Identification of a plasma actuated open-cavity under flow control

This paper addresses an input-output identification problem for a simulated incompressible open cavity flow. Despite the highly nonlinear and infinite-dimensional nature of the system, we look for a low complexity, linear, finite-dimensional model still capable of capturing the most salient features of the system. The inherent system instability, leading to the formation of its characteristic limit cycle, is a major obstacle in the application of classical identification schemes. To overcome such difficulty, we adopt a closed-loop identification method, which requires a preventive stabilization via an empirically designed controller. Being the controller perfectly known, an indirect approach is pursued. It consists of identiflying the closed-loop transfer function and then reconstructing the unstable open-loop model by loop inversion. Extensive experiments led us to opt for a frequency domain identification based on an Output Error model structure. The identified model proves to be consistent with the infinite-dimensional one and, in particular, to reproduce its main instabilities.