Transonic Aeroelastic Analysis of a High Speed Transport Wind Tunnel Model (2003)

Introduction

While the interaction between aerodynamic and structural phenomena have been understood for many years, most progress in accurately predicting aeroelastic interactions has been made in flight regimes where both the aerodynamics and the structure can be modeled as linear systems. It is now common practice in the aircraft industry to compute static aeroelastic effects as well as flutter behavior for complex configurations using software packages that model the structural dynamics using a linear finite element formulation, and that predict the aerodynamic forces using a linear aerodynamic theory such as the Doublet-Lattice Method. 

While these linear analysis methods have proven to be invaluable in predicting and solving aeroelastic problems, their limitations are widely recognized. In particular, it is well known that aeroelastic analysis methods based on linear aerodynamic theories do not give accurate results when applied in the transonic regime, where significant nonlinearities are present. However, with the increasing availability of high-power, low cost computing, it is rapidly becoming feasible to perform aeroelastic analyses using aerodynamics based on Computational Fluid Dynamics (CFD), which can accurately model many types of flow nonlinearities, including transonic shocks. 

One of the premier CFD flow solvers currently in use is CFL3D3,4,5, which has been developed by NASA for several years, and has been shown to accurately predict steady and unsteady aerodynamic forces in  the presence of flow nonlinearities. This code can model the aerodynamics using either the Euler or the Navier-Stokes equations, and has recently been modified to include a robust multiblock grid perturbation algorithm6 as well as a structural dynamic model using modal degrees of freedom similar to that used in CAP-TSD7. The resulting aeroelastic code is CFL3D-AE.BA, which has been in use for several years in performing nonlinear aeroelastic analyses on various configurations. 

In this paper, aeroelastic analyses are performed on a generic high speed transport configuration using linear aeroelastic methods as well as CFL3D.AE-BA. The configuration analyzed is an aeroelastically scaled wind tunnel model known as the Flexible Semispan Model (FSM)8,9. This model was also tested in the NASA Langley Research Center (LaRC) Transonic Dynamics Tunnel (TDT), and comparisons are made between the analysis results and the experimental data. It will be shown that the nonlinear analysis performed in CFL3DAE. BA using an aerodynamic model based on the Euler equations gives significantly better correlation with the wind tunnel results than the linear analysis.