Active flutter suppression for two-dimensional airfoils

Active flutter suppression for a two-dimensional typical airfoil in an incompressible flow is studied in this paper. The root loci of the systems described by three aerodynamical models, each with a single feedback variable, are first investigated to obtain a physical understanding of these systems. Practical systems that include actuator and gust models are considered next, using linear-quadratic regulator theory. Reduced-order models are constructed using a sequence of truncations based on the modal cost analysis, and modal truncation is examined for several weightings of the cost function. The resulting increases in the performance index and the closed-loop poles are then calculated for each truncation. The essential feedback modes and their associated gains for flutter suppression are determined using this analysis. For a reasonable degree of control, these reduced-order models are sufficiently robust.