Reduced order models for closed loop control: comparison between POD, BPOD, and global modes

Linear Quadratic Gaussian (LQG) control is a promising tool to control flows. Initially developed for systems of moderate size, it is not directly applicable to fluid mechanics problems, requiring a reduced model. Three popular ways of reducing the system will be presented and their ability to control the global instability of an incompressible cavity flow will be studied. A comparison between reduced models based on global modes, Proper Orthogonal Decomposition (POD) modes and Balanced POD (BPOD) modes permits to discuss the relevant quantities to be captured by the reduced model to insure a successful control.