AbstractThe use of CFD within the aerospace industry’s loads and dynamics groups continues to increase as improvements in computational power make coupled CFD/CSD simulations more feasible from a practical standpoint. At the same time, flutter certification is becoming an increasingly challenging task as engineers have to understand and quantify the aeroelastic behaviors of advanced aircraft designs in the transonic regime. This situation has created a strong need for validation efforts and for the generation of know-how regarding various computational-aeroelasticity simulation methodologies.Broadly, there are three approaches in computational aeroelasticity: fully coupled, loosely coupled and closely coupled analyses. In the fully coupled model, the governing equations are reformulated by combining fluid and structural equations of motion, which are then solved and integrated in time simultaneously. While using a fully coupled procedure, one must deal with fluid equations in an Eulerian reference system and structural equations in a Lagrangian system, This leads to the matrices being orders of magnitude stiffer for structure systems as compared to fluid systems, thereby making it virtually impossible to solve the equations using a monolithic numerical scheme for large-scale problems. In the class of loosely coupled methods, unlike the fully coupled analysis, the structural equations are solved using two separate solvers. This can result in two different computational grids, which are not likely to coincide at the boundary. This requires an interfacing technique to be developed to exchange information back and forth between the two modules. The loosely coupled approach has only external interaction between the fluid and structure modules; or the information is exchanged at each physical time step interval without occurring in pseudo-time or sub-iteration. The closely coupled approach is similar to the loosely coupled one in most procedures. Different solvers for fluid and structure models are exploited, but coupled in a tighter fashion thereby making it better accuracy for time-dependent problems. In this approach, the fluid and structure equations are solved separately using different solvers but coupled into one single module with exchange of information taking place at the interface or the boundary via an interface module. The information exchanged here is the surface loads, which are mapped from CFD surface grid onto the structure dynamics grid; and the displacement field, which are mapped from structure dynamics grid onto CFD surface grid. The advantage of closely coupled method is much more accurate compared to the loosely coupled method, since the information exchange is made in each sub-iteration within every physical time step.In this work the performance and issues associated with a closely-coupled CFD/CSD approach are explored for wing flutter predictions using a multi-physics&nbsp;CFD tool. The purpose of the investigation is to explore the numerical and method-related uncertainties in simulations of wing flutter, and also to validate (establish the limits and expected accuracy) the use of the tool for this application area on a common benchmark case.

Wing Flutter Analysis Using Computational Fluid-Structure Interaction Dynamics

Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2021/volume/85284

ASME 2021 Fluids Engineering Division Summer Meeting (FEDSM2021)

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