A structured input-output approach to evaluating the effects of uniform wall-suction on optimal perturbations in transitional boundary layers

In this work, structured input-output analysis is employed to investigate how asymptotic suction control affects the growth of different types of disturbances to boundary layer flow. Application of the method in both the Blasius and asymptotic suction boundary layer settings demonstrates that, as in the case of channel flow, structured analysis produces results consistent with non-linear optimal perturbation analysis and direct numerical simulations. A comparison of the structured response at $R e_{\delta^{*}}=610$ for the two configurations highlights changes in the structural features of the disturbances that require the least energy to induce transition (optimal perturbations), as well as an overall reduction in the structured response of the actuated boundary layer. Further efforts to understand how this well-known flow control technique achieves this broadband reduction in flow sensitivity can provide insight that can be exploited to develop new actuation strategies to delay transition in boundary layers.