3-D computation of parachute fluid-structure interactions: Performance and control

INTRODUCTION Fluid structure interactions (FSI) are involved at zil l stages of aircirop systerns perforntance, inclucling at init ial dcplovrnent, during inflation, at terrninal clescent (or gliding/maneuvering fbr steerable paraclnrtes). ancl at soft landing (i.c.. rctraction for rouncl paraclmtes. flared lancling for larn :rir piirachutes). The interaction betlveen tl ie parachrrte slrstem ancl the surrounding flou, fielcl is clotninant in rnost parachute operations, and thus the abil ity to predict parachute FSI is nccessary for accurate prediction of parachute behavior. Tli is paper l ' i l l clcscribe current efforts to develop a general l)urpose cornputer rnodel which carr accuratelJ predict 3 D F SI for various parachutc systcms uncler the different stagcs of performance. We rvill focus on the FSI performance during terminal descent stage to include control and maneuvering performarrce. Issues involved in performing simulations rvith the current moclcl rvill be presented to include the finite element formulations, coupling strategies. rnesh rnoving strategies, and implementation orr parallel supercomputers. \\'e prescnt a parallel computational strategv for carrying out 3 D simulations of paracliute fluicl--stmcture interaction (FSI), and (lemonstrate the strategv for sirnulations of airdrop performance and control phenomena in terminal descent. The strategy uses the Deforming'-SpatiaiDomairi/ Stabil izecl Space -Tirne (DSD/SST) formulationr'? of the time dependent. 3 D Navier--Stokes equations of incompressible flows for the fluid dynamics solution. Turbulent features of the flow are accounted for by using a zero-eqlration Smagorinsky turbulence model.r A finite element formulation derived frorrr the principle of r.irtual work is used for the structural dynamics (SD).4'5 The coupling of the FD with the SD is implemented over the fluid structure interface, v'hicir is the canopy surface. Large deformations of the structure are handied in the FD mesh b)' using an automatic mesh moving scheme with remeshing as needed. The DSD/SST procedure is rveli suited for problems involving deforming domains (spatial domains changing r,vitir time), such as the deformations cncountered during parachute ] ^ Y A , T a , ^ FSL0 This formulation has been rvell tested and applied to a large variety of fluid dynamics problems involving moving boundaries and interfaces. In the space time formulation, the finite element interpolation functions vary both spatially and temporalll', automaticalll' taking into account deforrnations in the spatial domain. In recent years, the DSD/SST procedure has been applied to a variety of FSI problems. Preliminarv DSD/SST simulations $,'ere successfuliy performed to simulate fluid-.structure interaction behaviors for flou,' problems involving mor.ing c1'linders ancl aerofoils.7,8 Later, the :rpproach rvas applied to simulate the FSI response of a flexibie pipe to internal flori'e and to trvo phase FSI flow problems including interior ball istics.10 Recentlv, thc approach has becn used to predict the FSI rcsponse for the inflation of an axisymmetric cable -rncrnbrane parachute stmcture.l1 to predict the ste:rdv state clescent charac:teristics for a, rarn air parachutc sr.stem.12 anci to predict terrninal descent charactcristics for a T 10 paraciiute svstem.13 For the FSI problerns presentecl, rve wil l give special attention to the transfer of coupling information betu' 'een "compatible" and "incornpatible" FD ancl SD interface meshes (i.e.. parachute canopy surface meshcs). For "r:ompatible" rneshes, the FD ancl SD have nodally equivalent interfacer meshes and transfer of coupling is straightforrvard. For "incompatible" meshes, coupling information must be transfered through more sophisticatcd pro.jection stratcq ies. la