Transonic And Supersonic Flutter Estimation Through Panel Methods And RANS based Coupled Aeroelastic Solvers

Abstract

Flutter is an undesirable phenomenon which occurs in elastic structures due to interaction of aerodynamic, inertial, and elastic forces on a body. Studies on such problems are multi-disciplinary, requiring including physics of structures and physics of fluid flow into account. This study focused on comparison of flutter boundary prediction using a panel methods-based linear solver (NASTRAN) and RANS-based non-linear solver. Although Nastran (SOL 145) can solve flutter problems with the help of linear aerodynamic models (doublet lattice method based aerodynamics) and works well for simple aerodynamic models in the subsonic regime, it fails in the transonic regime (due to nonlinearities in flow). The Navier Stokes (RANS) based CFD model is used to capture the transonic flow non-linearities. For this, separate solvers for structure and CFD are used, and the two are connected with a third module to efficiently transfer the data in real-time. A validation case of AGARD 445.6 wing successfully implemented with the coupled solver. The AGARD 445.6 wing is a 45-degree sweptback wing with a thin airfoil cross-section. The nonlinearities related to shock waves are minimum on such profiles. The linear aeroelastic solver yielded closely followed results to the coupled solver in predicting flutter boundary. Literature suggested that the angle of sweep is a vital function of shock-wave strength. The low sweep model produces strong shock waves, which are often termed a singularity in flow physics, thus significantly reducing the accuracy of linear solvers. These observations attained our attention to quantify the effect of angle of sweep on aeroelastic response estimation of the two solvers in transonic and supersonic flow regimes. The results compiled showed that about 22% difference is induced in flutter estimation of the two solvers for an angle of sweep-back of 30 degrees compared to 4.6% with the angle of sweep-back of 45 degrees in transonic flow. While for the supersonic flow regime, having a maximum of 8.3% for 45 and 11.9% with 30 degrees models. These studies are further extended by performing sensitivity analysis for iv the Agard 445.6 flutter boundary concerning its material properties, semi-span length, and angle of sweep-back. Also, a case of existing aircraft wings has been analyzed for an aeroelastic response via the coupled framework.