Aiaa 2002-2997 Computational Analysis of Towed Ballute Interactions

A ballute (balloon-parachute) is an inflatable, aerodynamic drag device for application to planetary entry vehicles. Ballutes may be directly attached to a vehicle, increasing its crosssectional area upon inflation, or towed behind the vehicle as a semi-independent device that can be quickly cut free when the requisite change in velocity is achieved. The aerothermodynamics of spherical and toroidal towed ballutes are considered in the present study. A limiting case of zero towline length (clamped system) is also considered. A toroidal system can be designed (ignoring influence of the tethers) such that all flow processed by the bow shock of the towing spacecraft passes through the hole in the toroid. For a spherical ballute, towline length is a critical parameter that affects aeroheating on the ballute being towed through the spacecraft wake. In both cases, complex and often unsteady interactions ensue in which the spacecraft and its wake resemble an aero spike situated in front of the ballute. The strength of the interactions depends upon system geometry and Reynolds number. We show how interactions may envelope the base of the towing spacecraft or impinge on the ballute surface with adverse consequences to its thermal protection system. Geometric constraints to minimize or eliminate such adverse interactions are discussed. The towed, toroidal system and the clamped, spherical system show greatest potential for a baseline design approach. † Senior Research Engineer, Aerothermodynamics Branch, Associate Fellow AIAA ‡ Graduate Student, Student Member AIAA Copyright © 2002 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental Purposes. All other rights are reserved by the copyright owner. Nomenclature D diameter, m L separation distance, m M Mach number 0 molecular weight, kg/kmole qw wall heat transfer rate, W/cm 2 r radial distance, m RC toroid cross-section radius, m RI toroid inner (hole) radius, m Re ∞ ∞ ∞ μ ρ / L V , Reynolds number T temperature, K V velocity, km/s x, y, z Cartesian coordinates χi mole fraction of species i ρ density, kg/m