Description
Even though, highly efficient structural and aerodynamic solvers are used widely in the industry, a true dynamic nonlinear aeroelastic solver requires information from both solvers (coupling) at every time step. This is only possible when one has access to the source code of the commercial structural solver at hand. Even if it were possible to access the source code of the structural solver, due to the complexity of the analysis and the code itself, it would require highly proficient programming skills to couple the structural solver with an aerodynamic solver. UVLM.OpenFSI developed at ZONA Technology, Inc. is one of the first commercially available codes that accounts for both structural and aerodynamic nonlinearities (in the subsonic regime) for a nonlinear aeroelastic analysis. This is achieved by coupling of MD Nastran's dynamic nonlinear structural solver with the unsteady vortex lattice method via the OpenFSI service recently introduced by MSC.Software. The Joined Wing configuration being a nonconvential and highly nonlinear structure, has been a sought after area of research for aeroelasticians. Capitalizing on the remarkable development of UVLM.OpenFSI, a complete nonlinear aeroelastic analysis is presented for the joined wing configuration. Using the structural model data provided by the U.S. Air Force Research Lab, a half span finite element structural beam model is created. The natural frequencies and mode shapes are regenerated and compared to the full blown finite element model to verify the reliablity of the half span beam model. A number of static nonlinear structural analyses are performed on the beam model to investigate the nonlinearities associated with the structure. The primary reason for the investigation of the structural nonlinearities is to make intelligible the effects it would have on the aeroelastic analysis. After a successful validation of UVLM.OpenFSI, an aerodynamic model is created as per the UVLM.OpenFSI input definitions. The aerodynamic model is splined with the structural model for accurate transfer of forces and displacements. During the dynamic nonlinear aeroelastic analysis, the aerodynamic model is modified at every time step by making use of the displacements communicated to the aerodynamic solver via OpenFSI. The evolution of the wake is part of the aerodynamic solver. Time domain responses of the lift generated by the joined wing configuration under various loading conditions is obtained. The flutter boundary of the joined wing configuration is calculated by interpolating between the dampings values evaluated for stable and unstable time domain responses. Clearly, the flutter boundary also shows a nonlinear behavior with increasing loads. A time domain gust analysis is also performed for the joined wing configuration, showing the onset of flutter due to external excitation and also predicting the post flutter behavior.
