Effect of the Transient Nature of Flow on Annular Parachute Drag Prediction

Abstract

The aerodynamics of parachute systems are highly unsteady, resulting from separated ∞ows, vortex shedding, etc., caused by complex interactions between a ∞exible canopy and its payload. However, when dynamically permitted, the ∞owflelds and resulting surface forces have often been approximated using the assumptions and characteristics of rigid bodies and steady-state simulations. For example, results from steady-state simulations have been used successfully to assist the determination of parachute loading and trajectory. They have even been used in the estimation of peak drag and canopy fllling times sustained by in∞ating parachutes. This paper compares ∞ow characteristics and canopy drag obtained from solving the steady-state equations with those calculated with the unsteady equations, using a Reynolds Reynolds-Averaged Navier Stokes ∞ow solver on a rigid concentric annular parachute geometry comprised of two concentric fabric rings. The rings have unequal diameters and are vertically ofiset. Under load, the in∞ated rings not only yield a canopy that is highly porous but one that is characterized by high drag, a result of the cambered proflle formed by the billowing of the rings. The simulations have been performed at two Reynolds numbers of 8:03 ¢ 10 6 and 10:04 ¢ 10 6 . In particular, drag forces and wake characteristics observed in the steady simulations are compared to the unsteady simulations in order to judge the ability of the steady-state equations to capture the behavior noted in the transient cases. Results also include velocity, vorticity, and turbulence contours to help clarify the ∞ow physics resulting from steady and unsteady simulations.