Executive Summary : | The study proposes an input-output-based resolvent analysis of flat plate boundary layer flow subjected to periodic blowing and suction to determine the optimal forcings that would most efficiently delay the transition of such a flow. This study aims to develop a robust control that predetermines the optimal location and nature of optimal forcings on the plate to delay the transition to turbulence even as flow conditions change. The proposed method offers a computationally attractive method to determine the optimal energy amplifications of linearized flow equations in the presence of periodic controls, which can be easily targeted to other types of flows. Once the model equations provide optimal answers, they will be verified through designing actual experiments on flat plate boundary layers in wind tunnels. For parameters where actual experiments are difficult, direct numerical simulations of flow equations will be conducted to verify predictions of the model-based control strategies. The proposal also aims to obtain deep mechanistic understanding of control via modal mechanisms based on Tollmien--Schlichting waves or non-modal mechanisms, such as Orr and linear lift-up processes, through computations of coherent structures extracted from experiments and direct simulations using the spectral proper orthogonal decomposition method. |