Department of Mechanical Engineering,Amirkabir University of Technology
In this paper, a 3-D, unsteady vortex lattice model to compute aerodynamic coefficients, using time domain eigenmode analysis, is presented. A computationally efficient technique for constructing a reduced order model of unsteady flow about a low aspect ratio wing, modeled as a cantilever plate of constant thickness, is presented. Analysis demonstrates that limit cycle oscillations of the order of the plate thickness are possible. The eigenmodes of the system, which may be considered as aerodynamic states, are computed and, subsequently, used to construct a computationally efficient, reduced order model of an unsteady flowfield. Only a handful of the most dominant eigenmodes are retained in the reduced order model. The effect of the remaining eigenmodes is included approximately, using a static correction technique. An advantage of the present method is that, once the eigenmode information has been computed, the reduced order model can be constructed for any number of arbitrary modes of wing motion very inexpensively. The method is particularly well suited for use in the active control of aeroelastic phenomena, as well as in standard aeroelastic analysis for flutter or gust response. Finally, a numerical example is presented that demonstrates the accuracy and computational efficiency of the present method.