OverviewThe architecture of the developed toolbox of free software for aeroelastic analysis in the transonic regime is well summarized by the block diagram below. Futher details about the single blocks can be found in the Documentation section.
Figure: Block diagram of the toolbox of free software for aeroelstic analysis.
Structural solver
 Code_Aster is a structural analysis free software originally developed as inhouse application by French company Electricité De France (EDF), and released as free software under the terms of GNU General Public Licence (GPL) in 2001. It is mainly written in Fortran 77 and Python programming laguages and since the quality labels required by the nuclear industry, the macros are validated by means of independent comparison with analytical and experimental solutions. The documentation (only in French) is very detailed and easy to use.
Figure: Electricité De France logo.  Salomé is a free generic platform for prepost/processing numerical results developed by OpenCASCADE. It is written in C++ programming language and it is based on a flexible architecture made of elementary modules, such as Geometry, Mesh and Postpro.
Aerodynamic solver OpenFOAM is an aerodynamic analysis software developed by OpenCFD and WIKKI and released as free software under the terms of GNU General Public License (GPL) in 2004. It is written in C++ programming language and the documentation is growing.
Figure: OpenCFD and WIKKI logos.  Gmsh is a free triangular and tetrahedral mesh generator developed by C. Geuzaine and J. F. Remacle. It is written in C++ programming language.
 ParaView is a free postprocessing software developed by Kitware Inc. It is written in C++ programming language.
After an evaluation of the existing inviscid compressible solvers, we decided to develop a new solver, called AeroFoam, for OpenFOAM v.1.4.1 release (original and nondevelopment) for the accurate numerical simulation of timedependent inviscid compressible fluid flows in the transonic and supersonic regimes.
Figure: Comparison between the numerical results of OpenFOAM v.1.4.1 builtin inviscid compressible solvers and those of AeroFoam for an oblique shock reflection problem. Aeroelastic interfaceThe target of the aeroelastic interface is to realize the closedloop connection between the structural and aerodynamic subsystems, satisfying the following requirements:
 connection between topologically different domains and nonconformal meshes;
 exact treatment of rigid motions;
 conservation of momentum and energy transfer (Lyapunov energetic stability):
Figure: Closed loop interaction between the structural and aerodynamic subsystems.
We implemented a simple but effective and robust composite linear interpolation scheme to build the interface matrix [ I ]. However more general and flexible strategies exist, such as the Moving Least Squares (MLS) one.
Figure: Structural and aerodynamic meshes and structural mesh overlapped to the aerodynamic one. Aeroelastic solverIn the framework of Classical Aeroelasticity (CA) it is convenient to build a Reduced Order Model (ROM) for the unsteady Generalized Aerodynamic Forces (GAF) consequent to a blended step small structural generalized displacement. The aerodynamic transfer functions matrix [ Ham(k, M, Re) ] is built with a distributed algorithm as shown in the block diagram below:
Figure: How to build the aerodynamic transfer functions matrix [ Ham(k, M, Re) ].
Postprocessing tools NAEMO and MCASE developed by L.Cavagna and G. Quaranta are used to build the aerodynamic transfer functions matrix and compute the Vf and Vg diagrams and the flutter point respectively.
