable with two different diameters in various vertical and horizontal distances. The diameter of lower canopy was considered as half of the upper one. Tandem canopies use in order to reduce the inflation shock of main parachute. The lateral relative displacement of lower canopy to upper one has been considered in order to stimulate true descending conditions. The results showed the interaction between flow fields of canopies has strong effect on drag coefficient of the cluster parachutes. Therefore, determining the length of the risers as the vertical distance and relative diameter of parachutes and their interactions found to have tremendous effect in designing cluster parachutes. The study showed that the most desirable longitudinal distance between two canopies was equal to the diameter of lower canopy.

Keywords: Parachute, Permeability, Drag, Cluster, Interaction

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