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Bushnell, “ Separation control: Review,” J. Possibilities and limitations of flow control strategies based on point vortex systems as reduced-order models are discussed. When applied to an actual cylinder wake at Re =75, the LQG compensator stabilizes the downstream region of the flow. Computational results show that thus designed LQG compensator stabilizes the stationary solution of the nonlinear Föppl system. The Linear-Quadratic-Gaussian (LQG) control design is performed based on the linearized Föppl system which has only four degrees of freedom. With centerline velocity measurements as the system output, the linearized Föppl model is also shown to be fully observable. When the cylinder rotation is used as flow actuation, the linearized Föppl system is shown to be stabilizable, but not controllable. The downstream location of the Föppl vortices is chosen so as to produce the same recirculation length as in the actual flow at a given Reynolds number. In this paper we use the Föppl point vortex system as a reduced-order model for stabilization of the steady symmetric solution in an unstable laminar wake.

Linear feedback