Permeability-induced scaling effects in parachute aerodynamics

Affected by the flexibility and air permeability of fabrics, parachutes often exhibit severe scaling effects in their opening and aerodynamic performance. Considering the phenomenon of thickness scaling distortion in actual scenarios, this study systematically investigates the impact of fabric air permeability on the scaling differences in parachute aerodynamic performance. First, by employing the reverse modeling method, the full-scale C9 canopy models and the 1/8-scale C9 canopy models are established, respectively. Second, the computational fluid dynamics simulations are conducted for both impermeable and permeable conditions to investigate the impact of fabric air permeability on aerodynamic scaling differences. Finally, the influence of effective permeability (Ce) and the viscosity/inertia coefficient ratio on aerodynamic performance differences at 1/8 scale is separately investigated. The results indicate that under the premise of canopy thickness scaling distortion, the fabric air permeability leads to a multiple-fold increase in the scaling differences of the drag coefficient (CD). As the Ce increases, the 1/8 scale difference of CD changes from positive to negative, following a logistic regression trend. As the viscosity/inertia coefficient ratio increases, the 1/8 scale difference of CD remains positive and gradually decreases, conforming to a single-exponential decay regression trend. This study provides relevant references for predicting corrections from scaled parachutes to full-scale parachutes.