Kopplungswerkzeuge für aeroelastische Simulationen

The direct numerical simulation of fluid-structure-interaction has received a lot of attention in recent years. Due to the growing size of planned commercial airplanes and the widespread use of lightweight-structures leading to large elastic deflections in flight, great interest of commercial applications of such simulation techniques has developed. The currently used simplified methods to estimate the stresses on the structure of a flying plane are not suitable any more, when a new highly elastic airplane is considered, since the complex interaction between fluid and structure is usually highly nonlinear. Here the need arises to use a direct simulation of the whole coupled, aeroelastic system. A set of tools to calculate these simulations reusing existing numerical flow-solvers is developed in this work. The coupling algorithm used treats the flow and the structure dynamics in the sense of an area separation. This leads to a set of separated solvers for each area and the development of a suitable data-exchange strategy. When the flight vehicle gets deformed due to aerodynamic (or other) loads, then it will be neccessary for the calculation grid of the flow solver to follow the deforming shape continously. An essential part of this work describes a novel technique to reshape the calculation mesh according to elastic deformation of the flight vehicle. Certain lines of the mesh were modeled as elastic beams, fixed on nodes to form an elastic framework, which will help to ensure grid deformations with good quality regarding intersection angles of gridlines at reasonable calculation costs. Although suited for any type of mesh, an implementation for structured multi-block grids, as used by the flow-solver FLOWer, is presented, which proved reliable in practical use even for complex geometries. The elastic flight vehicle is modeled via a finite-elemet-method using a set of simple elements, mainly beams, where the elastic structure is reduced to a few, simple components. Of great importance for the correct reproduction of the physics of the whole coupled aeroelastic system is the exchange of loads from fluid to structure on one hand and the transfer of strucutral deflections to the boundary-conditions of the flow-solver on the other hand. Further the possibility to simulate a free flight (i.e. plane-model not fixed in a wind-tunnel) is implemented. A new coordinate-system needs to be invented here, which moves with the vehicle accordingly, so that the calculation of elastic deformation and flow can be done inside the new, moved coordinate-system.