Wind tunnel experiments on characteristics of small-scale parachutes

Abstract

conditions and an alternate method is necessaryExperiments on small-scale parachute models require the consideration of effects of nondimensional parameters, such as the Reynolds number. Wind tunnel tests with a 6-inch nominal diameter, solid cloth canopy form the basis for this work. Force-time histories were acquired during inflation of the 6-inch model for a Reynolds number range of 6.2 x IO4 to 1.5 x 10’. Resulting data were characteristic of the infinite mass condition, with peak opening force clearly recognizable. The peak opening force, normalized by the fieestream dynamic pressure and constructed surface area, remained nearly constant and equal to 1.2 rtr 10% within the Reynolds number range. Nondimensional opening time decreased approximately by 50% over the tested Reynolds number range, reaching a plateau of approximately 8.7 beyond a Reynolds number of 105. Introduction Parachute inflation is an extremely complex physical phenomenon in aerodynamics consisting of unsteady, separated flows. Parachute inflation incorporates the elastic deformation of a boundary driven by a pressure differential that is, in turn, related to the boundary shape. Hence, parachute inflation is inherently a fluid-structure interaction phenomenon. Due to these complicated flow attributes, a need exists for complete flow field characterization during inflation. This characterization, however, cannot be thoroughly accomplished during full-scale, m-flight Parachute inflation studies have been previously conducted and analyzed for both full-scale parachutes’J and scale models. Full scale testing has provided numerous force-time histories in an attempt to model peak opening force and opening time of fullscale parachutes. In addition, scaling parameters, such as stifiess, have been investigated in relation to peak opening force and opening time. Scale testing has been conducted as both drop tests2 and wind tunnel tests3 The wind tunnel experiments of Heinrich are closest to those being conducted in this study. Heim-ich’s research was directed towards predicting force-time histories using model parachutes. He explored a finite mass inflation process for Reynolds numbers ranging corn 9.1 x lo5 to 1.54 x 106. The work was successful in proving that enough similarities existed between model and full-scale parachute force-time histories to warrant further research in the area. While some nondimensional analysis has been discussed in the past works, the issue of scaling effects on parachute inflation, most notably material stiffness, has been liited to large scale and full-scale parachutes.4 * Aerospace Engineer (Natick) & Graduate Student, Worcester Polytechnic Institute, AIAA member 7 Associate Professor, AIAA senior member $ Research Aerospace Engineer, AIAA member This material is a work of the U.S. Government and is not subject to copyright protection in the United States. The effects of scaling and Reynolds number on parachute inflation have received limited attention. Reynolds number is a nondimensional parameter that indicates the ratio of inertial forces to viscous forces acting on fluid particles, yet it is rarely the focus of model studies. The Reynolds number may be altered via freestream velocity or the kinematic viscosity of the surrounclmg fluid, among other means. This research is among the first studies to concentrate on the effects of Reynolds number on parachute inflation. Scaling effects are related to changes brought about by altering the size of the parachute, clearly a key concept when dealing with model parachutes. other studies have determined a list of effective nondimensional parameters for parachute inflation,3*5,6 but experimental data have yet to determine the extent of these parameters. Heinrich and Hektner4 introduced a nondimensional stiffness