Abstract
The flow past a parachute with and without a vent hole at the top is studied both experimentally and numerically. The effects of Reynolds number and vent ratio on the flow behaviour as well as on the drag coefficient are examined. The experiments were carried out under free-flow conditions. In the numerical simulations, the flow was considered as unsteady and turbulent and was modelled using the standard - turbulence model. The experimental results reveal good agreement with the numerical ones. In both the experiments and numerical simulations, the Reynolds number was varied from 85539 to 357250 and the vent ratio was increased from zero to 20%. The results show that the drag coefficient decreases by increasing the Reynolds number for all the cases tested. In addition, it was found that at low and high Reynolds numbers, the parachutes, respectively, with 4% vent ratio and without vent are deemed more efficient. One important result of the present work is related to the effect of vent ratio on the stability of the parachute.
Highlights
The study of bluff bodies involves the consideration of complex aerodynamic phenomena such as semiwake and vortex shedding
Different cases with various vent ratios are tested at different Reynolds numbers
The results show that for all cases as the Reynolds number is increased the drag coefficient is decreased
Summary
The study of bluff bodies involves the consideration of complex aerodynamic phenomena such as semiwake and vortex shedding. One important feature that may distinguish the computational fluid dynamics (CFD) modelling from the experimental analysis of the parachute behaviour is the geometry flexibility in the latter allowing large variations in the experiments [1]. The flow structure near the wake of canopy is responsible for the aerodynamic forces and moments it experiences. The relationship between the Reynolds number and flow field structure around spherical bodies in incompressible flow regime has been studied extensively. The numerical study carried out by Natarajan and Acrivos [2] indicated that the wake of a sphere became unstable at a Reynolds number of 105. Their research indicated that when the Reynolds number exceeds 6000, the vortex sheet separating from the surface of the sphere becomes completely turbulent
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