Abstract

Aeroelastic flutter analysis is a vital part of civil and military aircraft design and usually performed with a structural code for the subsonic and supersonic airspeeds. However, these codes cannot accurately predict the aeroelastic structural response for transonic airspeeds as unstable shockwaves form over the wings that cause unsteady spatial pressure fluctuations; thus, FSI analysis between CFD and FE codes is required to analyse this problem. Further, the mesh mismatch between CFD and FE codes make it hard to reuse existing simulation models. For example, typical aeroelastic FE models consist of a global shell representation of the airframe that considers stiffness and dynamic behaviour but does not accurately describe the other skin of the aircraft. In contrast, aerodynamic CFD models have a very detailed, fine mesh representation of the aircraft?s skin to accurately capture the lift and drag of the aircraft for different angles of attack. Therefore, FSI analysis often requires the user to create a FE model with a detailed representation of the aircraft?s surface that matches the CFD mesh to map pressure and deformation between the codes, so-called pressure-based load mapping. But even with a dedicated, detailed FE mesh, the pressure-based mapping procedure can introduce considerable errors in the load transfer between the codes. This presentation introduces a force-based load mapping approach between Hexagons scFLOW, a part of Cradle CFD, and MSC Nastran that eliminates the error introduced by the pressure-based mapping. The mapping procedure also supports a single FE shell mesh representing the whole wing structure while still accurately transferring the loads and deformations, including the leading and trailing edges of the wings represented by a free shell edge. Additionally, the presentation covers a quasi-implicit 2-way FSI coupling between scFLOW and MSC Nastran. This coupling allows steady-state CFD simulation to be combined with non-linear static FEA with large rotations to predict the steady condition of a wing profile with or without moving control surfaces for static aeroelastic analysis. Finally, the presentation introduces a dynamic and a static aeroelastic validation case. The dynamic validation case consists of a flutter simulation with comparison against wind tunnel tests of an AGARD 445.6 wing profile under transonic airspeeds. The static case is a study on the lift force produced by the flaperon for different angles of attack of a NACA 65A004 aerofoil, also under transonic airspeeds.