The effect of wall suction on optimal perturbations in transitional boundary layers

This work applies structured input-output analysis to investigate how asymptotic suction control alters the types of perturbations most likely to trigger transition, i.e., the optimal perturbations. This method is first shown to identify structures consistent with previous analyses of nonlinear optimal perturbations and direct numerical simulations in both Blasius and asymptotic suction boundary layers. A comparison of the results at $Re_{\delta^*}=610$ demonstrates that, as expected, the asymptotic wall suction reduces the flow sensitivity to transition-inducing disturbances and in particular suppresses the Tollmien-Schlichting (TS) waves. Moreover, the structures associated with asymptotic suction boundary layer have larger streamwise and spanwise extent compared to Blasius boundary layer flows.