Prediction and effect analysis for equilibrium profile of flexible porous canopy fabric

Abstract

Parachute is decelerator constructed of flexible porous fabrics that changes the motion state of the payload, aerodynamic characteristic in steady descent of which largely depends on equilibrium profile. A novel analytical method to predict the equilibrium profile of flexible porous canopy fabrics in steady decelerating stage is presented. This method introduces Forchheimer’s law and Ergun theory into Ross mechanical equilibrium model, and further considering both the flight status and the materials properties. The prediction error of projection radius of gore centreline is 3.83% compared with the airdrop test results, and the prediction errors of the projection radius of cord and gore centreline are 1.09% and 0.66% respectively compared with Fluid-Structure Interaction method. Results indicate that this proposed method can be an efficient way to obtain an accurate canopy profile with much less computation cost. Finally, some illustrative examples are given to evaluate the effect of structural parameters on the parachute equilibrium profile. It is found that the length of the suspension line should be somewhat longer than the nominal diameter and the spacing of suspension lines should be slightly longer than 1m. And it is recommended that the radius of apex vent should be 0.04 ∼ 0.1 times of the nominal radius of the parachute. The Young’s modulus of materials has little effect on the equilibrium profile. Overall, the new approach could predict the canopy profile quickly for the parachute design and provide an accurate shape basis for the subsequent aerodynamic research based on CFD method.